Preparation And Characterization Of Novel Methanol Resistant Composite Membranes

Proton exchange membrane is one of the key materials in direct methanol fuel cell(DMFC). Preparing good methanol resistant proton exchange membrane is one of the challenging basic subjects for DMFC. Owing to good methanol resistant performance of hydrocarbon membrane, novel proton exchange membranes are fabricated in order to reduce swelling degree, improve methanol resistant and oxidative stability of hydrocarbon membranes with high degree of sulfonation, and structure and performance of novel proton exchange membrane are examined. The innovative achievements obtained are mainly as follows:(1) Hydrocarbon membranes were modified by micro-porous poly(tetrafluoroethylene) (PTFE). Sulfonated poly(ether ether ketone) (SPEEK)/PTFE composite membrane and sulfonated poly(phthalazinone ether sulfone ketone)(SPPESK)/PTFE composite membrane were prepared separately. It was observed by Attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FT-IR) and scanning electron microscope (SEM) that micro-pores were filled with hydrocarbon resin. Compared with pristine membrane, liquid content of composite membrane reduced, swelling degree obviously descended and proton conductivity decreased, and methanol permeability reduced. Proton conductivity and methanol permeability both increased as temperature increased. Hydrocarbon membranes modified by micro-porous PTFE membranes have a potential to be considered for DMFC applications due to its good performance.(2) SPPESK membranes with high degree of sulfonation were modified by the methodology of polymer blend. SPPESK/poly(ether sulfone) (PES) and SPPESK/ poly(vinylidene fluoride)(PVDF) blend membranes were fabricated firstly. It was shown by ATR/FT-IR, SEM and XRD that phase separation existed in blend membranes. Compared with pristine SPPESK membrane, liquid content of blend membranes reduced and swelling degree also decreased at room temperature. Proton conductivity of blend membranes increased as the temperature increased, and reduced as the content of PES (or PVDF) increased. Proton conductivity of blend membranes was higher than 10^-4S/cm at 298K. Methanol permeability of blend membranes also increased as the temperature increased, and reduced as the content of PES (or PVDF) increased. Methanol permeability of blend membranes was about 10^-7 cm² /s. Blend membranes had good methanol resistant performance. It indicates that blend membranes are promising for possible use in DMFC.(3) Multilayer composite membranes were prepared by spraying two Nafion hybrid coated layer with capability of decomposing hydrogen peroxide on hydrocarbon membranes such as SPPESK membrane to prevent hydrocarbon membranes from degradation and keep the good methanol resistant performance. Multilayer composite membranes were prepared firstly including Pt/TiO₂-Nafion | SPPESK | Pt/TiO₂-Nafion(PSPP),Pt/TiO₂-Nafion | SPPESK-PES | Pt/TiO₂-Nafion(PSPSP),MnO_x/C-Nafion | SPPESK | MnO_x/C-Nafion(MSPM) and MnO_x/C-Nafion | SPPESK -PES | MnO_x/C-Nafion (MSPSM) composite membranes. Multilayer composite membranes had similar regularity. It was shown by SEM that catalyst particles were uniformly dispersed in surface of multilayer membrane, multilayer membrane was apparently composed of three layers as a sandwich structure, and the both external layers were with good adhesion to the central layer. It was found by XRD that catalyst particles did not agglomerate together in membrane. Compared with corresponding pristine membrane, proton conductivity of multilayer composite membrane increased, methanol permeability also increased, but methanol resistant performance was still superior to Nafion membrane. Oxidative stability of multilayer composite membrane was improved. Multilayer composite membranes are excellent candidate membrane materials for DMFC applications in virtue of its outstanding performance.There are 88 figures, 2 tables and 125 references in this thesis.