Cathode Humidification and Water Management of Proton Exchange Membrane Fuel Cell

Abstract: Proton Exchange Membrane Fuel Cell (PEMFC) has become one of the hotspot for its high-energy efficiency, low noise, pollution-free characteristics, simplicity in design and operation, low operation temperature and safety. It is necessary to humidify the PEMFC for strengthening proton conduction, decreasing membrane resistance and keeping it working well, but that will take some problems such as cathode flooding, concentration polarization at high current density and so on.At first the basic theory of fuel cell electrochemistry reactive was studied in this dissertation, including fuel cell efficiency, thermal of activation polarization and concentration polarization, kinetics characteristics of fuel cell electrochemistry reaction and limiting current. It will be helpful for understanding the process of electrode reactive deeply, provide guidance for improving the performance of full cell at high current density, so as to carry out the water, heat and gas management of PEMFC at last.Then, a three dimension mathematical model is described to model the working process of PEMFC, it accounts simultaneously for the fluid flow, gas diffusion in the porous media, water transfer in proton exchange membrane and electrochemical reaction. The geometrical model has two fluid channels in order to reflect the bank influence, which come from the water and gas transfer of the two side channels. The humidification and concentration polarization was studied with the model. The PEM module of computational fluid dynamics software Fluent analyzed the different humidification. The relationship between different humidification and the performance of the fuel cell was studied, especially the relationship between the performance of the fuel cell and concentration polarization at high current density was analyzed. The relationship between the performance of the fuel cell and the water concentration, oxygen concentration at concentration polarization area of the whole reaction was analyzed in detail. It makes show that concentration polarization happens in part region of fuel cell.Some improved methods including of two gas-inlet, converse gas-inlet and gas diffusion layer (GDL) with pore were put forward in order to weaken oxygen concentration when cathode is saturation humidification at high current density. Water and oxygen distribution in electrode was studied in order to research into the close relationship between the performance of the fuel cell and water, gas transfer and distribution. The results make show that improved methods including of gas inlet mode and the configuration of GDL make the distribution of water and oxygen better, and the methods solve the problem of concentration polarization caused by cathode flooding preferably. Finally, the performance of the fuel cell was increased when cathode is saturation humidification at high current density…
Key words: proton exchange membrane; fuel cell; humidification; concentration polarization; simulation; water management

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