Chlorine anion stabilized Cu2O/ZnO photocathode for selective CO2 reduction to CH4

Although Cu2O-based material is one of the most promising catalysts, the deactivation of surface severely limits its selectivity and stablity. Here, we present a chlorine (Cl)-modified Cu2O/ZnO heterostructure (CCZO) as photocathode with remarkable CH4 faradaic efficiency (88.6 %) and durability (over 5 h). The Cl ions in CCZO serve as a passivator to stabilize Cu2O against photo-corrosion. Stabilized Cu+ active sites promote the hydrogenation of *CO intermediate, which provides a strong driving force for CO2 reduction to CH4. Calculation results indicate that for CCZO the hydrogenation of *CO trends to form *CHO (energy barrier of 0.220 eV) rather than CO (0.344 eV), further confirming the high selectivity of CCZO to CH4. This work sheds insight on the catalytic mechanism of CCZO to modulate the energy barrier of intermediate *CO combined with H+, providing a new idea to develop high selectivity and stable catalysts for CO2 reduction. [Display omitted] •The Cl-modified Cu2O/ZnO exhibits outperformance of CO2 reduction to CH4 with FE of 88.6 %.•Cl ions contribution lies in stabilizing Cu+ active site in Cu2O.•CCZO boosts the *CO hydrogenation to form *CHO rather than CO.