Effects of Al content on the oxygen permeability through dual-phase membrane 60Ce_(0.9)Pr_(0.1)O_(2-δ)-40Pr_(0.6)Sr_(0.4)Fe_(1-x)Al_xO_(3-δ)
Pith reviewed 2026-05-25 10:00 UTC · model grok-4.3
The pith
Substituting aluminum for iron in dual-phase ceramic membranes increases oxygen permeability while preserving high-temperature and CO2 stability.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The partial replacement of Fe^{3+}/Fe^{4+} by Al^{3+} causes the material not only to exhibit good stability, but also to increase the oxygen permeability of the membranes. The maximum value of oxygen permeation rate for 60CPO-40PSF1-xAxO membranes with 0.4 mm thickness at 1000 °C is 1.12 mL min^{-1} cm^{-2} when x = 0.4. Cell parameters of the perovskite phase first increase and then decrease with rising Al content owing to the smaller radius of Al^{3+} and the formation of impurity phases. XRD shows the composites retain their structure at high temperature and remain CO2-tolerant.
What carries the argument
The Al-substituted perovskite phase Pr0.6Sr0.4Fe1-xAlxO3-δ inside the dual-phase composite, where Al^{3+} replaces Fe ions and thereby alters lattice parameters and oxygen-ion conduction paths.
If this is right
- Oxygen permeability reaches its maximum at 40 percent aluminum substitution.
- The composites remain structurally stable at high temperature.
- The materials retain their phase composition after exposure to CO2.
- Perovskite cell parameters vary non-monotonically with aluminum content because of both ionic radius and impurity formation.
Where Pith is reading between the lines
- The same substitution strategy could be tested in other fluorite-perovskite pairs to see whether an optimal aluminum fraction appears at comparable levels.
- Varying membrane thickness or operating temperature might shift the aluminum fraction that gives the highest flux.
- Controlling or eliminating the impurity phases observed at higher aluminum contents could raise permeability beyond the reported maximum.
Load-bearing premise
The measured rise in oxygen permeability is produced by the aluminum substitution rather than by impurity phases or differences in how the powders were prepared.
What would settle it
Prepare phase-pure samples at the same aluminum levels, free of the impurity phases noted in the study, and re-measure permeability to check whether the peak at x = 0.4 still appears.
Figures
read the original abstract
Ceramic dual-phase oxygen transport membranes with the composition of 60wt.% Ce0.9Pr0.1O2-{\delta}-40wt.%Pr0.6Sr0.4Fe1-xAlxO3-{\delta} (x = 0.05, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1.0) (60CPO-40PSF1-xAxO) based on 60Ce0.9Pr0.1O2-{\delta}-40Pr0.6Sr0.4FeO3-{\delta} doped Al was successfully synthesized through a modified Pechini method. Crystal structure, surface microtopography and oxygen permeability are investigated systematically. The cell parameters of perovskite phase first increased and then decreased with the increase of Al content, which is related to the radius of the Al3+ and the formation of impurity phase. As x ranges from 0.1 to 0.8, the oxygen permeability of the materials first increases and then decreases, and the maximum value of oxygen permeation rate for 60CPO-40PSF1-xAxO membranes with 0.4mm thickness at 1000 {\deg}C is 1.12 mL min-1 cm-2 when x = 0.4. XRD measurements revealed high temperature stability and CO2-tolerant property of the dual-phase composites. The partial replacement of Fe$^{3+}$/Fe$^{4+}$ by Al$^{3+}$ causes the material not only to exhibit good stability, but also to increase the oxygen permeability of the membranes.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports synthesis via modified Pechini method of dual-phase membranes 60Ce0.9Pr0.1O2-δ–40Pr0.6Sr0.4Fe1-xAlxO3-δ (x = 0.05–1.0), their crystal structure, microstructure, and oxygen permeability. It claims that Al substitution produces a non-monotonic permeability trend with a maximum of 1.12 mL min^{-1} cm^{-2} (0.4 mm, 1000 °C) at x = 0.4, together with high-temperature stability and CO2 tolerance as shown by XRD.
