It was recalled that the microcrystalline -layered hydrated phosphate was a proton conductor, but its conductivity of between 10-5 and 10-6S/cm (at 20C and a relative humidity of 90%) was too low for practical applications. An increase in conductivity was obtained by preparing membranes which were made up of highly-oriented particles (pellicular zirconium phosphate), by intercalating suitable organic molecules (especially hydrazine and pyrazole), or by synthesizing organic derivatives which contained acid ionogenic groups in the interlayer region. The best results were found for Zr alkylsulfophenyl phosphonates which contained -SO3H in the interlayer region. The highest conductivity was of the order of 0.01S/cm, at 100C and a relative humidity of 60%. Non-catalytic metal hydrides such as ZrHx and TiHx were very suitable solid reference electrodes for these materials as they were non-blocking electrodes for protons, but were also insensitive to molecular H.

G.Alberti, M.Casciola, R.Palombari: Elektrokhimiya, 1993, 29[12], 1433-41 (Russian Journal of Electrochemistry, 1993, 29[12], 1257-64)