Highly active dry methane reforming catalysts with boosted in situ grown Ni-Fe nanoparticles on perovskite via atomic layer deposition

Concurrent Amorphization and Nanocatalyst Formation in Cu-Substituted Perovskite Oxide Surface: Effects on Oxygen Reduction Reaction at Elevated Temperatures

The activity and durability of chemical/electrochemical catalysts are significantly influenced by their surface environments, highlighting the importance of thoroughly examining the catalyst surface. Here, Cu-substituted La0.6Sr0.4Co0.2Fe0.8O3-δ is selected, a state-of-the-art material for oxygen reduction reaction (ORR), to explore the real-time evolution of surface morphology and chemistry under a reducing atmosphere at elevated temperatures. Remarkably, in a pioneering observation, it is discovered that the perovskite surface starts to amorphize at an unusually low temperature of approximately 100 °C and multicomponent metal nanocatalysts additionally form on the amorphous surface as the temperature raises to 400 °C. Moreover, this investigation into the stability of the resulting amorphous layer under oxidizing conditions reveals that the amorphous structure can withstand a high-temperature oxidizing atmosphere (≥650 °C) only when it has undergone sufficient reduction for an extended period. Therefore, the coexistence of the active nanocatalysts and defective amorphous surface leads to a nearly 100% enhancement in the electrode resistance for the ORR over 200 h without significant degradation. These observations provide a new catalytic design strategy for using redox-dynamic perovskite oxide host materials.

Synergistic Bulk and Surface Engineering for Expeditious and Durable Reversible Protonic Ceramic Electrochemical Cells Air Electrode

Reversible protonic ceramic electrochemical cells (R-PCECs) offer the potential for high-efficiency power generation and green hydrogen production at intermediate temperatures. However, the commercial viability of R-PCECs is hampered by the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) within conventional air electrodes operating at reduced temperatures. To address this challenge, this work introduces a novel approach based on the simultaneous optimization of bulk-phase metal-oxygen bonds and in-situ formation of a metal oxide nano-catalyst surface modification. This strategy is designed to expedite the ORR/OER electrocatalytic activity of air electrodes exhibiting triple (O2-, H+, e-) conductivity. Specifically, this engineered air electrode nanocomposite-Ba(Co0.4Fe0.4Zr0.1Y0.1)0.95Ni0.05F0.1O2.9-δ demonstrates remarkable ORR/OER catalytic activity and exceptional durability in R-PCECs. This is evidenced by significantly improved peak power density from 626 to 996 mW cm-2 and highly stable reversibility over a 100-h cycling period. This research offers a rational design strategy to achieve high-performance R-PCEC air electrodes with superior operational activity and stability for efficient and sustainable energy conversion and storage.

New trends in nanoparticle exsolution

Many relevant high-temperature chemical processes require the use of oxide-supported metallic nanocatalysts. The harsh conditions under which these processes operate can trigger catalyst degradation via nanoparticle sintering, carbon depositions or poisoning, among others. This primarily affects metallic nanoparticles created via deposition methods with low metal-support interaction. In this respect, nanoparticle exsolution has emerged as a promising method for fabricating oxide-supported nanocatalysts with high interaction between the metal and the oxide support. This is due to the mechanism involved in nanoparticle exsolution, which is based on the migration of metal cations in the oxide support to its surface, where they nucleate and grow as metallic nanoparticles partially embedded in the oxide. This anchorage confers high robustness against sintering or coking-related problems. For these reasons, exsolution has attracted great interest in the last few years. Multiple works have been devoted to proving the high catalytic stability of exsolved metallic nanoparticles in several applications for high-temperature energy storage and conversion. Additionally, considerable attention has been directed towards understanding the underlying mechanism of metallic nanoparticle exsolution. However, this growing field has not been limited to these types of studies and recent discoveries at the forefront of materials design have opened new research avenues. In this work, we define six new trends in nanoparticle exsolution, taking a tour through the most important advances that have been recently reported.

