NiS x /NiO/MoS2 heterostructure for enhanced hydrogen evolution in acidic media and supercapacitor electrode applications.

This study demonstrates the synthesis and characterization of a NiS x /NiO/MoS2 (x = 1, 2) heterostructure using a hydrothermal method, demonstrating superior performance for the hydrogen evolution reaction (HER) in 1 M H2SO4. X-ray diffraction (XRD) confirmed the presence of cubic NiO, mixed NiS and NiS2 phases, and hexagonal MoS2, while scanning electron microscopy (SEM) revealed an interconnected nanosheet morphology with Ni, S, Mo, and O elements verified by energy-dispersive X-ray (EDX) spectroscopy. Fourier-transform infrared (FTIR) spectroscopy identified Ni-O, Ni-S, and Mo-S bonds, and UV-visible spectroscopy indicated a reduced bandgap of 2.81 eV for the composite. The composite achieved a low overpotential of 166 mV at 10 mA cm-2, a Tafel slope of 55 mV dec-1, and a charge transfer resistance of 52 Ω, outperforming individual NiO (582 mV, 91 mV dec-1, 266 Ω) and NiS x (357 mV, 72 mV dec-1, 170 Ω). Additionally, the composite exhibited a high specific capacitance of 428.24 F g-1 at 2 A g-1 and an electrochemical surface area (ECSA) of 0.7 mF cm-2, highlighting its potential as a dual-functional material for HER and supercapacitor applications. These results underscore the effectiveness of synergistic interactions in enhancing catalytic activity and charge storage capacity, offering a promising pathway for sustainable energy technologies.