S heteroatom doping in highly porous carbonaceous spheres for boosted oxygen reduction reaction of atomically dispersed Fe-N₄ active sites

Tuning of the coordination environment of atomically dispersed single atoms (SAs) by heteroatom doping is a promising strategy to boost the electrocatalytic activity for oxygen reduction reaction (ORR). The synergistic effect of dual heteroatom doping provides additional degrees of freedom to achieve higher ORR efficiency through decreased energy barriers of the intermediates in catalytic processes. Herein, Fe-SAs anchored within the N, S co-doped porous nanosized carbonaceous spheres (Fe-SAs@N/S-PCSs) was fabricated through the py-rolysis of anchored heteroatom sources and ferric precursors. Under the low catalyst loading capacity of 0.255 mg cm(-2), the obtained Fe-SAs@N/S-PCSs exhibits exceptionally high performance with ORR onset potential (E-onset) of 1.02 V, and half wave potential (E-1/2) of 0.90 V (vs. RHE) in 0.1 M KOH solution, outperforming benchmark Pt/C (E-onset = 1.01 V, E-1/2 = 0.86 V). Superior oxygen evolution reaction (OER) activity (450 mV at 10 mA cm(-2)) is also demonstrated, thus displaying outstanding performance for Zn-air battery. The porous structure, rich accessible Fe SAs, and the optimal binding of ORR-related species induced by S doping in carbon matrix generate the excellent ORR activity and durability. This work provides insights into the rational design of cost-effective single atom catalysts (SACs) with impressive electrocatalytic activities for efficient energy con-version applications.