Black reduced porous SnO₂ nanosheets for CO₂ electroreduction with high formate selectivity and low overpotential

The great bottleneck that lies in CO₂ reduction reaction (CO₂RR) electrocatalysts is to simultaneously enhance their conductivity and density of active sites. Herein, we developed a black reduced porous SnO₂ nanosheets electrocatalyst that enabled possessing both metallic conductivity and high density of active sites via vacancy engineering. The black reduced porous SnO₂ nanosheets showed high activity and selectivity for CO₂RR to formate, with maximum Faradaic efficiency (FE) of 92.4% at the low overpotential of 0.51 V and stable FE of 90 ± 2% in the large potential range from -0.6 to -1.1 V vs. reversible hydrogen electrode (RHE). Density functional theory (DFT) calculations indicated that the introduction of oxygen vacancy increased carrier density and lowered the adsorption of HCOO^- * and HCOOH by 0.29 and 0.17 eV, respectively, accounting for the improved CO₂RR to formate performance.