Triple Synergy Engineering via Metal-Free Dual-Atom Incorporation for Self-Sustaining Acidic Ammonia Electrosynthesis

Electrochemical nitrate reduction reaction (NO₃RR) for ammonia synthesis under acidic conditions offers significant advantages, like direct fertilizer production and prevention of ammonia volatilization. However, three critical challenges persist: instability of metal-based catalysts, competition from the hydrogen evolution reaction (HER), and proton depletion leading to species imbalance. Here, we developed a novel metal-free heteronuclear diatomic-based catalyst that simultaneously addresses these challenges through atomic-level triple synergy engineering. Silicon-iodine dual-atoms are precisely anchored on nickel oxide ultrathin nanosheets supported on carbon cloth (Si/I-NiO@CC) via a gradient-heating co-loading method. Si/I-NiO@CC establishes a self-sustaining catalytic system, achieving a remarkable Faradaic efficiency of 96.8% at -0.3 V versus RHE and record-breaking operational stability of 420 h in acidic electrolyte, surpassing the performance of all reported acid NO₃RR electrocatalysts to date. Advanced in situ spectroscopic characterization combined with electrochemical evaluation reveals the triple synergy mechanism: electron-deficient Ni^δ⁺ and oxygen vacancies generate abundant active sites while mitigating HER competition, iodine-mediated proton reservoirs dynamically regulate H* coverage to maintain species balance, and covalent Si─O─Ni interfacial bonding inhibits metal leaching and stabilizes the catalytic system. This work establishes a constructive guideline for the rational engineering of high-efficiency electrocatalysts for selective acidic NO₃RR.