Study On Membrane Humidification For PEM Fuel Cell Vehicles

The polymer electrolyte in PEMFC requires a supply of water to maintain proton conductivity. It is difficulty to maintain water balance when running PEMFC because of the lack of water. The humidification is essential for PEMFC. The paper analyze the ways of humidification and their characteristic , found a model of water vaporization on the face of the membrane, analyze the relationship between the humidity and humidification temperature ,discuss the effect of humidity on performance of PEMFC ,make some experiments of membrane humidifying. Some conclusions had been summarized as following:(1) It is found that vaporization causes the lack of water in membrane and the vaporization velocity is determined by the equation of (2-17). For the anode, vaporization and the pure migration from the anode to the cathode cause the loss of water. So the humidification is essential . Moreover, the humidification temperature must be higher than the temperature of the cell, which can be explained by the equation of (2-29). For the cathode, the airflow must carry the excessive water out of the cell, which can be explained by(2-36).(2) Model: The water content of the cathode get little increase when the humidification temperature of the cathode is increased, while the water content of the anode is almost steady. The water content of the anode get increase obviously if the humidification temperature of the anode is increased, while the water content of the cathode is almost steady. The humidity of the anode has more effect on the performance of the cell than that of the cathode.(3) The permeation of the Nafion membrane is linear with the time and the gas flow. At low temperature, the thickness of the membrane has little effect on the permeation because the vaporization is the control step. At high temperature, the penetration cross the membrane is the control step and the permeation increases with the decrease of the thickness of the membrane and humidity of the gas. The permeation increases with the increase of temperature.