Stepwise Construction of a Self-Supported VS2–V2O5@NF Sulfide/Oxide Composite Electrode for Alkaline Overall Water Splitting

Electrocatalytic water splitting provides a sustainable route for hydrogen production, but alkaline hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) still suffer from sluggish kinetics and large polarization losses. Herein, a self-supported VS2-V2O5(x:y)@NF composite electrode was constructed through a stepwise hydrothermal strategy. In this design, vertically grown VS2 on nickel foam provides a conductive and open scaffold, while V2O5-derived oxygen-containing domains are introduced into the surface and inter-array spaces to increase accessible reaction sites and regulate the local adsorption environment. Among the investigated compositions, VS2-V2O5(1:1)@NF exhibits the most balanced bifunctional response within the sample series, requiring overpotentials of 272.2 mV for HER and 292.8 mV for OER at 10 mA cm-2 in 1 M KOH. In a two-electrode overall water-splitting configuration, the symmetric electrolyzer requires cell voltages of 1.88 V and 2.27 V to deliver 10 and 100 mA cm-2, respectively. The performance variation among the samples prepared with different V2O5 precursor-feeding amounts is correlated with the self-supported sulfide/oxide architecture, electrochemically accessible interface, apparent charge-transfer behavior, wettability, and surface reconstruction. The present results do not directly establish Fermi-level equilibration or quantitative interfacial charge redistribution.