Preparation, characterization and proton conductivity of titanium phosphate sulfophenylphosphonate

Titanium phosphate sulfophenylphosphonate, Ti(HPO4)(1.00)(O3PC6H4SO3H)(0.85)(OH)(0.10). nH(2)O was synthesised and characterized by X-ray diffraction, solid state NMR, impedance measurements, TG and DSC analysis. The MAS-NMR Spectrum Of P-31 nucleus presents two resonances characteristic of monohydrogen phosphate and sulfophenylphosphonate groups coordinated to three Ti(IV) atoms through three non-protonated oxygen atoms. Water content, protonic conductivity (sigma) and activation energy for conduction (E-a) were determined in the range 20 to -20 degreesC for materials equilibrated at relative humidity (r.h.) in the range 5-90%. By increasing the number of water molecules per sulfonic group from 2 to 14, sigma rises by 3 orders of magnitude up to about 0.1 S cm(-1), while E-a decreases from 12.6 to 4.3 kcal/mol. Measurements were also carried out at 100 degreesC as a function of relative humidity in the range 30-100%; sigma values higher than 0.1 S cm(-1) were found at r.h. greater than or equal to 65%. The titanium phosphonate was used as a filler of Nafion 1100 hybrid membranes. At 100 degreesC and 80% r.h., the conductivity of the hybrid membranes containing from 5% to 20% phosphonate loading is very similar to that of a Nafion 1100 membrane prepared in-house by casting technique, but it drops by an order of magnitude when the loading is increased to 30%. (C) 2001 Elsevier Science B.V. All rights reserved.