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

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.