Targeted Adsorption Enhancement with Lewis Acid Site Regulation for Efficient Nitrate-to-Ammonium Conversion

Ammonia (NH3) is considered a promising carbon-free energy carrier and liquid hydrogen storage medium. There is an urgent requirement to exploit a clean and effective technological process for NH3 synthesis on a large scale. Herein, we propose a selective and efficient electroreduction of nitrate (NO3–) to NH3 on integrated Co3O4 nanowire arrays (NWAs) rich in Lewis acid sites. Density functional theory calculations together with kinetic analysis reveal that the Co atoms adjacent to oxygen vacancies endow Co3O4 NWAs with favorable kinetic characteristics, reflected in enhancing the NO3– adsorption ability, declining the energy barrier of the rate-determination step, and accelerating the hydrogenation of nitrogenous actives in NO3– electroreduction. Further, the integrated array configuration with a rough surface promotes the mass/electron transfer efficiency and the structure stability in NO3– electroreduction. Accordingly, the Co3O4 NWAs achieve a superior Faradaic efficiency of 96.10%, a brilliant NH3 yield rate of 125.78 mg h–1 cm–2, and a highest NH3 effective current density of 1584.80 mA cm–2, outperforming most of the previously reported electroreduction performance whether N2 or NO3– under the same conditions. The strategy of constructing strong targeted NO3– adsorption sites provides a novel idea for establishing an efficient and stable electrochemical ammonia synthesis system in the future.