In this paper we introduce polyelectrolyte membranes based on phosphonated poly(pentafluorostyrene) (PPFS) and their performances in a fuel cell. The polyelectrolytes were obtained via partial phosphonation of PPFS varying the phosphonation degree from 17 to 66%. These membranes showed a high resistance to temperature (T-decomp. = 355-381 degrees C) and radical attack (96-288 h in Fenton's test). A blend membrane consisting of 82 wt% fully phosphonated PPFS and 18 wt% poly(benzimidazole) is compared to the 66% phosphonated membrane having similar ion-conductivity (sigma = 57 mS cm(-1) at 120 degrees C, 90% RH). In the fuel cell the blend showed the best performance reaching 0.40 W cm(-2) against 0.34 W cm(-2) for the 42 wt% phosphonated membrane and 0.35 W cm(-2) for Nafion 212. Furthermore, the blend maintained its operation at potentiostatic regime (0.5 V) for 620 h without declining in its performance. The highest power density of 0.78 W cm(-2) was reached for the blend with a thickness of 15 mu m using humidified oxygen (RH > 90%) at the cathode side. The switch from humidified to dry gasses during operation reduced the current density down to 0.6 A cm(-2), but the cell maintained under operation for 66 h. (C) 2017 Elsevier B.V. All rights reserved.