Figures & data
Figure 1. Overview of the raw data obtained during the first measurement run at 600 °C on the pre-aged STF35 film. Measured light transmission (dark blue, left axis) is shown to change over time in response to changes in both gas oxygen partial pressure (orange curve, right axis) and DC bias across the substrate (light blue curve, left axis). Shaded areas indicate times during which AC-impedance measurements were performed (blue shaded for positive DC bias and red shaded for negative DC bias).
Figure 2. Example of OTR curve upon lowering oxygen partial pressure from 2.5 × 10−4 to 1.1 × 10−4 atm at 600 °C for the aged STF35 film.
Figure 3. Fit by Equation (Equation2(2)
(2) ) for surface exchange-limited kinetics, demonstrating the expected linear behavior and that was used to extract k
chem from the slope. Film thickness was ~200 nm.
Figure 4. AC impedance spectra measured on the porous Pt/YSZ/STF/porous Pt cell at 600 °C in different oxygen partial pressures, as shown in the legend. Selected frequencies are indicated on some points for the spectrum measured in 0.002 atm O2.
Figure 5. Oxygen partial pressure dependence of high frequency (YSZ), medium frequency (Pt counter electrode) and low frequency (STF) resistances, from equivalent circuit fitting of the impedance spectra, for the porous Pt/YSZ/STF/porous Pt cell at 600 °C. Dashed lines indicate guides to the eye showing the slopes for initial data prior to more significant degradation (~0 for YSZ, −0.61 for Pt, and −0.28 for STF). Increasing deviation from these slopes were observed for the Pt and STF contributions after increasingly long times (>100 h).
Figure 6. (a) Calculated bulk thermodynamic factor as expressed in Equation (Equation7(7)
(7) ), from thermogravimetric oxygen non-stoichiometry data, also shown with fit to a broader range of data, from Ref. [Citation48]. (b) Estimated thin film thermodynamic factors from the ratio of AC-IS derived k
chem to k
q
(or from the measured capacitance), as in Equations (Equation4–6), for different current collectors.
![Figure 6. (a) Calculated bulk thermodynamic factor as expressed in Equation (Equation7(7) γ=12∂lnpO2∂lnxO(7) ), from thermogravimetric oxygen non-stoichiometry data, also shown with fit to a broader range of data, from Ref. [Citation48]. (b) Estimated thin film thermodynamic factors from the ratio of AC-IS derived k chem to k q (or from the measured capacitance), as in Equations (Equation4–6), for different current collectors.](/cms/asset/a750bdb0-b028-40f3-b3f5-2a3e4045a187/tsta_a_1430448_f0006_oc.gif)
Figure 7. Comparison of (nearly) simultaneously measured k chem and k q values for STF35 at 600 °C (t.f. stands for bulk thermodynamic factor = γ) using a sputtered porous Pt current collector on a portion of the film. Inset is a photo of the sample for simultaneous OTR of the native film and AC-IS measurements using the porous Pt current collector.
Figure 8. Comparison of (nearly) simultaneously measured k chem and k q values for STF35 at 600 °C (t.f. stands for bulk thermodynamic factor = γ) using a painted porous Au current collector on a portion of the film. Sample is another piece of the sample used in Figure . Inset is a photo of this piece used for simultaneous OTR of the native film and AC-IS measurements with the porous Au current collector. Approximate data for buried Pt finger current collectors are also included.
