Search

This study investigates the effect of the exsolution behavior of alumina-rich spinel on the formation and distribution of CA6 (CaAl12O19) in corundum castables bonded with calcium aluminate cement. In this study, alumina-rich spinel is substituted for tabular corundum in the same proportions and grain size. The matrices after curing were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The phase composition and microstructure of the matrices containing alumina-rich spinel were analyzed after firing at 1600 °C. These results showed that the addition of alumina-rich spinel significantly improved the mechanical strength of the castables. This improvement was attributed to the alumina produced by spinel exsolution during firing at 1600 °C, which reacted in situ with CA2 (CaAl4O7) to form CA6. CA6 connects the different particles and forms an interspersed interlocking structure within the spinel. The CA6-MA interspersed interlocking structure replaces part of the CA6-Al2O3 structure and significantly improves the mechanical strength of the castables. [ABSTRACT FROM AUTHOR]

Quartzites of the Delhi Supergroup, exposed along the Firozpur-Jhirka ridge in Faridabad, Gurgaon areas of Delhi-National Capital Area, host detrital garnet grains. The garnet grains are studied for understanding provenance and diagenetic history. Samples were collected from the Badkhal lake area, Faridabad. X-ray diffraction study identifies quartz, garnet, magnetite and goethite as major mineral phases. Whereas quartzites show recrystallization texture, garnet grains record intense fractures and magnetites form large acicular grains. From electron probe microanalysis garnet grains are identified as almandine with high spessartine content and a pegmatite source is suggested. From preserved in-situ exsolution of magnetite from garnet it is inferred that a temperature exceeding 550°C (>17 km burial depth) in the course of burial history and magnetites exsolved below 550°C from garnet during the uplift of quartzite. [ABSTRACT FROM AUTHOR]

According to the magnesia-alumina phase diagram, the alumina-rich spinel may undergo exsolution of corundum during firing when incorporated into the castable. This research aimed to explore the phenomenon of alumina-rich spinel exsolution and its subsequent impact on the distribution of CaO·6Al 2 O 3 inside the spinel and the strength of the castables when subjected to a firing temperature of 1600 °C. The results indicated that the amount of exsolved corundum escalated as the alumina content within the spinel rose after heat treatment, and this exsolved corundum was predominantly found within the original spinel particle. The CaO·2Al 2 O 3 , which formed when calcium aluminate cement was heated above 1200 °C, reacted preferentially with the exsolved corundum rather than with pre-added α-Al 2 O 3 leading to the formation of CaO·6Al 2 O 3 inside the spinel after firing at temperatures exceeding 1400 °C. This reaction formed an interpenetrated "spinel-CaO·6Al 2 O 3 " structure during firing, which enhanced the strength of the castables. [ABSTRACT FROM AUTHOR]

The aim of this work was to verify the possibility of forming Ni-Fe and Co-Fe alloys via topotactic ion exchange exsolution in Fe-infiltrated (La,Sr,Ce)0.9(Ni,Ti)O3-δ or (La,Sr,Ce)0.9(Co,Ti)O3-δ ceramics. For this purpose, samples were synthesized using the Pechini method and then infiltrated with an iron nitrate solution. The reduction process in dry H2 forced the topotactic ion exchange exsolution, leading to the formation of additional round-shape structures on the surfaces of grains. EDS scans and XRD analysis confirmed the formation of bimetallic alloys, which suggests that these materials have great potential for further use as anode materials for Solid Oxide Fuel Cells (SOFCs).

Exsolution of metal nanoparticles (NPs) on perovskite oxides has been demonstrated as a reliable strategy for producing catalyst‐support systems. Conventional exsolution requires high temperatures for long periods of time, limiting the selection of support materials. Plasma direct exsolution is reported at room temperature and atmospheric pressure of Ni NPs from a model A‐site deficient perovskite oxide (La0.43Ca0.37Ni0.06Ti0.94O2.955). Plasma exsolution is carried out within minutes (up to 15 min) using a dielectric barrier discharge configuration both with He‐only gas as well as with He/H2 gas mixtures, yielding small NPs (<30 nm diameter). To prove the practical utility of exsolved NPs, various experiments aimed at assessing their catalytic performance for methanation from synthesis gas, CO, and CH4 oxidation are carried out. Low‐temperature and atmospheric pressure plasma exsolution are successfully demonstrated and suggest that this approach could contribute to the practical deployment of exsolution‐based stable catalyst systems. [ABSTRACT FROM AUTHOR]

The aim of this work was to verify the possibility of forming Ni-Fe and Co-Fe alloys via topotactic ion exchange exsolution in Fe-infiltrated (La,Sr,Ce)0.9(Ni,Ti)O3-δ or (La,Sr,Ce)0.9(Co,Ti)O3-δ ceramics. For this purpose, samples were synthesized using the Pechini method and then infiltrated with an iron nitrate solution. The reduction process in dry H2 forced the topotactic ion exchange exsolution, leading to the formation of additional round-shape structures on the surfaces of grains. EDS scans and XRD analysis confirmed the formation of bimetallic alloys, which suggests that these materials have great potential for further use as anode materials for Solid Oxide Fuel Cells (SOFCs). [ABSTRACT FROM AUTHOR]

In this review, we have assessed the possibility of metal–perovskite interfacial engineering to enhance the catalytic activity and selectivity in a range of heterogeneous catalytic reactions. We embarked on a literature screening of different perovskite material classes and reactions to show the versatility of the perovskite structures to induce the formation of such hetero-interfaces and the widespread nature of the phenomenon in catalytic research. There is almost no limitation on the chemical composition of the used perovskites and the nature of the catalyzed reaction, be it under reduction or oxidation conditions. We attempted to classify the perovskite materials, discuss the different strategies leading to the hetero-interfaces, and detail the synergistic action of the components of the respective interfaces. We also provide a critical assessment of the large body of data that is available in terms of a knowledge-based approach to the comparison of differently prepared interfaces with varying interfacial extent to gain a deeper understanding of the bi-functional operation of the interfaces and the urgent necessity to study and characterize such interfaces under realistic operation conditions.

