Development of low Pt content Membrane Electrode Assembly (MEA) of high efficiency using electrochemical techniques and composites membranes for intermediate temperature PEMFC .

Abstract

The main objective of this research project is the fabrication and characterization of Membrane Electrodes Assembly (MEA), using electrochemical techniques, seeking a significant reduction of Pt amount used in the electrodes, associated with the use of composites membranes (Nafion + inorganic nanoparticles), which allows an improvement in the water retention and proton conductivity and, finally, overall cost reduction of the produced MEA. The electrochemical performance of the previously characterized new MEAs will be evaluated in Proton Exchange Membrane Fuel Cell (PEMFC) single cells. A comparison with MEAs obtained by conventional methodology already available in the IPEN research group is planned. The electrodes (cathode and anode) will be prepared using an innovative electrochemical technique. The Sieve printing method is chosen for deposition of an ink containing C/Nafion® on the carbon cloth (carbon substrate). Previous to the electrodeposition process, the carbon substrate has to undergo an activation process to increase the hydrophilic character of the surface. Then the electrodeposition process will take place on carbon substrate by galvanostatic pulse and/or cyclic voltammetric in Pt and/or Pt alloy solutions, in the absence and presence of ultrasound (20 kHz). The composites membranes based on Nafion® and hygroscopic oxides will be prepared by hydrothermal process, using Nafion 115 Membrane as polymeric matrix. The fabrication process of the composites comprises the immersion of the polyeletrolites (Nafion membrane) in the precursor solution (with the hygroscopic oxides) in different times and different thermal treatments in autoclave. A systematic study associated to the developed process, characterization and applicability of the membranes and electrodes in MEAs is proposed. For the evaluation of the electrochemical behavior of the electrodes Cyclic Voltammetric and Single Cell Polarization measurements will be carried out. The following techniques are chosen for the morphologic and structural studies: Field Emission Gun - Scanning Electron Microscopy (FEG - SEM), Atomic Forces Microscopy (AFM), X-Ray Diffraction (DRX), Infrared Spectroscopy (FTIR) and Energy Dispersive X-ray (EDX), with the objectives of evaluating the degree of impregnation of the inorganic oxide, revealing the composites membranes morphology and determining the physical characterization of the electrodes. The capacity of water retention (water uptake) and the ionic conductivity will be studied by Impedance spectroscopy (EIS) measurements. Finally, the evaluation of the performance associated to the composites membranes together with the low Pt content electrodes prepared by electrochemical techniques will be carried out in PEMFC's at intermediate temperature.