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

Abstract

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 Ni⁰ and Ni₂P on carbon nitride nanosheets (CN) for photocatalytic reduction of CO₂ to CH₄ is presented. The highest CH₄ production rate of 69.03 μmol 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 Ni⁰ 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 Ni⁰ sites and Ni₂P. It shows that the Ni⁰ sites can stabilize the key intermediate *CO, while the Ni⁰–Ni₂P interface can promote *H transfer from Ni₂P to Ni⁰. 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.