Dissertations / Theses on the topic 'Solid oxide fuel cells. Anodes Ethanol as fuel'
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1
Corre, Gaël Pierre Germain. "Studies of alternative anodes and ethanol fuel for SOFCs /." St Andrews, 2009. http://hdl.handle.net/10023/841.
2
Corre, Gaël Pierre Germain. "Studies of alternatives anodes and ethanol fuel for SOFCs." Thesis, University of St Andrews, 2009. http://hdl.handle.net/10023/841.
Abstract:
This thesis explores the development of efficient engineered composite alternative anodes and the use of ethanol as a fuel for Solid Oxide Fuel Cells. SOFCs can in theory operate with fuels other than hydrogen. However, this requires the design of efficient alternative anode material that do not catalyze carbon formation and that are tolerant to redox cycles. An innovative concept has been developed that relies on the impregnation of perovskites into porous YSZ structures to form the anode functional layer. Catalysts are added to provide sufficient catalytic activity. Cells with anodes containing LSCM and Ce/Pd have displayed excellent performance. At 800°C, and with a 65 μm thick electrolyte, the power outputs were above 1W/cm² in humidified hydrogen and 0.7 W/cm² in humidified methane. These electrodes have shown the ability to reduce CO₂ electrochemically with an efficiency that is similar to that which can be achieved for H₂O electrolysis and the anodes could operate on pure CO₂. The importance of incorporating an efficient catalyst was demonstrated. The use of 0.5 wt% of Pd is sufficient to dramatically improve the performance in such electrodes. The microstructure of impregnated LSCM-YSZ composites plays an important role in the high performance obtained. A layer of LSCM nanoparticles covering the YSZ is formed upon reduction, offering a great surface area for electrochemical reactions. The fabrication method presented in this thesis is a powerful tool for designing microstructures in situ. Among the various fuels under consideration for SOFCs, ethanol offers outstanding advantages. Half cell measurements have been performed to characterize the performance of different types of anodes when operated on ethanol/steam mixtures. Steady performance was achieved on LSCM-CGO anodes. Carbon deposits from gas phase reactions have been evidenced and were found to be responsible for the performance enhancement when the cell is operated in diluted ethanol as compared to hydrogen. At high steam content, polarization resistances of LSCM-CGO-YSZ anodes in ethanol/ steam mixtures were shown to be below 0.3 Ω.cm² at 950°C.
3
Fagg, Duncan Paul. "Anodes for SOFCs (solid oxide fuel cells)." Thesis, University of Aberdeen, 1996. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU082955.
Abstract:
The success of Solid Oxide Fuel Cells (S.O.F.C) rests heavily on material selection. The performances of several compounds were investigated as possible anode materials, starting with reduced titanates such as the magnesium titanate and zirconium titanate. These compositions, although possessing many qualities beneficial for use as an anode material, were found to be too unstable for practical use. For this reason further work concentrated on stable, zirconia based, compounds with exhibited mixed conduction under reducing atmospheres. The mobility of electronic carriers is considered to be much higher than that of ionic defects, therefore, promising mixed conductors can be formed by doping a good ionic conductor with a small concentration of transition metal ions. Zirconia based mixed conductors were studied for two reasons. Firstly, zirconia stabilised in the cubic defect fluorite structure, exhibits a high level of ionic conductivity. Secondly, it is the most common electrolyte material for an S.O.F.C. An anode based on zirconia would, therefore, be expected to offer a good physical compatibility with the electrolyte material and to exhibit a high ionic contribution to total conductivity. Large defect fluorite solid solutions in the systems Y2O3-ZrO2-Nb2O5, Yb2O3-ZrO2-Nb2O5 and CaO-ZrO2-Nb2O5 were established, which enabled the effects of composition, dopant size and charge on conduction to be investigated. These effects were shown to be linked to structure. From these results and comparisons with the Y2O3-ZrO2-TiO2 system, optimum, mixed conducting, compositions were established. The sample Y0.25Ti0.15Zr0.60O1.875 exhibited the best mixed conducting properties to date, obtained for compositions based on zirconia.
4
Baron, Sylvia A. "Anodes for solid oxide fuel cells with ceria electrolytes." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410219.
5
Coe, Neil J. "A study of Ni based fuel reforming anodes for solid oxide fuel cells." Thesis, Keele University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343244.
Abstract:
The anode material in a conventional design of solid oxide fuel cell (SOFC) operating above 1123 K is typically made from NiO/Zirconia. NiO/Zirconia anodes are known to perform well in hydrogen but exhibit difficulties when natural gas is used as a fuel. Natural gas is much cheaper than hydrogen and widely available but causes carbon deposition and deactivation of the NiO/Zirconia SOFC anode. One objective of this work was to prepare and characterize NiO/Zirconia anodes both as powders and as applied to extruded zirconia tubes. The problem of carbon deposition when NiO/Zirconia anodes operate in methane, the main component of natural gas, was investigated. Another aim was to address the problem of coking with an effort to moderate carbon deposition by using additives to the NiO/Zirconia anode. Temperature programmed reduction (TPR) was used to study the reaction characteristicso f NiO/Zirconia anodes.T he carbon depositedo n thesea nodesa fter methane decomposition and reforming was characterized using temperature programmed oxidation (TPO). The anodes were placed in a reactor (stainless-steel, alumina or zirconia) tube in a test assembly developed for an extruded tubular SOFC. The reactor inlet was connected to a flexible gas handling system and the exhaust to a continuously sampling mass spectrometer. This system also allowed simultaneous study of electrical and catalytic measurementsThe various conditions for methane reforming have been shown to influence the character of carbon deposited and the quantity deposited. Conditions such as anode calcination temperature, anode reduction regime, reforming temperature and reforming time have all been shown to influence the reactions occuring on the anode including carbon deposition, subsequently characterized by TPO. NiO/Zirconia powders have also been shown to behave differently from NiO/Zirconia anodes adhered to zirconia tubes. An alkali metal additive has been shown to moderate carbon deposition and improve cell performance. Small additions of Li, typically 1 mol %, to the Ni/Zirconia anode cause a decrease in carbon deposition after reforming at temperatures of 1123 K and 1173 K. The activation energy of surface carbon removed by oxygen is lowered by approximately 50 kJ mot' for the 1 mol % Li doped Ni/Zirconia anode compared to the undoped powder. Anodes doped with Li displayed greater cell performances. The improvements seen with these additives show that their use could offer a viable alternative to conventional anodes in current SOFC systems. Tubular solid oxide fuel cells have been tested in a custom built rig whereby electronic and catalytic measurements can be sampled simultaneously. This was used to monitor the influence of drawing current on the reactions occurring on the anode. The presence of alkali Li on the doped Ni anode surface has been shown to interfere with surface reactions under electrochemical load/steam reforming
6
Ovalle, Alejandro. "Manganese titanium perovskites as anodes for solid oxide fuel cells." Thesis, St Andrews, 2008. http://hdl.handle.net/10023/567.
