Anion regulated the phase composition of tungsten carbide for efficient alkaline hydrogen evolution

Tungsten carbide (W_xC)-based nanomaterials are considered as promising and efficient electrocatalysts for the hydrogen evolution reaction (HER) owing to their Pt-like electronic structures. However, the coexistence of multiple crystalline phases of W_xC, including WC, W₂C, and WC_1-x, poses a challenge in identifying the active phase and optimizing catalytic performance. Herein, we present an effective approach to regulate the crystalline phase of W_xC-based catalysts by precisely tailoring the type of anions in the cobalt (Co) precursors. Detailed characterizations reveal that inorganic cobalt anions favor the formation of single phase of Co-WC, whereas organic cobalt anions lead to the development of a mixed phase composition of Co-WC and Co-W₂C (Co-W_xC). Structural analyses and electrocatalytic measurements, identify Co-WC as the active phase for alkaline HER. Notably, as-prepared pure Co-WC delivers outstanding alkaline HER performance, achieving an ultralow overpotential of 100 mV at a current density of 10 mA cm^-2 along with a favorable Tafel slope of 80 mV dec^-1, outperforming both the Co-W_xC counterpart and most reported W_xC-based HER catalysts. Our findings provide a straightforward strategy for regulating the crystalline phases of transition metal-carbides and the development of advanced electrocatalysts for HER and related reactions.