Comparative Study on Composite Electrodes for Medium Temperature PEFC

The purpose of the present study consists in the development of a MEA (Membrane-Electrode-Assembly) for Polymer Electrolyte Fuel Cells (PEFCs) applications at intermediate temperatures (T>100°C) through the introduction of inorganic compounds within the catalytic layer of the electrodes. For this aim, composite electrodes containing three inorganic compounds, with different chemical and physical properties, were developed with percentages ranging between 0-14 wt% of zeolite H-BETA, titania (TiO2) and yttria stabilized zirconia (YSZ) maintaining the same Platinum loading of 0.5 mg/cm2 and assembling the electrodes to a commercial N115 membrane. Electrochemical studies in terms of V-I curves were carried out in a temperature range of 80-130°C in order to select the optimal content of filler. A comparison between the standard electrode and the best composite electrode containing the optimal amount for each investigated inorganic material was carried out. The role of inorganic materials is to limit the ionomer swelling by maintaining the mechanical characteristics of the polymer quite unaltered and to enhance the durability of the electrocatalyst to degradation phenomena during the fuel cell operation at a temperature over the critical one. For each inorganic material, a different optimal amount was found to be dependent on their chemical-physical properties, in particular the particle size, acidity and intrinsic proton conductivity. At high temperature (130°C), the beneficial effect of oxides introduction is more evident: a reduced cell resistance, a reduced Tafel slope, increased OCV values and improved fuel cell performance for composite electrodes than the standard one. It was supposed that a limit in the oxide introduction exists and it depends on physical properties of the inorganic filler, in particular the grain size, the acidity, the intrinsic proton conductivity and the physical properties of the polymeric matrix used as an ionomer