Academic literature on the topic 'Alkaline Electrolysers'

Electrolysers is a novel component in the energy system and is expected to play a key role in the transition to a fossil free energy system and supply Green Hydrogen to a number of small- and large-scale applications within a number of industries e.g. transportation, industry etc. with several hundreds of GW is projected to be installed towards 2030. Modularity and mass production are key factors for the large scale deployment of electrolysis as envisioned in Hydrogen Strategies across the World. However, a number of different design strategies and modularities can be chosen in order to achieve this. This talk focuses on fundamental aspects of alkaline electrolysis including industrial requirements for catalysts and diaphragms, how to develop an electrolyser product and the development of multi-MW alkaline electrolysers plants with factory assembled modules allowing rapid on-site installation in order to keep up with the pace needed to reach deployment targets.

This paper proposes a model of an electrolyser in the form of a subcircuit dedicated for SPICE. It takes into account both the electric static and dynamic properties of the considered device and is devoted to the optimisation of the parameters of the signal feeding this electrolyser, making it possible to obtain a high productivity and efficiency of the electrolysis process. Parameter values the describing current-voltage characteristics of the electrolyser take into account the influence of the concentration of the potassium hydroxide (KOH) solution. A detailed description of the structure and all the components of this model is included in the paper. The correctness of the elaborated model is verified experimentally in a wide range of changes in the value of the feeding current and concentration of the KOH solution. Some computations illustrating the influence of the amplitude, average value, duty factor, and frequency of feeding current on the productivity and efficiency of the electrolysis process are performed. On the basis of the obtained results of the investigations, some recommendations for the operating conditions of electrolysers are formulated.

Introducción The yearly increase in energy demand has encouraged the scientific community to find new sources of energy production without affecting the environment. Renewable technologies have become extremely popular due to the low greenhouse emissions and availability of natural energy sources (wind, sun, water, earth, tides, etc.), However, because of the intermittent energy generation from renewable sources, it is complex to rely on these technologies to guarantee the energy supply. Therefore, over the last decade, hydrogen has become increasingly studied as an energy carrier to replace current energy production technologies based on fossil fuels. Hydrogen can be easily coupled with other energy sources, increasing the efficiency of the systems. Nevertheless, hydrogen cannot be found in nature on its own and needs to be produced, currently, the most efficient method for green hydrogen generation is based on the electrolysis of water, this electrochemical process relies on the availability of water and the efficiency and correct selection of the electrolyser. Thus, this research evaluates the Alkaline and Proton Exchange Membrane (PEM) electrolysers for green hydrogen generation using water from hydroelectric power plants in Ecuador. Objetivos Evaluate Alkaline and PEM electrolysers for green hydrogen generation from hydroelectric power in Ecuador Método The methodology consists of a literature review of different brands of alkaline and PEM electrolysers selecting the ones with the highest efficiencies. For the analysis of data and information processing, quantitative methods were used. Finally, a sample of 9 hydroelectric plants was obtained for the study (Molino, Mazar, Agoyán, San Francisco, Pucará, La Península, Illuchi N 1, Illuchi N 2, Marcel Laniado). Principales resultados Different electrolyser manufacturers were analysed: Nel ASA producer of alkaline as well as PEM electrolysers, among them several models were evaluated NEL A 300, NEL A 485, NEL A 1000, NEL A 3880 with alkaline technology, and NEL MC 250, NEL M 5000 with PEM technology. H-TECH Electronic Co.Ltd with its model H-TEC HCS 10 using PEM technology. SIEMENS Energy, with its electrolyser technology PEM Silyzer 300 and McPhy with Mclyzer alkaline technology. All models were evaluated with the data from the 9 hydroelectric plants. Using technical data from the selected electrolysers and availability factor (90 %) from the hydroelectric plants, the potential of hydrogen production per year was calculated. The NEL A 3880 model with a system factor of 94% and a power of 14.7 MW displays the highest hydrogen production for alkaline technology, while the NEL MC 250, with an efficiency of 79% and 1 MW of power using PEM technology shows the highest hydrogen generation, these results are achieved for the Agoyan hydroelectric plant. Conclusiones The alkaline electrolysers show a better hydrogen generation capacity, achieving a total of 300 x 10e6 Kg of H2 per year with the NEL A 3880 model, in comparison with the PEM electrolyser technology that accounts for a maximum hydrogen production of 214 x 10e6 Kg of H2 per year. These results from the evaluation of the electrolysers show that it is feasible to establish a system for green hydrogen production based on hydroelectric power plants in Ecuador. The authors acknowledge the financial support received from the Universidad Técnica de Ambato and Dirección de Investigación y Desarrollo (DIDE) through the research project number PFICM28 “ANÁLISIS DE FACTIBILIDAD DE GENERACIÓN DE HIDRÓGENO VERDE MEDIANTE FUENTES DE ENERGÍA HIDROELÉCTRICA EN EL ECUADOR”.