In Situ Self-Assembled Active and Stable Ir@MnOx/La0.7Sr0.3Cr0.9Ir0.1O3-δ Interfaces for CO2 Electrolysis

Solid oxide electrolysis cells are prospective approaches for CO2 utilization but face significant challenges due to the sluggish reaction kinetics and poor stability of the fuel electrodes. Herein, we strategically addressed the long-standing trade-off phenomenon between enhanced exsolution and improved structural stability via topotactic ion exchange. The surface dynamic reconstruction of the MnOx/La0.7Sr0.3Cr0.9Ir0.1O3-δ (LSCIr) catalyst was visualized at the atomic scale. Compared with the Ir@LSCIr interface, the in situ self-assembled Ir@MnOx/LSCIr interface exhibited greater CO2 activation and easily removable carbonate intermediates, thus reached a 42 % improvement in CO2 electrolysis performance at 1.6 V. Furthermore, an improved CO2 electrolysis stability was achieved due to the uniformly wrapped MnOx shell of the Ir@MnOx/LSCIr cathode. Our approach enables a detailed understanding of the dynamic microstructure evolution at active interfaces and provides a roadmap for the rational design and evaluation of efficient metal/oxide catalysts for CO2 electrolysis.

Formation of a Porous Crystalline Mg1-xAl2Oy Overlayer on Metal Catalysts via Controlled Solid-State Reactions for High-temperature Stable Catalysis

Catalyst deactivation by sintering and coking is a long-standing issue in metal-catalyzed harsh high-temperature hydrocarbon reactions. Ultrathin oxide coatings of metal nanocatalysts have recently appeared attractive to address this issue, while the porosity of the overlayer is difficult to control to preserve the accessibility of embedded metal nanoparticles, thus often leading to a large decrease in activity. Here, we report that a nanometer-thick alumina coating of MgAl2O4-supported metal catalysts followed by high-temperature reduction can transform a nonporous amorphous alumina overlayer into a porous Mg1-xAl2Oy crystalline spinel structure with a pore size of 2-3 nm and weakened acidity. The high porosity stems from the restrained Mg migration from the MgAl2O4 support to the alumina overlayer through solid-state reactions at high temperatures. The resulting Ni/MgAl2O4 and Pt/MgAl2O4 catalysts with a porous crystalline Mg1-xAl2Oy overlayer achieved remarkably high stability while preserving much higher activity than the corresponding alumina-coated Ni and Pt catalysts on MgO and Al2O3 supports in the reactions of dry reforming of methane and propane dehydrogenation, respectively.

Atomic/molecular layer deposition strategies for enhanced CO2 capture, utilisation and storage materials

Elevated levels of carbon dioxide (CO2) in the atmosphere and the diminishing reserves of fossil fuels have raised profound concerns regarding the resulting consequences of global climate change and the future supply of energy. Hence, the reduction and transformation of CO2 not only mitigates environmental pollution but also generates value-added chemicals, providing a dual remedy to address both energy and environmental challenges. Despite notable advancements, the low conversion efficiency of CO2 remains a major obstacle, largely attributed to its inert chemical nature. It is imperative to engineer catalysts/materials that exhibit high conversion efficiency, selectivity, and stability for CO2 transformation. With unparalleled precision at the atomic level, atomic layer deposition (ALD) and molecular layer deposition (MLD) methods utilize various strategies, including ultrathin modification, overcoating, interlayer coating, area-selective deposition, template-assisted deposition, and sacrificial-layer-assisted deposition, to synthesize numerous novel metal-based materials with diverse structures. These materials, functioning as active materials, passive materials or modifiers, have contributed to the enhancement of catalytic activity, selectivity, and stability, effectively addressing the challenges linked to CO2 transformation. Herein, this review focuses on ALD and MLD's role in fabricating materials for electro-, photo-, photoelectro-, and thermal catalytic CO2 reduction, CO2 capture and separation, and electrochemical CO2 sensing. Significant emphasis is dedicated to the ALD and MLD designed materials, their crucial role in enhancing performance, and exploring the relationship between their structures and catalytic activities for CO2 transformation. Finally, this comprehensive review presents the summary, challenges and prospects for ALD and MLD-designed materials for CO2 transformation.