7
Weston, Michael John. "Novel anodes for internal reforming in solid oxide fuel cells." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368890.
8
Primdahl, Søren. "Nickel/Yttria-stabilised zirconia cermet anodes for solid oxide fuel cells." Enschede : University of Twente [Host], 1999. http://doc.utwente.nl/58232.
9
Fisher, James C. "A novel fuel cell anode catalyst, perovskite LSCF compared in a fuel cell anode and tubular reactor testing /." Akron, OH : University of Akron, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1152215855.
Abstract:
Thesis (M.S.)--University of Akron, Dept. of Chemical Engineering, 2006."December, 2006." Title from electronic thesis title page (viewed 12/31/2008) Advisor, Steven S. C. Chuang; Faculty Readers, George Chase, Lu-Kwang Ju ; Department Chair, Lu-Kwang Ju; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
10
Kearney, Jonathan. "Cu/CeₓZr(₁₋ₓ)O₂ catalysts for solid oxide fuel cell anodes." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1845.
Abstract:
Ce[subscript(x)]Zr[subscript(1-x)]O₂ mixed oxides of varying compositions were prepared by a sol-gel citrate complexion technique. In order to improve the catalytic activity of the oxides they were impregnated with copper using two different impregnation techniques. The bare oxides and copper impregnated samples were investigated using a range of Temperature Programmed (TP) techniques, in an attempt to establish their effectiveness as anode materials for solid oxide fuel cells (SOFCs) run on hydrocarbon fuels. In order to conduct the TP experiments a novel system was designed and constructed. The high Ce containing mixed oxides were shown to be reduced at lower temperature than high Zr content samples. TPRx experiments were employed to investigate which of the oxides was most prone to carbon deposition when reacted in methane, with the high ceria sample displaying the lowest level of carbon deposition. Lightoff experiments were undertaken to establish which oxide composition was the most active for methane oxidation. The activity of the oxides increased with ceria content up to 75 mole% (ZCe75), before decreasing for ZCe90. All the mixed oxides were shown to be more active for methane oxidation than CeO₂.
11
Nasani, Narendar. "Anodes for protonic ceramic fuel cells (PCFCs)." Doctoral thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14133.
Abstract:
Doutoramento em Nanociências e NanotecnologiaOne of the more promising possibilities for future “green” electrical energy generation is the protonic ceramic fuel cell (PCFC). PCFCs offer a low-pollution technology to generate electricity electrochemically with high efficiency. Reducing the operating temperature of solid oxide fuel cells (SOFCs) to the 500-700°C range is desirable to reduce fabrication costs and improve overall longevity. This aim can be achieved by using protonic ceramic fuel cells (PCFCs) due to their higher electrolyte conductivity at these temperatures than traditional ceramic oxide-ion conducting membranes. This thesis deals with the state of the art Ni-BaZr0.85Y0.15O3-δ cermet anodes for PCFCs. The study of PCFCs is in its initial stage and currently only a few methods have been developed to prepare suitable anodes via solid state mechanical mixing of the relevant oxides or by combustion routes using nitrate precursors. This thesis aims to highlight the disadvantages of these traditional methods of anode preparation and to, instead, offer a novel, efficient and low cost nitrate free combustion route to prepare Ni-BaZr0.85Y0.15O3-δ cermet anodes for PCFCs. A wide range of techniques mainly X-ray diffraction (XRD), scanning electron microscopy (SEM), environmental scanning electron microscopy, (ESEM) and electrochemical impedance spectroscopy (EIS) were employed in the cermet anode study. The work also offers a fundamental examination of the effect of porosity, redox cycling behaviour, involvement of proton conducting oxide phase in PCFC cermet anodes and finally progresses to study the electrochemical performance of a state of the art anode supported PCFC. The polarisation behaviour of anodes has been assessed as a function of temperature (T), water vapour (pH2O), hydrogen partial pressures (pH2) and phase purity for electrodes of comparable microstructure. The impedance spectra generally show two arcs at high frequency R2 and low frequency R3 at 600 °C, which correspond to the electrode polarisation resistance. Work shows that the R2 and R3 terms correspond to proton transport and dissociative H2 adsorption on electrode surface, respectively. The polarization resistance of the cermet anode (Rp) was shown to be significantly affected by porosity, with the PCFC cermet anode with the lowest porosity exhibiting the lowest Rp under standard operating conditions. This result highlights that porogens are not required for peak performance in PCFC anodes, a result contrary to that of their oxide-ion conducting anode counterparts. In-situ redox cycling studies demonstrate that polarisation behaviour was drastically impaired by redox cycling. In-situ measurements using an environmental scanning electron microscopy (ESEM) reveal that degradation proceeds due to volume expansion of the Ni-phase during the re-oxidation stage of redox cycling.The anode supported thin BCZY44 based protonic ceramic fuel cell, formed using a peak performing Ni-BaZr0.85Y0.15O3-δ cermet anode with no porogen, shows promising results in fuel cell testing conditions at intermediate temperatures with good durability and an overall performance that exceeds current literature data.
