| Polymer electrolyte membrane fuel cells (PEMFCs) are ideally suited for future transportation applications because they are lightweight and low-cost. Current PEMFCs use Nafion membranes that require humidification to maintain proton conductivity and cannot work at temperatures above about 80°C. Yet high temperature is crucial in achieving favorable reaction kinetics, high efficiencies, high power densities, and reduced sensitivity to carbon monoxide (CO) poisoning in PEMFCs. Acid-doped Polybenzimidazole (PBI) membranes were found to meet the DOE's targets for high temperature PEMFCs operating under no humidification on both anode and cathode side. The proton conductivity of acid-doped PBI is derived from the acid and thus eliminating the need for water humidification equipment. It is expected that graphene-oxide/PBI (GO/PBI) nanocomposite membranes will further improve the performance of the fuel cell. GO nanosheets can increase proton conductivity of the PBI by forming hydrogen bonds with acid and water. In addition, GO can decrease acid-induced swelling of PBI and increase mechanical strength of PBI membrane. In this study, we incorporated different amounts of GO nanosheets (whose edges are 4--10% oxidized) in PBI solution prior to membrane casting. The nanocomposite membrane was doped in PA (85 wt%) at room temperature. The properties of the nanocomposite membrane were characterized using Acid doping levels, SEM and fuel cell performance. H3PO4 doping level (number of H3PO4 molecules per repeat unit of PBI) was found to increase with increase in acid concentration for all samples and the doping level was maximum for 10% GO/PBI compared to 5% GO/PBI and neat PBI. The membrane electrode assembly (MEA) was prepared by hot-pressing carbon electrodes (20 wt% platinum, loading of 0.5 mg/cm2) on both sides of the GO/PBI nanocomposite membrane. The MEA was evaluated using Scribner Associate's Fuel Cell Testing Module 850e. The polarization curves of the MEAs were obtained with non-humidified H2/air at 70°C, 100°C and 120°C, respectively. At cell potential of 0.6 V, we observed highest current density at 120°C for both 5% GO/PBI and 10% GO/PBI (80 mA/cm2 at 0.6V). At 120°C, 5% GO/PBI exhibited peak power density as high as 92.8 mWcm-2. At 100°C, 10% GO/PBI exhibited peak power density of 121.6 mWcm -2. All this was promising and addition experimental data of the GO/PBI study will be needed in order to optimize the membrane. |
