Constructing of CoP-NbO p-n heterojunction with built-in electric field to accelerate the charge migration in electrocatalytic hydrogen evolution.

Studying interfacial charge transfer is of great significance for the preparation of electrocatalysts with high activity for the hydrogen evolution reaction (HER). Particularly, exploring the in-depth catalytic mechanisms and facile fabrication methods of narrow bandgap metal phosphides remains worthwhile. This work successfully combined catalytically inert n-type NbO with p-type CoP to prepare a p-n heterojunction (CoP-NbO). The self-supporting heterojunction was fabricated by gas-phase phosphorization of the Co(OH)-NbO precursor obtained through hydrothermal-electrodeposition strategy. By analyzing the electronic and band structures of CoP and NbO, it was found that there exists a built-in electric field (BEF) in the heterojunction. This BEF can modulate the electronic structure of CoP at the interface, enhance its intrinsic activity and accelerate charge migration. The subsequent experimental results also demonstrate that NbO can significantly enhance the activity and stability of CoP. Our findings can serve as a novel perspective on the application of p-n heterojunction in the field of energy storage and conversion.