Operando condition modeling CO2 electrocatalytic reduction on Ni-N-C single atom catalysts

The performance of electrocatalysts is shaped not solely by the inherent structures of active sites but also by factors like the charge accumulation on the electrode surface and the electric double-layer (EDL) structure formed at the interface between the electrode and electrolyte. At present, accurately modeling the electrochemical reactions occurring at EDL is a great challenge, mainly because the dynamic chemical change cannot be adequately captured by the commonly used static configurations. Ab initio molecular dynamics (AIMD) simulations face difficulty sampling across both time and space scales. Here, utilizing Ni-N-C/G catalysis CO2 reduction to CO as a framework to examine, we explored the catalytic process affected by EDL and accumulated electron on electrode under operando conditions by integrating grand canonical density functional theory (GC-DFT) calculations with classical molecular dynamic (MD) simulations. The findings suggest that the negative charge accumulating on the cathode material plays a crucial role in facilitating the adsorption and activation of CO2. Additionally, incorporating two intermediates, *COO + OH- and *CO + OH-, can significantly enhance the accuracy of the free energy profile. Moreover, the EDL can not only enhance the adsorption of CO2 and promote the cleavage of the C-OH (in the *COOH intermediate) but also inhibit the desorption of CO to some extent. Compared to the promotional effect induced by cations coordinating with intermediates, the primary promoting factor lies in the electric field (EF around 85%) distributed around the intermediates. With the inclusion of the EDL correction, our calculations align well with experimental observations, showing that for the CO2 reduction to CO on the Ni-N-C site, as the applied potential becomes increasingly negative, the rate-determining step shifts from *COOH formation to CO desorption at -0.60 VRHE. Our work not only explains a long-standing puzzle for an important catalyst but also highlights the crucial roles of EDL effects, which provide guidance on investigating electrochemical reactions without compromising the complexity of the electrode environment.