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

Abstract

Due to the slow charge migration, weak adsorption capacity, and low visible light response of catalysts, efficient photocatalytic CO2 reduction reaction (CO2RR) with H2O for the eight-electron product CH4 still poses significant challenges. Herein, two-dimensional TiO2 nanosheets (NS) supported PdCu alloy were applied as photocatalytic CO2RR with H2O. The loading of PdCu alloy expanded the absorption range of TiO2 NS and effectively promotes the migration of photogenerated charge carriers. The CH4 yield of the best catalyst (PdCu)2-TiO2 NS in the absence of sacrificial agent reached 18.1 μmol·g-1·h-1, which was about 49 times greater than that of pure TiO2 NS, and had a high CH4 selectivity of 98.7% (electron selectivity was 99.7%). The improvement in CH4 yield could be attributed to the synergistic effect of 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 embedded Pd lattice, effectively solving the problem of easy oxidation of Cu. This study also indicated that 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 in improving CH4 yield and selectivity.