Interfacial engineering of metal-insulator-semiconductor junctions for efficient and stable photoelectrochemical water oxidation

Solar-assisted water splitting can potentially provide an efficient route for large-scale
renewable energy conversion and storage. It is essential for such a system to provide a
sufficiently high photocurrent and photovoltage to drive the water oxidation reaction. Here we
demonstrate a photoanode that is capable of achieving a high photovoltage by engineering
the interfacial energetics of metal–insulator–semiconductor junctions. We evaluate the
importance of using two metals to decouple the functionalities for a Schottky contact and a
highly efficient catalyst. We also illustrate the improvement of the photovoltage upon
incidental oxidation of the metallic surface layer in KOH solution. Additionally, we analyse the
role of the thin insulating layer to the pinning and depinning of Fermi level that is responsible
to the resulting photovoltage. Finally, we report the advantage of using dual metal overlayers
as a simple protection route for highly efficient metal–insulator–semiconductor photoanodes
by showing over 200 h of operational stability.