Water splitting principle

Figure 11.9 Principle of the sensitised water-splitting reaction using SrTiOj irradiated at 388 nm...

In addition to the properties of micelles described above, vesicles, which are bilayer structures and can be considered to be model membranes, separate two distinct aqueous phases an entrapped or inner water pool and the bulk aqueous phase. In principle, therefore, electron transfer may be possible across the bilayer and the sites of hydrogen and oxygen production in a water splitting system can be separated spatially. 

Although complete water splitting has not been observed in such a system, the principle can be tested since it is possible to form the vesicles in a solution containing one or more of the redox active components of an electron transfer system and then remove these components from the bulk solution, but not from the inner pools, by gel filtration or ion exchange. Other components of the electron transfer systems can then be added to the bulk water phase. 

Lubitz W, Reijerse EJ, Messinger J. Solar water-splitting into H2 and O2 design principles of photosystem II and hydrogenases. Energy Environ Sci. 2008 1(1) 15—31. 

The structure and function of this bacterial photosystem reveals important principles for the design of artificial photosystems. First, the sensitizer needs to be posi tioned close to secondary acceptors and donors which themselves are spatially iso lated from each other such that photoexcitation leads to rapid spatial separation of the electron hole pair. Second, compartmentalization of the photosynthetic assembly is likely to be necessary so as to prevent wasteful back reactions. For water splitting, a system in which H2 and O2 are generated in separate compartments would have both safety and efficiency advantages. 

Photocatalytic Decomposition of Water Principles of water-splitting reviewed including a section on semiconductor-based approaches. 72... 

Figure 1 The principle of photocatalytic water splitting (a) photoelectronic excitation in the phototcatalyst-generating electron-hole pairs and (b) processes occurring on photocatalyst particle following photoelectronic excitation (Mills and Le Hunte, 1997).

The principles of photochemical water splitting can be extended to the design of systems using photocatalytic semiconductors in the form of particles or powders suspended in aqueous solutions (Bard, 1979, 1980). In this system, each photocatalyst particle functions as a microphotoelectrode performing both oxidation and reduction of water on its surface (Figure 4). 

Figure 3 Principle of the photo-electrochemical water-splitting.

Figure 4 shows a diagram of the principle for the photo-catalytic water-splitting, where the photo-catalysis is assumed to be Ru[bpy]32+. The 2Ru3 reduce water to evolve 02 and 2H+. Solar photons induce the reaction ... 

Figure 4 Principle of the photo-catalytic water-splitting.

Fig. 5-8 Principle of water splitting process in an alkaline electrolyzer... 

The principle of "mediated" electron transfer, whereby electrons are passed from the reduced form of a relatively negative redox couple to the oxidized form of a relatively positive couple, has been demonstrated to occur between two polymer layers of slightly different Ru (bpy)3 complex polymers by Murray and coworkers (18), This kind of stepwise, unidirectional electron transfer may be very significant in future polymer coated PEC cells which seek to separate charge, and of additional Interest, Ru (bpy)3 complexes are frequently used as cyclic PEC catalysts in water splitting experiments. Some details of this experiment are thus Informative. 

The table shows that hydrogen can be produced directly from combustible fuels by gasification, partial oxidation, or steam reforming or from non-combustible resources, primarily by low- or high-temperature electrolysis (water splitting). Hydrogen could in principle be produced from electricity generated from combustible resources, but it would entail... 

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