Understanding the effect of molybdate incorporation on the structure, morphology, porosity, surface area and etching-induced enhanced electrocatalytic water splitting of low-cost transition metal hydroxides grown on inexpensive copper substrate.

Electrochemical water (H 2 O) splitting is one of the most promising technologies for energy storage by hydrogen (H 2 ) generation but suffers from the requirement of high overpotential in the anodic half-reaction (oxygen evolution), which is a four-electron process. Though transition-metal oxides and oxysulfides are increasingly researched and used as oxygen evolution electrocatalysts, the bases of their differential activities are not properly understood. In this article, we have synthesized NiCo 2 O 4 and NiCo 2 O x S 4– x by a chemical bath deposition technique, and the latter has shown better oxygen evolution performance, both in terms of stability and activity, under alkaline conditions. Comprehensive analysis through time-dependent cyclic voltammetry, microscopy, and elemental analysis reveal that the higher activity of NiCo 2 O x S 4– x may be attributed to the lower metal–sulfur bond energy that facilitates the activation process to form the active metal hydroxide/oxyhydroxide species, higher electrochemically active surface area, higher pore diameter and rugged morphology that prevents corrosion. This work provides significant insights on the advantages of sulfur-containing materials as electrochemical precatalysts over their oxide counterparts for oxygen evolution reaction.