Synthesis and characterization of triazole based nanocrystalline cellulose solid proton conductors

Abstract

• Successful preparation protocol of the anhydrous nanocomposite proton conductor. • The U.S. Department of Energy durability standards for fuel cell membranes met. • Proton transport determined by the molecular reorientation of the triazole ring. We designed and synthesized new proton-conducting materials (CNC-Tri) based on natural polymer composed of nanocrystalline cellulose (CNC) doped with different concentrations of 1 H -1,2,3 triazole (Tri). The CNC functionalization with Tri does not affect cellulose structure. The material has the form of semitransparent polymer film. The presence of Tri in the CNC matrix was confirmed by the infrared spectra. The activation energies for the desorption of water, triazole evaporation, and the degradation of the CNC matrix, were evaluated. The proton conduction takes place under anhydrous conditions up to 180 °C and the highest value of conductivity is equal to 4.0 × 10 -4 S/m at 160 °C. The behavior of conductivity is consistent with the Grotthuss mechanism and proton transport is conditioned by the triazole ring reorientation revealed by the solid-state 1 H- 13 C CPMAS NMR. CNC-Tri was found to show better thermal properties when compared to the previously tested CNC doped with imidazole (Im), but with lower conductivity. Possible reasons for these differences are discussed in this article.