A Study On The Modified Sulfonated Poly (Aryl Ether Ketone) Proton Exchange Membranes For DMFC

The development and application of DMFC are restricted by two major technological barriers: one is low methanol oxidation activity for anode catalyst, and the other is methanol crossover from anode to cathode through membrane. Therefore, developing new proton exchange membrane has been very important. In this study, new proton exchange membrane materials with low cost are explored.Sulfonated poly (ether ether ketone) (SPEEK) and sulfonated poly (phthazinone ethet ketone) (SPPEK) membranes are promising alternative to Nafion membrane in DMFC for their high conductivity and better methanol resistance. However, in SPEEK and SPPEK membrane, there exits conflicts among ionic conductivity, methanol resistance and dimensional stability. Generally, high sulfonation degree (DS) offers the membrane with high conductivity, as well as the reduced methanol resistance and dimensional stability, thereby lowered applicable temperature.In order to overcome the conflicts, insolvable 1,2,4-tricarboxybutyl-2- phosphonate zirconium (Zr(PBTC)) with high conductivity and thermal stability was synthesized and incorporated into the SPEEK and SPPEK to fabricate novel composite membranes. Results show that the hydrogen bond happened between Zr(PBTC) and the polymers, which helps to reduce the swelling and methanol permeability of the composite membranes, and improve their dimensional stability without sacrificing conductivity. For the Zr(PBTC)/SPEEK composite membranes, high conductivity can be achieved as the applicable temperature is improved.High temperature DMFC is the new developing direction. For the hygroscopic property of Zr(PBTC), the conductivity of composite membranes under low relative humidity at high temperature(>100℃) was improved efficiently, and so did their vapor-feed DMFC performance at 120℃.In order to improve the properties of SPEEK membrane with high DS, poly(ether sulfone) (PES) was chosen and blended into SPEEK to fabricate PES/SPEEK blend membrane. Results show that the DS of SPEEK affects the microcosmic conformation of blend membrane. By controlling the DS of SPEEK and PES content, the blend membrane with high conductivity and excellent methanol resistance can be fabricated. Furthermore, compared with pristine SPEEK membrane with the same ion-exchange capacity, the blend membrane has better methanol resistance and dimensional stability. Single cell performance experiment indicates that the 30wt.%PES/SPEEK (DS=68.3%) membrane has the better performance than that of Nafion? 115 in DMFC.The performance of direct fuel cells with our novel membranes were tested, using formic acid, isopropanol, ethylene glycol and dimethy ether as fuels respectively.