ASU and Argonne researchers report progress on artificial leaf for solar conversion of water to H2 and O2
Researchers at Arizona State University and Argonne National Laboratory reported advances toward perfecting a functional artificial leaf in a paper in Nature Chemistry. Designing an artificial leaf that uses solar energy to convert water cheaply and efficiently into hydrogen and oxygen is one of the goals of BISfuel (Bio-inspired Solar fuel production)—the Energy Frontier Research Center, funded by the Department of Energy, in the Department of Chemistry and Biochemistry 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. 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.—ASU chemistry professor Thomas Moore
The researchers took a closer look at how nature had overcome a related problem in the part of the photosynthetic process where water is oxidized to yield oxygen.
|An artificial photosynthetic reaction center containing a bioinspired electron relay (yellow) mimics some aspects of photosynthesis. Source: ASU. Click to enlarge.|
They found an intermediate step involving 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. They then designed an artificial relay based on the natural one and were rewarded with a major improvement.
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.
ASU chemistry professors involved in this specific project include Thomas Moore, Devens Gust, Ana Moore and Vladimiro Mujica. The department is a unit of the College of Liberal Arts and Sciences. Key collaborators in this work are Oleg Poluektov and Tijana Rajh from Argonne National Laboratory.
Jackson D. Megiatto Jr, Dalvin D. Méndez-Hernández, Marely E. Tejeda-Ferrari, Anne-Lucie Teillout, Manuel J. Llansola-Portolés, Gerdenis Kodis, Oleg G. Poluektov, Tijana Rajh, Vladimiro Mujica, Thomas L. Groy, Devens Gust, Thomas A. Moore & Ana L. Moore (2014) “A bioinspired redox relay that mimics radical interactions of the Tyr–His pairs of photosystem II,” Nature Chemistry doi: doi:10.1038/nchem.1862