Development of Alkaline Membrane Electrolyzers Using Cost-Effective Catalyst
A collaborative team from the Technical University of Berlin, HZB, IMTEK (University of Freiburg), and Siemens Energy has developed an alkaline membrane electrolyzer that shows promise in approaching the performance of established proton-exchange membrane (PEM) electrolyzers. The electrolyzer uses cost-effective nickel compounds for the anode catalyst, replacing the traditionally costly and rare iridium.
The team conducted operando measurements at BESSY II to examine catalytic processes in detail, with assistance from a theory team from the United States and Singapore, which provided a molecular understanding. Prototype cells built in Freiburg using a new coating process were tested in operation, and the findings have been published in the journal *Nature Catalysis*.
Hydrogen is expected to play a role in future energy systems, serving as an energy storage medium, fuel, and raw material for the chemical industry. It can be produced through the electrolysis of water in a climate-neutral manner, provided renewable energy sources like solar or wind are used.
Currently, scaling up for a green hydrogen economy is dominated by two electrolysis systems: PEM electrolysis and classic liquid alkaline electrolysis. Alkaline exchange membrane (AEM) electrolyzers aim to combine the benefits of both systems while avoiding the need for rare and expensive metals like iridium.
The AEM electrolyzer developed by the research teams from TU Berlin, HZB, IMTEK, and Siemens Energy shows efficiency that approaches that of PEM systems. It employs nickel double hydroxide compounds with iron, cobalt, or manganese, coated directly onto an alkaline ion exchange membrane through a newly developed process.
During the electrolysis experiments, the team used operando measurements at the BESSY II X-ray source in Berlin to gain insights into the molecular processes at the LiXEdrom end station. The theory team from Singapore and the U.S. played a role in interpreting the experimental data.
Prof. Peter Strasser of TU Berlin explained, "This allowed us to elucidate the key catalytic-chemical processes at the catalyst-coated membrane, especially the phase transition from a catalytically inactive alpha phase to a highly active gamma phase and the role of various O ligands and Ni4+ centers in the catalysis." According to Strasser, it is this gamma phase that makes the nickel-based catalyst comparable to current iridium-based catalysts. Their work has shown some similarities to iridium in the catalytic mechanism, as well as some molecular differences.
This research has contributed to the understanding of fundamental catalysis mechanisms for nickel-based electrode materials. The newly developed coating method for membrane electrodes also shows potential for scalability. A laboratory cell has already been tested at IMTEK, laying the foundation for further industrial evaluation and suggesting that an AEM electrolyzer could be cost-effective and efficient.
