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Zhou, Leyao. "Electroless Deposited Transitional Metal Phosphide for Oxygen/Hydrogen Evolution Reactions." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1522333083629295.
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Karimi, Shervedani Reza. "Kinetics of hydrogen evolution reaction on Ni-Me-P electrodes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq26382.pdf.
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Shervedani, Reza Karimi. "Kinetics of hydrogen evolution reaction on Ni-Me-P electrodes." Thèse, Sherbrooke : Université de Sherbrooke, 1997. http://savoirs.usherbrooke.ca/handle/11143/4954.
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Luo, Lin. "Novel Nanostructure Electrocatalysts for Oxygen Reduction and Hydrogen Evolution Reactions." University of the Western Cape, 2019. http://hdl.handle.net/11394/7315.
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Philosophiae Doctor - PhDThe widespread use of fossil energy has been most convenient to the world, while they also cause environmental pollution and global warming. Therefore, it is necessary to develop clean and renewable energy sources, among which, hydrogen is considered to be the most ideal choice, which forms the foundation of the hydrogen energy economy, and the research on hydrogen production and fuel cells involved in its production and utilization are naturally a vital research endeavor in the world. Electrocatalysts are one of the key materials for proton exchange member fuel cells (PEMFCs) and water splitting. The use of electrocatalysts can effectively reduce the reaction energy barriers and improve the energy conversion efficiency.
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Wright, Edward Anthony. "A study of the hydrogen evolution reaction on platinum group metals." Thesis, University of Exeter, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414258.
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Lee, Heung Chan. "Magnetic field effects on electron transfer reactions: heterogeneous photoelectrochemical hydrogen evolution and homogeneous self exchange reaction." Diss., University of Iowa, 2010. https://ir.uiowa.edu/etd/2562.
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Magnetic field effects (MFE) on electrochemical systems have been of interest to researchers for the past 60 years. MFEs on mass transport, such as magnetohydrodynamics and magnetic field gradients effects are reported, but MFEs on electron transfer kinetics have been rarely investigated. Magnetic modification of electrodes enhances electron transfer kinetics under conditions of high concentrations and low physical diffusion conditions, as shown by Leddy and coworkers. Magnetic microparticles embedded in an ion exchange polymer (e.g., Nafion) applied to electrode surfaces. Rates of electron transfer reactions to diffusing redox probes and to adsorbates are markedly enhanced.
This work reports MFEs on hydrogen evolution on illuminated p-Si; MFEs on hydrogen evolution on noncatalytic electrodes; a model for MFEs on homogeneous self-exchange reactions; and a convolution based voltammetric method for film modified electrodes.
First, a MFE on the photoelectrochemical hydrogen evolution reaction (HER) at p-Si semiconductors is demonstrated. The HER is an adsorbate reaction. Magnetic modification reduces the energetic cost of the HER by 400 - 500 mV as compared to Nafion modified electrodes and by 1200 mV as compared to unmodified p-Si. Magnetically modified p-Si achieves 6.2 % energy conversion efficiency. Second, from HER on noncatalytic electrodes, the MFE on photoelectrochemical cells arises from improved heterogeneous electron transfer kinetics. On glassy carbon electrodes, magnetic modification improves heterogeneous electron transfer rate constant, k₀,for HER 80,000 fold. Third, self exchange reaction rates are investigated under magnetic modification for various temperatures, outersphere redox probes, and magnetic particles. Arrhenius analyses of the rate constants collected from the experiments show a 30 - 40 % decrease in activation energy at magnetically modified electrodes. A kinetic model is established based on transition state theory. The model includes pre-polarization and electron nuclear spin polarization steps and characterizes a majority of the experimental results. Lastly, a convolution technique for modified with uniform films electrodes is developed and coded in Matlab (mathematical software) for simple and straightforward analysis of Nafion modified electrodes.
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Zou, Yu. "Supported Composite Electrocatalysts for Energy Conversion Applications." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/417198.
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Increasing energy demand and environmental awareness have promoted the development of efficient and environment-friendly hydrogen technologies. Water electrolysis (2𝐻2𝑂→2𝐻2+𝑂2) is a promising way to store renewable electricity generated by solar or wind energy into chemical fuel in the form of H2. Water electrolysis is comprised of a hydrogen evolution reaction (HER) on the cathode and an oxygen evolution reaction (OER) on the anode. For both HER and OER, highly catalytic active electrocatalysts are required to lower the overpotentials and to speed up the sluggish kinetics. To date, noble metal catalysts are still the most efficient electrocatalysts for these two reactions, but their high cost and low abundance on Earth limit the scalable application of water electrolysis. Therefore, investigation of alternative catalysts with low cost and high electrocatalytic activity is urgently needed.
This thesis focuses on alkaline electrocatalytic HER, as well as related reactions such as OER, and hydrazine oxidation(HzOR)-assistant HER. In terms of material design, the components are introduced to improve conductivity and mass transfer, as well as boost the intrinsic catalytic activity. Moreover, the mechanism was investigated through exploring the link between structure and performance, as well using density functional theory (DFT) calculations.
The first two experimental chapters employed a two-dimensional (2D) material, MXene, as support. In Chapter 2, ruthenium single atoms were incorporated onto ultrathin Ti3C2Tx MXene nanosheets to unlock its electrocatalytic activity. The RuSA@Ti3C2Tx presented a 1 A cm−2 HER current density with an over potential of 425.7 mV, outperforming the commercial Pt/C benchmark. Operando Raman test under HER potential showed the different protonation level between RuSA@Ti3C2Tx and Ti3C2Tx, suggesting the different hydrogen absorption energy of the oxygen terminal on the Ti3C2Tx basal plane. Finally, the theoretical calculations confirmed that the RuSA not only facilitates water dissociation, but also modulates the hydrogen After increasing the Ru content and conducting electroreduction, RuTi alloy nanoclusters were constructed on the surface of Ti3C2Tx. Surprisingly, the RuTi@Ti3C2Tx showed better performance in HER, and excellent hydrazine oxidation reaction (HzOR) performance. The overpotential to attain a current density of 10 mA cm−2 for HER was only 14 mV, lower than that of the commercial Pt/C. The HzOR catalytic activity also outperformed most reported work. In addition, the overall hydrazine spitting was conducted in an H-type electrolytic cell, demonstrating superior thermodynamic advantage and good stability.
Defect-abundant active carbon (AC-DCD) as support was prepared by the hydrothermal reaction with dicyanamide. Then, the Ru nanoparticles were grown on the surface. Compared to the catalyst with pristine AC as support prepared under same conditions, Ru600@AC-DCD presented a larger electrochemical special area with strain-abundant Ru nanoparticles. Ru600@AC-DCD delivered excellent HER performance in alkaline media, and good catalytic properties in acidic and neutral media.
Finally, another novel metal@carbon composite, Ni nanoparticles encapsulated in graphite carbon layers, was synthesized by directly annealing the Ni-imidazole framework precursors at 350 °C in H2/Ar. By tuning the annealing time under H2/Ar flow, Ni nanoparticles with different crystalline phases were synthesized. These Ni@C samples are di-function electrocatalysts for HER and OER in alkaline condition. The mixed-phase catalyst mix2-Ni@C delivered the highest activity to catalyze HER, while the pure hcp phase catalyst hcp-Ni@C showed best OER activity. This work provided a practical method to prepare low-cost difunctional electrocatalysts for overall water electrolysis.
In summary, the thesis innovatively contributes to the knowledge in material science and water electrolysis in the aspects of: (i) designing novel supported composite electrocatalysts with high catalytic activity for HER, OER, and HzOR; (ii) monitoring the changing of surface terminal by operando Raman spectroscopy to verify the HER mechanism; (iii) development of metal nanostructures, like RuTi alloy, hcp phase Ni and mixed-phase Ni, via facile methods, and investigation of their unique properties; and (iv) application of large current HER and exploration of the kinetics under different potentials.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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Xing, Shihui. "Rational design of bi-transition metal oxide electrocatalysts for hydrogen and oxygen evolutions." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/209307/1/Shihui_Xing_Thesis.pdf.
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This thesis mainly focuses on the rational design and preparation of bi-transition metal oxide materials for high-performance electrochemical catalysis, such as hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). To address the challenges of sluggish kinetics and large overpotentials in HER and OER, the effective strategy of morphology engineering, introducing a secondary metal element and supporting on carbon-based materials were carried out and discussed.
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Anthony, David M. "Effects of cyclic current modulation on cathode materials for the hydrogen evolution reaction." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0003/MQ40982.pdf.
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Smale, Simon. "Study of the hydrogen evolution reaction on platinum and platinum group metal surfaces." Thesis, Cardiff University, 2008. http://orca.cf.ac.uk/54760/.
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The hydrogen evolution reaction (HER) has been examined on a variety of Pt and Pt-group metal surfaces to investigate the rate of the reaction. Pt stepped single crystal surfaces were investigated in relation to the HER using cyclic voltammetry, linear sweep voltammetry and multi-frequency AC voltammetry. It was found that the hydrogen evolution reaction activity did not show a dependence on the structure of single crystal platinum electrode surfaces. Thick films of Au, Rh and Pd were deposited onto Pt {111} and successfully annealed to give pseudomorphic surfaces of the bulk metal. The aim of such measurements was to investigate whether strains within the crystal lattice of these films would result in enhanced HER activity. None of the surfaces investigated showed significant HER enhancement. Rather, results similar to those observed using the bulk metals were obtained. Rough Ir and Pt deposits on Pt{111} were also investigated. Enhanced HER activity was observed on these surfaces. This enhancement was interpreted in terms of the structural arrangement of the Ir and Pt deposits. For Pd films on Pt {111} (0 < fVPd < 2 monolayers) it was observed that Pt dominated the HER kinetics for Pd coverages up to one monolayer and was still influential on the HER at two monolayers of Pd. Similarly Pd-Pt surface alloys also showed that Pd had little or no influence on the HER kinetics even with 75 % Pd in the surface layer. Possible mechanisms for this behaviour have been proposed, in particular, the role of subsurface hydrogen in HER on Pt is discussed.
