A cost-effective nanoporous ultrathin film (NPUF) electrode based on nanoporous gold (NPG)/IrO2 composite has been constructed for proton exchange membrane (PEM) water electrolysis. The electrode was fabricated by integrating IrO2 nanoparticles into NPG through a facile dealloying and thermal decomposition method. The NPUF electrode is featured in its 3D interconnected nanoporosity and ultrathin thickness. The nanoporous ultrathin architecture is binder-free and beneficial for improving electrochemical active surface area, enhancing mass transport and facilitating releasing of oxygen produced during water electrolysis. Serving as anode, a single cell performance of 1.728 V (@ 2 A cm(-2)) has been achieved by NPUF electrode with a loading of IrO2 and Au at 86.43 and 100.0 mu g cm(-2) respectively, the electrolysis voltage is 58 mV lower than that.of conventional electrode with an Ir loading an order of magnitude higher. The electrolysis voltage kept relatively constant up to 300 h (@250 mA cm(-2)) during the course of durability test, manifesting that NPUF electrode is promising for gas evolution. (C) 2017 Elsevier B.V. All rights reserved.