Among the phenomena related to the surface rearrangement of cations in perovskite-based oxides, A-site cation enrichment, Sr in particular, near the surface has been frequently observed. Upon annealing in an oxidizing atmosphere, Sr is often enriched on the surface as compared with the bulk composition of the material, which eventually forms Sr-rich phases or rearranges the crystal structure of the surface. This Sr segregation changes the structure and composition of the perovskite surfaces and thus affects the stability of the materials and the reactivity with gas phases. In this regard, many studies have been carried out in the field of solid oxide electrochemical cells (SOCs). In this review, we summarize the latest research efforts on Sr segregation in perovskite-based SOC O 2 electrodes, with a focus on how excess Sr is present. We then discuss the origins of Sr segregation and suggest strategies for suppressing it to realize high-performance perovskite-based O 2 electrodes.
A precise
control of the size, density, and distribution of metal
nanoparticles dispersed on functional oxide supports is critical for
promoting catalytic activity and stability in renewable energy and
catalysis devices. Here, we measure the growth kinetics of individual
Co particles ex-solved on SrTi0.75Co0.25O3‑δ polycrystalline thin films under a high vacuum,
and at various temperatures and grain sizes using in situ transmission
electron microscopy. The ex-solution preferentially occurs at grain
boundaries and corners which appear essential for controlling particle
density and distribution, and enabling low temperature ex-solution.
The particle reaches a saturated size after a few minutes, and the
size depends on temperature. Quantitative measurements with a kinetic
model determine the rate limiting step, vacancy formation enthalpy,
ex-solution enthalpy, and activation energy for particle growth. The
ex-solved particles are tightly socketed, preventing interactions
among them over 800 °C. Furthermore, we obtain the first direct
clarification of the active reaction site for CO oxidationthe
Co-oxide interface, agreeing well with density functional theory calculations.
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Single-phase materials with mixed ionic and electronic conductivity underpin multiple solid-state electrochemical devices as promising electrodes. In particular, triple-conducting oxides that carry protons, oxygen ions, and electron holes simultaneously have...
Tuning of the cation–oxygen bond strength effectively promotes B-site ex-solution in a perovskite, thereby boosting the catalytic activity of CO oxidation.
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