Ammonia-Resistant Carbon-Encapsulated Cobalt Catalyst for Electrocatalytic Nitrate Reduction to Volatile Ammonia

Electrocatalytic nitrate reduction to ammonia presents a promising route for sustainable nitrogen utilization; however, current efforts remain largely confined to optimizing synthesis efficiency, with insufficient attention paid to the concurrent challenge of ammonia separation-a key bottleneck for scalable deployment. Here, we report carbon-shell-encapsulated cobalt nanoparticles (Co@C), which uniquely enable integrated ammonia synthesis and in situ gas-phase purification under strongly alkaline conditions. In both sequencing batch and continuous-flow electrolyzers, Co@C delivers a robust nitrate-to-ammonia Faradaic efficiency of 92.4%, maintaining performance even in the presence of exogenous ammonia. Critically, the high-pH environment shifts the NH₃/NH₄ ⁺ equilibrium toward volatile NH₃, enabling spontaneous volatilization and direct gaseous collection. Combined experimental and theoretical analyses demonstrate that the carbon shells confer dual functionality: they physically suppress Co leaching while electronically modulating surface adsorption to weaken NH₃ binding and accelerate desorption. Our work establishes a catalyst design principle centered on ammonia resistance and introduces an electrochemical platform that unifies synthesis, separation, and purification in a single step.