The source of conductivity and proton dynamics study in TEMPO-oxidized cellulose doped with various heterocyclic molecules

Our manuscript focuses on the study of proton conductivity phenomena caused by a high degree of mobility and dynamic movement of protons that occur in some hybrid composites obtained from TEMPO oxidized cellulose doped with three heterocyclic compounds. The first stage consists in the preparation of the organic matrix, the reaction conditions being chosen so as to allow the incorporation of as many carboxyl groups as possible. The numerous COOH groups, introduced after oxidation in the cellulose backbone, allow the successful attachment of N-base molecules, such as: 1-hydroxybenzotriazole (HBT), imidazole (IM), and 7-azaindole (AI). The as prepared cellulose-based powder composites (OxC-HBT, OxC-IM, OxC-AI) were firstly analyzed using extensive FTIR study. Different explanations regarding the nature and the source of the proton conductivity were proposed based on the FTIR experiments. A good thermal stability of the prepared samples has been revealed by thermal analyses. Moreover, the composites showed good values of proton conductivity both at lower and higher temperatures, for example, under anhydrous conditions, the proton conductivity has been found equal to 1.2 × 10−1 S/m for the composite containing IM and 2.3 × 10−2 S/m for the hybrid material containing HBT. The activation energies were also calculated and discussed for each heterocyclic dopant. The use of derivatives of natural polymers, i.e. TEMPO oxidized cellulose, create the prerequisite conditions for cheap, non-hazardous and environmentally safety approaches to find new biopolymer composites materials with proton conductive properties with potential application in fuel cell technology.