High pressure flux method for synthesizing high purity oxyhydrides

Adding flux during the synthesis of oxyhydrides is a promising strategy for obtaining pure and homogeneous products, say scientists from Tokyo Tech. A SrCl₂ the flux promotes partial melting of the reactants and facilitates their diffusion of the reactants, which proves to be key to producing highly pure SrVO_2.4H_0.6 or Sr₃V₂HI_6.2H_0.8 perovskite oxyhydrides in the high pressure and high temperature reaction. This compound has the potential as a catalyst and electrode material for lithium-ion batteries.

Perovskite oxyhydride containing oxide (O^2–) and hydrides (H^–) anions are promising compounds with applications in catalytic systems and batteries. Unfortunately, synthesizing oxyhydrides is usually quite challenging, especially because of the nature of H^– anions.

It is known that the reaction of high pressure and high temperature is effective for synthesizing oxyhydride. For example, Sr₂VO_4–XH_X perovskite can be synthesized directly from oxide and hydride precursors in high pressure and high temperature reactions. The main advantage of this reaction is that H^– the content in the final product can be adjusted by adjusting the composition and ratio of the precursors. This basically means that the electronic and magnetic properties of the product can also be adjusted. Unlike Sr₂VO_4–XH_Xsynthesize SrVO_3–XH_X has proved much more difficult, as the required high pressure and high temperature reactions lead to the formation of some impurities and inhomogeneous products, mainly due to insufficient diffusion of the solid components.

In a recent study published in Journal of the American Chemical Society, a research team led by Associate Professor Takafumi Yamamoto from the Institute of Innovative Research at the Tokyo Institute of Technology (Tokyo Tech) found a solution to this problem. They developed a new approach to synthesize highly purified SrVO_2.4H_0.6 and Sr₃V₂HI_6.2H_0.8, two new perovskite oxyhydrides. This study was carried out as part of a collaborative research project with the National Institutes for Quantum Science and Technology, Japan.

The researchers started with SrO, SrH₂and V₂HI₃and added SrCl₂ for this reactant. They observed differences in the composition of samples prepared under different conditions using a technique called in place synchrotron X-ray diffraction, explaining the role of SrCl₂ in reaction. It acts as a flux at a high temperature of 1200 ℃ and a high pressure of 2 GPa, facilitating the melting and dissolution of the reactant moieties, thereby promoting diffusion. As a result, the researchers succeeded in suppressing the development of inhomogeneous products that usually arise due to insufficient diffusion, obtaining highly pure SrVO_2.4H_0.6 or Sr₃V₂HI_6.2H_0.8 perovskite oxyhydride.

In addition, the team analyzed the electrochemical properties of perovskite oxyhydride prepared as an electrode material. “With its low working potential, excellent reversibility and high level characteristics, SrVO_3–XH_X could be suitable as a negative electrode for lithium-ion batteries, a first for oxyhydrides,” said Dr. Yamamoto.

Overall, using fluxes to enhance desired reaction pathways in high-pressure and high-temperature reactions could be a powerful strategy for opening many new compounds beyond perovskite oxyhydrides. Dr. Yamamoto comments: “The proposed synthesis approach will also be effective in the synthesis of many types of multi-component systems.”

Let’s hope that these findings lead to new breakthroughs in energy storage and other fields of applied chemistry!

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Dr Takafumi Yamamoto | Yamamoto Group

About the Tokyo Institute of Technology

Tokyo Tech stands at the forefront of research and higher education as the leading university for science and technology in Japan. Tokyo Tech researchers excel in fields ranging from materials science to biology, computer science, and physics. Founded in 1881, Tokyo Tech hosts over 10,000 undergraduate and graduate students annually, who develop into scientific leaders and some of the most sought-after engineers in the industry. Embodying the Japanese philosophy of “monotsukuri,” which means “technical ingenuity and innovation,” the Tokyo Tech community strives to contribute to society through high-impact research.

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