Study On The Oxygen Adsorption/Desorption Properties Of Doped-YBaCo₄O₇ And Its Oxygen Permeation Ability

Mixed ionic and electronic conductivity oxides are a type of widely used and investigated functional materials. Most of them are used as oxygen separation materials currently. The oxygen contant has close relationship with temperature and surrounding oxygen partial pressure. The oxygen ion could diffuse and migrate in the lattice because of the existence of the oxygen defects in mixed conductivity oxides. This behavior is the basis for their applications as oxygen permeation membranes, oxygen sensors, SOFC electrode and electrolyte.Recently, a type of mixed conducting oxides YBaCo407 was synthesized. It was reported that the oxygen adsorption and desorption proprety of YBaCo4O7 oxides is unique. It can experience two processes of oxygen intake and subsequent release when heated from room temperature to 1100℃in air or oxygen. The special oxygen adsorption/desorption properties of YBaCo4O7 should relate to its special crystal structure and the changeable valence of Co ions.The oxygen adsorption and diffusion behaviors are relatively rare in other mixed conducting oxides in the temperature range of 200-450℃, which makes this material has great potential application value in oxygen separation. In this paper, we expect to improve the rate and amount of oxygen adsorption in lower temperature by substituting Zr and Tb for Y with different ratio, and to reduce the costs of the materials without changing the oxygen adsorption obviously. The TG results show that Y0.9Zr0.1BaCo4O7 and Y0.50Tb0.50BaCo4O7 can partially improve the oxygen adsorption in low temperature. We also prepare successfully YBaCo2Fe2O7 by using different raw materials and different oxygen partial pressures when sintering the samples. The substitution of iron oxide for cobalt oxide can effectively reduce the costs of the materials. However, the oxygen adsorption capacity is reduced, which is not good for the application. Doping of Ni at the Co site also decrease the amount of oxygen adsorption in the temperature range of 200-450℃. The doping effect was discussed based on elements valence, binding energy between cations and oxygen ions, and distortion of crystal structure.Currently, the oxygen permeable membrane materials researched extensively have active oxygen diffusion only in higher temperature (800-900℃). The high working temperature not only could easily destroy the sample structure, but also have high energy consumption, which is unfavorable for practical application. Therefore, the key issue to develop the novel of oxygen separation material is to explore new materials, which have relatively active oxygen behavior in lower temperature. Considering the oxygen adsorption properties of YBaCo4O7 in the temperature rang of 200-450℃, we design a temperature gradient oxygen membrane to measure its oxygen permeation rates at 410℃, in which one side of the membrane is at oxygen adsorbent temperature, and the other side is at oxygen desorbent temperature.