'Artificial leaf' widens reach with self-healing capacity

9 April 2013
By Edd Gent
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The "artificial leaf" can harness sunlight to split water into hydrogen and oxygen without external connections (CREDIT: Dominick Reuter)

The world's first practical "artificial leaf” can now self-heal damage that occurs during production of energy.

The innovation means the leaf, which mimics the ability of real leaves to produce energy from nothing other than sunlight and water, can now be run on dirty water making it even more suitable for providing people in developing countries and remote areas with electricity.

Daniel Nocera, described the advance during the "Kavli Foundation Innovations in Chemistry Lecture" at the 245th National Meeting and Exposition of the American Chemical Society, which runs until Thursday.

Nocera, leader of the research team, explained the device is a simple catalyst-coated wafer of silicon, rather than a complicated reproduction of the photosynthesis mechanism in real leaves.

Dropped into a jar of water and exposed to sunlight, catalysts in the device break water down into its components, hydrogen and oxygen and those gases bubble up and can be collected and used as fuel to produce electricity in fuel cells.

"Surprisingly, some of the catalysts we've developed for use in the artificial leaf device actually heal themselves," Nocera said. "They are a kind of 'living catalyst.' This is an important innovation that eases one of the concerns about initial use of the leaf in developing countries and other remote areas."

Nocera, who is the Patterson Rockwood Professor of Energy at Harvard University, explained that the artificial leaf would probably find its first uses in providing "personalized" electricity to individual homes in areas that lack traditional electric power generating stations and electric transmission lines.

Less than one quart of drinking water, for instance, would be enough to provide about 100 watts of electricity 24 hours a day.

And while earlier versions of the leaf required pure water, because bacteria eventually formed biofilms on the leaf's surface shutting down production, the new “self-healing” design means it can be used in the natural environment.

"Self-healing enables the artificial leaf to run on the impure, bacteria-contaminated water found in nature," Nocera said. "We figured out a way to tweak the conditions so that part of the catalyst falls apart, denying bacteria the smooth surface needed to form a biofilm. Then the catalyst can heal and re-assemble."

Nocera said that about 3 billion people today live in areas that lack access to traditional electric production and distribution systems and about 1 billion people in the developing world already lack reliable access to clean water.

"It's kind of like providing 'fast-food energy,'" he noted. "We're interested in making lots of inexpensive units that may not be the most efficient, but that get the job done. It's kind of like going from huge mainframe computers to a personal laptop. This is personalized energy."

Earlier devices used rare, costly metals and other materials, involved complicated wiring and were expensive to manufacture, but Nocera's artificial leaf uses less-expensive materials and incorporates a design — called a "buried junction" — that is simple and would be inexpensive to mass produce.

And the leaf has advantages over solar panels, which are costly and produce energy only during daylight hours, as the leaf's hydrogen and oxygen can be stored and used at night.

"A lot of people are designing complicated, expensive energy-producing devices, and it is difficult to see them being adopted on a large scale," he said. "Ours is simple, less expensive, and it works. And with that, I think we've changed the dialog in the field."

Among the team's priorities for further development of the device is integrating it with technology for converting the hydrogen into a liquid fuel that could run traditional portable electric generators or even cars.

Nocera acknowledged research funding from the National Science Foundation, the Department of Energy and the Air Force Office of Scientific Research.

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