ENHANCEMENT OF THE PROTONIC CONDUCTIVITY OF ALPHA-M(IV)(HPO4)2.H2O,M(IV)=ZR,SN, BY INTERCALATION OF THE ALUMINUM KEGGIN ION, [AL13O4(OH)24.12H2O]7+

Expansion of the alpha-structured metal (IV) hydrogen phosphates by the aluminium Keggin ion [Al13O4(OH)24.l2H2O]7+ (''Al13'') has been performed by a method involving preswelling of the layered substrate by medium or long chain amines, followed by exchange with the inorganic cation for the interlayer alkylammonium ion. Solid state Al-27 MAS NMR has been used to show, for the first time, the presence of the Al13 species in the intercalation compounds. Impedance measurements on Al13-ZrP and Al13-SnP show significant conductivity enhancement compared with the pristine metal phosphates. The conductivity of both materials increases with temperature and with relative humidity (RH), indicative examples being: Al13-ZrP 3 x 10(-4) S cm-1 at 25-degrees-C/60% RH; Al13-SnP 3 x 10(-2) S cm-1 at 75-degrees-C/100% RH. These values are sufficiently high that their use as electrolytes in solid state fuel cells can be envisaged. dc measurement has confirmed the origin of the conductivity to be entirely protonic in nature.