The effect of an activation procedure applied to a proton exchange membrane fuel cell (PEMFC) was studied considering membranes of different natures: sulfonated poly(ether ether ketone) (sPEEK) (sulfonation degree, SD, of 42%), plain and loaded with zirconium oxide (2.5 wt% and 5.0 wt.%) and Nafion 112, 1135 and 117 (the effect of the thickness was also studied). Activation procedures can be understood as all the actions that can bring the MEA to its highest and stabilized performance. In this study we distinguish between pre-treatment and in situ activation procedures. The effect of the pre-treatment was evaluated by performing proton conductivity measurements. On the other hand, the in situ activation procedure effect was followed by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), polarization curves, methanol crossover and electro-osmotic drag measurements. It was found that both pre-treatment and in situ activation were effective to increase the power density of all the MEAs even using different PEMs. The activation of the thicker membranes benefits from higher activation temperatures, around 70 degrees C, while the thinner membranes show the best performance when activated at a temperature closer to 55 degrees C and 40 degrees C. respectively. (c) 2012 Elsevier B.V. All rights reserved.