Proton conductivity stability studies by modelling
Square, Lynndle Caroline
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In this thesis, some of the challenges experienced by high temperature polymer electrolyte membrane fuel cells are explored through material modelling techniques. A very important aspect for a fuel cell is that it should have high proton conductivity. As hydrogen enters a fuel cell it gets broken down into its constituents, protons and electrons. The electrons travel to an external load, whilst the protons travel through a diffusive layer, catalyst layer and membrane area, before recombining with oxygen to form water and leave the system. In this particular study, polytetrafluoroethylene and carbon form the diffusive layer, platinum the catalyst and poly(2,5-benzimidazole) doped with phosphoric acid the membrane area. The effects to proton conductivity are investigated as a result of the mixing of materials and adsorption of the phosphoric acid on the platinum active sites. A third study as an alternative avenue for proton conductivity improvements, is also explored. The results from these investigations promotes the idea that polytetrafluoroethylene, which is found in the ionomer layer, should be replaced as its mechanical properties decrease significantly with increase in temperature. Increasing pressure would further promote proton transfer over the doped polymer membrane region.