In this work, microporous polymeric membranes for use as diaphragms in advanced alkaline electrolysis were produced from poly(ethersulfone)s UDEL ยฎ, RADEL R ยฎ, RADEL A ยฎ and VICTREX ยฎ, and were tested as diaphragms in an electrolyzer cell. The membranes were produced by phase inversion precipitation. Different membrane morphologies have been obtained by systematically varying the polymer and polymer additive content, the type of solvent and nonsolvent, molecular mass of the additive, and the hydrophilicity of the polymer. The membranes were characterized by measurement of their electric resistance in an electrolysis cell, by scanning electron microscopy and by determination of their "bubble-point". Furthermore the membranes have been tested in a "zero gap" electrolyzer cell under intermittent conditions. The variation of gas purity with load factor has been determined by gas chromatography. With decreasing current density the H2 content in 02 increases significantly but still stays below the safety threshold. In addition, the internal Ohmic resistance of the diaphragm is promisingly low. The results show that the developed membranes meet all requirements as diaphragms, like low resistance connected with sufficiently high pressure stability to avoid gas intermixture in the electrolysis cell comparlments.