In Situ Grown (Fe,Mn,Ga)₃O_4–x Spinel/(Mn,Fe)₂O_3–y Bixbyite Dual-Phase Electrocatalyst for Preeminent Nitrogen Reduction to Ammonia: A Step toward the NH₃ Economy

Employing a non-noble trimetal oxide system toward an electrochemical nitrogen reduction reaction (eNRR) instead of a century-long and CO 2 -emission Haber–Bosch process reveals a green path for NH 3 production. In this work, the trimetal Fe–Mn–Ga oxide electrocatalyst was prepared with a facile one-pot hydrothermal method followed by annealing. Crystal structure, morphology, composition, and electrochemical properties were characterized. The flower-like (Fe,Mn,Ga) 3 O 4– x spinel/tabular crystal-like (Mn,Fe) 2 O 3– y bixbyite composite electrocatalyst was in situ formed with many active oxygen atoms on the oxygen vacancy sites and transition metals of Fe and Mn at multiple oxidation states. In a N 2 -saturated 0.1 M Na 2 SO 4 solution, the NH 3 yield rate at a potential of −0.6 V vs RHE is 814 μg h –1 mg cat –1 (2036 μg h –1 cm –2 ) with Faradaic efficiency (FE) of 5.77%, while the highest FE of 19.7% is achieved at −0.5 V with a yield rate of 599 μg h –1 mg cat –1 . The reaction mechanism for NH 3 production is investigated and explained.