Hydrogen: Breakthrough in alkaline membrane electrolysers
The AEM water electrolyser cell works with a newly developed membrane electrode (MEA) that is directly coated with a nickel-based anode catalyst. Its molecular mode of action has been elucidated, and the AEM cell has proven to be almost as powerful as a conventional PEM cell with iridium catalyst. © Flo Force Fotografie, Hahn-Schickard & IMTEK Universität Freiburg
The catalytically inactive alpha phase (left) transforms through a phase transition to the highly active gamma phase (right). The team was able to elucidate the chemical details of this phase transition in detail using X-ray experiments at the LiXEdrom at BESSY II, as well as electrochemical and computer-aided analyses. © Hanna Trzesniowski
A team from the Technical University of Berlin, HZB, IMTEK (University of Freiburg) and Siemens Energy has developed a highly efficient alkaline membrane electrolyser that approaches the performance of established PEM electrolysers. What makes this achievement remarkable is the use of inexpensive nickel compounds for the anode catalyst, replacing costly and rare iridium. At BESSY II, the team was able to elucidate the catalytic processes in detail using operando measurements, and a theory team (USA, Singapore) provided a consistent molecular description. In Freiburg, prototype cells were built using a new coating process and tested in operation. The results have been published in the prestigious journal Nature Catalysis.
Hydrogen will play a major role in the energy system of the future, as an energy storage medium, a fuel and valuable raw material for the chemical industry. Hydrogen can be produced by electrolysis of water in a virtually climate-neutral way, provided this is done with electricity from solar or wind power. Scale-up efforts for a green hydrogen economy are currently largely dominated by two systems: proton-conducting membrane electrolysis (PEM) and classic liquid alkaline electrolysis. AEM electrolysers combine the advantages of both systems and, for example, do not require rare precious metals such as iridium.
Alkaline Membrane (AEM) Electrolysers without Iridium
Now, research teams from TU Berlin and HZB, together with the Department of Microsystems Engineering (IMTEK) at the University of Freiburg and Siemens Energy, have presented the first AEM electrolyser that produces hydrogen almost as efficiently as a PEM electrolyser. Instead of iridium, they used nickel double hydroxide compounds with iron, cobalt or manganese and developed a process to coat them directly onto an alkaline ion exchange membrane.
Insight into molecular processes during electrolysis at BESSY II
During the electrolysis in the cell, they were able to carry out operando measurements at the Berlin X-ray source BESSY II at the LiXEdrom end station. A theory team from Singapore and the USA helped to interpret the experimental data. ‘This enabled us to elucidate the relevant catalytic-chemical processes at the catalyst-coated membrane, in particular the phase transition from a catalytically inactive alpha phase to a highly active gamma phase and the role of the various O ligands and Ni4+ centres in the catalysis,’ explains Prof. Peter Strasser, TU Berlin. ‘It is this gamma phase that makes our catalyst competitive with the current state-of-the-art iridium catalysts. Our work shows important similarities to iridium in the catalytic mechanism, but also some surprising molecular differences.’
The study has thus significantly advanced our understanding of the fundamental catalysis mechanisms of the new nickel-based electrode materials. In addition, the newly developed coating method for the membrane electrode promises excellent scalability. A first fully functional laboratory cell has already been tested at IMTEK. The work lays the foundation for further industrial evaluation and demonstrates that an AEM water electrolyser can also be highly efficient.
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