A team of researchers from several institutions in Spain, Germany, and Argentina, led by the ITQ-UPV-CSIC, has conducted a comprehensive exploration of the exsolution process in double perovskite oxides. The study, published in Journal of Materials Chemistry A, reveals important insights into how temperature controls nanoparticle composition, how these particles change during chemical cycling, and provides the first measurement of the reversibility of ternary alloyed nanoparticles.
Advanced X-ray techniques at the ALBA Synchrotron provided detailed views of both structural and surface changes during the exsolution process. This study is of great interest for the development of reversible electrochemical cells that can work in fuel cell and electrolyzer modes for renewable energy storage and production of green fuels.
Perovskite oxides are versatile materials prized for their tunable properties and diverse chemical characteristics, making them exceptional platforms for catalyst design in multiple clean energy technologies, including fuel cells and the conversion of CO₂ and water into CO and hydrogen. Their unique ability to release and—potentially—reabsorb metal nanoparticles makes these materials particularly valuable for creating stable, high-performance catalysts. Exsolution has emerged as a promising nanocatalyst fabrication route in the last decade. Through exsolution, perovskite oxides can produce well-anchored metal nanoparticles under controlled conditions. If this process can also work in reverse, it could enable catalyst regeneration.
However, little is known about how this release-reabsorb process works. For this reason, researchers at Instituto de Tecnología Química (ITQ-UPV-CSIC), the Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB) from Germany, the ALBA Synchrotron, and other research institutions in Spain and Argentina, used advanced X-ray techniques to observe the process in real-time in a quest to understand the dynamics of ternary alloyed nanoparticles. This study specifically examines how three metals—iron, cobalt, and nickel—combine to form nanoparticles within a complex oxide structure, aiming to understand what controls their formation and reversibility.
The researchers investigated the exsolution of ternary alloyed nanoparticles in a specially designed oxide material using a combination of in situ and ex situ techniques. They discovered that the exsolution temperature significantly influences the composition of the resulting nanoparticles. At lower temperatures, nickel-rich nanoparticles preferentially form due to the faster diffusion of nickel. Increasing the temperature promotes the exsolution of cobalt and iron, leading to a more homogeneous composition. This finding highlights the potential for tuning nanoparticle composition by controlling the exsolution temperature.
The study also explored the reversibility of the exsolution process, demonstrating that some nanoparticles can be reintegrated into the perovskite lattice upon oxidation, while others remain on the surface in an altered state. This reversibility has important implications for catalyst regeneration and stability.
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Image: Schematic representation and field emission scanning electron microscopy micrographs of the ex situ redox processes affecting exsolution, oxidation and re-exolution.