In situ decorated Ni₂P nanocrystal co-catalysts on g-C₃N₄ for efficient and stable photocatalytic hydrogen evolution via a facile co-heating method

Very recently, transition metal phosphides (TMPs) have emerged as low-cost and robust co-catalysts for decorating graphitic carbon nitride (g-C₃N₄) for photocatalytic hydrogen (H₂) evolution. However, to date, little work has been done regarding the decoration approaches to hybridize TMPs on the g-C₃N₄ surface with homogeneous dispersion and intimate interfacial contact. Herein, we present a facile and convenient route to in situ incorporate g-C₃N₄ nanosheets (NSs) and Ni₂P nanocrystal (NC) co-catalysts via a one-step co-heating solution approach. The Ni₂P/g-C₃N₄ (in situ) hybrid photocatalyst achieved a far superior H₂ production rate (2849.5 μmol g^-1 h^-1) and durability (no decrease after 4 cycles of reaction within 20 h) compared to the Ni₂P/g-C₃N₄ (self-assembly) sample. The apparent quantum yield (AQY) of 18.8% at 420 nm was also much higher than that of other TMP co-catalyst loaded g-C₃N₄ hybrid photocatalysts. A possible Ni(δ⁺)-N(δ^-) chemical coupling in the Ni₂P/g-C₃N₄ (in situ) hybrid composite was proposed and corroborated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy. The unique Ni(δ⁺)-N(δ^-) chemical bonding states between g-C₃N₄ and Ni₂P significantly accelerate the photo-generated charge-carrier separation and extraction from g-C₃N₄, as well as maintaining the H₂ production durability. We believe that the hybridization route presented in this work will be extended to construct other TMP integrated photocatalysts toward efficient and stable solar water splitting.