Identifying the significance of proton-electron transfer in CH4 production on Cu (100) in CO2 electro-reduction

- Free energy profiles for CH4 production via the proton-electron transfer were presented.
- C atoms in CHx* were negatively charged, allowing to react with protons directly.
- CH4 production in CO2 electroreduction differs from that in heterogeneous catalysis.

In electrocatalysis, there are two mechanisms for hydrogenation reactions: Heyrovsky mechanism via the proton-electron transfer and Tafel mechanism via surface coupling with adsorbed hydrogen. In CO/CO2 electroreduction over copper catalysts, CH4 is a final product from the subsequent hydrogenation of carbon. In this work, by performing the constrained ab initio molecular dynamics simulations, we firstly identify that CH4 production on Cu(100) via the proton-electron transfer is more kinetically favored than via surface coupling, due to the negatively charged C atoms in CHx*. Our findings highlight the significance of proton-electron transfer in CO2 electroreduction, and help understand the essential difference between electrocatalysis and heterogeneous catalysis.

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