Development of High Performance Proton Exchange Membranes in Fuel Cells Application

• Main Authors: Ye, Yun-Sheng, 葉昀昇
• Other Authors: Chang, Feng-Chih
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/71983928682815607129

博士 === 國立交通大學 === 應用化學研究所 === 98 === Among various types of proton exchange membranes (PEMs) for fuel cells, several nonfluorinated polymeric materials are attracting more attention as alternatives to perfluorinated polymer membranes. The nonfluorinated PEMs can achieve high proton conductivities by introducing high extent of sulfonic acid groups, but tend to deteriorate the mechanical strength and permeability of PEMs simultaneously. The aggregation of conductive sites will cause these PEMs highly swollen or dissolved in aqueous/alcoholic solutions. Crosslinking appears to be an efficient and simple approach to overcome these problems, however, it usually leads to a sacrifice in proton conductivity. In addition, microphase tends separation tends to occur in such crosslinking structure due to contraction of space or incompatibility between hydrophilic (sulfonic acid groups) and hydrophobic (crosslinker) components. The development of more efficient membranes with improved proton conductivity and reduced methanol crossover without detrimentally mechanical and chemical stabilities remains an important challenge. (Part 1) Our aim was to synthesize a novel benzoxazine derivative (SBa) that contains sulfonic acid groups to serve as a cross-linker and also a bridge for ionic clusters in SPEEK membrane. The incorporation of benzoxazine (Ba) or sulfonic acid containing benzoxazine (SBa) as a crosslinking agent in SPEEK proton exchange membrane (PEM) can substantially improve the SPEEK membrane performance. The SPEEK-SBa membranes give higher effective selectivity than corresponding SPEEK-Ba membranes under same crosslinker loading and thus are more suitable to be used in direct methanol fuel cells. (Part 2) The object of this work is the preparation of uracil-termminated telechelic SPI (SPI-U), followed by transforming into noncovalent network membranes by biocomplementary hydrogen bonding recognition in the presence of adenine-based crosslinking agent (SMA-A). The physically minimized network structure suppresses the formation of ionic cluster formation and results in better hydrophilic/hydrophobic distribution. Furthermore, the adenine-based crosslinking agent comprising N-heterocycles structure in the PEMs provides better proton conduction medium and promotes proton hopping under low humidity conditions. These favorable properties allow the application of the crosslinked supramolecular membrane in direct methanol fuel cells (DMFCs). (Part 3) Sulfonated polytriazole-clay (SPTA-clay) nanocomposites have been successfully prepared by in situ polymerization of SPTA using click chemistry in the presence of propargyl-functionality modified clay. The clay layers were found to be exfoliated and well dispersed in the SPTA matrix which resulted in improvement of thermal stability, mechanical strength, methanol permeatbility, water retention, ion channel size, and ionic cluster distribution by the incorporation of a small amount of clay (SPTA 1 and 3). The SPTA-clay nanocomposite membranes by incorporating a small amount of clay in SPTA matrix possess higher selectivity defined as ratio of proton conductivity to methanol permeability, therefore, it had potential usage of a proton exchange membrane (PEM) for direct methanol fuel cells (DMFCs).