Electrochemical reduction of CO2 may enable a promising route for sustainable production of chemicals and fuels as well as the recycling of CO2. However, a better understanding of reaction mechanisms in the complex electrochemical environment is still needed, such as the role of cations in the process. Recently, M. Koper et al. reported that metal cations play an essential role in CO2 reduction to CO, by stabilizing the CO2– intermediate via a short-range electrostatic interaction. Here we further explore the cation effect in CO2 reduction using non-metal cations, particularly quaternary ammonium cations, of which the size and structural symmetry can be tuned. We focus on CO2 reduction on Bi catalyst that produces both CO and formate, arising from two different adsorption geometries on Bi (‘V’ and ‘Λ’ shapes, respectively). The Faradaic efficiency for CO production increases apparently for the electrolyte with larger cations, while the Faradaic efficiency for formate production shows a weak dependence on the cation size, revealing a major impact of the cation size on the ‘V’-shaped adsorption geometry of CO2. Furthermore, we compared the cations with different structural symmetries and found that the non-symmetric ones are generally less effective in promoting CO2 adsorption and reduction. Grand canonical ab initio molecular dynamics (GC-AIMD) simulations were performed to elucidate the effects of size and shape of non-metal cations on the activation of CO2. Our work further elucidates the critical role of cations in CO2 adsorption and electroreduction and suggests a potential method to improve the electrocatalysis by selecting electrolyte cations.

Elucidating the cation effect in CO2 electroreduction catalysis using non-metal cations

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