Integrated Systems for Water Cleavage by Visible Light; Sensitization of TiO₂ Particles by Surface Derivatization with Ruthenium Complexes

Abstract

Irradiation of acidic (pH 2) solutions of RuLb+ 2C1-(L = diisopropyl 2,2'-bipyridine-4,4'-dicarboxylate) in the presence of TiO, at 100°C leads to the loss of one bipyridyl ligand and the chemical fixation of RuL, at the surface of the TiO, particles through formation of Ru-0-Ti bonds. These surface complexes are very stable and shift the absorption onset of TiO, beyond 600 nm. Efficient sensitization of H,-generation is achieved with this system beginning in the wavelength domain between 590 and 665 nm. Preliminary water cleavage experiments with the bifunctional TiO,/Pt/RuO, redox catalyst are reported.Introduction. -Spectral sensitization of large band-gap semiconductors is widely applied in silver halide [l] and electrophotography [2]. Optimum results are achieved with systems where intimate contact between dye and semiconductor is established. Thus, in the case of ZnO, a successful strategy for sensitization, applied in patents by Ada-Gevaert [3] and Lee [4] and established through the pioneering work of Zollinger et al. [5] and Haufle [6], consists of the chelation of Zn2+ ions at the particle surface by suitable chromophores. Surface modification of semiconductors such as TiO, and SnO, by adsorbed or covalently linked photoactive dyes is also a subject of increasing investigation [7-91 in view of the potential applications to solar energy conversion. In both photoelectrochemical cells [7] and H,-generating photochemical systems [8] (91, the phenomenon of photosensitized electron injection is used to effect charge separation with light of less than band-gap energy. Very interesting in this regard is our recent observation [9] that complexation of Ti4+ by 8-hydroxyquinoline on the surface of TiO, leads to in situ formation of an efficient sensitizer for H, generation by visible light. A drawback of the latter system, making necessary the use of sacrificial electron donors, is the inability of the oxidized sensitizer to produce oxygen from water. Here, we report on a new method for surface derivatization of TiO, by a more suitable chromophore which, we believe, should be of great importance for the design of reliable catalytic systems affording water cleavage by visible light with no assistance from sacrificial donors or acceptors.

Molecular photovoltaics that mimic photosynthesis

“…The binding constant and the area occupied by the dye at the surface were determined as 5 × 10 4 M -1 and 1.6 nm 2 /molecule, respectively. Molecular dynamics calculations have been used to model the interaction of this sensitizer with the (101) surface plane of anatase [13]. The most likely configuration which is compatible with the results from the adsorption isotherm measurements is shown in Fig.…”

Counter electrodes in dye-sensitized solar cells

“…[58][59][60] The Gratzel group replaced the planar semiconductor electrode with a mesoporous film of TiO 2 nanocrystalline particles, and the energy conversion efficiency of the solar cell increased by an order of magnitude. [61][62][63] Consequently, O'Regan and Gratzel published the landmark paper in Nature ''A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO 2 films'' (later was known as dye-sensitized solar cell, DSSC, or Gratzel cell), boasting an efficiency of 7.1-7.9%. 39 The development of dye-sensitized solar cells (DSSCs) in the 1990s opened up a new horizon and rapidly propelled photovoltaics technology into the era of the third generation solar cells.…”

Optimisation of Ruthenium Dye Sensitised Solar Cells Efficiency via Sn Diffusion into the TiO2 Mesoporous Layer

“…The DSC origin can be dated back to the 1960s, when it was shown by Gerischer and Tributsch [3] that photoexcited dye molecules can inject electrons into the conduction band of semiconductor substrates. Further improvements included the adsorption of dye molecules on the surface of the semiconductor [4], [5] and also the use of dispersed particles [6], [7] came as another important feature in the 1980s. Although semiconductors like ZnO sensitised with dyes like cyanine [8] have been tested, titanium dioxide has become the main semiconductor [9] employed in DSCs due to its widely known advantages.…”