New materials that convert water into fuel

Using a combination of computational approaches and laboratory experiments, researchers have identified twelve new materials that have the potential to be used in the development of solar fuel.

The researchers, from the California Institute of Technology (Caltech) and the Lawrence Berkeley National Laboratory, managed, in just two years, to almost double the number of materials known to have the potential to be used in the development of solar fuel. They succeeded in this by developing a process that allows the acceleration of the discovery of solar fuels with commercial applicability that could replace other forms of fuel such as coal, oil and the like. Solar fuels, the first research target of its kind in the field of clean energy, are obtained from only three sources: sunlight, water and carbon dioxide. Researchers are testing a variety of possible fuels, starting with hydrogen gas and ending with liquid hydrocarbons, while obtaining a fuel that is broken down from water molecules. Each water molecule consists of one oxygen atom and two hydrogen atoms. The hydrogen atoms are separated from the molecule and then they can be recombined to create highly flammable hydrogen gas or bind them to carbon dioxide to obtain hydrocarbons, while obtaining an abundance of renewable energy sources. The problem lies in the fact that the water molecules do not break up when the sun's rays hit them - if that were indeed the case, then the oceans would never have covered most of the Earth's surface. In order to break down the water molecule, help is needed - a catalyst activated by sunlight.

In order to create useful solar fuels, scientists are trying to develop cheap and efficient materials, known as photoanodes, devices capable of splitting water using visible light as the energy source. During the past four decades, researchers have been able to identify only 16 such substances. Now, using an innovative method to identify new materials, a team of researchers from the Caltech Institute found 12 photoanodes with high potential. The research findings have long been published in the scientific journal Proceedings of the National Academy of Sciences. "The importance of our research, which combines theory and experiments together, lies in the fact that in addition to identifying a number of new compounds that can be used in solar fuel applications, we were also able to learn something new about the electronic structure of these materials," adds the lead researcher.

Previous processes for material discovery relied on painstaking and cumbersome examination of individual compounds to determine their potential for use in defined applications. In the new process, on the other hand, the researchers combined computer approaches with practical experiments - first, scanning material databases in order to find the materials with the desired properties, and in the next step, testing the most promising compounds in laboratory experiments. As part of this study, the scientists scanned 174 compounds containing the metal vanadium together with oxygen atoms and another element from the periodic table. Thanks to this approach, the researchers discovered how varying options of the third element, other than vanadium and oxygen, can create materials with different properties, and how these properties can be tuned to achieve more efficient photoanodes. "The main progress we contributed was to combine the best capabilities from theory and supercomputers together with innovative experiments in order to produce scientific knowledge at an exceptional rate," says the lead researcher.

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