-The research team led by Prof. Junwoo Son of POSTECH demonstrated metal nanoparticle exsolution on a highly conductive perovskite stannate oxide.
-They secured original technology of the material. Their findings bring expectations of improvements in energy conversion and storage efficiency.

Recently, studies on a heterogeneous electrode, which attributes to catalytic properties and stability by forming metal nanoparticles on top of the conductive perovskite oxide supports, have been actively performed. Meanwhile, a research team from POSTECH has introduced a unique process of inducing the formation of metal nanoparticles embedded in perovskite stannate oxide to further increase the conductivity of an electrode while maintaining stability.

Prof. Junwoo Son (corresponding author) with Dr. Sangbae Yu and Daseob Yoon (co-first author) of the Department of Materials Science and Engineering at POSTECH have demonstrated exsolution^*1 of metal nanoparticles on top of perovskite stannate with high conductivity. Their research is published in the recent issue of Nano Letters, a scholastic journal in the field of nano and material science.

Among the many processes that form heterogeneous electrodes without impairing the structure of perovskite, in situ exsolution, which metal particles are doped inside the lattice of oxide and then separated to surface after heat treatment, is known to be the most efficient process.

Most demonstration of metal exsolution was performed on developed on LaxSr1-xTiO3 (hereafter LSTO) support as an electrode up to now. However, electron transfer of LSTO conducting oxide displayed difficulty in increasing electrical conductivity due to the limited electron transport by the narrow and directional distribution of Ti 3d orbital.

The research team focused on the perovskite stannate (LaxBa1-xSnO3, LSBO) which has not been much regarded as an electrode material for energy conversion. Unlike LSTO, LBSO is formed with delocalized and wide spherical orbitals of Sn 5s and so, it can efficiently conduct electric current without disturbance.

When a nickel is doped with this LBSO and then heat is treated under reducing atmosphere, high concentration and small size of nickel nanoparticles can be exsolved to surface while maintaining the lattice structure of the compound.

The synthesized nickel nanoparticles are adhered strongly to stannate and they are stable in high temperature and anode environment. They also showed the highest electrical conductivity (~700 Scm-1) of all the heterogeneous electrodes introduced so far. It is at least ten times higher than the electrical conductivity of the exsolved electrodes presented in previous studies.

This study has established a foundation that can develop electrode structures based on new materials which can improve functions of the existing exsolved heterogeneous electrode effectively. It is expected that this technology can applied not only to high temperature solid oxide fuel cells but also to room temperature energy conversion and storage electrodes.

Prof. Junwoo Son, who led the research as a corresponding author of the journal, explained, “This research is the first to demonstrate surface exsolution of metal nanoparticle with the oxide material, which is maximized for electron transfer, based on thermodynamic principle. By utilizing a new material for heterogeneous structure that has different electron conductivity mechanism, it is possible to attain high electrical conductivity effectively compared to the existing electrode. It can ultimately overcome the limits of electrodes of the existing energy conversion devices.”

This research is supported under the Basic Research in Science and Engineering Program of the Ministry of Science and ICT.
 

1. Exsolution
It is a phenomenon or a process that a metal placed inside a material is extracted/separated to surface of the material when the material is heated.