Photoelectrochemical cells or PECs are solar cells which generate electrical energy from light, including visible light. Some photoelectrochemical cells simply produce electrical energy, while others produce hydrogen in a process similar to the electrolysis of water.
In this type of photoelectrochemical cell, electrolysis of water to hydrogen and oxygen gas occurs when the anode is irradiated with electromagnetic radiation. This is also referred to as artificial photosynthesis and has been suggested as a way of storing solar energy in an energy carrier, namely hydrogen. This hydrogen can then be used as fuel.
There are two types of photochemical systems with photocatalysis. One uses semiconductor surfaces as catalysts. In these devices the semiconductor surface absorbs solar energy and acts as an electrode for water splitting. The other methodology uses in-solution metal complexes as catalysts.
Photogeneration cells have passed the 10 percent economic efficiency barrier. Lab tests confirmed the efficiency of the process. The main problem is the corrosion of the semiconductors, which are in direct contact with water. Research is now ongoing to reach a service life of 10000 hours, a requirement established by the United States Department of Energy.
In the simplest terms, the mechanism of PECs is based on the conversion of light energy into electricity within a cell involving two electrodes. Then the electricity is used for different aspects such as water electrolysis. In theory, there are three options for the arrangement of photo-electrodes in the assembly of PECs:
- photo-anode made of a n-type semiconductor and a cathode made of metal;
- photo-anode made of a n-type semiconductor and a photo-cathode made of a p-type semiconductor;
- photo-cathode made of a p-type semiconductor and an anode made of metal.
According to the principle of PECs, the two basic requirements for materials used as photo-electrodes are optical function, required to obtain maximal absorption of solar energy, and catalytic function, required for other reactions such as water decomposition.
Consequently, the development of high-efficiency photoelectrodes that satisfy the requirements entails processing of the materials in order to achieve optimized properties in terms of performance characteristics, including high efficiency of solar energy conversion, durability in aquatic environments, and low cost.
TiO2 is primarily used in the PECs to achieve substantial efficiency. Including SrTiO3 and BaTiO3, this kind of semiconducting titanates, the conduction band has mainly titanium 3d character and the valence band oxygen 2p character. The bands are separated by a wide band gap of at least 3 eV, so that these materials absorb only UV radiation. Change of the TiO2 microstructure has also been investigated to further improve the performance, such as porous nanocrystalline TiO2 photoelectrochemical cells. Meanwhile, other non-oxide semiconductors such as GaAs, MoS2, WSe2 and MoSe2 are also used to in the PECs as the n-type electrode due to their stability in multiplicity of chemical and electrochemical steps in the photocorrosion reactions.
- Artificial photosynthesis
- Glossary of fuel cell terms
- Photocatalytic water splitting
- Photochemical reaction
- Timeline of hydrogen technologies
- John A. Turner et al. (2007-05-17). "Photoelectrochemical Water Systems for H2 Production". National Renewable Energy Laboratory. Retrieved 2011-05-02.
- Berinstein, Paula (2001-06-30). Alternative energy: facts, statistics, and issues. Greenwood Publishing Group. ISBN 1-57356-248-3. "Another photoelectrochemical method involves using dissolved metal complexes as a catalyst, which absorbs energy and creates an electric charge separation that drives the water-splitting reaction."
- Deutsch, T. G.; Head, J. L.; Turner, J. A. (2008). "Photoelectrochemical Characterization and Durability Analysis of GaInPN Epilayers". Journal of the Electrochemical Society 155 (9): B903. doi:10.1149/1.2946478.
- Brad Plummer (2006-08-10). "A Microscopic Solution to an Enormous Problem". SLAC Today. SLAC National Accelerator Laboratory. Retrieved 2011-05-02.
- Wang, H.; Deutsch, T.; Turner, J. A. A. (2008). "Direct Water Splitting Under Visible Light with a Nanostructured Photoanode and GaInP2 Photocathode". ECS Transactions 6. p. 37. doi:10.1149/1.2832397.
- Tryk, D. (2000). "Recent topics in photoelectrochemistry: achievements and future prospects". Electrochimica Acta 45: 2363–2376. doi:10.1016/S0013-4686(00)00337-6.
- A. Fujishima, K. Honda, S. Kikuchi, Kogyo Kagaku Zasshi 72 (1969) 108–113
- De Haart, L.; De Vries, A. J.; Blasse, G. (1985). "On the photoluminescence of semiconducting titanates applied in photoelectrochemical cells". Journal of Solid State Chemistry 59 (3): 291–261. Bibcode:1985JSSCh..59..291D. doi:10.1016/0022-4596(85)90296-8.
- Cao, F.; Oskam, G.; Meyer, G. J.; Searson, P. C. (1996). "Electron Transport in Porous Nanocrystalline TiO2Photoelectrochemical Cells". The Journal of Physical Chemistry 100 (42): 17021. doi:10.1021/jp9616573.
- Kline, G.; Kam, K.; Canfield, D.; Parkinson, B. (1981). "Efficient and stable photoelectrochemical cells constructed with WSe2 and MoSe2 photoanodes". Solar Energy Materials 4 (3): 301. doi:10.1016/0165-1633(81)90068-X.
- EERE-Photoelectrochemical Generation of Hydrogen Using Heterostructural Titania Nanotube ArraysMano