Metal exsolution engineering has been regarded as a promising strategy for activating intrinsically inert perovskite oxide catalysts toward efficient oxygen evolution reaction. Traditional metal exsolution processes on perovskites are often achieved by using the reducing hydrogen gas; however, this is not effective for the relatively stable phase, such as Ruddlesden–Popper perovskite oxides. To address this issue, triphenylphosphine is proposed to be a reduction promotor for accelerating the reduction and migration of the target metal atoms, aiming to achieve the effective exsolution of metallic species from Ruddlesden–Popper‐type parent perovskites. Upon oxygen evolution reaction, these exsolved metallic aggregates are reconstructed into oxyhydroxides as the real active centers. After further modification by low‐percentage iridium oxide nanoclusters, the optimal catalyst delivered an overpotential as low as 305 mV for generating the density of 10 mA cm−2, outperforming these reported noble metal‐containing perovskite‐based alkaline oxygen evolution reaction electrocatalysts. This work provides a potential approach to activate catalytically inert oxides through promoting surface metal exsolution and explores a novel class of Ruddlesden–Popper‐type oxides for electrocatalytic applications. [ABSTRACT FROM AUTHOR]

In this review, we have assessed the possibility of metal–perovskite interfacial engineering to enhance the catalytic activity and selectivity in a range of heterogeneous catalytic reactions. We embarked on a literature screening of different perovskite material classes and reactions to show the versatility of the perovskite structures to induce the formation of such hetero-interfaces and the widespread nature of the phenomenon in catalytic research. There is almost no limitation on the chemical composition of the used perovskites and the nature of the catalyzed reaction, be it under reduction or oxidation conditions. We attempted to classify the perovskite materials, discuss the different strategies leading to the hetero-interfaces, and detail the synergistic action of the components of the respective interfaces. We also provide a critical assessment of the large body of data that is available in terms of a knowledge-based approach to the comparison of differently prepared interfaces with varying interfacial extent to gain a deeper understanding of the bi-functional operation of the interfaces and the urgent necessity to study and characterize such interfaces under realistic operation conditions. [ABSTRACT FROM AUTHOR]

In this work, we performed a preliminary investigation on the redox behaviour of Sr2FeMo0.6Ni0.4O6-δ (SFMN) double perovskite in H2-H2O and CH4-H2O redox cycles in order to explore the potential use of this oxide as an Oxygen Carrier (OC) in fuel-assisted Chemical Looping Water Splitting (CLWS) processes driven by concentrated solar energy. The results were compared with our previous findings on the Reverse Water Gas Shift Chemical Looping (RWGS-CL) reaction. The improvement in performance due to the bimetallic exsolution on the OC surface is observed. This OC exhibits interesting activity and stability over CH4-assisted CLWS cycling. Future investigations are planned to examine the structural transformations that might impact the redox behaviour of this material in water splitting processes.

Abstract Single silicate crystals hosting tiny magnetic inclusions are remarkable targets to study the paleointensities of the Earth and extraterrestrial samples. Since the pioneering work done in late 1990s, paleointensity studies using various silicate minerals such as feldspar, quartz, zircon, pyroxene, and olivine with magnetic inclusions trapped during grain growth or exsolved from the host phase have been reported. It has been shown that some single crystals have the ability to record paleomagnetic information as reliable or more reliable than the whole rock, by direct comparison of the obtained paleointensity estimate from single crystal and the whole-rock sample or the magnetic observatory data. Various rock-magnetic studies also support the fidelity of these crystals. Here, we provide a brief review of the rock-magnetic characteristics of the single crystals, the mineralogical background of the hosting silicates, and experimental procedures developed to obtain reliable data from magnetically weak samples with distinctive rock-magnetic features. We also overview the studies on paleointensity and related topics on various terrestrial and extraterrestrial samples published mainly after the comprehensive reviews in late 2000s. The present review covers the advantages as well as the limitations and caveats of paleointensity studies using single crystal samples and will help readers who wish to utilize this technique in their research. Graphical Abstract

Nanoparticle exsolution is a powerful technique for functionalizing redox oxides in energy applications, particularly at high temperatures. It shows promise for solid oxide fuel cells and electrolyzers. However, exsolution of other chemistries like metal oxides is not well studied, and the mechanism is poorly understood. This work explores oxide exsolution in PrBa _1− _x Co _2 O _6− _δ ( x = 0, 0.05, 0.1, 0.15) double perovskites, practiced electrodes in proton ceramic fuel cells and electrolyzers. Oxide exsolution in PrBa _1− _x Co _2 O _6− _δ aimed at boosting the electrocatalytic activity and was evaluated by varying intrinsic materials-related properties, viz. A-site deficiency and external parameters (temperature, under fixed time, and p O _2 = 10 ^−5 atm conditions). The materials were analyzed with conventional characterization tools and synchrotron-based small-angle x-ray scattering. Unlike metal-nanoparticle exsolution, increasing the A-site deficiency did not enhance the extent of oxide-nanoparticle exsolution, whereas larger nanoparticles were obtained by increasing the exsolution temperature. Combined Raman spectroscopy and electron microscopy analysis revealed that BaCoO _3 , Co _3 O _4 , and amorphous BaCO _3 nanoparticles were formed on the surface of the double perovskites after the reductive treatments. The present results demonstrate the complexity of oxide-nanoparticle exsolution in comparison with metal-nanoparticle exsolution. Further materials screening and mechanistic studies are needed to enhance our understanding of this method for functionalizing proton ceramic electrochemical cells (PCEC) electrodes.

