Adsorption Studies of Counterions Carried by the Sensitizer cis-Dithiocyanato(2,2‘-bipyridyl-4,4‘-dicarboxylate) Ruthenium(II) on Nanocrystalline TiO₂ Films

Abstract

Adsorption studies of counterions carried by the ruthenium(II) complexes (Bu4N)2[Ru(Hdcbpy)2(NCS)2] (1), (Bu4N)4[Ru(dcbpy)2(NCS)2] (2), and [Ru(H2dcbpy)2(NCS)2] (3) (dcbpy = 2,2‘-bipyridyl-4,4‘-dicarboxylate, Bu4N = tetrabutylammonium) on TiO2 have been carried out by using thermoanalytical techniques, NMR, and ATR−FTIR spectroscopic methods. The thermogravimetric analysis (TGA) data of the adsorbed complexes 1 and 2 on TiO2 show the presence of 1 and ≤1.3 cations coadsorbed per ruthenium center, respectively. These complexes in the adsorbed state on TiO2 show remarkable stability in air atmospheres at high temperatures up to 180 °C. The only process that is observed at lower temperatures is the dehydration, which occurs between 40 and 110 °C. At high temperature the processes are deamination of the tetrabutylammonium counterion as well as decarboxylation and decomposition of the complex between 200 and 400 °C. The NMR data of the desorbed complexes 1 and 2 from the TiO2 surface show the presence of 1 and ≤1.5 cations, which is in close agreement with the TGA data. Comparative analysis of the ATR−FTIR spectra of complexes 1 and 2 between the free and the adsorbed forms also indicates the presence of 1 and ≤1.5 cations per ruthenium center, respectively.

Exploring the regeneration process of ruthenium(II) dyes by cobalt mediator in dye-sensitized solar cells from first-principle calculations

“…The values of 0.44 eV and 0.55 eV for the N719(2H) 2À and N719(3H) À cases, respectively, are in good agreement with the reported oxidation potential difference between N719 dye and [Co(bpy) 3 ] 2þ of 0.52 V [18]. The difference between the values for the other cases and the experimental value may be explained by the fact that the N719 dye is known to be mainly present as a negatively charged species both in solution [59] and upon adsorption onto TiO 2 [60]. The calculated reorganization energies (0.71e0.73 eV) are in good agreement with the average reorganization energies (0.8 ± 0.1 eV) reported by Feldt et al for a series of cobalt mediators [31].…”

High‐Performance Ruthenium Sensitizers Containing Imidazolium Counterions for Efficient Dye Sensitization in Water

“…The thermal stabilities of [DMPI] 2 −Ru and the reference dye N719 adsorbed on TiO 2 were studied by thermogravimetric analysis (TGA) in a dynamic air atmosphere with a heating rate of 5 °C min −1 . The thermogravimetric (TG) curves of the TiO 2 powder adsorbed by dyes (Figure ) includes three main steps: 1) loss of water; 2) decomposition of the counterion (imidazolium or tetrabutylammonium); 3) decarboxylation followed by decomposition . Due to the better stability of the imidazolium salts, the thermal decomposition temperature of the counterion for [DMPI] 2 −Ru is higher than that for N719, and the decarboxylation temperature for [DMPI] 2 −Ru also increases accordingly.…”

“…Thus, we speculate that the replacement of the TBA cation of N719 with imidazolium (DMPI or DMHI) may endow the classical ruthenium sensitizer with good water solubility, while the high ionic conductivity of imidazolium cations may also be conducive to further improvement of the photovoltaic performance. In addition, owing to the coadsorption of about one TBA cation per N719 molecule on TiO 2 , the thermal stability of N719 adsorbed on TiO 2 toward decarboxylation is higher than that of N3 by 30 °C . Compared with TBA, the imidazolium cation (DMPI or DMHI) possesses a better thermal stability and a smaller geometric size .…”

Nanosized Anatase TiO2 Single Crystals with Tunable Exposed (001) Facets for Enhanced Energy Conversion Efficiency of Dye‐Sensitized Solar Cells

“…Thus, an increased J sc and efficiency was obtained for DSSCs fabricated with the NSCT‐a and NSCT‐b as a result of the lower charge recombination rate, and the NSCT‐a shows even lower recombination rate than that of the NSCT‐b due to its better crystallinity. Ideally, a monolayer of dye molecules is bonded to the TiO 2 surface by a carboxylate bidentate coordination or an ester bonding,21 thus leaving no space for the bonding between the electrolyte and TiO 2 . Therefore, the effect of the active (001) facets on the reduction reaction of electrolyte could be minor.…”