Characterization Of Sulfonated Poly(Ether Ether Ketone)/Hydrophilic Polytetrafluoroethylene Composite Membranes For Fuel Cell Applications

Proton Exchange Membrane Fuel Cell (PEMFC) is an electrochemical devicewhich directly converts the chemical energy of the fuel and oxidant into electricalenergy, and the fuel of PEMFC is H₂ or methanol. PEMFC has been considered as apromising alternative energy source because of their high efficiency and lowenvironmental impact. The proton-exchange membrane in PEMFC is one of the keymaterials, which plays the roles of separating the fuel from the oxidant andconducting proton. The PEMs (Proton Exchange Membrane) based on theperfluorosulfonic polymers have been used for practical PEMFC systems. However,further progress in this region has been restricted by the insufficient performance ofthese membranes. In addition to the high cost, these perfluorinated polymerelectrolytes could not be used above 100℃. Above this temperature,dehumidification of the hydrophobic perfluorinated matrix causes a dramaticdecrease in the proton conductivity. Another important drawback is related to theinability of these membranes for the application in direct methanol fuel cell (DMFC),considered as an attractive option for the automotive industry, due to their highmethanol crossover. Therefore, it is very important to empolder some new PEMmaterials with low price and good performance. In this paper, we put forward anovel technics to prepare composite membrane, which is composited by fillingSPEEK resin into the pores of hydrophilic PTFE. The structure and performance ofthe composite membrane were also analyzed.Sulfonated poly (ether ether ketone) samples with different sulfonation degreeswere prepared in concentrated sulfuric acid by controlling the reaction time andtemperature. The porous membrane of PTFE was proceed with hydrophilictreatment by chemical modifying method. The porous membrane of H-PTFE(Hydrophilic PTFE) was filled sufficiently with SPEEK resin by pressure differencetechnology. The SPEEK/H-PTFE composite membranes exhibit better water uptakerate, swelling rate and higher mechnical stabilities than SPEEK films with samesulfonation degrees. The result of single cell voltammetry test indicates that theperformance of the cell improves with the increase of the hole rate, the sulfonation degrees and the decrease of thickness on H-PTFE membrane. A single cellassembled with the composite membrane (DS=0.68 15μm) was operated with acurrent density of 600mA/cm² for 200 hours, and the voltage of the cell has nosignificant decrease, which indicates that the composite membrane is stable underthe cell operating condition. After operated for 200 hours, the electrodes did not peeloff from the composite membrane. All of above indicate that the compositemembrane can be applied to PEMFC. With the increase of SPEEK/H-PTFEsulfonation degree, the crossover rate of methanol increase at room temperature. Thecrossover rate of methanol is 5.2×10^-7cm²/s with a 75% sulfonation degree of theSPEEK resin. With the increase of operating temperature, the crossover rate ofmethanol also increase. Electrochemical voltammetric studies show that theseSPEEK/H-PTFE composite membranes have significant low methanol crossoverrate.