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Perfluororated proton exchange membrane Nafion is the mostly used type of ion exchange membrane in fuel cells. Over the past decades, various studies have been carried out on their structures at different scales, proton conduction mechanism, electrochemical performance, thermal and mechanical properties etc, but many problems are still open, such as the precise picture of proton conduction, degradation and aging of the membrane, even the distribution of pores and channels etc. Because membrane degradation is crucial for practical operation of fuel cells and its understanding offers insights for developing new generation membranes, more and more attention is paid to this issue. Methanol is used in direct methanol fuel cells (DMFC) and alcohols are sensitive to the structure and dynamics of Nafion. In addition, aqueous solutions of alcohols are known to have special mesoscopic structures. Therefore, this thesis employs the aqueous solution of methanol as a probe and investigate the physicochemical mechanism of the degradation of Nafion 117 by means of solid state NMR spectra, relaxation, exchange, diffusion and micro-imaging. A series of methanol-water binary solution samples covering the entire range of concentration (0% ~ 99%(w/w)) were prepared and the 1H,17O NMR spectra,T1¡BT2, exchange rate, diffusion coefficient of these samples in bulk and in Nafion were measured. In bulk samples, the OH peak of water and that of methanol could be resolved with concentration at or above 40% (w/w). The microscopic and mesoscopic structure and dynamics of methanol solutions (in bulk) were subsequently investigated with variable temperature and diffusion experiments. By measuring the variable temperature 1H and 17O spectra, T1, T2, diffusion and micro-images of the methanol solutions in Nafion 117, the structure and dynamics of methanol solutions in bulk and in Nafion 117 were then compared. Based on these data, the structure an dynamics of Nafion 117 and the correlations between methanol and proton conduction and membrane degradation are discussed. The results of this work provides valuable reference for further understanding the structure, dynamics and degradation of Nafion and their relationship with proton conduction.

Ecosystem degradation in Iceland has been severe since man arrived 1100 years ago. Birch woodlands cover has declined from 25% of the land area, to only 1%. The deforestation is considered to be the initial stage in the land degradation process, followed by surface destabilization, and later erosion. The objective of this study was to quantify and evaluate factors that contribute to the early stages of land degradation in Icelandic ecosystems. Specific objectives were to improve our understanding of how livestock grazing might initiate early degradation stages, elucidate field-based landscape metrics useful for characterizing degradation stages, and to determine if landscape metrics obtained from remote sensing data can be used to detect landscape structure changes and identify degraded and at risk rangelands in real time over extensive and remote areas. A State-and-Transition conceptual model was constructed for the experimental area to identify potential key processes in the degradation sequence, and to formalize research questions. Experimental plots were established in five plant community types representing a space-for-time degradation sequence. Birch seedling (Betula pubescens Ehrh.) growth and survival was reduced with repeated clipping treatment applied to simulate browsing, but the amount of decline varied with plant community type. This suggests that continuous grazing may contribute to deforestation, as regeneration will be reduced over time. Intense grazing treatments, simulating both grazing and trampling, increased surface instability and soil loss compared to grazing only or control, suggesting that intense grazing may contribute to surface destabilization and therefore to land degradation. Erosion appeared to be active in the most intense treatments, also within the woodlands. The data indicate that the woodlands may have lower resilience than the other plant communities as treatment effects appeared quicker there. The woodlands may thus be particularly vulnerable to intense grazing. The landscape metrics used to quantify changes in landscape surface properties over a 51 year period yielded inconclusive results, either because of data limitations or because of non-detectable erosion activity. The results do generally support the proposed S&T model for the experimental area. It is concluded that grazing may contribute to woodland decline, and intensify degradation processes.