Oxygen Permeation Properties of Dense Bi1.5Er0.5 O 3 ‐ Ag Cermet Membranes

Abstract

Oxygen permeation experiments were performed on dense mixed-conducting ceramic-metal composite membranes (thickness 0.2 to 2 mm) Bil,5Ero50,-Ag with 10.0, 27.8, and 40.0 volume percent (v/o) silver, respectively, in the temperature range 873 to 993 K and oxygen partial pressure range to 1 bar 0,. The oxygen fluxes increased with increasing silver content. In the cerinets with a nonpercolative silver phase (10.0 and 27.8 v/o), the increased oxygen flux relative to that of pure Bi,,ErO50, was attributed to faster kinetics of surface oxygen exchange in the presence of silver. Percolativity of the silver phase in the 40 v/o Ag composition enhances the ambipolar diffusion of oxygen ions and electrons. High oxygen fluxes (-0.25 mmol m-2 s-' at 873 K) were observed with the latter composition, which were shown to be fully limited by the surface exchange kinetics. The activation energy for oxygen permeation in the temperature range 848 to 1003 K is about 85 to 95 kJ/mol for the compositions without percolativity of silver and 115 kJ/mol for the composite with 40 V/O Ag, which reflects a change of the rate-limiting step upon passing the percolation threshold. Results from both permeation and isotopic exchange measurements on the composition with Ag percolativity indicated the kinetic order of the surface process in oxygen to be 1/4, indicating a process fundamentally different from that on pure Bi,,Er,,O,.

Oxygen permeation in bismuth-based materials. Part I: Sintering and oxygen permeation fluxes

“…Two parameters govern the oxygen transport in such membranes: i) the bulk diffusion controlled by the ambipolar conductivity (oxide ion conduction and electron hole conduction) and ii) the rate of exchange of O 2 molecules at the surface of the membrane. Ten Elshof et al [20] characterised the oxygen permeation properties of dense BE25-Ag cermet membranes with different silver contents. Under the percolation threshold, they evidenced an increase of oxygen flux when silver content increased and attributed this to faster kinetics of surface oxygen exchange in the presence of silver.…”

Influence of the preparation methods on the microstructure and oxygen permeability of a CO2‐stable dual phase membrane

“…Up to now, numerous dual phase materials have been developed which can be divided into two major groups: (1) The first generation of dual phase membranes were composites of noble metal powders as electronic and a ceramic particles as ionic conductors. [20][21][22] However, these composite membranes are expensive, a mismatch of the thermal expansion coefficients (TEC) of the metallic and the ceramic phase exists, and the oxygen permeabilities were found to be low. (2) The second generation of dual phase membranes were composites of two oxides, where one of the oxides acts as electron conductor instead of the noble metal.…”

Advanced Hydrogen Transport Membranes for Vision 21 Fossil Fuel Plants

“…Similar conclusion were derived from studies of BaCe 0.8 Y 2 O 3 /Ni and Bi 1.5 Er 0.5 O 3 /Ag cermets. 6,7 Therefore, the difference in ambipolar conductivity between the three curves in Figure 31 was the result of differences in the proton conductivity of the ceramic phases. The maximum conductivity for each curve was observed at a metal content of 44.4 wt.%, which corresponded to between 34 and 36 vol.% metal phase, and approximately 80 mol% metal phase.…”