▎ 摘　　要

In situ mixing of transition metal phosphides (TMPs), especially those with dissimilar metals, in ultrasmall spaces and assembling them on nanoscale supports for remarkably enhanced hydrogen evolution reaction (HER) activity are rather challenging. We have fabricated pristine graphenesupported ultrasmall, highly dispersed, and high-density Co-W-P nanoparticles (NPs) via phosphotungstic acid-mediated self-assembly. This nanohybrid exhibits outstanding activity with all of the onset overpotential, overpotential (10 mA cm(-2)), Tafel slope, and exchange current density in both 0.5 M H2SO4 and 1 M KOH superior to those of most reported non-noble-metal-based catalysts and excellent durability showing negligible current change after 24 h chronoamperometric measurement and after 2000 CV cycles. The superior catalytic performance is ascribed to in situ intimately grown Co-W-P NPs with ultrasmall sizes and high dispersion greatly promoting electron transfer, ultrasmall and well-dispersed Co-W-P NPs on graphene providing numerous electrochemically accessible active sites, and synergistic interaction between WP2 and CoP significantly enhancing intrinsic activity. This work not only develops a facile and economical strategy to synthesize pristine graphene supported mixed phosphides of dissimilar transition metals as low-cost and high-performance HER electrocatalysts, but sheds light on synergistic effects between TMPs for high activity and self-assembly mechanisms toward the synthesis of various unique nanohybrids.