Photoelectrosynthetic cells

In the photoelectrosynthetic cells, there are two effective redox couples in the electrolyte so that there is a net chemical change. When the net free energy change is positive, it is termed photoelectrolysis. However, when the net free energy change is negative, it is termed... 

This volume, based on the symposium Photoeffects at Semiconductor-Electrolyte Interfaces, consists of 25 invited and contributed papers. Although the emphasis of the symposium was on the more basic aspects of research in photoelectrochemistry, the covered topics included applied research on photoelectrochemical cells. This is natural since it is clear that the driving force for the intense current interest and activity in photoelectrochemistry is the potential development of photoelectrochemical cells for solar energy conversion. These versatile cells can be designed either to produce electricity (electrochemical photovoltaic cells) or to produce fuels and chemicals (photoelectrosynthetic cells). 

Figure 1. Schematic representation of regenerative and photo-electrosynthetic cells. S is the sensitizer excited state, D is an electron donor, and D is the oxidized electron donor. Regenerative cells convert light into electricity while photoelectrosynthetic cells convert light into electricity and also produce chemical products.

Maximum energy conversion efficiencies of (/ lax = 0.1086 have recently been measured and verified for dye-sensitized regenerative cells illuminated with air mass 1.5 simulated solar irradiation [27]. The efficiency of photoelectrosynthetic cells must also include contributions from the free energy stored in the chemical products of the reduction and oxidation reactions. 

Finally, in photocatalytic cells, the reaction, which is kinetically hindered, is conducted in its thermodynamically spontaneous direction by applying an external potential bias to the cell, with the light providing the necessary activation energy for the process. Here, the location of the potentials of the Ox/Red and OxVRed couples is inverse to the case of photoelectrosynthetic cells. 

Only in few instances, the mode of operation has been changed to one of photoelectrosynthetic cells, e.g. 

The research discussed within the framework of this volume aims to identify and provide solutions to these problems through the application of solar energy conversion schemes which involve the use of regenerative photoelectrochemical, photo-electrolytic or photoelectrosynthetic cells in which solar energy can be stored into chemical fuels and in the development of photocatalytic processes for selective photooxidation of organic compounds. 

Fig. 5 Energy diagrams for semiconductor-metal photoelectrosynthetic cells.

Fig. 6 Energy diagram for double semiconductor electrode (p/n) photoelectrosynthetic cells.

Fig. 7. Energy diagrams for endoergic (aG>0) and exoergic (aG<0) photoelectrosynthetic cells.

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