The Aquivion (R) short-side-chain (SSC) perfluorosulfonic acid (PFSA) ionomer was adopted in catalyst layers (CL) of polymer electrolyte membrane water electrolysers (PEMWE) instead of long-side-chain (LSC) Nafion (R) ionomer. The effects of SSC ionomer content in CL for oxygen evolution reaction were studied in half cell with cyclic voltammetry and steady state linear sweep. In a single cell test the MEA with SSC-PFSA Aquivion (R) ionomer exhibited better thermal stability than the one with LSC-PFSA Nafion (R) ionomer at 90 degrees C. The cell voltage at a current density of 1 A cm(-2) was 1.63 V at 90 degrees C using the SSC-PFSA Aquivion (R) ionomer binder, Nafion (R) 117 membrane, and without back pressurizing. In a continuous operation the cell voltage degradation rate of the MEA using Aquivion (R) ionomer binder was only about 0.82 mV h(-1). Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.