Structured Catalysts and Catalytic Processes: Transport and Reaction Perspectives

The structure of catalysts determines the performance of catalytic processes. Intrinsically, the electronic and geometric structures influence the interaction between active species and the surface of the catalyst, which subsequently regulates the adsorption, reaction, and desorption behaviors. In recent decades, the development of catalysts with complex structures, including bulk, interfacial, encapsulated, and atomically dispersed structures, can potentially affect the electronic and geometric structures of catalysts and lead to further control of the transport and reaction of molecules. This review describes comprehensive understandings on the influence of electronic and geometric properties and complex catalyst structures on the performance of relevant heterogeneous catalytic processes, especially for the transport and reaction over structured catalysts for the conversions of light alkanes and small molecules. The recent research progress of the electronic and geometric properties over the active sites, specifically for theoretical descriptors developed in the recent decades, is discussed at the atomic level. The designs and properties of catalysts with specific structures are summarized. The transport phenomena and reactions over structured catalysts for the conversions of light alkanes and small molecules are analyzed. At the end of this review, we present our perspectives on the challenges for the further development of structured catalysts and heterogeneous catalytic processes.

Challenging thermodynamics: combining immiscible elements in a single-phase nano-ceramic

The Hume-Rothery rules governing solid-state miscibility limit the compositional space for new inorganic material discovery. Here, we report a non-equilibrium, one-step, and scalable flame synthesis method to overcome thermodynamic limits and incorporate immiscible elements into single phase ceramic nanoshells. Starting from prototype examples including (NiMg)O, (NiAl)Ox, and (NiZr)Ox, we then extend this method to a broad range of Ni-containing ceramic solid solutions, and finally to general binary combinations of elements. Furthermore, we report an "encapsulated exsolution" phenomenon observed upon reducing the metastable porous (Ni0.07Al0.93)Ox to create ultra-stable Ni nanoparticles embedded within the walls of porous Al2O3 nanoshells. This nanoconfined structure demonstrated high sintering resistance during 640 h of catalysis of CO2 reforming of methane, maintaining constant 96% CH4 and CO2 conversion at 800 °C and dramatically outperforming conventional catalysts. Our findings could greatly expand opportunities to develop novel inorganic energy, structural, and functional materials.

Perovskites as oxygen storage materials for chemical looping partial oxidation and reforming of methane

The traditional partial oxidation, dry reforming and steam reforming of methane technologies are separated into two reactors for execution by chemical looping technology, which can avoid the defects exposed in the traditional process (avoiding carbon accumulation, reducing costs, etc.). The key to chemical looping technology is to find suitable oxygen carriers (OCs), which can store and release oxygen to form a closed loop in the chemical looping. The purpose of this review is to summarize the current status of perovskite oxides for partial oxidation and reforming of methane in chemical looping, describe the structure, oxygen capacity, oxygen migration rate and common synthesis methods of perovskites in chemical looping. In addition, the effects of impregnation loading, ion doping, and structural morphology on the catalytic conversion of CH4 by perovskite OCs and the reaction mechanism on the OCs are also discussed.

In situ electrochemical reconstruction of Sr2Fe1.45Ir0.05Mo0.5O6-δ perovskite cathode for CO2 electrolysis in solid oxide electrolysis cells

Solid oxide electrolysis cells provide a practical solution for the direct conversion of CO2 to other chemicals (i.e. CO), however, an in-depth mechanistic understanding of the dynamic reconstruction of active sites for perovskite cathodes during CO2 electrolysis remains a great challenge. Herein, we identify that iridium-doped Sr2Fe1.45Ir0.05Mo0.5O6-δ (SFIrM) perovskite displays a dynamic electrochemical reconstruction feature during CO2 electrolysis with abundant exsolution of highly dispersed IrFe alloy nanoparticles on the SFIrM surface. The in situ reconstructed IrFe@SFIrM interfaces deliver a current density of 1.46 A cm-2 while maintaining over 99% CO Faradaic efficiency, representing a 25.8% improvement compared with the Sr2Fe1.5Mo0.5O6-δ counterpart. In situ electrochemical spectroscopy measurements and density functional theory calculations suggest that the improved CO2 electrolysis activity originates from the facilitated formation of carbonate intermediates at the IrFe@SFIrM interfaces. Our work may open the possibility of using an in situ electrochemical poling method for CO2 electrolysis in practice.

