The Study On Ultra-Thin,Flexible,Self-Standing Composite Proton Exchange Membranes

Proton exchange membrane was the core material for fuel cell. Polymer electrolyte membranes ( typically for Nafion?, Dupont company, USA) had high proton conductivity and enough chemical stability, so they were widely used in low temperature fuel cell ( PEMFCs and DMFCs ). However, because of water absorbing and dehydration at working condition, it was easy to deform for these membranes, which caused the fuel penetration and then reduced the overall efficiency of the the fuel cell, particularly for DMFCs. Because inorganic proton conductive membrane had two advantages of low cost and high size stability, they were considered to be the ideal substitute for polymer electrolyte membrane.In this thesis, ultra-thin, flexible, self-supporting proton conductive membranes by constructing organic / inorganic / organic sandwich structure have been prepared. A thickness of 500nm Polyethylenimine(PEI)-Poly(o-cresyl glycidyl ether)-co-formaldehyde (PCGF)/P2O5-SiO₂/PEI-PCGF composite proton conducting membrane was successfully prepared by introducing the sacrificial PSS layer through Spin-coating method. Its proton conductivity was 10-5Scm^-1. A thickness of 960nm proton conduction Nafion / P2O5-SiO₂ / Nafion composite membranes was prepared by spin-coating method. It was notable that the preparation of Nafion / P2O5-SiO₂ / Nafion composite membranes did not need sacrificial layer. Nafion / P2O5-SiO₂ / Nafion composite membranes had sufficient proton conductivity ( 7.6×10-4Scm^-1 ) and very low methanol permeability ( 1×10-8cm²s^-1 ).In this thesis, a preliminary study on the intermediate temperature proton exchange membrane has been carried out. A thickness of 800nm CsH2PO4 / SiO₂ inorganic composite proton exchange membrane was prepared through the spin-coating method, its proton conductance and area specific resistivity (ASR) were tested from 80℃to 260℃temperature range, and at 160℃, its ASR reached a minimum, 0.1Ωcm².In this thesis, using sol gel method, by adding various nonionic surfactant as template, dry silica xerogels with microporous and mesoporous structure have been prepared. The relationship of pore structures and vapor adsorption-desorption properties of two kinds of silica gels were studied. Dry silica xerogels with microporous structure had high water retention characteristics, so they could be thought as ideal materials of proton exchange membranes.