Microwave-assisted synthesis of bifunctional multiphase nickel sulfide (Ni-S) and NiCo2S4 electrocatalysts for water splitting

Water splitting into hydrogen and oxygen with non-noble and efficient electrocatalysts is crucial for green energy demands. The transitional metal-based sulfides are owing to the interest due to their high activity in electrochemical processes, low cost, and earth abundance. Herein, we report the bi-functional catalytic performance of multiphase Nickel Sulfide NiS₂ and Ni₉S₈ (Ni-S) and Nickel Cobalt Sulfide (NiCo₂S₄), synthesized with the one-step microwave-assisted (MWA) method, for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The flower-like nanosheets of Ni-S show effective HER performance at a low overpotential 152 mV at 50 mA cm^-2, because of the surface morphology and electron adsorption ability. Furthermore, the bimetallic nanospheres of NiCo₂S₄ give a high current density of 160 mA cm^-2 at 275 mV overpotential for OER, because of the incorporation of nickel and cobalt species by stabilizing the sulfur phase for further improved activity and charge transfer capacity. Moreover, the NiCo₂S₄ has faster reaction kinetics with a low Tafel slope of 76 mV dec^‑1 for OER and 37 mV dec^‑1 for HER, rather than the Ni-S at 167 mV dec^‑1 and 65 mV dec^‑1 respectively.