Improving the Catalytic CO2 Reduction on Cs2AgBiBr6 by Halide Defect Engineering: A DFT Study

Pb-free double halide perovskites have drawn immense attention in the potential photocatalytic application, due to the regulatable bandgap energy and nontoxicity. Herein, we first present a study for CO₂ conversion on Pb-free halide perovskite Cs₂AgBiBr₆ under state-of-the-art first-principles calculation with dispersion correction. Compared with the previous CsPbBr₃, the cell parameter of Cs₂AgBiBr₆ underwent only a small decrease of 3.69%. By investigating the adsorption of CO, CO₂, NO, NO₂, and catalytic reduction of CO₂, we found Cs₂AgBiBr₆ exhibits modest adsorption ability and unsatisfied potential determining step energy of 2.68 eV in catalysis. We adopted defect engineering (Cl doping, I doping and Br-vacancy) to regulate the adsorption and CO₂ reduction behavior. It is found that CO₂ molecule can be chemically and preferably adsorbed on Br-vacancy doped Cs₂AgBiBr₆ with a negative adsorption energy of −1.16 eV. Studying the CO₂ reduction paths on pure and defect modified Cs₂AgBiBr₆, Br-vacancy is proved to play a critical role in decreasing the potential determining step energy to 1.25 eV. Finally, we probe into the electronic properties and demonstrate Br-vacancy will not obviously promote the process of catalysis deactivation, as there is no formation of deep-level electronic states acting as carrier recombination center. Our findings reveal the process of gas adsorption and CO₂ reduction on novel Pb-free Cs₂AgBiBr₆, and propose a potential strategy to improve the efficiency of catalytic CO₂ conversion towards practical implementation.