Cobalt sulfides as efficient catalyst towards oxygen reduction reactions

Developing low-cost and high performance catalysts to replace precious metal based catalysts for oxygen reduction reaction (ORR) is one of the most feasible ways to promote the commercial application of fuel cells. In this work, flower-like CoS and octahedral CoS₂ are synthesized by a facile one-pot hydrothermal method without any adjunction of surfactants or follow-up thermolysis, their catalytic performance towards ORR in alkaline electrolyte are comparatively investigated. The results reveal that CoS₂ outperforms CoS owing to the higher electron density around S[sbnd]S bond of S₂ ^2- in the crystal structure, which promotes the adsorption of oxygen on catalyst surface and facilitates the breakage of O[sbnd]O bond in oxygen, leading to direct 4-electron transfer ORR. When CoS₂ particles are dispersed on the surface of rGO with large surface area, their ORR performance could be further improved.