Membrane Electrode Assemblies (MEA) were prepared according to a method developed by Paganin et al. [39]: Considering the targeted ionomer to carbon (I/C) ratio, the desired amount of carbon catalyst was mixed with Nafion™ ionomer solution (Sigma-Aldrich, 5 wt.%) and 1.5 mL of isopropanol (AnalR NORMAPUR®, VWR). This solution was homogenized in an ultrasound bath for 10 min, followed by complete evaporation of the solvents at room temperature. The dried solids were dispersed in isopropanol (AnalR NORMAPUR®, VWR) and quantitatively deposited on a gas transport medium (Toray paper TGP 60 with microporous layer, Alfa Aesar). As anode electrodes, commercial Johnson Matthey platinum electrodes, with a platinum loading of 0.4 mgPt cm-2 (Alfa
Aesar, Johnson Matthey, Hydrogen Reformate/Cathode) were used. The MEAs were obtained by hot-pressing anode and cathode electrodes on both sides of a pre-treated Nafion™115 membrane (H+, DuPont) at 145°C and 400 kg cm-2, for 3 min. Pretreatment of the Nafion™ membranes consisted of first boiling in 3 vol% H2O2 (from 30wt% H2O2
solution ACS grade, Sigma-Aldrich) in H2O (MilliQ 18.2 MΩ cm) for 1h, then boiling
in 0.5M H2SO4 (from H2SO4 97% Aristar from VWR) for 1h and finally boiling in H2O
for 1h. The thicker Nafion™ 115 membranes was deliberately chosen over the thinner 221 membranes in order to avoid the possibility of any Pt crossover from the anode. Single PEFC tests refer to a 5 cm2 electrode area and single serpentine flow fields (PEFC
hardware from Fuel Cell Technologies, Inc.). During PEFC tests pure hydrogen (BIP plus-X47S, Air products) was used at a flow rate of 160 ccm and pure oxygen (BIP plus- X47S, Air products) at a flow rate of 550 ccm. Both anode and cathode compartments of the cell were pressurized with a backpressure of 2 bar (gauge). The fuel cell hardware was maintained at a temperature of 80 °C. Relative humidity (RH) values were achieved by adjusting the temperature of the humidification bottles. Moreover the backpressure of the system was corrected to account for the different water partial pressure and to
match the back pressure at 100% RH. Before any data collection it was ensured that the cell was stable at the respective current density, with a potential drift below 5 mV/hour. Polarization curves were performed utilizing an electronic load (Kikusui KFM2150). Gases were humidified via a humidification system from Fuel Cell Technologies, Inc.
3.5
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