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Novel Proton Exchange Membranes For Direct Methanol Fuel Cells

Posted on:2007-09-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:S Z RenFull Text:PDF
GTID:1102360182460776Subject:Applied Chemistry
Abstract/Summary:PDF Full Text Request
A fuel cell is an electrochemical device that converts the chemical energy of the fuel and oxidant directly into electrical energy. Direct methanol fuel cell (DMFC) using liquid methanol as fuel, is promising for portable application such as cell phone, laptop computer and other electronics because of its high energy density, simplicity of structure (no additional equipment such as fuel reformer) and maintenance.The proton-exchange membrane in DMFC is one of the key materials, which plays the roles of separating the fuel from the oxidant and conducting proton. In this paper, the efforts are mainly focused on the preparation and characterization of novel proton-exchange membranes, reducing methanol crossover and increasing the tolerance of temperature for DMFC. The results obtained are mainly as follows:1 Sulfonated poly(ether ether ketone) (SPEEK) samples with different degrees sulfonation have been prepared in concentrated sulfuric acid by controlling the reaction time and temperature. With degrees sulfonation of 4550%, the SPEEK membranes exhibit higher mechnical stabilities and proton conductivity. Electrochemical voltammetric studies show that these SPEEK membranes have significant lower methanol crossover than Nafion ?115 membrane.2 The Nafion/SPEEK/Nafion (NSN) composite membranes are prepared by immersing the selected SPEEK into the Nafion-containing casting solution in which the SPEEK polymer is used as barrier layer of methanol. The Nafion layeres of both sides of NSN membrane improve the physical and chemical compatibility between the membrane and catalyst layer, facilitating proton transfer in the membrane-electrode interface. As a result, the resistance of MEA is lowed obviously.3 The blend membranes of SPEEK and polyvinylidene fluoride (PVdF) have been prepared. These membranes exhibit desirable thermal stability in the hot water. The proton conductivity of the blend membranes reduces with the concentration of PVdF increasing. Although the proton conductivity of the SPEEK/PVdF (weight fraction is 9/1) blend membrane is about 1/10 of that of Nafion ?115, the methanol permeabilityof the blend membrane is about 1/20 of that of Nafion 115 under the same test condition.4 Two kinds of organo-inorganic membranes Nafion/S-SiO2 and PVdF/ S-S1O2 have been prepared for the operation of DMFC at temperatures higher than 90°C. (1) The Nafion/S-SiC>2 membrane has good proton conductivity, and the one with the weight composition of 5% Sid prepared from Nafion-TEOS-SCA902 materials shows better performance than Nafion?117 membrane at 120°C. (2) The proton conductivity of PVdF/ S-SiC>2 composite membrane is the highest at 90-100cC among the test temperature range.
Keywords/Search Tags:Direct methanol fuel cell, proton exchange membrane, proton conductivity, methanol crossover, sulfonated poly(ether ether ketone)
PDF Full Text Request
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