Afterwards the cathode catalyst layer was exposed to a series of cathode starvation steps (see below) followed by 2 h current hold at 500 mA cm -2 until a stable voltage was observed. After the starvation steps the MEA was ready for testing by a series of H2/O2 polarization curves for mass activity (MA) quantification at different stages of the protocol (50 kPa gauge, 100% RH and 80 °C). The polarization curves were recorded from low (i.e. 0.05 A cm -2 ) to high current (i.e. 2 A cm -2 ) ascending direction and backwards, descending direction. The current density was maintained for 3 minutes at each step and the MA value was obtained from the ascending polarization curve at 0.9 V by extrapolation resistance corrected. H2-crossover current densities were measured using the procedure described by Kocha et al . In this test the hydrogen that permeates through the membrane to the cathode is oxidized by the application of a voltage (typically 250-300 mV are sufficient, and the last one above 400 mV is in the mass transport limit) and the resulting current measured. Therefore, the cell was operated under H2/N2 and the gas crossover measurements were done at each of the operating conditions (i.e., temperature and H2-partial pressure). The catalyst activities were evaluated based on H2-crossover corrected current densities, ieff (i.e., ieff = i + ix, with ix being on the order of 2-5 A cm -2 ). MA reported in this article were not corrected for H2-crossover because the measured crossover currents accounted for a maximum of 10% at the loadings used in this study.