Moving boundary diffusion problem for hydration kinetics evidenced in non-monotonic conductivity relaxations of proton conducting perovskites

Kim, Gye-Rok; Seo, Hyun-Ho; Jo, Jung-Mo; Shin, Eui-Chol; Yu, Ji Haeng; Lee, Jong‐Sook

doi:10.1016/j.ssi.2015.01.003

Cited by 10 publications

(8 citation statements)

References 49 publications

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“…The details of the setup were reported elsewhere. 31) The humidity was controlled at a level up to 90% and was balanced with H 2 using a custom-made direct evaporator (ADrop, GmbH, DV2MK-TL, Germany) based on a liquid flow meter (LIQUI-FLOW, Bronkhorst High-Tech B.V., The Netherlands). To avoid flow rate effects on the electrode kinetics, total gas flow rates were controlled at 50 sccm, as in the previous work.…”

Section: Methodsmentioning

confidence: 99%

Application of a General Gas Electrode Model to Ni-YSZ Symmetric Cells: Humidity and Current Collector Effects

Shin¹,

Ahn²,

Seo³

et al. 2016

J. Korean Ceram. Soc

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Electrolyte-supported symmetric Ni-YSZ cermet electrodes of ca. 23 µm were prepared by screenprinting and the impedance was measured as a function of humidity from 2% to 90% balanced in H 2 at a total flow rate of 50 sccm. The Ni felt current collector of 1 mm thickness exhibited a Gerischer-like gas concentration impedance in the low frequency range, which was similarly observed in the cermet-supported solid oxide cells, while the Pt paste collector exhibited only electrochemical polarization. The electrochemical polarization of both samples was modeled by a non-ideal diffusion-reaction transmission line model including CPEs with α = 0.5. In the case of the Pt paste collector, all the Bisquert parameters exhibited humidity dependence to the -1/2 power, supporting a non-faradaic chemical reaction mechanism at three phase boundaries. Consequently, the surface diffusivity and reaction rate increased linearly with humidity. Less pronounced humidity dependence and somewhat lower utilization length with an Ni felt collector can be attributed to the diffusion-limited gas flow through the collector.

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Section: Methodsmentioning

confidence: 99%

Application of a General Gas Electrode Model to Ni-YSZ Symmetric Cells: Humidity and Current Collector Effects

Shin¹,

Ahn²,

Seo³

et al. 2016

J. Korean Ceram. Soc

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“…With n h ≫ c v the charge neutrality condition implies n h = c A and using Eq. (23) we get after some algebra the following expression for the electron chemical potential ν e (T ) = α 1 − π 2 12 kT α 2 (24) with α = (3c A /2g 0 ) 2/3 . This further implies that…”

Section: B High Hole Concentrationmentioning

confidence: 99%

Implications of the band gap problem on oxidation and hydration in acceptor-doped barium zirconate

Lindman

Erhart²,

Wahnström³

2015

Phys. Rev. B

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Charge carrier concentrations in acceptor-doped proton-conducting perovskites are to a large extent determined by the hydration and oxidation of oxygen vacancies, which introduce protons and holes, respectively. First-principles modeling of these reactions involves calculation of formation energies of charged defects, which requires an accurate description of the band gap and the position of the band edges. Since density-functional theory (DFT) with local and semi-local exchangecorrelation functionals (LDA and GGA) systematically fails to predict these quantities this can have serious implications on the modeling of defect reactions. In this study we investigate how the description of band gap and band edge positions affects the hydration and oxidation in acceptordoped BaZrO3. First-principles calculations are performed in combination with thermodynamic modeling in order to obtain equilibrium charge carrier concentrations at different temperatures and partial pressures. Three different methods have been considered: DFT with both semi-local (PBE) and hybrid (PBE0) exchange-correlation functionals, and many-body perturbation theory within the G0W0-approximation. All three methods yield similar results for the hydration reaction, which are consistent with experimental findings. For the oxidation reaction, on the other hand, there is a qualitative difference. PBE predicts the reaction to be exothermic while the two others predict an endothermic behavior. Results from thermodynamic modeling are compared with available experimental data, such as enthalpies, concentrations and conductivities, and only the results obtained with PBE0 and G0W0, with an endothermic oxidation behavior, give a satisfactory agreement with experiments.

