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The Artificial Leaf

Posted November 04, 2011 11:59 AM by cheme_wordsmithy

Led by professor Daniel Nocera, researchers at MIT have been working on technology which mimics the photosynthetic process in leaves to directly convert sunlight into chemical fuel. The breakthrough came about when the team came across an inexpensive combination of materials to catalyze the electrolysis of water. The design is meant to allow for simple and convenient solar energy capture.

The artificial leaf, shown with some real leaves, both which convert energy from sunlight into chemical form. Photo: Dominick Reuter

The 'artificial leaf', as it is called, is a silicon solar cell with catalytic materials layering both sides. When immersed in water, this device produces oxygen and hydrogen gas as it is exposed to sunlight. These gases can then be sent to a fuel cell to produce electricity. The device requires no external controls or wiring to use, and is made of inexpensive materials (mostly silicon, cobalt, and nickel). A video showing its operation can be seen here.

A diagram of the design and function of the artificial leaf. Photo: ScienceNow

This is not to be confused with separate artificial photosynthesis technology also sometimes referred to as an artificial leaf (discussed in a previous entry), which uses water and carbon dioxide to create a hydrogen/carbon monoxide syngas. A team at the University of Illinois leads this project, and has made progress in improving the poor efficiencies of the technology through the use of ionic solvents to stabilize carbon dioxide solutions.

MIT's device is not fully functional in its current form. The biggest obstacle is developing an effective and efficient way to collect and store the gases. Proper separation and safe storage of these extremely volatile gases much be achieved at a reasonable cost to keep the feasibility and of this project within reach. The nominal conversion efficiencies of the cells themselves are also lacking in comparison to commercial solar cells (2.5-4.7% as compared to >10%). "It's a step," Nocera says. "It's heading in the right direction."

The concept behind the artificial leaf is not a new one, but this device's steps towards practicality are commendable. Catalyzed electrolysis provides a means of capturing solar energy directly into fuel form, reducing the problems associated with intermittent and inconsistent generation. The device itself attempts to make the utilization of this process more feasible by creating technology that is less expensive to manufacture and less complex to operate or maintain than traditional solar cells.

Recently, a discovery was made at MIT regarding a new catalyst (discussed in the previous entry) for a similar process using an alkaline solution rather than pure water. Future developments will likely focus on implementing this catalyst in the artificial leaf to boost efficiency. In addition, the team will be working to build the device using other materials, including iron oxide, which may be even cheaper than silicon.

Sources:

MIT News

Wired - ScienceNow

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Re: The Artificial Leaf

11/17/2011 9:03 PM

What is the difference between this device and a PV immersed in water? Granted a PV must have conductive water, but is this process more efficient than a PV alone? If so, how much so? I read the original article, but there was no way to ask questions.

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