Coexisting Few-Layer Assemblies of NiO and MoO₃ Deposited on Vulcan Carbon as an Efficient and Durable Electrocatalyst for Water Oxidation

An efficient electrocatalyst for oxygen evolution reaction (OER) has been prepared by adopting a strategy wherein layered assembly of NiO and MoO3 could be dispersed on a Vulcan carbon support to simultaneously maintain exposure of the synergistically activated sites and electrical conductivity of the matrix. The assembly involves growth of layers of NiO on the surface of few-layer MoO3, which in turn is dispersed on Vulcan carbon (NiO@MoO3/VC) through a sequential hydrothermal process. The hydrothermal process played a key role in establishing the coexisting few-layer assembly of NiO and MoO3 on Vulcan carbon, which involved conversion of preformed MoS2 sheets to MoO3 and concomitant growth of Ni(OH)2 layer prior to its conversion to NiO during the subsequent heat treatment process. The NiO sheets have exposed edges, and they are instrumental in enhancing the OER activity of NiO@MoO3/VC. The higher activity is also credited to the lower charge transfer resistance (RCT) value possessed by NiO@MoO3/VC, which arises from the optimum combination of MoO3 and Vulcan carbon in the system. The overpotential of NiO@MoO3/VC for achieving the 10 mA cm–2 current density is 280 mV, which is an improved value over the 292 mV obtained in the case of the state-of-the-art RuO2 catalyst. NiO@MoO3/VC also demonstrates outstanding stability for 15 h in 1 M KOH solution at 1.51 V. The presence of surface nickel molybdate (NiMoO4) prevents the dissolution of MoO3 in the alkaline environment and provides excellent stability to the NiO@MoO3/VC in 1 M KOH solution.