Dissolution of WO<sub>3</sub> modified with IrO<i><sub>x</sub></i> overlayers during photoelectrochemical water splitting
Ken J. Jenewein, Julius Knöppel, André Hofer, Attila Kormányos, Britta Mayerhöfer, Florian Speck, Markus Bierling, Simon Thiele, Julien Bachmann, Serhiy Cherevko
Abstract
Abstract WO 3 , an abundant transition metal semiconductor, is one of the most discussed materials to be used as a photoanode in photoelectrochemical water‐splitting devices. The photoelectrochemical properties, such as photoactivity and selectivity of WO 3 in different electrolytes, are already well understood. However, the understanding of stability, one of the most important properties for utilization in a commercial device, is still in the early stages. In this work, a photoelectrochemical scanning flow cell coupled to an inductively coupled plasma mass spectrometer is applied to determine the influence of co‐catalyst overlayers on photoanode stability. Spray‐coated WO 3 photoanodes are used as a model system. Iridium is applied to the electrodes by atomic layer deposition in controlled layer thickness, as determined by ellipsometry and x‐ray photoelectron spectroscopy. Photoactivity of the iridium‐modified WO 3 photoanodes decreases with increasing iridium layer thickness. Partial blocking of the WO 3 surface by iridium is proposed as the main cause of the decreased photoelectrochemical performance. On the other hand, the stability of WO 3 is notably increased even in the presence of the thinnest investigated iridium overlayer. Based on our findings, we provide a set of strategies to synthesize nanocomposite photoelectrodes simultaneously possessing high photoelectrochemical activity and photostability.