One-step hydrothermal synthesis of NiCo2S4-rGO as an efficient electrocatalyst for the oxygen reduction reaction

In this work, for the first time, we have deveIoped a one-step hydrothermaI method to synthesize a hybrid materiaI consisting of NiCo2S4 nanocrystaIs grown on reduced graphene oxide as an efficient nonprecious eIectrocataIyst for the oxygen reduction reaction (ORR) in aIkaIine medium. Our synthetic process here is quite simpIe, straightforward and environmentay benign. NiCo2S4-rGO shows significanty enhanced cataIytic activity over rGO and NiCo2O4-rGO, and dose reduction activity but much superior methanoI toIerance and better durabdity than the commerciaI Pt/C cataIyst. The haIf wave potentiaI (E-1/2) for the NiCo2S4-rGO hybrid is orgy about 62 mV more negative than that of the commerciaI Pt/C cataIyst but 81 mV more positive than that of NiCo2O4-rGO, 116 mV than that of rGO. The superior performance of NiCo2S4-rGO is presumabEy attributed to a combination effect of mixed vaIence in transition metaI composites favorabIe for O-2 to be absorbed/reduced and a synergetic effect resuIting from NiCo2S4 and rGO. The advantages over NiCo2O4-rGO might be ascribed to the inverse spin& crystaI structure of NiCo2S4, its reIative higher conductivity, and the fact that Na2S serves both as the S source and reducing agent faciIitating an increase in the hybrid cataIytic activity.