Abstract
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.