Quantifying Electrochemical Driving Force for Exsolution in Perovskite Oxides by Designing Graded Oxygen Chemical Potential

Metal nanoparticles exsolved and anchored at the parent perovskite oxide surfaces can greatly enhance the activity and antisintering stability for high-temperature (electro-) chemical catalytic reactions. While exsolution of nanoparticles triggered by using conventional high-temperature thermal reduction suffers from slow kinetics, using an electrochemical driving force can promote the exsolution rate. However, a quantitative correlation between the applied electrochemical driving force and the spatial density of exsolved nanoparticles remains unknown. In this work, we use a specially designed electrochemical device to induce a spatially graded voltage in a La_0.43Ca_0.37Ti_0.94Ni_0.06O_3-δ electrode, in order to systematically investigate the effect of electrochemical switching on exsolution. With increasing driving force, which leads to decreasing oxygen chemical potential, the density of nanoparticles was observed to increase dramatically, while the average particle size remained roughly constant. We further identified oxygen vacancy pairs or clusters as the preferential nucleation sites for exsolution. Our work provided a high-throughput platform for the systematic study of exsolution of perovskite oxides targeted for fuel electrode materials with improved electrocatalytic performance and stability.

Exsolution on perovskite oxides: morphology and anchorage of nanoparticles

Perovskites are very promising materials for a wide range of applications (such as catalysis, solid oxide fuel cells…) due to beneficial general properties (e.g. stability at high temperatures) and tunability - doping both A- and B-site cations opens the path to a materials design approach that allows specific properties to be finely tuned towards applications. A major asset of perovskites is the ability to form nanoparticles on the surface under certain conditions in a process called "exsolution". Exsolution leads to the decoration of the material's surface with finely dispersed nanoparticles (which can be metallic or oxidic - depending on the experimental conditions) made from B-site cations of the perovskite lattice (here, doping comes into play, as B-site doping allows control over the constitution of the nanoparticles). In fact, the ability to undergo exsolution is one of the main reasons that perovskites are currently a hot topic of intensive research in catalysis and related fields. Exsolution on perovskites has been heavily researched in the last couple of years: various potential catalysts have been tested with different reactions, the oxide backbone materials and the exsolved nanoparticles have been investigated with a multitude of different methods, and the effect of different exsolution parameters on the resulting nanoparticles has been studied. Despite all this, to our knowledge no comprehensive effort was made so far to evaluate these studies with respect to the effect that the exsolution conditions have on anchorage and morphology of the nanoparticles. Therefore, this highlight aims to provide an overview of nanoparticles exsolved from oxide-based perovskites with a focus on the conditions leading to nanoparticle exsolution.

Synthesis of Highly Tunable Alloy Nanocatalyst through Heterogeneous Doping Method

The combination of supported metal nanoparticles and functional host oxides catalyze many major industrial reactions. However, uniform dispersion and ideal chemical configuration of such nanoparticles, which determines the catalytic activity, are often difficult to achieve. In this study, a unique combination is proposed of heterogeneous doping and ex-solution for the fabrication of Pt-Ni alloy nanoparticles on CeO₂ . By manipulating the reducing conditions, both the particle size and composition are precisely controlled, thereby achieving a highly dispersed and stable alloy nanocatalyst. The unique behavior of controlled alloy composition is elucidated through classical diffusion and precipitation kinetics with elemental analysis of the grain boundaries. Finally, Pt-Ni alloy nanocatalysts are successfully tuned showcasing a breakthrough performance compared to single element catalyst in reverse water gas shift reaction with superior stability and reproducibility.

