Ni–Mo Composites Deliver Performance Parity with Pt–Ru in Anion Exchange Membrane Water Electrolyzer Cathodes

The stringent cost and performance requirements of renewable hydrogen production systems dictate that next-generation electrolyzers benefit from the use of nonprecious catalysts only if they deliver the same level of activity and durability as their precious metal counterparts. Here we report on recent work to understand interrelationships between the intrinsic activity of Ni- and Pt-based electrolyzer cathode catalysts and their performance in zero-gap alkaline water electrolyzer assemblies. Our results suggest that nanoparticulate Ni--Mo exhibits approximately 5-fold lower HER activity than Pt--Ru on the basis of turnover frequency under low polarization conditions. We further found that the HER activity of Ni--Mo/C cathodes is dramatically inhibited by aryl piperidinium anion-exchange ionomers bearing bicarbonate counter-anions. After addressing this poisoning effect, we produced electrolyzer assemblies based on Ni--Mo/C cathodes that delivered statistically indistinguishable current density vs. cell potential relationships compared to otherwise identical assemblies with Pt--Ru cathodes, which we interpret as performance parity.