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Title: Promotional effect of surface hydroxyls on electrochemical reduction of CO 2 over SnO x/Sn electrode

In this study, tin oxide (SnO x) formation on tin-based electrode surfaces during CO 2 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 CO 2 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 H 2O dissociates on the perfect SnO monolayer into two hydroxyl groups symmetrically on the surface. CO 2 energetically prefers to react with the hydroxyl, forming a bicarbonate (HCO 3(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 H 2O via protonation. Whereas the oxygen vacancy (VO) in the oxide monolayer maybe formed by the reduction, it can be recovered by H 2O dissociation,more » resulting in two embedded hydroxyl groups. The results show that the hydroxylated surface with two symmetric hydroxyls is energetically more favorable for CO 2 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 CO 2 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
Authors:
ORCiD logo [1] ;  [2] ;  [2] ;  [2] ;  [2] ;  [3] ;  [1]
  1. Tianjin Univ., Tianjin (China); Southern Illinois Univ., Carbondale, IL (United States)
  2. Tianjin Univ., Tianjin (China)
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Grant/Contract Number:
#21373148; #21206117; CBET-1438440
Type:
Accepted Manuscript
Journal Name:
Journal of Catalysis
Additional Journal Information:
Journal Volume: 117; Journal Issue: C; Journal ID: ISSN 0021-9517
Publisher:
Elsevier
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; DFT; electrochemical reduction; CO2; SnOx; hydroxyl; bicarbonate
OSTI Identifier:
1250867
Alternate Identifier(s):
OSTI ID: 1398837