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Master assignment

The influence of thermal history on the oxygen surface exchange for SOFC cathode materials. 

Perovskite oxides belonging to the family; (La1-xSrx)s(Co1-yFey)O3-δ (1 ≥ x ≥ 0, 1 ≥ y ≥ 0, s = 1) have found use as electrodes for solid oxide cells (SOC) and oxygen sensors and are also being explored as potential materials for oxygen separation membranes. This is due to their good ionic and electronic transport properties, high activity for oxygen reduction/ evolution reactions (ORR/OER) and the fact that via tailoring the composition, properties can be ‘tuned’ with a view to the specific application. When assessing the performance of a particular perovskite composition, one usually compares the catalytic activity with a reference, a non-modified sample or a literature value. However, establishing a suitable reference point is not necessarily trivial. A good illustration is given by Bobing et al.1 where a literature review reveals that the results of surface exchange coefficient (kchem) differ over one order of magnitude even for the same cathode material (fig. 1). One of the factors responsible for this scatter in literature is that the thermal history of the samples prior to measurement is rarely detailed. Furthermore, it is often not clear how stable the reported enhancements are and whether the reference samples have representative and stable performance themselves.

Fig.1 Hu, B., & Xia, C. Asia-Pacific J. Chem. Eng. (2016)

 

In this project, the aim is to investigate the dependence of oxygen surface exchange rate on the thermal history of LAF64. The candidate will benefit of the expertise and equipment of Electrochemistry Research Group (ECRG) to:

  1. Synthesize LAF64 powder and dense pellets from the protocol described in literature and developed in ECRG previously.
  2. Characterize the as-prepared membranes by various techniques like LEIS, XRD, electron microscopy, XPS, etc...
  3. Finding key parameters (e.g. variations in composition, effect of microstructure and surface composition) that control membrane properties.
  4. Evaluate the electrochemical performance of the membranes by electrical conductivity relaxation (ECR)

 

Skills which will be developed during the Master assignment:

  • Synthesis of perovskite powders and dense membranes
  • Characterization of the as-prepared dense membranes by XRD and SEM
  • Surface composition and bulk profile analysis after post annealing treatments by LEIS and XPS
  • Evaluation of the membrane performances by ECR

 

For more information please contact:

 

[1] Hu, B.; Xia, C. Factors Influencing the Measured Surface Reaction Kinetics Parameters. Asia‐Pacific Journal of Chemical Engineering 2016, 11 (3), 327–337.