Tungsten Oxide-Based Materials as Catalyst Support for Oxygen Evolution Reaction

Abstract

The high cost of iridium (Ir) is a major concern for the large scale deployment of polymer electrolyte membrane water electrolysis (PEMWE). To mitigate its impact, the usage of Ir on the anode must be significantly reduced. Down-sizing the catalyst particle is a straight forward strategy but requires the use of appropriate support materials to disperse and anchor fine Ir nanoparticles. We have investigated the use of tungsten oxide-based materials as support for the oxygen evolution reaction (OER) Ir and ruthenium (Ru) catalyst. The synthesis of nanostructured substoichiometric tungsten oxide and the subsequent loading of ultrafine Ir/Ru-based nanoparticles is thoroughly studied. Due to the successful loading, the mass activity of the tungsten oxide-supported Ir/Ru-based catalyst shows significant improvements under rotating disk electrode (RDE) conditions compared with commercially available Ir/Ru-blacks. Furthermore, non-destructive depth profiling by synchrotron-based X-ray photoelectron spectroscopy (XPS) has revealed the strong catalyst-support interaction which suppressed the oxidation of the supported Ir/Ru-based catalysts, leading to much enhanced durability under accelerated durability testing conditions. To verify its performance under practical PEM electrolysis conditions, the tungsten oxide-supported OER catalyst is directly coated onto a polymer electrolyte membrane, i.e., forming a catalyst coated membrane (CCM), and tested under single cell testing conditions without pressure differential. The voltage dependent chemical state of the supported catalyst is also probed in-situ by synchrotron-based XPS where a potential dependent electron transfer between the catalyst and tungsten-oxide support is discovered. Our discovery is anticipated to aid the development of cost effective PEM electrolysis anodes.