Significance. If the permeability maximum can be unambiguously attributed to Al substitution, the work supplies a concrete composition that simultaneously improves flux and chemical stability in a dual-phase system, which is useful for membrane reactor design.
major comments (1)
- [Abstract] Abstract and results sections: the claim that 'partial replacement of Fe^{3+}/Fe^{4+} by Al^{3+}' is responsible for the permeability increase (maximum 1.12 mL min^{-1} cm^{-2} at x = 0.4) is not supported by quantitative phase-purity or microstructure data. The abstract itself states that cell-parameter variation arises from both Al^{3+} radius and impurity-phase formation; without Rietveld phase fractions, SEM/EDX grain-boundary analysis, or controlled single-phase comparisons, the non-monotonic trend could be produced by secondary phases altering local vacancy concentration or porosity rather than by the intended substitution.
Simulated Author's Rebuttal
We thank the referee for the constructive comments. We address the major concern point by point below.
read point-by-point responses
-
Referee: [Abstract] Abstract and results sections: the claim that 'partial replacement of Fe^{3+}/Fe^{4+} by Al^{3+}' is responsible for the permeability increase (maximum 1.12 mL min^{-1} cm^{-2} at x = 0.4) is not supported by quantitative phase-purity or microstructure data. The abstract itself states that cell-parameter variation arises from both Al^{3+} radius and impurity-phase formation; without Rietveld phase fractions, SEM/EDX grain-boundary analysis, or controlled single-phase comparisons, the non-monotonic trend could be produced by secondary phases altering local vacancy concentration or porosity rather than by the intended substitution.
Authors: We agree that the manuscript does not contain Rietveld quantitative phase fractions, detailed EDX grain-boundary mapping, or single-phase reference comparisons. The cell-parameter evolution is presented as resulting from both Al incorporation and impurity formation, and the permeability data are reported as measured. To address the concern, we will revise the abstract and relevant results/discussion text to describe the observed non-monotonic permeability trend as correlating with Al content and cell-parameter changes up to x = 0.4, while explicitly noting the increasing role of impurity phases at higher x, without asserting that the substitution is the direct cause of the flux maximum. revision: yes
Circularity Check
No circularity: experimental measurements only
full rationale
This is a purely experimental materials-science study. The authors synthesize compositions, perform XRD, SEM, and permeation measurements, and report observed trends (e.g., permeability maximum at x=0.4). No equations, fitted parameters, predictions, or derivations are present that could reduce to inputs by construction. The central claim is an empirical observation, not a self-referential derivation. Self-citations, if any, are irrelevant because no load-bearing theoretical step exists. Score 0 is the appropriate default for such work.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption The modified Pechini method produces the intended dual-phase structure with the specified compositions.
- domain assumption Oxygen permeability measurements accurately reflect the material properties without significant experimental artifacts.
Reference graph
