Image courtesy of Arizona State University
The structure on the left shows the arrangement of atoms in a portion of the photosynthetic PSII complex that uses light to oxidize water. The tyrosine (Tyrz) – histidine (His 190D1) pair of amino acids plays a crucial role in moving electrons from the water oxidation complex (OEC) to the chlorophylls (green). At right is the chemical structure of the artificial analog of PSII. In this molecule, the phenol-bisimidazole structure in yellow mimics the role of the Tyr-His pair as an electron shuttle.
Using nature to inspire design, EFRC researchers constructed an artificial photosynthetic apparatus that uses sunlight to break apart water into oxygen and hydrogen fuel.
This basic science discovery using sunlight to make renewable hydrogen is a step towards energy independence through development of solar fuel systems. Such systems also have the potential to reduce the environmental impacts of human energy use.
In natural photosynthesis, multiprotein complexes termed photosystems capture solar energy and convert it to chemical energy. Sunlight is absorbed by a pigment in the photosynthetic reaction center of the photosystem, causing electrons to increase in energy. These high-energy electrons are then transported through a series of components to the water splitting/oxygen evolving complex in the photosystem where via the energy from the electrons, water molecules are split into oxygen and hydrogen ions. Using natural photosynthesis as a model, The Center for Bio-Inspired Solar Fuel Production EFRC at Arizona State University designed a completely artificial photosynthetic fuel production system. Researchers constructed synthetic versions of each of the key parts of electron absorption and electron transfer found in a natural photosystem. Ultrafast laser studies verified that the synthetic version functioned in a manner similar to the natural version. The water splitting/oxygen evolving component was added through collaboration with Pennsylvania State University. When illuminated, the final completed solar water splitting device produces oxygen and hydrogen gas from water. While this artificial system is inefficient and currently operated only on the laboratory scale, it is a step forward in finding a way to a viable solar fuel technology.
Arizona State University, Director
Center for Bio-Inspired Solar Fuel Production EFRC
Thomas E. Mallouk
Pennsylvania State University
DOE Office of Science, Office of Basic Energy Sciences, Energy Frontier Research Centers (EFRC) Program (PSII mimic and phenol-bisimidazole) and Chemical Sciences, Geosciences, and Biosciences Division (iridium oxide cell preparation and characterization)
Megiatto, J. D. Jr.; Antoniuk-Pablant, A.; Sherman, B. D.; Kodis, G.; Gervaldo, M.; Moore, T. A.; Moore, A. L.; and Gust, D. “Mimicking the electron transfer chain in photosystem II with a molecular triad thermodynamically capable of water oxidation,” Proc. Natl. Acad. Sci. U. S. A., 109,15578 (2012). [DOI: 10.1073/pnas.1118348109].
Zhao, Y.; Swierk, J. R.; Megiatto, J. D. Jr., Sherman, B.; Youngblood, W. J.; Qin, D.; Lentz, D. M.; Moore, A. L.; Moore, T. A.; Gust, D.; and Mallouk, T. A. “Improving the efficiency of water splitting in dye-sensitized solar cells by using a biomimetic electron transfer mediator,” Proc. Natl. Acad. Sci. U. S. A., 109, 15612-15616, (2012). [DOI: 10.1073/pnas.1118339109]
Center for Bio-Inspired Solar Fuel Production (BISfuel) EFRC
BES, CSGB, EFRCs