title: Activation energies for the rate-limiting step in water photooxidation by nanostructured α-Fe2O3 and TiO2.
abstract: Competition between charge recombination and the forward reactions required for water splitting limits the efficiency of metal-oxide photocatalysts. A key requirement for the photochemical oxidation of water on both nanostructured α-Fe(2)O(3) and TiO(2) is the generation of photoholes with lifetimes on the order of milliseconds to seconds. Here we use transient absorption spectroscopy to directly probe the long-lived holes on both nc-TiO(2) and α-Fe(2)O(3) in complete PEC cells, and we investigate the factors controlling this slow hole decay, which can be described as the rate-limiting step in water oxidation. In both cases this rate-limiting step is tentatively assigned to the hole transfer from the metal oxide to a surface-bound water species. We demonstrate that one reason for the slow hole transfer on α-Fe(2)O(3) is the presence of a significant thermal barrier, the magnitude of which is found to be independent of the applied bias at the potentials examined. This is in contrast to nanocrystalline nc-TiO(2), where no distinct thermal barrier to hole transfer is observed.
authors.affiliation: Chemistry Department, Imperial College London, South Kensington Campus, SW7 2AZ, UK.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Cowan
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Barnett
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Pendlebury
authors.forename: Monica
authors.initials: M
authors.lastname: Barroso
authors.forename: Kevin
authors.initials: K
authors.lastname: Sivula
authors.forename: Michael
authors.initials: M
authors.lastname: Grätzel
authors.forename: James R
authors.initials: JR
authors.lastname: Durrant
authors.forename: David R
authors.initials: DR
authors.lastname: Klug