In this study the ex-situ and in-situ behavior of acid-base blend membranes from sulfonated polyethersulfone and a partially fluorinated sulfonated polymer (prepared by condensation of decafluorobipenyl with bisphenol AF, followed by sulfonation of the obtained polymer) and two different polybenzmidazoles (F-6-PBI and PBIOO(R)) was investigated. Two types of acid-base blend membranes from the abovementioned polymers were prepared and characterized: acid-base blend membranes with a molar excess of acidic blend component for low-T H-2 fuel cells (LT-FC) where the proton conductivity is overtaken by the sulfonic acid groups, and blend membranes comprising a molar excess of basic blend component which were subsequently doped with phosphoric acid for the usage in intermediate-T H-2 fuel cells (IT-FC) where the network of phosphoric acid molecules in the membrane provides the proton conduction. For elucidation of the radical stability of the membranes, the membranes were subjected to Fenton's Reagent and were operated in a H-2-PEMFC. After these tests, the membranes were investigated via SEC for molecular weight degradation. As a result, correlations could be found between degradation of the blend membranes in the fuel cell and after Fenton's test. Moreover, at IT-FC membranes, a correlation could be found between doping degree and fuel cell performance which are discussed in this paper. One of the membranes, a H3PO4-doped base-excess membrane from sPSU and PBIOO showed an excellent performance in an IT-K at 180 degrees C of 0.85 A/cm(2)@0.5 V without pressurization of the reactant gases. (C) 2013 Elsevier B.V. All rights reserved.