Overall water splitting

The extension of this approach to artificial leaves based on titanates, niobates, tantalates, metal nitrides and phosphides, metal sulfides, and other transition metal oxides appears possible and useful in order to enhance the photocatalytic efficiency. In addition, the construction of multicomponent systems such as Ti02-CdS or MoS2-CdSe for overall water splitting could also lead to further improvements. This... 

Domen, K., Kondo, J.N., Hara, M., and Takata, T., Photo- and mechano-catalytic overall water splitting reactions to form hydrogen and oxygen on heterogeneous catalysts, Bull. Chem. Soc. ]pn., 73,1307,2000. 

M. Matsumura, Photocatalytic activity of hydrothermally synthesized tantalite pyrochlores for overall water splitting, Appl. Cat. A Gen. 300 (2006) 186-190. 

Takata, T., Shinohara, K., Tanaka, A., Kara, M., Kondo, J.N., Domen, K. 1997a. A highly active photocatalyst for overall water splitting with a hydrated layered perovskite structure. J Pho-tochem PhotobiolA Chem 106 45 9. 

A portion of the supplied thermal energy is expelled with the products. The overall water splitting process, see Fig. 2.6, in general requires both heat and work input. In Fig. 2.6 qr represents the heat energy supplied at high temperature Tr, qo represents the heat rejected at lower temperature To, and Wi is the useful work input, if any, for the process. The enclosed region contains only water, or water and materials involved in different... 

Ikeda S, Takata T, Kondo T, Hitoki G, Kara M, Kondo JN, Domen K, Hosono H, Kawazoe H, Tanaka A (1998) Mechano-catalytic overall water splitting, Chem Commun 2185-2186... 

Hitoki G, Takata T, Ikeda S, Hara M, Kondo JN, Kakihana M, Domen K (2001) Mechano-catalytic overall water splitting on some mixed oxides. Catal Today 63 175-181... 

Ross DS (2004) Comment on A study of Mechano-Catalysis for overall water splitting . J Phys Chem B 108 19076-19077... 

Hara M, Kondo T, komoda M, Ikeda S, Shinohara K, Tanaka A, Kondo JN, Domen K (1998) CU2O as a photocatalyst for overall water splitting under visible light irradiation. Chem Commun 357-358... 

Iwase H, Kato H, Kudo A (2006) Nanosized gold particles as an efficient cocatalyst for photocatalytic overall water splitting. Catal Lett 108 6-9... 

Loaded with 10-20 nm nanoparticles of rhodium-chromium mixed oxide (Rh2-yCry03) as a cocatalyst on the surface of [(Gai xZnx)(Ni-xOx)], the quantum efficiency of overall water splitting is about 2.5% at 420-440 nm [55,180-182]. Use of AgN03 as a sacrificial electron acceptor leads to an increase in oxygen evolution. The mixed oxide exhibited high and stable photocatalytic activity in aqueous H2SO4 solution at pH 4.5 [182] both lower and higher pH... 

Fig. 7.12 Schematic representation of the overall water splitting mechanism on Rh2.yCry03/(Gai xZnx)(Ni x0x).

Maeda K, Teramura K, Lu D, Takata T, Saito N, Inoue Y, Domen K (2006) Characterization of Rh-Cr mixed-oxide nanoparticles dispersed on (Gai xZn x)(NixO x) as a cocatalyst for visible-light-driven overall water splitting. J Phys Chem B 110 13753-13758... 

Sato J, Saito N, Yamada Y, Maeda K, Takata T, Kondo JN, Hara M, Kobayashi H, Domen K, Inoue Y (2005) RUO2-loaded beta-Ge3N4 as a non-oxide photocatalyst for overall water splitting. J Am Chem Soc 127 4150-4151... 

The decomposition of liquid water and the following reactions are the results of a typical chemical effect. In this case, however, overall water splitting does not occur because oxygen is not obtained but hydrogen and hydrogen peroxide are. On the other hand, it is impossible to decompose water by photochemical reaction under illumination with a xenon lamp. Although it is possible to decompose water by photocatalytic reaction using a desirable photocatalyst and photoirradiation, it is difficult to decompose in practice because of rapid backward reaction, the formation and accumulation of intermediates onto the surface of photocatalyst,10) and other reasons. 

Overall water splitting, anyway, was accomplished by a combined effect of sonolysis and photocatalysis. 

The sonophotocatalytic system is effective for overall water splitting as shown in Fig. 12.2 and Table 12.1. This system requires, properly, a photocatalyst such as particulate Ti02. As ultrasonic waves pass through the solution, the properties of the solution influence a sonochemical reaction. In particular, negative effects are considered in the presence of powdered photocatalysts. The effects of fine particles in the solution on the sonochemical reaction have been noted so far. For example, Yasuda et al.19) reported the effects of insoluble particles, such as silicon oxide (Si02) or aluminum oxide (Al203), in the reactant solution on the sonochemical reaction and demonstrated that the reaction rate constant depended on particle properties, particle size and number of particles. It is assumed that a powdered photocatalyst suspended in the solution obstructs the transmission of ultrasonic waves. In this section, the influence of the photocatalyst powder suspended in solution on the sonochemical reaction is examined. 

It is thought that both active species react with each other and produce H2 and H202. It is apparent that H2 is pioduced by dimerization of H radicals and that H202 is produced by dimerization of OH radicals. The recombination of H and OH radicals may also occur. However, there is no distinction between K20 formed by the radical reaction and the one from solvent and/or the reactant. As a result, watei reacted to H2 and H202 by sonolysis In order to accomplish overall water splitting, H202 must be decomposed tc 02 and II20, as shown in Eq. (12.6). 

F. Overall Water Splitting Using Visible Light24) - An Attempt at Solar Energy Conversion... 

If a two-step mechanism, as shown in Eqs. (12.7) and (12.8), occurs, each product will be produced independently by alternating irradiation of ultrasound and light. An alternating irradiation was performed for overall water splitting under argon atmosphere. Ultrasonic wave must be irradiatea first followed by photoirradiation. This oraei of irradiation was decided from tbe scheme of sonophotocatalysis of water, as shown in Eqs. (12.7) and (12.8). As shown in Fig. 12.12, H2 and 02 were evolved by sonolysis and photocatalysis, respectively Thus each gaseous product was collected independently. 

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