Photochemical solar energy

As described in Section 3 of Chapter 2, multi-electron processes are important for designing conversion systems. Noble metals are most potent catalysts to realize a multi-electron catalytic reaction. It is well known that the activity of a metal catalyst increases remarkably in a colloidal dispersion. Synthetic polymers have often been used to stabilize the colloids. Colloidal platinum supported on synthetic polymers is attracting notice in the field of photochemical solar energy conversion, because it reduces protons by MV to evolve H2 gas.la)... 

Polymers are attracting much attention as functional materials to construct photochemical solar energy conversion systems. Polymers and molecular assemblies are of great value for a conversion system to realize the necessary one-directional electron flow. Colloids of polymer supported metal and polynuclear metal complex are especially effective as catalysts for water photolysis. Fixation and reduction of N2 or C02 are also attractive in solar energy utilization, although they were not described in this article. If the reduction products such as alcohols, hydrocarbons, and ammonia are to be used as fuels, water should be the electron source for the economical reduction. This is why water photolysis has to be studied first. 

During the 1970s and 1980s much work was carried out on photochemical solar energy conversion by semiconductors or sensitizers to produce fuels by solar energy.2-4 The most typical system for such fuel production is water cleavage by light. 

Photochemical solar energy conversion Is a vitally Important and extremely active area of research The excited state of... 

The emission spectrum of the sun consists approximately of 9 % UV light, 40 % visible, and 51 % IR [1]. Only UV, visible, and a small fraction of the near-IR can cause electronic excitation. Furthermore, we have to take into account that the excitation energy collected should be enough to drive the chemical reactions we would like to use to store the solar energy. Therefore, any practical photochemical solar energy conversion system has to be based on visible light absorption. 

Water photolysis is the simplest photochemical solar energy conversion system for which proton reduction catalysis is essential, but carbon dioxide reduction is still an attractive research subject as a synthetic model for CO2 reduction in photosynthesis. There has been much work on chemical and photochemical CO2 reduction [24], but it is not the aim of this section to review those projects that mainly involve low molecular weight compounds. 

Ross, R.T., Hsiao, T.L. Limits on the yield of photochemical solar energy conversion. J. Appl. Phys. 48, 4783 785 (1977)... 

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