Metal Oxide Co-catalyst Nanolayers on Photoelectrodes

Abstract

Metal oxide co-catalyst nanolayers are coated on light-absorbing semiconductor photoanode surfaces to improve the efficiency of photoelectrochemical (PEC) water oxidation. However, the precise roles of the metal oxide co-catalysts have been difficult to understand. The co-catalyst is expected to increase the reaction kinetics for water oxidation, but owing to the dynamic properties of metal oxides under PEC conditions, the effects can be more complicated. Understanding the dynamic changes of the metal oxide co-catalyst layers and interfacial charge transfer provides insights for improving the performance of the electrode. This chapter discusses both macroscopic and microscopic techniques to control and measure directly the state of the metal oxide co-catalyst nanolayers on different photoanodes using a second working electrode. Both dual working electrode (DWE) and potential-sensing electrochemical atomic force microscopy (PS-EC-AFM) techniques have been applied in PEC measurements of several photoanodes coated with metal oxide co-catalyst nanolayers. It is discussed how these techniques allow direct measurement of the interfacial properties of the semiconductors and co-catalysts in PEC water oxidation and thus help determine the role of the co-catalyst layers in improving the PEC performance. The chapter concludes by discussing future directions for understanding the reaction mechanisms of co-catalyst metal oxide nanolayers on the surface of semiconductors.