| Summary: | 碩士 === 雲林科技大學 === 化學工程與材料工程研究所 === 96 === Part I. The perfluorinated ionomer membrane (Nafion®115) used as the electrolyte material, The effects of metal ions、temperature and hydrogen peroxide concentration were investigated membrane degradation rate and the effect of deteriorated membrane properties such as chemical structure, thermal properties mechanical strength and proton conductivity etc. Ion Chromatography exhibits the presence of Fe2+ and Cu2+ ions enhanced the rate of membrane degradation. And high temperature, high hydrogen peroxide concentration and ferrous ions increased membrane degradation rate. The result of FTIR measurement of deteriorated membrane revealed that side chains absorbed peak strength apparent decreased, most probably because radicals attacked the side chain of Nafion®115. AC Impedance revealed the impedance enhanced with the increasing of degradation time. It is because that sulfonic acid contents reduced leads to proton conductivity decreased. The methanol permeability and water uptake increased with increasing degradation time. SEM revealed the breakdown of the membrane surface started from the formation of small bubbles and the bubbles gradually grew to the pinholes.
TGA and DSC shown ionic clusters oxidation by H2O2 at the primary stage, which ionic clusters hydrogen bonding interaction decrease and C-S bond decomposed easily, which leads to decomposition temperature of sulfonate groups and ionic clusters transition temperature decrease. Displacement of H+ reacting temperature (80℃) exactly to near ionic clusters transition temperature at a later stage, resulting in a part of ionic clusters enough be ability to molecular rearrangement, which decomposition temperature of sulfonate groups and ionic clusters transition temperature increased. DMA data shows that because of free radicals attack the membrane molecular chain to make the macromolecular chain breaking, resulting in the membrane molecular weight and store modulus decreased at the primary stage. The decomposition of molecular chain segment of macromolecular side chain, then the crystallinity of Nafion membrane and store modulus increased with amorphous side chain reduced. The crystalline domains melting、decomposition temperature of main chain and α glass transition temperature had no change with degradation time, which suggested the C-F composition of main chain have strong covalent bonds and have not suffered from chemical break easily.
This paper also TGA/MS was investigated, it is possible to suggest the Nafion membrane thermal degradation process. The first temperature low 240℃ can be attributed to the loss of residual water in the Nafion membrane. The decomposition temperature approached 280℃, the Nafion loses its the sulfonic acid groups and the release of sulfur dioxide, then side chain continuous decomposed the product of SOF2、CXFY、CXFYOZ、COF、COF2. Finally, as the decomposition temperature above 500℃, it began the thermal decomposition of main chain and the released of CXFY gas. At the same time, the thermal decomposition temperature between 300℃ and 600℃, the formation of CO2 and HF, due to a secondary reaction of CF2O and water.
Part II. Hydrocarbon proton exchange membrane base on polyvinyl alcohol (S20P80) was investigated. S20P80 membrane indicates 20% Sulfosuccinic acid as crosslinked agent and 80% poly(syrene sulfonic acid-co-male acid (PSSA-co-MA) as supply with the proton source. First of all, effect of the S20P80 membrane hydrolysis with different degradation temperature. FTIR study, At high temperature, the membrane suffers from hydrolysis easily, which it makes ester group chain scission and crosslink structure is broken, and the part of PSSA-MA flowed away, then water solution test result found electrode conductivity increased and pH value decreased.
The effect of S20P80 membrane degradation with hydrogen peroxide was investigated: FTIR results revealed, radicals attack ester group、aromatic and vinyl on the point of hydrogen atom at room temperature, resulting in C-O、SO3H and aromatic characteristic peak intensity decreased. The temperature increased, accelerating radicals attack on the membrane, leading to opposite of characteristic peak strong decreased. As the replacement of ferrous ions, the result is similar to above. In high temperature and high concentration condition, the membrane weight loss, water uptake and methanol permeability raised, due to the membrane crosslink structure was broken. XRD and FTIR exhibited that degradation temperature 35℃, the membrane crystalline decreased, and OH absorption peak moved to high waveumber. Degradation temperature increased, the membrane little increased and OH absorption peak moved to low waveumber, due to crosslink structure was broken and PVA crystalline decreased, resulting in PVA molecular chain more easy to move. With the water (plasticize effect), the glass transition temperature great decreased. As PVA glass transition temperature is near to degradation temperature, which accelerated PVA molecular chain a part of molecular rearrangement. Mechanical tensile and DMA results, degradation temperature increased, the Young’s modulus、tensile strength、elongation and store modulus decreased.
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