Ni₃S₂ Nanosheet Flowers Decorated with CdS Quantum Dots as a Highly Active Electrocatalysis Electrode for Synergistic Water Splitting

A facile and effective strategy for fabricating a three-dimensionally (3D) structured nanocomposite catalyst based on nonprecious metals for water splitting in alkaline electrolyzers is reported in this paper. This nanocomposite catalyst consists of the CdS quantum dots (QDs) decorated Ni₃S₂ nanosheet flowers deposited on the plasma-treated nickel foam (PNF). The NiO formed during the plasma treatment is shown to play an important role for pushing the hydrogen and oxygen evolution reactions (HER and OER) in alkaline media. The enhanced exposure of active sites on the nanopetalages results in superior catalytic performance for promoting HER and OER in alkaline electrolyzers. Specifically, a current density of 10 mA cm^–2 can be achieved for the HER with a 121 mV overpotential when the working electrode based on the 1 mM CdS/Ni₃S₂/PNF catalyst is employed in 1 M KOH. The corresponding Tafel slope is 110 mV/decade. For the OER, the onset potential can be as low as 1.25 V vs reversible hydrogen electrode (RHE) reference electrode, which is substantially lower than the commercial IrO₂ catalyst (∼1.47 V). This nanostructured catalyst has excellent long-term stability, and the linear scan voltammetry (LSV) curves of the HER and OER in 1 M KOH solution show negligible decay after undergoing 10⁴ cycles of cyclic voltammogram. The nanocomposite material developed in this study is an ideal candidate as a catalyst for splitting water in alkaline media with relatively low overpotentials at reasonably high current densities (≥100 mA cm^–2).