Abstract
Ambient pressure X-ray photoelectron spectroscopy was used to detect rigid shifts in photoelectron kinetic energies and material chemical states for operating solid oxide electrochemical cells. The kinetic energy shifts directly correspond to the surface electric potentials and therefore can be used to detect the local potentials / potential losses for operating cells. The ceria valence state changes under applied biases relative to equilibrium conditions (at open circuit voltage) reveal the electrochemically active regions ~150 μm away from the current collectors for ceria thin film electrodes. The results provide fundamental mechanistic information about the active length scales in ceria electrodes, the surface reaction kinetics, charge transport, as well as activities for oxidation and electrolysis on operating solid oxide electrochemical cells.