A pilha de combustível de cerâmicos protónicos (PCCP) é uma das mais promissoras possibilidades para a produção de energia elétrica “verde”. As PCCPs oferecem uma tecnologia limpa para a produção eletroquímica de energia elétrica com elevada eficiência. De forma a reduzir os custos de fabricação e melhorar a longevidade destes equipamentos é necessário reduzir a temperatura de operação das pilhas de combustível de óxido sólido (PCOSs) para o intervalo 500-700 °C. Este objetivo pode ser alcançado recorrendo às pilhas de combustível de cerâmicos protónicos (PCCPs) devido à superior condutividade do eletrólito face às tradicionais membranas condutoras iónicas. Esta tese baseia-se em cermetos anódicos de Ni-BaZr0.85Y0.15O3-δ, que correspondem ao material do estado-da-arte para PCCPs. O estudo das PCCPs encontra-se ainda no seu estágio inicial e até ao momento apenas alguns métodos foram desenvolvidos para preparar ânodos adequados através da moagem de alta-energia dos precursores de óxidos cerâmicos ou da síntese por combustão de nitratos. Esta tese pretende destacar as desvantagens destes métodos tradicionais de preparação de ânodos e, em vez disso, oferecer um novo, mais eficiente, de mais baixo custo e sem recorrência ao uso de nitratos, método de preparação de cermetos anódicos de Ni-BaZr0.85Y0.15O3-δ para PCCPs. No estudo dos cermetos anódicos foram utilizadas diversas técnicas experimentais, nomeadamente, difração de raios X (DRX), microscopia eletrónica de varrimento (MEV), microscopia eletrónica de varrimento ambiental (MEVA) e espetroscopia de impedância eletroquímica (EIE). Este trabalho inclui também uma análise fundamental dos aspetos relacionados com o efeito da porosidade, o comportamento redox, o papel da fase de óxido condutor protónico nos cermetos anódicos e ainda os últimos avanços do desempenho eletroquímico de um dos mais importantes materiais de ânodo para PCCPs. O estudo do comportamento sob polarização destes materiais foi executado em função da temperatura (T), da pressão parcial de vapor de água (pH2O), da pressão parcial de hidrogénio (pH2) e também da pureza da fase, em elétrodos de microestrutura comparável. A 600 °C, o espetro de impedância apresenta em geral dois arcos: R2 nas altas frequências e R3 nas baixas frequências, que correspondem à resistência de polarização do elétrodo (Rp). Os resultados mostram que as respostas R2 e R3 correspondem, respetivamente, ao transporte de espécies condutoras protónicas e ao fenómeno de adsorção dissociativa do H2 na superfície do elétrodo. Também, foi demonstrado que o valor de Rp é fortemente afetado pela porosidade, pelo que este atingiu o valor mais baixo no cermeto com menor nível de porosidade, em condições de operação.Deste modo, este resultado descarta o uso de agentes porogéneos, muitas vezes utilizados na preparação dos materiais de ânodos quando estes são constituídos por condutores de iões óxido. Relativamente à avaliação da estabilidade em conduções oxidantes e redutoras, foi demonstrado que o comportamento sob polarização é extremamente comprometido pelo ciclo redox utilizado. Medidas in-situ através de microscopia eletrónica de varrimento ambiental (MEVA) revelaram que a degradação continua devido à expansão em volume da fase de Ni durante o estágio de reoxidação. As células eletroquímicas testadas em condições reais de operação (pilha de combustível), constituídas por um suporte anódico otimizado de Ni-BaZr0.85Y0.15O3-δ, sem uso de porogéneos, e um filme fino de eletrólito de BCZY44 apresentam resultados promissores a temperaturas intermédias, assegurando uma boa durabilidade e um desempenho global que excede os dados encontrados na literatura até ao momento.
12
Cheng, Zhe. "Investigations into the interactions between sulfur and anodes for solid oxide fuel cells." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22678.
Abstract:
Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.Committee Chair: Liu, Meilin; Committee Member: Agrawal, Pradeep; Committee Member: Carter, W. Brent; Committee Member: Singh, Preet; Committee Member: Speyer, Robert; Committee Member: Summers, Christopher.
13
Lohsoontorn, Pattaraporn. "The impact of sulphur on Ni-based anodes for solid oxide fuel cells." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486595.
Abstract:
The research aims to explore the impact of sulphur on the Ni-based anodes used in solid oxide fuel cells (SOFCs). The work combines thermodynamic calculation, electrochemical measurements, anode microstructure analysis, and in-situ Raman techniques, to explore the interaction of hydrogen sulphide with nickel based anodes under SOFC operating conditions. Thermodynamic calculations have been made to predict the stability of SOFC·anode materials (Ni, Ceria, Zirconia) when exposed to hydrogen sulphide (H2S) in hydrogen/steam mixtures over a range of partial pressures of sulphur (pS2) and oxygen (p02) representative of fuel cell operating conditions. Measurements on a single fuel cells and anode half cells have been carried· out to study the effect of operating conditions (pH2S, pH2 • pH20, temperature) on the degree and nature of sulphur interaction with the anodes, correlating this with the thermodynamic predictions and microstructural analysis. Microstructural analysis used scanning electron microscopy on anode cermets, supported by work on Ni pellets, to explore anode surface structure alteration under the same test conditions as those used for electrochemical measurement. This allowed changes in anode microstructure induced by sulphur to be coupled to changes in anode electrochemical performance. Both ex-situ and in-situ Raman spectroscopy was also used to detect chemical species formed on the anode surface when exposed to sulphur. The work shows a correlation between electrochemical response and thermodynamic calculation. Nickel and ceria show differing behaviour depending on pH2S, pH2, pH20, or temperature. The impedance response of Ni anodes in hydrogen SUlphide atmospheres also shows a link with anode microstructure. Electrodes with relatively lower initial performance degraded at lower H2S concentrations than those with higher initial performance suggesting that the detrimental effect of sulphur on the anode is dominated by its interaction with three phase boundaries. Anode surface alteration induced by sulphur such as 'faceting' on Ni, and Ni agglomeration, was also observed and correlated with the impedance response. Raman spectroscopy offers promise as a probe to monitor surface electrolyte temperature as well as sulphur species on the nickel species.
14
Price, Robert. "Metal/metal oxide co-impregnated lanthanum strontium calcium titanate anodes for solid oxide fuel cells." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/16018.
