Identification of K + -determined reaction pathway for facilitated kinetics of CO 2 electroreduction.

Cations such as K + play a key part in the CO 2 electroreduction reaction, but their role in the reaction mechanism is still in debate. Here, we use a highly symmetric Ni-N 4 structure to selectively probe the mechanistic influence of K + and identify its interaction with chemisorbed CO 2 - . Our electrochemical kinetics study finds a shift in the rate-determining step in the presence of K + . Spectral evidence of chemisorbed CO 2 - from in-situ X-ray absorption spectroscopy and in-situ Raman spectroscopy pinpoints the origin of this rate-determining step shift. Grand canonical potential kinetics simulations - consistent with experimental results - further complement these findings. We thereby identify a long proposed non-covalent interaction between K + and chemisorbed CO 2 - . This interaction stabilizes chemisorbed CO 2 - and thus switches the rate-determining step from concerted proton electron transfer to independent proton transfer. Consequently, this rate-determining step shift lowers the reaction barrier by eliminating the contribution of the electron transfer step. This K + -determined reaction pathway enables a lower energy barrier for CO 2 electroreduction reaction than the competing hydrogen evolution reaction, leading to an exclusive selectivity for CO 2 electroreduction reaction.