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Structural Evolution of Ultrathin SrFeO_3-δ Films during Oxygen Evolution Reaction Revealed by In Situ Electrochemical Stress Measurements.

ABSTRACT: We report the electrochemical stress analysis of SrFeO_3-δ (SFO) films deposited on Au substrates during oxygen evolution reactions (OERs). Our in situ analysis of Au reveals conversion reactions from Au to Au(OH)₃, AuOOH, and AuO_x during the OER. Au reactions cause a monotonic compressive stress on surfaces assigned to the formation of Au hydroxides and oxides. Electrochemical stress analysis of SrFeO_3-δ/Au shows a dramatically different behavior during the OER, which we attribute to structural evolutions and conversion reactions, such as the conversion of SFO to iron (oxy)hydroxides. Interestingly, electrochemical stress analysis of SrFeO_3-δ/Au shows a tensile trend, which evolves with cycling history. Electrochemical stress analysis of SFO films before the onset of the OER shows in situ changes, which cause tensile stresses when cycling to 1.2 V. We attribute these stresses to the formation of Fe^2+δO_δ(OH)_2-δ (0 ≤ δ ≤ 1.5)-type materials where δ approaches 1.5 at higher potentials. At potentials higher than 1.2 V and during OER, surface stress response is rather stable, which we assign to the full conversion of SFO to iron (oxy)hydroxides. This analysis provides insight into the reaction mechanism and details of in situ structural changes of iron perovskites during the OER in alkaline environments.

SUBMITTER: Marquez E

PROVIDER: S-EPMC10716856 | biostudies-literature | 2023 Dec

REPOSITORIES: biostudies-literature

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Structural Evolution of Ultrathin SrFeO3-δ Films during Oxygen Evolution Reaction Revealed by In Situ Electrochemical Stress Measurements.

Marquez Emily E Keu Kim Hong KH Nelson Andrea A Lefler Benjamin M BM May Steven J SJ Tavassol Hadi H

ACS applied energy materials 20231116 23

We report the electrochemical stress analysis of SrFeO3-δ (SFO) films deposited on Au substrates during oxygen evolution reactions (OERs). Our in situ analysis of Au reveals conversion reactions from Au to Au(OH)3, AuOOH, and AuOx during the OER. Au reactions cause a monotonic compressive stress on surfaces assigned to the formation of Au hydroxides and oxides. Electrochemical stress analysis of SrFeO3-δ/Au shows a dramatically different ...[more]

PMID: 38098872

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Project description:The further development of solid oxide fuel and electrolysis cells (SOFC/SOEC) strongly relies on research activities dealing with electrode materials. Recent studies showed that under operating conditions many perovskite-type oxide electrodes are prone to changes of their surface composition, leading to severe changes of their electrochemical performance. This results in a large scatter of data in literature and complicates comparison of materials. Moreover, little information is available on the potentially excellent properties of surfaces immediately after preparation, that is, before any degradation by exposure to other gas compositions or temperature changes. Here, we introduce in situ impedance spectroscopy during pulsed laser deposition (IPLD) as a new method for electrochemical analysis of mixed ionic and electronic conducting (MIEC) thin films during growth. First, this approach can truly reveal the properties of as-prepared MIEC electrode materials, since it avoids any alterations of their surface between preparation and investigation. Second, the measurements during growth give information on the thickness dependence of film properties. This technique is applied to La0.6Sr0.4CoO3-δ (LSC), one of the most promising SOFC/SOEC oxygen electrode material. From the earliest stages of LSC film deposition on yttria-stabilized zirconia (YSZ) to a fully grown thin film of 100 nm thickness, data are gained on the oxygen exchange kinetics and the defect chemistry of LSC. A remarkable reproducibility is found in repeated film growth experiments, not only for the bulk related chemical capacitance but also for the surface related polarization resistance (±10%). Polarization resistances of as-prepared LSC films are extraordinarily low (2.0 Ω cm2 in 40 μbar O2 at 600 °C). LSC films on YSZ and on La0.95Sr0.05Ga0.95Mg0.05O3-δ (LSGM) single crystals exhibit significantly different electrochemical properties, possibly associated with the tensile strain of LSC on LSGM.

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Structural Evolution of Ultrathin SrFeO_3-δ Films during Oxygen Evolution Reaction Revealed by In Situ Electrochemical Stress Measurements.

Publications

Structural Evolution of Ultrathin SrFeO<sub>3-δ</sub> Films during Oxygen Evolution Reaction Revealed by <i>In Situ</i> Electrochemical Stress Measurements.

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