University Chemists Work on Creating Stable Materials for Fuel Elements

09:23, May 22, 2020

Scientists are exploring the thermodynamic properties of double perovskite

A group of chemists at UrFU investigated the thermodynamic properties of the double perovskite gadolinium-barium-carbon dioxide-oxygen (GdBaCo2O6-δ). This substance is the base in the development of new cathode materials for solid oxide fuel cells.

Scientists set the task of making samples of the substance and establishing some of its thermodynamic characteristics. In the future, the obtained information will be used to predict the stability of double perovskite in atmospheres of various compositions and in contact with other components of the fuel cell. An article on the contents and results of experiments was published in the international scientific journal Thermochimica Acta.

“Many devices operate at fairly high temperatures - from 500 ° C and above. Under such conditions, the materials inside the devices that are stable at room temperature become reactive, that is, they enter into chemical reactions between themselves and with the components of the surrounding atmosphere. The final characteristics of the device largely depend on how the materials manifest themselves in contact with each other. If the materials interact intensively with each other, this leads to a rapid drop in the electric power supplied by the fuel cell to the external circuit and to its termination. We strive to create materials with such desired qualities and properties that ensure their long-term performance inside the device in contact with other materials, ”explains Dmitri Tsvetkov, head of the research group, leading researcher in the chemical design laboratory of new multifunctional materials at UrFU.

The stability of the contacting materials can be determined by direct experiment, for example, heating their mixture and determining what interaction products were formed and in what quantity. The problem in this case is the uncertainty of the time period during which the materials must interact. A more reliable and accurate way is to calculate the stability of the contacting materials according to the principles of thermodynamics, and for this it is necessary to establish their thermodynamic characteristics.

The problem is an important feature of materials like GdBaCo2O6-δ: their chemical composition is variable. Depending on the conditions in which these materials are located, oxygen content may vary in them. This greatly complicates the study of thermodynamic properties at high temperatures and requires serious preliminary studies of the chemical composition of materials in various states.

To obtain GdBaCo2O6-δ, chemists of UrFU calcined a mixture of metal oxides and carbonates at high temperature. To establish the pattern of how the composition of the material changes under certain conditions, scientists used the method of thermogravimetry. They weighed the sample, successively heating it to a temperature of 1000 ° C in different atmospheres - from pure oxygen to oxygen-free (inert gas, nitrogen). Thermodynamic characteristics, namely the amount of heat that is required to heat the material from room temperature to the required to obtain a given composition of the substance, was measured using a calorimeter.

“Using a calorimeter, we demonstrated the division caused by the thermal effect into contributions due to heating of the sample and a change in its composition. The acquired knowledge will be further used to conduct thermodynamic calculations and assess the stability of the double perovskite GdBaCo2O6-δ and derived materials based on it,” explains Doctor Tsvetkov.

Tsvetkov and his colleagues have been studying compounds of barium, cobalt and rare earth oxides for almost a decade and have made a fundamental contribution to understanding their nature, features and practical applications, synthesized electrode materials with high characteristics. For these purposes, along with and in addition to gadolinium, chemists also used other rare-earth elements - europium, yttrium, lanthanum, praseodymium, and samarium.

For Your Reference

Perovskites are rare natural minerals (in our country, their deposits are located on the Kola Peninsula, the North Caucasus, the Urals, Siberia, the Far East), which have a unique crystalline structure and have a wide range of applications in batteries, catalytic, laser, membrane technologies, and electronics. In particular, double perovskites, characterized by a doubled crystal lattice, are considered as materials for membranes, as well as electrodes and catalysts in fuel cells.

Solid oxide fuel cells, SOFCs are environmentally friendly devices with high, up to 70%, efficiency, in which the energy of the chemical reaction of oxidation of fuel is directly converted into electricity. The electrolyte in SOFC is a solid oxide having oxygen-ionic and / or conductivity. Oxygen ions formed at high temperature (700–900 degrees Сelcium) on the cathode, or / and hydrogen ions formed on the anode, when the cell is working, pass through the electrolyte layer and react with hydrogen on the anode andoxygen at the cathode, respectively. In this case, an electric current arises in the external circuit.

High operating temperatures are the main problem in this technology: the need to use unique and expensive ceramic materials leads to a significant increase in the cost of solid oxide fuel cells. Scientists of the world solve the problem of lowering operating temperatures, which will open up the possibility of using more common and cheaper materials and, as a result, will reduce the cost of energy production.