Atomic-Level Insights into Cation-Mediated Mechanism in Electrochemical Nitrogen Reduction

Abstract

The electrochemical nitrogen reduction reaction (NRR) provides a sustainable alternative to green ammonia synthesis. However, challenges persist due to limited accessibility of N₂ molecules at the electrode interface and competition from abundant protons at catalytic active sites, resulting in low N₂ coverage and compromised selectivity. In this work, we investigate the critical role of potassium cations (K⁺) in modulating the interfacial environment, particularly focusing on how varying K⁺ concentrations influence N₂ adsorption, *NH₃ desorption, and hydrogen transfer (HT) mechanisms under operating electrochemical conditions. Our results demonstrate that a highly concentrated K⁺ electrode interface significantly enhances N₂ adsorption and *NH₃ desorption, collectively leading to improved NRR selectivity, in alignment with the experimental observations. We further uncover insights into HT kinetics, identifying two key steps: protonation (HT₁) and diffusion (HT₂). Among these, diffusion (HT₂) is the rate-limiting step, driven by hydrogen bond connectivity and proton shuttling strength within the cation-induced microenvironments. Specifically, at a low applied potential, a highly concentrated K⁺ interface exhibits weak connectivity and sluggish proton shuttling, therefore limiting NRR efficiency. However, microkinetic modeling (MKM) analysis indicates that optimizing electrode potential and electrolyte compositions can overcome these limitations by promoting proton shuttling. Last but not least, we also provide a detailed map of the interplay among K⁺ molarity, electrode potential, and NH₃ selectivity. Our work offers critical insights to guide the improvement of NRR efficiency through electrolyte and microenvironmental modulation.