Room temperature redox reaction by oxide ion migration at carbon/Gd-doped CeO₂heterointerface probed by anin situhard x-ray photoemission and soft x-ray absorption spectroscopies

Abstract

In situ hard x-ray photoemission spectroscopy (HX-PES) and soft x-ray absorption spectroscopy (SX-XAS) have been employed to investigate a local redox reaction at the carbon/Gd-doped CeO2 (GDC) thin film heterointerface under applied dc bias. In HX-PES, Ce3d and O1s core levels show a parallel chemical shift as large as 3.2 eV, corresponding to the redox window where ionic conductivity is predominant. The window width is equal to the energy gap between donor and acceptor levels of the GDC electrolyte. The Ce M-edge SX-XAS spectra also show a considerable increase of Ce3+ satellite peak intensity, corresponding to electrochemical reduction by oxide ion migration. In addition to the reversible redox reaction, two distinct phenomena by the electrochemical transport of oxide ions are observed as an irreversible reduction of the entire oxide film by O2 evolution from the GDC film to the gas phase, as well as a vigorous precipitation of oxygen gas at the bottom electrode to lift off the GDC film. These in situ spectroscopic observations describe well the electrochemical polarization behavior of a metal/GDC/metal capacitor-like two-electrode cell at room temperature.

Ultrasmall Metal-Doped CeO2 Nanoparticles for Low-Temperature CO Oxidation

“…It is generally accepted that these peaks are due to dopants and oxygen vacancies following the dopant addition, but their true origin is still a debate in the open literature. Among the most popular hypotheses is that the above peaks correspond to oxygen vacancies 50 or clusters between the dopants and the oxygen vacancies. 45 In addition, the intensity of the 240 cm −1 peak seems to be affected by the dopant.…”

In Situ Tuning of Magnetization and Magnetoresistance in Fe3O4 Thin Film Achieved with All-Solid-State Redox Device

“…In situ hard X-ray photoelectron spectroscopy (HX-PES) was performed at the undulator beamline BL15XU of SPring-8 to examine the valence modulation of the Fe ions during device operation. − The Fe 2s core-level spectra of the Fe 3 O 4 thin film were observed under various applied DC voltage conditions (see Methods and section S4 for experimental details). The HX-PES spectra were calibrated using Pt 4f peaks of the top Pt film which is very stable for electrochemical reaction and thus can be reliable reference.…”

“…The overall resolution of the instrument estimated is 0.15 at 5948 eV of photon energy, while the binding energy values are referenced to the metallic Au Fermi edge. The present measurements were performed using the excitation by hard X-ray source at an incident angle of 82°, which can penetrate to micrometer range, and the detection of photoelectron with an escape depth of 10–20 nm. − All HX-PES measurements were conducted in a high vacuum, typically 7.0 × 10 –8 Pa.…”

<i>In-Situ</i> Monitoring of Oxide Ion Induced Breakdown in Amorphous Tantalum Oxide Thin Film Using Acoustic Emission Measurement

“…The same behavior was observed at Pt/Gd doped CeO 2 oxide ion conductor interface. 17) It is noted that no blisters were found by the FE-SEM observation after 18 V was applied, as shown in Fig. 2(e).…”