Volume 90 Issue 35 | p. 10 | News of The Week
Issue Date: August 27, 2012 | Web Date: August 23, 2012

Organocatalyst Splits Water

ACS Meeting News: Flavinium ion is first nonmetal catalyst to generate O2 during electrolysis
Department: Science & Technology | Collection: Sustainability
News Channels: Environmental SCENE, Materials SCENE
Keywords: splitting water, fuel cell, oxygen-evolving catalyst, solar fuels, electrolysis, hydrogen
N-Ethylflavinium ion (blue).
N-Ethylflavinium ion (blue).

In the quest to find better catalysts for splitting water into oxygen and hydrogen, chemists have discovered that a small organic molecule related to the vitamin riboflavin can substitute for transition-metal catalysts traditionally used in electrolysis. The research, reported at the American Chemical Society national meeting in Philadelphia on Aug. 20, could lead to a simple, low-cost way to generate H2 to power fuel cells.

To facilitate the splitting of water, chemists usually use costly precious-metal catalysts deposited on electrodes. In one half of the electrochemical system, water is oxidized to liberate O2. In the other half, the protons generated can readily combine to give H2. The electricity needed to drive the overall reaction would ideally come from a solar cell.

Borrowing from biological systems, where metal-free, flavin-based enzymes are important catalysts for reduction and oxidation processes, a team led by Ksenija D. Glusac of Bowling Green State University has now shown that the N-ethylflavinium ion catalytically oxidizes water to form O2 (Nat. Chem., DOI: 10.1038/nchem.1439). The researchers propose that O2 evolution occurs via formation of a flavin peroxide intermediate on the electrode surface, analogous to the mechanism of water oxidation with transition-metal oxide catalysts.

Speaking in the Division of Energy & Fuels, Glusac acknowledged that the flavinium catalyst has its limitations. The catalyst requires a high oxidation potential of 1.9 V, and it recycles only 13 times on average before becoming inactivated. But Glusac told C&EN she considers the flavinium ion a prototype.

“The water-oxidation reaction is of key importance to solar-fuel technology,” observed Thomas E. Mallouk, director of the Center for Solar Nanomaterials at Pennsylvania State University. “The discovery of a metal-free, molecular water-oxidation catalyst is unprecedented. Although the oxidation potential of this molecular catalyst is too high to be practical, the discovery suggests it may be possible to design more easily oxidized organic molecules to catalyze water oxidation.”

Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
Desertphile (Mon Aug 27 13:51:52 EDT 2012)
Interesting, and thank you. I wonder at what recycle rate such a process would become economically feasible: perhaps several hundred thousand.
Ksenija D. Glusac (Tue Sep 04 09:41:26 EDT 2012)
Indeed, the recycle rate should be high. But, the answer is probably not a single number, as the rate will depend on how expensive the catalyst is. Also, the feasibility of catalyst recycling itself should be considered.
Prof Ali A Hosseini (Mon Aug 27 14:14:02 EDT 2012)
Dear Sir,
Is this technique applicable in wast water purification?
How about using nano structured materials?
Most regards
Ksenija D. Glusac (Tue Sep 04 09:32:06 EDT 2012)
Thank you for your interest in our research.

Regarding waste water purification: it is my understanding that the treatment using electro-oxidation proceeds via the formation of H2O2, which then oxidizes the waste molecules? If that is the case, our flavinium ion might not be suitable. Hydrogen peroxide was not detected in our experiments using rotating ring-disc electrode (RRDE) setup (described in the article).
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