Synergistic integration of PdCu alloy on TiO2 for efficient photocatalytic CO2 reduction to CH4 with H2O

Abstract

Owing to the slow charge migration, weak adsorption capacity, and low visible-light response of catalysts, the efficient photocatalytic CO₂ reduction reaction (CO₂RR) with H₂O for the eight-electron product CH₄ still poses significant challenges. Herein, PdCu alloy supported on two-dimensional TiO₂ nanosheets (NSs) were applied for the photocatalytic CO₂RR with H₂O. The loading of the PdCu alloy expanded the absorption range of the TiO₂ NSs and effectively promoted the migration of photogenerated charge carriers. The CH₄ yield of the best catalyst (PdCu)₂–TiO₂ NS in the absence of a sacrificial agent reached 18.1 μmol g⁻¹ h⁻¹, which was about 49 times greater than that of pure TiO₂ NSs, and had a high CH₄ selectivity of 98.7% (electron selectivity was 99.7%). The improvement in the CH₄ yield could be attributed to the synergistic effect of the PdCu alloy, in which Cu was an excellent CO₂ active site, Pd provided more protons for subsequent reactions by inhibiting the generation of H₂, and Cu existed in the form of an embedded Pd lattice, thus effectively solving the problem of the easy oxidation of Cu. This study also found that the CH₄ production rate increased with increasing CO₂ dosage and gradually reached saturation and increased and then decreased with increasing H₂O dosage. Finally, density functional theory (DFT) calculations showed that the synergistic effect of the PdCu alloy enhanced the adsorption of CO₂ and H₂O over the catalyst and reduced the total activation energy barrier for the generation of CH₄, which is a key factor for improving the CH₄ yield and selectivity.