Works this paper leans on
-
[1]
Z. Shao, S. Haile, A high-performance cathode for the next generation of solid- oxide fuel cells, Nature 431 (2004) 170 -173. https://doi.org/10.1038/nature02863
-
[2]
K. Eguchi, T. Setoguchi, T. Inoue, H. Arai, Electrical properties of ceria-based oxidesand their application to solid oxide fuel cells, Solid State Ion. 52 (1992) 165-172. https://doi.org/10.1016/0167-2738(92)90102-U
-
[3]
J. Kniep, Y . S. Lin, Partial oxidation of methane and oxygen permeation in SrCoFeOx membrane reactor with different catalysts, Ind. Eng. Chem. Res. 50 (2011) 7941-7948. https://doi.org/10.1021/ie2001346
-
[4]
C. S. Chen, S. J. Feng, S. Ran , D. C. Zhu, W. Liu, J. Henny, Conversion of Methane to Syngas by a Membrane -Based Oxidation –Reforming Process, Angew. Chem., Int. Ed. 42 (2003) 5196 -5198. https://doi.org/10.1002/anie.200351085
-
[5]
V . Kharton, A. Yaremchenko, A. Kovalevsky, A. Viskup, E. Mnaumovich, P. Kerko, Perovskite-type oxides for high -temperature oxygen separation membranes, J. Membr. Sci. 163 (1999) 307 -317. https://doi.org/10.1016/S0376-7388(99)00172-6
-
[6]
J. Zhu, S. Guo, Z. Chu, W. Jin, CO2-tolerant oxygen-permeable perovskite- type membranes with high permeability , J. Mater. Chem. A 3 (2015) 22564 - 22573. https://doi.org/10.1039/C5TA04598C
-
[7]
J. Caro, K. Caspary, C. Hamel, B. Hoting, P. Koelsch, B. Langanke, A. Wolf, Catalytic membrane reactors for partial oxidation using perovskite hollow fiber membranes and for partial hydrogenation using a catalytic membrane contactor, Ind. Eng. Chem. Res. 46 (2007) 2286 -2294. https://doi.org/10.1021/ie0609620
-
[8]
C. Tsai, A. Dixon, W. Moser, Dense perovskite membrane reactors for partial oxidation of methan e to syngas, AIChE J. 43 (2010) 2741 -2750. https://doi.org/10.1002/aic.690431320
-
[9]
W. Chen, C. S. Chen, J. Henny, A. Nijmeijer, L. Winnubst, Oxygen-selective membranes integrated with oxy -fuel combustion, J. Membr. Sci. 463 (2014) 166-172. https://doi.org/10.1016/j.memsci.2014.03.063
-
[10]
S. Smart, C. Lin, L. Ding, K. Thambimuthu, J. Costa, Ceramic membranes for gas processing in coal gasification, Energy Environ. Sci. 3 (2010) 268 -278. https://doi.org/10.1039/B924327E
-
[11]
N. MacDowell, N. Florin, A. Buchard, J. Ha llett, A. Galindo, G. Jackson, C. Adjiman, C. Williams, N. Shahb, P. Fennell, An overview of CO 2 capture technologies, Energy Environ. Sci. 3 (2010) 1645 -1669. https://doi.org/10.1039/c004106h
-
[12]
C. Li, W. Li, J. Chew, S. Liu, X. Zhu. J. Sunarso, Rate determi ning step in SDC-SSAF dual -phase oxygen permeation membrane, J. Membr. Sci. 573 (2019) 628-638. https://doi.org/10.1016/j.memsci.2018.12.044
-
[14]
M. Schulz, R. Kriegel, A. Kampfer, Assessment of CO2 stability and oxygen flux of oxygen permeable membranes, J. Membr. Sci. 378 (2011) 10 -17. https://doi.org/10.1016/j.memsci.2011.02.037
-
[15]
A. Waindich, A. Mobius, M. Muller, Corrosion of Ba 1-xSrxCo1-yFeyO3-δ and La0.3Ba0.7Co0.2Fe0.8O3-δ materials for oxygen separating membranes under Oxycoal conditions, J. Membr. Sci. 337 (2009) 182 -187. https://doi.org/10.1016/j.memsci.2009.03.041
-
[16]
Y . Teraoka, H. M. Zhang, S. Furukawa, N. Yamazoe, Oxygen permeation through perovskite -type oxides, Chem. Let t. 11 (1985) 1743 -1746. https://doi.org/10.1246/cl.1985.1743
-
[17]
Z. P. Shao, H. Dong, G. X. Xiong, W. S. Yang, Perfromance of a mixed-con ducting ceramic membrane reactor with high oxygen permeability for methane conversion, J. Membr Sci. 183 (2001) 181 -192. https://doi.org/10.1016/S0376-7388(00)00591-3
