Imidazole-Doped Chitin Oligosaccharides and Chitosan Biopolymer Composites for Anhydrous High-Temperature Proton Conduction

Imidazole-doped chitin oligosaccharide (CHOS-Im) and chitosan (Chitosan-Im) biopolymer composites were investigated as model systems for anhydrous high-temperature proton conduction. Solid-state films were characterized by thermogravimetric analysis (TGA/DTG), electrical impedance spectroscopy (EIS), and variable-temperature 13C and 15N CP MAS NMR. Proton conductivity increases markedly above 100 °C under dry N2, reaching 3 × 10–3 S/m at 150 °C for CHOS-Im and 1 × 10–2 S/m at 130 °C for Chitosan-Im. Solid-state NMR provides direct evidence for proton exchange between imidazole and the polymer functional groups and reveals that thermally activated imidazole reorientation is a key dynamic process governing charge transport. The lower activation energy and increased molecular mobility observed in Chitosan-Im are attributed to acetic acid-induced plasticization, which increases proton accessibility and promotes hydrogen bond network dynamics. These results indicate a direct link between local molecular dynamics and macroscopic proton conductivity under anhydrous high-temperature conditions.