OH-enriched NiS/Ni₃S₂–Zr Heterostructure for Overall Water Splitting Performance in Alkaline Media

The development of highly efficient Ni-sulfide-based catalysts is desirable but limited due to slow kinetics in alkaline hydrogen evolution reactions (HER) and water electrolysis. Herein, we report the design of a high-valent doping strategy combined with selective surface etching to generate an OH-enriched porous heterostructure NiS/Ni 3 S 2 nanosphere with an optimal electronic structure. The E-NiS/Ni 3 S 2 –Zr (6 mM) electrocatalyst requires only 50 mV to achieve 10 mA cm –2 for the HER. Oxygen evolution reaction (OER) requires 205 and 282 mV to reach 10 and 100 mA cm –2, respectively. In addition, for total water splitting in alkaline medium, the assembled cell with E-NiS/Ni 3 S 2 –Zr (6 mM) as both the positive and negative electrodes requires ultralow voltages of 1.41 and 1.51 V at 10 mA and 20 mA cm –2 current densities, respectively. Notably, E-NiS/Ni 3 S 2 –Zr (6 mM) showed excellent stability for 30 h in HER, OER, and water electrolysis. Delving into the underlying electrochemical processes and electron transfer kinetics, a diverse array of techniques such as linear sweep voltammogram, electrochemical impedance spectroscopy, electrochemical active surface area, C dl, cyclic voltammetry, chronoamperometric, and turn over frequency were employed. Comprehensive characterization encompassing X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared, Raman, scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy was conducted to explore the electronic and morphological attributes of the synthesized materials. The approach formulated in this study paves the way for achieving optimal electrocatalyst performance, positioning them as compelling alternatives to noble metal-based electrocatalysts.