Enhancing the Performance of Ni-Mo Alkaline Hydrogen Evolution Electrocatalysts with Carbon Supports

Alkaline water electrolysis offers the use of lowcost active materials and ancillary components, making it attractive for hydrogen production from renewables. Nevertheless, the practical performance of nonprecious electrocatalysts for alkaline hydrogen evolution still lags behind platinum-group metals. This disparity motivates work to understand how the solid-state chemistry of nonprecious transition metal alloys influences their activity toward alkaline hydrogen evolution. To this end, we have clarified the composition, chemical structure, and morphology of a previously reported Ni-Mo nanopowder electrocatalyst. The as-synthesized catalyst is mixed phase, comprising crystalline Ni-rich alloy nanoparticles embedded in a Mo-rich oxide matrix, and exhibits low activity toward hydrogen evolution. Its activity markedly increases upon activation by postdeposition reductive annealing or by including carbon black as a catalyst support. These results are consistent with a physical picture in which activity is limited not by kinetics but by electrical resistivity arising from thin oxide layers at the interfaces between the Ni-Mo alloy nanoparticles. Additional efforts to optimize the dispersion on carbon black supports resulted in mass activities exceeding 60 mA/mg (on the basis of Ni-Mo mass) at 100 mV overpotential. This was over 5-fold greater than we observed for activation by hydrogen annealing, and we postulate that it still represents a lower-bound estimate of the true activity of this catalyst.