Electrical Performance of PEM Fuel Cells With Different Gas Diffusion Layers

The microporous layer (MPL) is a key component of polymer electrolyte membrane fuel cells (PEM-FCs), and it is in charge of the gas and water management at the electrodegas diffusion layer (GDL) interfaces. A MPL was prepared and coated onto two different commercial GDLs: a carbon paper (woven-non-woven (WNW)) and a carbon cloth (CC). Electrical performances of the so-obtained gas diffusion media (GDM), i.e., GDL coated with the MPL, were investigated in single cell testing (steady-state polarization curves) using a Nafion® catalyst coated membrane with a platinum loading of 0.5 mg/cm2 both for the anode and the cathode. Moreover, in order to better understand the polarization phenomena during the running of the FC, impedance spectroscopy was carried out in galvanostatic mode at different current densities. In particular, the effect of the air relative humidity (RH 100%, 80%, and 60%) was investigated, while the hydrogen was fed always fully humidified (100%). The WNW substrate has demonstrated to be superior to CC in a vast range of current densities (from open circuit voltage to 0.8 A/cm2). However, at high current density, the WNW GDM has some problems in water management. ISI 5 PAGE

Design Approach for the Development of the Flow Field of Bipolar Plates for a PEMFC Stack Prototype

This work is part of a project whose final aim is the realization of an auxiliary power fuel cell generator. It was necessary to design and develop bipolar plates that would be suitable for this application. Bipolar plates have a relevant influence on the final performances of the entire device. A gas leakage or a bad management of the water produced during the reaction could be determinant during operations and would cause the failure of the stack. The development of the bipolar plates was performed in different steps. First, the necessity to make an esteem of the dynamics that happen inside the feeding channels led to perform analytical calculations. The values found were cross-checked performing a computational fluid dynamics (CFD) simulation; finally, it was defined the best pattern for the feeding channels, so that to enhance mass transport and achieve the best velocity profile. The bipolar plates designed were machined and assembled in a laboratory scale two cells prototype stack. Influences of the temperature and of the humidity were evaluated performing experiments at 60 deg and 70 deg and between 60% and 100% of humidity of the reactant gasses. The best operating point achieved in one of these conditions was improved by modifying the flow rates of the reactant, in order to obtain the highest output power, and it evaluated the reliability of the plates in experiments performed for longer times, at fixed voltages