کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
9685016 | 1456220 | 2005 | 6 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
An NMR study of methanol diffusion in polymer electrolyte fuel cell membranes
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
مهندسی شیمی
تصفیه و جداسازی
پیش نمایش صفحه اول مقاله
![عکس صفحه اول مقاله: An NMR study of methanol diffusion in polymer electrolyte fuel cell membranes An NMR study of methanol diffusion in polymer electrolyte fuel cell membranes](/preview/png/9685016.png)
چکیده انگلیسی
Methanol diffusion in two polymer electrolyte membranes, Nafion 117 and BPSH 40 (a 40% disulfonated wholly aromatic polyarylene ether sulfone), was measured using a modified pulsed field gradient NMR method. This method allowed for the diffusion coefficient of methanol within the membrane to be determined while immersed in a methanol solution of known concentration. A second set of gradient pulses suppressed the signal from the solvent in solution, thus allowing the methanol within the membrane to be monitored unambiguously. Over a methanol concentration range of 0.5-8 M, methanol diffusion coefficients in Nafion 117 were found to increase from 2.9 Ã 10â6 to 4.0 Ã 10â6 cm2 sâ1. For BPSH 40, the diffusion coefficient dropped significantly over the same concentration range, from 7.7 Ã 10â6 to 2.5 Ã 10â6cm2 sâ1. The difference in diffusion behavior is largely related to the amount of solvent sorbed by the membranes. Increasing the methanol concentration results in an increase in solvent uptake for Nafion 117, while BPSH 40 actually excludes the solvent at higher concentrations. In contrast, diffusion of methanol measured via permeability measurements (assuming a partition coefficient of 1) was lower (1.3 Ã 10â6 and 6.4 Ã 10â7 cm2 sâ1 for Nafion 117 and BPSH 40 respectively) and showed no concentration dependence. The differences observed between the two techniques are related to the length scale over which diffusion is monitored and the partition coefficient, or solubility, of methanol in the membranes as a function of concentration. For the permeability measurements, this length is equal to the thickness of the membrane (178 and 132 μm for Nafion 117 and BPSH 40 respectively) whereas the NMR method observes diffusion over a length of approximately 4-8 μm. Regardless of the measurement technique, BPSH 40 is a greater barrier to methanol permeability at high methanol concentrations.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Membrane Science - Volume 250, Issues 1â2, 15 March 2005, Pages 183-188
Journal: Journal of Membrane Science - Volume 250, Issues 1â2, 15 March 2005, Pages 183-188
نویسندگان
Hayley A. Every, Michael A. Hickner, James E. McGrath, Thomas A. Jr.,