X-ray photoelectron spectroscopy studies were systematically carried out on the electrodes before and after the electrochemical stress tests in an aqueous electrolyte at 20 degrees C and 70 degrees C. The electrodes have different ionomer structures (no ionomer, only ionomer, physically mixed ionomer and hot pressed ionomer) but have identical, commercial catalyst and catalyst loading. A significant degree of carbon corrosion, platinum migration and ionomer degradation were observed in the electrodes after the treatment. The degradation of the ionomer in the electrode is more severe than that of membrane. The electrode structure and the corresponding interface are crucial for the catalyst performance and durability. (C) 2015 Elsevier B.V. All rights reserved.