In this thesis, the treatments of MEA and the special structures within carbon fiber bunch unipolar plates on the performance of PEMFC are studied. At first, the factors affecting on the water content within MEA will be studied. A passive HFC stack usually exposes in the ambient no matter that it works or not. However, the ambient is far from saturated. The water within MEA will vaporize continuously. Especially, if the stack is shutdown for a long period, there is no water generation in the cathode and then the membrane will be short in water. If it occurs, the conductivity of H+ will decrease greatly, and the electrode of MEA is also possible to separate from its membrane. This separation will make the performance of the stack an unrecovered decay. On the other hand, in order to improve the performance of a air-breathing HFC, the inner structure within cathode carbon fiber bunch unipolar plates is modified. The structure of the unipolar plates is modified in the following three aspects: 1. Increasing soft end height of carbon fiber bunch, 2. Increasing the number of silver-coated wires in carbon fiber bunch, 3. Cutting several serrated slots on the soft end of carbon fiber bunch. In the MEA treatment, firstly, a MEA is boiled in 80oC, 0.5M H2SO4 solution and then boiled in 80oC DI water for an hour, respectively. When the single-cell HFC operates in hydrogen inlet pressure 0.1 bar, air-breathing, and room temperature, experimental results display that the power density of this HFC with the aforementioned treatments and the special structure of unipolar plates can reach a value about 185mW/cm2. This value is about 130% higher than that of the untreated MEA and about 50% higher than that of the treatment of MEA only immersed in DI water. In addition, the comparison of the performance of HFC between with carbon fiber bunch unipolar plates and with graphite unipolar plates are also studied. The experimental result displays that the performance of HFC with the carbon fiber bunch unipolar plates is superior to that with graphite unipolar plates, especially the fuel cell operating under low gas inlet pressure.

¡@¡@In this thesis, we develop a self-humidifying PEMFC. The humidifying effects on the stability and impedance of the fuel cell are studied. A portable and passive PEMFC stack usually exposes in the ambient no matter that it works or not. However, the ambient is far from saturated. The water within MEA will diffuse to the membrane¡¦s surface and evaporate continuously. The membrane will be short in water without water supplying. Because the conductivity of H+ of the membrane is highly dependent on water content, the dehydration of the membrane will reduce the interconnected passageway of H+ and affect the performance of fuel cell directly. And because of the different expansion rate the electrode of MEA is also possible to separate from its membrane when it operates repeatedly. This separation will make the performance of fuel cell an unrecovered decay. ¡@¡@At first, the hydration status of the dry membrane is observed. We measure the addition weight of water into membrane by using cotton thread humidifying, and estimate the water permeation distances. The maximum water supply rate of cotton thread is 4.26mg/min, and the permeation rate of water through membrane where is 2.5cm from water surface is 0.15mg/cm¡Dmin. Then we design the self-humidifying devices of PEMFC stack. The humidifying effects on performance and stability of the fuel cell are studied. ¡@¡@When the active area is 0.7¡Ñ4.5cm2 and the cotton thread is 5mm from the center of electrode the supplying water can arrive at the reaction area under the electrode through the membrane in one minute. The difference of the supplying water between the bottom and top is 7% by using 6cm cotton thread. Therefore water can hydrate the membrane and the difference of the supplying water between bottom and top is not oversize. The higher current load, the voltage efficiency is lower. The increasing heat generation rate results in the water evaporation rate would be greater than the water generation rate. So the drop of voltage under higher current is greater than lower current. By comparing with the difference of high frequency impedance the change of humidifying is smaller between 1hr operating. It indicates that humidifying by cotton thread keeps the membrane hydration.