(517c) Enhanced Electrocatalytic CO2 Reduction on Thiol-Functionalized Gold
AIChE Annual Meeting
Wednesday, November 16, 2016 - 1:06pm to 1:24pm
CO2 can potentially be used as a renewable feedstock for distributed electrochemical production of fuels and chemicals, either as an energy carrier to store energy generated from intermittent sources such as wind and the sun, or as a renewable source of carbon for chemical production. The key to enabling these uses of CO2 is maximizing the selectivity and energy efficiency of electrocatalytic CO2 reduction. Hori and co-workers have shown that some metals (Au, Ag and Cu, etc.) can catalyze the reaction and produce CO or hydrocarbons [Hori, in Modern Aspects of Electrochemistry, ed. Vayenas et al., Springer (2008)]. A significant challenge is posed by the competing hydrogen evolution reaction (HER), which tends to occur with a smaller overpotential and consumes a significant fraction of the current and protons. Furthermore, Nørskov and co-workers have shown that the catalytic activity for CO2 electroreduction is limited by the strong scaling relation that exists between the key reaction intermediate, COOH, and the reaction product, CO [Shi et al., Phys. Chem. Chem. Phys. 16 (2014) 4720]. In present work, we take inspiration from biological enzymes that catalyze CO2 reduction (e.g. CO dehydrogenase) and attempt to mimic their active sites by functionalizing Au electrodes with a series of organic thiol-based ligands, to seek to potentially overcome these challenges. This has resulted in significantly altered activity for CO formation and selectivity between CO and H2. The CO yield was increased dramatically and nearly doubled in the presence of 2-phenylethanethiol (2-PET) compared to the blank gold foil electrode. On the contrary, 2-merceptanpropanic acid (MPA) suppresses the yield of CO to negligible amounts. The 2-PET-modified gold electrode also reduced the faradaic efficiency for HER by half, whereas the MPA-modified Au electrode increased it. Density function theory based modeling suggest that ligand-induced surface reconstruction of the Au surface is a major factor in the altered catalytic activity compared to blank Au, which creates sites that favor CO production over HER. Moreover, the surface-bound thiol ligands modify the adsorption energies of surface reduction intermediates through electronic interaction and further contribute to the altered activities for CO2 reduction and HER.