In situ formation of iron-cobalt sulfides embedded in N,S-doped mesoporous carbon as efficient electrocatalysts for oxygen reduction reaction

Transition metal sulfides-based materials, as one type of promising oxygen reduction reaction (ORR) electrocatalysts have drawn increasing attention. Herein, we proposed a facile strategy to prepare iron-cobalt sulfides embedded in N,S-doped mesoporous carbon (Fe_xCo_1-xS-T@NS-MC) via in situ polymerization and pyrolysis. Various characterization methods (e.g., Raman, BET, XPS, and electrochemical tests) are used to explore the differences between the microstructure and catalytic activity of these electrocatalysts. Notably, the sample Fe_0.5Co_0.5S-1000@NS-MC pyrolyzed at 1000 °C with an optimal iron/cobalt molar ratio (x = 0.5) exhibits the best ORR performance, which has the positive onset potential of 0.947 V vs. RHE, half-wave potential of 0.842 V vs. RHE and a large limiting current density of 5.63 mA cm⁻². Moreover, the results obtained from RRDE measurements indicate a four-electron process towards ORR for Fe_0.5Co_0.5S-1000@NS-MC catalyst. The combination and synergy of the controllable active centers (Fe-adjusted Co₉S₈/CoS with appropriate ratios) and hierarchical porous structures with large specific surface area render the outstanding ORR activity and electrochemical stability. Those results indicate that bimetallic sulfides-based materials are promising as ORR electrocatalysts.