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Jiang, Bing. "Nickel and cobalt bis (imino)pyridine complexes as catalysts for the hydrogen evolution reaction." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/667777.
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El subministrament d'energia sostenible és un desafiament crític que enfronta la humanitat. La dependència dels combustibles fòssils ha despertat l'interès en el desenvolupament de fonts d'energia lliures de carboni, entre les quals el dihidrogen que té una alta densitat d'energia seria un dels més prometedors sempre que es generi a partir d'alternatives renovables. En aquest context, dissociar l'aigua per produir hidrogen com a combustible és de gran interès i, per tant, s'estan desenvolupant una gran quantitat de catalitzadors per accelerar la velocitat d'aquesta reacció, preferiblement obtinguts a partir de metalls de transició abundants. Amb l'objectiu d'optimitzar l'economia de l'àtom de metall i facilitar l'anàlisi mecanístic, els complexos moleculars són una bona opció com a catalitzadors homogenis. En aquest tipus de compostos, els centres metal·lics que generalment es requereixen poden accedir a múltiples estats d'oxidació, de vegades a través d'intermedis de tipus metall-hidrur. No obstant això, el disseny de catalitzadors per a la reacció d'evolució de l'hidrogen (HER) inclou també una família de complexos amb lligands no innocents que poden operar com un reservori d'electrons i / o un lloc de protonació. El primer capítol d'aquesta tesi doctoral introdueix la necessitat i les tècniques per a la producció d'hidrogen per recolzar la demanda d'energia, incloent els electrocatalitzadors per HER basats en els metalls no nobles, níquel i cobalt. El segon capítol descriu els objectius d'aquesta Tesi, és a dir, la síntesi i caracterització dels lligands basats en diiminpiridina (PDI), actius en redox, juntament amb els complexos de níquel i cobalt obtingut a partir d'aquests lligands. Es presenten també com a objectius la seva avaluació electrocatalítica en HER així com la descripció dels processos des del punt de vista mecanístic. El tercer capítol presenta la preparació d'un conjunt de lligands PDI pentadentats, juntament amb la síntesi i caracterització completa de complexos de Ni(II) de hexacoordinats [Ni(Ph2PPrPDI)(Cl)](Cl) (1(Cl)) i [Ni(Ph2PPrPDI)(p)Cl)(Cl)](Cl) (2(Cl)). La ubicació dels electrons després de la reducció electroquímica d'1(Cl) es va examinar mitjançant càlculs de la teoria del funcional de la densitat (DFT) juntament amb la ressonància paramagnètica electrònica (EPR), la qual cosa va mostrar que la primera reducció d'un electró es produeix en el metall i la segona en el lligand. Es van estudiar també les propietats redox i catalítiques d'ambdós complexos. D'una banda, es va observar un potencial redox més positiu i, per tant, un sobrepotencial més baix per a 2(Cl), el que indica que la presència del substituent electroatraient Cl al lligand PDI millora l'activitat electrocatalítica. D'altra banda, 1(Cl) és més actiu per al HER en termes de TOF i constant de velocitat. Els estudis d'estabilitat a curt termini per a 1(Cl) i 2(Cl) en condicions de HER per CV indiquen que la catàlisi és homogènia sense descomposició, mentre que l'estabilitat a llarg termini analitzada per electròlisi potencial controlada mostra la generació d'una nova espècie transitòria que pot desencadenar la reacció d'oxidació d'hidrogen i al seu torn reduir el sobrepotencial per a la HER. El quart capítol s'enfoca en la síntesi i caracterització de complexos de Co coordinats de cinc amb els lligands aplicats en el tercer capítol ([CoI(Ph2PPrPDI](BF4), 3(BF4) i [CoI(Ph2PPrPDI(p)Cl](BF4), 4(BF4)). Les dades de l'electroquímica mostren que aquests complexos són actius per a la HER en medi orgànic, passant després de la reacció amb protons per espècies d'hidrur de Co(III) que es van identificar mitjançant espectroscòpia UV-vis i RMN. Sobre la base de l'espectroscòpia RMN, el compost de Co(I) inicial es va recuperar després d'un cicle de reacció catalític, el que demostra un mecanisme homolític per HER. Finalment, el cinquè capítol enumera les conclusions més rellevants extretes del treball realitzat.Sustainable energy supply is a critical challenge humanity is facing. The dependence of fossil fuels have ignited interest in the development of carbon-free energy sources, among which energy-dense dihydrogen would be one of the most promising when generated from renewable alternatives. In this context, splitting water to produce hydrogen as fuel is of great interest, and hence a large number of catalysts made from earth-abundant transition metals have been developed to accelerate the reaction rate. For the purpose of effectively using metal-atom economy and facilitating mechanistic analysis, molecular complexes as homogenous catalysts got much attention. In this kind of compounds, metal centres are usually required to accommodate multiple redox states and experience metal-hydride intermediates. However, there has been a renaissance in catalysts’ design for the hydrogen evolution reaction (HER) by coordinating the metal centre with non-innocent ligands who can operate as an electron reservoir or/and protonation site. The first Chapter of this PhD Thesis generally introduce the need and techniques for hydrogen production to support the energy demand, reviewing electrocatalysts for the HER based on the non-noble metals nickel and cobalt. The second Chapter describes the objectives of this Thesis, i.e., the synthesis and characterization of redox-active pyridine diimine (PDI)-based ligands and the corresponding nickel and cobalt complexes. Their electrocatalytic evaluation in HER is aimed, as well as the description of the processes from the mechanistic point of view. The third Chapter presents the preparation of a set of pentadentate PDI ligands, synthesis and full characterization of six-coordinated Ni(II) complexes [Ni(Ph2PPrPDI)(Cl)](Cl) (1(Cl)) and [Ni(Ph2PPrPDI(p)Cl)(Cl)](Cl) (2(Cl)) using techniques including mass spectroscopy, UV-vis spectroscopy, X-ray crystallography and elemental (C, H, N) analysis. The electron location upon electrochemical reduction of 1(Cl) was examined by density functional theory (DFT) calculations along with electron paramagnetic resonance (EPR), revealing the metal-based nature for the first one-electron reduction and ligand-based for the second one. The redox and catalytic properties of both complexes were studied. On the one hand, more positive redox potential and therefore lower overpotential were observed for 2(Cl), indicating that the presence of the electron-withdrawing Cl substituent in the PDI ligand scaffold improves the electrocatalytic activity. On the other hand, 1(Cl) is more active for the HER in terms of turnover frequency and rate constant. Short-term stability studies for 1(Cl) and 2(Cl) in the course of HER by CV indicates homogenous catalysis without decomposition, whereas long-term stability analysed by controlled potential electrolysis shows the generation of a new transitory species which can trigger the hydrogen oxidation reaction and reduce the overpotential for the HER. The fourth Chapter focus on the synthesis and characterization of five-coordinated Co complexes bearing the ligands applied in the third Chapter ([CoI(Ph2PPrPDI](BF4), 3(BF4) and [CoI(Ph2PPrPDI(p)Cl](BF4), 4(BF4)). Electrochemistry data shows that these complexes are active for the HER in organic media, undergoing protonation to form Co(III) hydride species which were identified by UV-vis and NMR spectroscopy. On the basis of NMR spectroscopy, the initial Co(I) compound was recovered after a catalytic reaction cycle, demonstrating a homolytic mechanism for HER by this system. Finally, the fifth Chapter lists the most relevant conclusions extracted from the work carried out.
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Brousseau, Rejean. "Evaluation of the coverage by kinetically involved H intermediates during the hydrogen evolution reaction." Thesis, University of Ottawa (Canada), 1989. http://hdl.handle.net/10393/21143.
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Wang, Haozhu. "Cobalt Phosphide Single Site Electrocatalysts derived from 2D ZIF-8 for Hydrogen Evolution Reaction." Thesis, University of Sydney, 2021. https://hdl.handle.net/2123/26246.
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Hydrogen (H2) is a promising energy carrier due to its high gravimetric energy density and environmental friendliness. Among different approaches of H2 production, hydrogen evolution reaction (HER) via electrochemical water splitting has attracted significant research interests when electricity can be supplied by sustainable energy sources, such as solar, wind, and tidal energy. Electrocatalysts play a crucial role in accelerating HER's kinetics. Platinum (Pt)-based electrocatalysts have excellent catalytic activities for HER due to their optimal adsorption/desorption energy for hydrogen and have been are widely used in industrial water electrolyzers. However, their high cost and poor stability seriously limit their broad adoption. Tremendous research efforts have been devoted to developing electrocatalysts based on earth-abundant transition metals, such as iron (Fe), cobalt (Co), nickel (Ni), and molybdenum (Mo). In this regard, emerging single-atom catalysts (SACs) with maximum atom utilization is considered as one of the most promising solutions.
Here, a new cobalt phosphide single site HER electrocatalyst was synthesized from ultrathin 2D ZIF-8 metal-organic framework (MOF) nanosheets using a mixed solution containing Zn2+, Co2+, 2-methylimidazole. The 2D MOF nanosheets facilitate the phosphating of single atom Co sites rather than forming cobalt phosphide nanoparticles. Structural characterizations indicated that the as-synthesized electrocatalyst (denoted as CoPSS) has a CoN2P2 coordination structure, where Co metal centres coordinate with two P atoms and two N atoms. CoPSS demonstrates an excellent HER performance in an alkaline electrolyte with an overpotential of 117 mV at 10 mA cm-2 and a Tafel slope of 55 mV dec-1. This work provides a facile and cost-effective strategy for preparing high efficient HER electrocatalysts.
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Cochran, Colin John. "Electrochemical study of the hydrogen evolution reaction on nickel-palladium-phosphorous amorphous metal alloys for use in alkaline hydrogen systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ51556.pdf.
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Bai, Lijun. "Determination of the adsorption behaviour of O.P.D. H species in the cathodic hydrogen evolution reaction." Thesis, University of Ottawa (Canada), 1986. http://hdl.handle.net/10393/4626.
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Zhang, Tianhou. "Theoretical Studies of Fuel Cell Reaction Mechanisms: Water and Oxygen on Platinum Electrodes." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1215456813.
