LAUSR

Noble-metal-free electrocatalysts are highly desired for hydrogen evolution reaction (HER). As a promising candidate, transition-metal phosphides however suffer from inevitable surface oxidation that will obstruct active-site exposure. Herein, a facile reduction followed by a surface phosphorization is introduced to convert surface-oxidized cobalt phosphides to Co2(P2O7)-CoP heterostructures within N-doped carbon matrix (Co2(P2O7)-CoP/NC), which accomplish high HER performance in both acidic and alkaline electrolytes. They affords low overpotentials (η10) of only 88 and 97 mV at a current density of -10 mA cm-2, and small Tafel slopes of 51 and 61 mV dec-1 in 0.5 M H2SO4 and 1.0 M KOH, respectively. They outperforms the parent surface-oxidized Co2P and most of previously reported Pt-free electrocatalysts. The remarkably improved electrocatalysis should be ascribed to the strong surface acidity of Co2(P2O7) component and thereby the promoted HER kinetics on Co2(P2O7)-CoP interfaces. This work is anticipated to encourage the development of cost-efficient electrocatalysts via surface engineering.