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PRESS RELEASE（2014/5/23）

Hydrogenase S–77 — A New Frontier for Fuel Cells(637 Times Mass Activity of Platinum)

Summary
Professor Seiji Ogo and his coworkers at Kyushu University (President, Setsuo Arikawa),
Japan, have announced the application of a newly discovered hydrogenase (H 2ase) in a fuel cellwhich is more efficient than conventional fuel cells. The new enzyme, named H 2ase S–77, canrelease the electrons from hydrogen molecules and these electrons can be used in a fuel cell togenerate electric current. Though H2ases 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.
H2ase S–77, however, remains active in the presence of oxygen, which enabled Ogo and hiscoworkers to construct a working fuel cell with no platinum in the hydrogen anode component. Anenzymatic 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 themass 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 theexclusive use of this rare and precious metal in commercial fuel cells. The H 2ase 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 H2ase S–77 so that hisresearch group can produce a stripped-down working model. Such a model would be expected to beeven more efficient, as well as stable, in the hot, acidic conditions of commercial fuel cells. H 2ase
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 dedicatedthis discovery to her, taking her first initial for the name, S–77.
This work was supported by Specially promoted Research ―New Energy Sources fromHydrogenase–Photosysnthesis Models‖ from the Japan Society for the Promotion of Science; theBasic Research Programs CREST Type from the Japan Science and Technology Agency; andScientific Research on Innovative Areas from MEXT.

■BackgroundA hydrogen–oxygen fuel cell is a promising device that generates electricity from hydrogen gas(H2) and oxygen gas (O2), with the formation of water (H2O) as a waste product. Platinum isgenerally used as an electrode catalyst of the fuel cell. However, an alternative catalyst is necessary
because platinum is scarce and expensive. Hydrogenase (H2ase) (Note 1) is an enzyme that extracts
electrons from hydrogen gas under ambient conditions. This enzyme was tested for application to afuel cell electrode because it surpasses platinum with regard to hydrogen activation ability. However,
the application of H2ase to the fuel cell was not achieved due to its instability toward oxygen gas.

■ContentProfessor Seiji Ogo and his coworkers at Kyushu University have showed that H2ase 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. H2ase 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 H2ase S–77 between platinum (Note 5). In
this work, we have succeeded in the application of high ability derived from H2ase to polymer electrolyte
fuel cell (PEFC) (Note 6).
–1–■EffectThis achievement will facilitate the development of various hydrogenase electrodes and functionalhydrogenase models.

■Future Development
Professor Seiji Ogo and his coworkers have found a new hydrogenase (Note 7) and synthesized its
model complexes (Science 2007, 16, 585 and 2013, 339, 682). Based on the achievement of this work, they
have begun the development of an artificial catalyst that surpasses the previous catalyst, which has
been reported as a press release (September 6, 2011, the artificial catalyst demonstrated 1/25
performance of fuel cell with platinum catalyst) and started collaborative research with an automanufacturer.

■Publication

Title: [NiFe]Hydrogenase from Citrobacter sp. S–77 Surpasses Platinum as an Electrode for H2
Oxidation Reaction
Authors: Takahiro Matsumoto, Shigenobu Eguchi, Hidetaka Nakai, Takashi Hibino, Ki-Seok Yoon, Seiji
Ogo
Journal: Angewandte Chemie International Edition
DOI: 10.1002/anie.201404701R1–2–【Glossary】(Note 1) Nickel–iron hydrogenase is a natural enzyme that activates the hydrogen molecule. Its active
center has nickel (Ni) and iron (Fe) atoms, which are tethered by sulfur atoms (S) of cysteine residue asshown in Figure 1. X indicates water (H2O), hydroxide ion (OH–) or oxide ion (O2–) in a resting state, andhydride ion (H–) in an active state.

Figure 1. Active site structure of nickel–iron hydrogenase.
(Note 2) Figure 2 indicates activities of platinum and hydrogenase S–77 with regard to extraction ofelectrons from hydrogen gas. The horizontal axis is mass activity (current per catalyst 1 mg) and thevertical axis is iR–free over potential (subtraction of iR (resistance polarization) from observed voltage).
When iR–free overvoltage is 50 mV, H2ase S–77 has 637 times higher mass activity than platinum.

Figure 2. iR–free overvoltage versus mass activity.
(At an iR–free overvoltage of 50 mV, platinum: 0.859 A mg–1, H2ase S–77: 547 A mg–1)(Note 3) Figure 3 indicates cell voltage versus current density produced from fuel cells with platinumand H2ase S–77 as anode catalyst and platinum as cathode catalyst. The horizontal axis is current
density (current per 1 cm2) and the vertical axis is cell voltage (voltage of fuel cell).

Figure 3. Cell voltage versus current density produced from fuel cellswith platinum and H2ase S–77 as the anode catalyst and platinum as the cathode catalyst.
–3–(Note 4) Figure 4 indicates power density versus current density produced from fuel cells with platinumand H2ase S–77 as the anode catalyst and platinum as the cathode catalyst. The horizontal axis iscurrent density (current per 1 cm2) and the vertical axis is power density (product of cell voltage andcurrent density). H2ase S–77 has 1.8 times higher maximum power density than platinum.

Figure 4. Power density versus current density produced from fuel cellswith platinum and H2ase S–77 as the anode catalyst and platinum as the cathode catalyst.
(Note 5) Figure 5 shows hydrogen activation ways with platinum and H2ase S–77. Platinum
homolytically activates (cleaves) the hydrogen molecule to produce two hydrogen radicals (H•) while
H2ase S–77 heterolytically activates the hydrogen molecule to produce hydride ion (H–) and proton (H+).

Figure 5. Homolytic and heterolytic activation of hydrogen molecule by platinum and H 2ase S–77.
(Note 6) Figure 6 shows electric power generated by a fuel cell with H2ase S–77.

Figure 6. Electric power generated by a fuel cell with H2ase S–77.

–4–(Note 7) Figure 7 shows the image of finding of H2ase S–77 from Mt. Aso.

Figure 7. Image of finding of H2ase S–77.
Selected for the cover picture of Angewandte Chemie International Edition (ACIE)【INQUIRIES-Research】
Seiji Ogo, Professor
International Institute for Carbon-Neutral Energy Research (I2CNER)
Department of Chemistry and Biochemistry, Faculty of Engineering
Kyusyu UniversityTel: +81-92-802-2818 Fax: +81-92-802-2823
Mail: ogo.seiji.872@m.kyushu-u.ac.jp
Ms. Yumiko Masumoto, Ms. Ruri Hirashima
Administrative Office PR GroupInternational Institute for Carbon-Neutral Energy Research (I2CNER)
Kyushu University
Tel: +81-92-802-6935 Fax: +81-92-802-6939
Mail: wpisyogai@jimu.kyushu-u.ac.jp–5–