Single silicate crystals hosting tiny magnetic inclusions are remarkable targets to study the paleointensities of the Earth and extraterrestrial samples. Since the pioneering work done in late 1990s, paleointensity studies using various silicate minerals such as feldspar, quartz, zircon, pyroxene, and olivine with magnetic inclusions trapped during grain growth or exsolved from the host phase have been reported. It has been shown that some single crystals have the ability to record paleomagnetic information as reliable or more reliable than the whole rock, by direct comparison of the obtained paleointensity estimate from single crystal and the whole-rock sample or the magnetic observatory data. Various rock-magnetic studies also support the fidelity of these crystals. Here, we provide a brief review of the rock-magnetic characteristics of the single crystals, the mineralogical background of the hosting silicates, and experimental procedures developed to obtain reliable data from magnetically weak samples with distinctive rock-magnetic features. We also overview the studies on paleointensity and related topics on various terrestrial and extraterrestrial samples published mainly after the comprehensive reviews in late 2000s. The present review covers the advantages as well as the limitations and caveats of paleointensity studies using single crystal samples and will help readers who wish to utilize this technique in their research. [ABSTRACT FROM AUTHOR]

The reverse water-gas shift reaction (rWGS) is of particular interest as it is the first step to producing high-added-value products from carbon dioxide (CO2) and renewable hydrogen (H2), such as synthetic fuels or other chemical building blocks (e.g. methanol) through a modified Fischer-Tropsch process. However, side reactions and material deactivation issues, depending on the conditions used, still make it challenging. Efforts have been put into developing and improving scalable catalysts that can deliver high selectivity while at the same time being able to avoid deactivation through high temperature sintering and/or carbon deposition. Here we design a set of perovskite ferrites specifically tailored to the hydrogenation of CO2 via the reverse water-gas shift reaction. We tailor the oxygen vacancies, proven to play a major role in the process, by partially substituting the primary A-site element (Barium, Ba) with Praseodymium (Pr) and Samarium (Sm), and also dope the B-site with a small amount of Nickel (Ni). We also take advantage of the exsolution process and manage to produce highly selective Fe-Ni alloys that suppress the formation of any by-products, leading to up to 100% CO selectivity.

Perovskite-type oxides (ABO3) are a highly versatile class of materials. They are compositionally flexible, as their constituents can be chosen from a wide range of elements across the periodic table with a vast number of possible combinations. This flexibility enables the tuning of the materials’ properties by doping the A- and/or B-sites of the base structure, facilitating the application-oriented design of materials. The ability to undergo exsolution under reductive conditions makes perovskite-type oxides particularly well-suited for catalytic applications. Exsolution is a process during which B-site elements migrate to the surface of the material where they form anchored and finely dispersed nanoparticles that are crucially important for obtaining a good catalytic performance, while the perovskite base provides a stable support. Recently, exsolution catalysts have been investigated as possible materials for CO2 utilization reactions like reverse water–gas shift reactions or methane dry reforming.

High catalytic performances of metal-semiconductor heterostructures have gained significant attention in recent years. However, developing fast and low-cost synthesis of multiphase heterojunction catalysts has long been a challenge. Herein, three phases of Cu-CeO2-SrTiO3-δ heterojunction catalyst are successfully synthesized by combining with sol-gel and rapid plasma exsolution method. Using dielectric barrier discharge plasma (DBD), Cu nanoparticles are exsolved and uniformly distributed on the surface of CeO2-SrTiO3-δ. This unique multiphase heterojunction catalyst exhibits superior performance in photothermal reverse water gas shift (RWGS) reactions. The yield of CO from this catalyst is impressive at 11.32 mmol g−1 h−1, 9 times greater than pure SrTiO3, and the selectivity for CO is high (99.95%). The enhanced activity is primarily attributed to the synergistic effect resulting from the incorporation of three phases of Cu nanoparticles, CeO2, and SrTiO3-δ, as well as their interfaces. The increase in oxygen vacancy sites in CeO2 enhances the adsorption of CO2, whereas the doping and exsolution of Cu help to broaden the light absorption range. A significant role is played by the localized surface plasmon resonance (LSPR) effect of Cu nanoparticles in promoting the catalytic performance of RWGS. This study demonstrates a simple and efficient method for fabricating multiphase heterojunction catalysts, providing new strategies for photothermal CO2 reduction.

The helium (He) contents of the Weiyuan and Anyue gas fields in the Sichuan Basin (China) differ significantly despite their similar helium‐nitrogen (N2) coupling characteristics, that is, the positive correlation between the N2 and He contents, and the negative correlation between the nitrogen/helium (N2/He) ratio and depth. To determine the factors influencing the differential enrichment of He resources and He–N2 coupling in the Weiyuan and Anyue gas fields, this study analysed the compositions of natural gases within the study area and established a computational model for evaluating the dissolution and exsolution amount of He and N2 in the pore water. The results indicated that: the uplift of the basement granite was crucial for the exsolution and enrichment of dissolved helium, and it was also the main reason for He–N2 coupling. The differential uplift that occurred in the Leshan–Longnvsi palaeo‐uplift during the Himalayan period further promoted the differential enrichment of He resources, thus also impacting the N2/He ratio in the study area. The distinct quantities of N2 and He exsolution during the uplift directly affected the negative correlation between the N2/He ratio and the depth. Within the same depth range of the uplift, the average and variations of the N2/He ratio in the crust‐derived helium‐rich natural gas reservoir were inversely proportional to the in situ molar partial pressure of He. The uplift of the crystalline basement is an important mechanism that causes the enrichment of helium resources and the coupling of helium‐nitrogen in the crust‐derived helium‐rich natural gas reservoir, which is of great significance for understanding the variation of N2/He ratio and exploration of He resources. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Definition: Perovskite-type oxides (ABO3) are a highly versatile class of materials. They are compositionally flexible, as their constituents can be chosen from a wide range of elements across the periodic table with a vast number of possible combinations. This flexibility enables the tuning of the materials' properties by doping the A- and/or B-sites of the base structure, facilitating the application-oriented design of materials. The ability to undergo exsolution under reductive conditions makes perovskite-type oxides particularly well-suited for catalytic applications. Exsolution is a process during which B-site elements migrate to the surface of the material where they form anchored and finely dispersed nanoparticles that are crucially important for obtaining a good catalytic performance, while the perovskite base provides a stable support. Recently, exsolution catalysts have been investigated as possible materials for CO2 utilization reactions like reverse water–gas shift reactions or methane dry reforming. [ABSTRACT FROM AUTHOR]

