Abstract
Fe single-atom catalysts open up broad prospects for oxygen reduction reaction (ORR), but the chemical state evolution of Fe species before forming isolated sites is rarely understood. Herein, mechanistic investigation on the formation of isolated Fe sites is presented through solvent-mediated oxidative pyrrole polymerization strategy. The slow reaction kinetics of oxidative Fe3+ ions with the predesigned methanol solvent molecules can endow highly dispersed Fe sites in polypyrrole and thus Fe single-atom catalysts after pyrolysis. The Fe single-atom catalyst (Fe-SA/PNC) performs superior ORR activity with a half-wave potential of 0.90 V versus RHE and 12.8 times higher turnover frequency than that of commercial Pt/C. When assembled into Zn-air batteries, the Fe-SA/PNC cathode delivers a 1.68 V open circuit potential and ultra-long cycling stability over 9000 cycles, superior to the most reported catalysts so far. Experimental and theoretical results reveal that the rich adjacent non-coordinated graphitic nitrogen atoms can enhance electronic conductivity and promote O2 adsorption and OH- desorption, thus enabling high oxygen reduction and battery performances.
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