The synergy of in situ-generated Ni⁰ and Ni₂P to enhance CO adsorption and protonation for selective CH₄ production from photocatalytic CO₂ reduction

The selective photocatalytic reduction of CO2 to CH4 remains a challenge because there is a need for not only strong adsorption sites for the intermediates, but also optimal proton-feeding sites on the photocatalyst surface. Herein, a synergistic dual-site function between in situ-generated Ni-0 and Ni2P on carbon nitride nanosheets (CN) for photocatalytic reduction of CO2 to CH4 is presented. The highest CH4 production rate of 69.03 mu mol g(-1) h(-1) is achieved on Ni2P/CN-0.5 in an aqueous suspension. Detailed analyses show that the promotion of CH4 is closely correlated with the formation of Ni-0 sites due to light irradiation, which is confirmed by tracking the compositions of Ni2P/CN-0.5 through XPS and HRTEM characterization. Density functional theory calculations have been combined with CO-TPD and in situ FTIR spectra to reveal the synergy between in situ-generated Ni-0 sites and Ni2P. It shows that the Ni-0 sites can stabilize the key intermediate *CO, while the Ni-0-Ni2P interface can promote *H transfer from Ni2P to Ni-0. Therefore, the CO intermediates are rapidly protonated to form CHO* instead of being desorbed from the surface to produce CO, and subsequently CHO* will be converted into CH4. This work demonstrates a new strategy of designing highly efficient photocatalysts with synergistic catalytic sites for CO2 conversion to hydrocarbons.