Given that the attempts to head toward a hydrogen economy are gathering pace, the dry reforming of methane (DRM) to produce hydrogen-rich syngas is a reaction that is worthy of investigation. Nickel-based catalysts have been extensively examined as a cost-effective solution for DRM, though they suffer from fast deactivation caused by coke accumulation. However, a number of published studies report high catalytic performance in terms of both activity and stability for La–Ni-based perovskite-derived catalysts used in DRM in comparison to other corresponding materials. In the work presented herein, a thorough analysis regarding the application of La–Ni-based perovskite catalysts for DRM is carried out. LaNiO3 is known for its anti-coking ability owing to the strong interaction between CO2 and La2O3. A further modification to improve the catalytic performance can be achieved by the partial or complete substitution of A or/and B sites of the perovskite catalysts. The latest developments with respect to this topic are also discussed in this manuscript. Even though the low surface area of perovskite catalysts has always been an obstacle for their commercialization, new supported and porous perovskite materials have recently emerged to address, at least partly, the challenge. Finally, conclusions and future outlooks for developing novel perovskite catalysts that may potentially pioneer new technology are included. [ABSTRACT FROM AUTHOR]

Apatite is an important petrogenetic indicator in extraterrestrial materials. Here, we report the mineralogical features of apatite and associated phases in three brachinites Northwest Africa (NWA) 4969, NWA 10637, and NWA 11756. Two types of apatite are observed: intergranular apatite and apatite inclusion within chromite and silicate minerals. The intergranular chlorapatite is enclosed by or penetrated by irregular porous merrillite, indicating chlorapatite replacement by merrillite. The intergranular chlorapatite is closely associated with a fine-grained pyroxene-troilite intergrowth along olivine grain boundaries, which is a sulfidization product of olivine. High-Ca pyroxene is observed as a constituent phase in the intergrowth for the first time. The apatite inclusions are either monomineralic or closely associated with subhedral-euhedral pore-free merrillite. In NWA 4969, the apatite inclusions show a large compositional variation from chlorapatite to fluorapatite and are systematically more F-rich than intergranular apatite; while the apatite inclusions in NWA 10637 and NWA 11756 are chlorapatite. Most of the two apatite types in brachinites contain oriented tiny or acicular chromite grains, suggesting the exsolution of chromite from apatite. We propose that apatite replacement by merrillite, formation of pyroxene-troilite intergrowth, and exsolution of chromite in apatite were caused by a shock-induced, transient heating event (~930–1000 °C) on the brachinite parent body. This heating event resulted in halogen devolatilization during replacement of the intergranular apatite by merrillite, which probably disturbed the Mn-Cr isotopic system in brachinites as well. We also propose that the apatite inclusions could be a residual precursor material of the brachinites. [ABSTRACT FROM AUTHOR]

Elemental vacancies are proposed as an effective approach to tuning the electronic structure of catalysts that are critical for energy conversion. However, for reactions such as the sluggish oxygen evolution reaction, the excess of oxygen vacancies (VO) is inevitable and detrimental to catalysts' electrochemical stability and activities, e.g., in the most active RuO2. While significant work is carried out to hinder the formation of VO, the development of a fast and efficient strategy is limited. Herein, a protection SrO layer produced successfully at the surface of RuO2 with the in situ exsolution method with perovskite SrRuO3 as the precatalyst, which could significantly hinder the generation of VO. Benefited from the suppression of VO, the surface‐modified RuO2 requires a low overpotential of 290 mV at 100 mA cm−2, accompanied by remarkably high electrochemical stability (100 h) and Faraday efficiency (≈100%). Theoretical investigation reveals that the formation energy of VO in RuO2 is almost doubled in the exsolved RuO2 phase as a result of the weakened RuO bond covalency. This work not only provides insight into the structural evolution of perovskite oxide catalysts but also demonstrates the feasibility of controlling vacancy formation via in situ exsolution. [ABSTRACT FROM AUTHOR]

Solid solutions Nd2−xSrxNiO4±δ (x = 0, 0.5, 1, 1.2, 1.4) with a K2NiF4 structure can be obtained from freeze-dried precursors. The end members of this series can be obtained at T ≥ 1000 °C only, while complex oxides with x = 1; 1.5 are formed at T ≥ 700 °C. Thermal analysis revealed the two stages of Nd2−xSrxNiO4±δ thermal reduction in a 10%H2/Ar gas mixture that was completed at 900 °C. For x < 0.2, the reduction products demonstrated an exsolution-like morphology with Ni nanoparticles allocated at the surface of oxide grains. As-obtained nanocomposites with x = 0 and x > 1 revealed the outstanding catalytic activity and selectivity in the dry reforming of the methane (DRM) reaction at 800 °C with CH4 conversion close to the thermodynamic values. The appearance of two different maxima of the catalytic properties of Ni/(Nd2O3,SrCO3) nanocomposites could be affiliated with the domination of the positive contributions of Nd2O3 and SrCO3, respectively. [ABSTRACT FROM AUTHOR]

