Study On The Performance Of PEM Fuel Cell, Under Different Working Condition

The high power density and rapid adjustment to power demands make proton exchange membrane fuel cells (PEMFCs) one of the best candidates for a clean alternative energy source of 21th century. A comprehensive two-dimensional mathematic model is developed for PEMFC with both conventional single parallel flow field and interdigital flow field. In this model, transport of the two charged species– electrons and ions– as well as that of the chemical species is considered. The model also describes phenomena of liquid water flooding and water transport through membrane. The influence of pressure, temperature and relative humidity on the fuel cell performance is investigated respectively. The distribution of liquid water in the cathode and water content of membrane are compared under different condition, such as different temperature, relative humidity of feeded gas and output voltage of the cell. The polarization curves predicted by the model of two kinds of cells agree well with the published experimental data. The result indicates that liquid water flooding is more serious with smaller output voltage, lower work temperature and higher relative humidity of reactant in cathode; liquid water condensation is good for keeping high conductivity of membrane near the cathode, but it will flood the electrode and minish the effective area, which depresses the performance of the cell; higher relative humidity is favorable for membrane soakage near the anode. It also indicates that fuel cell with interdigital flow field performs better than that with conventional single parallel flow field, as the structure is better for drainage and increase the limitation of reactant transport.The second part is experimental study of a single cell with serpentine flow field and a self-breath fuel cell stack made up with four single cells. Firstly, the steady state performances of the single cell and cell stack are tested to investigate the influence of gas feed parameters. Then, the transition performances of the cell stack are tested. The output characteristics of the stack are tested under varying load with a certain flow rate of hydrogen. The performance curve responsing to different feed style of air are investigated under different flow rate of hydrogen. The result shows that: a fan for air feeding improves the performance obviously; and when the feed fan is used, hydrogen flow rate have a great influence on the transition output characteristic.