TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The solution in the step (a) comprises at least one strong protic acid, preferably phosphoric acid and/or sulfuric acid. The phosphoric acid comprises polyphosphoric acid, phosphonic acid, orthophosphoric acid, pyrophosphoric acid, triphosphoric acid, metaphosphoric acid and derivatives, preferably organic derivatives, such as cyclic organophosphoric acids, or their derivatives, such as acid esters.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The membrane has a solubility of less than 0.5 wt.% of polyazole polymer in 99% phosphoric acid over the temperature of 85-120 degrees C.    TECHNOLOGY FOCUS - POLYMERS - Preferred Process: The process comprises: (a1) producing a film comprising at least one polyazole with at least one amino group in a repeat unit, (b1) treating the film from the step (a1) with the solution, (c1) performing the stabilization reaction in the membrane obtained in the step (b1) directly or in a subsequent membrane processing step by heating to a temperature of greater than 25 degrees C, and (d1) optionally additionally doping the membrane obtained in the step (c1) with a strong acid or concentrating the strong acid by removing water; and (a2) preparing a solution or dispersion of at least one polyazole with at least one amino group in a repeat unit in orthophosphoric acid and/or polyphosphoric acid, (b2) mixing the solution or dispersion from the step (a2) with the solution, (c2) performing the stabilization reaction in the solution or dispersion obtained in the step (b2) directly or in a downstream processing step by heating to a temperature of greater than 25 degrees C, and (d2) optionally additionally doping the polymer obtained in the step (c2) with a strong acid or concentrating the strong acid by removing water. Preferred Components: The polyazole has a molecular weight (measured as the intrinsic viscosity) of at least 1.8 dl/g. The polyether is prepared from triethylene glycol/pentaerythritol mixture with a molar ratio of 1:10-10:1. The polyether has: a number-average molecular weight of 100-5000 g/mole; and a weight-average molecular weight of 1000-100000 g/mole. EXAMPLE - No suitable example given.