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 FePₓ with higher electrochemical activity. FeP₂.₀ 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</sup>−</sup>−N, 99.3% ammonia (NH₃ selectivity (yield of 1.79 mg h</sup>−</sup>¹ cm</sup>−2</sup>), 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</sup>−</sup> to NH₃ products over iron-based electrocatalysts.