-
[18]
D. Schlehuber, E. Wessel, L. Singheiser, T. Markus, Long-term operation of a La 0.58Sr0.4Co0.2Fe0.8O3-δ membrane for oxygen separation, J. Membr. Sci. 351(2010) 16-20. https://doi.org/10.1016/j.memsci.2010.01.022
-
[19]
K. Danjela, J. Holc, M. Hrovat, D. Kolar, Correlation between the defect structure, conductivity and chemical stability of La 1-ySryFe1-xAlxO3-δ cathodes for SOFC, J. Eur. Ceram. Soc. 21 (2001) 1817 -1820. https://doi.org/10.1016/S0955-2219(01)00122-4
-
[20]
J. Holc, D. Kuscer, M. Hrovat, S. Bernik, D. Kolar, Electrical and Microstructural Characterization of (La 0.8Sr0.2)(Fe1-xAlx)O3 and (La 0.8Sr0.2) (Mn1-xAlx)O3 as Possible SOFC Cathode Materials, Solid State Ionics, 95 (1997) 259-268. https://doi.org/10.1016/S0167-2738(96)00595-4
-
[21]
J. H. Tong, W. S. Yang, R. Cai, B. C. Zhu, L. W. Lin, Novel and ideal zirconium based dense membrane reactors f or partial oxidation of methane to syngas. Catal. Lett. 78 (2002) 129-137. https://doi.org/10.1023/a:1014950027492
-
[22]
W. Liang, S. Megarajan, F. Liang, Y . Zhang, G. He, Z. Liu, H. Jiang, Coupling of N 2O decomposition with CO 2 reforming of CH 4 in novel cobalt -free BaFe0.9Zr0.05Al0.05O3-δ oxygen transport membrane reactor. Chem. Eng. J. 305 (2016) 176-181. https://doi.org/10.1016/j.cej.2015.10.067
-
[23]
J. Martynczuk, F. Liang, M. Arnold, V . Sepelak, A. Feldhoff, Aluminum-doped perovskites as high-performance oxygen permeation materials. Chem. Mater. 21 (2009) 1586-1594. https://doi.org/10.1021/cm803217t
-
[24]
M. Kajitani, M. Matsuda, M. Miyake, Effect of Al doping on crystal structure and electrical conduction properties of LaGa 0.9Mg0.1O2.95 perovskite compound, Solid State Ionics, 178 (2007) 355 -358. https://doi.org/10.1016/j.ssi.2007.01.005
-
[25]
V . V . Kharton, A. L. Shaula, F. M. M. Snijkers, J. F. C. Cooymans, J. J. Luyten, I. P. Marozau, A. P. Viskup, F. M. B. Marques, J. R. J. Frade, Oxygen transport in ferrite -based ceramic membranes: Effects of alumina sintering aid, Eur. Ceram. Soc. 26 (2006) 3695 -3704. https://doi.org/10.1016/j.jeurceramsoc.2005.10.013
-
[26]
X. Dong, Z. Xu, X. Chang, C. Zhan g, W. Jin, Chemical Expansion, Crystal Structural Stability, and Oxygen Permeability of SrCo0.4Fe0.6-xAlxO3-δ Oxides, J. Am. Ceram. Soc. 90 (2007) 3923 -3929. https://doi.org/10.1111/j.1551 - 2916.2007.02053.x
-
[27]
V . V . Kharton, E. V . Tsipis, A. A. Yaremchenko, I. P. Marozau, A. P. Viskup, J. R. Frade, E. N. Naumovich, Oxygen permeability, electronic conductivity and stability of La0.3Sr0.7CoO3-δ perovskites, Mater. Sci. Eng. B, 134 (2006) 80-88. https://doi.org/10.1016/j.mseb.2006.07.024
-
[28]
A. L. Shaula, V . V . Kharton, N. P. Vyshatko, E. V . Tsipis, M. V . Patrakeev, F. M. B. Marques, J. R. Frade, Oxygen ionic transport in SrFe 1-yAlyO3-δ and Sr1- xCaxFe0.5Al0.5O3-δ ceramics, J. Eur. Ceram. Soc. 25 (2005) 489 -499. https://doi.org/10.1016/j.jeurceramsoc.2004.03.011
-
[29]
E. Babakhania, J. Towfighib, L. Shirazia, A. Nakhaeipoura, A. Zamaniyana, Z. Shafieia, Structure Stability and Oxygen Permeability of Perovskite -type Oxides of Ba0.5Sr0.5Co0.8Fe0.1R0.1O3-δ (R = Al, Mn, Fe, Ce, Cr, Ni, Co), J. Mater. Sci. Technol. 28 (2012) 17 7-183. https://doi.org/10.1016/S1005 - 0302(12)60039-5
-
[30]