Abstract:
Solid Oxide Fuel Cells (SOFC) are electrochemical energy conversion devices which allow fuel gases, e.g. hydrogen or natural gas, to be converted to electricity and heat at much high efficiencies than combustion-based energy conversion technologies. SOFC are particularly suited to employment in stationary energy conversion applications, e.g. micro-combined heat and power (μ-CHP) and base load, which are certain to play a large role in worldwide decentralisation of power distribution and supply over the coming decades. Use of high-temperature SOFC technology within these systems is also a vital requirement in order to utilise fuel gases which are readily available in different areas of the world. Unfortunately, the limiting factor to the long-term commercialisation of SOFC systems is the redox instability, coking intolerance and sulphur poisoning of the state-of-the-art Ni-based cermet composite anode material. This research explores the ‘powder to power' development of alternative SOFC anode catalyst systems by impregnation of an A-site deficient La0.20Sr0.25Ca0.45TiO3 (LSCT[sub](A-)) anode ‘backbone' microstructure with coatings of ceria-based oxide ion conductors and metallic electrocatalyst particles, in order to create a SOFC anode which exhibits high redox stability, tolerance to sulphur poisoning and low voltage degradation rates under operating conditions. A 75 weight percent (wt. %) solids loading LSCT[sub](A-) ink, exhibiting ideal properties for screen printing of thick-film SOFC anode layers, was screen printed with 325 and 230 mesh counts (per inch) screens onto electrolyte supports. Sintering of anode layers between 1250 °C and 1350 °C for 1 to 2 hours indicated that microstructures printed with the 230 mesh screen provided a higher porosity and improved grain connectivity than those printed with the 325 mesh screen. Sintering anode layers at 1350 °C for 2 hours provided an anode microstructure with an advantageous combination of lateral grain connectivity and porosity, giving rise to an ‘effective' electrical conductivity of 17.5 S cm−1 at 850 °C. Impregnation of this optimised LSCT[sub](A-) anode scaffold with 13-16 wt. % (of the anode mass) Ce0.80Gd0.20O1.90 (CGO) and either Ni (5 wt. %), Pd, Pt, Rh or Ru (2-3 wt. %) and integration into SOFC resulted in achievement of Area Specific Resistances (ASR) of as low as 0.39 Ω cm−2, using thick (160 μm) 6ScSZ electrolytes. Durability testing of SOFC with Ni/CGO, Ni/CeO2, Pt/CGO and Rh/CGO impregnated LSCT[sub](A-) anodes was subsequently carried out in industrial button cell test rigs at HEXIS AG, Winterthur, Switzerland. Both Ni/CGO and Pt/CGO cells showed unacceptable levels of degradation (14.9% and 13.4%, respectively) during a ~960 hour period of operation, including redox/thermo/thermoredox cycling treatments. Significantly, by exchanging the CGO component for the CeO2 component in the SOFC containing Ni, the degradation over the same time period was almost halved. Most importantly, galvanostatic operation of the SOFC with a Rh/CGO impregnated anode for >3000 hours (without cycling treatments) resulted in an average voltage degradation rate of < 1.9% kh−1 which, to the author's knowledge, has not previously been reported for an alternative, SrTiO3-based anode material. Finally, transfer of the Rh/CGO impregnated LSCT[sub](A-) anode to industrial short stack (5 cells) scale at HEXIS AG revealed that operation in relevant conditions, with low gas flow rates, resulted in accelerated degradation of the Rh/CGO anode. During a 1451 hour period of galvanostatic operation, with redox cycles and overload treatments, a voltage degradation of 19.2% was observed. Redox cycling was noted to briefly recover performance of the stack before rapidly degrading back to the pre-redox cycling performance, though redox cycling does not affect this anode detrimentally. Instead, a more severe, underlying degradation mechanism, most likely caused by instability and agglomeration of Rh nanoparticles under operating conditions, is responsible for this observed degradation. Furthermore, exposure of the SOFC to fuel utilisations of >100% (overloading) had little effect on the Rh/CGO co-impregnated LSCT[sub](A-) anodes, giving a direct advantage over the standard HEXIS SOFC. Finally, elevated ohmic resistances caused by imperfect contacting with the Ni-based current collector materials highlighted that a new method of current collection must be developed for use with these anode materials.
15
Wu, Chieh-Chun. "Evaluation of Ceria Based Anodes of Solid Oxide Fuel Cells and their Sulfur Tolerance." Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1291324978.
16
Puengjinda, Pramote. "A Study on Ni-cermet and Alternative Ceramic Anodes for Solid Oxide Fuel Cells." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157601.
17
Yates, Christopher Lee. "The study of anode materials for an intermediate temperature solid oxide fuel cell utilizing hydrogen sulfide as the fuel." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/10054.
18
Finnerty, Caine M. "The catalysis and electrical performance of nickel-based/zirconia fuel reforming anodes in solid oxide fuel cells running on methane." Thesis, Keele University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267358.
19
Jawlik, Paul Francis. "Effects of ceria addition on nickel/YSZ anodes in solid oxide fuel cells operating on hydrogen and syngas fuel feeds." College Park, Md.: University of Maryland, 2008. http://hdl.handle.net/1903/8924.
Abstract:
Thesis (M.S.) -- University of Maryland, College Park, 2008.Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
20
Eccleston, Kelcey Lynne. "Solid oxide steam electrolysis for high temperature hydrogen production /." St Andrews, 2007. http://hdl.handle.net/10023/322.
21
Choi, Song Ho. "Development of SOFC anodes resistant to sulfur poisoning and carbon deposition." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/26601.
Abstract:
Thesis (Ph.D)--Materials Science and Engineering, Georgia Institute of Technology, 2008.Committee Chair: Meilin Liu; Committee Member: Arun Gokhale; Committee Member: Christoper Summers; Committee Member: Preet Singh; Committee Member: Tom Fuller. Part of the SMARTech Electronic Thesis and Dissertation Collection.
22
Hackett, Gregory A. "Interaction of nickel-based SOFC anodes with trace contaminants from coal-derived synthesis gas." Morgantown, W. Va. : [West Virginia University Libraries], 2009. http://hdl.handle.net/10450/10728.
Abstract:
Thesis (Ph. D.)--West Virginia University, 2009.Title from document title page. Document formatted into pages; contains xii, 122 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 115-122).
23
Cooper, Matthew E. "Energy production from coal syngas containing H₂S via solid oxide fuel cells utilizing lanthanum strontium vanadate anodes." Ohio : Ohio University, 2008. http://www.ohiolink.edu/etd/view.cgi?ohiou1219867679.
24
Cooper, Matthew E. "Energy Production from Coal Syngas Containing H2S via Solid Oxide Fuel Cells Utilizing Lanthanum Strontium Vanadate Anodes." Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1219867679.
25
Eccleston, Kelcey L. "Solid oxide steam electrolysis for high temperature hydrogen production." Thesis, University of St Andrews, 2007. http://hdl.handle.net/10023/322.
Abstract:
This study has focused on solid oxide electrolyser cells for high temperature steam electrolysis. Solid oxide electrolysis is the reverse operation of solid oxide fuel cells (SOFC), so many of the same component materials may be used. However, other electrode materials are of interest to improve performance and efficiency. In this work anode materials were investigated for use in solid oxide electrolysers. Perovskite materials of the form L₁₋ｘSrｘMO₃ , where M is Mn, Co, or Fe. LSM is a well understood electrode material for the SOFC. Under electrolysis operation LSM performed well and no interface reactions were observed between the anode and YSZ electrolyte. LSM has a relatively low conductivity and the electrode reaction is limited to the triple phase boundary regions. Mixed ionic-electronic conductors of LSCo and LSF were investigated, with these materials the anode reaction is not limited to triple phase boundaries. The LSCo anode had adherence problems in the electrolysis cells due to the thermal expansion coefficient mismatch with the YSZ electrolyte. The LSCo reacted with the YSZ at the anode/electrolyte interface forming insulating zirconate phases. Due to these issues the LSCo anode cells performed the poorest of the three. The performance of electrolysis cells with LSF anode exceeded both LSM and LSCo, particularly under steam operation, although an interface reaction between the LSF anode and YSZ electrolyte was observed. In addition to the anode material studies this work included the development of solid oxide electrolyser tubes from tape cast precursor materials. Tape casting is a cheap processing method, which allows for co-firing of all ceramic components. The design development resulted in a solid design, which can be fabricated reliably, and balances strength with performance. The design used LSM anode, YSZ electrolyte, and Ni-YSZ cathode materials but could easily be adapted for the use of other component materials. Proper sintering rates, cathode tape formulation, tube length, tape thickness, and electrolyte thickness were factors explored in this work to improve the electrolyser tubes.
