Effect of Cations on Electrocatalytic CO2-to-Methanol Conversion by Heterogenized Molecular Catalyst

Catalytic benefit and role of electrolyte cations for electrochemical CO 2 reduction reaction have recently received significant research attention. It has been experimentally and theoretically demonstrated that cations can stabilize the key intermediate species, for example, *CO 2 – , through mid- or short-range electrostatic interactions, facilitating the CO 2 activation step. 1-2 However, to date, these discussions are mostly limited to CO 2 -to-CO conversion (a two electron/proton transfer reaction) and electrostatic stabilization of reaction intermediate species. In present work, we show that cations play a crucial role in further reducing CO 2 to methanol. We found that cations engage as a promoter in the rate determining step of the CO 2 -to-methanol conversion, which involves a proton-coupled electron transfer, beyond the first CO 2 activation step. For this study, heterogenized molecular catalyst with a cobalt single site (Co-N 4 ) was employed, achieving ~25% methanol selectivity at –0.78 V vs. RHE. Through an isotope labeling experiment ( 13 CO 2 reduction reaction), we validated that methanol is produced by the CO 2 reduction reaction. Furthermore, electrolytes with different cation species and concentrations were tested in a systematic manner to investigate the promoting effect of cations on methanol production. In addition, using deuterated electrolytes, we studied kinetic isotope effect, proposing a reaction pathway for CO 2 -to-methanol conversion on the cobalt single site. Our findings offer new insights into the beneficial effect of cations on electrochemical CO 2 reduction reaction kinetics besides their widely acknowledged stabilizing effect. Our discovery also opens up new research directions where non-covalent interactions between electrolyte species and reaction intermediates are utilized to enhance electrocatalytic production of a desired product in CO 2 reduction reaction beyond two-electron transfer products. In this talk, I will discuss the promoting effect of cations on the electrochemical reduction of CO 2 to methanol and conclude by proposing potential strategies to further improve the electrocatalytic CO 2 -to-methanol conversion. References Monteiro, M. C. O.; Dattila, F.; Hagedoorn, B.; García-Muelas, R.; López, N.; Koper, M. T. , Absence of CO 2 electroreduction on copper, gold and silver electrodes without metal cations in solution. Nature Catalysis 2021, 4 (8), 654-662. Resasco, J.; Chen, L. D.; Clark, E.; Tsai, C.; Hahn, C.; Jaramillo, T. F.; Chan, K.; Bell, A. T., Promoter Effects of Alkali Metal Cations on the Electrochemical Reduction of Carbon Dioxide. Journal of the American Chemical Society 2017, 139 (32), 11277-11287.