Hydrogen electrolysers
Current technology
Water electrolysis is a key technology for producing green hydrogen, utilising various methods that differ in terms of efficiency and materials used. The most established methods include alkaline water electrolysis (AWE) and proton exchange membrane water electrolysis (PEMWE). AWE employs a liquid alkaline solution as the electrolyte, allowing hydroxide ions to facilitate the reaction, while PEMWE uses a solid polymer membrane to separate the electrodes and requires pure water, leading to high-purity hydrogen production.
The materials used in these technologies significantly impact their performance and cost. AWE typically utilises non-precious metals such as nickel for its electrodes, while PEMWE relies on noble metals like platinum and iridium for its electrocatalysts.
Emerging technologies like anion exchange membrane (AEM) electrolysis are gaining attention due to their potential for using less expensive transition metal catalysts instead of noble metals. AEM operates similarly to AWE but with an anion exchange membrane that allows for efficient ion transport while maintaining lower costs. As research progresses, these innovations aim to enhance the efficiency and reduce the costs of hydrogen production through electrolysis.
Electrolysis processes are environmentally safe, allow high current density, and therefore provide high productivity. By using different types of electrolysers, electrochemical water decomposition can be carried out at both low and high temperatures and pressures.
Market
Hydrogen production via electrolysis has been growing steadily.
According to the consensus estimates of analysts (IEA, Metals Focus), the annual commissioning of electrolysers amounted to 3 GW in 2023. By 2030, the commissioning of new electrolysis capacities is expected to reach 29 GW.
In 2023, most of the new commissioning of electrolysers falls to alkaline ones, representing about 80%. The rest of the share is occupied by PEM electrolyser bushings.
By 2030, however, the commissioning of PEM electrolysers is set to hit 45%, while alkaline will account for 40%. The remaining 15% will be taken up by AEM.
Challenges of current technology
Modern electrolysis technologies face a number of challenges that may hinder their scalability and economic feasibility.
Alkaline electrolysis
In alkaline electrolysers, the use of liquid electrolytes – usually potassium hydroxide (KOH) – can lead to corrosion of the electrodes, which affects the durability and maintenance requirements of the system. Therefore, increasing the durability and efficiency of alkaline electrolysers while reducing operating costs remains an important task for researchers.
Also, alkaline electrolysers are often characterised by a lower current density compared to other technologies, which creates an incentive to search for new types of electrode coatings capable of withstanding an increase in current density.
PEM electrolysis
Iridium, an expensive and very rare material, is used as a key catalyst in PEM electrolysers. This material limits widespread adoption.
PEM systems operate in conditions of high acidity, which places significant stress on the materials, requiring constant research to improve the durability and stability of these components. Reducing dependence on iridium without compromising productivity is a key objective in increasing the economic feasibility of PEM electrolysers for large-scale hydrogen production. One strategy for achieving the abovementioned goal involves substituting iridium with a precious metal that has the same levels of acid resistance and catalytic activity.
Positive impact of palladium
As a catalyst, palladium increases the efficiency of hydrogen production in both PEM and alkaline electrolysers.
In PEM electrolysers, palladium-containing catalysts maintain resistance to oxidation while increasing the catalytic activity, reducing energy consumption for hydrogen production.
In addition, palladium’s ability to absorb 900 times its own volume in hydrogen makes it an ideal material for safe hydrogen storage, ensuring stability and minimising the risks associated with hydrogen volatility.
The role of palladium in increasing the stability of oxygen electrodes in PEM electrolysers solves one of the key tasks when it comes to boosting the durability and reliability of these systems.
In alkaline electrolysers, palladium and platinum-palladium electrodes have low overvoltage, excellent strength and slow fracture rates, which makes them highly efficient during prolonged use.
While alkaline systems often use nickel-based catalysts to reduce costs, palladium-based catalysts are still valuable for their superior performance in harsh environments.
Palladium’s versatility extends to its use in nanoparticle form, where it is deposited on conductive supports to create electrodes with a high surface area, increasing the mass activity of catalysts like platinum, iridium and their alloys. This innovation not only improves the efficiency of hydrogen and oxygen evolution reactions but also contributes to the overall cost-effectiveness of electrolysers. By enabling safer hydrogen storage, enhancing catalytic performance, and supporting the development of advanced electrolyser technologies, palladium is poised to play a pivotal role in the transition to a sustainable hydrogen economy.
To find out more about the electrochemical qualities of palladium, see – Chemistry.
To find out more about palladium in electrolyser technologies, see the following scientific publications:
- Chatenet, M., Pollet, B. G., Dekel, D. R., Dionigi, F., Deseure, J., Millet, P., … & Schäfer, H. (2022). Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments. Chemical society reviews, 51(11), 4583-4762. DOI: https://doi.org/10.1039/d0cs01079k
- Sanij, F. D., Balakrishnan, P., Leung, P., Shah, A., Su, H., & Xu, Q. (2021). Advanced Pd-based nanomaterials for electro-catalytic oxygen reduction in fuel cells: A review. International Journal of Hydrogen Energy, 46(27), 14596-14627. DOI: https://doi.org/10.1016/j.ijhydene.2021.01.185
- Henkensmeier, D., Najibah, M., Harms, C., Žitka, J., Hnát, J., & Bouzek, K. (2021). Overview: State-of-the art commercial membranes for anion exchange membrane water electrolysis. Journal of Electrochemical Energy Conversion and Storage, 18(2), 024001. DOI: https://doi.org/10.1115/1.4047963