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Ekspong, Joakim. "Hydrogen Fuel from Water - An Advanced Electrocatalyst based on Nitrogen doped Carbon Nanotubes." Thesis, Umeå universitet, Institutionen för fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-105553.
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The production of cost-effective catalysts for the production of hydrogen by electrolysis of water is important for clean energy production. In this work we report on a study of molybdenum disulfide (MoS2) as catalyst for the hydrogen evolution reaction (HER). Nitrogen doped carbon nanotubes (NCNTs) directly synthesized onto carbon paper have been decorated with MoS2. The electrodes utilize the improved conductivity of the NCNTs and the carbon paper for electron transport, combined with the high catalytic activity of MoS2. The NCNTs were successfully decorated with co-axial nano-flakes of MoS2 by a single step solvothermal process using Dimethylformamide (DMF) and ammonium tetrathiomolybdate. MoS2 was also prepared with alternative methods for comparison. The effects of supporting MoS2 on NCNTs were studied by simulations with density functional theory (DFT). The most active adsorption sites for hydrogen on MoS2 were identified and were on the edges. The catalyst showed competitive activity with other earth-abun- dant catalysts with an onset potential of 170 mV and a small Tafel slope of 40 mV/dec. The improved catalytic activity of HER by having NCNTs as support was confirmed by DFT and experimental results.
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Sinanan, Anson R. "Nickel-based amorphous alloys with Cr/V additions for the hydrogen evolution reaction in alkaline solution." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ63143.pdf.
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Sultana, Ummul Khair. "Electrochemical synthesis of water splitting nanomaterials." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/126972/1/Ummul%20Khair_Sultana_Thesis.pdf.
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This project was a step forward in electrochemically synthesizing nanomaterials for the water splitting reaction which directly produces hydrogen and oxygen. The thesis investigated the performances of newly developed nanomaterials for the energetically demanding water splitting reaction. In order to understand the reaction mechanism, thorough materials characterization was carried out to identify structure-activity relationships. This study also answers some fundamental questions such as "bifunctionality" in the field of water electrolysis. It also presents the modification of a readily available and cheap material, stainless steel, into an efficient water splitting catalyst that operates under industrial conditions.
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Wakisaka, Takuo. "Rational Syntheses of New Metal Nanoparticles and Investigation of Catalytic Activity." Kyoto University, 2020. http://hdl.handle.net/2433/253114.
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Li, Junwei. "Investigation of Structural-Catalytic Relationship of Mixed-Metal Layered Oxide Materials for Photocatalytic Overall Water Splitting." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29385.
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Hydrogen can be generated renewably by sunlight driven, photocatalytic water splitting. Metal oxides, including those with a Ruddlesden-Popper type structures are being studied as potential photocatalysts. From the initial testing of multiple metal oxides, KLaTiO4 and Na3Co2SbO6 was found to be particularly effective as catalyst for hydrogen evolution.
During testing, the solid-state synthesis of KLaTiO4 was found to be unreliable, with most samples found with K2La2Ti3O10 impurities. Two main factors were found to have significantly impacted the yield of KLaTiO4. The first factor to consider is the volatility of alkali metal ions at elevated temperatures. Successful synthesis of KLaTiO4 required 50 % (minimum tested) alkali metal reagent excess. The second factor to consider is related to sintering temperature. From the results of the synthetic experiments, the ideal heating temperature of KLaTiO4 is 800 °C, and the ideal heating temperature of K2La2Ti3O10 is850 °C, which is lower than other literature reports.
As a Hydrogen Evolution Catalyst (HEC), the main disadvantage of KLaTiO4 is its high bandgap of 4.09(13) eV. To reduce the bandgap of KLaTiO4, both cationic and anionic doping of the sample is attempted. Cationic doping of KLaTiO4 was achieved by partially replacing lanthanum with ytterbium, yielding KLa1-xYbxTiO4 (x = 0.005, 0.01 and 0.03). In comparison to KLaTiO4, ytterbium doped samples have a reduced catalytic activity compared to the undoped sample. Anionic doping of KLaTiO4 was attempted by nitrogen doping using TiN as a reagent in place of TiO2, and have the sample annealed under N2 flow, at 800 °C, yielding KLaTiO3N. KLaTiO3N shows good crystallinity, and no observable structural difference to KLaTiO4. When tested as HEC in identical testing condition, KLaTiO3N had a third rate of hydrogen evolution in comparison to KLaTiO4.
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Rodríguez, Hernández Fermín. "Theoretical description of water splitting on TiO2 and combined Mo2C-graphene based materials." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-227530.
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The electrocatalytic water decomposition has been investigated in this thesis by means of its two half standard reactions: the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). These reactions occur in different locations in a typical electrochemical cell: the anode and the cathode, respectively. Motivated by the lack of understanding about the reaction mechanisms occurring at the anodes and cathodes, we have proposed first: novel representations of typical TiO2 surfaces, based on small cluster systems, which can be used for a quick and more detailed assessment of the OER activities at modified TiO2 surfaces, and secondly we investigated the HER in two sets of model surfaces which represent recently synthesized materials, based on Mo2C and graphene with promising activities toward the HER. We have employed Density Functional Theory (DFT) based methods within both localized and extended basis sets, as implemented in GAMESS and VASP packages, respectively, to examine the structural, electronic and vibrational properties of the proposed models.
We propose new reaction mechanisms for the OER on a number of molecular representations of TiO2 electrodes. For each reaction pathway, the free energy profile is computed, at different biases, from the DFT energies, the entropic and the zero-point energy contributions. The mechanisms explored in this thesis are found to be energetically more feasible than alternative reaction pathways considered in previous theoretical works based on molecular representations of the TiO2 surfaces. The representation of the surface of specific, commonly occurring, titanium dioxide crystals (e.g., rutile and anatase) within the small cluster approximation is able to reproduce qualitatively the rutile (110) outperforming of the anatase (001) surface.
We subsequently investigate the influence of doping TiO2 surfaces with transition metals (TMs) on the performance of TiO2 -based electrodes for the water splitting electrochemical reaction. Two cluster models of the TM-doped active sites which resemble both the TiO2 anatase (001) and rutile (110) surfaces, respectively, are considered for the evaluation of the water decomposition reaction when a Ti is replaced by a TM atom. A set of TMs spanning from Vanadium to Nickel is considered. The late TMs explored here: Fe, Co and Ni are found to reproduce the observed experimental trends for the overpotentials in TiO2-doped electrodes. In the case of Cr and Mn, the present study predicts an enhancement of the OER activity for the anatase-like clusters while a reduction of this activity is found for the rutile-like ones. The vanadium-doped structures do not show relevant influence in the OER activity compared to pure TiO2-based cluster models.
The last part of this work is devoted to the theoretical study of the HER on recently found materials based on the synergistic combination of molybdenum carbide and graphene layers. We propose two major structural models to describe the HER mechanism within the framework of DFT: Mo2C-based clusters adsorbed on carbon nanosheets and the Mo2C (001) surface covered by pure and nitrogen-doped graphene layers. The former system evaluates the influence of Mo2C nanoparticles adsorbed on carbon nanosheets towards the HER. The second one is employed to gain insight about the high HER activity observed in molybdenum carbide anchored on nitrogen-doped porous carbon nanosheets (Mo2C@2D-NPC), recently synthesized. The H-adsorption free energy has been used as a principal descriptor to asses the HER activity at the proposed model active sites. It resembles the value for the best state of the art catalyst for the HER (i.e., platinum at carbon substrate Pt@C) in some of the proposed structural models. Furthermore, a pH-correction is added within a simplified model, to the H-adsorption free energy barrier in every proposed structure. The pH dependence of the H-adsorption free energy barriers allows the assessment of the HER at acidic and alkaline conditions simultaneously. An overall agreement with experimental results is found and further predictions, promoting the development of better HER catalysts, have been done.
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Gao, Guoping. "Computational design of catalysts for clean energy conversion and storage." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/109443/1/Guoping_Gao_Thesis.pdf.
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This project focuses on the computational design of novel catalyst for artificial synthesis: converting sunlight into fuels. With the atomic-scale insight of catalysts obtained by theoretical calculations, many efficient and optimum catalysts for these processes have been designed and engineered. The outcomes of this thesis are expected to provide theoretical solutions for current global energy and environmental challenges.
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He, Tianwei. "Computational discovery and design of nanocatalysts for high efficiency electrochemical reactions." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/203969/1/Tianwei_He_Thesis.pdf.
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This thesis reports a computational discovery and design of highly efficient electrocatalysts for various of electrochemical reactions. The method is based on the Density Functional Theory (DFT) by using Vienna ab initio simulation package (VASP). This project is a step forward in developing the low-cost, high activity, selectivity, stability and scalability for the electrochemical reactions, which could make a contribution to the global-scale green energy system for a clean and sustainable energy future.
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Dolgikh, O. V., N. V. Sotskaya, and L. V. Sapronova. "Electrochemical Behavior of Electrodeposited Ni-P Coatings in Acidic Solutions." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35466.
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The paper is devoted to the investigation of cathodic and anodic behavior of electrodeposited Ni-P alloys
of different composition in H2SO4 solutions. It was established that increase of phosphorous content
enhances anticorrosion ability of Ni-P coatings and decreases their catalytic activity toward to hydrogen
evolution reaction. The most probable mechanism of this reaction was suggested on the basis of analysis of
experimental data. It assumes that at low overpotentials hydrogen evolution proceeds by Volmer-
Heyrovsky route with limiting step of charge transfer. At higher potentials Volmer-Tafel mechanism with
slow chemical recombination step takes place.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35466
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Jiang, Nan. "Inorganic Electrocatalysts for Innovative Water Splitting and Organic Upgrading." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/7386.
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The booming worldwide demand for energy and the increasing concerns about global warming due to fossil fuel consumption have urged the development of techniques for storing and converting renewable and clean energy resources. Electrocatlytic or photoelectrocatalytic water splitting to generate green energy carrier H2 with sustainable energy input, like solar, has been regarded as an attractive strategy for carbon-neutral energy needs. However, the sluggish kinetics for both half reactions (HER and OER), high overpotentials and thermodynamic requirements, and H2 and O2 gas crossover have been regarded as the major challenges, which limit its widespread application.
