Few-Layered Trigonal WS2 Nanosheet-Coated Graphite Foam as an Efficient Free-Standing Electrode for a Hydrogen Evolution Reaction.

Few-layered tungsten disulfide (WS2) with a controlled-phase ratio (the highest trigonal-phase ratio being 67%) was exfoliated via lithium insertion. The exfoliated WS2 nanosheets were then anchored onto three-dimensional (3D) graphite foam (GF) to fabricate free-standing binder-free electrodes. The 3D GF can increase the interfacial contact between the WS2 nanosheets and the electrolyte and facilitate ion transfer. Without the nonconductive binder, an intimate contact between the WS2 and GF interface can be created, leading to the improvement of electrical conductivity. In comparison to the pure WS2 nanosheets, the overpotential for a hydrogen evolution reaction is significantly decreased from 350 mV to 190 mV at 10 mA/cm2, and no deactivation occurs after 1000 cycles. The density functional theory computations reveal that the efficient catalytic activity of the trigonal-phase WS2/GF electrode is attributed to the lower Gibbs free energy for H* adsorption and higher electrical conductivity.