NOVELTY - Proton-conducting, polyazole-based polymer membranes are obtained by heating a mixture of (hetero)aromatic monomers (tetra-amino compounds and polycarboxylic acids, or diamino-carboxylic acids, at least some of which have phosphonic acid groups) in polyphosphoric acid at up to 350degreesC and then processing to form a self-supporting membrane.    USE - In membrane-electrode units, especially for use in fuel cells. Other applications include electrolysis, condensers and battery systems.    ADVANTAGE - Polymer-electrolyte membranes with a high level of efficiency (especially high conductivity over a wide temperature range, even without added moisture), enabling the production of fuel cells which can be operated at low temperature (e.g. 80degreesC) without a considerable reduction in service life. These membranes are produced by a simple, low-cost method, without using expensive solvents such as dimethylacetamide which are difficult to remove.    DETAILED DESCRIPTION - A proton-conducting polymer membrane containing polyazoles with phosphonic acid groups, obtained by (A) mixing (hetero)aromatic tetra-amino compounds with (hetero)aromatic carboxylic acids containing at least two acid groups (or their derivatives), where at least part of the amino and/or acid compounds have at least one phosphonic acid group, or mixing (hetero)aromatic diaminocarboxylic acids (at least part of which contains phosphonic acid groups) in polyphosphoric acid (PPA) to form a solution and/or dispersion, (B) heating at up to 350degreesC under inert gas to form polyazoles, (C) coating the mixture from (A) and/or (B) onto a support and (D) treating the membrane thus formed until it is self-supporting.    INDEPENDENT CLAIMS are also included for    (1) electrodes with a conductive polymer coating, obtained by the above process but using an electrode as the support in step (C)    (2) membrane-electrode units comprising electrode(s) and membrane(s) as above    (3) fuel cells containing such membrane-electrode units