Light-Enhanced Electrochemical Performance of Fish Waste-Derived Carbon-TiO2 Composites for Sustainable Energy Storage Systems

This work reports on the synthesis and electrochemical investigation of sustainable carbon–TiO2 nanocomposites derived from marine biowaste, designed to elucidate light-assisted charge storage mechanisms in non-aqueous electrolytes. Porous carbons obtained from prawn chitin and blue shark gelatin were decorated in situ with TiO2 nanoparticles using a deep eutectic solvent (DES) as a green synthesis medium. Structural and morphological characterisation revealed that TiO2 incorporation induces significant nanoscale reorganisation of the carbon framework, resulting in hierarchical porosity, increased surface area, and intimate semiconductor–carbon interfaces. Electrochemical evaluation in a three-electrode configuration using an ethaline-based DES electrolyte demonstrated that TiO2 decoration substantially enhances capacitive performance and cycling stability, with the prawn chitin-derived composite achieving a specific capacitance of 54 ± 3 F g−1 and 91% retention after 10,000 cycles. Under illumination, all TiO2-containing composites exhibited a pronounced increase in anodic current response and discharge time, indicating photo-assisted surface charge accumulation. Although the absolute capacitance values are modest compared to those of aqueous supercapacitor systems, the results provide mechanistic insight into the interplay among nanostructure, semiconductor photoactivity, and ion transport in viscous, hydrogen-bonded DES electrolytes. By combining waste-derived carbons, green synthesis routes, and photo-responsive nanostructures, this study highlights a sustainable strategy for developing multifunctional carbon-based nanomaterials with light-modulated electrochemical behaviour.