Ural Federal University: Scientists Have Improved the Composition of Ceramic Membranes
Chemists at Ural Federal University have improved ceramic membranes that selectively release oxygen from gas mixtures. Scientists added manganese to the chemical composition of the material, which improved the selective oxygen permeability of the membranes. In other words, the new chemistry enabled the membranes to “scavenge” oxygen faster and deliver it more efficiently. A description of the research method and detailed calculations are published in the Journal of the European Ceramic Society.
“Such membranes can be used for the production of pure oxygen in medicine, for dosed oxygen delivery to chemical hydrocarbon partial oxidation reactors, and for oxygen extraction from gas mixtures. The scope of application of these materials is not limited to membrane technology. Due to their mixed oxygen-ion and electronic conductivity, they can be used in hydrogen power engineering as cathode materials for high-temperature solid oxide fuel cells. These are current sources that convert the energy of a chemical reaction into electrical energy in the most efficient and environmentally friendly way,” explains Evgeny Kiselev, associate professor at the Department of Physical and Inorganic Chemistry at UrFU.
The ceramic membranes are complex oxides of lanthanum, strontium, nickel, and manganese. The main advantages of the investigated membranes are their mechanical strength and chemical inertness to carbon dioxide compared to oxide membranes based on strontium, barium, iron and cobalt. Chemical interaction of the latter with carbon dioxide limits their industrial application. The disadvantages of the investigated membranes include relatively low oxygen permeability.
“Our research aims at solving the fundamental problem – to find out which factors and to what extent improve the functional properties of the studied materials. Modifying the chemical composition of the membrane by partially replacing nickel with manganese increased the oxygen exchange rate of the membrane surface with the gas phase by an order of magnitude. As a result of this modification, the specific oxygen permeability of the membrane increased by more than one order of magnitude,” says Evgeny Kiselev.
Simplified, the transfer of oxygen through the membrane takes place in three stages. First, molecular oxygen from the gas phase is incorporated into the surface layers of the ceramic membrane in the form of oxygen ions. Then oxygen ions diffuse through the membrane thickness and finally oxygen ions are converted back on the opposite membrane surface with the release of gaseous oxygen. Depending on the chemical composition, the microstructure of the membrane surface and the external thermodynamic conditions – temperature and oxygen content in the gas phase – the rates of these stages can vary greatly. The slowest stage will limit the total flow of oxygen through the membrane.
“To transfer oxygen ions across the membrane faster, we can make several improvements. Increasing the surface oxygen exchange rate by adding manganese to the compound is just one of the key factors we found that determines the speed of the process. The slowest process of oxygen transport through the studied membranes – diffusion – can be optimized by reducing membrane thickness and increasing temperature,” the scientist explains.