Catalysis of Alloys: Classification, Principles, and Design for a Variety of Materials and Reactions

Alloying has long been used as a promising methodology to improve the catalytic performance of metallic materials. In recent years, the field of alloy catalysis has made remarkable progress with the emergence of a variety of novel alloy materials and their functions. Therefore, a comprehensive disciplinary framework for catalytic chemistry of alloys that provides a cross-sectional understanding of the broad research field is in high demand. In this review, we provide a comprehensive classification of various alloy materials based on metallurgy, thermodynamics, and inorganic chemistry and summarize the roles of alloying in catalysis and its principles with a brief introduction of the historical background of this research field. Furthermore, we explain how each type of alloy can be used as a catalyst material and how to design a functional catalyst for the target reaction by introducing representative case studies. This review includes two approaches, namely, from materials and reactions, to provide a better understanding of the catalytic chemistry of alloys. Our review offers a perspective on this research field and can be used encyclopedically according to the readers' individual interests.

In Situ Control of the Eluted Ni Nanoparticles from Highly Doped Perovskite for Effective Methane Dry Reforming

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 La_0.8Ce_0.1Ti_0.6Ni_0.4O₃ (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.

Boosting the stability of perovskites with exsolved nanoparticles by B-site supplement mechanism

Perovskites with exsolved nanoparticles (P-eNs) have immense potentials for carbon dioxide (CO₂) reduction in solid oxide electrolysis cell. Despite the recent achievements in promoting the B-site cation exsolution for enhanced catalytic activities, the unsatisfactory stability of P-eNs at high voltages greatly impedes their practical applications and this issue has not been elucidated. In this study, we reveal that the formation of B-site vacancies in perovskite scaffold is the major contributor to the degradation of P-eNs; we then address this issue by fine-regulating the B-site supplement of the reduced Sr₂Fe_1.3Ni_0.2Mo_0.5O_6-δ using foreign Fe sources, achieving a robust perovskite scaffold and prolonged stability performance. Furthermore, the degradation mechanism from the perspective of structure stability of perovskite has also been proposed to understand the origins of performance deterioration. The B-site supplement endows P-eNs with the capability to become appealing electrocatalysts for CO₂ reduction and more broadly, for other energy storage and conversion systems.

Emerging natural and tailored perovskite-type mixed oxides–based catalysts for CO2 conversions

The rapid economic and societal development have led to unprecedented energy demand and consumption resulting in the harmful emission of pollutants. Hence, the conversion of greenhouse gases into valuable chemicals and fuels has become an urgent challenge for the scientific community. In recent decades, perovskite-type mixed oxide-based catalysts have attracted significant attention as efficient CO2 conversion catalysts due to the characteristics of both reversible oxygen storage capacity and stable structure compared to traditional oxide-supported catalysts. In this review, we hand over a comprehensive overview of the research for CO2 conversion by these emerging perovskite-type mixed oxide-based catalysts. Three main CO2 conversions, namely reverse water gas shift reaction, CO2 methanation, and CO2 reforming of methane have been introduced over perovskite-type mixed oxide-based catalysts and their reaction mechanisms. Different approaches for promoting activity and resisting carbon deposition have also been discussed, involving increased oxygen vacancies, enhanced dispersion of active metal, and fine-tuning strong metal-support interactions. Finally, the current challenges are mooted, and we have proposed future research prospects in this field to inspire more sensational breakthroughs in the material and environment fields.

Improving Anti-Coking Properties of Ni/Al2O3 Catalysts via Synergistic Effect of Metallic Nickel and Nickel Phosphides in Dry Methane Reforming

A series of NiP-x/Al₂O₃ catalysts containing different ratio of metallic nickel to nickel phosphides, prepared by varying Ni/P molar ratio of 4, 3, 2 through a co-impregnation method, were employed to investigate the synergistic effect of metallic nickel-nickel phosphides in dry methane reforming reaction. The Ni/Al₂O₃ catalyst indicates good activity along with severe carbon deposition. The presence of phosphorus increases nickel dispersion as well as the interaction between nickel and alumina support, which results in smaller nickel particles. The co-existence of metallic nickel and nickel phosphides species is confirmed at all the P contained catalysts. Due to the relative stronger CO₂ dissociation ability, the NiP-x/Al₂O₃ catalysts indicate obvious higher resistance of carbon deposition. Furthermore, because of good balance between CH₄ dissociation and CO₂ dissociation, NiP-2/Al₂O₃ catalyst exhibits best resistance of carbon deposition, few carbon depositions were formed after 50 h of dry methane reforming.

