IntroductionThe construction of an artificial photosynthetic system is attracting a great deal of attention because of the potential to create fuels from solar visible-light energy and water. For this purpose photoinduced charge separation in an aqueous phase is of primary importance. Photochemical charge separations have been investigated using a Ru(bpy) 3 2þ sensitizer in aqueous solution, but these have been studied only in transient states or in the presence of sacrificial donors or acceptors. [1,2] Sensitization of a large band-gap TiO 2 photo anode, reported by Honda and Fujishima, [3] has also been one of the topics for photoinduced charge separation. The photosensitized solar cell composed of a nanoparticulate TiO 2 porous film and adsorbing dye reported by Grätzel's group [4] has shown a great success in the relevant research area. Substitution of this organic liquid by a solid-state electrolyte such as a polymer gel to stabilize the cell is one of the important research topics in this area. [5,6] On the other hand, the photochemical charge separation has only been possible in an organic medium with this sensitized solar cell. In an aqueous phase, the dye is detached from the TiO 2 surface, such that the cell does not show any stable characteristics. If sensitization is also possible in the water phase, it might lead to a widely interesting and important research area of water cleavage by solar irradiation.The present authors are interested in utilizing this sensitized TiO 2 as a photoinduced charge separation system in water, with the view to generating artificial photosynthesis to create fuels from solar energy and water in the future. Thus, the behavior of the cell in a water medium has been investigated. Rabani and Dai have reported the use of natural pigments from pomegranate adsorbed on a TiO 2 nanocrystalline film in an aqueous medium and obtained some good Communication: Solar cells comprised of nanoparticulate TiO 2 porous film photosensitized with an adsorbing dye have been utilized as photoinduced charge separation systems in aqueous media with the view to forming future artificial photosynthetic systems able to create fuels from solar energy and water. The photoinduced charge separation of the sensitized TiO 2 cell in a quasi-solid, made from agarose or k-carrageenan, was investigated.I-V curves under 98 mW Á cm À2 irradiation of ITO/TiO 2 / Ru(dcbpy) 2 (NCS) 2 . Electrolyte: 0.1 M LiI/0.01 M I 2 in a quasi-solid of 0.2 wt.-% gelatin containing a large excess of water.results. [7] However, the dye is a mixture of natural products so that its structure and activity are difficult to investigate. In addition, only the photocurrent value was given without the electrode area data, so that comparison with other data is difficult. We have reported that polysaccharides such as agarose (1) and k-carrageenan (2) can form a tight and elastic solid which contains excess water, and that electrochemical and photochemical reactions can take place in the solid the same as in pure water. [8] We have expected...

A virtual bipolar photogalvanic cell was developed using Visual Basic. On the basis of the simulation, it is indicated that the charge separation (k d ) and the charge recombination (k r ) rate constants can be estimated using the photocurrent response. The thickness of the charge separation region can be anticipated by photocurrent response at various layer thicknesses. The increase in diffusion coefficients raises the short-circuit photocurrent to enhance the performance of the photogalvanic cell. An actual device was fabricated using tris(bipyridine)ruthenium ( 2+* ] to Prussian Blue. The charge separation and the recombination rate constants were estimated, using the virtual device, to be 5 10 2 mol -1 cm 3 s -1 and 6 10 9 mol -1 cm 3 s -1 , respectively.

A program written in JAVA language was developed for the virtual electrochemical measurement of a modified electrode with a finite diffusion thickness, e.g., an electrode coated with polymer film in which functional molecules were dispersed. This program, called ES-2, can simulate cyclic voltammetry and potential-step chronoamperospectrometry by considering the rate of charge injection from the electrode to the functional molecule and the diffusion of charge. The results are shown by a voltammogram (I-V curve), and concentration distribution in the layer at a series of voltages at cyclic voltammogram mode, I-t curve, and time dependence of concentration distribution in the layer at potential step mode and a text of current values, the fraction of the oxidized molecules (R CT ) and parameters used for the simulation in both modes. A dynamic textbook of electrochemistry can be constructed by this program combined with HTML text.

Electrochemical measurements in a three electrode system under finite conditions, e.g., at an electrode coated with a polymer film incorporating functional molecules have been simulated using a program written in the JAVA language. The simulation with or without a catalytic reaction by the functional molecules has been performed using the program. The shape of a cyclic voltammogram under finite conditions is different from that under infinite conditions applied to ordinary solution electrochemistry. The fraction of the functional molecules that accepted charges (R CT) has been calculated by integrating a concentration distribution. The current under finite conditions in a potentialstep measurement deviated from that under infinite conditions above R CT 0.5. The program was introduced to a document on the electrochemistry written in HTML. It can be used by many students in an electrochemistry class without heavy loads on the server computer.

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