Elucidating the Synergetic Mechanism of Ni-Mo Electrocatalysts for the Hydrogen Evolution Reaction

Abstract

Hydrogen is a potential future energy vector and a current industrial feedstock. Currently, most hydrogen is produced through the fossil fuel dependent steam reforming reaction. Water electrolysis is a promising alternative, but is currently limited by the availability of non noble metal catalysts that are stable in acid and by the lack of highly active non-noble metal catalysts in base. Nickel based electrcatalysts are a promising option for active catalysts in base. While it is well known that molybdenum enhances the activity of nickel catalysts, the heterogeneous nature of electrode surfaces complicates efforts to gain a fundamental understanding of this enhancement. In our work, we create a series of electrodes by depositing three different sizes of nickel nanoparticles onto molybdenum substrates. This allows us to investigate the effect that distinct domains of molybdenum, rather than an alloy or co-deposited material, has on nickel. We find that the activity is highest for the largest particles, a result that suggests that the enhancement is not occurring solely at the interface. As it is been demonstrated that the coexistence of multiple nickel oxidation states in pure nickel systems increases activity, we posit that the molybdenum acts to maintain the requisite plurality of oxidations states on the nickel nanoparticles.