A Mn0.2Zr0.8O2−δ mixed oxide catalyst was synthesized via the co-precipitation method and studied in a CO oxidation reaction after different redox pretreatments. The surface and structural properties of the catalyst were studied before and after the pretreatment using XRD, XANES, XPS, and TEM techniques. Operando XRD was used to monitor the changes in the crystal structure under pretreatment and reaction conditions. The catalytic properties were found to depend on the activation procedure: reducing the CO atmosphere at 400–600 °C and the reaction mixture (O2 excess) or oxidative O2 atmosphere at 250–400 °C. A maximum catalytic effect characterized by decreasing T50 from 193 to 171 °C was observed after a reduction at 400 °C and further oxidation in the CO/O2 reaction mixture was observed at 250 °C. Operando XRD showed a reversible reduction-oxidation of Mn cations in the volume of Mn0.2Zr0.8O2−δ solid solution. XPS and TEM detected the segregation of manganese cations on the surface of the mixed oxide. TEM showed that Mn-rich regions have a structure of MnO2. The pretreatment caused the partial decomposition of the Mn0.2Zr0.8O2−δ solid solution and the formation of surface Mn-rich areas that are active in catalytic CO oxidation. In this work it was shown that the introduction of oxidation-reduction pretreatment cycles leads to an increase in catalytic activity due to changes in the origin of active states. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of CO2 into valuable fuels and chemicals has become a contemporary research area, where the heterogeneous catalyst plays a critical role. Metal nanoparticles supported on oxides performing as active sites of electrochemical reactions have been the focus of intensive investigation. Here, we review the CO2 reduction with active materials prepared by exsolution. The fundamental of exsolution was summarized in terms of mechanism and models, materials, and driven forces. The advances in the exsolved materials used in hightemperature CO2 electrolysis were catalogued into tailored interfaces, synergistic effects on alloy particles, phase transition, reversibility and electrochemical switching. [ABSTRACT FROM AUTHOR]

Solid oxide electrolysis cell (SOEC) is a promising technology for CO2 conversion and renewable energy storage with high efficiency. It is highly desirable to develop catalytically active cathodes for CO2 electrolysis. Herein, cathode materials with different structural stabilities are designed by Nb substitution on La0.5Sr0.5Fe0.8Co0.2O3-δ (LSFC82) to obtain La0.5Sr0.5Fe0.7Co0.2Nb0.1O3-δ (LSFCN721) and La0.5Sr0.5Fe0.8Co0.1Nb0.1O3-δ (LSFCN811), respectively. LSFC82-Sm0.2Ce0.8O2-δ (SDC) cathode with inferior structural stability (ability to maintain the structure) shows desirable CO2 electrolysis performance with the generated current density of 1.80 A cm−2 at 1.6 V and stable performance during 110 h operation at 1.2 V and 800 °C. However, LSFC82 particles are collapsed into pieces after stability test with the generation of Co nanoparticles simultaneously. The frameworks of LSFCN721 and LSFCN811 particles maintain well because of the high-valent niobium, but Co exsolution, oxygen vacancy content and the corresponding CO2 electrolysis performance are restricted. This work confirms that Co nanoparticles can be exsolved from LSFC82-SDC cathode during CO2 electrolysis, providing references for constructing metallic nanoparticles decorated-perovskite cathodes for SOECs.

Abstract Elemental vacancies are proposed as an effective approach to tuning the electronic structure of catalysts that are critical for energy conversion. However, for reactions such as the sluggish oxygen evolution reaction, the excess of oxygen vacancies (VO) is inevitable and detrimental to catalysts’ electrochemical stability and activities, e.g., in the most active RuO2. While significant work is carried out to hinder the formation of VO, the development of a fast and efficient strategy is limited. Herein, a protection SrO layer produced successfully at the surface of RuO2 with the in situ exsolution method with perovskite SrRuO3 as the precatalyst, which could significantly hinder the generation of VO. Benefited from the suppression of VO, the surface‐modified RuO2 requires a low overpotential of 290 mV at 100 mA cm−2, accompanied by remarkably high electrochemical stability (100 h) and Faraday efficiency (≈100%). Theoretical investigation reveals that the formation energy of VO in RuO2 is almost doubled in the exsolved RuO2 phase as a result of the weakened RuO bond covalency. This work not only provides insight into the structural evolution of perovskite oxide catalysts but also demonstrates the feasibility of controlling vacancy formation via in situ exsolution.

Abstract The benefits of perovskite oxides include their low cost, customizable composition, ordered atomic structure, and extremely flexible electronic structure. They are the ideal substitute for precious metal catalysts in various electrocatalytic reactions. However, the initial activity of perovskite oxides is often quite limited, which is extremely related to their crystal structure and electronic structure. In this regard, component regulation is the simplest and most effective strategy to increase their stability and catalytic activity. In this review, we briefly outline the recent progress in the modulating component of perovskite oxides to enhance their catalytic properties. The outline was categorized according to the sites in the ABO3‐type perovskite structure, including A‐site, B‐site, and O‐site regulation. Finally, potential research directions aimed at modulating of perovskite oxide constituents are discussed.

Electrochemical reduction of CO2 into valuable fuels and chemicals has become a contemporary research area, where the heterogeneous catalyst plays a critical role. Metal nanoparticles supported on oxides performing as active sites of electrochemical reactions have been the focus of intensive investigation. Here, we review the CO2 reduction with active materials prepared by exsolution. The fundamental of exsolution was summarized in terms of mechanism and models, materials, and driven forces. The advances in the exsolved materials used in high-temperature CO2 electrolysis were catalogued into tailored interfaces, synergistic effects on alloy particles, phase transition, reversibility and electrochemical switching.

