Dual-cathode plasma-induced exfoliated WSe₂/graphene nanosheet composite mediating an efficient hydrogen evolution reaction

With the goal of obtaining a sustainable earth-abundant electrocatalyst that displays high performance in the hydrogen evolution reaction (HER), herein we describe a new electrochemical process for the simultaneous dual-cathodic plasma-induced exfoliations of two different bulk materials—graphite and WSe₂—into two-dimensional (2D) nanosheets for the fabrication of a homogeneous composite. Using this approach, we produced unique structures of graphene nanosheet-engulfed ultrathin WSe₂ nanosheets (WSe₂@GN), stabilized through van der Waals and π–π interactions between the WSe₂ and GNs, possessing various morphologies and featuring large edge and defect densities on the basal plane of the GNs—potential active sites for HER catalysis. This synthesis of WSe₂@GN structures not only increased the number of active sites in the semiconducting WSe₂ nanosheets but also enhanced their conductivity. Our dual-cathode plasma produced WSe₂@GN nanosheet composites exhibited high HER performance, characterized by a low overpotential of 106 mV at a current density of 10 mA cm^–2, a Tafel slope of 66 mV dec^–1, and long-term stability in 0.5 M H₂SO₄ (80% activity retention after >48 h); these performance metrics were much better than those of the corresponding WSe₂/GN composite, prepared through two sequential single-cathode electrochemical plasma exfoliation and mixed together (233 mV, 111 mV dec^–1), and are among the best ever reported for a composite involving WSe₂ and GNs, prepared through simultaneous exfoliation at a low temperature and over a short period of time, for the HER. This in situ dual-plasma-exfoliation synthetic approach allows the effective production of homogeneous 2D/2D heterostructures with great potential for various energy-related applications, while being an effective and simple strategy for tuning the morphologies of composites of graphene and transition metal dichalcogenide materials for a broad range of energy applications.