کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1288840 973275 2011 7 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Estimation of hydrogen crossover through Nafion® membranes in PEMFCs
موضوعات مرتبط
مهندسی و علوم پایه شیمی الکتروشیمی
پیش نمایش صفحه اول مقاله
Estimation of hydrogen crossover through Nafion® membranes in PEMFCs
چکیده انگلیسی

It is well known that the membrane electrode assembly (MEA) of proton exchange membrane fuel cells (PEMFCs) can undergo deterioration, during long term operation, of both the electrode materials and the membrane. Hydrogen crossover, i.e., the undesired diffusion of the gas from the anode to the cathode through the membrane, has been ascribed as one of the main causes of deterioration of perfluorinated ionomer membranes, normally employed in PEMFCs. One of the effects of the hydrogen permeation across the membrane is the decrease of the cell's open circuit voltage (OCV), due to the reaction between the fuel and the oxidant at the cathode surface. Such reaction can lead to the production of peroxide radicals, causing the degradation of both the PEM and the catalyst layer. Hydrogen crossover increases when temperature, pressure and humidity of the cell rise. The hydrogen permeation rate through a very thin PEM is typically lower than 1 mA cm−2 for a new MEA, but it can exceed 10–20 mA cm−2 after long term operation. Various methods have been proposed to measure the rate of hydrogen crossover, mainly based on electrochemical tests on a single FC with a flow of nitrogen at the cathode, so that the steady state current corresponds to the oxidation of crossed hydrogen. Hydrogen crossover has been also determined indirectly by assuming that the changes in the OCV values are due to the passage of fuel from the anode to the cathode.In this paper, a simplified mathematical model for the direct determination of hydrogen crossover permeation rate is presented. Such a model is based on analytical expressions of the polarization terms and it is employed to determine the hydrogen crossover rate. The main results show that the hydrogen crossover current densities increased from 0.12 to 0.32 mA cm−2, by decreasing the thickness of the membranes and increasing the operating cell temperature. Moreover, the hydrogen crossover determined for a fresh MEA was compared with that of a degraded one, exposed to repetitive freezing/thawing cycles. It was found that the hydrogen crossover for the degraded MEA was more than twice the value obtained with the fresh one at the same temperature.

The hydrogen crossover current is obtained by best-fitting the initial part of the experimental polarization curve. This can result in a simpler experimental approach to the investigation of PEMFC degradation.Figure optionsDownload as PowerPoint slide

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Power Sources - Volume 196, Issue 4, 15 February 2011, Pages 1833–1839
نویسندگان
, , , ,