Phosphorization of α‐Fe2O3 boosts active hydrogen mediated electrochemical nitrate reduction to ammonia

Abstract

Inexpensive iron-based materials are considered promising electrocatalysts for nitrate (NO₃</sup>−</sup>) 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</sub>2.0</sub> optimizes the adsorption energy of NO</sub>3</sub></sup>−</sup> and its reduction intermediates, meanwhile promote the generation of active hydrogen (*H) but inhibit its generation of H</sub>2</sub>. More importantly, Fe and P can serve as binding sites for NO</sub>3</sub></sup>−</sup> and *H, respectively, which improves the electron utilization of NO</sub>3</sub></sup>−</sup> deoxygenation and the efficiency of the subsequent hydrogenation for the selective synthesis of NH</sub>3</sub>. 91.7% NO</sub>3</sub></sup>−</sup> conversion rate is achieved for the reduction of 100 mL 200 mg L</sup>−1</sup> NO</sub>3</sub></sup>−</sup>−N, 99.3% ammonia (NH</sub>3</sub> selectivity (yield of 1.79 mg h</sup>−1</sup> cm</sup>−2</sup>), and 91.4% Faraday efficiency in 3 h. The high-purity solid NH</sub>4</sub>Cl is finally extracted by gas extraction and vacuum distillation (81.4% recovery). This study provides new insights and strategies for the conversion of NO</sub>3</sub></sup>−</sup> to NH</sub>3</sub> products over iron-based electrocatalysts.