Synergistic modulation of electrochemical and structural properties in agarose: phytagel biopolymer blends as sustainable polymer electrolyte host matrices

The electrochemical stability and charge-transport properties of biopolymer blend films are significantly affected by blend composition, as each polymer component contributes uniquely to segmental mobility, bulk resistance, amorphous structure, and interfacial stability. In this study, salt-free agarose:phytagel (AG:PY) biopolymer blend films were fabricated at various weight ratios using the solution-casting method to identify an optimal host matrix for the development of salt-doped electrolytes. Linear voltammetry measurements showed that the 50:50 mass ratio AG:PY mixture has an electrochemical stability window of 3.25 V, indicating substantial resistance to electrochemical decomposition within the tested potential range. Electrochemical impedance spectro­scopy analysis showed that the 50:50 blend achieved the highest room-temperature conductivity of 1.56 mS cm⁻¹, attributed to reduced bulk resistance and indicating more favourable charge-transport characteristics within the polymer host. X-ray diffraction analysis verified this finding, revealing the lowest crystallinity in the 50:50 mass ratio, suggesting increased amorphous content and greater polymer chain flexibility. Fourier-transform infrared spectroscopy spectral shifts confirmed interactions between the functional groups of agarose and phytagel, indicating improved blend compatibility. Collectively, the 50:50 mass ratio AG:PY blend exhibited the most advantageous combination of electrochemical stability, ionic conductivity, amorphous structure, and polymer interaction, establishing it as a promising sustainable host matrix for future salt-doped biopolymer electrolyte applications.