Polybenzimidazoles (PBI) Membranes and Platinum - Cobalt/Carbon (Pt-Co/C) Alloy Catalysts for High Temperature Proton Exchange Membrane Fuel Cells (HT-PEMFCs)

Proton conducting phosphoric acid doped polybenzimidazole membranes for High Temperature PEM fuel cells (HT-PEMFCs) were prepared and tested in the temperature range 140-200°C. To study the effect of PBI content on the performance of fuel cells, different electrodes were prepared by varying the %wt. of PBI from 1 to 30. Performance of fuel cell with different electrodes was studied with polarization curves. AC impedance spectroscopy was used to estimate the cathode ionic resistance and mass transfer resistances of cathode. Cyclic voltammetry(CV) and Linear Sweep Voltametry(LSV) were used to calculate the electrochemical active surface area of the catalyst and fuel crossover respectively. When PBI content was raised from 1 to 10 wt. %, at 180°C the ionic resistance decreased from 0.29 to 0.14 Ohm-cm2 and further increase of PBI content has no effect. In the case of 5 wt. % electrodes, a 3-fold increase in the cathode resistance was observed when the temperature was raised from 140 to 180oC. When PBI concentration increased from 5 to 30 wt. %, Warburg impedance increased 2.5 times reaching values as high as 6 Ohm-cm2. Warburg impedance was also reduced by an increase in temperature. Analysis of polarization data revealed that best performance was obtained with electrodes having 5 wt. % PBI at 180°C.;For higher electrocatalytic activities towards the oxygen reduction reaction (ORR) Carbon-supported Pt-Co alloy catalysts of varying Pt:Co atomic rations of 1:1 to 4:1 were prepared by borohydride reduction method. These were characterized and tested in PEMFCs. Face centered cubic structure of Pt is evident from XRD. These catalysts were used as cathode in the Polybenizimidazoles-based MEA and tested at 160 and 180°C.The results indicate the good performance of Pt-Co alloys than that of Pt under the PEM fuel cell conditions. Pt-Co (1:1)/C and Pt-Co (2:1)/C exhibited good fuel cell performances. Durability tests also indicated the good stability of Pt-Co (1:1)/C and Pt-Co (2:1)/C compared to Pt/C.