P–N heterojunction-enhanced structural stability of tungsten disulfide nanosheets for highly efficient, stable alkaline water electrolysis

Tungsten disulfide (WS₂) exhibits decent electrocatalytic performance toward the hydrogen evolution reaction (HER) in acidic conditions; however, poor structural stability under alkaline conditions limits its widespread application in electrocatalysis. We developed a robust exfoliation strategy using water-soluble sodium-ion-functionalized chitosan to obtain stable, well-dispersed WS₂ nanosheets with excellent resistance to alkaline environments. Through subsequent electropolymerization and electroactivation, N-type WS₂ nanosheets were combined with P-type polyaniline on nickel foam, creating a stable organic-inorganic P-N heterojunction electrocatalytic electrode. The electrode demonstrates high HER electrocatalytic performance in 1.0 M potassium hydroxide solution, achieving a low overpotential of 24.5 mV at 10 mA cm^-2, a Tafel slope of 48.2 mV dec^-1 and a low resistance of around 0.5 Ω, equivalent to the conventional noble-metal Pt/C electrocatalyst. More importantly, the electrode maintained excellent long-term electrocatalytic performance and structural integrity after 1000 cycles of cyclic voltammetry and 24 h of continuous operation at 100 mA cm^-2. In contrast, the catalytic activity of commercial Pt/C declined substantially, indicating poor stability under alkaline conditions. Therefore, these findings overcome the limitations of WS₂ under alkaline conditions and provide a cost-effective strategy for producing highly active, pH-universal electrocatalysts suitable for water electrolysis and sustainable hydrogen production.