Biomass in situ conversion to Fe single atomic sites coupled with Fe2O3 clusters embedded in porous carbons for the oxygen reduction reaction

Abstract

Small metal clusters have received increasing attention due to their attractive and superior performance in electrocatalytic energy conversion. However, the design and synthesis of well-dispersed metal clusters is a great challenge owing to their ease of aggregation. Here, we develop a biomass in situ conversion strategy to synthesize Fe single atomic sites (Fe–N₄) combined with ultra-small Fe₂O₃ nanoclusters embedded in N, S codoped porous carbons (Fe_SA/FeO_NC/NSC) for the oxygen reduction reaction (ORR). The resultant Fe_SA/FeO_NC/NSC exhibits a high half-wave potential (E_1/2 = 0.86 V vs. RHE) and an outstanding kinetic current density at 0.80 V (J_k = 32.15 mA cm⁻²), which even surpasses those of commercial Pt/C (E_1/2 = 0.85 V, J_k = 16.5 mA cm⁻²). Atomic level dispersed Fe–N₄ sites integrated with Fe₂O₃ clusters embedded in N, S-mediated carbon are mainly responsible for the excellent ORR activity. More importantly, the assembled Zn–air battery can output a prominent power density of 179.0 mW cm⁻² and energy density of 837.4 W h kg⁻¹ along with robust stability, outperforming the commercial Pt/C and most non-platinum catalysts. This work opens up an avenue for biomass in situ conversion into non-precious metal electrocatalysts for energy conversion and storage technologies.