Comparing Intrinsic Catalytic Activity and Practical Performance of Ni- and Pt-Based Alkaline Anion Exchange Membrane Water Electrolyzer Cathodes.

The stringent cost and performance requirements of renewable hydrogen production systems dictate that 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 HER activity that is roughly 10-fold lower than Pt-Ru on the basis of turnover frequency under low (≤100 mV) polarization conditions. We further found that the HER activity of Ni-Mo/C cathodes is 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 indistinguishable current density vs cell potential relationships compared to otherwise identical assemblies with Pt-Ru cathodes. This result indicates that the contribution of the cathode to the total cell polarization is small, even for the less active Ni-Mo/C catalyst, and further implies that Pt-based cathodes can indeed be replaced by nonprecious alternatives with no loss in performance.