High-Pressure Performance of Mixed-Conducting Oxygen Electrodes: Effect of Interstitial versus Vacancy Conductivity

Abstract

Electrochemical response was measured as a function of oxygen pressure pO2 up to 10 bar for four different mixed-conducting oxygen electrode materials, the oxygen-vacancy-conducting perovskites (Sm0.5Sr0.5)CoO3 (SSC) and (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF), and the interstitial-oxygen-conducting nickelates Pr2NiO4 (PNO) and Nd2NiO4 (NNO). The impedance spectroscopy (IS) measurements were done on symmetrical cells with either single-phase or two-phase infiltrated electrode structures. The polarization resistance decreased with increasing pressure in all cases, but the nickelates decreased more rapidly than the perovskites. It is proposed that this difference is a direct result of the different pO2 dependences of the defect concentrations – the oxygen vacancy concentration decreases with increasing pO2, whereas interstitial concentrations increase. In order to test this hypothesis, point defect concentrations were calculated for LSCF and NNO single-phase electrodes using the Adler-Lane-Steele model from electrochemical data and electrode microstructural parameters obtained by three-dimensional tomography. The results verified that the observed changes with increasing pO2 can be explained by reasonable decreases in LSCF vacancy concentration and increases in NNO interstitial concentration. These results suggest that nickelate electrodes can be advantageous for pressurized devices.

Cobalt-substituted SrTi0.3Fe0.7O3−δ: a stable high-performance oxygen electrode material for intermediate-temperature solid oxide electrochemical cells

“…In previous studies, it was shown that EIS data combined with 3D tomographic data can be used in the Adler-Lane-Steele (ALS) model to determine the oxygen solid state diffusion coefficient D * and the oxygen surface exchange coefficient k * . [71][72][73] This analysis is carried out here to obtain these fundamental transport parameters for STFC electrodes. These values are useful for understanding the reasons for the good electrode performance, and for making comparisons between STFC and other materials independent of electrode microstructure.…”

LSCF–WO3 semiconductor composite electrolytes for low-temperature solid oxide fuel cells

“…It has been widely reported that a lower oxygen pressure is benecial for increasing the oxygen content of LSCF and WO 3 . 41,42 The oxygen vacancy content of 8LSCF-2WO 3 is obviously higher than that of LSCF, which is mainly due to the introduction of heterointerfaces possessing a large amount of oxygen vacancies. 43,44 It is contributed to the decreased activation energy of O 2− conduction and increased ionic conductivity of the composite compared with pure LSCF.…”

Model-Based Optimization of Solid Oxide Electrolysis Cells and Stacks for Power-to-Gas Applications

“…determine activation energies, partial pressure dependencies, CT coefficients and pre-exponential factors independently from each other, due to convolutions of the different loss contributions. Thus, in order to reduce the number of fit parameters, activation energies and partial pressure exponents were extracted from literature EIS data for the different cell materials (11)(12)(13)(14), so that exclusively pre-exponential factors and CT coefficients were used for fitting. Table 1 lists the Butler-Volmer fit parameters reproducing the single cell measurements obtained in this way.…”