A fundamental understanding of H2 and CO oxidation on the surface of solid oxide catalyst and their reverse reactions is crucial to both achieving the goal of exploiting cleaner hydrocarbon fuel and making artificial photosynthesis a reality. While recent years have seen a successful use of ceria-based materials in splitting H2O and CO2 into chemical fuels, a microscopic picture of the electrochemical processes at the solid-gas interface that control the device efficiency is still elusive. A challenge to approaching this critical interface is a lack of proper in-situ non-intrusive probe that can monitor the change of the interface while the device is in operation.
In this project, we study the reactions mentioned above using combined tools of synchrotron based ambient pressure x-ray photoelectron spectroscopy and electrochemical impedance measurement. We fabricate ceria-based model electrodes of high purity and polarized the electrochemical cell in a single chamber environment. The polarization drove the cell to non-equilibrium steady states. Then we examine the evolution of surface adsorbates, oxygen ions, electrons, and also the surface dipole that influences the charge transfer process across the interface as a function of applied bias. Based on our experimental findings, we related thermodynamic driving forces with kinetic phenomena, creating new insight into the mechanism of ceria-gas interaction.
 Z. A. Feng et al. Fast vacancy-mediated oxygen ion incorporation across the ceria–gas electrochemical interface. Nature Comm. 5, 4374 (2014)