Solar energy conversion and storage

If the reverse back reaction is prevented or is forbidden by other considerations, the energy remains stored in the photoproducts. Some simple photorearrangement reactions which are governed by Woodward-Hoffman rules have been found useful. These rules provide the stereochemical course of photochemical rearrangement based on symmetry properties of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecule (Section 8.6). A reaction which is photochemically allowed may be thermally forbidden. Front the principle of microscopic reversibility, the same will be true for the reverse reaction also. Thermally forbidden back reaction will produce. ble - photoproducts. Such electrocyclic rearrangements are given in . ..ure 

Most interesting and fairly successful experiment is the photosensitized decomposition of water. The decomposition of water to H2 and 02 is a highly endothermic process 

Hydrogen is a nonpolluting fuel which bums in air to produce water again releasing large amount of heat. Alternatively, H2 and 02 may be made to recombine in a fuel cell generating electrical energy. 

The thermodynamic breakdown energy for water is 1.23 eV. The electrochemical decomposition of water requires two electrons in consecutive steps. 

Therefore it should be possible to decompose water with two quantum photochemical process with the input of at least 237 kJ or 2.46 eV per molecule. For a one quantum process, the light of wavelength shorter than 500 nm can only be effective, which means poor utilization of solar spectrum. Semiconductor electrodes with suitable band gaps can act as- 

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Tributsch H (1985) Interfacial processes involving strong electronic interactions in solar energy conversion and storage. J Photochem 29 89-113... 

The accumulation of data on these metallic complexes in the area of solar energy conversion and storage [2], has allowed a rationalisation of the photochemistry of these compounds [3,4], Therefore they can now be easily applied in the context of DNA biochemistry. 

Photochemical Aspects of Solar Energy Conversion and Storage... 

A number of chromium(III) complexes with bipy, phen, terpy and related ligands have been prepared and their photochemical and photophysical properties investigated, mainly because of their potential applicability as photosensitizers for solar energy conversion and storage. Much of this work has recently been thoroughly and critically reviewed523 524 and a later article... 

We hope that this collaborative programme will continue in bringing together photochemists and photobiologists to help to ultimately devise practical systems for solar energy conversion and storage of useful compounds for energy and chemicals. 

Excited-state electron transfer (ET) is a fundamental complex phenomenon playing a crucial role in a variety of photophysical, photochemical and biochemical reactions (for reviews see, for example. Refs. [ I - 3 ). Owing to the essential role of ET in many processes and in photochemical applications (e.g., solar energy conversion and storage [4-6], photocatalysis [7], photopolymerization [8], information processing and storage [9] and photomedicine [10]) the understanding of the factors which determine the thermodynamics, kinetics and dynamics of the ET processes is very important. 

G. Hodes, L. Thompson, J. DuBow, and K. Rajeshwar, Heterojunction sihcon/indium tin oxide photoelectrodes Development of stable systems in aqueous electrolytes and their applicability to solar energy conversion and storage, J. Am. Chem. Soc. 105, 324, 1983. 

Conversion of a regenerative PEC to a PECS can incorporate several increasingly sophisticated solar energy conversion and storage configurations, which we shall discuss in this section. 

Measurements with crystals of moderate photoelectrical quality non-specific reaction with holes specific photoreaction e.g. with C) photocurrents shift characteristically with redox potential photointercalation solar energy conversion and storage regenerative electrochemical solar cells photodecomposition of HI into jHj + photoelectroanalytical probe. 

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