| AVS 65th International Symposium & Exhibition | |
| Applied Surface Science Division | Thursday Sessions |
| Session AS+SE-ThM |
| Session: | Applied Surface Analysis of Novel, Complex or Challenging Materials |
| Presenter: | John Kilner, Imperial College London, UK |
| Authors: | J.A. Kilner, Imperial College London, UK J.W. Druce, International Institute for Carbon Neutral Energy Research (I2CNER), Japan H. Tellez, International Institute for Carbon Neutral Energy Research (I2CNER) A. Staykov, International Institute for Carbon Neutral Energy Research (I2CNER) |
| Correspondent: | Click to Email |
High temperature electrochemical devices, such as solid oxide fuel cells and electrolyzers, have been under development for application in clean energy systems for many years. Although acceptable performance can be achieved, the requirements of low cost and high durability have been a major hurdle to commercialization. This has necessitated a lowering of the operating temperature from circa 800-900ºC, to temperatures in the region of 500-600ºC, with a consequent loss of electrochemical activity of the electrodes, particularly the air electrode. Key to optimizing performance is gaining an understanding of the gas/solid interface between the Mixed Ionic Electronic Conducting (MIEC) electrodes and the oxygen-rich ambient, and how the structure, composition and activity evolves with time. We have used a multifaceted approach to probe the surfaces of ceramic mixed conductors, after treatment in typical SOFC cathode operating conditions. This has involved ion beam based techniques such as Low Energy Ion Scattering (LEIS) to sample the composition of the outermost atomic layers of ceramic materials, Secondary Ion Mass Spectrometry (SIMS) to measure oxygen exchange activity, complemented by Density Functional Theory (DFT) to clarify possible mechanisms.
The surface termination of substituted (AA’)(BB’)O3perovskite-based MIEC materials, such as La1‑xSrxCo1‑yFeyO3-δ (LSCF), has been studied using LEIS [1] and shown to be dominated by A cations and oxygen, and in particular by segregation of the Sr substituent. For selected (AA’)(BB’)O3 compositions, we have investigated the rate of oxygen exchange and shown changes in surface activity that are related to changes in surface chemistry. We have used the knowledge gained from experiment to guide theoretical investigations, to aid in the optimization of candidate air electrode materials. This theoretical study was performed using DFT to simulate the interaction of an oxygen molecule with representative AO and A’O segregated surfaces [2,3].
This combination of theoretical studies guided by advanced surface analysis techniques (i.e. LEIS and SIMS) is enhancing our understanding of processes which determine the performance of these important clean energy devices.
[1] Druce, J., H. Téllez, M. Burriel, M.D. Sharp, L.J. Fawcett, S.N. Cook, D.S. McPhail, T. Ishihara, H.H. Brongersma, and J.A. Kilner, Energy & Environmental Science, 2014. 7(11): p. 3593-3599.
[2] A. Staykov, H. Téllez, T. Akbay, J. Druce, T. Ishihara, J. Kilner, Chemistry of Materials27(2015) (24) 8273.
[3] T. Akbay, A. Staykov, J. Druce, H. Téllez, T. Ishihara, J.A. Kilner, Journal of Materials Chemistry A4(2016) (34) 13113.