Photocatalytic reduction of CO2 into value-added products is a promising strategy for mitigating environmental and energy problems simultaneously.Herein,we developed Au sheets with subtle grain boundaries on ultrathin Ni(OH)2 nanosheets as efficient photocatalysts for CO2 reduction.According to mechanistic studies,grain boundaries on the Au sheets served as electron trapping sites which enabled the optimization of electron-hole separation.Moreover,grain boundaries perturbed electron distribution,which assisted in stabilizing CO2δ-and HCOO* intermediates.As a result,the unique hybrid structure achieved a high rate of 75.2 μmol g-1 h-1 for CO2 photoreduction.This work demonstrates the importance of defect engineering in designing active photocatalysts and also provides insight into development of related photo-energy conversion schemes.