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In the perovskite oxide BaFeO3, inducing a tensile in-plane strain or introducing a larger radius cation suppresses the surface Ba enrichment. In turn, a reduced surface Ba concentration improves the surface electrocatalytic activity.

The conversion of methane to a value-added chemical is important for methane utilization and industrial demand for primary chemicals. Oxidative coupling of methane (OCM) to C2 hydrocarbons is one of the most attractive ways to use natural gas. However, it is difficult to obtain higher C2 yield in classic OCM reaction due to a favorable COx formation. Regarding this, various catalysts for OCM have been studied to fulfill desirable C2 yields. In this review, we briefly overview the single metal oxide types of OCM catalysts (alkaline-earth metal oxides and rare-earth metal oxides) and highlight the characteristics of catalysts in OCM reaction such as methane activation, surface basicity and lattice oxygen.

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.

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 SrTi

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

Thin-film solid oxide fuel cells (TF-SOFCs) using a dense and thin electrolyte have attracted much attention as a promising portable power generator because they can lower the operating temperature of devices, which is a key issue related to conventional SOFCs, to below 500 °C and are compatible with several microfabrication processes. Highly porous interconnected Pt thin films are now widely used as oxygen electrodes, but their poor thermal stability seriously hampers the sustainable operation of TF-SOFCs. Here, we demonstrate how Al2O3 layers coated through atomic layer deposition effectively suppress the degradation of nanoporous Pt thin-film electrodes. Although Al2O3 is an electrical insulator, the selection of an appropriate overcoat thickness ensures stable electrochemical reaction sites of the Pt electrode at high temperatures even without serious current collection or gas flow issues. As a result, a 3.6-nm-thick Al2O3 layer maintains the high specific surface area morphology of Pt thin films at 450 °C and improves the electrode activity by more than twofold compared to an uncoated sample. These results suggest that a simple and scalable coating strategy enables the implementation of TF-SOFCs with ideal performance and durability outcomes.

The organophosphorus compounds tris(trimethylsilyl) phosphite (TMSP) and vinylene carbonate (VC) have been considered for use as functional additives to improve the electrochemical performance of Li 1.1 Mn 1.86 Mg 0.04 O 4 (LMO)/graphite full cells. Our investigation reveals that the combination of VC and TMSP as additives enhances the cycling properties and storage performance of full cells at 60 °C. The unique functions of the TMSP additive in the VC electrolyte are investigated via ex situ X-ray photoelectron spectroscopy (XPS) and 19 F nuclear magnetic resonance (NMR) measurements. The TMSP additive effectively eliminates trace water and hydrogen fluoride (HF) and produces a protective film on the LMO cathode that alleviates manganese dissolution at 60 °C.

We present a promising electrolyte candidate, Mg(TFSI)2 dissolved in glyme/diglyme, for future design of advanced magnesium (Mg) batteries. This electrolyte shows high anodic stability on an aluminum current collector and allows Mg stripping at the Mg electrode and Mg deposition on the stainless steel or the copper electrode. It is clearly shown that nondendritic and agglomerated Mg secondary particles composed of ca. 50 nm primary particles alleviating safety concern are formed in glyme/diglyme with 0.3 M Mg(TFSI)2 at a high rate of 1C. Moreover, a Mg(TFSI)2-based electrolyte presents the compatibility toward a Chevrel phase Mo6S8, a radical polymer charged up to a high voltage of 3.4 V versus Mg/Mg(2+) and a carbon-sulfur composite as cathodes.

Tris(pentafluorophenyl) borane (TPFPB) is evaluated as an additive for improving electrochemical performance of lithium peroxide (Li 2 O 2 )-based electrodes. It is found that TPFPB significantly reduced the charge potential of Li 2 O 2 -based electrodes during the first charge process and improved reversible capacity during cycling without adding air (or O 2 ) to the cell. To confirm the effect of TPFPB on electrolyte decomposition, the surface chemistry of Li 2 O 2 -based electrodes cycled in electrolytes with and without TPFPB was investigated.

A novel dimeric ionic liquid based on imidazolium cation and bis(trifluoromethanesulfonyl) imide (TFSI) anion has been synthesized through a metathesis reaction. Its chemical shift values and thermal properties are identified via 1 H nuclear magnetic resonance (NMR) imaging and differential scanning calorimetry (DSC). The effect of the synthesized dimeric ionic liquid on the interfacial resistance of gel polymer electrolytes is described. Differences in the SEM images of lithium electrodes after lithium deposition with and without the 1,1′-pentyl-bis(2,3-dimethylimidazolium) bis(trifluoromethane-sulfonyl)imide (PDMITFSI) ionic liquid in gel polymer electrolytes are clearly discernible. This occurs because the PDMITFSI ionic liquid with hydrophobic moieties and polar groups modulates lithium deposit pathways onto the lithium metal anode. Moreover, high anodic stability for a gel polymer electrolyte with the PDMITFSI ionic liquid was clearly observed.