Operando high-temperature near-ambient pressure X-ray photoelectron spectroscopy and impedance spectroscopy study of Ni - Ce_(0.9)Gd_(0.1)O_(2-δ) solid oxide fuel cell anode

摘要

In this study we present the results of operando high temperature near-ambient-pressure x-ray photoelectron spectroscopy (HT-NAP-XPS) measurements of a pulsed laser deposited thin film Ni - Ce_(0.9)Gd_(0.1)O_(2-δ) model electrode. In our measurements, we have used the novel three electrode dual-chamber electrochemical cell developed in our previous work at different H_2 pressures and at different electrochemical conditions at around 650 °C. The possible redox reactions on the anode surface (Ni~(2+) ↔ Ni~0, Ce~(4+) ↔ Ce~(3+)) were investigated by HT-NAP-XPS technique simultaneously with electrochemical impedance spectroscopy measurements. The oxygen partial pressure in counter and reference electrode compartment was controlled at 0.2 bar. Changes in electronic structure of the Ce 3d and Ni 2p photoelectron spectra caused by electrode potential and H_2 pressure variations were observed and estimated by curve fitting procedure. The O 1s and valence band photoelectron signals were used for depth probing of the chemical composition and redox changes at Ni-GDC and for studying the influence of the electrochemical polarization on the chemical state of Ni-GDC surface atoms. As a result changes in oxidation state of electrode surface atoms caused by electrode polarization and oxide ion flux through the membrane were detected with simultaneous significant variation of electrochemical impedance.