(544hi) Interaction of Thiol Ligands with Gold and Its Effect on Electrocatalytic CO2 Reduction

CO₂ can potentially be used as an energy carrier to store energy generated from intermittent, distributed sources or as a renewable source of carbon for chemical production. The key to enabling these uses is to maximize the selectivity and energy efficiency of the electrocatalytic CO₂ reduction reaction (CO₂RR) toward the desired product.^1,2 We have explored the functionalization of Au electrodes with various organic thiol ligands to modify the activity and selectivity of Au electrodes. Our work shows that different thiol species can enhance the formation of different CO₂ reduction products. For instance, 2-merceptanpropionic acid effectively reduces the yield of CO to negligible amounts and enhances H₂ evolution to nearly 100% faradaic efficiency, whereas 2-phenylethanethiol strongly promotes CO evolution over H₂ evolution (HER) and 4-pyridinylethanemercaptan enhances formate production.³ In addition, we have performed density functional theory calculations and theoretical modeling in conjunction with our electrochemical experiments to elucidate the role of the thiol ligands in CO₂RR on Au. We propose that certain thiol ligands reconstruct Au surfaces at ambient conditions by extracting Au atoms to generate new defect sites. The resultant Au-dithiolate complexes are stable in the potential range relevant to CO₂RR and serve to stabilize under-coordinated sites, which promote CO₂ reduction whereas the effect on HER is less significant. Our study suggests that functionalization of Au holds significant promise for promoting CO₂ reduction and achieving different product selectivity with appropriately chosen ligands.

References

(1) Y. Hori, A. Murata, R. Takahashi, J. Chem. Soc. Farad. T. 1 1989, 85, 2309.

(2) B.A. Rosen, A. Salehi-Khojin, M.R. Thorson, W. Zhu, D.T. Whipple, P.J.A. Kenis, R.I. Masel, Science 2011, 334, 643.

(3) Y. Fang, J.C. Flake, J. Am. Chem. Soc. 2017, 139, 3399.