Electrochemically Fabricated Ni−P, Ni−S and Ni−Se Materials for Overall Water Splitting: Investigating the Concept of Bifunctional Electrocatalysis

Abstract Transition‐metal‐based electrocatalysts containing chalcogenides (S and Se) or phosphorous have been extensively reported as bifunctional electrocatalysts for overall water splitting. However, there remains the question as to whether the pristine material is truly bifunctional with regards to inherent activity for both the hydrogen evolution reaction (HER) and the oxygen evolution (OER), which has implications for their use in commercial electrolyzers when coupled with renewable energy sources. Herein, we present a case study on electrochemically synthesized NiS x , NiP x and NiSe x films by using a cyclic voltammetric deposition technique. The HER and OER performances of these electrocatalysts were evaluated in 1 M NaOH, where good activity was observed. Post‐OER catalysis analysis with scanning electron microscopy and X‐ray photoelectron spectroscopy revealed that structural changes are limited to the surface of the materials, but that extensive oxidation occurs. Subsequent HER experiments revealed a significant deterioration in performance in all cases. This raises the question if materials of this type in their pristine state can truly be regarded as bifunctional for overall electrochemical water splitting?