Photocorrosion of ZnO Single Crystals during Electrochemical Water Splitting

Abstract

Degradation and dissolution of transparent semiconductingoxides is central to various areas, including design of catalysts and catalysisconditions, as well as passivation of metal surfaces. In particular,photocorrosion can be significant and plays a central role duringphotoelectrochemical activity of transparent semiconducting oxides. Here,we utilize an electrochemicalflow cell combined with an inductively coupledplasma mass spectrometer (ICP-MS) to enable the in situ study of the time-resolved release of zinc into solution under simultaneous radiation of UV-light. With this system we study the dissolution of zinc oxide single crystalswith (0001) and (101̅0) orientations. At acidic and alkaline pH, wecharacterized potential dependent dissolution rates into both the oxygen andthe hydrogen evolving conditions. A significant influence of the UV radiation and the pH of the electrolyte was observed. Theobserved dissolution behavior agrees well with the surface chemistry and stabilization mechanism of ZnO surfaces. In particular,polar ZnO(0001) shows ideal stability at low potentials and under hydrogen evolution conditions. Whereas ZnO(101̅0) sustainshigher dissolution rates, while it is inactive for water splitting. Our data demonstrates that surface design and fundamentalunderstanding of surface chemistry provides an effective path to rendering electroactive surfaces stable under operating conditions.