الفهرس 
Introduction
Current densityOnly 14 pages are availabe for public view
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Abstract
A fuel cell system is a chemical power generation device that converts the chemical energy of a clean fuel (e.g., hydrogen) directly into electrical energy, so they are not limited by Carnot cycle efficiency as is the case with chemical combustion reactions. Among all kinds of fuel cells, proton exchange membrane fuel cells (PEMFC) are compact and lightweight, work at low temperatures with a high output power density, and offer superior system startup and shutdown performance. In the most basic form of a fuel cell, two electrodes surround an electrolytic material. The composition of the electrodes and the electrolyte distinguish one fuel cell from another. In a PEMFC, the electrolyte material is a polymer and the electrodes are carbon paper water-proofed with Teflon. The fuel cell reactions occur in the catalyst layer located between the carbon paper and the membrane. The electrode on the hydrogen side is the anode, and the electrode on the oxygen side is the cathode. Collectively, this assembly is called a Membrane Electrode Assembly (MEA). A cell is formed when two bipolar collector plates with flow channels are added on either side of an MEA. Finally, each catalyst layer is in contact with a gas diffusion layer. The hydrogen fed to the anode is oxidized on the catalyst surface into protons and electrons. Protons are transferred through the electrolyte membrane and electrons via an external circuit to the cathode. The oxygen fed to the cathode is combined with the protons and electrons producing water and heat. An Experimental study has been carried out to investigate the effect of different operating parameters on the performance of H2/air proton-exchange-membrane fuel cell, (PEMFC). Effects of hydrogen flow rate, cathode air flow rate, its temperature and relative humidity, have been considered. A 25 cm2 single cell with serpentine anode and straight cathode flow channels is used as a test unit. The fuel cell stack system is equipped with two developed units in order to facilitate each of orientation and vibration of the stack. Effects of cell orientation position and vibration frequency and amplitude are also considered. Performance of the fuel cell is characterized through analysis of the polarization and the power density vs. current density curves as well as the hydrogen utilization and the cell electric efficiency. Obtained results show that, operating conditions as well as cell orientation and vibration frequency and amplitude have a significant effect on the performance of the fuel cell. The influence of the cathode air relative humidity is more significant compared to other operating parameters. The overall cell performance is improved as the cathode air relative humidity increases as well as its temperature and vibration frequency and amplitude are decreased. The cell electric efficiency shows values up to 60 % at low power density and values around 35% at maximum power density. Key words (Not more than ten): Fuel cell, Membrane, Electrolyte, Hydrogen