In-situ phosphating to synthesize Ni₂P decorated NiO/g-C₃N₄ p-n junction for enhanced photocatalytic hydrogen production

Photocatalysis is a promising method to obtain hydrogen without any pollution. The key to improve the efficiency of photocatalytic reaction is to design an excellent catalyst structure which can effectively promote the separation and transfer of photogenerated electrons and holes. In this work, a novel photocatalyst, Ni₂P decorated NiO/g-C₃N₄ p-n junction (NiO/Ni₂P/CN, abbreviating g-C₃N₄ as CN) is successfully developed by a one-step in-situ phosphating of Ni(OH)₂/CN. The optimized NiO/Ni₂P/CN exhibits an impressive photocatalytic H₂ evolution rate of 5.04 μmol h⁻¹ under visible-light irradiation (λ > 420 nm) without any noble metal as co-catalyst, which is 126 times higher than that of pristine CN. This high photocatalytic performance is mainly based on the intimated contact of the three components (Ni₂P, NiO and CN), where the photogenerated holes on the valence band (VB) of CN can be transferred to the VB of NiO due to the internal-built electric field created by p-n junction, while the photoexcited electrons on the conduction band (CB) of CN can be migrated to Ni₂P co-catalyst with a low overpotential, thus the separation and transfer of charge carriers are significantly promoted, and finally the photocatalytic activity of NiO/Ni₂P/CN for the hydrogen evolution from water splitting is enhanced. This work may enlighten on the design of photocatalysts with high efficiency by constructing p-n junction and metal phosphide co-catalyst with low overpotential.