TY - JOUR
T1 - Effects of water on low-overpotential CO2 reduction in ionic liquid studied by sum-frequency generation spectroscopy
AU - García Rey, Natalia
AU - Dlott, Dana D.
N1 - The research described in this study is based on work supported by the Air Force Office of Scientific Research under awards FA8650-13-C2429 and FA9550-14-1-0142, and the National Science Foundation under award CHE-1405997.
PY - 2017
Y1 - 2017
N2 - We used vibrational sum-frequency generation spectroscopy (SFG) to investigate low-overpotential CO2 reduction on a polycrystalline Ag electrode using room temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium tetrafluorborate (EMIM-BF4) electrolyte mixtures with 0.3 mol%, 45 mol% and 77 mol% water. Adding water dramatically increases CO2 reduction efficiency up to 87.5 mol%. We found added water reduces the (negative) threshold potential for CO2 reduction from -1.33 V to -0.9 V. Added water also moved the potentials of the nonresonant (NR) SFG minima and caused the CO Stark shift to increase in concert with the reduction threshold. In previous work (N. García Rey and D. D. Dlott, J. Phys. Chem. C, 2015, 119, 20892-20899), with nearly-dry RTIL electrolyte (0.3 mol% water), we concluded a potential-driven structural transition of RTIL in the double layer controlled CO2 reduction. At lower water concentrations, where CO2 reduction was less efficient, CO product appeared primarily on Ag atop sites. At higher water concentrations where CO2 reduction efficiency was greater, adsorbed CO was observed on multiply-bonded sites, which are likely more efficient catalytic sites.
AB - We used vibrational sum-frequency generation spectroscopy (SFG) to investigate low-overpotential CO2 reduction on a polycrystalline Ag electrode using room temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium tetrafluorborate (EMIM-BF4) electrolyte mixtures with 0.3 mol%, 45 mol% and 77 mol% water. Adding water dramatically increases CO2 reduction efficiency up to 87.5 mol%. We found added water reduces the (negative) threshold potential for CO2 reduction from -1.33 V to -0.9 V. Added water also moved the potentials of the nonresonant (NR) SFG minima and caused the CO Stark shift to increase in concert with the reduction threshold. In previous work (N. García Rey and D. D. Dlott, J. Phys. Chem. C, 2015, 119, 20892-20899), with nearly-dry RTIL electrolyte (0.3 mol% water), we concluded a potential-driven structural transition of RTIL in the double layer controlled CO2 reduction. At lower water concentrations, where CO2 reduction was less efficient, CO product appeared primarily on Ag atop sites. At higher water concentrations where CO2 reduction efficiency was greater, adsorbed CO was observed on multiply-bonded sites, which are likely more efficient catalytic sites.
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U2 - 10.1039/c7cp00118e
DO - 10.1039/c7cp00118e
M3 - Article
C2 - 28383582
AN - SCOPUS:85020041334
SN - 1463-9076
VL - 19
SP - 10491
EP - 10501
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
IS - 16
ER -