Creating an artificial leaf would be a big step toward a plentiful, inexpensive, zero emission fuel source.
Researchers at Arizona State University and Argonne National Laboratory report that they are close to creating an artificial leaf.
The purpose of the leaf is similar to that of its organic counterpart. It would use solar power to efficiently and inexpensively turn water into hydrogen and oxygen. Hydrogen fuel has no emissions and can be used in electrochemical cells, or for combustion in internal engines. It can also be used in the propulsion of spacecraft.
Pure hydrogen, however, does not occur naturally and it takes a substantial amount of energy to manufacture it. The creation of the artificial leaf would result in a widely distributed, environmentally friendly and inexpensive source of fuel for the world.
Recreating a process which occurs in nature is not always as easy as it sounds.
“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,” said 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.”
“We looked in detail and found that nature had used an intermediate step,” added Moore. “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.”
After observing the natural process, researchers designed an artificial relay based on the natural one and saw a major improvement. According to ASU News:
“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.”
The researchers found that the electronic structure of the relay not only mirrored but improved upon the natural systems they had observed. This is seen as an important step toward developing eco-friendly technology that will help to provide people with the solar energy needed to produce food, fuel and fiber in the future.
The project is one of the goals of BISfuel, in ASU’s Department of Chemistry and Biochemistry an Energy Frontier Research Center funded by the US Department of Energy (DoE).
There are currently 46 Energy Froentier Research Centers funded by DoE. Their goal is to transform “how we generate, transmit, store and use energy,” according to U.S. Energy Secretary Ernest Moniz.
The most recent findings can be found in the online edition of the journal Nature Chemistry.
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