Hydrogen production from biogas over alumina-supported Ce1−xNixO2−x catalysts was studied in a temperature range of 600–850 °C with an initial gas composition of CH4/CO2/H2O of 1/0.8/0.4. To achieve a high and stable hydrogen yield, highly dispersed Ni catalysts were prepared through the exsolution approach. A solid solution of Ce1−xNixO2−x was firstly formed on the surface of Al2O3 and then activated in H2/Ar at 800 °C. The genesis and properties of the Ce1−xNixO2−x/Al2O3 catalysts were established using X-ray fluorescence analysis, thermal analysis, N2 adsorption, ex situ and in situ X-ray diffraction, Raman spectroscopy, electron microscopy, EDX analysis, and temperature-programmed hydrogen reduction. The performance of Ce1−xNixO2−x/Al2O3 catalysts in biogas conversion was tuned by regulation of the dispersion and reducibility of the active component through variation of content (5–20 wt.%) and composition (x = 0.2, 0.5, 0.8) of Ce1−xNixO2−x as well as the mode of its loading (co-impregnation (CI), citrate sol–gel method (SG)). For the 20 wt.% Ce1−xNixO2−x/Al2O3 catalyst, the rate of the coke formation decreased by a factor of 10 as x increased from 0.2 to 0.8. The optimal catalyst composition (20 wt.% Ce0.2Ni0.8O1.8/80 wt.% Al2O3) and preparation mode (citrate sol–gel method) were determined. At 850 °C, the 20 wt.% Ce0.2Ni0.8O1.8/Al2O3-SG catalyst provides 100% hydrogen yield at full CH4 conversion and 85% CO2 utilization. [ABSTRACT FROM AUTHOR]

The escalating increase in global temperatures has highlighted hydrogen (H 2) as a promising alternative clean energy carrier. Hydrogen can be derived from biofuels such as bioethanol, offering an efficient liquid carrier that addresses availability, storage, and distribution issues hindering a widespread use of H 2. This study reports on the synthesis of La 0.4 Sr 0.4 Ti 0.8 Ni 0.2 O 3-δ catalysts followed by the exsolution process to enhance catalytic activity for H 2 production via ethanol steam reforming (ESR) reaction. Single-phase compounds with exsolved metallic nanoparticles were successfully tested for ESR, revealing an ethanol conversion rate of 40 % and over 40 % H 2 production for the catalyst reduced at 1000 °C for 12 hours. Stability tests demonstrated the catalyst's capacity for regeneration in both water vapor and N 2. The experimental data demonstrate that exsolving metallic nanoparticles is a viable strategy for producing a stable catalyst for the ESR reaction. • Ni exsolution in lanthanun-titanate perovskite was studied for ethanol reforming. • Temperature and time of exsolution influenced size and number per unit area of Ni0 particles. • Catalysts exsolved at 1000 °C for 12 hours showed 40 % H 2 production at 600 °C. • The catalyst can be regenerated in water vapor and N 2. [ABSTRACT FROM AUTHOR]

An effective strategy for CO 2 electrolysis by solid oxide electrolysis cells (SOECs) is to design high-performance cathode material by interface engineering. In this work, a Ni-doped Sr 0.95 Ti 0.3 Fe 0.7 O 3-δ /Ce 0.9 Gd 0.1 O 2-δ (denoted as STFN/GDCN) nanofiber composite is directly obtained via electrospinning. Then, Ni nanoparticles are dual-exsolved by 10%H 2 /Ar reduction to in-situ anchor on the surface of STFN and GDCN (denoted as Ni@STFN/GDCN), which is used as SOECs cathode. This developed composite cathode not only facilitates CO 2 reduction reaction (CO 2 RR) rate but also resists thermal aggregation and carbon deposition. The Ni@STFN/GDCN cathode operating in pure CO 2 with an applied voltage of 1.6 V achieves a current density of 1.85 A cm−2, surpassing most of the advanced electrodes reports by other works. Furthermore, the CO 2 RR testing at a current density of 1.5 A cm−2 shows no significant voltage fluctuations during 180 h, demonstrating excellent long-term stability. Our testing results show that the in-situ dual-exsolved nanometal anchoring on heterogeneous composite nanofiber is a reliable and stable SOEC cathode for direct and highly efficient CO 2 electrolysis. [Display omitted] • Highly active and robust STFN/GDCN heterogeneous nanofiber cathode. • Nanofibers with exsolved nanometal boost electrolysis performance. • The excellent electrolysis activity of 1.85 A cm−2 is achieved at 1.6V. • Ni@STFN/GDCN exhibits remarkable electrolysis stability over 180 h. [ABSTRACT FROM AUTHOR]

Exsolution, as an effective approach to constructing particle-decorated interfaces, is still challenging to yield interfacial films rather than isolated particles. Inspired by in vivo near-infrared laser photothermal therapy, using 3 mol% Y _2 O _3 stabilized tetragonal zirconia polycrystals (3Y-TZP) as host oxide matrix and iron-oxide (Fe _3 O _4 / γ -Fe _2 O _3 / α -Fe _2 O _3 ) materials as photothermal modulator and exsolution resource, femtosecond laser ultrafast exsolution approach is presented enabling to conquer this challenge. The key is to trigger photothermal annealing behavior via femtosecond laser ablation to initialize phase transition from monoclinic zirconia (m-ZrO _2 ) to tetragonal zirconia (t-ZrO _2 ) and induce t-ZrO _2 columnar crystal growth. Fe-ions rapidly segregate along grain boundaries and diffuse towards the outmost surface, and become ‘frozen’, highlighting the potential to use photothermal materials and ultrafast heating/quenching behaviors of femtosecond laser ablation for interfacial exsolution. Triggering interfacial iron-oxide coloring exsolution is composition and concentration dependent. Photothermal materials themselves and corresponding photothermal transition capacity play a crucial role, initializing at 2 wt%, 3 wt%, and 5 wt% for Fe _3 O _4 / γ -Fe _2 O _3 / α -Fe _2 O _3 doped 3Y-TZP samples. Due to different photothermal effects, exsolution states of ablated 5 wt% Fe _3 O _4 / γ -Fe _2 O _3 / α -Fe _2 O _3 -doped 3Y-TZP samples are totally different, with whole coverage, exhaustion (ablated away) and partial exsolution (rich in the grain boundaries in subsurface), respectively. Femtosecond laser ultrafast photothermal exsolution is uniquely featured by up to now the deepest microscale (10 μ m from 5 wt%-Fe _3 O _4 -3Y-TZP sample) Fe-elemental deficient layer for exsolution and the whole coverage of exsolved materials rather than the formation of isolated exsolved particles by other methods. It is believed that this novel exsolution method may pave a good way to modulate interfacial properties for extensive applications in the fields of biology, optics/photonics, energy, catalysis, environment, etc.

