Designing of electrocatalysts for the Hydrogen Evolution Reaction (HER) with the Use of (CoxNi1-x)2Mo3N (x = 0-0.6)

Abstract

We describe how cobalt (Co) incorporation influences the electrocatalytic activity of the hydrogen evolution reaction (HER) on Ni2Mo3N. A series of homogeneous phase-pure (CoxNi1-x)2Mo3N electrocatalysts with varying Co content (x) was synthesized and thoroughly investigated. The possibility of forming different crystal structures among the two end members limits the accessibility of single-phase solid solutions across the entire doping range (x = 0 – 1). A citrate-based polymeric gel-type synthesis method enables successful Co doping at least up to x = 0.6. Co-doping enhances HER activity within x: 0.05-0.2, but a sharp activity drop occurs at x>0.2 due to long range structural defects. The HER electrocatalytic activity (both current density at -400 mV and the potential to reach -2 mA cm-2 vs. RHE) thus varies nonlinearly with x. The local structure and coordination environment of the as-prepared catalysts with x ≤ 0.6 do not change; however, some variations in the long-range structure may exist. Surprisingly, there is no correlation between local (nearest-neighbor coordination environment) or average bulk (lattice parameters) structures and the HER electrocatalytic activity of the (CoxNi1-x)2Mo3N series, regardless of x. These preliminary findings will enable the design of better-performing mixed metal nitride-based catalysts for various chemical and electrochemical reactions.

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ORCID for Andrew L. Hector: orcid.org/0000-0002-9964-2163

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