Structural and ion transport characteristics of transparent proton conducting biopolymer electrolytes based on chitosan and cold water fish skin gelatin

In the current study transparent solid ion conducting biopolymer blend electrolytes consisting of chitosan/cold water fish skin gelatin were prepared utilizing casting methodology. Ammonium thiocyanate (NH₄SCN) salt as a source of proton provider was added to the polymer blends. The ion conductor films were characterized by various methods including XRD, FTIR and EIS. The area under crystalline and amorphous peaks in the XRD patterns were determined and used to estimate the degree of crystallinity. The bands of FTIR pattern associated with anions of the added salt was deconvoluted to determine the fractions of free ions, ion aggregate and ion triplets. Comprehensive investigations of the electrical properties, including DC and AC conductivity, dielectric constant, dielectric loss and electric modulus, were studied to understand the ion conduction mechanism. The ion transport parameters obtained from both EIS and FTIR approach were in good agreement. The shift of peaks to higher frequencies in the loss tangent spectra indicated enhanced ion mobility at shorter time scales. The observation of relaxation peaks in the electric modulus (M'') spectra, which are absent in the dielectric loss (ε'') spectra, underscores the effectiveness of the modulus formalism in suppressing the contribution of electrode polarization and emphasizing bulk relaxation. AC conductivity spectra revealed three distinct conduction regimes, while the Argand plots provided insights into the ion relaxation dynamics within the current solid biopolymer electrolytes. The highest room-temperature ionic conductivity of 1.19 × 10^-5 S/cm was achieved at 40 wt% NH₄SCN, attributed to the optimal balance between free ion concentration and polymer segmental mobility, as revealed by FTIR and EIS analyses.