Promising TiOSO₄ composite polybenzimidazole-based membranes for high temperature PEMFCs

Composite membranes were prepared from poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (polybenzimidazole: PBI), and titanium oxysulfate (TiOSO₄) with the aim of using these systems as electrolytes in high temperature proton exchange membrane fuel cells (PEMFCs). The presence of TiOSO₄ was confirmed by using Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analyses. Energy-dispersive X-ray spectroscopy (EDS) mapping of titanium and sulphur revealed that the titanium salt was homogenously distributed on the surface of the membrane. The presence of the titanium salt did not change the thermal behaviour of the doped membranes. The composite membrane was used as an electrolyte in an actual fuel cell operating at 150 °C. The cell showed a lower performance than a cell operated with the standard PBI membrane, but this was attributable to the electrodes rather than the membrane. The most remarkable result was that the fuel cell operating with the composite membrane showed the best stability during the preliminary long-term test because of the better acid retention capability of these titanium-based materials.