Boosting the electrocatalytic activity of single atom iron catalysts through sulfur-doping engineering for liquid and flexible rechargeable Zn–air batteries

Exploring effective electrocatalysts for the oxygen reduction reaction (ORR) is of great significance for rechargeable Zn–air batteries (ZABs). In particular, heteroatom-doping in metal-nitrogen-carbon single-atom catalysts (SACs) is considered an effective strategy to promote the electrocatalytic ORR. Herein, we report a practical strategy for designing single-Fe atom decorated S/N-doped carbon (Fe SAs@S/N–C) through the polymerization of phenylenediamine materials as an efficient ORR catalyst for ZABs. The introduction of S facilitates the high-density doping of Fe–N4 active sites, and regulates the adsorption energy of oxygen-containing intermediates by altering the electronic structure of Fe–N4 active sites. Benefiting from the S-doped carbon structure, the Fe SAs@S/N–C catalyst exhibits outstanding ORR performance (E1/2 = 0.84 V) under alkaline conditions, possesses superior durability after 10 K cyclic voltammetry cycles and methanol resistance, outperforming the commercial 20 wt% Pt/C catalyst. Moreover, the Fe SAs@S/N–C catalyst can be easily synthesized at the gram scale, meeting the requirement of practical applications. The liquid-state ZABs assembled with the Fe SAs@S/N–C catalyst as the air cathode demonstrate a large peak power density of 156 mW cm−2 and long-cycling over 300 h. Moreover, the as-assembled flexible all-solid-state ZABs exhibit excellent cycle stability under various bending conditions, demonstrating the promising potential of substituting Pt-based catalysts in practical applications.