H. Luo, T. Klande, Z. Cao, F. Liang, H. Wang, A CO2-stable reduction-tolerant Nd-containing dual phase membrane for oxyfuel CO2 capture, J. Mater. Chem. A 2 (2014) 7780-7787. https://doi.org/10.1039/c3ta14870j
-
[31]
K. Partovi, M. Bittner, J. Caro, Novel CO2-tolerant Al-containing membranes for high-temperature oxygen separation, J. Mater. Chem. A, 3 (2015) 24008 - 24015. https://doi.org/10.1039/c5ta04405g
-
[32]
Z. Cao, X. Zhu, W. Li, B. Xu, L. Yang, W. Yang, symmet ric dual -phase membranes prepared via tape -casting and co -lamination for oxygen permeation, Mater. Lett. 147 (2015) 88 -97. https://doi.org/10.1016/j.matlet.2015.02.033
-
[33]
Q. Li, X. Zhu, W. Yang, Single -step fabrication of asymmetric dual -phase composite membranes for oxygen separation, J. Membr. Sci. 325 (2008) 11 -
work page 2008
-
[34]
https://doi.org/10.1016/j.memsci.2008.08.002
-
[35]
X. Zhu, Q. Li, Y . Cong, W. Yang, Syngas generation in a membrane reactor with a highly stable ceramic composite membrane, Catal. Commun. 10 (2008) 309-312. https://doi.org/10.1016/j.catcom.2008.09.014
-
[36]
H. Luo, H. Jiang, T. Klande, Z. Cao, F. Liang, Novel Cobalt -Free, Noble Metal-free oxygen -permeable 40Pr 0.6Sr0.4FeO3-δ-60Ce0.9Pr0.1O2-δ, dual -phase membrane, Chem. Mater. 24 (2012) 2148 -2154. https://doi.org/10.1021/cm300710p
-
[37]
H. Luo, H. Jiang, K. Efimov, J. Caro, H. Wang, Influence of the preparation methods on the microstructure and oxygen permeability of a CO 2-stable dual phase membrane, AIChE J. 57 (2011) 2738 -2745. https://doi.org/10.1002/aic.12488
-
[38]
H. Luo, B. Tian, Y . Wei, J. Caro, H. Wang, Oxygen permeability and structural stability of a novel tantalum-doped perovskite BaCo0.7Fe0.2Ta0.1O3-δ, AIChE J. 56 (2010) 604-610. https://doi.org/10.1002/aic.12044
-
[39]
K. Partovi, F. Liang, O. Ravkina , J. Caro, High -flux oxygen -transporting membrane Pr0.6Sr0.4Co0.5Fe0.5O3-δ: CO2 stability and microstructure, Acs Appl. Mater. Inter. 6 (2014) 10274-10282. https://doi.org/10.1021/am501657j
-
[40]
H. Luo, H. Jiang, K. Efimov, F. Liang, H. Wang, J. Caro, CO2-tolerant oxygen- permeable Fe2O3-δ-Ce0.9Gd0.1O2-δ dual phase membranes, Ind. Eng. Chem. Res. 50 (2011) 13508-13507. https://doi.org/10.1021/ie200517t
-
[41]
C. Chen, H. Kruidhof, H. Bouwmeester, H. Verweij, A. Burggraaf, Thickness dependence of oxygen permeation thro ugh erbiastabilized bismuth oxide - silver composites, Solid State Ionics 99 (1997) 215 -219. https://doi.org/10.1016/s0167-2738(97)00271-3
-
[42]
I. D. Brown, D. Altermatt, Bond -Valence Parameters Obtained from a Systematic Analysis of the Inorganic Crystal Structure Database, Acta. Cryst. B 41 (1985) 244-247. https://doi.org/0108-7681/85/040244-04501.50
work page 1985
-
[43]
Z. Wu, C. Zhang, X. Chang, W. Jin, N. Xu, Properties of novel Al2O3-doped SrCo0.8Fe0.2O3-δ mixed conducting oxides. J. Chem. Ind. Eng. 57 (2006) 1979-
work page 2006
-
[44]
https://doi.org/10.3321/j.issn:0438-1157.2006.08.039
-
[45]
Oxygen ion conductors and their technological applications
STEELE B H. Oxygen ion conductors and their technological applications. Mater. Sci. Eng. 1992, 13(2): 79-87. Fig. 1. Rietveld refinement XRD patterns of 60CPO-40PSF1-xAxO (x = 0.05, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, and 1.0) powders after calcined at 950 °C for 10 h in air. Fig. 2. Crystal structure characterization of 60CPO -40PSF1-xAxO: (a) the CPO phase cr...
work page 1992
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.