Schottky Barrier-Induced Surface Electric Field Boosts Universal Reduction of NO_x⁻ in Water to Ammonia

NO_x⁻ reduction acts a pivotal part in sustaining globally balanced nitrogen cycle and restoring ecological environment, ammonia (NH₃) is an excellent energy carrier and the most valuable product among all the products of NO_x⁻ reduction reaction, the selectivity of which is far from satisfaction due to the intrinsic complexity of multiple-electron NO_x⁻-to-NH₃ process. Here, we utilize the Schottky barrier-induced surface electric field, by the construction of high density of electron-deficient Ni nanoparticles inside nitrogen-rich carbons, to facilitate the enrichment and fixation of all NO_x⁻ anions on the electrode surface, including NO₃⁻ and NO₂⁻, and thus ensure the final selectivity to NH₃. Both theoretical and experimental results demonstrate that NO_x⁻ anions were continuously captured by the electrode with largely enhanced surface electric field, providing excellent Faradaic efficiency of 99 % from both electrocatalytic NO₃⁻ and NO₂⁻ reduction. Remarkably, the NH₃ yield rate could reach the maximum of 25.1 mg h⁻¹ cm⁻² in electrocatalytic NO₂⁻ reduction reaction, outperforming the maximum in the literature by a factor of 6.3 in neutral solution. With the universality of our electrocatalyst, all sorts of available electrolytes containing NO_x⁻ pollutants, including seawater or wastewater, could be directly used for ammonia production in potential through sustainable electrochemical technology.