Study On Gradient Gas Diffusion Layer For Proton Exchange Membrane Fuel Cell

Gas diffusion layer (GDL) of Proton exchange membrane fuel cell (PEMFC) is composed of porous materials such as carbon fibers or carbon papers, which has the function of diffusing gas, discharging water and electric conduction. Excessive liquid water is generated at large current density, which blocks gas channel and reduces the effect of gas diffusion. A lot of researches attach importance to the characters of GDL. Especially, the pore frame of the GDL, It plays an important role in the water transmission and gas transmission to the GDL, It is the one of the vital factors to influence fuel cells performance, also it is the one of the research hotspots.At first, a mathematical model is described to model the working process of PEMFC in this dissertation, it accounts simultaneously for the fluid flow, water transfer in proton exchange membrane and electrochemical reaction. The studied domain consists of fluid channels, diffusion layers and catalyst layers of anode and cathode, and membrane. Each region transport phenomena occurred in the whole fuel cell is described by the generalized equation; also take into account the correlation equation to influence the PEMFC, in order to modeling the transport phenomena in the PEMFC with clearing the actual statusThen, according to the Unsaturated Flow Theory that one dimensional liquid water transport about porous media equations are deduced in the GDL, based on these equations, these parameters like liquid saturation, liquid flux, liquid remaining in GDL, gas diffusion coefficient are calculated for GDL with Micro Pore Layer (MPL) and with different gradient porosity structures. Emphasized on discussing the influence to the capacity of draining water and to the gas diffuses in GDL with different gradient porosity structures.At last, the PEM module of computational fluid dynamics software Fluent is used to analyze performance of the PEMFC with different gradient porosity structures. Considered such factors as humidifying the reaction gas, electrochemistry reaction, phase change in water, analyzed the influence to the distribution of the liquid water saturation and the oxygen concentration in GDL with different gradient porosity structures.This paper's main content is based on change the pore frame (i.e. the porosity in GDL) to accomplish the optimization of the water management and the gas management, to make sure the water be unable to flood the electrode and enhance the Oxygen diffuse capacity, to improve the performance of PEMFC consequently...