Photoelectrolysis Principles

This cell employs a solid state photovoltaic to generate electricity that is then passed to a commercial-type water electrolyzer (see Chapter 2). An alternative system involves the semiconductor photovoltaic cell configured as a monolithic structure and immersed directly in the aqueous solution, see Chapter 8 this cell involves a solid-state p-n or schottky junction to produce the required internal electric field for efficient charge separation and the production of a photovoltage sufficient to decompose water [49-51]. 

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Photoelectrolysis Principles 135 Potential Distribution Across the Interface... 

Fig. 3.4b Illustration of the operating principle of a photoelectrochemical cell producing hydrogen and oxygen during water photoelectrolysis.

As noted, the water photoelectrolysis field is inherently interdisciplinary, variously attracting and mixing the work of chemists, electrical engineers, material scientists, and physicists. Each field has its own nuances of description, which makes a book such as this a mix of units, terminology, and symbols. We have done our best to concisely describe the subject matter in way a generic scientist, regardless of the discipline in which they hope to or have received their Ph.D., could understand. Certainly the successful researcher in the field must be able to appreciate and integrate concepts and principles that cut across traditional disciplinary boundaries. 

Photoelectrolysis of Water. Figure 6.25 shows the principle of this type of cell, based on the chemical system... 

Heterogeneous semiconductor systems involve either suspensions or slurries of larger-sized semiconductor powders, or smaller colloids in solution. In principle, these semiconductor particles may act as tiny photoelectrolysis cells, similar to the photoelectrochemical systems discussed above. However, as many of the materials used for bulk electrodes are also described here in particulate form, both similar and new problems may arise, most notably irreproducibility in particle preparation, stability issues, and low C02 reduction rates. 

In a single-crystal semiconductor (n-type) based photoelectrochemical cell, the problem of achieving charge separation is easily overcome by applying an anodic bias as was first demonstrated by Honda and Fujishima [263]. Using a single crystal Ti02, they were able to carry out the photoelectrolysis of water under the influence of an anodic bias. This concept to manipulate the photocatalytic reaction by electrochemical method can be extended to nanostructured semiconductor thin films [39,116]. The principle of electrochemically assisted photocatalysis is illustrated in Fig. 10. 

Hydrogen Evolving Solar Cells Principles in the design of semiconductor electrodes, surface modification strategies, p-n junction cells, and photoelectrolysis by suspended semiconductor particles, discussed. 66... 

In principle, another anodic reaction can take place instead of semiconductor decomposition (dissolution), for example, oxidation of dissolved substance or oxygen evolution from water. Apparently, in the latter case, the illumination of semiconductor leads to photoelectrolysis of water with the formation of hydrogen and oxygen, that is, conversion of the energy of light into chemical energy of the photoelectrolysis products. 

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