On account of high efficiency and fast reaction rate, proton exchange membrane electrolyzer (PEME) has been developed as a mature technology for water splitting under acidic conditions. Nonetheless, it requires noble metals as robust and competent catalysts (like Pt for HER and IrO2 for OER), which is economically unfavorable. Owing to the thermodynamic convenience for OER and the integration of HER and OER in the same electrolyte, anion exchange membrane electrolyzer (AEME) has also been explored under alkaline conditions, utilizing first-row transition metals as bifunctional catalysts. However, for both PEME and AEME, H2 and O2 are generated simultaneously. Even though “gas impermeable” membranes are employed, the formation of H2/O2 mixture is inevitable. So one part of my research introduced a new strategy to couple HER with more thermodynamically favorable biomass-derived upgrading in alkaline solution, which requires lower energy input than overall water splitting and produces more valuable and non-gas products. However, the solubility of biomass-derived organic compounds as well as the competing reaction of water oxidation limits the catalytic current density.
Therefore, we further introduce the concept of redox mediator (RM) to divide conventional water splitting into two separate steps. This allows H2 and O2 to be produced at different times as well as in different spaces and reduces the energy input required to conduct a productive step. This strategy not only prevents H2/O2 mixing but also reduces the voltage input as the redox potential of RM+/0 will be within the HER and OER thermodynamic potentials, hence allowing water splitting to be driven by photovoltaic cells with small photovoltage.
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Shi, Zhangsheng. "Strain engineering of Co-N-C catalyst toward enhancing the HER and ORR electrocatalytic activities." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/207078/8/Zhangsheng_Shi_Thesis.pdf.
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This thesis presents a comprehensive review of practical strategies to enhance the catalytic activity of M-N-C materials. The practical strategies can be extended to engineer external factors to break the linear scaling relationships and to further enhance the catalytic performances. In order to design the next-generation higher-performance catalysts, this project was a step forward in developing strain and heterostructure method to achieve a superior HER performance and a ORR performance beyond the limit.
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Gottschling, Kerstin [Verfasser], and Bettina [Akademischer Betreuer] Lotsch. "Towards single-site heterogeneous catalysts for the hydrogen evolution reaction based on covalent organic frameworks / Kerstin Gottschling ; Betreuer: Bettina Lotsch." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2020. http://d-nb.info/1218466081/34.
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Fan, Kaicai. "Development of High Performance Electrocatalyst for Water Splitting Application." Thesis, Griffith University, 2018. http://hdl.handle.net/10072/382229.
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With increasing global demand for energy, rapid depletion of fossil fuels and intensification of environmental concerns, exploring clean and sustainable energy carriers to replace fossil fuel is becoming critical. Among the various alternatives, hydrogen has been intensively regarded as a promising energy carrier to fulfill the increasing energy demand due to its large energy density per unit mass and eco-friendly production possibilities. However, hydrogen does not exist in molecular structure in nature, and it is essential to obtain efficient and sustainable H2 production technologies. Alkaline water electrolysis is an effective, clean and sustainable process to produce high-quality hydrogen. In this process, highly active electrocatalysts for the hydrogen evolution reaction (HER) are required to accelerate the sluggish kinetics and lower the overpotentials (η) for efficient hydrogen evolution. To date, a noble metal, platinum (Pt), is the state-of-art electrocatalyst for HER. However, exploration of alternative electrocatalysts with low cost and excellent electrocatalytic activity is of vital importance to realize large-scale hydrogen production through water electrolysis. Generally, an electrochemically active catalyst should have an optimal hydrogen adsorption free energy to allow efficient catalytic hydrogen adsorption/desorption. In alkaline solution, dissociation of water onto the electrocatalyst determines the overall HER efficiency.
This thesis focuses on rational design and synthesis of different earth-abundant electrocatalysts for electrocatalytic HER in alkaline media. Through facile anion or cation doping strategies, electrocatalysts with abundant accessible active sites, enhanced electronic conductivity and accelerated HER kinetics have been systematically fabricated, characterized and evaluated.
First, an efficient HER electrocatalyst in alkaline media was fabricated by incorporating sulfur atoms into a cobalt (hydro)oxide crystal structure. The resultant catalyst exhibits a remarkably enhanced HER activity with a low-overpotential of 119 mV at 10 mA/cm2 and an excellent durability. The results suggest that cobalt hydroxide benefits water adsorption and cleavage, while the negatively charged sulfur ligands facilitate hydrogen adsorption and desorption on the surface of electrocatalysts, leading to significantly promoted Volmer and Heyrovsky steps for HER in alkaline media.
Second, exploring bifunctional electrocatalysts which can simultaneously accelerate the HER and oxygen evolution reaction (OER) activities plays a key role in alkaline water splitting. Here, sulfur atoms were incorporated into the mixed transition metal hydroxide with high OER performance to render excellent HER activity. The enhanced catalytic activity towards HER was confirmed by a synergistic effect between the retained metal hydroxide host and the incorporated sulfur atoms. In addition, the full water splitting electrolyzer equipped with fabricated bifunctional electrocatalysts as anode and cathode materials exhibited remarkable overall water splitting performance comparable to that with benchmark Pt and RuO2 electrocatalysts.
The S/Se co-doped Co3O4 nanosheets on carbon cloth were fabricated by a facile room temperature chalcogen atom incorporation methodology and were applied as the electrocatalyst for HER in alkaline media. The sulfur and selenium atoms were homogeneously distributed on the surface by forming Co-S or Co-Se bonds which play a key role in the structural change in electrochemical activation. The obtained electrocatalysts demonstrated remarkably improved HER activity compared to that of the original Co3O4.
Finally, molybdenum doped cobalt hydroxide was fabricated with significantly accelerated HER kinetics. The introduced Mo sites not only effectively facilitate water dissociation process and desorption of the OHads intermediates, but also simultaneously optimize the hydrogen adsorption free energy. Therefore, the in situ-generated Mo-doped amorphous cobalt hydroxide exhibited a remarkable HER performance in alkaline media with an overpotential of only -80 mV at a current density of 10 mA/cm2.
This thesis innovatively explores strategies to improve the catalytic activity towards HER of metal (hydro)oxide in alkaline media. The surface foreign atom doping was demonstrated to manipulate the surface structure of catalysts, thus not only improving the water dissociation processes, but also facilitating the hydrogen adsorption/desorption on the catalysts. The demonstrated facile and effective strategies could be adopted for the fabrication of cost-effective and highly active catalysts for other important chemical reactions for energy conversion applications.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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Jiang, Nan. "First-Row Transition Metal Sulfides and Phosphides as Competent Electrocatalysts for Water Splitting." DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/6480.
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Conversion of renewable energy resources (such as solar and wind) through water splitting to hydrogen and oxygen has attracted increasing attention. The sole product of hydrogen combustion is water, rendering a carbon-neutral energy cycle. Water splitting consists of two redox half reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Both of these two transformations involve multi- electron/proton movement and thus are kinetically sluggish. In order to accelerate the reaction rates for practical application, efficient catalysts are needed. State-of-the-art catalysts for water splitting are usually composed of noble metals, such as platinum, ruthenium, and iridium, whose scarcity and high cost limit their wide employment. Consequently, it is of critical importance to develop competent and non-precious catalysts via low-cost preparation.
Owing to the thermodynamic convenience and potential application in proton exchange membrane and alkaline electrolyzers, traditionally, most HER catalysts were developed under strongly acidic conditions while OER catalysts under strongly alkaline conditions. In order to accomplish overall water splitting, the coupling of HER and OER catalysts in the same electrolyte is mandatory. This thesis will summarize our recent efforts towards developing 1st-row transition metal-based sulfides and phosphides for electrocatalytic water splitting under ambient conditions.
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Oshchepkov, Alexandr. "Investigation of the hydrogen electrode reactions on Ni electrocatalysts in alkaline medium." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAF071/document.
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La thèse présentée traite principalement de l'influence de la composition et de l’état de surface d’électrodes à base de Ni sur la cinétique et le mécanisme des réactions d'oxydation/dégagement de l'hydrogène (HOR/HER) en milieu alcalin. En combinant les résultats de mesures électrochimiques avec une modélisation microcinétique, il a pu être montré que l'activité spécifique du Ni pour l’HOR/HER augmente jusqu'à 10 fois en présence à la fois d’oxydes de Ni et de Ni métallique à la surface de l'électrode. En outre, l'influence de l'addition d’un second métal aux électrocatalyseurs à base Ni sur leurs activités pour l’HOR/HER a été étudiée dans le cas des systèmes NiMo/C et NiCu/C. Dans les deux cas, une augmentation de l'activité spécifique a été observée par rapport à l'échantillon Ni/C de référence et a été attribuée à une diminution de l'énergie d'adsorption de l'hydrogène adsorbé sur Ni, espèce intermédiaire de l’HOR/HERThe present thesis is mainly focused on the influence of the surface state of Ni electrodes on the kinetics and the mechanism of the hydrogen oxidation/evolution reactions (HOR/HER) in alkaline medium. By combining the results of electrochemical measurements with microkinetic modeling, it was shown that specific activity of Ni in the HOR/HER increases up to 10 times if along with metallic Ni, Ni oxide species are present on the electrode surface. In addition, the effect of the addition of a second metal to Ni electrocatalysts on their activity in the HOR/HER was investigated for NiMo/C and NiCu/C systems. In both cases an enhancement of specific activity was observed in comparison with the reference Ni/C sample, which was assigned to a decrease of the adsorption energy of the hydrogen intermediate on Ni participating in the HOR/HER
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Beauchamp, Damian Richard. "Molecular Engineering of Organic Photosensitizes for P-type Dye-Sensitized Solar Cells and the Immobilization of Molecular Catalyst for the Hydrogen Evolution Reaction." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1456917343.
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Ma, Lu. "Mo-S Chemistry: From 2D Material to Molecular Clusters." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480268313180315.
