Study On The Performance Optimization Of High-Temperature Proton Exchange Membrane Fuel Cell Based On Nafion/SiO₂ Composite Membrane

The proton exchange membrane fuel cell (PEMFC) not only has the general characteristics of the fuel cell (such as high energy conversion efficiency, environmentally friendly, etc.), but also has characteristics of zero emission, simple structure, and fast start-up at room temperature, etc. The PEMFC is particularly suitable for use in mobile power, regarded as ideal power candidate for the electric car and air-independent propulsion submarines. Since the high temperature proton exchange membrane fuel cell (HT-PEMFC) has more advantages than normal temperature PEMFC, such as the high electrode kinetics, resistance to CO poisoning and simple water or heat management, it has becoming the focus of recent research.In this paper, the high temperature proton exchange membrane fuel cells has been studied in two ways based on the research of traditional PEMFC performance.The electro-osmotic drag (EOD) coefficients of the Nafion212/SiO2 composite membranes were studied in first part of this paper. Nafion212/SiO2 composite membranes with different SiO2 contents were prepared via in-situ sol-gel method. Then the EOD coefficients of composite membranes and pure Nafion212 were measured by the method of hydrogen pump cell under similar condition to operating PEMFC. It is found that the EOD coefficient of Nafion212/SiO2 composite membranes decreases with the increase of SiO2 content in the composite membranes and increases with the increase of relative humidity, but remains essentially constant for various levels of applied currents. At the same SiO2 content, electro-osmotic drag coefficient increased significantly with increasing temperature. An empirical equation of the EOD coefficient of Nafion212/SiO2 composite membranes as a function of SiO2 content and temperature is proposed through numerical fitting while the temperature ranges from 323 to 363K and SiO2 content in the composite membranes ranges from 0 to 19.8%. These works will provide relative parameters for the numerical study on the PEMFC based on Nafion212/SiO2 composite membranes.A two-dimensional non-isothermal steady state numerical model for HT-PEMFC based on Nafion212/SiO2 composite membrane was developed in second part of this paper. Finite element method was used to solve electrochemical kinetics coupled with multi-component transport, flow, charge balance and energy conservation. The model-predicted fuel cell performance curve was compared with published experimental result and a good agreement was found. The distributions of species and temperature in the HT-PEMFC were predicted and the effects of the porosity of gas diffusion layer, Pt catalyst loading and pressure on the performance of HT-PEMFC were also evaluated. A temperature rise of 15.6K was deserved when the HT-PEMFC operated pressure was 2atm, cathode relative humidity 59% and current density 500mA cm-2. The increasing of pressure, porosity of gas diffusion layer and Pt catalyst loading were found to be beneficial to the HT-PEMFC performance. These simulated result have important reference value for the preparation and performance optimization of the HT-PEMFC.