Boosting Hydrogen Evolution Electrocatalysis via Regulating the Electronic Structure in a Crystalline–Amorphous CoP/CeO_x p–n Heterojunction

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 CeOx is successfully combined with p-type CoP to form the CoP/CeOx heterojunction. The crystalline–amorphous CoP/CeOx heterojunction is fabricated by the phosphorization of predesigned Co(OH)2/CeOx via the as-developed reduction–hydrolysis strategy. The p–n CoP/CeOx 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 CeOx 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/CeOx-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.