Protonic conductivity of layered zirconium phosphonates containing -SO3H groups .3. Preparation and characterization of gamma-zirconium sulfoaryl phosphonates

Five gamma-layered zirconium phosphonates containing sulfophenyl, sulfobenzyl, as well as mono- and di-fluorinated sulfobenzyl groups in the interlayer region, have been prepared by topotactic exchange starting from gamma-zirconium phosphate in the hydrogen form. They were characterised for their composition, interlayer distance and thermal stability. Conductivity measurements were carried out at 100 degrees C as a function of relative humidity. At 5% relative humidity, the ac conductivity extends over the range 10(-5)-10(-6) S cm(-1) the sulfophenyl and the difluoro-sulfobenzyl phosphonates being the most conductive compounds. However, the conductivities of all five compounds become progressively closer and tend to the same upper limit as the relative humidity approaches 100%. The highest conductivity (0.05 S cm(-1)) was measured for gamma-zirconium sulfophenyl phosphonate at 100 degrees C and 95% relative humidity. Combined ac/dc measurements, carried out on the latter compound at 100 degrees C and 47% relative humidity, have proved the conduction process to be of the protonic type. Considerations based on conductivity and surface area data indicate that the conduction process is mainly due to bulk proton transport.