Correlating vacancy-defect density with CO2 activation for promoted CO2 methanation over CsPbBr3 photocatalyst

Abstract

Constructing vacancy-decorated metal halide perovskites (MHPs) have emerged as promising pathway to enhance photocatalytic activity and selectivity for solar CO₂ reduction. However, the controllable construction of vacancy defects is still challenging, and our understanding of the roles of these defects, particularly their effects on the adsorption activation of surface reaction molecules, is still insufficient. Herein, we elaborately designed and synthesized adjustable Br vacancies in CsPbBr₃ catalysts by manipulating the dissolution and recrystallization speed of precursors during the ball milling process using solvents with gradient polarities. We found that the Br vacancies could promote the charge separation, while having slight influence on the band structure of CsPbBr₃. More importantly, temperature-programmed desorption results combined with theoretical calculations revealed that Br vacancies can significantly enhance the adsorption of CO₂ and CO on the surface, specifically increasing the adsorption strength between CO and the active sites. This finding provides a substantial opportunity for achieving high activity and selectivity in photocatalytic CO₂ methanation. Accordingly, a high rate of CO₂ photoreduction to CH₄ up to 17.94 ± 0.81 μmol g^-1 h^-1 along with superior selectivity of 95.8% were acquired for CsPbBr₃HX featuring with the richest Br vacancy defects, which is 18.9-fold compared that of CsPbBr₃CAN with the lowest Br vacancy defects. This investigation deepens insights into action mechanism of defects on halide perovskites catalysts, offering a novel strategy for the high-effective conversion of CO₂ into valuable products.