Advanced Photoelectrochemical Characterization: Principles and Applications of Dual-Working-Electrode Photoelectrochemistry

The performance of a photoelectrode for photoelectrochemical solar fuel production can be enhanced by integrating an overlayer of electrocatalyst (EC) with the light-absorbing semiconductor (SC). However, the mechanisms through which the EC overlayer improves performance of composite photoelectrodes are not well understood. While the simple view is that the addition of the EC increases reaction kinetics, real systems are more complicated due to the existence of multiple, interacting components. Knowledge about the dynamic state of each critical component in complex photoelectrochemical (PEC) systems such as catalyzed photoelectrodes (and, e.g., dye-sensitized solar cells) could provide important insights. This information, however, is typically not directly accessible through a conventional three-electrode PEC cell setup with a single-working electrode (SWE) connected to the SC, a counter electrode, and a reference electrode. In this chapter we discuss the “dual-working-electrode” (DWE) PEC experimental technique that features an additional working electrode, which could be used to directly monitor or control the state of crucial components, such as the EC layer of a composite photoelectrode. We illustrate how this DWE PEC technique was employed to directly measure the in situ properties of SC|EC junctions in model water-oxidizing photoanodes and thus help answer the question of how the EC layer improves the PEC performance of composite photoelectrodes. We further discuss directions for future efforts in this area.