Liquid-solid interface, solar energy

Interfaces between two different media provide a place for conversion of energy and materials. Heterogeneous catalysts and photocatalysts act in vapor or liquid environments. Selective conversion and transport of materials occurs at membranes of biological tissues in water. Electron transport across solid/solid interfaces determines the efficiency of dye-sensitized solar cells or organic electroluminescence devices. There is hence an increasing need to apply molecular science to buried interfaces. 

The recent recognition that the surfaces of n-type semiconductors become effective redox catalysts when irradiated with light has captured the attention of a wide range of scientists interested in solar energy conversion and has spawned innumerable studies by electrochemists, physical chemists, and solid state physicists in the last decade. Most of these investigations have concentrated on detailed depictions of the semiconductor or the interface formed as the semiconductor is brought into contact with a metal, with another semiconductor, or with a liquid phase electrolyte. 

The interfaces of importance in SECS are the solid/solid (S/S), solid/gas (S/G), and solid/ liquid (S/L) (4). The area-intensive nature of SECS components was established in the previous section. The major problem is collecting solar energy at a cost that is competitive with other energy forms. Thus, low initial cost is required for the materials, support structures, and production processes in the SECS of interest in Fig. 1 (6). This requires, for example, using thin films in mirrors, in photovoltaic systems, for antireflection coatings on windows, for passive collection, etc. in addition, these films must be made from inexpensive, durable, and easily processed materials (5). Inexpensive long-life materials in flat-plate collectors and durable, stable absorber coatings are also necessary. 

Another essential requirement for the photocatalyst is its resistance to reactions at the solid/liquid interface that may result in a degradation of its properties. These reactions include electrochemical corrosion, photocorrosion, and dissolution (Morrison, 1980). A large group of photocatalysts with suitable semiconducting properties for solar energy conversion (CdS, GaP, etc.) are not stable in the water-oxidation reaction because the anions of these materials are more susceptible to oxidation than water, causing their degradation by oxidation of the material (Ellis et al., 1977 Williams, 1960). 

Ionic liquids are involved in chemical processes at surfaces that may be sohd-hquid, solid-gas, and liquid-liquid interfaces. They are found in homogeneous or biphasic catalytic processes where they serve as process catalytic enhancement, immobilization medium, cocatalyst, or electrolytes [7, 9-12]. They may also find applications in nanotechnology, surface coatings, adsorbent materials, and solar energy storage cells [13, 14]. 

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