Modeling On Transport Processes And Electro-Chemical Reactions In Direct Methanol Fuel Cell

Fuel Cells have emerged as one of the most promising technologies for the power source of the future. The fuel cell is an electrochemical device that converts energy into electricity and heat without combustion. Fuel cell technology is now becoming applicable for a large variety of technical areas. These include portable power, transportation and stationary power supplies. In order to optimize and improve fuel cell design, repeated experimentation must be carried out, which may be costly and time consuming. One viable alternative is to use a mathematical model to uncover the design limitations and to determine where improvements can be made.Oxygen diffusion transport and electrochemical reaction in the oxygen cathode of direct methanol fuel cell (DMFC) have been expressed with the TFFA model. Model calculation has been carried out to investigate the effects of structural parameters of the DMFC cathode on the electrode performance, which is respectively represented by the curve of cathode overpotential versus current density. Much attention has been paid to parameters including the porosity of the reaction layer, the thickness of the thin-film on the flooded-agglomerate, the radius of the flooded-agglomerate, the volume fraction of the flooded-agglomerates in the reaction layer. The calculation results show that the radius of the gas channels in the reaction layer and the porosity and average pore radius of the gas-diffusion layer seem to be less important for the performance of the electrode.A mathematical model for the anode of a direct methanol fuel cell (DMFC) considering the mass transport in the whole anode compartment and the proton exchange membrane (PEM), together with the kinetic and ohmic resistance effects through the catalyst layer is developed. The influences of key parameters on methanol crossover and anode performance are investigated. Model indicates that, at low current density and high methanol concentration, the methanol crossover poses a serious problem for a DMFC. The anodic overpotential and reaction-rate distributions throughout the catalyst layer are affected by increasing the protonic conductivity toenhance the performance of a DMFC.According to the cathode model and anode model, together with effect of the methanol crossover on cathode, a simulation of single DMFC is developed. The influence of key parameters on cell performance is investigated by the curve of cell voltage versus current density. The calculation results show that the thickness of the reaction layer and the porosity are important for the performance of the electrode. The optimization of fuel cell is discussed to attain a maximum cell performance.At last, pore-filling type polymer electrolyte membranes reduced methanol permeability is discussed using the single DMFC model and shows that it effectively improves cell performance.