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“…Mixtures were homogenized by ball milling for 24 h in ethanol and dried cakes were ground, cold-isostatically pressed (CIP) at 1500 kg{cm 2 for 15 min, and sintered at 1400 °C for 3 h. As-received powders of GDC, LSM, and LSCF were similarly pressed and sintered. Samples with high fluorite amount or perovskite phase below 20% were prepared using a mold of 7 mm diameter using a powder mass of ~0.2 g. Samples with perovskite phase of 20% and above were prepared using a bigger mold of 24 mm size with a powder mass of around 6 g, for disk samples of radius 17 mm and thickness ~2 mm for a high temperature van der Pauw setup previously reported [26].…”

Section: Methodsmentioning

confidence: 99%

“…Reversed polarity and reciprocal measurements reduces the errors due to thermal voltages and poor electrode condition. LabVIEW automated DC van der Pauw conductivity measurement involving eight voltage measurements and the numerical calculation takes about 44 s. Measurements were performed quasi-continuously while temperature was controlled at "1 °C/min between room temperature and 800 °C for the samples loaded in a custom-designed sample holder [26] positioned in a vertical tube furnace with flowing synthetic air of humidity 50 ppm in 100 SCCM, and between 177 °C to ´73 °C for the samples loaded in a cryostat with a high temperature option (Janis CCS-450, LakeShore Cryotronics, Westerville, OH, USA) in a vacuum condition. In the cryostat setup, control and monitoring of the temperature was made using two Pt sensors connected to a temperature controller (331, LakeShore Cryotronics, Westerville, OH, USA).…”

Section: Methodsmentioning

confidence: 99%

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Conductivity Transitions of La0.7Sr0.3MnO3±δ and La0.6Sr0.4Co0.2Fe0.8O3−δ in Ce0.9Gd0.1O2−δ Matrix for Dual-Phase Oxygen Transport Membranes

Pham

Lee

2021

Crystals

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Using van der Pauw method, the conductivity of disk samples of La0.7Sr0.3MnO3±δ (LSM) and La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) in a Ce0.9Gd0.1O2−δ (GDC) matrix was accurately quasi-continuously measured over 800 °C to −73 °C, and the transition points in Arrhenius behavior were systematically obtained from the extremum points of the second derivatives. While LSM-containing samples showed reproducible conductivity trajectories, the LSCF system exhibited unsystematic changes which may be related to the substantial oxidation/reduction reactions accompanying the ferroelastic–paraelastic transitions with a substantial thermal hysteresis at 650 °C to 750 °C, corresponding to conductivity maxima. A sudden decrease in activation energies on cooling corresponds to the para-to-ferromagnetic, weak insulator–metal transitions and the Curie temperature of LSM appears to gradually decrease in composites to 90 °C, while LSCF composites exhibit blurred transitions at approximately −40 °C. Relatively insulating paramagnetic phases are characterized by activation energy values ~0.2 eV, change to the high temperature phase exhibiting activation energy 0.1 eV for small polaron hopping mechanisms at 300 °C to 500 °C with increasing GDC content in the LSM composites and by two transitions at ∼60 °C and ∼245 °C for the LSCF composites. LSCF single phase shows distinctly lower transition points which appear to match with the singularly large c lattice parameter whereas the composites exhibit decreasing c with LSCF amount together with increasing lattice parameter of GDC. Van der Pauw conductivity is a feasible and sensitive in situ tool for monitoring the status of oxygen transport membranes.

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Moving boundary diffusion problem for hydration kinetics evidenced in non-monotonic conductivity relaxations of proton conducting perovskites

Cited by 10 publications

References 49 publications

Application of a General Gas Electrode Model to Ni-YSZ Symmetric Cells: Humidity and Current Collector Effects

Application of a General Gas Electrode Model to Ni-YSZ Symmetric Cells: Humidity and Current Collector Effects

Implications of the band gap problem on oxidation and hydration in acceptor-doped barium zirconate

Conductivity Transitions of La0.7Sr0.3MnO3±δ and La0.6Sr0.4Co0.2Fe0.8O3−δ in Ce0.9Gd0.1O2−δ Matrix for Dual-Phase Oxygen Transport Membranes

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