Reversible Redox Probes to Determine Band‐Edge Locations and Dopant Concentrations of Nano‐TiO ₂ Thin‐Films: Settling the Mott‐Schottky Conundrum

Abstract Knowing the exact location of the semiconductor band‐edges is key for mechanistic insights into their use for water and CO 2 photo/electrocatalysis. In this regard, a reliable strategy for nano‐semiconductors did not exist yet. We demonstrate the use of reversible redox probes on nano‐semiconductor electrodes to determine their band‐edge locations in aqueous solutions. Rectifying current‐potential (i‐U) characteristics with the high work function (i.e. more positive formal potential) Fe(CN) 6 3− /Fe(CN) 6 4− redox couple yielded the exact flatband potential at various pH whereas the reversible i‐U characteristics with the low work function (i.e. more negative formal potential) Ru(NH 3 ) 6 3+ /Ru(NH 3 ) 6 2+ redox couple provided the conduction band‐edge location and dopant concentration for a 30 nm thin‐film n‐TiO 2 . The methodology can be extended to other nano‐semiconductors and serves as an alternative to and goes beyond the capabilities of the Mott‐Schottky procedure for bulk semiconductor electrodes.