TY - JOUR
T1 - Oxygen surface exchange kinetics measurement by simultaneous optical transmission relaxation and impedance spectroscopy
T2 - Sr(Ti,Fe)O3-x thin film case study
AU - Perry, Nicola H.
AU - Kim, Jae Jin
AU - Tuller, Harry L.
N1 - Funding Information:
This work was supported by the JSPS Kakenhi Grant-in-Aid for Young Scientists (B) [project number JP15K18213] (to N.H. Perry) and by the International Institute for Carbon-Neutral Energy Research (WPI-I2CNER, MEXT) at Kyushu University, Japan. J.J. Kim and H.L. Tuller thank US-DOE Basic Energy Sciences [grant number DE-SC0002633] for financial support. N.H. Perry would like to acknowledge D. Pergolesi for initial support in PLD growth and T. Chen for helpful discussions.
Funding Information:
This work was supported by the JSPS Kakenhi Grant-in-Aid for Young Scientists (B) [project number JP15K18213] (to N.H. Perry) and by the International Institute for Carbon-Neutral Energy Research (WPI-I2CNER, MEXT) at Kyushu University, Japan. J.J. Kim and H.L. Tuller thank US-DOE Basic Energy Sciences [grant number DE-SC0002633] for financial support.
Publisher Copyright:
© 2018 The Author(s). Published by National Institute for Materials Science in partnership with Taylor & Francis.
PY - 2018/12/31
Y1 - 2018/12/31
N2 - 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.
AB - 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.
KW - Thin films
KW - impedance spectroscopy
KW - mixed ionic and electronic conductor
KW - optical absorption
KW - oxygen surface exchange
KW - perovskite
UR - http://www.scopus.com/inward/record.url?scp=85042402571&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85042402571&partnerID=8YFLogxK
U2 - 10.1080/14686996.2018.1430448
DO - 10.1080/14686996.2018.1430448
M3 - Article
AN - SCOPUS:85042402571
SN - 1468-6996
VL - 19
SP - 130
EP - 141
JO - Science and Technology of Advanced Materials
JF - Science and Technology of Advanced Materials
IS - 1
ER -