Size-controlled hydrothermal synthesis and high electrocatalytic performance of CoS2 nanocatalysts as non-precious metal cathode materials for fuel cells

Abstract

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 (E_1/2) 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.