A proton conductor is an electrolyte, typically a solid electrolyte, in which H+ are the primary charge carriers.
Composition
For practical applications, proton conductors are usually solid materials. Typical materials are polymers or ceramic. Typically, the pores in practical materials are small such that protons dominate direct current and transport of bulk solvent is prevented. Ice is a proton conductor through the Grotthuss mechanism, albeit a relatively poor one.
Proton conduction was first suggested by Alfred Rene Jean Paul Ubbelohde and S. E. Rogers. in 1950.
Proton conduction has also been observed in the new type of proton conductors for fuel cells - protic organic ionic plastic crystals (POIPCs), such as 1,2,4-triazolium perfluorobutanesulfonate and imidazolium methanesulfonate. In particular, a high ionic conductivity of 10 mS/cm is reached at 185 °C in the plastic phase of imidazolium methanesulfonate.
When in the form of thin membranes, proton conductors are an essential part of small, inexpensive fuel cells. The polymer nafion is a typical proton conductor in fuel cells. A jelly-like substance similar to navion residing in the Ampullae of Lorenzini of sharks has been found to have proton conductivity only slightly lower than navion.
High proton conductivity has been reported among alkaline-earth cerates and zirconate based perovskite materials such as acceptor doped SrCeO3, BaCeO3 and BaZrO3. Relatively high proton conductivity has also been found in rare-earth ortho-niobates and ortho-tantalates as well as rare-earth tungstates.