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The oxidative coupling of methane (OCM) is an attractive technology for the production of ethane (C2H6) and ethylene (C2H4); and significant performance and efficiency gains as well as reduced carb...

The ex-solution process, in which metal nanoparticles are grown on a host oxide, can be used to synthesize nanocatalysts with excellent thermal and chemical durability via spontaneous heterogeneous nucleation. However, this technique lacks a means to control the particle size and density because the amounts of ex-solved metal elements vary with the reduction conditions. Here, we devise a strategy to achieve small particle sizes and high particle densities concurrently by controlling the temperature (

Surface Sr segregation and phase separation are the key reasons behind the chemical instability of Sr-containing perovskite oxide surfaces and the corresponding performance degradation of solid oxide fuel cell O2-electrodes, but to date, practical solutions to prevent this phenomenon are limited. Here, we investigate how isovalent doping (in this case, Zr substitution of Ti) changes the surface morphology, chemical composition, and thus the O2 activation kinetics under actual operating conditions. Thin films of SrTi0.5Fe0.5O3−δ as a representative model perovskite O2-electrode, with Zr doping, are fabricated via pulsed laser deposition and their surface oxygen exchange rates are then characterized via electrical conductivity relaxation assessments. Zr dopants strengthen the Sr–O bonds in the oxide lattice, inhibiting the formation of surface SrOx clusters and significantly reducing the deterioration of the oxygen exchange rates compared to the results from undoped film at 650 °C for 30 h. These observations suggest a new strategy for ensuring the surface stability of Sr-containing perovskite oxides for fuel cell O2-electrodes.

We demonstrate theoretically and experimentally that engineering of cation–oxygen bond strength in a perovskite structure can control redox ex-solution of B-site metals and thus the formation of metal nanoparticles at the oxide surface upon high-temperature reduction. In particular, we show that large isovalent doping significantly promotes the B-site ex-solution via tuning of the cation–oxygen bond strength, leading to high catalytic activity of CO oxidation. This method to promote ex-solution can be readily applied to various heterogeneous catalysts.

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...

Summary 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 O2 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 O2 electrodes.

Aqueous-based colloidal synthesis using alkyltrimethylammonium bromide (CnTABr), a cationic surfactant, has attracted much attention recently as a simple and facile method to fabricate size- and shape-tunable metal nanoparticles. Despite the many related studies, however, the underlying synthesis mechanism and the exact role of the cationic surfactant have not yet been clarified. Here, we report how the size of Pt nanoparticles varies by using a wide range of chain lengths (n = 10, 12, 14, 16, and 18) and concentrations (0.005 to 0.18 M) of CnTABr in aqueous-based colloidal synthesis. Highly monodisperse Pt particles with a size between 8 and 26 nm were obtained and confirmed by TEM analysis. Significantly, unlike other surfactants, when CnTABr with a small chain length was used, the particle size increased with the concentration, which is different from the typical particle growth behavior by other surfactants. The UV-vis spectroscopy analysis results show that the chemical affinity between real precursors and micelles generated in solution is an important factor in determining the size of the Pt nanoparticles. Based on this insight, we successfully demonstrated that the particle size is also controllable by modifying the critical micelle concentration with a KBr additive. Our results provide useful guidelines for nanoparticle synthesis using cationic surfactants.

Surface cation segregation and phase separation, of strontium in particular, have been suggested to be the key reason behind the chemical instability of perovskite oxide surfaces and the corresponding performance degradation of solid oxide electrochemical cell electrodes. However, there is no well-established solution for effectively suppressing Sr-related surface instabilities. Here, we control the degree of Sr-excess at the surface of SrTi0.5Fe0.5O3−δ thin films, a model mixed conducting perovskite O2-electrode, through lattice strain, which significantly improves the electrode surface reactivity. Combined theoretical and experimental analyses reveal that Sr cations are intrinsically under a compressive state in the SrTi0.5Fe0.5O3−δ lattice and that the Sr–O bonds are weakened by the local pressure around the Sr cation, which is the key origin of surface Sr enrichment. Based on these findings, we successfully demonstrate that when a large-sized isovalent dopant is added, Sr-excess can be remarkably alleviated, improving the chemical stability of the resulting perovskite O2-electrodes.

(La,Sr)MnO3−δ has received a great deal of attention as an oxygen carrier that can replace the state-of-the-art carrier CeO2 for solar-driven thermochemical fuel production. Despite the many relevant studies, however, the redox reaction kinetics of this material, which determines the fuel production rate, has rarely been reported. Here, we investigate the surface reaction rate of reduced Sr-doped lanthanum manganite thin films, as a model for a gas/solid interface of a perovskite-structured oxygen carrier under a condition, in which carbon monoxide is produced from CO2 in a two-step thermochemical cycling process. Thin films of La1−xSrxMnO3−δ (x = 0.1, 0.2, 0.3, 0.4) with dense and flat surfaces are fabricated via pulsed laser deposition, and their surface oxygen exchange rates are then characterized via electrical conductivity relaxation under actual operating conditions (T = 650 to 800 °C and pO2 = 2.9 × 10−19 to 9.0 × 10−13 atm). As the Sr content increases, the oxygen exchange greatly decelerates. On the other hand, for a given Sr content, the oxygen exchange does not vary much over a wide range of pO2 near the target temperature of 800 °C. We also observe the surface oxygen exchange rate has a direct impact on the CO production rate. These observations can guide the selection of an ideal oxygen carrier composition for high-performance fuel production.

Thin-film based, low temperature solid oxide fuel cells (LT-SOFCs) have gained much attention due to their capability to reduce the operating temperature (