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

Alkaline
water electrolysis offers the use of low-cost 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.