Proton conductivity of the azole composites based on BEA zeolites with different pore systems

Abstract

There is a need for a stable and economical solid proton-conducting electrolyte capable of operating at elevated temperatures (>373 K), suitable for high-performance hydrogen fuel cells. In its search, imidazole (Im) or 1,2,4-triazole (Tri) is introduced into the channels of BEA zeolites with different porosity (i.e. the conventional microporous BEA (BEA-O) and two hierarchical materials with structural (BEA-C) or interparticle (BEA-TF) mesoporosity). The proton conductivity of obtained composites increases with increasing azole loading and temperature. The generation of mesopores in BEA zeolites leads to a decrease in the activation energy of proton conductivity in composites and favors the dispersion of a large amount of azoles. Zeolites with structural porosity (BEA-C) allow to introduce the highest amount of the azole molecules (0.29 wt% of imidazole), however the highest proton conductivity and the lowest activation energy is recorded for BEA-TF-0.25Im (σ = 5.86 × 10−4 S cm−1 at 393 K). A comparison of azole composites (with Im and Tri) of equal azole loadings shows that imidazole-containing materials exhibit significantly higher proton conductivity, regardless of the type of zeolite matrix.