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Larrieu, Axelle. "Vers la production d'hydrogène par photocatalyse : élaboration de structures organiques covalentes colloïdales induites par auto-assemblage réactif." Electronic Thesis or Diss., Pau, 2024. http://www.theses.fr/2024PAUU3052.
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Produit à partir d'eau, l’hydrogène vert représente une alternative potentielle à l’utilisation des énergies fossiles. Cependant, une transition énergétique vers l’hydrogène n’a de sens que s’il est produit à partir de ressources renouvelables et non obtenu grâce à des électrolyseurs alimentés par le réseau national d’électricité. Dans ce contexte, l’utilisation de catalyseurs photosensibles, capables de produire du H2 à partir d’énergie solaire, offre des perspectives prometteuses. Parmi les différents systèmes photocatalytiques, on trouve les « Covalent Organic Frameworks » (COFs).Les COFs sont constitués de molécules organiques capables de former des réseaux périodiques covalents bidimensionnels (feuillets) pouvant être empilés grâce à des interactions π-π pour former une structure tridimensionnelle. Ce sont des matériaux cristallins poreux, qui possèdent une grande résistance thermique et chimique. Grâce à ces propriétés, les COFs représentent de bons candidats pour la photocatalyse applicable à la réduction des protons en hydrogène (H2). Cependant, leur croissance cristalline rapide réduit leur solubilité, limitant le contrôle de leur morphologie ainsi que leur mise en œuvre. L’objectif de cette thèse est donc de contrôler la croissance cristalline des COFs en solution, en élaborant des objets auto-assemblés colloïdaux, pour faciliter leur utilisation. Dans cette optique, des agents bloquants de croissance ont été ajoutés lors de leur synthèse pour stopper leur croissance dans une direction de l’espace et ainsi confiner le réseau COF dans un cœur, stabilisé par l’agent bloquant. Un agent bloquant moléculaire et macromoléculaire ont été utilisés, dans le but d’apporter davantage de stabilité grâce à la formation d’encombrement stérique.De plus, l’utilisation d’un polymère hydrophile (Poly(2-(DiMéthylAmino)Ethyl MéthAcrylate)) comme agent bloquant, a permis d’obtenir des COFs colloïdaux stables dans l’eau. L’application de ces COFs colloïdaux à la photocatalyse a finalement montré que ces systèmes étaient capables de produire de l’hydrogène sous irradiation solaire à partir d’eau, ouvrant ainsi la voie à l’utilisation de COFs colloïdaux pour la production d’hydrogèneGreen hydrogen represents a potential alternative to fossil fuels as it is produced from water. However, an energy transition to hydrogen only makes sense if it is produced from renewable resources and not from electrolyzers fed by the national electricity grid. In this context, using photosensitive catalysts capable of producing H2 from solar energy offers promising prospects. Among the various photocatalytic systems are Covalent Organic Frameworks (COFs).COFs are made up of organic molecules capable of forming two-dimensional covalent periodic networks (sheets) that can be stacked by π-π interactions to form a three-dimensional structure. They are porous crystalline materials with high thermal and chemical resistance. Thanks to these properties, COFs are good candidates for photocatalysis applicable to the reduction of protons to hydrogen (H2). However, their rapid crystal growth reduces their solubility, limiting control of their morphology and their processing. The aim of this PhD is to control the crystalline growth of COFs in solution, by developing colloidal self-assembled objects, to facilitate their use. To this end, growth blocking agents were added during their synthesis to stop their growth in one direction in space and thus confine the COF network to a core, stabilized by the blocking agent. Molecular and macromolecular blocking agents were used to provide additional stability through the formation of steric hindrance.In addition, the use of a hydrophilic polymer (Poly(2-(DiMethylAmino)Ethyl MethAcrylate)) as a blocking agent made it possible to obtain colloidal COFs that were stable in water. The application of these colloidal COFs to photocatalysis finally showed that these systems were capable of producing hydrogen from water under visible light irradiation, paving the way for the use of colloidal COFs for hydrogen production
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Eguchi, Daichi. "High Functionalization of Nanomaterials by Controlling Organic-Inorganic Interface." Kyoto University, 2017. http://hdl.handle.net/2433/227580.
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Naderinasrabadi, Mahtab. "A Continuous Electrochemical Process to Convert Lignin to Low Molecular Weight Aromatic Compounds and Cogeneration of Hydrogen." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1584622583669502.
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Oloye, Olawale. "Design and engineering of nanostructured liquid metal composites for catalytic applications." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/227405/1/Olawale_Oloye_Thesis.pdf.
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This thesis concentrated on the study of the room temperature liquid metal, gallium and its eutectics. The application of liquid metal-based alloys to new areas of catalysis was extended by encompassing energy and environmental applications. A significant advancement in the potential application of liquid metal-based alloys in electrocatalysis, photocatalysis and sonocatalysis has resulted from this research. Significantly, research conducted on carbon dioxide capture/conversion to metal carbonates during this graduate study is currently being explored for industrial waste management.
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Meng, Yao. "Hydrogen electrochemistry in room temperature ionic liquids." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:be24c6ea-c351-4855-ad9c-98e747ac87e4.
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This thesis primarily focuses on the electrochemical properties of the H2/H+ redox couple, at various metallic electrodes in room temperature ionic liquids. Initially, a comprehensive overview of room temperature ionic liquids, RTILs, compared to conventional organic solvents is presented which identifies their favourable properties and applications, followed by a second chapter describing the basic theory of electrochemistry. A third chapter presents the general experimental reagents, instruments and measurements used in this thesis. The results presented in this thesis are summarized in six further chapters and shown as follows. (1) Hydrogenolysis, hydrogen loaded palladium electrodes by electrolysis of H[NTf2] in a RTIL [C2mim][NTf2]. (2) Palladium nanoparticle-modified carbon nanotubes for electrochemical hydrogenolysis in RTILs. (3) Electrochemistry of hydrogen in the RTIL [C2mim][NTf2]: dissolved hydrogen lubricates diffusional transport. (4) The hydrogen evolution reaction in a room temperature ionic liquid: mechanism and electrocatalyst trends. (5) The formal potentials and electrode kinetics of the proton_hydrogen couple in various room temperature ionic liquids. (6) The electroreduction of benzoic acid: voltammetric observation of adsorbed hydrogen at a Platinum microelectrode in room temperature ionic liquids. The first two studies show electrochemically formed adsorbed H atoms at a metallic Pt or Pd surface can be used for clean, efficient, safe electrochemical hydrogenolysis of organic compounds in RTIL media. The next study shows the physicochemical changes of RTIL properties, arising from dissolved hydrogen gas. The last three studies looked at the electrochemical properties of H2/H+ redox couple at various metallic electrodes over a range of RTILs vs a stable Ag/Ag+ reference couple, using H[NTf2] and benzoic acid as proton sources. The kinetic and thermodynamic mechanisms of some reactions or processes are the same in RTILs as in conventional organic or aqueous solvents, but other remarkably different behaviours are presented. Most importantly significant constants are seen for platinum, gold and molybdenum electrodes in term of the mechanism of proton reduction to form hydrogen.
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Bernsmeier, Denis Robert [Verfasser], Ralph [Akademischer Betreuer] Krähnert, Ralph [Gutachter] Krähnert, Peter [Gutachter] Strasser, and Christina [Gutachter] Roth. "Noble metal nanoparticles supported in ordered mesoporous carbon coatings as efficient electrocatalysts for the hydrogen evolution reaction / Denis Robert Bernsmeier ; Gutachter: Ralph Krähnert, Peter Strasser, Christina Roth ; Betreuer: Ralph Krähnert." Berlin : Technische Universität Berlin, 2017. http://d-nb.info/1156014301/34.
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Dessources, Samuel. "Conception de matériaux de type PtxM1-x/C (M=Ni, Nb) et PtxNi1-x/CeO2/C pour l'électroréduction de l'eau (HER) et l'électrooxydation du dihydrogène (HOR)." Thesis, Poitiers, 2015. http://www.theses.fr/2015POIT2317/document.
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Le platine constitue le matériau de référence pour l’électroréduction de l’eau (HER) et l’électrooxydation du dihydrogène (HOR). Les propriétés physicochimiques de ce matériau d’électrode synthétisé sous forme Pt/C par la méthode BAE et les paramètres cinétiques des réactions électrochimiques HOR et HER à sa surface en milieu alcalin ont été déterminés. Le palladium et l’or ont aussi des activités intéressantes vis-à-vis de ces réactions. L’activité de ces métaux nobles supportés sur carbone et obtenus par la même méthode de synthèse a été étudiée dans les mêmes conditions pour établir une étude comparative.L’effet de Ni et Nb sur l’activité catalytique de Pt pour HOR et HER a aussi été étudié. Des catalyseurs de type PtxM1-x/C (M=Ni, Nb) ont été préparés et leurs propriétés physicochimiques ainsi que leurs activités électrocatalytiques étudiées. Bien que Ni et Nb ne catalysent pas ces réactions dans le domaine de potentiel scruté, leur présence induit des modifications du site catalytique et influence l’activité catalytique des différents matériaux d’électrode. Pour chaque catalyseur les paramètres cinétiques ont été déterminés et les résultats révèlent des catalyseurs bimétalliques très prometteurs. Les mesures de CO-stripping ont ensuite mis en évidence un effet électronique sur le platine favorable à l’oxydation du CO à bas potentiel sur les catalyseurs PtxNi1-x/C.Des résultats très encourageants ont montré que la modification du support de l’électrode (ajout de CeO2) a permis d’obtenir un catalyseur (Pt0,5Ni0,5/CeO2/C) possédant des activités catalytiques en HER et HOR similaires à celles de Pt/C tout en diminuant de 50% la quantité de PtPlatinum is the reference material for the electroreduction of water (HER) and the electrooxidation of hydrogen (HOR). The starting point of this work was the synthesis of Pt/C by the BAE method. The physicochemical properties of this material and the corresponding kinetic parameters for HOR and HER in alkaline medium were obtained. Palladium and gold also exhibit interesting activities towards these reactions. The activity of these metals supported on carbon and obtained by the same synthesis method was therefore studied in the same conditions so as to perform a comparative investigation.The effect of Ni and Nb on the catalytic activity of Pt for both reactions (HOR and HER) was also investigated. Thus, two sets of PtxM1-x/C (M = Ni, Nb) catalysts were prepared and their physicochemical properties and electrocatalytic activities studied in alkaline medium. Although Ni and Nb do not catalyze HOR nor HER in the scrutinized potential range, their presence can lead to changes in the catalytic site and consequently influence the electrocatalytic activity of the various materials towards the studied reactions. For each material, the kinetic parameters were determined for both HER and HOR and compared with those obtained for Pt/C. The results revealed very promising bimetallic catalysts. Moreover, the CO-stripping measurement highlighted an electronic effect on platinum favorable to the CO oxidation at low potential values for the PtxNi1-x/C materials.Finally, the modification of the electrode support by adding CeO2 resulted in a Pt0,5Ni0,5/CeO2/C catalyst exhibiting excellent catalytic activities towards HER and HOR while decreasing significantly (50%) the amount of Pt
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Ying, Qiling. "Preparation and characterization of highly active nano pt/c electrocatalyst for proton exchange membrane fuel cell." Thesis, University of the Western Cape, 2006. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_3791_1188474883.
