Supported metal nanoparticles hold great promise for many fields, including catalysis and renewable energy. Here we report a novel methodology for the in situ growth of architecturally tailored, regenerative metal nanocatalysts that is applicable to a wide range of materials. The main idea underlying this strategy is to selectively diffuse catalytically active metals along the grain boundaries of host oxides and then to reduce the diffused metallic species to form nanoclusters. As a case study, we choose ceria and zirconia, the most recognized oxide supports, and spontaneously form various metal particles on their surface with controlled size and distribution. Metal atoms move back and forth between the interior (as cations) and the exterior (as clusters) of the host oxide lattice as the reductive and oxidative atmospheres repeat, even at temperatures below 700 °C. Furthermore, they exhibit excellent sintering/coking resistance and reactivity toward chemical/electrochemical reactions, demonstrating potential to be used in various applications.
Cerium oxide (ceria) is widely used in relation to solid electrolytes in multiple high‐temperature devices, allowing metal components in contact to penetrate into the ceria, especially along the grain boundaries. However, few researchers have concentrated on the migration of metal cations at the operating temperatures (e.g., 600–750 °C) of these devices. Here, the diffusion and solubility of transition metals are investigated through acceptor‐doped ceria grain boundaries as a function of the temperature, pO2, dopant type, and doping concentration. The use of thin‐film samples with high grain boundary density levels and time‐of‐flight secondary ion mass spectrometry with ppb‐level chemical resolution enables an accurate analysis of the concentration profiles of metal species present inside the grain boundaries at such low temperatures. Ni, Fe, and Pt migrate unexpectedly rapidly, and the amounts and types of rare‐earth dopants have a considerable effect on the diffusion of the transition metal. Furthermore, transition metals (Mn, Fe, Co, Ni, and, Cu) are present at the grain boundaries at substantial solubility levels of ≈1022 cm−3, i.e., 1–2 orders of magnitude greater than in the bulk lattice. The observed dynamic behaviors of transition metals present a new perspective on the performance and durability of ceria‐containing applications.
Stabilized BiO has gained a considerable amount of attention as a solid electrolyte material for low-temperature solid oxide fuel cells due to its superior oxygen-ion conductivity at the temperature of relevance (≤500 °C). Despite many research efforts to measure the transport properties of stabilized BiO, the effects of grain boundaries on the electrical conductivity have rarely been reported and their results are even controversial. Here, we attempt quantitatively to assess the grain boundary contribution out of the total ionic conductivity at elevated temperatures (350-500 °C) by fabricating epitaxial and nano-polycrystalline thin films of yttrium-stabilized BiO. Surprisingly, both epitaxial and polycrystalline films show nearly identical levels of ionic conductivity, as measured by alternating current impedance spectroscopy and this is the case despite the fact that the polyfilm possesses nanosized columnar grains and thus an extremely high density of the grain boundaries. The highly conductive nature of grain boundaries in stabilized BiO is discussed in terms of the clean and chemically uniform grain boundary without segregates, and the implications for device application are suggested.
For the first time, the surface reaction kinetics of La1−xSrxMnO3−δ with different compositions was characterized for solar thermochemical fuel production.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.