Scalable solid-state synthesis of MoS2–NiS2/graphene nanohybrids as bifunctional electrocatalysts for enhanced overall water splitting

Abstract

In a confined nanoarchitecture, the transition metal sulphides (TMDs) exhibit a synergistic contribution towards exceptional electrocatalytic performance. Herein, we proposed an environment-friendly, in situ synthesis approach for MoS₂ wrapped NiS₂ nanohybrids uniformly dispersed on conductive graphene sheets. This solventless and technologically scalable process involves solid-state mixing of molybdenum and nickel salts and surfeit yet non-toxic elemental sulphur using ball-milling followed by thermal annealing. The resulting nanohybrids are composed of defect rich, heterostructured MoS₂–NiS₂ uniformly distributed within the surface of graphene and were used as a bifunctional electrocatalyst for overall water splitting. This synergistic hybridization of MoS₂–NiS₂/graphene has promoted a highly expanded surface, abundant electroactive centers, and a tailored conductive network, leading to enhanced water splitting efficacy. The nanohybrid exhibited superior catalytic performance for the HER with exceptionally low overpotentials in acidic (152 mV) and alkaline (141 mV) media, at a current density of 10 mA cm⁻². Likewise, a small OER overpotential of 320 mV was achieved under an alkaline medium. The resulting nanohybrid also evolved as a competent bifunctional electrocatalyst for optimal overall water splitting with a final cell voltage of 1.58 V with superior activity and stability. Therefore, the presented cost-effective and environment-friendly strategy provides high potential in the rational design and large-scale production of other nonprecious nanostructured bi-metallic sulphide materials for various energy and environmental applications.