Artificial Leaf Technology Clears Major Development Hurdle

February 20th, 2014 by James Ayre

The technology of artificial photosynthesis has cleared a major hurdle in its development — researchers from Arizona State University and Argonne National Laboratory have identified and addressed one of the primary limitations in their design of a functional artificial leaf.

The creation of a functional artificial leaf — one capable of using the sun’s energy to cheaply and efficiently convert water into hydrogen fuel and oxygen — is one of the primary goals of BISfuel, the Energy Frontier Research Center at Arizona State University.

“Initially, our artificial leaf did not work very well, and our diagnostic studies on why indicated that a step where a fast chemical reaction had to interact with a slow chemical reaction was not efficient,” stated ASU chemistry professor Thomas Moore. “The fast one is the step where light energy is converted to chemical energy, and the slow one is the step where the chemical energy is used to convert water into its elements viz. hydrogen and oxygen.”

So the researchers began a more thorough investigation of these processes, and looked to nature for inspiration — how had nature overcome the similar problem, occurring during photosynthesis, of oxidizing water to yield oxygen?

“We looked in detail and found that nature had used an intermediate step,” Moore continued. “This intermediate step involved a relay for electrons in which one half of the relay interacted with the fast step in an optimal way to satisfy it, and the other half of the relay then had time to do the slow step of water oxidation in an efficient way.”

Following this observation, the researchers created an artificial relay modeled after the natural one, and observed a great improvement.

Arizona State University provides more:

Seeking to understand what they had achieved, the team then looked in detail at the atomic level to figure out how this might work. They used X-ray crystallography and optical and magnetic resonance spectroscopy techniques to determine the local electromagnetic environment of the electrons and protons participating in the relay, and with the help of theory (proton coupled electron transfer mechanism), identified a unique structural feature of the relay. This was an unusually short bond between a hydrogen atom and a nitrogen atom that facilitates the correct working of the relay.

They also found subtle magnetic features of the electronic structure of the artificial relay that mirrored those found in the natural system. Not only has the artificial system been improved, but the team understands better how the natural system works. This will be important as scientists develop the artificial leaf approach to sustainably harnessing the solar energy needed to provide the food, fuel and fiber that human needs are increasingly demanding.

The new research was just published in the journal Nature Chemistry.

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