| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 98 === The aim of this study is to develop a new polymer electrolyte membrane for low temperature proton exchange membrane fuel cells (PEMFCs), which is taken as a possible alternative to the state-of-the-art Nafion membrane having drawbacks such as high cost and high methanol crossover. The low cost, easy film-fabrication and good chemical stability of poly(vinyl alcohol) (PVA) is chosen as the matrix backbone of proton exchange membranes. Dimethylsulfoxid (DMSO) is the cross-linked agent for the reaction.
In addition, 4-Formyl-1,3-Benzenedisulfonic acid disodium salt (DSDSBA) is employed as the sulfonated agent to increase the sulfonic acid groups of PVA. The degree of sulfonation for PVA is controlled with different ratios of 4,4'-oxygen double-phthalic anhydride (4,4'-Oxydiphthalic anhydride, referred to as ODPA) and epoxy resin (Epoxy), and the whole cross-linked-type structure is therefore formed. The corresponding physical and thermal properties are characterized and correlated with its electrochemical properties.
First of all the FTIR spectra provide the evidence for the condensation reaction between hydroxyl groups and aldehyde groups. The TEM images of the prepared membrane indicate better homogeneous dispersion of ion clusters in the polymer matrix for low-degree cross-linked proton exchange membrane (SOE3), which implies a shorter distance in between the ionic clusters. Nevertheless the proton transfer between ionic clusters becomes easier, resulting in an improvement of the bulk ionic conductivity. (2.70 × 10-2 S cm-1@ 20 oC and 0.208 S cm-1@ 70 oC. For high-degree cross-linked exchange membrane (SOE50), hydrophobic/hydrophilic phase separation results in the increase of the proton transfer distance. The ionic conductivity is therefore reduced (2.46 × 10-3 S cm-1@ 20 oC).
The degree of sulfonation of cross-linked structure increases with reducing cross-linked agent. The highest IEC value is up to 1.69 mmole g-1(SOE3) with water content up to 133.07 wt% at room temperature. However the ionic conductivity of the SOE3 membrane is not as good as the prediction, which may be due to the low degree of cross-linked, which the structure was destroyed during activation and only delivers a peak power density of 154 mW cm-2 with wet H2/O2 at 70 oC. The proposed reason can be evidenced by the performance of the membrane (SOE7) of higher degree of cross-linked, which the peak power density can be enhanced up to 443 mW cm-2.
|
|---|
