Hydrogen-Evolution Catalysts Based on NiMo Nitride Nanosheets
A heterogeneous electrocatalytic hydrogen evolving system has been created from earth-abundant and inexpensive components. With highly exposed reactive sites and a synergism among its components, the NiMoNx/C nanosheet catalyst exhibited an excellent activity for the HER with a small overpotential of 78 mV, a high exchange current density, and a Tafel slope as small as 35 mV dec-1. This is the smallest Tafel slope reported to date for a non-platinum catalyst, suggesting Tafel-like recombination as the rate limiting step in the catalyzed HER. In acidic media, the NiMoNx nanosheets can be used without noticeable corrosion. Our XANES results provided an approach to understanding the electronic properties and the stabilizing effect of nitrogen on the metallic states of Ni and Mo. Further work is needed to characterize the local distribution of surface Ni and to optimize the ratio of components to improve the performance of this promising type of catalyst for the HER. See figures below (TEM images of NiMoNx nanosheets - left and comparative electrocatalytic activity at pH 1 - right).
Last Modified: September 13, 2012