Hollow Capsule NiCo2 NS Prepared by Self-Sacrificing Template Method for High-Efficiency Bifunctional Catalyst and Its Application in Zn-Air Battery

Exploring the application of high-efficiency bifunctional oxygen catalysts to rechargeable zinc-air batteries has been a research hotspot in recent years. We succeeded in obtaining NiCo₂ NS with a hollow capsule structure through the self-sacrificing template method, which has a larger specific surface area and can provide more active sites for electrocatalysis relative to his solid. The introduction of S can change the valence distribution of N and the electronic structure of the M-N bond, so that NiCo₂ NS exhibits excellent performance in the overpotential and stability of the oxygen reduction and oxygen evolution reactions. It shows an overpotential of 154 mV at 10 mA cm^-2 and a half-wave potential of 0.76 V. When used as a bi-functional catalyst in zinc-air batteries, it exhibits good stability within 400 h. The flexible battery assembled by NiCo₂ NS also shows excellent performance, and can be cycled stably for 20 h. The current maintains good stability when it is bent at different angles during the cycle.

A New Durable Surface Nanoparticles-Modified Perovskite Cathode for Protonic Ceramic Fuel Cells from Selective Cation Exsolution under Oxidizing Atmosphere

A high-performance cathode of a protonic ceramic fuel cell (PCFC) should possess excellent oxygen reduction reactivity, high proton/oxygen-ion/electron conductivity, and sufficient operational stability, thus requiring a delicate tuning of both the bulk and surface properties of the electrode material. Although surface modification of perovskites with nanoparticles from reducing-atmosphere exsolution has been demonstrated effective at improving the electrochemical anodic oxidation, such nanoparticles would easily re-incorporate into the perovskite lattice causing a big challenge for their application as a cathode. Here, a durable perovskite-based nanocomposite cathode for PCFCs is reported, which is facilely prepared via the exsolution of nanoparticles in an oxidizing atmosphere. Through composition and cation nonstoichiometry manipulation, a precursor with the nominal composition of Ba_0.95 (Co_0.4 Fe_0.4 Zr_0.1 Y_0.1 )_0.95 Ni_0.05 O_3-δ (BCFZYN-095) is designed, synthesized, and investigated, which, upon calcination, gives rise to the formation of a perovskite-based nanocomposite comprising a major perovskite phase and a minor NiO phase enriched on the perovskite surface. The major perovskite phase enabled by the proper cation nonstoichiometry manipulation promotes bulk proton conduction while the NiO nanoparticles facilitate the oxygen surface exchange process, leading to a superior cathodic performance with a maximum peak power density of 1040 mW cm^-2 at 650 °C and excellent operational stability of 400 h at 550 °C.

Nanoscale interface engineering for solid oxide fuel cells using atomic layer deposition

Atomic layer deposition (ALD), which is already actively used in the semiconductor industry, has been in the spotlight in various energy fields, such as batteries and fuel cells, given its unique ability to enable the nanoscale deposition of diverse materials with a variety of compositions onto complex 3D structures. In particular, with regard to ceramic fuel cells, ALD has attracted attention because it facilitates the manufacturing of thin and dense electrolytes. Furthermore, recently, electrode surfaces and electrode/electrolyte interface modification are arising as new research strategies to fabricate robust fuel cells. In this mini-review, we present a brief overview of ALD and recent studies that utilize ALD in ceramic fuel cells, such as manufacturing thin film electrolytes, stabilizing electrodes, functionalizing electrodes, and modifying the chemistry of electrode surfaces. We also propose research directions to expand the utility and functionality of the ALD techniques.

Effects of alloying for steam or dry reforming of methane: a review of recent studies

A survey on the catalytic nature of Ni-based alloy catalysts in recent years provides a direction for future catalyst development.

