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Photoelectrochemical Cells - Coggle Diagram
Photoelectrochemical Cells
Background
Chemical cells that based on junctions formed between liquids and semiconductors
The liquid induces a barrier in the semiconductor much in the same way as does a metal.
The liquid contains a species known as a redox couple with two charge states.
The species changes from an oxidized to a reduced state if it accepts an electron, or undergoes the opposite process of oxidization if it gives up an electron.
Light is absorbed in the semiconductor, creating an electron-hole pair, as in a standard cell.
Typically, the anode or the cathode consists of a semiconductor that absorbs sunlight, and the other electrode is typically a metal.
Photons with energies greater than the semiconductor band gap can be absorbed by the semiconductor, creating electron-hole pairs which are split by the electric field in the space-charge region between the semiconductor and the electrolyte.
Materials: TiO₂
Titanium dioxide (TiO₂) is one of the most studied heterogeneous photocatalyst because of its good chemical stability, absence of toxicity, relative low cost, photostability and simple processing.
Semiconductor TiO₂ is a benchmark photocatalyst for the successful removal of organic pollutants in both liquid and gas phases.
However, TiO₂ has a large band gap (3.3eV) and absorbs only near UV-region, which is approximately 5% of the solar radiation
Its wide band gap requires that UV radiation is used to trigger this attractive photocatalyst, which would greatly hinder the commercialization of TiO₂ photocatalysis
Application
Hydrogen-Producing Photoelectrochemical Cell (HPPEC)
Hydrogen is generally produced by splitting water in a PEC involving one semiconductor photoelectrode and another dark metal electrode.
Photoelectrochemical (PEC) water splitting represents one of the most promising energy conversion processes capable of directly producing hydrogen from renewable energy sources.
Hydrogen is produced from water using sunlight and specialized semiconductors called photoelectrochemical materials, which use light energy to directly dissociate water molecules into hydrogen and oxygen.
Electricity-producing Photoelectrochemical Cells (EPPEC)
Must be self-driven such that no external potential is needed to drive the cell.
Using solar energy is its conversion from solar radiation into electric energy.
Environmental Protection
Taking advantages of unique physical and electronic properties of MWCNTs, the use of composites of MWCNTs and TiO₂ may have interesting potential applications in photocatalysis and therefore enhance the photocatalytic activity of TiO₂
Due to their good mechanical properties, chemical stability, large specific surface area, small pore size, hollow and layered structures, carbon nanotubes have been proven to possess a great potential as superior adsorbents for removing many kinds of organic and inorganic contaminants from aqueous solution.
It is believed that the dispersion of TiO₂ on the surface of MWCNTs favors the appearance of active sites for photocatalytic degradation
Reference
A. Jitianu, T. Cacciaguerra, R. Benoit, S. Delpeux, F. Beguin, S. Bonnamy, (2004). Carbon 42, 1147 – 1151.
Hui Wang, Hui-Long Wang, Wen-Feng Jiang, Zhe-Qi Li, (2008). Photocatalytic degradation of 2,4-dinitrophenol (DNP) by multi-walled carbon nanotubes (MWCNTs)/ TiO2 composite in aqueous solution under solar irradiation. Water Research 43, 204-210.
Ochiai, T. and Fujishima, A., 2012. Photoelectrochemical properties of TiO2 photocatalyst and its applications for environmental purification. Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 13(4), pp.247-262.
KHAN, S., 2005. Materials for photoelectrochemical devices. Materials for Energy Conversion Devices, pp.35-62.