Breakthrough in alkaline membrane electrolyzers
Helmholtz-Zentrum Berlin für Materialien und Energie
A team 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.
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.
- M. Klingenhof, H. Trzesniowski, S. Koch, J. Zhu, Z. Zeng, L. Metzler, A. Klinger, M. Elshamy, F. Lehmann, P. W. Buchheister, A. Weisser, G. Schmid, S. Vierrath, F. Dionigi, P. Strasser. High-performance anion-exchange membrane water electrolysers using NiX (X = Fe,Co,Mn) catalyst-coated membranes with redox-active Ni–O ligands. Nature Catalysis, 2024; DOI: 10.1038/s41929-024-01238-w
Recent efforts in anion-exchange membrane water electrolysis (AEMWE) focus on developing superior catalysts and membrane electrode assemblies to narrow the performance gaps compared with proton-exchange membrane water electrolysis (PEMWE). Here we present and characterize Ir-free AEMWE cells with NiX (X = Fe, Co or Mn) layered double hydroxide (LDH) catalyst-coated membranes with polarization characteristics and hydrogen productivities approaching those of acidic PEMWE cells, achieving >5 A cm−2 at <2.2 V. Operando spectroscopy revealed a correlation between Ni4+ centres and redox-active O ligands with an O K-edge feature, attributed to µ3-O ligands in the γ-LDH catalytic phase via density functional theory calculations. This computational–experimental study challenges the previously assumed correlation between spectral O K-edge features and oxygen evolution reaction performance in Ni-based LDH catalysts and provides insights from the molecular to the technological level demonstrating how redox-active Ni–O species and innovative catalyst-coated membrane preparation boost AEMWE performance to values rivalling state-of-the-art PEMWE cell technology.
Hydrogen: Breakthrough in alkaline membrane electrolyzers | ScienceDaily