Extraordinary electrochemical water splitting performance of chemically grown Nickel Sulphide/Ni(OH)2 intertwined nanoflakes and nanoworms on defect-modulated N-rGO sheets

Herein, we have developed a novel defect-modulated Nickel Sulphide/Ni(OH) 2 @N-rGO electrocatalyst using the modified Hummers' method followed by a hydrothermal process. The materials possess a combination of intertwined nanoflakes and nanoworms of Nickel Sulphide/Ni(OH) 2 on the N-rGO sheets. The material's high defect density and electronic environment modulation are investigated with Raman and X-ray photoelectron spectroscopy, respectively. Electronic modulation resulting from the higher defect density and formed heterostructures enhances the electron mobility and electrochemically active surface area (ECSA), ensuring outstanding overall water splitting (OWS) performance of the synthesized material. The material showed hydrogen evolution reaction (HER) in 0.5 M H 2 SO 4 at an overpotential of 325 mV@10 mA.cm −2 along with excellent oxygen evolution reaction (OER) at overpotential of 245 mV@50 mA.cm −2 in 1 M KOH with Tafel slope as low as 84.85 mV.dec −1 for HER and 32.18 mV.dec −1 for OER. For OWS the two-electrode cell assembly requires a potential of 1.57 V@10 mA.cm −2 having an outstanding 84 h of long-term stability with faradaic efficiency of ∼98 %, which makes it a viable option for OWS commercial electrocatalysis. • NiS/Ni(OH) 2 was grown on N-rGO sheet by the simple hydrothermal technique. • The electronic environment modulation was achieved by optimized NH 4 OH addition. • An overpotential of 325 mV@10 mA.cm −2 and Tafel slope of 84.85 mV.dec −1 for HER. • An overpotential of 245 mV@50 mA.cm −2 and Tafel slope of 32.18 mV.dec −1 for OER. • A potential of 1.57 V@10 mA.cm −2 is required for OWS with 84 h of stability.