Highly selective electrochemical reduction of nitrate-to-ammonia using iron phosphide self-supported electrode

Nitrate electrocatalytic reduction (NO₃RR) is a potential approach to ammonia (NH₃) production, and the limited NH₄⁺–N selectivity and NH₄⁺–N yield rate are great challenges in NO₃RR to NH₃. Herein, the self-supported iron phosphide electrodes were successfully prepared by electrodeposition and low-temperature pyrolysis method. The characterization results shown that 0.2Fe_xP/Fe⁰-300 electrode consisted of amorphous Fe_xP and crystalline Fe⁰ particles. 0.2Fe_xP/Fe⁰-300 electrode exhibited the good NO₃RR performance with high NO₃⁻–N removal efficiency of 96.04%, NH₄⁺–N selectivity of 97.52%, and NH₄⁺–N yield rate of 57.24 μmol·cm⁻²·h⁻¹ at initial NO₃⁻–N concentration of 50 mg·L⁻¹, while 96.47% NH₄⁺–N FE was obtained at initial NO₃⁻–N concentration of 200 mg·L⁻¹. In direct reduction pathway, amorphous Fe_xP, serving as an electron mediator, and crystalline Fe⁰, acting as the electron donor, facilitated the electron-transfer. However, in indirect reduction pathway, the generated atomic H^* with strong reducibility, contributed marginally to NO₃⁻–N reduction in 0.2Fe_xP/Fe⁰-300 electrode.