|Natalya Tarasova works on the creation of new proton conductors. |
Photo credit: Ilya Safarov.
Scientists from the Ural Federal University and the Institute of High Temperature Electrochemistry of the Ural Branch of the Russian Academy of Sciences carried out the first demonstration of donor and acceptor doping of perovskite with a barium-lanthanum indite block-layer structure. The fundamental possibility of such a method to significantly improve the conducting properties of the material was shown. The work opens a new way to the creation of solid oxide fuel cell electrolytes. An article describing the research and its results was published in Ceramics International.
One of the goals of global materials science is to obtain the highest possible electrical conductivity of electrolytes for their further use in solid oxide fuel cells. For this purpose, doping is the replacement of part of the atoms in the starting materials by atoms of another chemical element (acceptor doping is replacement by atoms with a lower valence, donor doping is replacement by atoms with a higher valence).
"We used barium-lanthanum iodate as the initial structure and during our studies we substituted some indium atoms for titanium (donor doping) and some lanthanum atoms for calcium (acceptor doping) in it. When acceptor doping, oxygen defects - oxygen vacancies - appeared in the crystal lattice of the initial material. This can ensure the transfer of protons - positively charged hydrogen ions - along the crystal lattice. They get into the structure of layered perovskite from humidified air at 300-500°C. The more oxygen defects and, consequently, the greater the concentration of protons in the perovskite crystal lattice and their mobility, i.e. speed, the higher the values of the electrical conductivity of the material," explains Natalya Tarasova, Professor of the Department of Physical Chemistry and Leading Researcher of the Institute of Hydrogen Energy at UrFU.
The choice of perovskite with a block-layer structure as the starting substance is explained by the fact that in such compounds perovskite blocks alternate with salt layers. Therefore, the researchers assumed that there is enough space in block-layer perovskites for the introduction of protons.
At the same time, the introduction of titanium ions into the barium-lanthanum indite structure led to difficulties in oxygen transport. The fact is that as a result of donor doping in the salt layer of the perovskite crystal lattice, "additional", interstitial oxygen is formed. It becomes caught between the perovskite layers, and it is much more difficult for the oxygen ion to move within this structure. Therefore, the electrical conductivity of titanium-doped perovskite for oxygen ions has not increased.
"Doping with titanium not only did not improve the conductivity values, but also resulted in their insignificant decrease. However, it changed the conductivity type from mixed oxygen-ion and electron conductivity to fully oxygen-ion conductivity. In turn, the acceptor doping with calcium improved the electrical conductivity. Thus, we concluded that in bilayer perovskite, only the acceptor doping improves the transport properties and leads to increased electrical conductivity," explains Natalya Tarasova.
The work of scientists from the Ural Federal University and the Institute of High Temperature Electrochemistry of the Ural Branch of the Russian Academy of Sciences opens a new way to obtain highly conductive conductors with a two-layer (block-layer) perovskite structure. Further research will be related to the search for the most effective dopants. The ultimate goal of the researchers is not only to study the fundamental aspects of proton transfer in block-layer structures, but also to develop a prototype of an environmentally friendly, high-performance, and economically affordable proton fuel cell.
It should be added that the work was done at the recently established Ural Federal University Institute of Hydrogen Energy and reflects one of the topics of the strategic project "Materials and Technologies for Hydrogen and Nuclear Power Engineering", which is implemented as part of the "Priority 2030" strategic academic leadership program.
Source/Credit: Ural Federal University