Ultrasmall and phase-pure W₂C nanoparticles for efficient electrocatalytic and photoelectrochemical hydrogen...

Earlier research has been primarily focused on WC as one of the most promising earth-abundant electrocatalysts for hydrogen evolution reaction (HER), whereas the other compound in this carbide family-W₂C-has received far less attention. Our theoretical calculations suggest that such a focus is misplaced and W₂C is potentially more HER-active than WC. Nevertheless, the preparation of phase pure and sintering-free W₂C nanostructures represents a formidable challenge. Here we develop an improved carburization method and successfully prepare ultrasmall and phase-pure W₂C nanoparticles. When evaluated for HER electrocatalysis, W₂C nanoparticles exhibit a small onset overpotential of 50 mV, a Tafel slope of 45 mV dec^-1 and outstanding long-term cycling stability, which are dramatically improved over all existing WC-based materials. In addition, the integration of W₂C nanoparticles with p-type Si nanowires enables highly active and sustainable solar-driven hydrogen production. Our results highlight the great potential of this traditionally non-popular material in HER electrocatalysis.