26
O'Brien, Julie Suzanne. "Cermet Anodes for Solid Oxide Fuel Cells (SOFC) Systems Operating in Multiple Fuel Environments: Effects of Sulfur and Carbon Composition as well as Microstructure." Thesis, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20634.
Abstract:
A series of cermet powders of composition NixCo(1-x)O-YSZ were synthesized for testing as cermet anode materials for SOFCs. The Co is found by powder XRD to become incorporated into the crystal lattice of the NiO, thus forming a true alloyed material. SEM and EDS results show two types of particles upon sintering to 1380oC: small, amorphous particles of YSZ and large, crystalline particles of nickel.
The electrochemical oxidation of hydrogen on a cermet anode composed of Ni0.7Co0.3O-YSZ was investigated using a series of many button cells. Through EIS data, cyclic voltammetry data, the exchange current densities for these button cells were determined. Although a relatively large variation was found (expected to be due to microstructural variation) the average values for both methods of measurement is in good agreement in hydrogen.
Following reduction in pure hydrogen, the fuel was changed to a mixture with high concentration of H2S. It was found that a concentration of 10 % H2S/H2 produced a sudden change in anode microstructure and resulted in loss of exchange current density. Lowering the amount of H2S in the initial fuel feed, which allowed for a more gradual microstructural change, allowed the cell to eventually function at concentrations in excess of 10 % H2S/H2. It was determined by OCV values in various concentrations of H2S/H2 that hydrogen is the predominant fuel of choice, even if H2S is available. Following electrochemical testing, slow cooling in a 10 % H2S/H2 mixture following produced metal sulfide spheres, as determined by SEM and EDS.
Investigation in hydrocarbon, alcohol and biodiesel fuels was then undertaken to test the fuel variability of the given cermet anode material. Methane containing 10 % H2S was found to have increased exchange current density relative to poisoned hydrogen. Ethane and biodiesel experienced no increase in exchange current density, but a lengthening of the functional lifetime of the cell was observed, indicating reduced carbon poisoning. Methanol is a promising oxygen-containing SOFC fuel since it produced exchange current density values larger than hydrogen, and showed no evidence of coke formation by post-mortem SEM.
Since oxygen-containing fuels are known to decompose in the gas phase at typical SOFC operating temperatures, the performance in a mixture of various CO/H2 fuels was then investigated. The Ni0.7Co0.3O-YSZ cermet anode gave higher exchange current density values for low ratio of CO/H2 fuels in the range 20/80 and 30/70 compared to pure H2. This is the first example of a Ni-based anode providing higher performance with a CO/H2 mixed fuel than for a pure H2 fuel. Finally, continuous running of a cell with fuel ratio 25/75 CO/H2 for 7 days produced exchange current density values, which were observed to increase significantly above the values for pure H2 during days 1-4 followed by deterioration below the value for hydrogen on subsequent days.
27
De, Silva Kandaudage Channa R. "A High Temperature Planar Solid Oxide Fuel Cell Operating on Phosphine Contaminated Coal Syngas." Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1304609820.
28
Sano, Mitsuru, Ushio Harada, Takashi Hibino, Atsuko Hashimoto, and Daisuke Hirabayashi. "Bi-Based Oxide Anodes for Direct Hydrocarbon SOFCs at Intermediate Temperatures." The Electrochemical Society, 2004. http://hdl.handle.net/2237/18432.
29
Riegraf, Matthias [Verfasser], and K. Andreas [Akademischer Betreuer] Friedrich. "Investigation of sulfur poisoning of Ni-based anodes in solid oxide fuel cells / Matthias Riegraf ; Betreuer: K. Andreas Friedrich." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/118671042X/34.
30
Chen, Yan. "Scandia and ceria stabilized zirconia based electrolytes and anodes for intermediate temperature solid oxide fuel cells: Manufacturing and properties." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5921.
Abstract:
Scandia and ceria stabilized zirconia (10 mol% Sc2O3 – 1 mol% CeO2 – ZrO2, SCSZ) has superior ionic conductivity in the intermediate temperature range for the operation of solid oxide fuel cells, but it does not exhibit good phase stability in comparison with yttria stabilized zirconia (8 mol% Y2O3 – ZrO2, YSZ). To maintain high ionic conductivity and improve the stability of the electrolyte, layered structures with YSZ outer layers and SCSZ inner layers were designed, along with the referential electrolytes containing pure SCSZ or YSZ. The electrolytes were manufactured by tape casting, laminating, and pressureless sintering techniques. After sintering, while the thickness of YSZ outer layers remained constant at ~30 ?m, the thickness of inner layers of SCSZ for the 3-, 4- and 6-layer designs varied at ~30, ~60 and ~120 ?m, respectively. Selected characterizations were employed to study the structure, morphology, impurity content and the density of the electrolytes. Furthermore, in situ X-ray diffraction, neutron diffraction and Raman scattering were carried out to study the phase transition and lattice distortion during long-term annealing at 350 °C and 275 °C for SCSZ and YSZ, respectively, where the dynamic damping occurred when Young's modulus was measured.
In YSZ/SCSZ electrolytes, thermal residual stresses and strains were generated due to the mismatch of coefficients of thermal expansion from each layer of different compositions. They could be adjusted by varying the thickness ratios of each layer in different designs of laminates. The theoretical residual stresses have been calculated for different thickness ratios. The effect of thermal residual stress on the biaxial flexural strength was studied in layered electrolytes. The biaxial flexure tests of electrolytes with various layered designs were performed using a ring-on-ring method at both room temperature and 800 °C. The maximum principal stress during fracture indicated an increase of flexural strength in the electrolytes with layered structure at both temperatures in comparison with the electrolytes without compositional gradient. Such an increase of strength is the result of the existence of residual compressive stresses in the outer YSZ layer. In addition, Weibull statistics of the strength values were built for the layered electrolytes tested at room temperature, and the effect of thermal residual stresses on Weibull distribution was established. The calculation of residual stress present at the outer layers was verified.
The high ionic conductivity was maintained with layered electrolyte designs in the intermediate temperature range. It was also established that the ionic conductivity of layered electrolytes exhibited 7% – 11% improvement at 800 °C due to the stress/strain effects, and the largest improvements in a certain electrolyte was found to nearly coincide with the largest residual compressive strain in the outer YSZ layer.
