Experimental Study On Dynamic Characteristics Of Proton Exchange Membrane Fuel Cells (PEMFC) Under Subzero Temperatures

With the shortage of fossil fuels and increasing environmental pollution, the demand of efficient and alternative energy is growing. Proton Exchange Membrane Fuel Cell (PEMFC) becomes one of the most appropriate alternative energy sources because of its higher efficiency and lower pollution, especially in the automotive field. However, PEMFC also faces the challenge in cold start capability and survivability, which becomes an crucial issue.Based on investigation of the mechanism of internal water transfer and heat transfer, a two Membrane Electrode Assembly (MEA) single PEMFC is used to work out cold start behavior and survivability at subzero temperature. In order to investigate the effect of current density and anode stoichiometric ratio at -3℃and -5℃, a series of cold start experiment are carried out at different current densities and different anode stoichiometric ratios as follows:100mA/cm2,150 mA/cm2,200mA/cm2,2.5,3and 3.5. The results also compare with those at normal temperature. Different from the experiment about humidifying reactant gas at normal temperature, this paper carried out humidifying reacttant gas around 0℃. Thermodynamics calculations on humidification are executed, which shows an increase in membrane water content.The voltage could arrive at 1.15V when PEMFC startup at different current densities in normal condition. The output voltage decreases and performance degrades especially at -5℃.The output voltage is high when FC startup is at low current density. The FC temperature increases consistently, and the performance recover well. As a result, FC should cold start at low current density first, until the temperature rise and reaction rate are stable. Application of high current density load is then used to promote the water and heat production. The water content of the membrane will increase at the same time.The output voltage increases while anode stoichiometric ratio increases when chamber temperature under -3℃and -5℃. In this paper, on external gas humidifying method is used to find out FC performance at 0℃,-3℃. The result shows that humidifying gas could enhance ultimate current density when the chamber temperature is around 0℃. The performance is best when humidifying temperature is 45℃.