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Catalysts play an essential role in nearly every chemical production process. Platinum supported on high surface area carbon substrates (Pt/C) is one of the promising candidates as an electrocatalyst in low temperature polymer electrolyte fuel cells. Developing the activity of the Pt/C catalyst with narrow Pt particle size distribution and good dispersion has been a main concern in current research.
In this study, the main objective was the development and characterization of inexpensive and effective nanophase Pt/C electrocatalysts. A set of modified Pt/C electrocatalysts with high electrochemical activity and low loading of noble metal was prepared by the impregnation-reduction method in this research. The four home-made catalysts synthesized by different treatments conditions were characterized by several techniques such as EDS, TEM, XRD, AAS, TGA, BET and CV.
Pt electrocatalysts supported on acid treatment Vulcan XC-72 electrocatalysts were produced successfully. The results showed that Pt particle sizes of Pt/C (PrOH)x catalysts between 2.45 and 2.81nm were obtained with homogeneous dispersion, which were more uniform than the commercial Pt/C (JM) catalyst. In the electrochemical activity tests, ORR was confirmed as a structure-sensitive reaction. The Pt/C (PrOH/pH2.5) showed promising results during chemically-active surface area investigation, which compared well with that of the commercial standard Johnson Matthey Pt/C catalyst. The active surface area of Pt/C (PrOH/pH2.5) at 17.98m2/g, was higher than that of the commercial catalyst (17.22 m2/g ) under the conditions applied. In a CV electrochemical activity test of Pt/C catalysts using a Fe2+/Fe3+ mediator system study, Pt/C (PrOH/pH2.5) (67mA/cm2) also showed promise as a catalyst as the current density is comparable to that of the commercial Pt/C (JM) (62mA/cm2).
A remarkable achievement was attained in this study: the electrocatalyst Pt supported on CNTs was synthesized effectively. This method resulted in the smallest Pt particle size 2.15nm. In the electrochemically-active surface area study, the Pt/CNT exhibited a significantly greater active surface area (27.03 m2/g) and higher current density (100 mA/cm2) in the Fe2+/Fe3+ electrochemical mediator system than the other home-made Pt/C catalysts, as well as being significantly higher than the commercial Pt/C (JM) catalysts. Pt/CNT catalyst produced the best electrochemical activities in both H2SO4 and K4[Fe(CN)6] electrolytes. As a result of the characteristics of Pt/CNTï¼it can be deduced that the Pt/CNT is the best electrocatalyst prepared in this study and has great potential for use in fuel cell applications.
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Benchakar, Mohamed. "Synthèse et caractérisation de nouveaux composés bidimensionnels, les MXènes, pour le stockage et la conversion de l'énergie." Thesis, Poitiers, 2020. http://www.theses.fr/2020POIT2271.
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L'hydrogène est le vecteur énergétique le plus prometteur pour l’implémentation de la grille énergétique du futur. Il peut être obtenu en employant diverses méthodes de production. Parmi tous ces procédés, l’électrolyse de l’eau est d’intérêt car elle permet d’obtenir directement du dihydrogène de grande pureté qui peut donc être utilisé au sein d’une pile à combustible H2/O2. Toutefois, l’élaboration d’électrodes peu coûteuses, actives et stables est nécessaire pour entreprendre le développement des électrolyseurs à grande échelle. Dans ce contexte, les matériaux 2D suscitent un engouement important pour l’élaboration de catalyseurs en raison de l’élévation du rapport entre atomes de surface et atomes de volume, qui leur confère des propriétés extrêmement différentes de celles de leurs analogues massifs. À ce titre, les MXènes (découverts en 2011) sont des matériaux particulièrement intéressants. Leurs caractéristiques intrinsèques (conductivité électronique élevée, hydrophilie, chimie versatile) renforcent encore l’intérêt qu’ils suscitent et font de ces matériaux des candidats de choix pour l’élaboration de matériaux catalytiques.Au cours de cette thèse les MXènes de type Ti3C2Tx ont tout d’abord été synthétisés à l’aide de différents milieux exfoliants, puis caractérisés dans le but d’en appréhender la chimie d’hydratation, la composition, la structure, la microstructure, la chimie de surface et les propriétés macroscopiques. Ce MXène, présentant néanmoins une faible activité pour les réactions de dégagement de dihydrogène et de dioxygène, a été utilisé comme support d’hydroxydes doubles lamellaires à base de cobalt. La présence de nombreux groupements terminaux à la surface du MXène permet d’obtenir une bonne dispersion de la phase active. De plus, le MXène assure la bonne conductivité électronique de l’électrode favorisant les transferts de charge. Les propriétés structurales du matériau résultant (Co-LDH@Ti3C2Tx) ont été étudiées et reliées à son excellente activité catalytique envers la réaction de dégagement de dioxygène en milieu alcalin. Cette performance a pu être associée au travers de l’étude de l’interaction électronique existant entre phase active et MXène. Suite à ces premiers travaux, des MXènes de type Mo2CTx ont aussi été synthétisés, caractérisés et utilisés en tant que précurseur pour la synthèse d’une hétérostructure bidimensionnelle de type MoS2/Mo2CTx. Ce matériau innovant fut obtenu par transformation topotactique (sulfuration) de Mo2CTx. Ce composite s’est avéré être un excellent catalyseur envers la réaction de dégagement de dihydrogène en milieu électrolytique alcalin. Cette augmentation d’activité a pu d’une part être attribuée au contact intime existant entre les phases MoS2 et Mo2CTx., permettant notamment une activation du plan basal du sulfure 2D et d’autre part à la présence d’atomes faiblement coordonnés permettant une activation de l’eau à de faibles surtensions.Ainsi, des catalyseurs à base de MXènes, performants et stables pour les deux réactions en jeu dans un électrolyseur alcalin, ont été élaborés. Les perspectives de ce travail afin d’obtenir des électrodes encore plus performantes sont nombreuses compte-tenu de la richesse de la chimie de ces nouveaux matériaux 2DHydrogen is the most promising energy vector for the future energy grid implementation. It can be obtained from different methods of production. However, an eco-friendly hydrogen with a high purity can only be produced using water electrolysis. Furthermore, the design of low cost, active and stable electrodes is required for the development of large scale electrolysis systems. In this context, 2D materials are of upmost interest for the development of catalysts in reason of their high surface to volume ratio, conferring them unique properties far from those of their bulk counterparts. In this way, MXene family (discovered in 2011) is a good candidate. Their intrinsic properties (high electronic conductivity, hydrophilicity, versatile chemistry) reinforces the passion they arouse and make these materials as promising candidates for the design of efficient catalysts. In this work, several Ti3C2Tx MXenes were first synthesized using different etching agents and characterized in order to elucidate the hydration chemistry, composition, structure, surface chemistry and macroscopic properties. This MXene, which nevertheless exhibits a low catalytic performance toward hydrogen and oxygen evolution reactions, has been used as a support for cobalt-based layered double hydroxides. The presence of numerous terminal groups on the MXene surface allows obtaining a good dispersion of the active phase. In addition, MXene ensures the good electronic conductivity of the electrode which promotes the charge transfer. The structural properties of the resulting material (Co-LDH@ Ti3C2Tx) were studied and correlated to its good catalytic activity toward oxygen evolution reaction in alkaline medium. This performance could be associated to the electronic interaction occurring between the active phase and the MXene. Further, Mo2CTx MXenes were also synthesized, characterized and used as a precursor for the synthesis of a MoS2/Mo2CTx two-dimensional heterostructure. This innovative material was obtained by topotactic transformation (sulfurization) of Mo2CTx. This composite has proven to be an excellent catalyst toward hydrogen evolution reaction in alkaline medium. This high activity could be attributed to the intimate contact existing between the MoS2 and Mo2CTx phases on one hand, allowing an activation of the 2D sulfide basal plane and to the presence of weakly coordinated atoms on the other hand, allowing the water activation at low overpotentials.Thus, efficient and stable MXene-based catalysts have been developed for oxygen and hydrogen evolution reaction. The prospects for this work are numerous considering the chemistry richness of these new 2D materials in order to obtain more efficient electrodes
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Zang, Dejin. "Hybrid polyoxometalate@M NP photosensitized systems for the generation of photocurrent or for the generation of dihydrogen." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAF032.
