Nanocrystals and nickel catalyst substantially improve light-based hydrogen production

Nov 08, 2012
Cadmium selenide nanocrystals absorb light and transfer electrons to a nickel catalyst (blue), which subsequently generates hydrogen (white). Credit: Ted Pawlicki/University of Rochester

Hydrogen is an attractive fuel source because it can easily be converted into electric energy and gives off no greenhouse emissions. A group of chemists at the University of Rochester is adding to its appeal by increasing the output and lowering the cost of current light-driven hydrogen-production systems.

The work, funded by the U.S. Department of Energy, was led by chemistry professors Richard Eisenberg, Todd Krauss, and Patrick Holland, and included graduate students Zhiji Han and Fen Qiu. Their paper will be published later this month (Nov. 23) in the journal Science.

The say their work advances what is sometimes considered the "holy grail" of energy science—efficiently using sunlight to provide clean, carbon- for vehicles and anything that requires electricity.

One disadvantage of current methods of has been the lack of durability, but the Rochester scientists were able to overcome that problem by incorporating nanocrystals. " are typically used to capture light in photocatalytic systems," said Krauss, who has been working in the field of nanocrystals for over 20 years. "The problem is they only last hours, or, if you're lucky, a day. These nanocrystals performed without any sign of deterioration for at least two weeks."

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Nanocrystals and nickel catalyst substantially improve light-based hydrogen production. Credit: Matthew Mann/University of Rochester

Richard Eisenberg, the Tracy H. Harris Professor of Chemistry, has spent two decades working on . During that time, his systems have typically generated 10,000 instances—called turnovers—of being formed without having to replace any components. With the nanocrystals, Eisenberg and his colleagues witnessed turnovers in excess of 600,000.

The researchers managed to overcome other disadvantages of traditional photocatalytic systems. "People have typically used catalysts made from platinum and other expensive metals," Holland said. "It would be much more sustainable if we used metals that were more easily found on the Earth, more affordable, and lower in toxicity. That would include metals, such as nickel."

Holland said their work is still in the "basic research stage," making it impossible to provide cost comparisons with other energy production systems. But he points out that nickel currently sells for about $8 per pound, while the cost of platinum is $24,000 per pound.

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

The process developed by Holland, Eisenberg, and Krauss is similar to other photocatalytic systems; they needed a chromophore (the light-absorbing material), a to combine protons and electrons, and a solution, which in this case is water. Krauss, an expert in nanocrystals, provided cadmium selenide (CdSe) quantum dots (nanocrystals) as the chromophore. Holland, whose expertise lies in catalysis and nickel research, supplied a nickel catalyst (nickel nitrate). The nanocrystals were capped with DHLA (dihydrolipoic acid) to make them soluble, and ascorbic acid was added to the water as an electron donor.

Photons from a light source excite electrons in the nanocrystals and transfer them to the . When two electrons are available, they combine on the catalyst with protons from water, to form a hydrogen molecule (H2).

This system was so robust that it kept producing hydrogen until the source of electrons was removed after two weeks. "Presumably, it could continue even longer, but we ran out of patience!" said Holland.

One of the next steps will be to look at the nature of the nanocrystal. "Some nanocrystals are like M&Ms – they have a core with a shell around it," said Eisenberg. "Ours is just like the core. So we need to consider if they would they work better if they were enclosed in shells."

Explore further: Quantum mechanical calculations reveal the hidden states of enzyme active sites

More information: "Robust Photogeneration of H2 in Water Using Semiconductor Nanocrystals and a Nickel Catalyst," by Z. Han, Science, 2012. www.sciencemag.org/content/ear… 1/07/science.1227775

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User comments : 6

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DTC
3.5 / 5 (2) Nov 08, 2012
It's exciting to see so much recent progress in the sustainable production of Hydrogen!
tthb
1 / 5 (1) Nov 08, 2012
no good news, . . . .
Urgelt
not rated yet Nov 09, 2012
Hydrogen isn't an energy source. It's a fuel. It doesn't compete against energy sources like nuclear power plants, hydroelectric dams, coal-burning generators, etc. Its competition is batteries, and it's useful to think of hydrogen as 'storing and releasing energy' like batteries do.

Storing hydrogen is the main problem. Hydrogen is tricky to hold in storage; it leaks. And it has to be pressurized to be useful as a fuel, which requires a daunting amount of energy. There is no distribution infrastructure, as there is for gasoline or electricity. These facts make hydrogen a dark horse in the race to power vehicles.

Batteries will get better: more energy density, faster recharging, better durability. I honestly don't see what is holding up optimism for hydrogen advocates. The economics for hydrogen are not favorable.
elektron
1 / 5 (1) Nov 09, 2012
@Urgeit, er everything is in principle and energy source.
JustAnyone
not rated yet Nov 09, 2012
1. >> Hydrogen isn't an energy source.

Incorrect here: commercial hydrogen is produced from petrochemical sources. THIS setup produces H2 from SUNLIGHT, which is an energy source.

2. You're correct about storage being difficult in car-sized situations. But, storing H2 is very easy with a big tank. Or, most fuel cells convert H2 and atmospheric O2 into electricity with reasonable efficiencies.

Hydrogen production economics, when just discussing using it for auto fuel, don't make sense. otherwise, they very much do.
ValeriaT
1 / 5 (2) Nov 09, 2012
This paradigm is based on assumption, the sustainable human expansion can run on some solar cells filled with some aqueous solutions, which is complete nonsense from both technological, both economical perspective. The scientists who are dealing with such research will always ignore the cold fusion competition, or they would jobs as a single man. They will lose them anyway.

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