2 Search Results

Tin oxide (SnOx) formation on tin-based electrode surfaces during CO2 electrochemical reduction can have a significant impact on the activity and selectivity of the reaction. In the present study, density functional theory (DFT) calculations have been performed to understand the role of SnOx in CO2 reduction using a SnO monolayer on the Sn(112) surface as a model for SnOx. Water molecules have been treated explicitly and considered actively participating in the reaction. The results showed that H2O dissociates on the perfect SnO monolayer into two hydroxyl groups symmetrically on the surface. CO2 energetically prefers to react with the hydroxyl, formingmore » a bicarbonate (HCO3(t)*) intermediate, which can then be reduced to either formate (HCOO*) by hydrogenating the carbon atom or carboxyl (COOH*) by protonating the oxygen atom. Both steps involve a simultaneous C-O bond breaking. Further reduction of HCOO* species leads to the formation of formic acid in the acidic solution at pH < 4, while the COOH* will decompose to CO and H2O via protonation. Whereas the oxygen vacancy (VO) in the monolayer maybe formed by the reduction of the monolayer, it can be recovered by H2O dissociation, resulting in two embedded hydroxyl groups. However, the hydroxylated surface with two symmetric hydroxyls is energetically more favorable for CO2 reduction than the hydroxylated VO surface with two embedded hydroxyls. The reduction potential for the former has a limiting-potential of -0.20 V (RHE), lower than that for the latter (-0.74 V (RHE)). Compared to the pure Sn electrode, the formation of SnOx monolayer on the electrode under the operating conditions promotes CO2 reduction more effectively by forming surface hydroxyls, thereby, providing a new channel via COOH* to the CO formation, although formic acid is still the major reduction product. The work was supported in part by National Natural Sciences Foundation of China (Grant #21373148 and #21206117). The High Performance Computing Center of Tianjin University is acknowledged for providing services to the computing cluster. CC acknowledges the support of 24 China Scholarship Council (CSC). QG acknowledges the support of NSF-CBET program (Award no. CBET-1438440). DM was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. The computations were performed in part using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), which is a U.S. Department of Energy national scientific user facility located at Pacific Northwest National Laboratory (PNNL) in Richland, Washington.« less

In this study, tin oxide (SnO_x) formation on tin-based electrode surfaces during CO₂ electrochemical reduction can have a significant impact on the activity and selectivity of the reaction. In the present study, density functional theory (DFT) calculations have been performed to understand the role of SnO_x in CO₂ reduction using a SnO monolayer on the Sn(112) surface as a model for SnO_x. Water molecules have been treated explicitly and considered actively participating in the reaction. The results showed that H₂O dissociates on the perfect SnO monolayer into two hydroxyl groups symmetrically on the surface. CO₂ energetically prefers to react withmore » the hydroxyl, forming a bicarbonate (HCO₃(t)*) intermediate, which can then be reduced to either formate (HCOO*) by hydrogenating the carbon atom or carboxyl (COOH*) by protonating the oxygen atom. Both steps involve a simultaneous Csingle bondO bond breaking. Further reduction of HCOO* species leads to the formation of formic acid in the acidic solution at pH < 4, while the COOH* will decompose to CO and H₂O via protonation. Whereas the oxygen vacancy (VO) in the oxide monolayer maybe formed by the reduction, it can be recovered by H₂O dissociation, resulting in two embedded hydroxyl groups. The results show that the hydroxylated surface with two symmetric hydroxyls is energetically more favorable for CO₂ reduction than the hydroxylated VO surface with two embedded hydroxyls. The reduction potential for the former has a limiting-potential of –0.20 V (RHE), lower than that for the latter (–0.74 V (RHE)). Compared to the pure Sn electrode, the formation of SnO_x monolayer on the electrode under the operating conditions promotes CO₂ reduction more effectively by forming surface hydroxyls, thereby providing a new channel via COOH* to the CO formation, although formic acid is still the major reduction product.« less