Introducing foreign elements into a crystal lattice could trigger phase transformation, serving as an excellent means to fabricate highly electrocatalytic phases. NiCo2S4 is a notably electrocatalytic thiospinel phase, normally synthesized via two-step route and rarely explored for electrocatalytic hydrazine oxidation reaction (HzOR). This work reports one-step hydrothermal syntheses of NiCo2S4 and CuCo2S4 and their performance for HzOR and oxygen evolution reaction (OER). Time-dependent syntheses suggest formation of (M, Co)9S8; M=Ni/Cu phase, followed by conversion to the respective thiospinel phase. Computational study validates that the incorporation of Ni into Co9S8 disrupts its stability and induces the formation of a stable bi-metallic thiospinel phase. Even without the assistance of metal foam substrate, NiCo2S4 displayed remarkable activity for HzOR requiring potentials of 153 and 350 mV to afford current densities of 10 and 500 mA/​cm2, respectively. Furthermore, NiCo2S4 showed good activity for OER, providing 10 mA/​cm2 at 290 mV. For hydrazine-assisted H2 production, the two-electrode setup, NiCo2S4||Pt/C attained a current density of 10 mA/​cm2 at 140 mV, which is 1.39 V less than that required for conventional water electrolyzer (1.53 V). Long-term durability of NiCo2S4 for both HzOR and OER at high current densities highlights the suitability of the catalyst for practical applications.

Author/​s: Diya Raveendran, Viplove Mishra, Athma E. Praveen, Avishek Roy, Aditi Chandrasekar, Venkataramanan Mahalingam, Ananda Basak