Zeolitic imidazolate framework derived Fe-Cu carbonaceous catalyst for efficient electrocatalytic nitrate reduction to ammonia

Electrocatalytic nitrate reduction (NO 3 RR) process presents a green and sustainable approach for mitigating environmental nitrate pollution while enabling ambient NH 3 synthesis. However, it was hindered by the challenge of developing non-noble electrodes that exhibited both high activity and low cost. Herein, iron and copper-doped ZIF-8 electrocatalysts (FeCuO x @CN) with varying Fe/Cu molar ratios (Fe/Cu = 2/1, 1/1 and 1/2) were synthesized. The process involved doping iron into the ZIF-8 precursor, followed by pyrolysis at 700, 800 or 900°C to embed copper with ZIF-8. Synergistic effects between Fe and Cu were observed in the FeCuO x @CN catalysts and an appropriate molar ratio of Fe/Cu was found to effectively balance the reduction rates of NO 3 – and NO 2 – , leading to a high NH 3 yield rate. Among the synthesized catalysts, Fe 1 Cu 2 O x @CN-800 exhibited the best NO 3 RR performance, achieving an NH 3 yield rate of 1975.4 μg h −1 mg cat -1 and a faradaic efficiency of 98.3 % at −0.6 V ( vs. RHE). Furthermore, it exhibited excellent cycling stability, maintaining a faradaic efficiency above 96 % over 20 cycles. The NO 3 RR mechanism over Fe 1 Cu 2 O x @CN-800 was determined to be proceeded with a sequence of deoxygenation steps: NO 3 – → *NO 3 → *NO 2 → *NO → *NOH → *NH 2 O → *NH 2 OH → *NH 2 → *NH 3 .