Low-Valent Single-Atom Indium Site Regulating Ionic Interference and Adsorbed Hydrogen for Near-Unity Electrosynthesis of Ammonia

Microenvironment modulation, involving the selective adsorption of ions and the engineering of hydrogen radicals, is critical for the neutral electrochemical reduction of nitrate to ammonia at high current densities. In this work, self-adaptive low-valent indium single atoms SAs decorated copper-based nanosheets were investigated as a prototype. The catalyst exhibits a maximum ammonia Faradaic efficiency (FE_NH3) of 99.36% and a high NH₃ yield rate of 29.02 mg h⁻¹ mg_cat.⁻¹ in neutral electrolyte. In-depth experiments and theoretical calculations suggest that the indium SAs optimize the local electronic distribution of the derived Cu matrix through strong p-d orbital couplings, with the electron-relay effect, thereby enhancing electron transfer and regulating the supply of hydrogen radicals to accelerate the hydrogenation process. Furthermore, in situ Raman results and molecular dynamics simulations reveal that the indium SAs can act as solid-state buffering sites by inducing a potential-dependent adsorption behavior of NO₃⁻ over SO₄²⁻ as a supporting oxoanion in the electric double layer, consequently maintaining high reaction activity and selectivity. Herein, the as-designed electrode operates stably at 200 mA cm⁻² for 150 h in a bipolar membrane electrode assembly electrolyzer with a FE_NH3 of ∼83%, indicating promising practical applications.