Unveiling the key factor for the phase reconstruction and exsolved metallic particle distribution in perovskites

To significantly increase the amount of exsolved particles, the complete phase reconstruction from simple perovskite to Ruddlesden-Popper (R-P) perovskite is greatly desirable. However, a comprehensive understanding of key parameters affecting the phase reconstruction to R-P perovskite is still unexplored. Herein, we propose the Gibbs free energy for oxygen vacancy formation in Pr_0.5(Ba/Sr)_0.5TO_3-δ (T = Mn, Fe, Co, and Ni) as the important factor in determining the type of phase reconstruction. Furthermore, using in-situ temperature & environment-controlled X-ray diffraction measurements, we report the phase diagram and optimum 'x' range required for the complete phase reconstruction to R-P perovskite in Pr_0.5Ba_0.5-xSr_xFeO_3-δ system. Among the Pr_0.5Ba_0.5-xSr_xFeO_3-δ, (Pr_0.5Ba_0.2Sr_0.3)₂FeO_4+δ - Fe metal demonstrates the smallest size of exsolved Fe metal particles when the phase reconstruction occurs under reducing condition. The exsolved nano-Fe metal particles exhibit high particle density and are well-distributed on the perovskite surface, showing great catalytic activity in fuel cell and syngas production.

Promoting exsolution of RuFe alloy nanoparticles on Sr2Fe1.4Ru0.1Mo0.5O6-δ via repeated redox manipulations for CO2 electrolysis

Metal nanoparticles anchored on perovskite through in situ exsolution under reducing atmosphere provide catalytically active metal/oxide interfaces for CO₂ electrolysis in solid oxide electrolysis cell. However, there are critical challenges to obtain abundant metal/oxide interfaces due to the sluggish diffusion process of dopant cations inside the bulk perovskite. Herein, we propose a strategy to promote exsolution of RuFe alloy nanoparticles on Sr₂Fe_1.4Ru_0.1Mo_0.5O_6−δ perovskite by enriching the active Ru underneath the perovskite surface via repeated redox manipulations. In situ scanning transmission electron microscopy demonstrates the dynamic structure evolution of Sr₂Fe_1.4Ru_0.1Mo_0.5O_6−δ perovskite under reducing and oxidizing atmosphere, as well as the facilitated CO₂ adsorption at RuFe@Sr₂Fe_1.4Ru_0.1Mo_0.5O_6−δ interfaces. Solid oxide electrolysis cell with RuFe@Sr₂Fe_1.4Ru_0.1Mo_0.5O_6−δ interfaces shows over 74.6% enhancement in current density of CO₂ electrolysis compared to that with Sr₂Fe_1.4Ru_0.1Mo_0.5O_6−δ counterpart as well as impressive stability for 1000 h at 1.2 V and 800 °C.

Metal nanoparticles anchored on perovskite provide catalytically active interfaces for CO2 electrolysis. The authors promote exsolution of RuFe alloy nanoparticles on Sr2Fe1.4Ru0.1Mo0.5 O6−δ perovskite by enriching the active Ru underneath the perovskite surface via repeated redox manipulations.

Anti-Coking and Anti-Sintering Ni/Al2O3 Catalysts in the Dry Reforming of Methane: Recent Progress and Prospects

Coking and metal sintering are limitations of large-scale applications of Ni/Al2O3 catalysts in DRM reactions. In this review, several modification strategies to enhance the anti-deactivation property of Ni/Al2O3 are proposed and discussed with the recently developed catalyst systems, including structure and morphology control, surface acidity/basicity, interfacial engineering and oxygen defects. In addition, the structure–performance relationship and deactivation/anti-deactivation mechanisms are illustrated in depth, followed by prospects for future work.

Enhancing Thermocatalytic Activities by Upshifting the d-Band Center of Exsolved Co-Ni-Fe Ternary Alloy Nanoparticles for the Dry Reforming of Methane

Dry reforming of methane (DRM) is a feasible solution to address the reduction of greenhouse gases stipulated by the Paris Climate Agreement, given that it adds value by converting trivial gases, CO₂ and CH₄ , simultaneously into useful syngas. However, the conventional Ni catalyst undergoes deactivation due to carbon coking and particle agglomeration. Here we demonstrate a highly efficient and durable DRM catalyst: exsolved Co-Ni-Fe ternary alloy nanoparticles on the layered perovskite PrBaMn_1.7 Co_0.1 Ni_0.2 O_5+δ produced by topotactic exsolution. This method readily allows the generation of a larger number of exsolved nanoparticles with enhanced catalytic activity above that of Ni monometallic and Co-Ni bimetallic particles. The enhancement is achieved by the upshift of the d-band center of Co-Ni-Fe relative to those of Co-Ni and Ni, meaning easier charge donation to the adsorbate. Furthermore, the exsolved catalyst shows exceptional stability, with continuous DRM operation for about 350 hours.

