Highly stable tungsten disulfide supported on a self-standing nickel phosphide foam as a hybrid electrocatalyst for efficient electrolytic hydrogen evolution

The detrimental impacts on environment brought by the combustion of fossil fuel have urged scientists to search for various green substituents. In particular, molecular hydrogen is proposed as one of the competitive candidates among the wide spectrum of different energy sources due to the high gravimetric energy density, cleanliness and renewability. However, the batch production of H-2 via electrolytic route requires the cost-effective and high-performance electrocatalysts to minimize the energy loss during conversion. Tungsten disulfides (2H-WS2) is an earth-abundant HER electrocatalyst which possesses high intrinsic catalytic activity and chemical stability. Nonetheless, the HER performance of WS2 is limited by the sparse catalytic edge sites and the unsatisfactory on-plane electrical conductivity. On the other hand, the self-standing nickel phosphide (Ni5P4-Ni2P) grown directly on the Ni foam is a compelling structure for water splitting due to its macroporosity and the metallic nature of 3D networks. Here, we report the hybridization of WS2 and the 3D porous metallic Ni5P4-Ni2P foam induced through a thermal process in a CVD furnace. The resultant hybridized WS2/Ni5P4-Ni2P electrode demonstrated intriguing synergistic effects that improve the overall electrode performances considerably. Experimentally, it was found that the surface of WS2/Ni5P4-Ni2P electrode contains a ternary WS2 P-(1-x)(2x) constituent, bringing the advent of desired electronic perturbations. Notably, the 3D porous metallic WS2/Ni5P4Ni2P electrode only requires 94 mV (vs. RHE) to drive a geometric current density of -10 mA cm(-2) with a relatively small Tafel slope of 74 mV dec(-1). Such enhancements are correlated to the rational designs of WS2/Ni5P4-Ni2P electrode which (i) optimize the hydrogen adsorption Gibbs free energy; (ii) increase of the number of active sites of overall electrode; (iii) facilitate the electron transport from higher Fermi-level Ni5P4-Ni2P foam to the lower Fermi-level WS2; (iV) promote the access of electrolyte and the escape of hydrogen molecules. Additionally, such catalytic performances of the WS2/Ni5P4-Ni2P electrode can last for 22 h without significant degradations, clearly demonstrating the superior long-term operation stability in the acid environment (0.5M H2SO4). This work provides a versatile platform for fabricating the 3D porous hybridized electrocatalysts for modulating the intrinsic catalytic activity of various transition metal dichalcogenides (TMDs) on nickel phosphide.