Selenium‐Deficient FeSe₂/Fe₃O₄ Electrocatalyst for Nitrate Reduction to Ammonia

Abstract Electrocatalytic reduction of NO 3 − is a green and sustainable method that not only helps to treat industrial pollutants in wastewater, but also produces valuable chemicals. However, the slow dynamics of the proton‐coupled electron transfer process results in a high barrier and low conversion efficiency. In this work, the Se‐deficient FeSe 2 /Fe 3 O 4 heterojunction was synthesized, which showed excellent electrochemical performance in 0.1 M nitrate reduction reaction, superior to most currently reported catalysts. The high activity of Se‐deficient FeSe 2 /Fe 3 O 4 is due to the synergistic effect between FeSe 2 and Fe 3 O 4 to achieve relay catalytic NO 3 − reduction. Among them, the Se‐deficient FeSe 2 contributes to NO 3 − deoxygenation and subsequent hydrogenation, and Fe 3 O 4 promotes H 2 O decomposition to provide H proton, jointly promote NO 3 RR. Finally, the online differential electrochemical mass spectra (DEMS), in situ Raman and DFT calculation confirmed the optimal pathway for NO 3 RR to NH 3 on Se‐deficient FeSe 2 /Fe 3 O 4 (100). This strategy of relay catalysis provides a potential way to treat wastewater with high concentration nitrate.