Alkaline water electrolysers are widespread in many industries, including systems with hydrogen cycle of energy storage. One of the problems of modern alkaline water electrolysers is insufficient purity of generated electrolysis gases relative to electrolysis systems with solid-polymer electrolyte. In this regard, work on modification of existing porous diaphragms is actively carried out. One new area of research is the impregnation of new hydrophilic fillers into the composition of existing diaphragms and the transition to ion-solvate membranes. In this work the synthesis of zirconium hydroxide hydrogel inside a porous diaphragm with the hydrophilic filler TiO2 was carried out. This synthesis makes it possible to obtain a membrane with anion-exchange properties. A possible mechanism of OH- hydroxyl ion transfer by immobilized K+ ion was also proposed. The obtained results demonstrated the resistance of the membrane to concentrated alkaline solutions.

Shunt-currents in bipolar cell stack design with a common electrolyte-feed and -outlet is an inevitable physical phenomenon governed by Ohms law that causes some extra challenges when alkaline water-electrolysers shall operate on renewable energy that is both dynamic and intermittent. Shunt-currents are also referred to as bypass-current or creep-current. The shunt-currents are to much degree governed by the electrolyte inside the cell stack manifold system that transports lye in and out of the cells. The electrolyte inside the manifold system also electrically connects the individual cells together and enables transport of ions/electricity in parallel to the cell stack. Thus, a small portion of the rectifier current is being shunted outside the cells and does not contribute to any production. Previous work on shunt-current modelling brought new insight on how to design the manifolds and raised the awareness on shunt-current and the use of metallic manifolds which both reduced the ohmic resistivity of the manifold system and was a source of secondary electrolysis. Classic alkaline water-electrolysers are typically using an internal manifold system where the inlet ports are located at the bottom of the cell stack and the outlet ports are located at the top, and where the ports connecting the cell-interior and the common manifold channel are short and straight. Such design has in the past worked satisfactory for alkaline water-electrolysers that have been working on a high nominal load and only being shut-down for maintenance a few times over the stack-lifetime, mainly causing a modest reduction in the current efficiency. Membrane-chlorine electrolysers on the other hand, are designed for very small shunt-currents by using an external manifold system, which enables a current protection system that protects electrodes from corrosion under shutdown conditions. Shunt-currents bypassing the cell stack does not contribute to any product and therefore constitutes a loss in current efficiency and, hence, an accordingly loss in the energy efficiency (the shunt-currents still adds to the electricity bill). The atmospheric alkaline electrolyser has a modest loss in current efficiency at nominal load where the high gas volume blocks much of the current path in the rather open outlet ports. The high-pressure alkaline electrolysers on the other hand, where the gas volumes are much smaller, the current efficiency can be as low as 89% at nominal load due to shunt-currents when using simple internal manifold system. For an electrolyser with already low current efficiency at the nominal load, the current efficiency will drop dramatically as the electrolyser is taken to lower load, severely compromising the energy efficiency. The impact on shunt-currents also dramatically increases for increased number of cells in a cell stack, and eventually limits the number of cells that can be assembled in one single cell stack operating on the same common lye system. Shutdown and discharge of the electrodes may further lead to corrosion and degradation of the electrodes, strongly influenced by the shunt-currents and the manifold system. Large cell stacks will discharge faster and deeper, eventually causing corrosion of the electrodes. As the cell stack is discharged the current in the cell stack is reversed where the hydrogen electrode is being polarized to anodic potentials, and the oxygen electrode is polarized to low cathodic potentials which eventually may challenging the material stability. Thus, evaluation of electrode potentials must be an integral part of development of industrial electrodes [LeRoy] and especially in intermittent operation where frequent shutdown will occur. A good integration of the manifold system into the cell stack can potentially mitigate both the loss of current efficiency under dynamic operation and the electrode corrosion under intermittent operation.

