Cu(II) coordination complex doped PVA/NaAlg polymer blend as a redox active composite electrodes for energy storage devices

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Polymer-based composite electrodes with tunable electrochemical properties are of growing interest for energy storage applications. In this work, flexible PVA/NaAlg polymer blend films were modified via molecular coordination doping using a Cu(II) coordination complex as filler to elucidate the structure–property-performance relationship governing their electrochemical behavior. The induced increase in the amorphous structure of the PVA/NaAlg mix and the development of intermolecular contacts between the host polymer and the additional filler were shown by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectra. The direct and indirect band gaps decreased from 4.75 to 3.50 eV and from 4.49 to 3.11 eV, respectively, as filler loading increased, according to UV–visible spectroscopy. Cyclic voltammetry (CV) measurements in acidic electrolyte demonstrated a transition from weakly capacitive behavior in the pristine blend to a mixed electric double-layer/pseudocapacitive response in the doped films, driven by redox-active coordination centers. The specific capacitance, calculated from CV curves, increased markedly upon Cu(II) complex incorporation and decreased with increasing scan rate, consistent with diffusion and kinetics-limited pseudocapacitive systems. The 1.00 wt% Cu(II) doped film exhibited the highest capacitance, while intermediate loadings showed improved rate capability. Overall, the results highlight coordination-based molecular doping as an effective strategy for tailoring the structural, electronic, and electrochemical properties of polymer composites for energy storage applications.