Hironobu Ozawa

A photo-hydrogen-evolving molecular device made up of a tris(2,2'-bipyridine)ruthenium(II) derivative and a dichloro(2,2'-bipyridine)platinum(II) derivative has been found to serve as the first effective model of a "molecular device" which evolves molecular hydrogen from water in the presence of a sacrificial electron donor (EDTA), under the visible-light illumination.

This article summarizes the ongoing studies on the photo-hydrogen-evolving molecular devices (PHEMDs) made up of polypyridyl Ru(II) photosensitizers and Pt(II)-based molecular catalysts, carried out in the authors' group in the last two decades. The H(2)-evolving activities of Pt(II)-based molecular catalysts demonstrated by various experimental evidences are first described. Then the structure-activity relationship, some important factors required for the higher catalytic activity, and several

The photo-hydrogen-evolving activity (activity to enhance the photochemical EDTA-reduction of water into molecular hydrogen) was evaluated for three different Ru(II)Pt(II) dimers with a general formula of [(bpy)2Ru(micro-bridge)PtCl2]2+(bpy = 2,2'-bipyridine; bridge = 4,4'-bis(N-(3-aminopropyl)carbamoyl)-2,2'-bipyridine (L1), 2,3-bis(2-pyridyl)pyrazine (L2), and 4,4'-bis(N-(4-pyridyl)methylcarbamoyl)-2,2'-bipyridine (L3); EDTA = ethylenediaminetetraacetic acid disodium salt). A new Ru(II)Pt(II)

The conversion efficiency of black-dye-based dye-sensitized solar cell (DSC) was improved by cosensitization with organic dye (NKX-2553 or D131). This improved conversion efficiency was further enhanced by employing deoxycholic acid (DCA) as a coadsobent. The highest conversion efficiency, 11.6% under AM 1.5 irradiation (100 mW cm−2), was obtained in DSC with black dye and D131 in the presence of DCA.

An extremely high conversion efficiency (11.9%) can be achieved for a dye-sensitized solar cell with a ruthenium sensitizer (<bold>TUS-38</bold>) by optimizing the dye-adsorption conditions and the electrolyte composition.

A polypyridyl ruthenium sensitizer possessing pyridyl anchors (Ru-py) forms much stronger chemical linkages to TiO₂ surfaces compared to the conventional carboxylate and phosphonate ones. A highly stable dye-sensitized photoelectrochemical cell for water reduction is successfully demonstrated using this technique.

The effects of the dye-adsorption solvent on the performances of the dye-sensitized solar cells (DSSCs) based on black dye have been investigated. The highest conversion efficiency (10.6 %) was obtained in the cases for which 1-PrOH and the mixed solvent of EtOH and tBuOH (3:1 v/v) were employed as dye-adsorption solvents. The optimized value for the dielectric constant of the dye-adsorption solvent was found to be around 20. The DSSCs that used MeOH as a dye-adsorption solvent showed inferior s

The mechanism of photoinduced hydrogen evolution from water driven by the first photo-hydrogen-evolving molecular catalyst (1), given by a coupling of [Ru(bpy)(2)(5-amino-phen)](2+) and [PtCl(2)(4,4'-dicarboxy-bpy)] (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline), was investigated in detail. The H(2) evolution rate was found to obey Michaelis-Menten enzymatic kinetics with regard to the concentration of EDTA (ethylenediamine tetra-acetic acid disodium salt, sacrificial electron donor), which

Dependence of the suppression of the backward electron transfer reaction from the TiO2 photoelectrode to I3(-) in the electrolyte on the alkyl chain length of the quaternary ammonium cation has been investigated for further efficiency improvement of high-performance cosensitized dye-sensitized solar cells (DSCs). The tetraheptylammonium cation was found to be more effective than the tetraethylammonium and tetrabutylammonium cations for the suppression of the backward electron transfer reaction w

Abstract The second example of a photo-hydrogen-evolving (PHE) molecular device consisting of a Ru(bpy)32+ (bpy = 2,2′-bipyridine) derivative and a cis-PtCl2 unit has been successfully prepared and characterized to reveal that the PHE activity is quite sensitive to the structural modification at the bridging spacer unit connecting the RuII and PtII centers.

Effective enhancement of the performance of black dye based dye-sensitized solar cells has been achieved by MgO or Al(2)O(3) surface modification of the TiO(2) photoelectrode. The conversion efficiency was improved from 10.4% to 10.8% due to the blocking effect of the thin overlayer at the TiO(2) surface.

Photoelectrochemical overall water splitting by semiconductor electrodes modified with functional molecules has attracted considerable attention in recent years. Various kinds of molecular-based photoanodes consisting of a semiconductor thin film modified with both a photosensitizer (PS) and a water oxidation catalyst (WOC) have been developed thus far, and overall water splitting is achieved by using such a molecular-based photoanode and a Pt cathode. Nevertheless, due to the desorption of a PS

The onset potential for H₂ production from neutral water (pH 7) catalyzed by a platinum(ii) porphyrin (PtP-py) modified TiO₂ electrode positions very close to the standard water reduction potential (less than 50 mV). H₂ production is driven by the conduction band edge potential of TiO₂ at the PtP-py-modified TiO₂ cathode.

Two novel ruthenium sensitizers with a hexylthiophene-modified terpyridine ligand (TUS-35 and TUS-36) were synthesized to improve the molar absorptivity of the previously reported ruthenium sensitizer (TBA)[Ru{4'-(3,4-dicarboxyphenyl)-4,4″-dicarboxyterpyridine}(NCS)3], TBA = tetrabutylammonium (TUS-21). A relatively strong absorption appeared at ∼380 nm, and the molar absorption coefficient at the metal-to-ligand charge transfer (MLCT) band decreased in TUS-35 by introducing a 2-hexylthiophene u

The effects of the addition of the tetrabutylammonium cation in the electrolyte on the performance of a black dye-based dye-sensitized solar cell (DSC) have been investigated. The conversion efficiency of the cosensitized DSC with black dye and D131 was improved to 11.8% by using an electrolyte containing three kinds of cations.