Nickel Cobalt oxide/sulfide heterostructure electrocatalyst for the oxygen evolution reaction

초록

As global warming intensifies, the development of sustainable and pollution-free energy storage systems has become imperative. Hydrogen is regarded as a promising energy carrier due to its high energy density and potential to support clean energy technologies. Water electrolysis is a highly attractive strategy for producing ultra-high-purity hydrogen without environmental pollution. However, the slow reaction kinetics and large overpotential of the oxygen evolution reaction (OER) at the anode significantly limit the overall efficiency of water electrolysis. Precious metal-based oxides, such as IrO2 and RuO2, are considered advanced OER electrocatalysts, but their high cost, scarcity, and limited stability during prolonged operation hinder their large-scale commercialization. Consequently, substantial efforts have been dedicated to developing non-noble metal-based electrocatalysts with high activity and stability. Recently, transition metal-based materials, including sulfides, oxides, and phosphides, have gained significant attention due to their excellent electrochemical activity, stable operation, and low cost. In this study, a nickel cobalt oxide/sulfide heterostructure was synthesized through a solvothermal process followed by annealing. Polystyrene (PS) spheres were prepared via emulsion polymerization and subsequently functionalized with polyvinylpyrrolidone (PVP) to obtain PVP-PS spheres. These spheres were then mixed with Co2+ ions and 2-methylimidazole were mixed, forming ZIF-67 coatings on the PVP-PS surface. The resulting ZIF-67@PS composite was combined with Ni2+ ions in ethanol and subjected to solvothermal treatment at 90°C for 6h. During this process, ZIF-67 was etched, releasing Co2+ ions, which coprecipitated with Ni2+ ions to form NiCo-LDH. The NiCo-LDH@PS composite was annealed in air at 450°C for 3h, leading to the complete removal of the PS spheres. Finally, the NiCo oxide underwent a sulfidation process at 500°C for 3h, resulting in the