In addition to the study of layered electrolytes, mechanical properties of porous Ni/SCSZ cermet were studied. The anode materials were reduced by 65 wt% NiO – 35 wt% SCSZ (N65) and 50 wt% NiO – 50 wt% SCSZ (N50) porous ceramics in the forming gas. Young's modulus as well as strength and fracture toughness of non-reduced and reduced anodes has been measured, both at room and high temperatures. High temperature experiments were performed in the reducing environment of forming gas. It was shown that while at 700 °C and 800 °C the anode specimens exhibited purely brittle deformation, a brittle-to-ductile transition occurred at 800 – 900 °C, and the anode deformed plastically at 900 °C. Fractography of the anode specimens were studied to identify the fracture modes of the anodes tested at different temperatures.Ph.D.
Doctorate
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
31
Yang, Lei. "New materials for intermediate-temperature solid oxide fuel cells to be powered by carbon- and sulfur-containing fuels." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39575.
Abstract:
Unlike polymer electrolyte fuel cells, solid-oxide fuel cells (SOFCs) have the potential to use a wide variety of fuels, including hydrocarbons and gasified coal or different types of ample carbonaceous solids. However, the conventional anode for an SOFC, a composite consisting of nickel and yttria-stabilized-zirconia (YSZ), is highly susceptible to carbon buildup (coking) and deactivation (poisoning) by contaminants commonly encountered in readily available fuels. Further, the low ionic conductivity of the electrolyte and the poor performance of the cathode at lower temperatures require SOFCs to operate at high temperatures (>800°C), thereby increasing costs and reduce system operation life. Thus, in order to make SOFCs fully fuel-flexible, cost-effective power systems, the issues of anode tolerance to coking and sulfur poisoning as well as the slow ionic conduction in the electrolyte and the sluggish kinetics at the cathode need to be addressed. In this thesis, a novel electrolyte was shown to have the highest ionic conductivity below 750°C of all known electrolyte materials for SOFCs applications, which allowed for fabrication of a thin-electrolyte cell with high power output at lower temperatures. The detailed electrochemical analyses of BZCYYb conductor revealed that the conductivities were sensitive to doping and partial pressure of oxygen, hydrogen, and water. When used in combination with Ni as a composite anode (Ni-BZCYYb), it was shown to provide excellent tolerance to coking and sulfur poisoning. Extensive investigations on surfaces of BZCYYb and Ni by Raman Spectroscopy and Scanning Auger Nanoprobe disclosed that its unique ability appears linked to the mixed conductor's enhanced catalytic activity for sulfur oxidation and hydrocarbon cracking/reforming, as well as enhanced multilayer water adsorption capability. In addition, the nanostructured oxide layers on Ni from dispersion of BZCYYb traces during high-temperature calcinations may effectively suppress the formation of carbon from dehydrogenation. Based on the fundamental understanding on surface properties, a new and simple modification strategy was developed to hinder the carbon-induced deactivation of the state-of-the-art Ni-YSZ anode. Compared to the complex Ni-BZCYYb anode, this modified Ni-YSZ anode could be readily adopted in the latest fuel cell systems based on YSZ electrolyte. The much-improved power output and tolerance to coking of the modified Ni-YSZ anode were attributed to the nanostructured BaO/Ni interfaces observed by synchrotron-based X-ray and advanced electron microscopy, which readily adsorbed water and facilitated water-mediated carbon removal reactions. Density functional theory (DFT) calculations predicted that the dissociated OH from H₂O on BaO reacted with C on Ni near the BaO/Ni interface to produce CO and H species, which were then electrochemically oxidized at the triple-phase boundaries of the anode. Also, some new insights into the sulfur poisoning behavior of the Ni-YSZ anode have been revealed. The so-called "second-stage poisoning" commonly reported in the literatures can be avoided by using a new sealant, indicating that this poisoning is unlikely the inherent electrochemical behavior of a Ni-YSZ anode but associated with other complications. Furthermore, a new composite cathode with simultaneous transport of proton, oxygen vacancies and electronic defects was developed for low-temperature SOFCs based on oxide proton conductors. Compared to the conventional oxygen ion-electron conducting cathode, this cathode is very active for oxygen reduction, extending the electrochemically active sites and significantly reducing the cathodic polarization resistance. Towards the end, these findings have great potential to dramatically improve the economical competitiveness and commercial viability of SOFCs that are driven by cost-effective and renewable fuels.
32
NOBREGA, SHAYENNE D. da. "Fabricação e testes de células a combustível de óxido sólido a etanol direto usando camada catalítica." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10184.
Abstract:
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
33
Howell, Thomas G. "Perovskites for use as sulfur tolerant anodes." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397467868.
34
Steenken, Valentin [Verfasser], and Hoffmann M. [Akademischer Betreuer] J. "Oxidation of Ni-8YSZ anodes in Solid Oxide Fuel Cells - An "In status operandi" measurement method / Valentin Steenken ; Betreuer: M. J. Hoffmann." Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1187343277/34.
35
Manga, Venkateswara Rao. "Effect of H 2 S on the thermodynamic stability and electrochemical performance of Ni cermet-type of anodes for solid oxide fuel cells." [S.l. : s.n.], 2006. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-29554.
36
Hibino, Takashi, Atsuko Tomita, Mitsuru Sano, Masahiro Nagao, Kohsuke Okamoto, Takanori Kawai, and Masaya Yano. "Single-Chamber SOFCs Using Dimethyl Ether and Ethanol." The Electrochemical Society, 2007. http://hdl.handle.net/2237/18431.
37
Manga, Venkateswara Rao [Verfasser]. "Effect of H2S on the thermodynamic stability and electrochemical performance of Ni cermet-type of anodes for solid oxide fuel cells / vorgelegt von Manga Venkateswara Rao." Stuttgart : Max-Planck-Inst. für Metallforschung, 2006. http://d-nb.info/995374937/34.
38
YOSHITO, WALTER K. "Estudo de rotas de síntese e processamento cerâmico do compósito NiO-YSZ para aplicação como anodo em células a combustível do tipo óxido sólido (SOFC)." reponame:Repositório Institucional do IPEN, 2011. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9966.
Abstract:
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
39
MONTEIRO, NATALIA K. "Síntese e caracterização de manganita-cromita de lantânio dopada com rutênio para anodos de células a combustível de óxidos sólidos." reponame:Repositório Institucional do IPEN, 2011. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10041.
Abstract:
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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
40
Julião, Paulo Sérgio Barros. "Electrolytic cells for plastic waste recycling." Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/15804.
