title: Crossing the divide between homogeneous and heterogeneous catalysis in water oxidation.
abstract: Enhancing the surface binding stability of chromophores, catalysts, and chromophore-catalyst assemblies attached to metal oxide surfaces is an important element in furthering the development of dye sensitized solar cells, photoelectrosynthesis cells, and interfacial molecular catalysis. Phosphonate-derivatized catalysts and molecular assemblies provide a basis for sustained water oxidation on these surfaces in acidic solution but are unstable toward hydrolysis and loss from surfaces as the pH is increased. Here, we report enhanced surface binding stability of a phosphonate-derivatized water oxidation catalyst over a wide pH range (1-12) by atomic layer deposition of an overlayer of TiO2. Increased stability of surface binding, and the reactivity of the bound catalyst, provides a hybrid approach to heterogeneous catalysis combining the advantages of systematic modifications possible by chemical synthesis with heterogeneous reactivity. For the surface-stabilized catalyst, greatly enhanced rates of water oxidation are observed upon addition of buffer bases -H2PO(-)(4)/HPO(2-)(4), B(OH)3/B(OH)2 O-, HPO(2-)4 /PO(3-)(4) - and with a pathway identified in which O-atom transfer to OH(-) occurs with a rate constant increase of 10(6) compared to water oxidation in acid.
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.
authors.forename: Aaron K
authors.initials: AK
authors.lastname: Vannucci
authors.forename: Leila
authors.initials: L
authors.lastname: Alibabaei
authors.forename: Mark D
authors.initials: MD
authors.lastname: Losego
authors.forename: Javier J
authors.initials: JJ
authors.lastname: Concepcion
authors.forename: Berç
authors.initials: B
authors.lastname: Kalanyan
authors.forename: Gregory N
authors.initials: GN
authors.lastname: Parsons
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Meyer
mesh_terms: D002384:Catalysis; D055664:Electrochemical Techniques; D004566:Electrodes; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D015394:Molecular Structure; D049329:Nanostructures / Q000737:chemistry*; D010084:Oxidation-Reduction; D013499:Surface Properties; D017971:Tin Compounds / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D017971:Tin Compounds; D014867:Water; C009495:titanium dioxide; C109984:indium tin oxide; D014025:Titanium
keywords: electrocatalysis; surface stabilization