Non-precious metal chalcogenides are considered as a potential alternative to Pt-based cathode catalysts in polymer electrolyte membrane fuel cells because of their promising electrocatalytic performance and low cost. However, size-controlled synthesis of this class of materials still remains a big challenge. In this paper, we directly prepared CoS2 nanocatalysts by a hydrothermal route without any post treatment, developed a facile way to tune the particle size by adjusting the initial Co2+ concentration in the reaction system in the presence of a surfactant, and investigated the corresponding electrocatalytic performance for the oxygen reduction reaction (ORR) in alkaline medium in detail. The results show that the ORR activity mainly depends on the CoS2 mass loading on the electrode disk surface and the average particle size of the CoS2 nanocatalysts. The CoS2 catalyst with an average particle size of 30.7 nm exhibits excellent electrocatalytic performance with an OCP (open circuit potential) of 0.94 V vs. RHE, a half-wave potential (E1/2)of ca. 0.71 V vs. RHE, and complete methanol tolerance for the ORR in 0.1 M KOH. This OCP value is the largest among non-precious metal chalcogenides to date, much close to that of 0.99 V vs. RHE for commercial Pt/C catalyst (E-TEK). In addition, the CoS2 nanocatalyst has comparable durability to the Pt/C catalyst in 0.1 M KOH. The CoS2 nanocatalyst is a promising candidate for alkaline membraneless fuel cell systems.
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