Nanocrystal Seeded Growth of High Activity Ni-Mo Electrocatalysts for the Hydrogen Evolution Reaction

Abstract

Nickel-molybdenum-based materials are widely used functional oxide electrocatalysts for the hydrogen evolution reaction. While molybdenum co-deposits improve the activity of bare Ni, the origin of the synergetic mechanism between Ni and Mo remains poorly understood, largely because of the ill-defined nature of systems employed for interpreting this effect. In this work, we directly investigate the interaction between Ni and Mo phases by depositing size-controlled Ni nanocrystals onto Ti and Mo substrates, and subjecting the synthesized materials to electrocatalytic conditions with and without dissolved molybdenum species.Thanks to the uniformity of the active phases employed in this work, we are able to disentangle the competing effects of a bulk electronic interaction between Ni and Mo, and a separate enhancement mechanism centered on the formation of a Mo-rich alloy phase. Potentiostatic and impedance techniques shed light on the electrochemical activity of the NiMo surfaces, while Auger spectroscopy and in-situ TEM are used to elucidate the nature of the samples and the changes that occur during electrochemical testing. Finally, the information gained is used to design a Ni-nanocrystal seeded Mo deposition procedure that yields an electrocatalytic surface with a hydrogen evolution onset overpotential of <0.15V at pH 14. This work not only provides crucial information for improving the activity of current Ni-Mo systems, but also a general paradigm for investigating fundamental interactions and synergic effects in electrocatalytic materials.