Superprotonic conductivity in crystalline and amorphous framework materials under anhydrous conditions

Abstract

Fast proton conduction under anhydrous conditions is pivotal for advancing intermediate-temperature (100–300 °C) hydrogen (H₂) energy technologies, such as fuel cells and electrolysers. However, identifying suitable proton conductors for this temperature range remains challenging: the temperature is too high for water-mediated transport but too low for defect-driven conduction. Framework materials, including crystalline and glassy coordination polymers (CPs) or metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs), have emerged as promising candidates, offering tunable structures and unique pathways for anhydrous proton conduction, with some exhibiting “superprotonic-like” conductivity. This review covers the fundamental mechanisms and design principles governing proton transport, emphasising the roles of structural features, defects, dynamic disorder, and functional groups. Emerging materials, including CP/MOF glasses with isotropic structures and COFs with aligned one-dimensional nanoscale channels, are highlighted as promising candidates. Beyond intrinsic conductivity, we evaluate practical considerations essential for device integration, including mechanical processability, thin-film fabrication, long-term thermal and chemical stability, and stimuli-responsive conductivity. The comparative advantages and limitations of CPs/MOFs, their glass derivatives, and COFs are critically analysed. Finally, the review discusses key challenges and future directions toward realising stable, high-performance anhydrous proton conductors for practical hydrogen energy applications.