Graphene oxide-mediated scalable preparation of heterostructured MoS2–MoO2/graphene nanohybrids for efficient energy storage and hydrogen evolution reaction

Abstract

A nanostructured hybrid of MoS₂–MoO₂ and graphene was synthesized by employing a simple in situ solvent-free strategy. In this solid-state method, the precursors were ball-milled for homogeneous intercalation and distribution, which upon thermal treatment resulted in uniformly dispersed and in situ formed MoS₂–MoO₂/graphene nanohybrids. The graphene oxide (GO) not only provides the basis for the conductive graphene support but also mediates the partial oxidative transformation of MoS₂ into MoO₂ to form heterostructured MoS₂:MoO₂ nanohybrids within graphene layers. Consequently, the resulting nanohybrid electrodes showed an excellent specific capacitance of 872 F g⁻¹ at 1 A g⁻¹ current density and remarkable stability with high rate capability. Similarly, the asymmetric supercapacitor device based on the MoS₂–MoO₂/G nanohybrid and activated carbon (AC) exhibited a maximum energy density of 85.5 W h kg⁻¹ and a power density of 2 kW kg⁻¹. The device also displayed high stability with 95.8% initial capacitance retention after 5000 continuous GCD cycles at a current density of 3 A g⁻¹. Moreover, the resulting nanohybrid also showed an enhanced electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in an alkaline medium with an onset potential (η₁₀) of 82 mV and a Tafel slope of 63 mV dec⁻¹. The excellent electrochemical performance was attributed to the unique synergy between heterostructured MoS₂–MoO₂ and graphene, which elevated the efficient ion diffusion, charge transfer and offered plenty of exposed yet active sites for the HER. Overall, the proposed solid-state method holds great potential in realizing the large-scale preparation of other bifunctional sulphides/oxide hybrid materials with practical utility.