Suppression of phosphine-protected Au9 cluster agglomeration on SrTiO3 particles using a chromium hydroxide layer

Abstract

Gold clusters have been shown to have great potential for use as co-catalysts in photocatalytic water splitting. Agglomeration of Au clusters deposited onto semiconductor surfaces into larger particles is a major challenge. Metal oxide overlayers can be used to improve the stability of Au clusters on surfaces and avoid their agglomeration. The aim of this work is to investigate the inhibition of phosphine-protected Au₉ clusters beneath a Cr(OH)₃ overlayer to agglomerate under conditions of photocatalytic water splitting (i.e. UV irradiation). Au₉ was deposited on the surface of SrTiO₃ using a solution impregnation method followed by photodeposition of a Cr(OH)₃ layer. After UV light irradiation for 7 hours for photocatalytic water splitting, uncovered Au clusters on SrTiO₃ agglomerated into larger particles. However, agglomeration was inhibited when a thin Cr(OH)₃ layer was deposited onto the SrTiO₃-Au₉ system. From careful XPS measurements, the chemical state of the overlayer is initially determined to be Cr(OH)₃ but upon heating at 200 °C for 10 min it converts to Cr₂O₃. Through photocatalysis experiments it was found that the Cr(OH)₃ overlayer blocks the sites for O evolution reaction on the SrTiO₃-Au₉.