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.