Hydrogen is the way for connecting the renewable energy plants and consumers. However, achieving cheap, widespread hydrogen production and storage is complicated task. For hydrogen production the alkaline and acidic membrane electrolysers are used most widely. The membrane electrolysers have their limits, for example high standard potential of water splitting reaction, moderate efficiency, high cost and low durability. Decoupling oxygen evaluation reaction (OER) and hydrogen evaluation reaction (HER) is promising strategy to avoid using of membrane. Water electrolysis in separate cells was reported in 2017 by A. Landman et al., reaching the efficiency of 58% [1]. In 2022, we reported for the first time the amphoteric decoupled electrolysis by combining acid and alkaline cells [2]. The efficiency was enhanced due to reduced standard potential for water splitting by realizing HER in acidic environment but OER in alkaline. For maintaining decoupled amphoteric electrolysis, we connected acid and alkaline cell with the primary Pt electrodes and pseudocapacitive auxiliary electrodes (AE). For acid cell the AE electrode based on WO3 was used while for the alkaline cell electrodes based on Ni(OH)2. In proposed electrolyser two separate working cycles can be distinguished – different chemical processes occur at different polarities applied between primary Pt electrodes. The potential for gas generation depends on the polarity of the applied potential due to different chemical processes. In both polarities, hydrogen and oxygen are generated in separate cells. At the first cycle, ions are diffusing into the AEs and gases are generated with the Faradaic efficiency of 98 % and energetical efficiency of 43 %. At the second cycle, ions are released from AEs and gasses are generated with the Faradaic efficiency of 98 % and energetical efficiency of 201 %, providing the total energetical efficiency for whole operation of 71 %. Herein we will discuss the effect of acid OER catalyst or the structure and composition of AEs on the performance of decoupled electrolysis, illuminating the pathways for bringing this concept as the main strategy for water splitting. References [1] A. Landman, H. Dotan, G.E. Shter, M. Wullenkord, A. Houaijia, A. Maljusch, G.S. Grader, A. Rothschild, Photoelectrochemical water splitting in separate oxygen and hydrogen cells, Nature Materials 16 (2017) 646-651. [2] M. Vanags, G. Kulikovskis, J. Kostjukovs, L. Jekabsons, A. Sarakovskis, K. Smits, L. Bikse, A. Šutka, Membrane-less amphoteric decoupled water electrolysis using WO3 and Ni(OH)2 auxiliary electrodes, Energy Environ. Sci., 15 (2022) 2021-2028.

Alkaline electrolysis is an industrially mature and promising method for the production of green hydrogen at scale [1]. Alkaline electrolysers are typically characterized by low investment costs compared to other electrolysis technologies [2]. Despite being used for industrial applications for almost 100 years, the efficiency of alkaline systems can still be significantly improved. To this end, rigorous testing and optimisation of cell components is paramount. Here, we report a multi-functional alkaline electrolysis setup, designed to facilitate testing of various cell components, including electrodes, diaphragms, and catalyst. The setup is a further development of the setup originally reported by Ju et al. [3]. Importantly, the setup allows cell components to be tested under industrially relevant conditions: temperatures up to 80°C, concentrated KOH, pressures of up to 30 barg. The setup features KOH recirculation, a drying column and gas analysers for estimating the purity of produced hydrogen and oxygen. The measurement setup further allows the use of different cell configurations, enabling comparative analysis and the identification of optimal combinations of cell components for specific use-cases. Example experimental results collected at various test conditions, including the EU harmonized test conditions for low-temperature electrolysis cells [4], are reported. References: Mueller-Langer, E. Tzimas, M. Kaltschmitt, S. Peteves, Int. J. Hydrogen En., 32, 3797–3810 (2007). Buttler, H. Spliethoff, Renewable and Sustainable Energy Reviews, 82, 2440–2454 (2018). Ju, M. V. F. Heinz, L. Pusterla, M. Hofer, B. Fumey, R. Castiglioni, M. Pagani, C. Battaglia, U. F. Vogt, ACS Sustainable Chem. Eng., 6 (4), 4829–4837 (2018). Tsotridis, A. Pilenga, EU harmonised protocols for testing of low temperature water electrolysers, EUR 30752 EN, Publications Office of the European Union, Luxembourg (2021). Figure 1

