A Study On The Flow Field And Cell Performance Of PEMFC By Mathematical Modeling

The proton exchange membrane fuel cell (PEMFC) is a electrochemical device that convert chemical energy in fuels directly into electrical energy, with high efficiency and low environmental impact. The flow field plate, which the performance, efficiency and cost of PEMFC strongly depend on, is a very important component. The flow field on the bipolar plate is constituted of channel (length, width, depth), rib and channel patterns. Different mathematical models have been established to improve fundamental understanding of transport phenomena in PEMFC and to investigate the impact of various parameters on performance and efficiency.First, the microstructure of catalyst layer is studied based upon a lattice model with the Monte Carlo simulation. The model can predict how the catalyst layer components such as Pt/C, electrolyte and gas pores affect the utilization of catalyst and the cell performance. In addition, diffusion of reaction gas in the catalyst layer has been studied based on the lattice model with random walking method. It provides theory basis of electrochemical reactions in PEMFC and structure parameters of the whole models.Next, a two-dimensional, two-phase cross the channel computational model of PEMFC is established. It accounts for all major transport phenomena including: water and proton transport through the membrane; electrochemical reaction; transport of electrons; transport and phase change of water in the gas diffusion electrodes; diffusion of multi-component gas mixtures in the electrode. The performance of the cathode was found to be dominated by the dynamics of water, especially in the high current density range. The simulation results show that for a fixed electrode width, a greater number of channels and shorter shoulder widths are preferred for the high humidity inlet PEMFC, whereas a shorter number of channels and greater number of shoulder widths are preferred to promote slower water removal for the low humidity inlet PEMFC.Third, through theoretical analysis by along the channel model, a pseudo-three-dimensional model for conventional gas channels is expanding our two-dimensional model. Base case simulations are presented and analyzed with a focus on the physical insight and fundamental understanding afforded by the availability of detailed distributions of reactant concentrations, current densities along the channel. Simulation results show that the reactant concentration, current density and flow velocity decays monotonically along the channel for the high humidity inlet PEMFC, while the current density increases and then decreases along the channel for the low humidity inlet PEMFC. Therefore, a depth gradual change channel is recommended for the high humidity PEMFCto facilitate better water removal, and a rib width gradual change channel is recommended for the low humidity PEMFC to facilitate better water reservation upriver and better oxygen transport downriver.Last, the influence of different flow channels including serpentine channel, parallel channels, parallel serpentine channels, spiral channels and mesh channels on the current density distribution of PEMFC was investigated by a computational fluid dynamics (CFD) model. The results show that significant improvements in current density distribution can be obtained by putting inlet channels and outlet channels closer.