High-Activity Fe₃ C as pH-Universal Electrocatalyst for Boosting Oxygen Reduction Reaction and Zinc-Air Battery

Transition metal catalysts are regarded as one of promising alternatives to replace traditional Pt-based catalysts for oxygen reduction reaction (ORR). In this work, an efficient ORR catalyst is synthesized by confining Fe₃ C nanoparticles into N, S co-doped porous carbon nanosheets (Fe₃ C/N,S-CNS) via high-temperature pyrolysis, in which 5-sulfosalicylic acid (SSA) demonstrates as an ideal complexing agent for iron (ΙΙΙ) acetylacetonate while g-C₃ N₄ behaves as a nitrogen source. The influence of the pyrolysis temperature on the ORR performance is strictly examined in the controlled experiments. The obtained catalyst exhibits excellent ORR performance (E_1/2  = 0.86 V; E_onset  = 0.98 V) in alkaline electrolyte, coupled by exhibiting the superior catalytic activity and stability (E_1/2  = 0.83 V, E_onset  = 0.95 V) to Pt/C in acidic media. In parallel, its ORR mechanism is carefully illustrated by the density functional theory (DFT) calculations, especially the role of the incorporated Fe₃ C played in the catalytic process. The catalyst-assembled Zn-air battery also exhibits a much higher power density (163 mW cm^-2 ) and ultralong cyclic stability in the charge-discharge test for 750 h with a gap increase down to 20 mV. This study provides some constructive insights for preparation of advanced ORR catalysts in green energy conversion units correlated systems.