MEAs for Polymer Electrolyte Fuel Cell (PEFC) Working at Medium Temperature

Abstract

Recently, the CNR-ITAE activity has been addressed to the components development (electrodes and membranes) able to work in medium temperature PEFCs (80-130°C). One of the main problems to work at these temperatures is the proton conductivity loss due to a not full hydration of the membrane. For this reason a study on the modification of perfluorosulphonic membranes (like Nafion) was carried out by introducing different percentages of inorganic oxides (like SiO2, ZrO2) in the polymer matrix. These compounds have the function to improve the properties of the materials at high temperature due to their characteristics of softly proton conductor and/or hygroscopicity. The membranes were prepared by the Doctor-Blade casting technique that permits a good check of the thickness and a good reproducibility. A commercial ZrO2 was used to prepare the membranes varying the inorganic amount between 3 and 20wt%. The most promising results were obtained at 120°C with a Nafion-recast membrane loaded with a 10wt%ZrO2; a power density value of about 330mW∕cm2 at 0.6V was reached. On the other side, an optimization of the electrode structure was carried out, by introducing the inorganic oxide in the catalyst layer in order to improve the performance in the range of considered temperature. By using a spray technique, thin film electrodes with a Pt loading of 0.5mg∕cm2 in the catalyst layer, low PTFE content in the diffusion layer and a 30% Pt/Vulcan (E-Tek, Inc.) as an electro catalyst were prepared. Different amounts of ZrO2 were introduced in the catalytic layer of the electrodes to increase the working temperature and help the water management of the fuel cell. These electrodes assembled to the modified membrane have shown a better performance at higher cell temperature than standard MEA with a power density of about 330mWcm−2 at 130°C.