Hydrogen-fed PEMFC: Overvoltage analysis during an activation procedure

The present study aims at obtaining a better understanding on the changes that the membrane electrode assembly (MEA) of a H2-fed fuel cell experiences along an activation procedure. An activation protocol was set-up considering six loading cycles performed at 25 °C. After each loading cycle, the electrochemical characterization was performed using polarization curves, Linear Sweep Voltammetry (LSV), Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). Polarization curves showed an effective increase of the MEA performance along the activation procedure, with the maximum power density increasing from 116.1 mW cm−2 to 229.9 mW cm−2 and the overall efficiency increasing from 9.3% to 19.7%. Simultaneously, it was observed a decrease on the Tafel slope and an increase on the exchange current density, indicating improved catalyst characteristics. From the LSV experiments it was concluded that hydrogen crossover at open circuit increases along the activation procedure, however the open circuit voltage (OCV) also increases, mainly due to an overvoltage decrease caused by mixed potential. CV experiments showed that the available catalyst area also increases. From the impedance experiments it was observed that the proton exchange membrane (PEM) and the anode and cathode charge transfer resistances decrease along the activation cycles. The opposite trend was verified for the anode and cathode double layer capacitances.