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Empa’s “chaos crystals” could have the potential to convert CO2 from biogas and sewage treatment plants into methane.

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Crystals are usually characterised by their highly ordered structures, but since 2015 scientists have been working on a class of synthetic ceramic crystals that are stabilized by the "power of disorder". These so-called high-entropy materials with their excellent catalytic properties and chemical stability are now being investigated for their use in chemical production and energy storage technologies.

A research team at the Empa Materials Science and Technology institute in Switzerland has already succeeded in inserting nine different atoms into a crystal that remains stable even at high temperatures due to the atoms’ “natural striving” towards maximum disorder. "With up to four components in the crystal, everything is still normal; with five components and more, the world changes... we can stabilise crystals that would otherwise disintegrate due to internal stresses… we can create highly active crystal surfaces that have never existed before,” explains Michael Stuer, a researcher at Empa in a press release.

The chemical reaction Stuer and his colleagues are focusing on in partnership with the Paul Scherrer Institute, involves combining carbon dioxide and hydrogen to form methane, a sustainable fuel. "We know that CO2 molecules adsorb particularly well on certain surfaces and that the desired reaction then takes place more easily and quickly," says Amy Knorpp. "Now we are trying to produce entropic crystals on whose surfaces such highly active regions exist."

To speed progress, the Empa team has created a “segmented flow tubular reactor” for testing several chemical mixtures in sequence as if on an assembly line. Running through the tube are regular-sized bubbles in which the respective reaction takes place. At the end, the powder they contain can be extracted and formed into crystals.

The ultimate goal is to develop an experimental crystal reactor to convert CO2 from biogas and sewage treatment plants into methane. Empa’s “chaos crystals” also have potential to be used in high-performance batteries, superconducting ceramics, catalysts for car exhausts and other chemical production processes.