FeS encapsulated hierarchical porous S, N-dual-doped carbon for oxygen reduction reaction facilitation in Zn-air batteries

The rational optimization of active sites and the porous structure is critical for nonprecious metal-based oxygen reduction reaction (ORR) catalysts in Zn-air batteries. We synthesize FeS encapsulated hierarchical porous S, N-dual-doped carbon (Fe-S, N-C-950) by coordinating ZIF-8 with an FeSO4-Phen complex, followed by carbonization at 950 °C in a H2/Ar atmosphere. 1, 10-phenanthroline (Phen) is used as the template to construct a hierarchical porous structure with a large specific surface area (586.8158 m2 g-1). Simultaneously, Phen is employed as the additional nitrogen source to enhance the doping level of active nitrogen-containing species. Density functional theory (DFT) calculations prove that FeS protected by the graphitic-N, S doped carbon shell is the main catalytic active site. Benefiting synergistically from the high porosity and abundant active sites, the Fe-S, N-C-950 catalyst exhibits a 0.9 V half-wave potential in 0.1 M KOH, as well as good stability. The satisfactory ORR performance of Fe-S, N-C-950 is further confirmed in aqueous and all-solid-state Zn-air batteries, with high power density (109 and 68 mW cm-2, respectively) and good discharge stability. This work lays the foundation for the rational design and construction of efficient ORR electrocatalysts for energy storage and conversion.