Introduction: Innovating technologies to efficiently reduce carbon dioxide (CO2) emission or covert it into useful products has never been more crucial in light of the urgent need to transition to a net-zero economy by 2050. The design of efficient catalysts that can make the above a viable solution is of essence. Many noble metal catalysts already display high activity, but are usually expensive. Thus, alternative methods for their production are necessary to ensure more efficient use of noble metals.Methods: Exsolution has been shown to be an approach to produce strained nanoparticles, stable against agglomeration while displaying enhanced activity. Here we explore the effect of a low level of substitution of Ni into a Rh based A-site deficienttitanate aiming to investigate the formation of more efficient, low loading noblemetal catalysts.Results: We find that with the addition of Ni in a Rh based titanate exsolution is increased by up to ∼4 times in terms of particle population which in turn results in up to 50% increase in its catalytic activity for CO2 conversion.Discussion: We show that this design principle not only fulfills a major research need in the conversion of CO2 but also provides a step-change advancement in the design and synthesis of tandem catalysts by the formation of distinct catalytically active sites.

Spinodal decomposition is an important mechanism of exsolution. However, spinodal decomposition has not been observed in natural sulfide intergrowths. We utilized focused ion beam (FIB) and transmission electron microscopy (TEM) techniques to confirm spinodal decomposition in natural sulfide intergrowths (chalcopyrite and bornite). According to FIB and TEM analyses, spinodal decomposition occurred as small and curving alternating dark and bright fluctuations in natural bornite–chalcopyrite intergrowths. Due to the low temperature that drove the exsolution mechanism, fluctuations ~10 nm wide and 20–200 nm long contained non-stoichiometric and tetragonal bornite and chalcopyrite. The corresponding electron diffraction of spinodal decomposition displayed a satellite spot in the [−210] direction for bornite, and the (200)* and (224)* of chalcopyrite paralleled the (24−2)* and (242)* of bornite, respectively. These observations all agreed with spinodal decomposition, two coexisting phases formed with a crystallographic orientation relationship, which indicated the first observation of spinodal decomposition in natural sulfide intergrowths. These findings confirmed that spinodal decomposition is a mechanism for natural crystal growth. As spinodal decomposition is larger in extent and faster than nucleation and growth, other Cu ore deposits may also form via this mechanism. [ABSTRACT FROM AUTHOR]

Hydrogen production through the bi-reforming of methane over exsolution-derived Ni catalysts has been studied. Nickel-based catalysts were prepared through the activation of (CeM)1−xNixOy (M = Al, La, Mg) solid solutions in a reducing gaseous medium. Their performance and resistance to coking under the reaction conditions were controlled by regulating their textural, structural, morphological, and redox properties through adjustments to the composition of the oxide matrix (M/Ce = 0–4; x = 0.2–0.8; y = 1.0–2.0). The role of the M-dopant type in the genesis and properties of the catalysts was established. The efficiency of the catalysts in the bi-reforming of methane increased in the following series of M: M-free < La < Al < Mg, correlating with the structural behavior of the nickel active component and the anti-coking properties of the support matrix. The preferred M-type and M/Ce ratio determined the best performance of (CeM)1−xNixOy catalysts. At 800 °C the optimum Ce0.6Mg0.2Ni0.2O1.6 catalyst provided a stable H2 yield of 90% at a high level of CO2 and CH4 conversions (>85%). [ABSTRACT FROM AUTHOR]

Six different perovskite-type oxides were investigated with respect to their ability for methanol synthesis via H2 and CO2: Fe-, Mn-, and Ti-based perovskites were prepared with and without Cu doping. For assessment, the catalysts were subjected to preliminary tests at atmospheric pressure to evaluate their ability to activate CO2. Additional catalytic tests with the doped versions of each catalyst type were carried out in a pressured reactor at 21 bar. After the measurements, the catalysts were characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM). All catalysts were able to produce methanol in the pressure tests. CO2 conversions between 14% and 23% were reached at 400 °C, with the highest methanol selectivity at the lower temperature of 250 °C. The combination of XRD and SEM revealed that the Fe-based and Ti-based perovskites were stable under reaction conditions and that catalytically highly active and stable nanoparticles had formed. The minor formation of CaCO3, which is a deactivating phase, was observed for one catalyst. These nanoparticles showed resistance to coking and sintering. However, the yield and selectivity for methanol need to be improved via the further tailoring of the perovskite composition. [ABSTRACT FROM AUTHOR]

Solid oxide cells (SOCs) are promising energy-conversion devices due to their high efficiency under flexible operational modes. Yet, the sluggish kinetics of fuel electrodes remain a major obstacle to their practical applications. Since the electrochemically active region only extends a few micrometers, manipulating surface architecture is vital to endow highly efficient and stable fuel electrodes for SOCs. Herein, a simple selective etching method of nanosurface reconstruction is reported to achieve catalytically optimized hierarchical morphology for boosting the SOCs under different operational modes simultaneously. The selective etching can create many corrosion pits and exposure of more B-site active atoms in Sr 2 Co 0.4 Fe 1.2 Mo 0.4 O 6-δ fuel electrode, as well as promote the exsolution of CoFe alloy nanoparticles. An outstanding electrochemical performance of the fabricated cell with the power density increased by 1.47 times to 1.31 W cm -2 at fuel cell mode is demonstrated, while the current density reaches 1.85 A cm -2 under 1.6 V at CO 2 electrolysis mode (800 °C). This novel selective etching method in perovskite oxides provides an appealing strategy to fabricate hierarchical electrocatalysts for highly efficient and stable SOCs with broad implications for clean energy systems and CO 2 utilization., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

