Defect-engineered La-modified NiCo2O4@SCS composites for high-stability supercapacitor electrodes across acidic, alkaline, and neutral electrolytes

The development of efficient, cost-effective, sustainable, and multifunctional nanomaterials composites is crucial for advancing energy-storage technologies, tunable optoelectronic devices and environmental remediation. In this study, Syzygium cumini seed-derived nanoparticles (SCS NPs) were incorporated into NiCo 2 O 4 and its La-modified derivative (NiCo 2 O 4 @La) through a green hydrothermal synthesis method. This work introduces, for the first time, SCS derived carbonaceous nanoparticles as a multifunctional precursor enabling simultaneous supercapacitive, photocatalytic, and solvatochromic behavior within a single material platform. The excitation-dependent photoluminescence and strong solvatochromism by the SCS NPs indicate their suitability for sensing and light-emitting applications. Structural, morphological, and compositional analysis (XRD, FTIR, SEM-EDX) confirmed the formation of nanostructured spinel ferrites and the successful incorporation of Lanthanum. Electrochemical performance was evaluated in acidic, neutral, and alkaline electrolytes where pristine NiCo 2 O 4 exhibited typical pseudocapacitive behavior that was significantly enhanced upon lanthanum modification. Among the samples the NiCo 2 O 4 @La composite delivered the highest specific capacitance of 1145.69 Fg −1 in alkaline electrolyte (1 M KOH, pH ≈ 14). The electrode also demonstrated a notable cyclic activation of ̴ 125–126% of its initial value after 1000 cycles in HCl and maintained this performance up to 10,000 cycles, indicating sustained electrochemical activation. The multifunctional potential of the synthesized materials was further demonstrated through sunlight driven photocatalytic degradation studies. Pristine NiCo 2 O 4 achieved 79.40% degradation of methylene blue, while La doped composites exhibited significantly higher degradation efficiency of 90.43%. These findings present a green and effective strategy for developing multifunctional NiCo 2 O 4 based composites with promising applications in energy storage, photocatalysis and optical sensing technologies.