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

The electroreduction of nitrogen oxidative species emerges as a route for producing hydroxylamine (NH 2 OH). However, the mechanism governing its selective generation over the byproduct ammonia (NH 3 ) 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 NH 2 OH desorption kinetics, which is responsible for selective NH 2 OH 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 NH 2 OH 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 *NH 2 OH predominantly undergoes hydrogenation to NH 3 . This mechanism also rationalizes other typical NH 2 OH-producing catalysts, highlighting the cation effect and *NH 2 OH-based branching point. We further demonstrate the potential of axial coordination engineering for enhancing NH 2 OH production. This work advances the understanding of NH 2 OH electrosynthesis and provides practical guidance for catalyst design.