Electrolyte Cation Engineering Selectively Regulates Competing Urea Oxidation Pathways

Abstract

The electrochemical urea oxidation reaction (UOR) has emerged as an attractive anodic reaction for various energy conversion systems. Recently, increasing attention has been directed toward controlling UOR selectivity on Ni-based electrocatalysts following the recognition that the UOR can produce over-oxidized products. However, existing studies have focused predominantly on catalyst design to regulate surface-bound intermediates, whereas whether electrolyte-mediated noncovalent interactions can selectively control competing UOR pathways remains poorly understood. Here, we show that rational electrolyte engineering using alkali-metal cations selectively regulates the UOR pathway by modulating the interfacial hydrogen-bonding network. Electrochemical rate deconvolution and product analysis reveal that weakly hydrated cations selectively accelerate the direct oxidation pathway, promoting the formation of the over-oxidized NO2– and NCO– products, while leaving the indirect pathway essentially unaffected. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) measurements, together with molecular dynamics simulations of cation hydration dynamics, indicate that weakly hydrated cations create a more dynamic interfacial water environment with faster water exchange, thereby facilitating interfacial OH–-mediated successive dehydrogenation during direct urea oxidation. Leveraging this mechanistic understanding, the electrolyte-engineering strategy was applied to a cascade urea-to-ammonia conversion system, achieving a urea-to-ammonia conversion efficiency of 77.5% and approximately threefold higher ammonia productivity in CsOH than in LiOH. These findings establish electrolyte engineering as a complementary strategy to catalyst design and highlight noncovalent electrolyte–electrode interactions as an effective handle for controlling reaction pathways and product selectivity in an integrated UOR-based nitrogen conversion system.