Insights into Decomposition Pathways and Fate of Ru(bpy)32+ during Photocatalytic Water Oxidation with S2O82– as Sacrificial Electron Acceptor

Abstract

The most widely accepted system for homogeneous photocatalytic water oxidation process consists of a water oxidation catalyst, RuII(bpy)32+ as a photopump, and S2O82– as the sacrificial electron acceptor. However, this system is far less than ideal because RuII(bpy)32+ undergoes very rapid decomposition and as a result the process stops before all of the S2O82– is consumed. In this regard its decomposition pathways and the fate of RuII(bpy)32+ should be elucidated to design more efficient photocatalytic water oxidation systems. We found that two pathways exist for decomposition of RuII(bpy)32+ in the light–RuII(bpy)32+–S2O82– system. The first is the formation of OH• radicals at pH >6 through oxidation of OH– by RuIII(bpy)33+ in the dark, which attack the bpy ligand of RuII(bpy)32+. This is a minor, dark decomposition pathway. During irradiation not only RuII(bpy)32+ but also RuIII(bpy)33+ becomes photoexcited and the photoexcited RuIII(bpy)33+ reacts with S2O82– to produce an intermediate which decompose...