This work demonstrates, for the first time, NiSO₄ quantum dots uniformly attached to g-C₃N₄ nanosheets. It reveals sulfate-driven enhancement of Ni2+/Ni3+ redox pseudocapacitance in alkaline media, activating g-C₃N₄ via NiSO₄(1-x)@g-C₃N₄(x) (x = 1.0, 0.9, 0.5, 0.2) systematically tuning loading effects. XRD confirms the coexistence of anhydrous NiSO₄ and NiSO₄·6H₂O phases with average crystallite size between 7 and 11 nm. HRTEM verifies uniformly distributed NiSO₄ quantum dots with an average size of ∼7 nm (2–10 nm distribution), and XPS confirms Ni2+ oxysulfate species strongly bound to g-C₃N₄ with abundant accessible redox sites for Ni2+/Ni3+ ions. For the optimized nanostructures with x = 0.2 and 0.5, higher charge-storage capacitance is observed, with maximal specific capacitances of 503.8 F g−1 at a scan rate of 2 mV s−1 and 492.9 F g−1 at a current density of 0.5 A g−1. Trasatti and Randles-Sevcik analyses EIS reveals dominant pseudocapacitive contributions. Furthermore, full cell exhibits a capacitance of 39.4 F g−1 at 0.25 A g−1, establishing NiSO₄ quantum-dot decoration as the first sulfate-driven pseudocapacitance strategy for activating g-C₃N₄ and providing new mechanistic insight into -enhanced Ni redox kinetics for high-performance supercapacitor applications. Post-cycling analyses reveal gradual leaching from NiSO₄ QDs into the alkaline media, forming Ni-oxide/hydroxide phases while preserving Ni2+/Ni3+ redox activity, demonstrating sulfates as initial conductivity enhancers with stable Ni-phases sustaining long-term pseudocapacitance.
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