Abstract Green hydrogen produced from wind, solar or hydro power is a suitable electricity storage medium. Hydrogen is typically employed as mid- to long-term energy storage, whereas batteries cover short-term energy storage. Green hydrogen can be produced by any available electrolyser technology [alkaline electrolysis cell (AEC), polymer electrolyte membrane (PEM), anion exchange membrane (AEM), solid oxide electrolysis cell (SOEC)] if the electrolysis is fed by renewable electricity. If the electrolysis operates under elevated pressure, the simplest way to store the gaseous hydrogen is to feed it directly into an ordinary pressure vessel without any external compression. The most efficient way to generate electricity from hydrogen is by utilizing a fuel cell. PEM fuel cells seem to be the most favourable way to do so. To increase the capacity factor of fuel cells and electrolysers, both functionalities can be integrated into one device by using the same stack. Within this article, different reversible technologies as well as their advantages and readiness levels are presented, and their potential limitations are also discussed.

In recent years, the EU policy identified the hydrogen as one of the main energy vectors to support the power production from renewable sources. Coherently, electrolysis is suitable to convert energy in hydrogen with no carbon emission and high purity level. Among the electrolysis technologies, the anion exchange membrane (AEM) seems to be promising for the performance and the development potential at relatively high cost. In the present work, AEM electrolysers, and their technological bottlenecks, have been investigated, in comparison with other electrolysers’ technology such as alkaline water electrolysis and proton exchange membranes. Major efforts and improvements are investigated about innovative materials design and the corresponding novel approach as main focus of the present review. In particular, this work evaluated new materials design studies, to enhance membrane resistance due to working cycles at temperatures close to 80 °C in alkaline environment, avoiding the employment of toxic and expensive compounds, such as fluorinated polymers. Different strategies have been explored, as tailored membranes could be designed as, for example, the inclusion of inorganic nanoparticles or the employment of not-fluorinated copolymers could improve membranes resistance and limit their environmental impact and cost. The comparison among materials’ membrane is actually limited by differences in the environmental conditions in which tests have been conducted, thereafter, this work aims to derive reliable information useful to improve the AEM cell efficiency among long-term working periods.

Electrochemical CO reduction (ECOR) can act as a potential bridge between CO2-to-CO technologies and renewable production of C2+ chemicals. Copper has been the most widely studied cathode catalyst for ECOR because of its unique ability to produce multicarbon products. Iridium and nickel are the most-widely used anode materials for acidic and alkaline electrolysis, respectively. However, recent reports on the instability of Ir in alkaline conditions and Ni in near neutral conditions has made it imperative to understand the anodic processes for achieving stable long term operation at high current densities for CO2/CO electrolysers. In this work, our aim was to investigate anode catalysts for ECOR at high current densities in zero gap electrolyser. Commercial Cu nanoparticles (25 nm) was used as the cathode catalysts with Ir black anode in alkaline conditions. Initially, CORR was studied in a hybrid cell with a catalyst coated anion exchange membrane and recirculated catholyte and anolyte. In this cell configuration we observe stable production of ethylene, acetate and ethanol for a total current density of upto 500 mA cm-2. However, in the zero gap electrolyser the catalytic activity decays rapidly (2-3 minutes) and leads to predominance of hydrogen evolution reaction (HER). Analysis of the cathode and anolyte after electrolysis reveals the dissolution of Ir and subsequent deposition at the cathode. This rapid decay is counter intuitive since the dissolution of Ir in alkaline solutions is very slow and should take a few hours to affect the catalytic activity. More importantly this dissolution of Ir does not happen when Ar is circulated at the cathode instead of CO, which indicates that the Ir dissolution is not entirely due to the alkaline environment. NMR analysis of the anolyte shows the presence of CO reduction products acetate and ethanol. Therefore, it is possible that the presence of CO reduction products could aggravate the Ir dissolution. This study is currently underway to analyse the possible Ir dissolution mechanisms. This is an important observations since Ir is still the most widely used anode catalyst for CO electrolysis. This also stresses on the need to explore alternative anode catalysts and/or design strategies that can circumvent the migration of reduction products to the anode.