Fe3+ is a common ion contaminant for the proton exchange membrane water electrolyser (PEMWE). In this work, three-electrode-system was employed to study the effect of Fe3+ on Nafion-bonded IrO2 catalyst which is conventional anode catalyst for PEMWE. Study results showed that Fe3+ contamination decreased IrO2 catalytic activity significantly only when the following two conditions were both satisfied: 1) Nafion resin exists in working electrode; 2) working electrode potential was over 1.471 V (vs. NHE) which is around the initial voltage of oxygen evolution reaction (OER). Besides, the contaminated working electrode activity was recovered to about 16% by being immersed into 3 M H2SO4 solution, but it was recovered to about 59% by ethanol washing method. These study results revealed that Fe3+ plays a role of catalyst for H2O2 production during OER process, which leads to Nafion resin decomposition. The degradation products covered working electrode surface, and thus decreased effective active sites of IrO2. Nafion degradation was further confirmed by analyzing 1) F- content in anode water and 2) FTIR of contaminated Nafion membrane. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.