Light-based hydrogen production

Print edition : December 14, 2012

Photons from a light source excite electrons in the nanocrystals and transfer them to the nickel catalyst (blue). When two electrons are available, they combine on the catalyst with protons from water to form a hydrogen molecule (white).-BY SPECIAL ARRANGEMENT Photons from a light source excite electrons in the nanocrystals and transfer them to the nickel catalyst (blue). When two electrons are available, they combine on the catalyst with protons from water to form a hydrogen molecule (white).

A group of chemists at the University of Rochester has succeeded in increasing the output and lowering the cost of current light-driven hydrogen production systems. The paper based on the work, which was led by the chemistry professors Richard Eisenberg, Todd Krauss and Patrick Holland, has been published in the journal Science.

One disadvantage of current methods of hydrogen production is the lack of durability. The Rochester scientists were able to overcome that problem by incorporating nanocrystals. Generally, organic molecules are used to capture light in photocatalytic systems. The problem is that, Krauss points out, they only last hours, or, if youre lucky, a day. These nanocrystals performed without any sign of deterioration for at least two weeks.

Systems used over the last decades by Eisenberg typically generated 10,000 instancescalled turnoversof hydrogen atoms being formed without needing to have any component replaced. With the nanocrystals, the researchers witnessed turnovers in excess of 600,000. Further, the present work used a catalyst made from nickel, which is more easily available, more affordable, and lower in toxicity compared with expensive metals such as platinum.

The work is still in the basic research stage, making it impossible to provide cost comparisons with other energy-production systems. Currently, nickel costs about $8 a pound (1 lb is 0.454 kg) and platinum costs $24,000 a pound.

While the commercial implementation of their work is years off, Holland points out that an efficient, low-cost system will have uses beyond energy. Any industry that requires large amounts of hydrogen would benefit, including pharmaceuticals and fertilizers, he says.

The process developed by the group is similar to other photocatalytic systems, which have a chromophore (the light-absorbing material), a catalyst to combine protons and electrons, and a solution. The group used cadmium selenide (CdSe), in the form of quantum dots (nanocrystals), as the chromophore, nickel nitrate as the catalyst and ascorbic acid added to water as the electron donor. This system was so robust that it kept producing hydrogen until the source of electrons was removed after two weeks.

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