Protonconducting

Proton-conducting materials are substances that enable the transport of protons (H+) through solid or liquid media, supporting protonic current in electrochemical devices. Proton transport occurs mainly via two mechanisms: the Grotthuss mechanism, where protons hop along a network of hydrogen bonds, and the vehicle mechanism, in which protons are carried by diffusing species such as hydronium or water. The rate of conduction depends on temperature, humidity, and the chemical structure that provides proton donors and a connected hydrogen-bond network.

Representative classes include polymeric electrolytes, inorganic/ceramic conductors, solid acids, and hybrid systems. Polymeric proton conductors, such as sulfonated polymers including Nafion, conduct protons through fixed acid groups and absorbed water. High-temperature polymers like phosphoric-acid-doped polybenzimidazole extend operation to elevated temperatures with reduced humidity. Inorganic conductors, including doped perovskites (for example BaZrO3 and BaCeO3), support proton hopping in hydrated lattices. Solid acids, such as CsHSO4 and phosphoric-acid-based systems, can show high conductivity near phase transitions. Hybrid approaches, including metal–organic frameworks and composite electrolytes, aim to combine processability with robust proton transport.

Key properties for proton-conducting materials include proton conductivity (typically measured in siemens per centimeter), temperature and humidity dependence, chemical stability, and mechanical integrity. Conductivity values span several orders of magnitude across classes, with high performance often contingent on maintaining a hydrated network and chemical compatibility with the operating environment.

Applications center on proton-exchange membrane technologies: proton-exchange membrane fuel cells, electrolyzers, and related sensors and separations. Challenges include maintaining high conductivity across wide temperature and humidity ranges, ensuring long-term stability, and achieving cost-effective scalable synthesis. Continued research seeks to improve conductivity, durability, and compatibility with practical devices.