Membrane electrode assemblies (MEAs) for water electrolysis were prepared by decal transferring an Ir black anode and a Pt black cathode on the two sides of a perfluorosulfonate solid polymer electrolyte (SPE) Nafion112 membrane. Performance stability of an MEA with 4 cm(2) effective electrode area was tested for 208 h in a single cell water electrolysis setup. The catalysts of both electrodes on the MEAs were characterized by means of XPS and XRD. Samples of feed water were analyzed by using conductivity meter, inductance coupling plasma optical emission spectroscopy (ICP-OES), ionic chromatography and total organic carbon (TOC) analyzer. Surface oxidation of the anodic Ir catalyst was evidenced, from the original metal Ir to 71.5% Ir(2)O(3) and 28.5% IrO(2) after 208 h of electrolysis. While the metallic state of Pt on the cathode did not change during the same period of operation, the crystallite size of the Pt catalyst increased from 9.1 nm to 9.8 nm. Water analysis shows there is significant accumulation of impurities in the feed water, which can contaminate the MEA. Fortunately, the MEA restored more than 98% of its original performance after a simple treatment with 1 mol/L H(2)SO(4) solution. This indicates the short period performance decline of the MEA is mainly caused by a recoverable contamination. Crown Copyright (C) 2010 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. All rights reserved.