Fundamental Insights on the Electrochemical Nitrogen Oxidation over Metal Oxides

Electrocatalytic nitrogen oxidation reaction (eN2OR) has emerged as a sustainable strategy for nitrogen fixation. In this work, density functional theory calculations were performed to rationalize the reaction mechanisms, activity, and selectivity of eN2OR on metal dioxides. The anatase (101), anatase (100), and rutile (110) surfaces were investigated to obtain more generalized insights. Based on the reaction phase diagram analysis, the thermochemical mechanisms were identified as most energetically favorable for N2 and *N2O oxidation, and a theoretical activity map was constructed for eN2OR, explaining well the experimental activity trend. Anatase PtO2(100) was screened as the most active catalyst for nitrate production, which could be covered by a monolayer of *OH under the reaction conditions according to the Pourbaix diagram. A method of electric field controlling constant potential was used to calculate the electrochemical barriers on anatase PtO2(100). It was found that the electrochemical barriers of the oxygen evolution reaction will increase with the decrease of potential, while the thermochemical limiting step of the eN2OR is insensitive to potential. Thus, the eN2OR selectivity can be improved by lowering the applied potential. This work unveils fundamental insights into eN2OR and provides a unified understanding to experiments.