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Growth Kinetics of Individual Co Particles Ex-solved on SrTi₀.₇₅Co₀.₂₅O₃₋δ Polycrystalline Perovskite Thin Films

Jo, Yong-Ryun, Koo, Bonjae, Seo, Min-Ji, Kim, Jun Kyu, Lee, Siwon, Kim, Kyeounghak, Han, Jeong Woo, Jung, WooChul, Kim, Bong-Joong
Journal of the American Chemical Society 2019 v.141 no.16 pp. 6690-6697
activation energy, catalytic activity, cobalt, density functional theory, enthalpy, growth models, kinetics, nanoparticles, quantitative analysis, renewable energy sources, temperature, transmission electron microscopy
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 oxidation—the Co-oxide interface, agreeing well with density functional theory calculations.