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

Abstract

Catalytic benefit and role of electrolyte cations for electrochemical CO2 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, *CO2 –, through mid- or short-range electrostatic interactions, facilitating the CO2 activation step.1-2 However, to date, these discussions are mostly limited to CO2-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 CO2 to methanol. We found that cations engage as a promoter in the rate determining step of the CO2-to-methanol conversion, which involves a proton-coupled electron transfer, beyond the first CO2 activation step. For this study, heterogenized molecular catalyst with a cobalt single site (Co-N4) was employed, achieving ~25% methanol selectivity at –0.78 V vs. RHE. Through an isotope labeling experiment (13CO2 reduction reaction), we validated that methanol is produced by the CO2 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 CO2-to-methanol conversion on the cobalt single site. Our findings offer new insights into the beneficial effect of cations on electrochemical CO2 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 CO2 reduction reaction beyond two-electron transfer products.In this talk, I will discuss the promoting effect of cations on the electrochemical reduction of CO2 to methanol and conclude by proposing potential strategies to further improve the electrocatalytic CO2-to-methanol conversion.References Monteiro, M. C. O.; Dattila, F.; Hagedoorn, B.; García-Muelas, R.; López, N.; Koper, M. T. , Absence of CO2 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.