Oxygen surface exchange kinetics measurement by simultaneous optical transmission relaxation and impedance spectroscopy: Sr(Ti,Fe)O_3-x thin film case study

Abstract

We compare approaches to measure oxygen surface exchange kinetics, by simultaneous optical transmission relaxation (OTR) and AC-impedance spectroscopy (AC-IS), on the same mixed conducting SrTi0.65Fe0.35O3-x film. Surface exchange coefficients were evaluated as a function of oxygen activity in the film, controlled by gas partial pressure and/or DC bias applied across the ionically conducting yttria-stabilized zirconia substrate. Changes in measured light transmission through the film over time (relaxations) resulted from optical absorption changes in the film corresponding to changes in its oxygen and oxidized Fe (~Fe4+) concentrations; such relaxation profiles were successfully described by the equation for surface exchange-limited kinetics appropriate for the film geometry. The kchem values obtained by OTR were significantly lower than the AC-IS derived kchem values and kq values multiplied by the thermodynamic factor (bulk or thin film), suggesting a possible enhancement in k by the metal current collectors (Pt, Au). Long-term degradation in kchem and kq values obtained by AC-IS was also attributed to deterioration of the porous Pt current collector, while no significant degradation was observed in the optically derived kchem values. The results suggest that, while the current collector might influence measurements by AC-IS, the OTR method offers a continuous, in situ, and contact-free method to measure oxygen exchange kinetics at the native surfaces of thin films.

Barium-Strontium Titanate/Porous Glass Structures for Microwave Applications

“…It is obvious that annealing in an oxygen atmosphere restores the missing oxygen in the crystal lattice and, as a result, reduces losses by two to three times. A change in the charge state of iron ions (as a result of oxidation from Fe 3+ to Fe 4+ ) may be another possible reason for the change in losses due to high-temperature treatment of iron-containing samples in oxygen [ 31 , 32 , 33 ].…”

“…When k is equal to three, it gives a Maxwell–Garnett equation [ 42 ], which is a model based on the analysis of the average field values for a single spherical inclusion in a continuous medium of a polymer matrix. In another study [ 31 ], it was established that the composite sample was satisfactorily described with k equal to 20.…”

Effect of sintering temperature on electrochemical performance of porous SrTi1-xFexO3-δ (x = 0.35, 0.5, 0.7) oxygen electrodes for solid oxide cells

“…There are several features of porous MIEC materials that have an impact on the performance of the electrode. The microstructure of the electrode (porosity, tortuosity, particle size) [2,3], intrinsic oxygen activity (surface exchange, oxygen diffusion) [4,5], interface between the electrode and electrolyte or the barrier layer [6], and the electronic transport properties are all very important. The most studied group of MIEC oxygen electrode materials are the perovskites [7][8][9].…”

“…Also, other materials groups have been studied: double perovskites, Ruddlesden-Popper-type phases [15], and others [16][17][18][19][20][21]. Typical electrode materials have high ionic and electronic conductivity levels, with total conductivities exceeding 100 S cm −1 ; however, the exact role of the influence of the individual partial conductivity levels on the resulting electrode performance is yet to be established, and is currently an active research topic [5,22,23]. In this respect, materials with relatively low total conductivities (or materials with a low electronic-to-ionic conductivity ratio) and good oxygen catalyst properties are very interesting for research.…”

Focus on carbon-neutral energy science and technology

“…Perry and her collaborators compare approaches to measure oxygen surface exchange kinetics, by simultaneous optical transmission relaxation (OTR) and AC-impedance spectroscopy (AC-IS) in the same mixed conducting SrTi 0.65 Fe 0.35 O 3−x film by accounting for the presence and condition of the metal current collectors (Pt, Au). The results suggest that, while the current collector might influence measurements by AC-IS, the OTR method offers a continuous, in situ , and contact-free method to measure oxygen exchange kinetics at the native surfaces of thin films [ 2 ]. The team of Kilner uses secondary ion mass spectrometry (SIMS) depth profiling to study 18 O and 2 H diffusion at 300 °C temperature in the double perovskite material PrBaCo 2 O 5+δ (PBCO) in flowing air containing 200 mbar of 2 H 2 16 O.…”