Phosphorization of α-Fe₂O₃ Boosts Active Hydrogen Mediated Electrochemical Nitrate Reduction to Ammonia

Inexpensive iron-based materials are considered promising electrocatalysts for nitrate (NO₃ ^-) reduction, but their catalytic activity and spontaneous corrosion remain challenges. Here, the α-Fe₂O₃ active surface is reconstructed by gradient phosphorization to obtain FeP_x with higher electrochemical activity. FeP_2.0 optimizes the adsorption energy of NO₃ ^- and its reduction intermediates, meanwhile promote the generation of active hydrogen (^*H) but inhibit its generation of H₂. More importantly, Fe and P can serve as binding sites for NO₃ ^- and ^*H, respectively, which improves the electron utilization of NO₃ ^- deoxygenation and the efficiency of the subsequent hydrogenation for the selective synthesis of NH₃. 91.7% NO₃ ^- conversion rate is achieved for the reduction of 100 mL 200 mg L^-1 NO₃ ^--N, 99.3% ammonia (NH₃ selectivity (yield of 1.79 mg h^-1 cm^-2), and 91.4% Faraday efficiency in 3 h. The high-purity solid NH₄Cl is finally extracted by gas extraction and vacuum distillation (81.4% recovery). This study provides new insights and strategies for the conversion of NO₃ ^- to NH₃ products over iron-based electrocatalysts.