Fast Surface Oxygen Release Kinetics Accelerate Nanoparticle Exsolution in Perovskite Oxides

Abstract

Exsolution is a recent advancement for fabricating oxide-supported metal nanoparticle catalysts via phase precipitation out of a host oxide. A fundamental understanding and control of the exsolution kinetics are needed to engineer exsolved nanoparticles to obtain higher catalytic activity toward clean energy and fuel conversion. Since oxygen release via oxygen vacancy formation in the host oxide is behind oxide reduction and metal exsolution, we hypothesize that the kinetics of metal exsolution should depend on the kinetics of oxygen release, in addition to the kinetics of metal cation diffusion. Here, we probe the surface exsolution kinetics both experimentally and theoretically using thin-film perovskite SrTi0.65Fe0.35O3 (STF) as a model system. We quantitatively demonstrated that in this system the surface oxygen release governs the metal nanoparticle exsolution kinetics. As a result, by increasing the oxygen release rate in STF, either by reducing the sample thickness or by increasing the surface reactivity, one can effectively accelerate the Fe0 exsolution kinetics. Fast oxygen release kinetics in STF not only shortened the prereduction time prior to the exsolution onset, but also increased the total quantity of exsolved Fe0 over time, which agrees well with the predictions from our analytical kinetic modeling. The consistency between the results obtained from in situ experiments and analytical modeling provides a predictive capability for tailoring exsolution, and highlights the importance of engineering host oxide surface oxygen release kinetics in designing exsolved nanocatalysts.

Ion irradiation to control size, composition and dispersion of metal nanoparticle exsolution

“…38,39 Previous studies have shown that STF can exsolve metallic Fe nanoparticles upon reduction of this material. 40,41 In accordance with our hypotheses, we found that Ni irradiation can downsize the surface exsolved nanoparticles on STF to 2 nm in radius and change their compositions from unitary Fe to bimetallic Fe–Ni alloy. In addition to the surface, irradiation-induced defects also promoted bulk exsolution 14,15 in STF.…”

Advances and challenges in symmetrical solid oxide electrolysis cells: materials development and resource utilization

“…6b shows the precipitation diagram inside the particles. 73,74 The precipitation of nanoparticles can occur through direct and indirect methods (Fig. 6c), 75 and the gradual precipitation process is closely linked to the oxygen partial pressure, which affects the rate of surface oxygen release reaction and oxygen anion diffusion in the bulk.…”

“…6d confirms that more oxygen release leads to more metal nanoparticles precipitation, resulting in more oxygen vacancies and creating more reaction space. 74 The nanoparticles precipitated from in situ metal can be single metal or alloy. Common transition metals used for precipitation include non-noble metals such as Fe, Co, and Ni, and noble metals such as Pd, Rh, and Ru.…”

“…6d confirms that more oxygen release leads to more metal nanoparticles precipitation, resulting in more oxygen vacancies and creating more reaction space. 74…”

Fluorine-Stabilized BO6 Octahedron of Host Perovskites for Robust Carbon Dioxide Electrolysis on Exsolved Catalysts

“…The significant enhancement in the catalytic activity of perovskites through an in situ exsolution technique has stimulated extensive studies to promote the exsolution of nanoparticles. − Although the increased surface nanoparticles and oxygen vacancies significantly extend the triple phase boundaries, − it should also be pointed out that the facilitated process is at the cost of consuming the host perovskite, which accelerates A-site surface segregation, formation of B-site vacancies, and even phase reconstruction of the host perovskite in the extreme case of promoting exsolution. − …”