Oxygen transport in Ce0.8Gd0.2O2−-based composite membranes

Abstract

Gadolinia-doped ceria electrolyte Ce 0.8 Gd 0.2 O 2 À d (CGO) and perovskite-type mixed conductor La 0.8 Sr 0.2 Fe 0.8 Co 0.2 O 3 À d (LSFC), having compatible thermal expansion coefficients (TECs), were combined in dual-phase ceramic membranes for oxygen separation. Oxygen permeability of both LSFC and composite LSFC/CGO membranes at 970 -1220 K was found to be limited by the bulk ambipolar conductivity. LSFC exhibits a relatively low ionic conductivity and high activation energy for ionic transport ( f 200 kJ/mol) in comparison with doped ceria. As a result, oxygen permeation through LSFC/CGO composite membranes, containing similar volume fractions of the phases, is determined by the ionic transport in CGO. The permeation fluxes through LSFC/CGO and La 0.7 Sr 0.3 MnO 3 À d /Ce 0.8 Gd 0.2 O 2 À d (LSM/CGO) composites have comparable values. An increase in the p-type electronic conductivity of ceria in oxidizing conditions, which can be achieved by co-doping with variable-valence metal cations, such as Pr, leads to a greater permeability. The oxygen ionic conductivity of the composites consisting of CGO and perovskite oxides depends strongly of processing conditions, decreasing with interdiffusion of the phase components, particularly lanthanum and strontium cations from the perovskite into the CGO phase. D

Design and experimental investigation of oxide ceramic dual-phase membranes

“…The composite powder for pressing dual-phase membrane disks was usually prepared by mixing two as-synthesized powders [34][35][36][37]42,[45][46][47][48]. In previous research, we found that dual-phase membranes derived from the one-pot method show higher oxygen permeability than those derived from mixing two as-synthesized powders [40], and other researchers have also verified our findings [49].…”

“…Other researchers also observed this phenomenon for fluorite-perovskite dual-phase membranes [36,49] and perovskite single-phase membranes [53]. Adjustment of membrane bulks was usually accounted for the above unsteady stage phenomenon.…”

“…Dual-phase materials consisting of Gd-doped CeO 2 (CGO) as an ion-conductive matrix and Sr-doped LaMnO 3 (LSM) or Ca-doped GdCoO 3 (GCC) as the electronic conduction path have been reported exhibiting mixed conductivity. However, the oxygen permeation fluxes of these membranes are far lower than those of perovskite membranes [34][35][36][37]. Recently, our group demonstrated a new kind of dual-phase membranes, which consist of a fast ionic conductor for oxide ionic transport and a mixed conductor for both ionic and electronic transport, and show high oxygen permeation flux and good stability for the partial oxidation of natural gas [38][39][40][41].…”

Unsteady-state permeation and surface exchange of dual-phase membranes

“…The E a for the SDC-SSF-IV membrane (62.1 ± 0.8 kJ/mol) is close to the value of SDC ionic conductivity (75 kJ/ mol) [31]. The permeation E a of dual-phase composite membranes is usually much higher than the corresponding ionic conduction E a of ionic conductors, as reported for GDC-LSM [19], GDC-LSCF [20], SDC-LSCr [21], and BaBi 8 O 13 -Ag [26]. This is because oxygen surface exchange plays an important role in the high E a for dual-phase membranes.…”

Assessment of the Effect of Transition Metal Oxide Addition on the Conductivity of Commercial Gd-Doped Ceria

“…[1][2][3][4][5] It has been observed that during cosintering of ceria and various transition metal oxides, part of the metal oxide dissolves with interdiffusion of the additional cations between both phases. [6][7][8] This may lead to a less defined trace metal concentration in the main ceria phase. A similar mechanism can take place, if ceria is in contact to metal interconnects e.g.…”