title: Unraveling the charge transfer/electron transport in mesoporous semiconductive TiO2 films by voltabsorptometry.
abstract: In this work, we demonstrate that chronoabsorptometry and more specifically cyclic voltabsorptometry are particularly well suited techniques for acquiring a comprehensive understanding of the dynamics of electron transfer/charge transport within a transparent mesoporous semiconductive metal oxide film loaded with a redox-active dye. This is illustrated with the quantitative analysis of the spectroelectrochemical responses of two distinct heme-based redox probes adsorbed in highly-ordered mesoporous TiO2 thin films (prepared from evaporation-induced self-assembly, EISA). On the basis of a finite linear diffusion-reaction model as well as the establishment of the analytical expressions governing the limiting cases, it was possible to quantitatively analyse, predict and interpret the unusual voltabsorptometric responses of the adsorbed redox species as a function of the potential applied to the semiconductive film (i.e., as a function of the transition from an insulating to a conductive state or vice versa). In particular, we were able to accurately determine the interfacial charge transfer rates between the adsorbed redox species and the porous semiconductor. Another important and unexpected finding, inferred from the voltabsorptograms, is an interfacial electron transfer process predominantly governed by the extended conduction band states of the EISA TiO2 film and not by the localized traps in the bandgap. This is a significant result that contrasts those previously observed for dye-sensitized solar cells formed of randomly sintered TiO2 nanoparticles, a behaviour that was ascribed to a particularly low density of localized surface states in EISA TiO2. The present methodology also provides a unique and straightforward access to an activation-driving force relationship according to the Marcus theory, thus opening new opportunities not only to investigate the driving-force effects on electron recombination dynamics in dye-sensitized solar cells but also to study the electron transfer/transport mechanisms in heterogeneous photoelectrocatalytic systems combining nanostructured semiconductor electrodes and heterogeneous redox-active catalysts.
authors: Laboratoire d'Electrochimie Moléculaire, UMR 7591 CNRS, Université Paris Diderot, Sorbonne Paris Cité, 15 rue Jean-Antoine de Baïf, F-75205 Paris Cedex 13, France. limoges.benoit@univ-paris-diderot.fr.
authors: Christophe
authors: C
authors: Renault
authors: Lionel
authors: L
authors: Nicole
authors: Clément
authors: C
authors: Sanchez
authors: Cyrille
authors: C
authors: Costentin
authors: Véronique
authors: V
authors: Balland
authors: Benoît
authors: B
authors: Limoges
mesh_terms: D065966:Absorption, Physicochemical; D004553:Electric Conductivity; D004563:Electrochemistry; D004579:Electron Transport; D049329:Nanostructures / Q000737:chemistry; D016062:Porosity; D014025:Titanium / Q000737:chemistry*; D014835:Volatilization
chemical_list: C009495:titanium dioxide; D014025:Titanium