Coking-resistant dry reforming of methane over Ni/γ-Al2O3 catalysts by rationally steering metal-support interaction

The coking issue is the main challenge for dry reforming of methane (DRM) over Ni-based catalysts. Herein, we excavate the reasons for the enhanced coking resistance of the bounded Ni over the free state Ni in Ni/γ-Al₂O₃ catalysts for DRM. Rational metal-support interaction of the bounded Ni would facilitate desorption of CO, thus suppressing CO disproportionation and decreasing carbon deposition. The higher activity of the bounded Ni is ascribed to better methane cracking ability, stronger adsorption, and activation of CO₂ by forming polydentate carbonate. The better activation of CO₂ over the bounded Ni would also contribute to the gasification of formed coke. We gain an insight into the anti-coking mechanism of DRM determined by metal-support interaction in Ni/γ-Al₂O₃ catalysts through mechanistic studies. It is believed that our findings would enlighten the design of more efficient catalysts for DRM.

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The anti-coking ability of the bounded Ni is better than the free state Ni

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The bounded Ni has a stronger ability to activate CO₂ to produce active O∗ species

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High reactivity and stable polydentate carbonate enables efficient reaction

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Rational metal-support interaction results in good resistance to CO poisoning

Trends and Prospects of Bimetallic Exsolution

Supported bimetallic nanoparticles used for various chemical transformations appear to be more appealing than their monometallic counterparts, because of their unique properties mainly originating from the synergistic effects between the two different metals. Exsolution, a relatively new preparation method for supported nanoparticles, has earned increasing attention for bimetallic systems in the past decade, not only due to the high stability of the resulting nanoparticles but also for the potential to control key particle properties (size, composition, structure, morphology, etc.). In this review, we summarize the trends and advances on exsolution of bimetallic systems and provide prospects for future studies in this field.

Nanoparticle Ex-solution for Supported Catalysts: Materials Design, Mechanism and Future Perspectives

Supported metal catalysts represent one of the major milestones in heterogeneous catalysis. Such catalytic systems are feasible for use in a broad range of applications, including renewable energy devices, sensors, automotive emission control systems, and chemical reformers. The lifetimes of these catalytic platforms depend strongly on the stability of the supported nanoparticles. With this regard, nanoparticles synthesized via ex-solution process emphasize exceptional robustness as they are socketed in the host oxide. Ex-solution refers to a phenomenon which yields selective growth of fine and uniformly distributed metal nanocatalysts on oxide supports upon partial reduction. This type of advanced structural engineering is a game-changer in the field of heterogeneous catalysis with numerous studies showing the benefits of ex-solution process. In this review, we highlight the latest research efforts regarding the origin of the ex-solution phenomenon and the mechanism underpinning particle formation. We also propose research directions to expand the utility and functionality of the current ex-solution techniques.

Metal Exsolution to Enhance the Catalytic Activity of Electrodes in Solid Oxide Fuel Cells

Exsolution is a novel technology for attaching metal catalyst particles onto ceramic anodes in the solid oxide fuel cells (SOFCs). The exsolved metal particles in the anode exhibit unique properties for reaction and have demonstrated remarkable stabilities under conditions that normally lead to coking. Despite extensive investigations, the underlying principles behind exsolution are still under investigation. In this review, the present status of exsolution materials for SOFC applications is reported, including a description of the fundamental concepts behind metal incorporation in oxide lattices, a listing of proposed mechanisms and thermodynamics of the exsolution process and a discussion on the catalytic properties of the resulting materials. Prospects and opportunities to use materials produced by exsolution for SOFC are discussed.