Electrical Transport Properties and Defect Structure of SrFeCo0.5 O  x

Abstract

By using a gastight electrochemical cell with flowing air as the reference environment, we were able to achieve an oxygen partial pressure (P02) as low as 1016 atm inside the cell. The conductivity of SrFeCo05O, has been studied as a function of P02 and temperature. It was found that in the high-P0, range, interstitial oxygen ions (Or') and electron holes (Fe,= h') are the dominant charge carriers, while in the low-P02 range, oxygen vacancies (V) and electrons (e') are dominant. At 800°C in air; total conductivity and ionic conductivity of SrFeCo05O, are 17 and 7 5 cm', respectively, and the ionic transference number is 0.4. A semiconductor-metal-semiconductor transition is found in this system in a reducedoxygen environment. Defect dynamics in this system can be understood by means of the trivalence-to-divalence transition of Fe ions when P02 is reduced. A defect model has been proposed. By using the conductivity results, we were able to estimate oxygen permeation through a ceramic membrane made of SrFeCo55O. The oxygen permeability we calculated is consistent with that measured at the conversion reactor. To confirm the ionic transference number measured by electron-blocking method, electromotive force measurement was carried out and obtained consistent results.

Supported Dense Ceramic Membranes for Oxygen Separation

“…[1][2][3][4] The performance of several compositions of this type of membrane has been demonstrated using thick-walled ceramic membranes (wall thickness of 0.5 -1.0 mm). [4][5][6][7][8][9] The Sr-Co-Fe-O family of perovskite-related phases are one of the highly promising materials for dense ceramic oxygen-transporting membranes. 4,9 There is a drive to develop reliable methods to fabricate thin or thick film membranes so that solid-state diffusional resistance can be minimized, and oxygen flux thus maximized.…”

“…[4][5][6][7][8][9] The Sr-Co-Fe-O family of perovskite-related phases are one of the highly promising materials for dense ceramic oxygen-transporting membranes. 4,9 There is a drive to develop reliable methods to fabricate thin or thick film membranes so that solid-state diffusional resistance can be minimized, and oxygen flux thus maximized. Reliable fabrication of dense ceramic membrane films on porous supports has been a challenging task that has still not been solved, though there have been some instances of reported success.…”

“…The SrCo 0.5 FeO x composition has been reported to have a high oxygen permeability, while also possessing good phase stability in reducing environments that are typical of important applications involving synthesis gas (CO/H 2 ). 4,9,[12][13][14] In the previous project years, we have reported on the fabrication of the porous support, fabrication of the aerosol-derived SCFO powder, and our first results depositing membranes from that powder using a doctor blading procedure with pastes prepared using various diluents with the aerosol powder. The best and most extensive results reported previously were obtained using polyethylene glycol (MW 400) as the diluent with SCFO powder loadings of 15-20 wt%.…”

99/00248 Development of mixed-conducting oxides for gas separation

“…Oxygen permeation flux determined from reactor experiments (with tubular SFC membrane) [24], calculated from conductivity data [20], and determined from out-of-reactor experiments in a gas-tight electrochemical cell have been plotted in Fig. 4 as a function of temperature.…”

Comparative investigation of dual-phase membranes containing cobalt and iron-based mixed conducting perovskite for oxygen permeation

“…In the past decades, perovskite-type oxides with high oxygen ionic and electronic conductivity were synthesized and characterized as ceramic membranes for oxygen separation and membrane reactors [4][5][6][7][8][9][10]. MIEC membranes usually have a perovskite (ABO 3 ) structure with Ba 2 þ and/or Sr 2 þ doped in the A-site.…”