Cobalt-gluconate-derived high-density cobalt sulfides nanocrystals encapsulated within nitrogen and sulfur dual-doped micro/mesoporous carbon spheres for efficient electrocatalysis of oxygen reduction

The exploration of an efficient nonprecious electrocatalyst for oxygen reduction reaction (ORR) is critical to the commercialization of various electrochemical energy-conversion devices. Herein, a cobalt-gluconate-derived nitrogen and sulfur dual-doped micro/mesoporous carbon sphere (Co 9 S 8 /N, S-MCS) with encapsulated high-density cobalt sulfide (Co 9 S 8 ) nanocrystals is developed by annealing and subsequent high-temperature vulcanization. Particularly, the vulcanization temperature has a critical impact on the formation of high-density Co 9 S 8 nanocrystals. Benefiting from the favorable material characteristics of large surface area, abundant micro/mesopores and high graphitic nanostructures, as well as the synergistic effects between high-density Co 9 S 8 nanocrystals and N, S-dual doped graphitic carbon shells, the resulting catalyst demonstrates superior ORR catalytic activity and durability compared to platinum/carbon (Pt/C) catalyst. More notably, the proposed approach can be extended potentially to fabricate other transition metal sulfide (or oxide, carbide) based electrocatalysts.