Report title: Characterization of surface chemistry and defect balance of electrode materials for solid oxide batteries by in situ X-ray photoelectron spectroscopy

Reporter: Lu Qiyang

Report time: 9:00-10:00, November 21, 2021

Location: Conference room B5-102, University Town Campus, South China University of Technology

Abstract: In situ characterization of the surface chemical composition and electronic structure of solid oxide fuel cell and electrolytic cell (SOFC / SOEC) electrode materials under real working conditions is of great significance for understanding the structure-activity relationship of electrode materials and designing materials to improve the high-temperature electrocatalytic performance and stability. This requires us to be able to characterize the solid/gas interface under high temperature (at least 500 ° C), reaction atmosphere (air electrode oxidation atmosphere or fuel electrode reduction atmosphere) and applied voltage, which is difficult to be met by general traditional surface scientific characterization methods. In recent years, the newly developed near atmospheric pressure X-ray photoelectron spectroscopy and absorption spectroscopy (AP-XPS/XAS) based on synchrotron radiation has broken through the experimental conditions of ordinary X-ray photoelectron spectroscopy. So we can deeply reveal the changes of chemical composition, element valence and oxygen vacancy defect concentration on the electrode surface under working conditions. We will illustrate the application of AP-XPS/XAS in the characterization of electrode materials of solid oxide fuel cells through three specific examples: 

  1) we found that the addition of metal cations that are not easy to be reduced (such as Hf, Zr, Ti, etc.) on the surface can effectively improve the catalytic stability of high-temperature oxygen reduction of (LA, SR) coO₃ as SOFC cathode material. Through AP-XPS / XAS, we found that the reduction of surface oxygen vacancy inhibited the surface segregation of Sr and improved the stability of electrode performance.

  2) Using AP-XAS, we can not only detect the changes of electronic structure in the process of SrcoO_x phase transition, but also analyze the kinetics and speed determination steps of the phase transition process caused by the change of oxygen vacancy concentration by means of the relaxation process; 

  3) Using AP-XPS/XAS, we analyzed the difference of chemical equilibrium between (PR, CE) O_2-x surface and bulk phase defects. The results showed that the concentration of surface oxygen vacancy was much greater than that of the bulk phase, and its variation law with oxygen partial pressure PO₂ was also very different. 

  We will also briefly describe how to expand the AP-XPS characterization method from solid/gas interface to solid/liquid interface, so as to expand the application scope of this powerful in-situ characterization method and make it widely used in aqueous solution electrocatalysis, pseudocapacitance and heterogeneous catalysis.

Introduction about the reporter: Dr. Lu Qiyang is now a distinguished researcher at the school of technology of Westlake University and the head of the solid-state ion laboratory. Dr. Lu Qiyang graduated from the Department of materials science and engineering of Tsinghua University in 2012 with a Bachelor of engineering. After graduation, he studied for a doctorate at the Massachusetts Institute of Technology (MIT) under Professor bilge Yildiz. In January 2018, he obtained the doctor degree in engineering and won the Best Doctoral Thesis Award of MIT materials department in that year. Subsequently, he conducted postdoctoral research at Oak Ridge National Laboratory, Stanford University and Lawrence Berkeley National Laboratory advanced light source. He has won the MRS GSA Gold Award and the Ross coffin Purdy Award (co-winner) of the American Ceramic Society. Dr. Lu Qiyang's research field is the cross-field of surface science, solid-state electrochemistry and material science. The frontier in-situ surface and interface research methods and knowledge are applied to the basic research of material science, and the electronic structure, chemical composition and defects of material surface and interface are successfully detected on a nanoscale under extreme conditions such as high temperature, reaction atmosphere and applied voltage. The influence mechanism of the microscopic properties of the material surface and interface on the surface chemical reaction kinetics was clarified. It has been published in nature material (two articles), Nano Letters, adv. Function Mater. And other top international journals.