Oxygen separation membranes

The reduction of CO₂ emissions is a major issue with respect of the increasing demand for energy. However, the lack of large-scale energy storage solutions still forces to rely on fossil power plants. Therefore, carbon capture and storage technology (CCS) is essential. A key technology for CCS power plants is the cheap production of pure oxygen on basis of so-called MIEC (mixed ionic electronic conducting) ceramic membranes.

The schematic function principle of an oxygen separation membrane is shown in Fig. 1 (left). The main part consists of a MIEC material that transports O^2- anions in direction of an oxygen concentration gradient. Charge equilibrium is established by electrons flowing in opposite direction.

A promising material for oxygen separation membranes is (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3-d (BSCF) which crystallizes in the cubic perovskite structure (Fig. 2). This material exhibits excellent oxygen ion conductivity in the desired temperature range between 600-800 °C. However, the limiting factor in the development of BSCF-based oxygen separation membranes is the long-term instability of the desired cubic BSCF phase resulting in decreasing oxygen flux rates. Hence, the understanding of the degradation mechanism is of key importance. One approach to enhance the thermodynamical stability of the cubic BSCF phase is specific B-site co-doping with monovalent transition metal cations like Y or Zr.

 

Electron microscopy is employed to investigate the microstructural origin of the degradation of oxygen-ion transport in the BSCF material system. Scanning Electron Microscopy (SEM) is a fast method for analyzing a large quantity of samples, whereas Transmission Electron Microscopy (TEM) combines atomic-resolution imaging with electron diffraction and high spatial resolution analytical techniques like Electron-Energy-Loss Spec­tros­copy (EELS) and Energy-Dispersive X-Ray Spectroscopy (EDXS).

Selected conference poster presentations:

Electron microscopy study of yttrium doped Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (pdf)

Selected publications:

V. Weber, Weber, M. Meffert, S. Wagner, H. Störmer, L. –S. Unger, E. Ivers-Tiffée, D. Gerthsen,
Influence of B‑site doping with Ti and Nb on microstructure and phase constitution of (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3-δ,
J. Mater. Sci. 55, 947 (2020)

M. Meffert, L.-S. Unger, T. Kresse, H. Störmer, C. Niedrig, S. F. Wagner, E. Ivers-Tiffée_, D. Gerthsen,
The effect of B-site Y substitution on cubic phase stabilization in (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3-δ,
J. Am. Ceram. Soc. 102, 4929 (2019)

L.-S. Unger, R. Ruhl, M. Meffert, C. Niedrig, W. Menesklou, S. F. Wagner, D. Gerthsen, H. J. M. Bouwmeester, E. Ivers-Tiffée,
Yttrium Doping of (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3-δ Part II: Influence on oxygen transport and phase stability,
J. Electrochem. Soc. 38, 2388 (2018)

L. Almar, H. Störmer, M. Meffert, J. Szász, F. Wankmüller, D. Gerthsen, E. Ivers‑Tiffée,
Investigation of phase stability and CO₂-poisoning effect on a high performance Y-doped Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ SOFC cathode,
ACS Applied Energy Materials 1, 1316 (2018)

M. Meffert, L.-S. Unger, L. Grünewald, H. Störmer, S.F. Wagner, E. Ivers-Tiffée, D. Gerthsen,
The impact of grain size and A/B-cation ratio on secondary phase formation in (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3-δ,
J. Mater. Sci. 52, 2705 (2017)

M. Meffert, H. Störmer, D. Gerthsen,
The role of mixed-site occupation in Y- and Sc-doped (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3-δ on secondary phase formation,
Micros. Microanal. 22, 113 (2016)

P. Müller, Dissertation KIT (2013)

P. Müller, M. Meffert, H. Störmer, D. Gerthsen,
Fast Mapping of the Cobalt-Valence State in Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-d by Electron Energy Loss Spectroscopy,
Microscopy and Microanalysis, 19, 1595-1605 (2013).

P. Müller, H. Störmer, M. Meffert, L. Dieterle, C. Niedrig, S. Wagner, E. Ivers-Tiffée, D. Gerthsen,
Secondary Phase Formation in Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-d Studied by Electron Microscopy,
Chemistry of Materials (2013)

P. Müller, H. Störmer, L. Dieterle, C. Niedrig, E. Ivers-Tiffée, D. Gerthsen,
Decomposition Pathway of cubic Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-d between 700 °C and 1000 °C analyzed by electron microscopic techniques,
Solid State Ionics, 206 57-66(2012)

M. Burriel, C. Niedrig, W. Menesklou, S.F. Wagner, J. Santiso, and E.Ivers-Tiffée,
BSCF epitaxial thin films: Electrical transport and oxygen surface exchange,
Solid State Ionics 181, 602 (2010)

C. Niedrig, S. Taufall, P. Müller, S.F. Wagner, H. Störmer, D. Gerthsen, and E. Ivers-Tiffée,
Thermal Stability of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-d,
Proc. 1st International Conf. on Materials for Energy Karlsruhe,48(2010)

P. Müller, L. Dieterle, E. Müller, H. Störmer, D. Gerthsen, C. Niedrig, S. Taufall, S.F. Wagner, and E. Ivers-Tiffée,
Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-d for Oxygen Separation Membranes,
ECS Transactions 28(11), 309-314 (2010)