In order to clarify the role of R2O3 in the metal-oxide catalysts derived from complex oxide precursors, a series of R1.5Ca0.5NiO4 (R = Nd, Sm, Eu) complex oxides was obtained. A significant systematic increase in the orthorhombic distortion of the R1.5Ca0.5NiO4 structure (K2NiF4 type, Cmce) from Nd to Eu correlates with a corresponding decrease in their ionic radii. A reduction of R1.5Ca0.5NiO4 in the Ar/H2 gas mixture at 800 °C causes a formation of dense agglomerates of CaO and R2O3 coated with spherical 25–30 nm particles of Ni metal. The size of metal particles and oxide agglomerates is similar in all Ni/(R2O3,CaO) composites in the study. Their morphology is rather similar to the products of redox exsolution obtained by the partial reduction of complex oxides. All obtained composites demonstrated a significant catalytic activity in the dry reforming (DRM) and partial oxidation (POM) of methane at 700–800 °C. A systematic decrease in the DRM catalytic activity of composites from Nd to Eu could be attributed to the basicity reduction of R2O3 components of the composite catalysts. The maximum CH4 conversion in POM reaction was observed for Ni/(Sm2O3,CaO), while the maximum selectivity was demonstrated by Nd2O3-based composite. The possible reasons for the observed difference are discussed. [ABSTRACT FROM AUTHOR]

To design metal nanoparticles (NPs) on a perovskite surface, the exsolution method has been extensively used for efficient catalytic reactions. However, there are still the challenges of finding a combination and optimization for the NPs' control. Thus, we report in situ control of the exsolved Ni NPs from perovskite to apply as a catalyst for dry reforming of methane (DRM). The La0.8Ce0.1Ti0.6Ni0.4O3 (LCTN) is designed by Ce doping to incorporate high amounts of Ni in the perovskite lattice and also facilitate the exsolution phenomenon. By control of the eluted Ni NPs through exsolution, the morphological properties of exsolved Ni NPs are observed to have a size range of 10~49 nm, while the reduction temperatures are changed. At the same time, the chemical structure of the eluted Ni NPs is also changed by an increased reduction temperature to a highly metallic Ni phase with an increased oxygen vacancy at the perovskite oxide surface. The optimized composite nanomaterial displays outstanding catalytic performance of 85.5% CH4 conversion to produce H2 with a value of 15.5 × 1011 mol/s·gcat at 60.2% CO conversion, which shows the importance of the control of the exsolution mechanism for catalytic applications. [ABSTRACT FROM AUTHOR]

Because the 6p orbital of Bi is easily combined with the 2p orbital of N, doping Bi can effectively inhibit HER and boost NRR. [Display omitted] • A high-performance NRR electrocatalyst La 0.9 Bi 0.1 FeO 3-δ was developed. • The electron reconstruction of the catalyst surface facilitates the electron transfer. • A new electron transfer chain Bi3+/Bi2+/Bi0 was created. • The electrocatalytic machnism for inhibit HER and improve eNRR was explored. The electrochemical nitrogen reduction reaction (eNRR) displays significant potential for the synthesis of ammonia. However, eNRR electrocatalysts with high catalytic activity and selectivity still need to be developed. In this study, a Bi-doped La 0.9 Bi 0.1 FeO 3-δ (LBiF) perovskite was fabricated as a potential cathode catalyst and incorporated into a protonic ceramic electrolysis cell (PCEC) for eNRR. Electrochemical tests demonstrated that the LBiF cathode reveals higher eNRR catalytic activity and enhanced hydrogen evolution reaction (HER) inhibition compared to undoped LaFeO 3 (LF). Characterization of the LBiF cathode following 90 h of NH 3 synthesis revealed surface reconstruction of the catalyst during eNRR. Particularly, Bi3+ is partially reduced to Bi2+ and metallic Bi, resulting in A-site defects and an increased concentration of oxygen vacancies (OVs) and Fe4+ in accordance with the charge neutrality principle. Both the OVs and Fe4+ can accept electron pairs provided by N 2 due to their unsaturated electronic structures. Furthermore, Bi doping inhibits the HER because Bi preferentially binds to N instead of H. Bi doping creates new Bi3+/Bi2+/Bi0 redox electron pairs, establishing an electron transfer path that improves perovskite conductivity and eNRR electrocatalytic activity. This study sets a foundation for designing eNRR catalysts aimed at suppressing the HER. [ABSTRACT FROM AUTHOR]

A novel dual-exsolution strategy is proposed to boost CO 2 electrolysis properties of LSCFN cathode in solid state electrolysis cell. Benefiting from simultaneously exsolved CoFe alloy and Bi nanoparticles, additional oxygen vacancies are created, and the kinetics of CO 2 adsorption/dissociation/activation are greatly accelerated. [Display omitted] • A novel dual-exsolution strategy is reported; • Both CoFe alloy and metallic Bi nanoparticles are simultaneously exsolved; • More CoFe exsolution and additional oxygen vacancies are obtained; • Exsolution of metallic Bi nanoparticles greatly reinforce chemical adsorption of CO 2 ; • Electrochemical performances for CO 2 electrolysis are boosted. Accelerating sluggish kinetics of CO 2 reduction reaction (CO2RR) is of great importance for efficiently converting CO 2 into valuable chemical products in solid oxide electrolysis cells (SOECs). Here, a novel dual-exsolution strategy is proposed to enhance CO 2 electrolysis properties of La 0.4 Sr 0.6 Co 0.2 Fe 0.7 Nb 0.1 O 3-δ (LSCFN) cathode. With simultaneously exsolved CoFe alloy and Bi nanoparticles on LSCFN cathodic matrix, the as-prepared SOEC delivers a high current density of 539 mA cm−2 for CO 2 electrolysis at 800 °C and 1.5 V, and successfully runs over 170 h without any attenuation. The introduction of Bi exsolution not only promotes CoFe exsolution, provides additional oxygen vacancies, but also greatly boost the kinetics of CO 2 adsorption/dissociation/activation. This work offers new insights into tailoring perovskite electrocatalysts for the CO 2 electrolysis via dual-exsolution strategy. [ABSTRACT FROM AUTHOR]