Artificial Leaf Technology Generates Clean, Efficient Fuel

October 20, 2015 | Sarah Tse

Caltech's artificial "leaf" technology.
Photo credit: Lance Hayashida/Caltech

Researchers at Caltech have made a breakthrough in clean energy technology with their “artificial leaf” system, which mimics plant photosynthesis to produce hydrogen fuel.

Plants are the gods of the renewable energy world: all they need to generate clean, efficient fuel is sunlight, water, and carbon dioxide. So far, we’ve only been able to worship at their feet while mucking around with coal, oil, and other fossil fuels.

But the Joint Center for Artificial Photosynthesis at the California Institute of Technology has brought us one step closer to making our own sustainable fuel. After five years of collaboration with the U.S. Department of Energy’s Energy Innovation Hub, JCAP researchers have successfully developed an efficient, safe, and cost-effective system that uses solar energy to create hydrogen fuel — essentially, an artificial leaf. Hydrogen fuel is one of our best hopes for replacing “dirty” fuels because it only produces water as an emission. If used in an electrochemical cell, it could efficiently power vehicles and electrical devices.

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The artificial leaf system produces hydrogen using three components: a photoanode, a photocathode, and a membrane. The photoanode uses sunlight to oxidize water molecules, which removes electrons and protons and leaves behind oxygen gas. Anyone who still remembers high school biology will spot the similarities to photosynthesis, except plants use those electrons and protons to create ATP, a form of molecular energy, as well as sugar molecules that they can store for food and use for building cell structures. In this system, the photocathode instead re-assembles those free-floating electrons and protons into hydrogen gas. The plastic membrane isolates the hydrogen gas so it can be collected through a pipeline and used as fuel.

Watch the leaf in action. Credit: Erik Verlage and Chengxiang Xiang/Caltech

What distinguishes this new system from previous attempts at copying photosynthesis are the innovations in design and construction. The anode and cathode are coated with an extremely thin layer of titanium dioxide, the compound in sunscreen that leaves a chalky film on your skin. Here, it serves the purpose of keeping the metallic surfaces of the electrodes from rusting in the water, while still allowing light and electrons to pass through. On top of the titanium dioxide lies another layer of nickel, which acts as a super-efficient and inexpensive catalyst to propel the water-splitting reaction. Finally, the plastic membrane keeps the oxygen and hydrogen gases from mixing in a deadly explosion, ensuring the system’s safety and stability.

A single device takes up only one square centimeter in area, but it packs a massive punch: it can convert 10 percent of the energy from sunlight into hydrogen fuel, and continuously operates for over 40 hours. "This new system shatters all of the combined safety, performance, and stability records for artificial leaf technology by factors of 5 to 10 or more," said Nate Lewis, the JCAP scientific director.

Although the system requires a bit more tweaking before it can be mass-produced, it’s a huge breakthrough in energy technology that will help us break our addiction to fossil fuels.


Based on materials provided by the California Institute of Technology.

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