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Différents systèmes polyoxométallates@M-colorants ont été réalisés dans cette thèse pour électrochimique dégagement d'hydrogène catalytique et génération photocourant.• Des films hybrides, basés sur des interactions électrostatiques entre une porphyrine tetracationique et des nanoparticules stabilisées par des POMs du type POM@Pt sur ITO, ont été formés par la méthode dite couche par couche et ont été utilisés pour la génération de H2 ou de photocourant. • Pour améliorer le transfert de charge entre les nanoparticules POM@M et le substrat, la réduction de l'oxyde de graphène a été réalisée pour former des systèmes hybrides rGO/POM@Pt. Le dégagement d'hydrogène a été mesuré.• Les copolymères polycationiques bis-porphyrine ont également été obtenus par électropolymérisation avec des espaceurs bis-pyridinium. Par réaction de métathèse, l’incorporation avec divers POM de type Keggin ou des nanoparticules du type POM@Ag ont ensuite été realise. Leurs performances photovoltaïques ont ensuite été étudiées.• Enfin des films hybrides PEDOT dopés avec des nanoparticules du type POM@M ont également été fabriqués. Les performances photovoltaïques ont été examinés montrant une forte amélioration sous illumination dans le domaine du visible. L’ensemble de ces matériaux hybrides ont montré des propriétés intéressantes pour des applications photovoltaïques et la conversion d'énergiePolyoxometalates@M NPs-dyes molecular hybrid systems were realized in this thesis for electrochemical catalytic hydrogen evolution and photocurrent generation. • First, hybrid films, based on electrostatic interactions between the tetracationic porphyrin and POMs@Pt NPs composites on ITO slides, were formed by the so called Layer-by-Layer method for HER and photocurrent generation.• To improve the charge transfer between POMs@M NPs and the substrate, reduced graphene oxide was introduced to form rGO/POMs@Pt NPs hybrid systems. Hydrogen evolution was measured after dropping this composites onto the surface of glassy carbon electrodes.• Polycationic bis-porphyrin copolymers have been also obtained by an electropolymerization leading to the formation of new bis-porphyrin copolymers with pyridinium as spacers. Incorporation with various Keggin type POMs or POMs@Ag was then achieved, their photovoltaic performances were also studied.• POMs@M NPs doped PEDOT hybrids films have been also fabricated. The photovoltaic performances has been examined showing particularly strong enhancement under visible light. In conclusion, these polyoxometalates based hybrids materials have shown interesting properties for photovoltaic application and energy conversion
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Lekbir, Choukri. "Effet de la déformation plastique du nickel monocristallin sur l'état d'équilibre de l'hydrogène en surface et subsurface." Thesis, La Rochelle, 2012. http://www.theses.fr/2012LAROS368.
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Le présent travail a pour objectif d’étudier la synergie entre la déformation plastique et les processus d’adsorption et d’absorption de l’hydrogène en surface et en subsurface du nickel monocristallin. La Réaction d’Evolution de l’Hydrogène (REH) et l’absorption de l’hydrogène en subsurface (RAH)partagent le plus souvent l’intermédiaire commun : l’hydrogène adsorbé (Hads). Le chemin réactionnel de la REH sur des surfaces de nickel (100) en milieu acide sulfurique peut être présenté par un mécanisme de Volmer-Heyrovsky. Les paramètres cinétiques élémentaires correspondants comme les coefficients de symétrie, les enthalpies d'activation, le nombre de sites actifs, ont été simulés via un modèle thermocinétique en utilisant les données expérimentales. Ces paramètres peuvent être affectés par la déformation plastique. Cette dernière modifie la densité et la distribution des dislocations stockées affectant la rugosité de surface à l'échelle atomique et engendrant des sites actifs supplémentaires d'adsorption. En revanche, l’émergence de ligne de glissement à la surface conduit à un phénomène de désactivation associé la formation de plan plus compact (111). L’entrée d’atomes d’hydrogène associée à l’étape de transfert surface-Subsurface peut être mesurée à l’aide d’une méthode potentiostatique de type pulsé. Cette dernière a permis de caractériser la diffusion et le piégeage de l'hydrogène en subsurface. Deux zones peuvent être distinguées, l’une proche de la surface (subsurface) et l’autre au coeur de l'échantillon. Dans ce cas, le coefficient de diffusion associé à la subsurface semble être beaucoup plus élevé que celui obtenu au coeur du métal. En revanche,l’application d’une contrainte mécanique conduit à une augmentation de la densité de pièges. Cette dernière, développée au voisinage de la surface : « subsurface », est plus faible que celle à coeur du matériau, ce qui suggère un effet adoucissant en subsurfaceThe present work has for objective to study the synergy between the plastic strain and the processes of adsorption and absorption of hydrogen on the surface and the subsurface of nickel single crystal.Hydrogen Evolution Reaction (HER) and Hydrogen Absorption in subsurface (HAR) share mostly the common intermediate: the adsorbed hydrogen (Hads). The HER pathway on nickel (100) single crystal surfaces in sulphuric acid medium can be related by a Volmer-Heyrovsky mechanism. The corresponding elementary kinetic parameters as symmetry coefficients, activation enthalpies, number of active sites, have been identified via a thermokinetic model using experimental data. These parameters can be affected by defects associted with plastic strain. Irreversible plastic strain modifies the density and the distribution of storage dislocations affecting the surface roughness at atomic scale and generating additional active adsorption sites. Further more, surface emergence of mobile dislocations induces the formation of slip bands, which modify the surface roughness and the electronic state of the surface and increases the (111) surface density. The entry of hydrogen atoms associated to the transfer step surface-Subsurface can be measured using a potentiostatic double-Steptechnique (pulse method). This last allowed to characterizing the diffusion and trapping of hydrogen in the subsurface. Two domains can be distinguished, that of the subsurface and that of the bulk of the sample. In this case, the diffusion coefficient near the surface (subsurface) seems to be much higher than that obtained in the bulk of the metal. On the other hand, the application of mechanical stressleads to an increase of traps density. This last, developed near the surface: « subsurface », is lower than that at the bulk of material, which suggest a softening effect in the subsurface
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Zhou, Zheng. "Non-Noble Metal-Based Electrocatalysts for Efficient Hydrogen Evolution Reactions." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20956.
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Electrolysis of water by electricity generated from renewable energy sources is promising sustainable hydrogen (H2) production method. A critical task to realize the widespread application of this method is to develop high performance, low price, and stable electrocatalysts for hydrogen evolution reaction (HER). This thesis focuses on the understanding of the stability of non-noble metal-based electrocatalysts in electrolytes with a wide range of pH and the development of novel high-performance non-noble metal-based electrocatalysts for HER. First, using Ni2P as a reprehensive 3d transition metal-based electrocatalyst, its pHdependent performance stability was studied in detail. The pH of electrolytes strongly influences the HER activity of the Ni2P electrocatalyst. Tests in 19 electrolytes with pH ranging from 0.52 to 13.53, my results show that Ni2P is much more active in acidic and alkaline electrolytes. With the increase of pH, lower H+ concentration reduces the formation of adsorbed H atoms in the Volmer reaction, resulting in more impoverished activities. However, the high activity observed in the strong alkaline electrolytes is not the intrinsic property of Ni2P. Ni oxides/hydroxides are formed in strong alkaline electrolytes under applied potentials, resulting in improved activities. Next, I demonstrated the synthesis of ultrafine β-Mo2C nanoparticles with narrow size distribution (2.2 ± 0.3 nm) and high mass loading (up to 27.5 wt.%.) on graphene substrate using a giant Mo-based polyoxomolybdate (POM) cluster, Mo132 ((NH4)46[Mo132O372(H2O)72(CH3COO)30]). A nitrogen-containing polymeric binder (polyethyleneimine) was used to create Mo-N bonds between Mo2C nanoparticles and nitrogen-doped graphene layers, which dramatically improve the catalytic performance of the Mo2C electrocatalyst for HER as revealed by X-ray photoelectron spectroscopy and density functional theory calculations. The optimized Mo2C electrocatalyst shows a large exchange current density of 1.19 mA cm–2, a high turnover frequency of 0.70 s–1 as well as excellent durability. This new synthesis strategy opens the possibility of developing practical platinum substitutes based on Mo2C for practical HER applications.
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Al-Odail, Faisal. "High-throughput synthesis and screening of binary alloys for hydrogen evolution and oxidation reactions." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/173967/.
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High throughput methods were employed for the physical vapour deposition (PVD) and electrochemical screening of random and equilibrated (annealed at 300 ºC for 15 minutes) binary metal alloys for the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR). Results are presented for the Pd-Au, Pd-Bi and Ru-Au alloy systems. Thin films of each alloy system were synthesized on a series of 10x10 array electrodes with a graded composition. A variety of analytical techniques including Energy Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and powder X-ray Diffraction (XRD) were used for the analysis of bulk composition, surface composition and structure respectively. The compositional analysis reveals that alloy formation and synthesis of nearly the whole compositional range of the alloy systems were achieved. Surface segregation of Au in the Pd-Au alloy system and Ru in the Ru-Au alloy system was observed. The surface segregation in the equilibrated Pd-Bi alloy system did not take place. The HER and HOR activity on all the examined alloy systems exhibit a similar compositional dependence. This suggests that the HER activity provides a good descriptor for the HOR activity for systems with low overpotentials. An exception of this occurs, however, at high concentrations of Au and Bi where the HER activity decreases monotonically towards 100 at. %, while the HOR activity decreases more rapidly at alloy compositions of ca. 90 at. %. An enhancement in the activity was found on a variety of alloy compositions over the constituent components. The optimum Pd-Au alloy composition for the HER and HOR was found to be at a composition of ca. Pd50Au50 (more active than pure Pd). A comparable activity to pure Pd was found on Birich alloys (ca. Pd25Bi75) in the Pd-Bi alloy system. The activity on ca. Ru90Au10 and 60-80 % Au was found to be higher than pure Ru. The CO-tolerance in the HOR along the whole compositional range of each alloy system was also assessed in the presence of a mixture of hydrogen and 500 ppm CO. The results suggest that the Ru-Au alloy system is more CO tolerant than the other two systems
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Nylén, Linda. "Influence of the electrolyte on the electrode reactions in the chlorate process." Doctoral thesis, KTH, Tillämpad elektrokemi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4681.
