[font face=Serif]2014.06.04
[font size=5]|NiFe|Hydrogenase from Citrobacter sp. S–77 Surpasses Platinum as an Electrode for H[font size=1]
2[/font] Oxidation Reaction[/font]
[font size=4]The Paper of Prof. Seiji Ogo (Principal Investigator, Catalytic Materials Transformations Research Division, I²CNER) and his collaborators was published online in "
Angewandte Chemie International Edition"[/font]
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■ Summary
Professor Seiji Ogo and his coworkers at Kyushu University (President, Setsuo Arikawa), Japan, have announced the application of a newly discovered hydrogenase (H[font size=1]
2[/font]ase) in a fuel cell which is more efficient than conventional fuel cells. The new enzyme, named H[font size=1]
2[/font]ase S–77, can release the electrons from hydrogen molecules and these electrons can be used in a fuel cell to generate electric current. Though H[font size=1]
2[/font]ases are not new, their application to the polymer electrolyte fuel cell (PEFC) has not been possible until now because they deactivate upon exposure to oxygen. H[font size=1]
2[/font]ase S–77, however, remains active in the presence of oxygen, which enabled Ogo and his coworkers to construct a working fuel cell with no platinum in the hydrogen anode component. An enzymatic fuel cell catalyst is a worthy goal in itself, but of particular interest was its surprising efficiency. This enzyme demonstrated a mass activity (roughly the current obtained divided by the mass of catalyst per cm2 of electrode) that was over 600 times greater than that of platinum. Until now, platinum has far exceeded any other catalyst in terms of mass activity, resulting in the exclusive use of this rare and precious metal in commercial fuel cells. The H[font size=1]
2[/font]ase S–77 result, however, demonstrates that molecular catalysts could be serious contenders as a replacement for metallic platinum. Professor Ogo intends to study the working mechanism of H[font size=1]
2[/font]ase S–77 so that his research group can produce a stripped-down working model. Such a model would be expected to be even more efficient, as well as stable, in the hot, acidic conditions of commercial fuel cells.
H[font size=1]2[/font]ase S–77 was discovered by Professor Ogo and his family on an expedition to Mt. Aso, an active volcano on the island of Kyushu, Japan. He was greatly helped by his wife, Saori Ogo, and has dedicated this discovery to her, taking her first initial for the name, S–77.
This work was supported by Specially promoted Research “New Energy Sources from Hydrogenase–Photosysnthesis Models” from the Japan Society for the Promotion of Science; the Basic Research Programs CREST Type from the Japan Science and Technology Agency; and Scientific Research on Innovative Areas from MEXT.
■ Background
A hydrogen–oxygen fuel cell is a promising device that generates electricity from hydrogen gas (H[font size=1]
2[/font]) and oxygen gas (O[font size=1]
2[/font]), with the formation of water (H[font size=1]
2[/font]O) as a waste product. Platinum is generally used as an electrode catalyst of the fuel cell. However, an alternative catalyst is necessary because platinum is scarce and expensive. Hydrogenase (H[font size=1]
2[/font]ase) (Note 1) is an enzyme that extracts electrons from hydrogen gas under ambient conditions. This enzyme was tested for application to a fuel cell electrode because it surpasses platinum with regard to hydrogen activation ability. However, the application of H[font size=1]
2[/font]ase to the fuel cell was not achieved due to its instability toward oxygen gas.
■ Content
Professor Seiji Ogo and his coworkers at Kyushu University have showed that H[font size=1]
2[/font]ase S–77,
which was found by them in Mt. Aso, an active volcano on Kyushu Island, is stable toward oxygen gas and its hydrogen activation ability surpasses that of platinum as an anode catalyst of fuel cells. H[font size=1]
2[/font]ase S–77 has 637 times higher mass activity (Note 2), 1.8 times higher current density (Note 3), and 1.8 times higher power density (Note 4) than platinum. These high performances are caused by the totally different mechanisms to activate (cleave) the hydrogen molecule with H[font size=1]
2[/font]ase S–77 between platinum (Note 5). In this work, we have succeeded in the application of high ability derived from H[font size=1]
2[/font]ase to polymer electrolyte fuel cell (PEFC) (Note 6).
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