Search

Abstract: The potentiostatic anodization of metallic tungsten has been investigated in different solvent/electrolyte compositions with the aim of improving the photoelectrochemical performances of the tungsten oxide layer. Among the explored electrolytes, the anodization in the NMF/H2O/NH4F solvent mixture was found to produce the most efficient WO3 photoanodes, which, combining spectral sensitivity, high electrochemically active surface and improved charge transfer kinetics, outperform, under simulated solar illumination, most of the reported nanocrystalline substrates produced by anodization in aqueous electrolytes and by sol gel methods. While the preparation of the photoelectrodes is a slow process at room temperature (20°C), it could be greatly accelerated (x 10) by carrying out the anodization at 40-50°C, thus proving to be a fast and convenient approach to the production of high performing WO3 photoactive substrates directly connected to a metal electron collector. [Copyright &y& Elsevier]

New ruthenium complexes based on bipyiridine and terpyridyne type ligands, containing boronic acid functions, of formulae: [Ru(bpy-Φ-B(OH)2)2(CN)2], 6, (bpy-Φ-B(OH)2 = 4-(2,2′-dipyridil)phenylboronic acid), [Ru(trpy-B(OH)2)(tb2bpy)Cl](PF6), 11, (trpy-B(OH)2 = 4-[4′-(2,2′:6′,2″-terpyridil]-boronic acid), [Ru(trpy)-Φ-B(OH)2)(tb2bpy)Cl] (PF6), 12, (trpy)-Φ-B(OH)2 = 4-[4′-(2,2′:6′,2″-terpyridil]-phenylboronic acid), have been prepared, characterized, and tested in dye-sensitized solar cells (DSSCs). The results of this first study indicate that: (i) the boronic acid function acts as interlocking group between sensitizer and mesoporous titanium dioxide; (ii) only the presence of two B(OH)2 groups/molecule allow to obtain high photoanode surface coverages with optical densities > 1; (iii) The presence of the phenyl spacer in 12 reduces the photocurrent efficiency with respect to complex 11, most probably for a reduced electronic coupling between excited sensitizer and semiconductor conduction band. The insights gained from this work suggest that better photoelectrochemical performances should be obtained with dye molecules based on bpy type ligands bearing two boronic acid functions directly bound to the aromatic ring. [Copyright &y& Elsevier]

Abstract: Recently, the complex Co(dtb)3 n+ (dtb=4,4 di tert-butyl-2,2′ bipyridine) in methoxypropionitrile (MPN) solvent has been proposed as an alternative redox mediator in the thin-layer dye sensitized solar cells. The electrochemical properties of this new mediator as a function of temperature were investigated by mean of symmetric golden electrodes thin-layer cell, using three electro-analytical techniques: electrochemical impedance spectroscopy (EIS), slow scan cyclic voltammetry (SCCV) and chronoamperometry (CA). Our study pointed out that, at room temperature, both the electron transfer rate k°=1.24 10−4 cms−1 as well as the diffusion coefficient D =5.85×10−7 cms−1 are rather low. Raising the temperature has a beneficial effect, increasing more than 6 times the standard rate constant of electron transfer and more than 3 times the ionic diffusion coefficient at 80°C. However, for all the studied temperatures, the slow mass transport of Co(III)/Co(II) species still remains the rate determining step. Viscosity measurements have demonstrated that the ionic mass transport in MPN follows the Stokes’ law and the Walden product is constant, in the temperature range investigated. [Copyright &y& Elsevier]