Our lab is developing nonprecious nanocatalysts for the alkaline hydrogen evolution and oxidation reactions. These types of materials are integral to the development of alkaline anion exchange membrane electrolyzers and fuel cells, which promise massive cost reductions relative to state-of-the-art devices based on proton exchange membranes. This presentation will summarize our recent work on Ni–Mo composites which, despite decades of study, remain poorly understood with respect to their precise nanoscale composition. Using environmental transmission electron microscopy (ETEM), we observed in real time the progressive transformation from a nominally single phase NiMoOx catalyst precursor to a Ni0.9Mo0.1@MoOx core/shell composite. We also used identical-location TEM to characterize failure modes of these catalysts after continuous hydrogen evolution/oxidation treatments on the timescale of hours to tens of hours. Our findings suggest that the oxide shell is integral to the high catalytic activity of Ni–Mo composites (less than 10x lower than Pt based on total metal content), but it also gives rise to a characteristic electron transport limitations. We also saw that optimized Ni–Mo composites reversibly evolve and oxidize hydrogen in aqueous base, but hydrogen oxidation reactivity is limited at low overpotentials by internal mass transfer and at higher overpotentials by oxidative degradation. These results show, on one hand, that it is clearly possible to close the gap in catalytic activity between nonprecious and precious hydrogen evolution/oxidation electrocatalysts, but a key challenge remains in stabilizing nonprecious catalysts toward oxidation.

On the activity and stability of Ni–Mo composites for alkaline hydrogen electrochemistry

ACS Fall 2021

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