Abstract:
Mestrado em Sistemas Energéticos SustentáveisThe current project assesses potential molten alloy anodes for Solid Oxide Fuel Cells (SOFC) running on solid waste. A detailed phase diagram study was performed to locate probable anode systems. The molten metal oxide system PbO-Sb2O3 was selected as a possible molten alloy anode for this application. A detailed vapour pressure study of this system was performed. Several cells were fabricated to experimentally assess the electrochemical properties of this system. The work reveals several unexpected limiting features such as the incompatibility between the platinum and the chosen alloy. A second cell was built, this time using rhenium wires instead, preventing such reaction. However, the rhenium wire sublimes under oxidizing conditions (air) and the sealing glass and the chosen alloy system react with each other under long term use. Considering all these issues, a third cell design was conceived, surpassing some obstacles and providing some initial information regarding the electrochemical behaviour. The current project shows that many parameters need to be taken into account to ensure materials compatibility. For the PbOSb2O3 system, the high volatility of Sb2O3 was a serious limitation that can only be addressed through the application of new contact wires or sealing materials and conditions. Nonetheless, the project highlights several other potential systems that can be considered, such as Pb11Ge3O17, Pb3GeO5, Pb5Ge3O11, Bi2CuO4, Bi2PdO4, Bi12GeO20.
Este estudo incidiu sobre potenciais ânodos líquidos de ligas metálicas para células electrolíticas (do tipo SOFC) alimentadas por resíduos sólidos. Alguns sistemas de ânodos possíveis foram identificados através de um estudo detalhado de diagramas de fase. O sistema de óxidos metálicos PbO-Sb2O3 foi selecionado como uma possível liga metálica para esta aplicação. Este sistema foi sujeito a um estudo detalhado de pressão de vapor. Algumas células foram fabricadas para avaliar experimentalmente as propriedades electro-químicas deste sistema. Este trabalho revela imensas características que inesperadamente limitaram este estudo, tal como a incompatibilidade entre platina e a liga metálica escolhida. Uma segunda célula foi construída, desta vez usando um fio de rénio, prevenindo tal reacção. No entanto, o fio de rénio sublima sobre condições oxidantes (ar) e, perante um uso prolongado, o vidro selante e a liga metálica reagem entre si. Considerando todas estas incompatibilidades, um terceiro modelo de célula foi criado, ultrapassando alguns obstáculos e fornecendo alguma informação inicial relativa ao comportamento electro-químico. O presente trabalho mostra que vários parâmetros precisam precisam de ser abordados de modo a assegurar a compatibilidade dos materiais. Relativamente ao sistema PbO-Sb2O3, a elevada volatilidade de Sb2O3 foi uma grave limitação que só pode ser contornada através da aplicação de novos fios conectores, materiais e condições de selamento. No entanto, este projecto destaca outros potenciais sistemas que podem ser estudados, como Pb11Ge3O17, Pb3GeO5, Pb5Ge3O11, Bi2CuO4, Bi2PdO4, Bi12GeO20.
41
ARAKAKI, ALEXANDER R. "Estudos de síntese e processamento de compósitos de óxido de níquel-céria dopada utilizados como anodo de células a combustível de óxido sólido de temperatura intermediária (IT-SOFC)." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11811.
Abstract:
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Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
42
SETZ, LUIZ F. G. "Processamento coloidal de cromito de lantanio." reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11522.
Abstract:
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
43
Mesguich, David. "Elaboration de matériaux nanostructurés pour piles à combustible SOFC : application à Nd2NiO4+d et Ce1-xAxO2-y." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14036/document.
Abstract:
Le développement actuel des piles à combustible SOFC fonctionnant à température intermédiaire suppose l'optimisation des méthodes de synthèse et de mise en forme pour les matériaux nouveaux développés au cours des dernières années. En effet, les propriétés électrochimiques de ces dispositifs sont étroitement liées aux caractéristiques des poudres de départ ainsi qu'à la microstructure des électrodes (ou de l'électrolyte) après leur mise en forme. Une amélioration significative des dites propriétés peut être obtenue par la nanostructuration des matériaux. Dans ce contexte, ce travail de thèse est consacré à l’élaboration du matériau de cathode Nd2NiO4+d ainsi que du matériau d'électrolyte Ce1-xAxO2-d. Les méthodes mises en œuvre sont la synthèse de nanopoudres en milieux éthanol/eau supercritiques et par voie pyrosol ainsi que le dépôt de couches minces en milieu CO2 supercritique. Les objets obtenus ont enfin été caractérisés par spectroscopie d'impédance électrochimique afin de quantifier leur performance pour l’application SOFCThe ongoing development of Intermediate Temperature Solid Oxide Fuel Cells implies the optimization of the synthesis and deposition methods for the new materials developed these past years. Indeed, electrochemical properties of these materials are closely linked to the initial powder characteristics as well as the electrode (or electrolyte) microstructure after deposition. Significant improvement of the aforementioned properties can be obtained via nanostructuration of the materials. Thus, this thesis is dedicated to the synthesis of the cathode material Nd2NiO4+d and the electrolyte material Ce1-xAxO2-d. Methods employed are namely nanopowder synthesis in water/ethanol supercritical mixtures and spray pyrolysis as well as thin film deposition in supercritical fluids. The obtained objects have finally been characterized by electrochemical impedance spectroscopy in order to assess their performance for the SOFC application
44
Danilovic, Nemanja. "Anode materials for sour natural gas solid oxide fuel cells." 2010. http://hdl.handle.net/10048/1008.
Abstract:
Thesis (Ph. D.)--University of Alberta, 2010.Title from pdf file main screen (viewed on June 25, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Materials Engineering, [Department of] Chemical and Materials Engineering, University of Alberta. Includes bibliographical references.
45
Yoon, Daeil. "Novel heterogeneous catalyst anodes for high-performance natural gas-fueled solid oxide fuel cells." Thesis, 2014. http://hdl.handle.net/2152/28078.
Abstract:
Solid oxide fuel cells (SOFCs) are electrochemical energy conversion devices that directly transform the chemical energy of fuel into electrical energy. They generate electricity far more efficiently and with fewer emissions per megawatt-hour compared to any combustion-based power generation system. More remarkably, SOFCs can directly use hydrocarbon fuels without requiring external fuel reforming, employing low-cost Ni catalyst instead of noble-metal catalysts used for low-temperature fuel cells. However, the conventional SOFCs using Ni-based anodes fed with carbon-containing fuels have one pitfall; the carbon produced by hydrocarbon cracking is deposited on the Ni surface, thereby precluding the surface of the Ni-based anodes from being available for further fuel oxidation and consequently impeding SOFC operation. This dissertation focuses on overcoming this critical drawback to allow for the simultaneous use of Ni-based anodes and hydrocarbon fuels. Further work focuses on improving SOFC performance to provide the highest efficiencies possible. To boost the power densities of SOFCs, a novel, facile approach to modify the surface structure of anode powders and thereby enlarge the three-phase boundary (TPB) regions of anodes is presented. One such powder preparation method based on the electric charge variation of oxides depending upon the pH of the solution results in significantly extended TPB regions and thus a remarkable increase in power densities of SOFCs. Another method involves the formation of Ce₁₋[subscript x]Gd₁₋[subscript y]Ni[subscript x+y]VO₄₋[subscript delta] at the phase boundaries between NiO and Ce₀.₈Gd₀.₂O₁.₉ (GDC) by V⁵⁺-incorporation onto NiO surface; this method improves the microstructure of Ni-GDC-based anodes and considerably lowers GDC electrolyte sintering temperature, thereby enhancing the SOFC performance. With these high performance anodes, natural gas-fueled SOFCs are studied through two strategies to alleviate coking: incorporation of catalytic materials onto the Ni surface and the introduction of catalytic functional layers (CFLs) to the outer surface of an anode-supported single cell. Hydrogen tungsten bronze and hydroxylated Sn formed on the Ni surface provide hydroxyls for the deposited solid carbon, removing it from the anodes as CO₂. Moreover, the use of hydrophilic Sn or Sb-incorporated Ni-GDC CFLs prevents the anode from being exposed directly to hydrocarbon fuels and controls the solid carbon accumulation similarly to the former strategy.text
46
Tsai, Chia-Fen, and 蔡佳芬. "Synthesis and Charaterization of Ti-doped LaCrO3 as Anodes for Solid Oxide Fuel Cells." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/89708738560398572445.
