Boosting Hydrogen Evolution Electrocatalysis via Regulating the Electronic Structure in a Crystalline–Amorphous CoP/CeO_<i>x</i> p–n Heterojunction

Abstract

The modulation of the electronic structure is the effective access to achieve highly active electrocatalysts for the hydrogen evolution reaction (HER). Transition-metal phosphide-based heterostructures are very promising in enhancing HER performance but the facile fabrication and an in-depth study of the catalytic mechanisms still remain a challenge. In this work, the catalytically inactive n-type CeO_<i>x</i> is successfully combined with p-type CoP to form the CoP/CeO_<i>x</i> heterojunction. The crystalline-amorphous CoP/CeO_<i>x</i> heterojunction is fabricated by the phosphorization of predesigned Co(OH)₂/CeO_<i>x</i> via the as-developed reduction-hydrolysis strategy. The p-n CoP/CeO_<i>x</i> heterojunction with a strong built-in potential of 1.38 V enables the regulation of the electronic structure of active CoP within the space-charge region to enhance its intrinsic activity and facilitate the electron transfer. The functional CeO_<i>x</i> entity and the negatively charged CoP can promote the water dissociation and optimize H adsorption, synergistically boosting the electrocatalytic HER output. As expected, the heterostructured CoP/CeO_<i>x</i>-20:1 with the optimal ratio of Co/Ce shows significantly improved HER activity and favorable kinetics (overpotential of 118 mV at a current density of 10 mA cm^-2 and Tafel slope of 77.26 mV dec^-1). The present study may provide new insight into the integration of crystalline and amorphous entities into the p-n heterojunction as a highly efficient electrocatalyst for energy storage and conversion.