Elucidating the Activity of Electrochemical Nitrate Reduction: High-Valent Anionic Intermediates as Kinetic Gatekeepers

The persistent paradox in electrochemical nitrate reduction (NO3–RR)─the requirement of high overpotentials despite its highly exothermic nature─remains a critical roadblock for efficient ammonia electrosynthesis. Here, we resolve this conundrum by identifying a high-valent anionic intermediate as kinetic gatekeepers during the nitrate reduction on a single-atom catalyst by using AIMD simulations under explicit solvation and electrode potentials. Employing our self-developed constant-potential thermodynamic integration method, we reveal a stark kinetic barrier dichotomy: while the reaction is thermodynamically favorable governed by the N–O break, the protonation to oxygen at a low anionic state necessitates substantial activation energy. Mechanistic analysis uncovers that electrode polarization preactivates *NO3– into a metastable high-valent *NO32– intermediate, which serves as the key step to the following protonation process. Crucially, this intermediate’s stabilization requires a highly negative potential, directly linking its formation to the observed overpotential. Furthermore, molecular dynamics simulations also demonstrate that K+ cations play a key role in electrostatically stabilizing the adsorption of negatively charged NO3– onto the negatively polarized cathode. This work calls for the urgent reconsideration of conventional nitrate reduction mechanisms and the exigency of refined interface design principles for improved nitrate electrocatalysis.