Beyond Thermodynamics-Determined Selectivity: Cation-Mediated Interfacial Microenvironment Promotes Desorption Kinetics To Enable Selective Hydroxylamine Electrosynthesis

Abstract The electroreduction of nitrogen oxidative species emerges as a route for producing hydroxylamine (NH2OH). However, the mechanism governing its selective generation over the byproduct ammonia (NH3) is not well understood, impeding the rational design of high-performance catalysts. Here, we disclose a common phenomenon of cation-mediated interfacial microenvironment in promoting NO activation and NH2OH desorption kinetics, which is responsible for selective NH2OH electrosynthesis. Focusing on the established Co single-atom catalysts, our constant-potential modeling reveals that cations (e.g., K+) modulate the interfacial microenvironment and electronic structures, which not only facilitate the nonelectrochemical NH2OH desorption but also promote the rate-limiting hydrogenation of *NO to *NHO via the improved electron donation and back-donation. By contrast, such a K+-mediated interfacial environment is absent on Cu catalysts, where *NH2OH predominantly undergoes hydrogenation to NH3. This mechanism also rationalizes other typical NH2OH-producing catalysts, highlighting the cation effect and *NH2OH-based branching point. We further demonstrate the potential of axial coordination engineering for enhancing NH2OH production. This work advances the understanding of NH2OH electrosynthesis and provides practical guidance for catalyst design.