A new artificial leaf may, one day, produce enough hydrogen to fuel humanities' needs for the clean-burning fuel. Or, at least that's what the researchers of Arizona State University (ASU) think.
In the presence of oxygen, hydrogen can generate large amounts of energy, in a highly-efficient process. The end by-product is ordinary water. Hydrogen may one day be able to provide vast quantities of energy, in an environmentally-safe manner. This could lead to what futurists call a "hydrogen economy."
Due to the scarcity of free hydrogen, it is not possible, from an economic standpoint, to produce electricity through this process. Vast quantities of hydrogen exist in the form of water in the world's oceans. But it takes more energy to extract the element than a plant can extract from burning.
Plants, algae and other living organisms are able to utilize the gas to help power their biological mechanisms. Chemists, physicists and engineers are striving to find a way to utilize these natural systems to produce an artificial version of leaves.
"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. 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 - hydrogen and oxygen," Thomas Moore, ASU chemistry professor, said.
As they studied the phenomenon, the team found nature used an intermediary step between the two processes. Electrons were utilized to slow the conversion of light into chemicals capable of energy storage. Water oxidation then had a chance to release oxygen, timed with the absorption of light.
Once researchers at the university carried this experiment out, they saw a major improvement in the way their artificial leaf behaved. The leaf also answered a great mystery of photosynthesis - how the process could be as efficient as we see in the world around us.
Magnetic resonance spectroscopy and X-ray crystallography were used to investigate the mechanism behind this process. These techniques gave them the ability to visualize the movement of magnetic fields. They found a natural relay necessary for the process had an unusually short bond between a pair of atoms of hydrogen and nitrogen. This single atomic bond makes photosynthesis far more efficent than it would be without it.
Replicating the behavior of that bond may just be the long-sought secret of creating a hydrogen economy.
Along with Moore, Devens Gust, Ana Moore and Vladimiro Mujica also took part in the study. Research into the new artificial leaf has been detailed in the journal Nature Chemistry.