TECHNOLOGY FOCUS - POLYMERS - Preferred features: The crystalline phase represents 20-30 % (pref 25%) of the amorphous phase. The thermal treatment is controlled by an X-ray diffraction spectrometer. The fuels are fed at a temp below 100degreesC. The hydrogen coming from the processing of hydrocarbons or alcohols contains more than 10 ppm of carbon monoxide. The processing of hydrocarbons or alcohols contains more than 10ppm of carbon monoxide. EXAMPLE - In 100g of a hydroalcoholic suspension of Nafion perfluorosulfonic acid (5 wt%), a quantity of Aerosil 200 corresponding to 3 wt%, in the form of a fine particulate, with particle diameter below 1 micrometer was dispersed. The mixture obtained was stirred in an ultrasonic bath for 30 minutes. Subsequently, the mixture was deposited on a Petri disc and heated for 30 minutes at 80degreesC. The film of the recast Nafion was detached by adding distilled water, and let dry for 15 hours at ambient temp, then interposed between two polytetrafluoroethylene sheets, and compressed at 3 bar. The sample, housed in a Paar HTK-10 chamber for high temperature inserted in a Philips X'Pert System PW 1830 X-ray diffractometer, was subjected to a thermal ramp up to 160degreesC controlling the subsequent transition phase of the polymer by XRD. The thermal treatment was stopped when the peak in the correspondence of 2q=17degrees (CuKalpha) was shifted to 2q = 17.8degrees(CuKalpha), corresponding to a conversion of 25% of the amorphous phase to the crystalline phase. The membrane was cut out in the desired shape and two ELAT electrodes were hot pressed on the membrane. The electode-membrane assembly was inserted into a fuel cell fed with air at 1.5 bar absolute at the cathode and pure hydrogen at the same pressure at the anode. The humidification temp of the reactants and the cell temp were maintained at 70degreesC. A second cell was equipped with an alternative membrane, Nafion 115. The cells having a 50cm2 active area, were operated at a constant current density of 5 kA/M2 for 8 hours, continuously recording the cell voltage. For both cells, the cell voltage was between 690 and 700mV, substantially constant with time. After an overnight shutdown, both cells were operated at 100degreesC with reactants humidified at 85degreesC, the other parameters being kept constant. The cell equipped with the thermally treated membrane at a current density of 5 kA/m2 showed a cell voltage comprised between 705 and 715 mV, constant with time during 8 hours of operation. The cell equipped with the alternative membrane showed an initial voltage of 710 mV which decrease progressively to zero within 30 minutes.