Ion-exchange controlled surface engineering of cobalt phosphide nanowires for enhanced hydrogen evolution

Transition metal phosphides are promising alternatives to the precious metal catalysts for various electrocatalysis applications. Controllable and precise surface engineering of electrocatalysts is the key challenge to enhance their performance. Herein, we demonstrate an ion-exchange strategy to produce cobalt phosphide nanowires which have a conductive core and a thickness-controlled surface layer with sulfur dopants, phosphorus vacancies, and amorphous domains. They are applied for hydrogen evolution reaction with high stability, achieving a current density of 100 mA cm^-2 at an overpotential of 114 mV. Based on both comprehensive state-of-the-art experimental characterizations and theoretical investigations, the excellent catalytic performance is attributed to increased active sites, facilitated charge transfer and transport, as well as weakened H adsorption and strengthened H₂O adsorption due to the synergistic effects of S dopants and P vacancies.