Energy storage device face several fundamental challenges in the present and the future, including the need for improved performance and safety benchmarks that take into account the introduction of environmentally friendly materials and creation of upgradable and easily recyclable products. To prevent environmental contamination problems, biopolymers are believed to be a key component on emerging new ways to overcome recent synthetic polymer electrolytes. Thus, alginate polymers have a great potential for development into solid biopolymer electrolytes (SBEs). The aims of this research are to develop and characterize the feasibility of alginate-based SBE systems doped with varying compositions of glycolic acid (GA) (System I) and plasticized with varying compositions of ethylene carbonate (EC) (System II) to be applied in an electrical double layer capacitor (EDLC). The solution casting technique was used to prepare both systems that possess flexible, transparent, and free-standing films. The lone pair oxygen from the host polymer (alginate) interacted with the H+ ion from the carboxylate group (COO----H+) of the charge carrier, which was shown by the shifting and disappearance of the peak in the Fourier-transform infrared spectroscopy (FTIR) analysis. The x-ray diffraction (XRD) peak intensity decreased gradually for both systems as the amorphous nature of the SBEs improved, demonstrating that movement of H+ ion through polymer matrix, lowered the degree of crystallinity (Xc) when introduced with GA and EC. The most amorphous SBEs discovered for System I and System II were composed of 20 wt. % GA (Xc = 26.99 %) and 5 wt. % EC (Xc = 18.85 %), respectively with smooth and homogeneous morphology without phase separation. Adding EC into the alginate-GA SBEs increased the Tg value due to the EC structure’s cyclic compound, which entangled the polymer chain leading to reduced flexibility in the complexes. Thermal stability was determined using thermogravimetric analysis (TGA) while the maximum decomposition temperature was elevated to 300 °C. These findings imply that the SBEs system is thermally stable and capable of meeting the device requirements. In System I, the optimum ionic conductivity (σ) of 5.32 x 10-4 S cm-1 at ambient temperature was achieved by adding 20 wt. % GA (GA-4). Meanwhile, the optimum ionic conductivity (σ) for System II (9.06 x 10-4 S cm-1) at ambient temperature was achieved by adding 6 wt. % EC (EC-3). Both SBEs systems obeyed the Arrhenius behaviour completely, with acceptable regression values (R2 ~ 1). The FTIR deconvolution approach was used to compute ionic transport parameters for both systems. The σ of both systems were predominantly influenced by ionic mobility (μ) and diffusion coefficient number (D) of H+ ion. Transference number measurement (TNM) was used to determine cation transference number (tн+), which was raised from 0.22 (GA-4) to 0.45 (EC-3). This proved that the plasticization effect successfully promoted greater H+ dissociation from the acidic salt which was utilized in this study. The linear sweep voltammetry (LSV) analysis demonstrated that Systems I and II were relatively stable at room temperature. For the EDLC cell fabrication, the highest ionic conducting sample from each SBEs was used. The plasticized SBEs, represented by System II Cell, outperformed the un-plasticized cell (System I Cell) in terms of power density (Pd), energy density (Ed), specific capacitance (Csp) and equivalent series resistance (ESR), which were improved by a higher current density that can withstand 10,000 cycles. These findings suggest that alginate-based SBE systems offer a significant potential for EDLC applications
