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Heat and Mass Transfer Modeling and Simulation Part 3

Tham khảo tài liệu 'heat and mass transfer modeling and simulation part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | The Gas Diffusion Layer in High Temperature Polymer Electrolyte Membrane Fuel Cells 31 0.9-r 0.8- 0.7- 0.6- without MPL --O-- 10 Teflon in the MPL A 20 Teflon in the MPL -V-- 40 Teflon in the MPL -O- 60 Teflon in the MPL 0.5- 0.0 0.4 0.3 0.2 0.1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Z ohm cm2 Fig. 13. Impedance spectra of the cell when electrodes with different Teflon percentage in the MPL were used Current density mA cm-2 Fig. 14. Influence of the Teflon percentage in the MPL on the cell performance. Hydrogen stoichometry at 1 A cm-2 1 Points experimental data lines fitting to the model As it can be observed the influence of the Teflon percentage in the MPL on the cell performance as in the case of the carbon support appears almost at the values corresponding to the limiting current density. However a close look at the curves shows that the limiting current densities slightly diminishes as the Teflon percentage in the MPL increases reflecting the higher limitation of the mass transport when a less porous or permeable GDL is used. In order to assist for interpretation of the fuel cell results values of the hydrogen limiting current density are collected in Table 6. Values in Table 6 display the benefits of using an open GDL. In fact the highest hydrogen limiting current density was obtained for the MPL free GDL even though the protection of the catalytic layer plays a more important role in terms of global performance lower performance in almost the whole range of current densities . Therefore in terms of global performance it is also advisable to use a MPL with a low Teflon percentage. 32 Heat and Mass Transfer - Modeling and Simulation PTFE content jHL hydrogen mA cm-2 Without MPL 1.000 8 10 1 000.4 20 990.2 40 980.9 60 964.9 Table 6. Limiting current density for the hydrogen oxidation for the different Teflon percentages of the MPL 3.2.2 Influence of the carbon content in the microporous layer For this study microporous layers with a Teflon percentage of .