Artificial Photosynthesis

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The artificial photosynthesis refers to a chemical process in which with the help of sunlight are manufactured chemical products. Analogous to biotic photosynthesis , artificial photosynthesis is supposed to produce various products such as fuels , chemicals or carbohydrates and oxygen from sunlight, carbon dioxide and water .

history

The production of fuels from solar energy by means of artificial photosynthesis is one of the most demanding tasks in chemistry . Its history goes back to 1912, when the Italian chemist Giacomo Ciamician gave a lecture, which was later published in Science , in which he pointed out the civilizational advantages of the direct use of solar energy through artificial photosynthesis compared to burning coal . However, it was not until 1973 that efforts were first made to actually achieve this goal. In the 1960s, Akira Fujishima described the photocatalytic properties of titanium dioxide and the Honda-Fujishima effect of hydrolysis . In 1983 William Ayers demonstrated the arrangement of catalysts for water splitting on a silicon wafer and a more efficient method was developed by Daniel G. Nocera in 2010. Pioneering work on the catalytic reduction of carbon dioxide with the absorption of visible light was carried out in 1982 by Jean-Marie Lehn and Raymond Ziessel (with organic rubidium complexes). In 2008 Andrew Bocarsly demonstrated the conversion of carbon dioxide to methanol and he pursued this (conversion of carbon dioxide from the air into hydrocarbons using electrochemical methods) in the company Liquid Lights, which he co-founded.

properties

Artificial photosynthesis includes both the photocatalytic splitting of water , in which water is split into hydrogen and oxygen , as well as the reduction of carbon dioxide with light and processes in which more complex hydrocarbons are formed. This latter process mimics natural photosynthesis, as it occurs, among other things, in the leaves of green plants . The use of carbon dioxide to build up carbohydrates occurs in plants in the course of the dark reaction in the Calvin cycle , regardless of the presence of light.

The way to achieve artificial photosynthesis is to mimic natural photosynthesis. However, problems arise, among other things, from the fact that the splitting of water into hydrogen and oxygen is a multi-electron process, while light absorption is a one-photon process. Great progress had been made in the individual sub-processes up to 2007, but the complete reaction in a functioning overall system had not yet been achieved. In the meantime (as of 2015) there are first prototypes on a laboratory scale, but large-scale use is still pending.

Artificial photosynthesis is seen as a promising component of a future sustainable energy supply that is to be achieved with the energy transition . While natural photosynthesis can theoretically store a maximum of 6.7% of sunlight chemically - values ​​that are significantly lower in practice - offers the possibility of higher degrees of efficiency through artificial photosynthesis and thus advantages in terms of future energy supply. It is generally assumed that systems for artificial photosynthesis, in addition to long-term stability, must have an efficiency of more than 10% in order to be considered as an alternative. The previous highest efficiency achieved is 22.4% (as of August 2015), where instead of an expensive catalyst to platinum-based electrodes made of nickel were used, which is more cost-effective disposal as opposed to platinum in large quantities. Compared to this, natural photosynthesis achieves a maximum theoretical efficiency of approx. 4.5%. In practice, however, the values ​​are significantly lower; only a few crops such as sugar cane grown in tropical climates achieve values ​​above 1%. In total, only 0.1% of the total solar radiation hitting the earth's surface is converted by natural photosynthesis and stored in biomass.

The designs are spatially separated (compartmentalized) catalytic converters and catalytic converters with a common gas space. Analogous to the electrolytic splitting of water, the latter produces a mixture of hydrogen and oxygen ( oxyhydrogen ), which is explosive and is therefore further separated.

literature

Individual evidence

  1. ^ Giacomo Ciamician , The Photochemistry of the Future . In: Science 36, No. 926, (1912), 385-394, doi : 10.1126 / science.36.926.385 .
  2. ^ Vincenzo Balzani et al., Photochemical Conversion of Solar Energy . In: ChemSusChem 1, (2008), 26-58, doi : 10.1002 / cssc.200700087 .
  3. ↑ Jessica Marshall, Solar energy: Springtime for the artificial leaf . In: Nature 510, Issue 7503, 2014, pp. 22-24, doi : 10.1038 / 510022a .
  4. ↑ Titanium dioxide photocatalysis . In: Journal of Photochemistry and Photobiology C: Photochemistry Reviews . 1, No. 1, June 29, 2000, pp. 1-21. doi : 10.1016 / S1389-5567 (00) 00002-2 .
  5. ↑ Lehn, Ziessel: Photochemical Generation of Carbon Monoxide and Hydrogen-by Reduction of Carbon Dioxide and Water Under Visible Light Irradiation , Proceedings of the National Academy of Sciences USA, Vol 79, 1982, pp 701-704
  6. ↑ E. Cole, Bocarsly et al. a .: Using a One-Electron Shuttle for the Multielectron of CO2 to Methanol: Kinetic, Mechanistic, and Structural Insights, Journal of the American Chemical Society, Volume 132, 2010, pp. 11539-11551
  7. ^ A b Nicola Armaroli , Vincenzo Balzani , The Future of Energy Supply: Challenges and Opportunities . In: Angewandte Chemie International Edition 46, (2007), 52–66, doi : 10.1002 / anie.200602373 .
  8. ↑ Artificial leaf generates electricity ( Memento of the original from May 5, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . In: National Geographic . Retrieved August 17, 2015. @1@ 2Template: Webachiv / IABot / www.nationalgeographic.de
  9. ↑ Shannon A. Bonke et al., Renewable fuels from concentrated solar power: towards practical artificial photosynthesis . In: Energy and Environmental Science 8, (2015), 2791-2796, doi : 10.1039 / c5ee02214b .
  10. ^ Nicola Armaroli , Vincenzo Balzani : Solar Electricity and Solar Fuels: Status and Perspectives in the Context of the Energy Transition . In: Chemistry - A European Journal 22, Issue 1, (2016), 32–57, doi : 10.1002 / chem.201503580 .
  11. ↑ Eugene S. Andreiadis, Murielle Chavarot-Kerlidou, Marc Fontecave, Vincent Artero: Artificial Photosynthesis: From Molecular Catalysts for Light-driven water splitting to Photo Electrochemical Cells. In: Photochemistry and Photobiology. 87, 2011, p. 946, doi : 10.1111 / j.1751-1097.2011.00966.x .