Unveiling the Protonation Kinetics-Dependent Selectivity in Nitrogen Electroreduction: Achieving 75.05 % Selectivity

Abstract

Copyright © 1999-2023 John Wiley & Sons, Inc. All rights reserved. While higher selectivity of nitrogen reduction reaction (NRR) to ammonia (NH3) is always achieved in alkali, the selectivity dependence on nitrogen (N2) protonation and mechanisms therein are unrevealed. Herein, we profile how the NRR selectivity theoretically relies upon the first protonation that is collectively regulated by proton (H) abundance and adsorption-desorption, along with intermediate-*NNH formation. By incorporating electronic metal modulators (M=Co, Ni, Cu, Zn) in nitrogenase-imitated model-iron polysulfide (FeSx), a series of FeMSx catalysts with tailorable protonation kinetics are obtained. The key intermediates behaviors traced by in situ FT-IR and Raman spectroscopy and operando electrochemical impedance spectroscopy demonstrate the strong protonation kinetics-dependent selectivity that mathematically follows a log-linear Bradley curve. Strikingly, FeCuSx exhibits a record-high selectivity of 75.05 % at −0.1 V (vs. RHE) for NH3 production in 0.1 M KOH electrolyte. © 2022 Wiley-VCH GmbH.