Studies On The Water Transport In Membrane Of Proton Exchange Membrane Fuel Cell

The fuel cell is one kind of the electric power facility which turns directly chemical energy stored in the fuel and the oxidant to the electrical energy through the electrode reaction, its most major characteristic is that it does not pass through the heat engine process, therefore, it does not limited by cycle, its energy conversion efficiency is high, moreover its environmental pollution is small, the noise is low, and it is recognized for the first choices of clean, the highly effective electricity generation technology in 21st century. Proton exchange membrane fuel cell (PEMFC) because of its low operating temperature, short starting time, high power density, is taken the new generation of electric automobile power supply, the portable small power source, the family and so on receive enterprise's the and so on, various countries' government and energy, automobile, electrical and other corporations give widespread attention, high take and vigorous support.The proton exchange membrane is one of key materials of the proton exchange membrane fuel cell (PEMFC), its performance directly affects the battery performance. At present, PEMFC generally uses the solid polymer membrane, the proton conducts in the membrane by H₂O/H⁺ from the anode to the negative, and the water is the carrier of the proton in the membrane. The water content is higher in the same kind of polymer membrane, the speed of proton is quicker, and the membrane conductivity is higher. Maintenance proton exchange membrane has sufficient water content is extremely important for PEMFC.Because the thickness of the proton exchange membrane generally only has several ten microns, and this limited the test of the water content distributed in the membrane of fuel cell. In present, the study of water management research mainly adopts simulation based on model, T.E.Springer has established the new model based on diffusion model and obtains water content and the water activity relations based on test result, the obtained electro osmosis coefficient and diffusion coefficient used by many scholars.This present paper has analyzed the influence of pressure differences,humidity differences both on two sides of the membrane and current density in membrane to the water content in membrane according to the Springer fuel cell model, and carries on the test from the experiment. We uses the several proton exchange membranes to increase thickness of membrane and to weight separately in the experiments, and this overcomes the difficulty that the proton exchange membrane is thin and not easy to test, obtains directly the water content distributed in the membrane when there is pressure difference,humidity differences both on two sides of the membrane and current density in membrane. The research discovered that,(1) when the battery current is zero, and also does not exchange the water and heat with the outside, there is only the pressure difference on the two sides of membrane, the water content in membrane is basically even, and it is slightly high only at low pressure side, and with the increase of pressure difference, the water content in membrane changes slightly. But the model analysis result showed that, along the direction at the thickness of membrane, the water content weakens according to the rule of index from the side of low pressure to the side of high pressure on membrane, and when the pressure difference is higher, the water content weakens seriously, and this test result is different with the model analysis result. Analyzes its reason, it mainly is that the pressure is not evenly distributes in the membrane, but act on the surface of membrane.(2) when the pressure difference on the two sides of membrane is zero, and also does not exchange the water and heat with the outside, and the current in membrane is I, the water content in membrane is basically even along the direction at the thickness of membrane, and the increase of the pressure difference influence the water content in membrane obviously. But the model analysis result showed that, along the direction at the thickness of membrane, the water content weakens according to the rule of index, and with the increase of current density, the water content weakens seriously. This experimental result is incompletely consistent with the theoretic analysis, and the reason possibly is the function of capillary pore in the membrane.(3) When the battery current is zero, the pressure difference on the two sides of membrane is zero, and there is different humidity both on the two sides of membrane, the water content slightly high at the membrane of high humidity side, and it is even basically at other part of membrane along the direction at the thickness of membrane, but this is not completely consistent with the theoretic analysis that the water content reduces according to the linear rule from higher side to the lower side of water content of membrane.The test result indicated that, the experimental results are different obviously with the theoretic analysis, and there are some places need the further revision in model, to establish theoretical model closer with the battery, provide the theory basis for the battery operation simulation or the design optimization.