Proton Conductivity of Simple Ionic Hydroxides Part I: The Proton Conductivities of Al(OH)3, Ca(OH)2, and Mg(OH)2

Abstract Proton conductivity is an outstanding feature of Al(OH) 3 , Mg(OH) 2 , and Ca(OH) 2 powders between room temperature and their respective dehydration temperatures. It can be measured by using Pd‐black electrodes in H 2 either by d.c. conductivity measurements, applying high injection voltages (> 10 4 V/cm), or by thermopotential measurements. Two conductivity mechanisms are observed which can be assigned to proton conductivity σ* H and defect proton conductivity σ H '. The activation energies σ' H are 1.65, 2.0, and 2.2 eV for Al(OH) 3 , Mg(OH) 2 , and Ca(OH) 2 respectively. The activation energies σ H * are lower, ranging between 0.5–1.0 eV. σ' H occurs 20–60 K below the on‐set temperature of dehydration. It is enhanced by the adsorption of CH 3 COOH vapor and suppressed by NH 3 vapor acting as proton donator and proton acceptor or traps respectively.