20-Jun-2018 - University of Oxford

New material for splitting water

Solar energy is clean and abundant. But when the sun isn't shining, you must store the energy in batteries or through a process called photocatalysis -- in which solar energy is used to make fuels. In photocatalytic water splitting, sunlight separates water into hydrogen and oxygen. The hydrogen and oxygen can then be recombined in a fuel cell to release energy.

Now, a new class of materials -- halide double perovskites -- may have just the right properties to split water, according to a newly published paper.

"If we can come up with a material that can be useful as a water-splitting photocatalyst, then it would be an enormous breakthrough," said Feliciano Giustino, a co-author on the paper.

Researchers have experimented with many photocatalytic materials before, such as titanium dioxide (TiO2). While TiO2 can harness sunlight to split water, it's inefficient because it doesn't absorb visible light well. So far, no photocatalytic material for general water splitting has become commercially available.

Using supercomputers to calculate the quantum energy states of four halide double perovskites, George Volonakis and Giustino, both of the University of Oxford, found that Cs2BiAgCl6 and Cs2BiAgBr6 are promising photocatalytic materials because they absorb visible light much better than TiO2. They also generate electrons and holes (the positively charges absence of electrons) that have sufficient energy (or nearly ideal energies) to split water into hydrogen and oxygen.

Very few other materials have all these features at once, Giustino said. "We can't say this will work for sure, but these compounds seem to have all the right properties."

Giustino and his team originally discovered this type of perovskite while looking for materials to make solar cells. Over the last several years, perovskites have garnered interest as materials to boost the efficiency of silicon-based solar cells through tandem designs that integrate a perovskite cell directly onto a high-efficiency silicon cell, but they contain a small amount of lead. If they were used for energy harvesting in a solar farm, the lead could pose a potential environmental hazard.

In 2016, using computer simulations to identify alternative materials, the researchers found a new type of lead-free perovskite with potential for high-efficiency solar cells. The present paper shows these new materials may also split water. "These new double perovskites are not only promising as a complementary material for tandem solar cells, but they can also be promising in areas like photocatalysis," Volonakis said.

Still, the new analysis is theoretical, assuming the compounds form perfect crystals. The next step, the authors said, is for experimentalists to see if the material works in the real world as well as predicted. In the meantime, the researchers are using their computational techniques to explore whether these double perovskites have properties useful for other applications like light detectors.

Facts, background information, dossiers
  • halide double perovskites
  • water splitting
  • metal halide perovskites
More about University of Oxford
  • News

    New kind of interaction discovered in hydrogen-producing enzymes

    In hydrogenase enzymes, the transports of protons and electrons have been considered to be separate events until now. However, coupling is the key to success here. Hydrogenases can convert hydrogen just as efficiently as expensive platinum catalysts. In order to make them usable for biotech ... more

    Polymers and Fuels from Renewable Resources

    Prof. Charlotte K. Williams from Oxford University receives the Otto Roelen Medal 2018. This prize will be awarded by DECHEMA and the German Catalysis Society in recognition of her developments in the field of highly active catalysts for carbon dioxide copolymerization. This enables renewab ... more

    Google provides open source library for quantum chemistry

    Since physicists have been dealing with the theoretical description of molecules, the solving of quantum mechanical equations has been a major obstacle. This is supposed to be a thing of the past with the release of an open source based system. Google has introduced such a system to the pub ... more

More about Cornell University
  • News

    Chemistry discovery could remove micropollutants from environment

    Using a pioneering imaging technique, Cornell University researchers obtained a high-resolution snapshot of how ligands, molecules that bind to other molecules or metals, interact with the surface of nanoparticles. In doing so, they made an unexpected breakthrough discovery. They determined ... more

    The beginning of a new era in resolution

    Scientists at Cornell University (USA) have succeeded in building an electron microscope pixel array detector (EMPAD) with sophisticated 3D reconstruction algorithms that make it possible to multiply the resolution of a state-of-the-art electron microscope. The Leibniz-Institut für Kristall ... more

    Engineering team images tiny quasicrystals as they form

    When Israeli scientist Daniel Shechtman first saw a quasicrystal through his microscope in 1982, he reportedly thought to himself, "Eyn chaya kazo" -- Hebrew for, "There can be no such creature." But there is, and the quasicrystal has become a subject of much research in the 35 years since ... more

More about American Institute of Physics