Electrical conductivity and defect equilibria of Pr0.1Ce0.9O2−δ

The effect of addition of transition metal oxides on the charge transport of commercially available Gd-doped ceria (Ce 0.9 Gd 0.1 O 2-δ ) was assessed with special emphasis on the electronic partial conductivity. The samples were doped by adding 2, 4 or 6 cat% of CoO 3/4 or FeO 2/3 , or 2 mol% of the transition metal oxides V 2 O 5 , MnO 2 , and CuO, respectively. It was found that even small amounts of transition metal oxides severely change the partial electronic conductivity of ceria while the majority oxygen ion conductivity was only mildly affected: for high oxygen ion conductivity, Fe or Mn oxide addition as well as small amounts of Co oxide are beneficial, as especially the grain boundary conductivity is slightly increased. Addition of V or Cu oxide in contrast increases the minority charge carrier conductivity of electrons and thus enhances the mixed ionic-electronic conductivity. For Co oxide addition, an increasing electronic conductivity with decreasing oxygen partial pressure from 10 −8 to 10 −4 bar at temperatures below 600 • C indicates the changing redox state of Co from divalent at low oxygen partial pressures to trivalent under ambient oxygen partial pressure.

mentioning

confidence: 99%

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

Neuhaus¹,

Dolle²,

Wiemhöfer³

2018

“…Gd / Ce = 0.1 [10] Under oxidizing conditions, where [Ce 20,21 Assuming the reduction of cerium under oxidizing conditions to be negligible, the variation in oxygen non-stoichiometry (δ) (arising from redox of Pr only) can be calculated by the following equation:…”

Section: Theoretical Considerationmentioning

confidence: 99%

Ionic/Electronic Conductivity, Thermal/Chemical Expansion and Oxygen Permeation in Pr and Gd Co-Doped Ceria Pr_xGd_0.1Ce_0.9-xO_1.95-δ

Cheng

Chatzichristodoulou

Søgaard

et al. 2017

The oxygen permeation flux of Ce 0.9 Gd 0.1 O 1.95-δ (CGO)-based oxygen transport membranes under oxidizing conditions is limited by the electronic conductivity of the material. This work aims to enhance the bulk ambipolar conductivity of CGO by partial substitution of Ce with the redox active element Pr. A series of compositions of Pr x Gd 0.1 Ce 0.9-x O 1.95-δ (x = 0, 0.02, 0.05, 0.08, 0.15, 0.25, 0.3 and 0.4) was prepared by solid state reaction. X-ray powder diffraction (XPD) indicates that Pr is completely dissolved in the fluorite structure up to 40 at.%. Pronounced nonlinear thermal expansion behavior was observed as a function of temperature, due to the simultaneous contributions of both thermal and chemical expansion. The electronic and ionic conductivities were measured as a function of temperature and oxygen partial pressure. Within the range from 10 to 15 at.% Pr, a drastic drop of the activation energy of the hole mobility and an abrupt increase of the hole conductivity at low temperature was observed. The behavior could be rationalized by a simple percolation model. Oxygen permeation fluxes through disk shaped samples fed with air on one side and N 2 on the other side were also measured. The oxygen flux through Pr 0.05 Gd 0.1 Ce 0.85 O 1.95-δ was higher than that for CGO by one order of magnitude owing to the enhanced electronic conductivity albeit the flux is still limited by the electronic conductivity. In terms of the electronic and ionic conductivity, the estimated maximum oxygen permeation flux of a 10 μm Pr 0.4 Gd 0.1 Ce 0.9 O 1.95-δ -based membrane exceeds 10 Nml cm −2 min −1 at 900 • C under a small oxygen potential gradient (0.21/10 −3 bar) which is promising for use in oxygen production and in oxy-fuel combustion. Also the material may be well applicable to SOFC/SOEC composite electrodes where mixed conductivity is also desirable. Dense ceramic oxygen transport membranes (OTMs) could potentially be applied for production of high purity oxygen for medical purposes, supply of oxygen in the steel industry, oxy-fuel combustion schemes, as well as in the cement and glass industries. Also, importantly, OTMs can beneficially be integrated with a biomass gasifier, allowing production of syngas (CO and H 2 ), which is a precursor for a variety of high value chemicals. 1 Besides being applicable for OTMs, 2 acceptor doped-ceria has been intensively studied for use in a number of other applications e.g. solid oxide fuel cells (SOFCs), 3 solid oxide electrolysis cells (SOECs) 4 and for electrocatalysis. 5 In particular, acceptor doped ceria (e.g. CGO) is interesting owing to high oxide ion conductivity (0.12 Scm −1 for Gd 0.1 Ce 0.9 O 1.95-δ at 900• C 6 ), appreciable electrocatalytic activity, high electronic conductivity under reducing conditions, and excellent chemical stability under harsh reducing and even corrosive gaseous conditions. 3,7 Kaiser et al. 8 reported that the oxygen permeation flux of a 27 μm asymmetric 10 at.% Gd-doped ceria-based membrane exceeds 10 ml cm −2 min −1 under a gradie...

“…21 The electronic conductivity of CGO10 under the operating conditions was found to be the limiting factor for oxygen permeation. 21 Doping with Pr or Tb has been shown to increase the electronic conductivity of ceria at relatively high oxygen partial pressures 1,[22][23][24][25][26][27][28][29][30][31][32][33][34][35] and is therefore expected to improve oxygen permeation.…”

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confidence: 99%

Electronic and Ionic Transport in Ce_0.8Pr_xTb_0.2−xO_2−δand Evaluation of Performance as Oxygen Permeation Membranes

Chatzichristodoulou

Hendriksen

2012

The electronic conductivity of Ce 0.8 Pr x Tb 0.2−x O 2−δ (x = 0, 0.05, 0.10, 0.15, 0.20) was determined in the oxygen activity range a O2 ≈ 10 3 -10 −17 at 700-900 • C by Hebb-Wagner polarization. The electronic conductivity of all the Ce 0.8 Pr x Tb 0.2−x O 2−δ compositions was significantly enhanced as compared to that of Ce 0.9 Gd 0.1 O 1.95−δ , and was found to increase with increasing Pr/Tb ratio. The oxide ion mobility in Ce 0.8 Pr x Tb 0.2−x O 2−δ is similar to that in Ce 1−2δ Gd 2δ O 2−δ at the same oxygen vacancy concentration. Based on the measured ionic and electronic conductivities, fluxes through thin film Ce 0.8 Pr x Tb 0.2−x O 2−δ membranes were calculated. Calculated fluxes exceed 10 Nml min −1 cm −2 under oxyfuel relevant conditions (T = 800 • C, a O2,permeate side = 10 −3 ). Hence, in terms of transport properties, these materials are promising for this application. Interference between the ionic and electronic flows has a significant positive effect on the deliverable oxygen flux, as evaluated for Ce 0.8 Pr 0.2 O 2−δ . 1