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The chlorate process is very energy intensive and a major part of the production costs are for electrical energy. Since the electricity prices are constantly increasing and may also vary periodically, the chlorate plants may be forced to adjust their production rate to the price at each moment in order to minimise their costs. Variation of current load requires increased knowledge regarding the electrode behaviour in a wide current range. In this thesis, the aim was to study the impact of the electrolyte on the electrode reactions in order to reduce the energy consumption. The work has mainly been experimental and additionally mathematical modelling has been carried out. A wide current range has been investigated in order to increase the understanding of the phenomena and to obtain results useful for low-load operation during the periods of high electricity cost. To operate the anode as energy efficiently as possible, the anode potential should not exceed the critical potential (Ecr), where the slope of the anodic polarisation curve increases, most likely due to ruthenium(VIII)-formation, and where the side reaction of oxygen evolution increases. In this work, the influence of different electrolyte parameters on Ecr has been studied. It was shown that a higher chloride concentration and an increased temperature lowered Ecr, which was expected to increase the risk of exceeding Ecr. However, this was not observed due to a simultaneous favouring of the chloride oxidation. Hence it was concluded that the electrolyte parameters should be optimised so that the lowest possible anode potential is obtained, which would enable higher current densities without exceeding Ecr. A further conclusion is that the increased slope of the polarisation curve at Ecr was possibly related to the lower activity for chloride oxidation on ruthenium oxidised to ruthenium(VIII). At full-load operation, the cathode potential was shown to be rather independent of the electrolyte composition despite a large variation of electrolyte parameters. The cathode composition appears to be more critical than the electrolyte composition when aiming at reducing the energy consumption. A strategy to increase the cathode activity could be to in situ apply a catalytic film onto the electrode surface. Therefore, Y(III) was added to a chloride electrolyte in order to form a yttrium hydroxide film on the alkaline cathode surface during hydrogen evolution. The yttrium-hydroxide film activated reduction of water (hydrogen evolution) and hindered hypochlorite reduction, proton reduction and nitrate reduction. The inhibiting properties are important for the prevention of side reactions, which currently are avoided by reducing Cr(VI) of the electrolyte on the cathode, producing an inhibiting chromium-hydroxide film. The studies on Y(III) increase the expectations for finding alternatives to the toxic Cr(VI). The addition of chromate to the chlorate electrolyte gives a high cathodic current efficiency and chromate has buffering properties in the electrolyte. The role of the buffer has been investigated for the oxygen evolution from water (one possible anodic side reaction), as well as cathodic hydrogen evolution. Models have been developed for these systems to increase the understanding of the interaction between buffer, electrode reactions and mass transport; the results have been verified experimentally. The chromate buffer increased the limiting current significantly for the cathodic H+ reduction and the cathodic overpotential was reduced drastically at currents lower than the limited current. A too low overpotential could result in the cathodic protection being lost. The presence of chromate buffer increased the limiting current for the oxygen evolution from OH-. The modelling of these systems revealed that the homogeneous reactions connected to the electrode reactions were not in equilibrium at the electrode surface. Further, a good resolution of the interface at the electrode surface was crucial since the, for the electrode reactions, important buffering takes place in an nm-thick reaction layer.Framställning av klorat är mycket energiintensiv och kräver stora mängder elenergi. Stigande elpriser, som dessutom ofta varierar under dygnet eller säsongsvis, gör att man vill reducera onödiga förluster samt ibland försöka anpassa produktionen så att man när elpriset är högt minskar den, för att sedan öka produktionen igen då elpriset sjunker. Denna flexibla drift kräver ny kunskap om hur elektroderna beter sig i ett större strömintervall än vad som tidigare varit av intresse. Målet med detta arbete var att, med fokus på elektrolytens betydelse, identifiera möjliga förbättringar för kloratprocessen och därmed minska energiförbrukningen. Studierna har i huvudsak varit experimentella men även matematisk modellering har använts. Ett brett strömintervall har undersökts för att bättre förstå fenomenen och för att även kunna använda resultaten då höga elpriser gör att man vill köra processen vid lägre laster än normalt. För att driften av anoden ska vara så energieffektiv som möjligt bör anodpotentialen inte överskrida den kritiska potentialen (Ecr), där den anodiska polarisationskurvan får en högre lutning (troligtvis pga Ru(VIII)-bildning) och bireaktionen syrgasutveckling ökar. I detta arbete har påverkan av olika elektrolytparametrar på Ecr undersökts. Det visade sig att en ökad kloridkoncentration och ökad temperatur sänkte Ecr. Trots att detta borde göra att Ecr lättare överskrids, blev inte detta fallet eftersom kloridoxidationen samtidigt gynnades. Slutsatsen blir därför att elektrolytparametrarna bör optimeras så att lägsta möjliga anodpotential uppnås, vilket då även gör att strömtätheten kan ökas utan att Ecr överskrids. Slutsatsen är vidare att polarisationskurvans högre lutning vid Ecr kan ha att göra med att rutenium oxiderat till rutenium(VIII) har lägre aktivitet för kloridoxidation. Vid full last visade sig katodens potential vara relativt oberoende av elektrolytsammansättningen trots att denna varierades kraftigt. Katodens sammansättning verkar vara viktigare att ta hänsyn till än elektrolytens för kunna åstadkomma en större energibesparing. Ett alternativ till att öka katodens aktivitet skulle vara att in-situ belägga elektrodytan med en katalytisk film. Försök gjordes att sätta till Y(III) till kloridelektrolyt för att under vätgasutveckling fälla ut en yttriumhydroxidfilm på den alkaliska katodytan. Yttriumhydroxidfilmen aktiverade vattenreduktion (vätgasutveckling) och inhiberade hypokloritreduktion, protonreduktion och nitratreduktion. De inhiberande egenskaperna är viktiga för att förhindra bireaktioner, vilka idag hindras av att Cr(VI) i elektrolyten reduceras på katoden och bildar en hindrande kromhydroxidfilm. Försöken med Y(III) visar att det finns goda möjligheter att hitta alternativ till det miljöfarliga Cr(VI). Kromattillsatsen i kloratelektrolyt ger förutom ett högt katodiskt strömutbyte även en buffrande effekt till elektrolyten. Effekten av buffert har undersökts för en av de anodiska bireaktionerna, syrgasutveckling ur vatten, samt för vätgasutvecklingen på katoden. Dessa system har modellerats för att bättre förstå samspelet mellan buffert, elektrodreaktioner och materietransport och resultaten har verifierats experimentellt. Kromatbufferten ökade gränsströmmen för katodisk H+-reduktion betydligt och katodöverpotentialen sjönk kraftigt vid lägre strömmar än gränsströmmen. Detta kan vara ett problem om överpotentialen sjunker så lågt att elektroden inte är katodiskt skyddad. För syrgasutvecklingen ökade närvaron av kromatbuffert gränsströmmen för syrgasutveckling ur OH-. Modellering av dessa system visar att de homogena reaktioner som var kopplade till elektrodreaktionerna inte var i jämvikt vid elektrodytan. Vidare visade det sig vara mycket viktigt med en bra upplösning av gränsskiktet vid elektrodytan, då den buffring som är viktig för elektrodreaktionerna sker i ett mycket tunt reaktionsskikt (nanometertjockt).
QC 20100901
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Lin, Meng-Ying, and 林孟穎. "Hydrogen Evolution Reaction Promoted by Molecular Catalyst-Electrodeposited Electrode." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/k8g9p7.
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Alarawi, Abeer A. "Molybdenum Disulfide as an Efficient Catalyst for Hydrogen Evolution Reaction." Diss., 2018. http://hdl.handle.net/10754/630133.
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Hydrogen is a carrier energy gas that can be utilized as a clean energy source instead of oil and natural gas. Splitting the water into hydrogen and oxygen is one of the most favorable methods to generate hydrogen. The catalytic properties of molybdenum disulfide (MoS2) could be valuable in this role, particularly due to its unique structure and ability to be chemically modified, enabling its catalytic activity to be further enhanced or made comparable to that of Pt-based materials. In general, these modification strategies may involve either structural engineering of MoS2 or enhancing the kinetics of charge transfer, including by confining to single metal atoms and clusters or integrating with a conductive substrate.
We present the results of synergetic integration of MoS2 films with a Si-heterojunction solar cell for generating H2 via the photochemical water splitting approach. The results of the photochemical measurements demonstrated an efficient photocurrent of 36. 3 mA cm-2 at 0 V vs. RHE and an onset potential of 0.56 V vs. RHE. In addition to 25 hours of continuous photon conversion to H2 generation, this study points out that the integration of the Si-HJ with MoS2 is an effective strategy for enhancing the internal conductivity of MoS2 towards efficient and stable hydrogen production.
Moreover, we studied the effect of doping an atomic scale of Pt on the catalytic activity of MoS2. The electrochemical results indicated that the optimum single Pt atoms loading amount demonstrated a distinct enhancement in the hydrogen generating, in which the overpotential was minimized to -0.0505 V to reach a current density of 10 mA cm−2 using only 10 ALD cycles of Pt. The Tafel slopes of the ALD Pt/ML-MoS2 electrodes were in the range of 55–120 mV/decade, which indicates a fast improvement in the HER velocity as a result of the increased potential. Stability is another important parameter for evaluating a catalyst. The same (10 ALD cycles) Pt/ML-MoS2 electrode was able to continuously generate hydrogen molecules at for 150 hours.
These superior results demonstrate that the low conductivity of semiconductive MoS2 can be enhanced by anchoring the film with Pt SAs and clusters, leading to sufficient charge transport and a decrease in the overpotential.
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Chun-Tasi, Po, and 蔡博鈞. "Silicon nanowires with FeP as electrocatalysts for hydrogen evolution reaction." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/58170425341671904976.
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碩士國立雲林科技大學
材料科技研究所
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A photoelectrochemical cell (PEC) with a structure of modified Si nanowire anode/K2SO4.H2SO4 (pH=1)/Pt cathode was prepared and studied。The Si nanowires were first formed by immersing p-Si chip in an etching solution of HF + AgNO3 and FeP nanoparticles were deposited on the surface of Si nanowires。The modified anode was characterized by a scanning electron microscope for the surface and cross section view, and by anTransmission electron microscopefor the morphology and structure。The properties of the photoelectrochemical cell were measuredcurrent density andelectrochemical impedance spectroscopy under standard AM 1.5 simulated sunlight (100mW/cm2)。The result showed that PEC devices produce cathodic current densities (J) of 8.75 and 13.44mA/cm2 were ƞ=0mV and ƞ=200mV,respectively。