A series of three membrane types has been screened for medium temperature solid polymer electrolyte water electrolysis in membrane electrode assemblies coated with 2 mg cm(-2) of iridium oxide as a catalyst for the oxygen evolution reaction, synthesised via a hydrolysis method from the hexachloroiridic acid precursor, and deposited on the membrane either directly by spray deposition or by decal transfer. The short-side-chain perfluorosulfonic acid Aquivion (R) ionomer of equivalent weight 870 meq g(-1), in membranes of thickness 120 mu m, gives higher water electrolysis performance at 120 degrees C than a composite membrane of Aquivion (R) with zirconium phosphate, while a sulfonated ether-linked polybenzimidazole, sulfonated poly-[(1-(4,4'-diphenylether)-5-oxybenzimidazole)-benzimidazole], shows promising performance and no transport limitations up to 2 A cm(-2). The lowest cell voltage was observed at 120 degrees C for an MEA prepared using spray-coating directly on the Aquivion (R) membrane, 1.57 V at 1 A cm(-2). Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.