Abstract:
碩士國立交通大學
應用化學系碩博士班
99
In the present study, Ti-doped LaCrO3 perovskite materials were successfully synthesized from EDTA-chelating precursor solution containing the respective aqueous solution of metal nitrate, nitric acid, and EDTA. The phase presence and redox stability of Ti-doped LaCrO3 was characterized by powder X-ray diffraction. Ti-doped LaCrO3 powder with single phase orthorhombic perovskite were synthesized under 800°C, which is lower than the one reported to form other perovskite materials. The structure remains its orthorhombic phase when the content of dopant is less than 0.15 as observed by PXRD. As the content of dopant is more than 0.15, it tends to form La2Ti2O7 pyrochlore second phase. Furthermore, the electronic conductivity investigated by four-probe method increased with raising amount of Ti, but it is still lower than the requirement, 1S/cm. Yet, outstanding ionic conductivity of 15% Ti-doped LaCrO3, 0.107S/cm, is observed by electrochemical impedance spectroscopy. Also, it’s shown that electronic and ionic conductivity both in O2 and H2 increases with raising amount of Ti, indicating Ti-doped LaCrO3 is a p-type semiconductor. Further study on surface characteristics by X-ray photoelectron spectroscopy exhibits that the change in conductivity with concentration of charge carriers is closely related to the altering in oxidation states of ions. Dropping conductivity in reducing atmosphere and low electronic conductivity are great concerns for its application on anode for SOFCs, hence further investigation in cell testing needs to be carried out.
47
Zarzalejo, Maria. "Design and Development of Atmospheric Plasma Sprayed Ceramic Anodes for Solid Oxide Fuel Cells Operating under High Fuel Utilization Conditions." Thesis, 2012. http://hdl.handle.net/1807/42429.
Abstract:
High fuel utilization SOFCs could eliminate emissions from systems that include afterburners and potentially be suitable for carbon sequestration, while producing electricity more efficiently. Current fuel utilization operating points are typically chosen at approximately 85% for Ni-cermet anodes because higher fuel utilization frequently results in the formation of nickel oxide and reduces drastically the performance of the SOFC. In this work the feasibility of an in-plane graded anode architecture with a transition from a material with high catalytic activity to materials more stable under high fuel utilization conditions was evaluated through a steady-state SOFC finite element model. Thereafter, plasma spraying of solution precursor feedstock (SPPS) and suspension feedstock (SPS) was used to fabricate ceramic coatings that could potentially be used as SOFC anodes for high fuel utilization conditions. Microstructural, electrical and electrochemical properties of LST, LSBT and LSFCr coatings with additions of carbon black pore former were investigated.
48
Lu, Xiaochuan. "Composite anodes for utilization of H₂ and methane fuels in intermediate-temperature solid oxide fuel cell : a thesis presented to the faculty of the Graduate School, Tennessee Technological University /." 2008. http://proquest.umi.com/pqdweb?index=0&did=1609597831&SrchMode=1&sid=3&Fmt=6&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1249476995&clientId=28564.
49
Froitzheim, Jan Henrik [Verfasser]. "Ferritic steel interconnectors and their interactions with Ni base anodes in solid oxide fuel cells (SOFC) / Jan Henrik Froitzheim." 2008. http://d-nb.info/990438643/34.
50
Metcalfe, Thomas Craig. "Development and Characterization of Nickel and Yttria-stabilized Zirconia Anodes for Metal-Supported Solid Oxide Fuel Cells Fabricated by Atmospheric Plasma Spraying." Thesis, 2013. http://hdl.handle.net/1807/43667.
Abstract:
Research was performed on the development of relationships between the microstructure of nickel and yttria-stabilized zirconia (YSZ) coatings and the processing parameters used for their deposition by atmospheric plasma spraying (APS). Research was also performed on the development of relationships between the microstructure of plasma sprayed Ni-YSZ coatings and the electrochemical performance of metal-supported solid oxide fuel cells (SOFCs) incorporating these coatings as anodes.
Three APS processes were used to deposit Ni-YSZ coatings: dry-powder plasma spraying (DPPS), suspension plasma spraying (SPS), and solution precursor plasma spraying (SPPS). These processes differ in the form of the feedstock injected into the plasma. The composition of the Ni-YSZ coatings deposited with each spray process could be controlled through adjustment of the plasma gas composition and stand-off distance, as well as adjustment of feedstock properties including agglomerate size fraction for DPPS, NiO particle size and suspension feed rate in SPS, and the enthalpy of decomposition of the precursors used in SPPS. The porosity of the Ni-YSZ coatings could be controlled through the addition of a sacrificial pore forming material to each feedstock, with coating porosities up to approximately 35% being achieved for each coating type.
Metal-supported SOFCs were fabricated to each have anodes deposited with a different plasma spray process, where all anodes had nominally identical composition. The microstructures obtained for each anode type were distinctly different. SPPS led to the most uniform mixing of the smallest Ni and YSZ particles. These anodes most resembled typical structures from anodes fabricated using conventional methods. It was found that the polarization resistance, Rp, associated with the high frequency (> 1 kHz) range of the impedance spectrum correlated to the three phase boundary length (TPBL) density of each anode, with lower Rp values corresponding to higher TPBL densities. It was also found that the Knudsen diffusion coefficient and effective ordinary diffusion coefficient of the porous anodes correlated with the Rp associated with the low frequency (< 1 kHz) range of the impedance spectrum. Therefore, the impedance spectrum can be used to compare microstructural differences among plasma sprayed Ni-YSZ anodes.