Proton conduction mechanism and the stability of sol–gel titanium phosphates

Proton conducting sol–gel titanium phosphates were synthesised and characterised with a specific focus on the structural characteristics of the materials which enable proton conductivity and on testing the stability of the chemical groups which facilitate proton conduction under fuel cell conditions. The chemical structure of the materials before and after stability tests was probed using 31P MAS NMR, FTIR and powder X-Ray diffraction. After refluxing the materials in boiling water the conductivity of the titanium phosphates at 100% relative humidity and 100 °C was 0.0044 S cm− 1 and 0.0019 S cm− 1 for the two different samples. 31P MAS NMR and FTIR tests demonstrated that the presence of (H2PO4)− and (HPO4)2− groups in the materials, even after heat treatment, was responsible for the high conductivity of the materials when in the presence of water vapour. Stable solid acid proton conductors such as these have the potential to extend the operating temperature of PEM fuel cells beyond the glass transition temperatures of the current state of the art polymer technology.