Proton conducting membranes composed of hydronium alunite

High proton conductivity, of 3 × 10−4 ohm−1 cm−1 at 20°C, has been found in hydrated pressed discs of hydronium alunite, of formula (H3O)Al3(SO4)2(OH)6. The conduction occurs within the hydrated interparticle regions into which protons have been donated, probably from the H3O+ groups exposed on the crystal surfaces. The general utility of the membranes is discussed.