Nanoparticle Exsolution on Perovskite Oxides:Insights into Mechanism,Characteristics and Novel Strategies

Supported nanoparticles have attracted considerable attention as a promising catalyst for achieving unique properties in numerous applications,including fuel cells,chemical conversion,and batteries.Nanocatalysts demonstrate high activity by expanding the number of active sites,but they also intensify deactivation issues,such as agglomeration and poisoning,simultaneously.Exsolution for bottomup synthesis of supported nanoparticles has emerged as a breakthrough technique to overcome limitations associated with conventional nanomaterials.Nanoparticles are uniformly exsolved from perovskite oxide supports and socketed into the oxide support by a one-step reduction process.Their uniformity and stability,resulting from the socketed structure,play a crucial role in the development of novel nanocatalysts.Recently,tremendous research efforts have been dedicated to further controlling exsolution particles.To effectively address exsolution at a more precise level,understanding the underlying mechanism is essential.This review presents a comprehensive overview of the exsolution mechanism,with a focus on its driving force,processes,properties,and synergetic strategies,as well as new pathways for optimizing nanocatalysts in diverse applications.

Tuning exsolution of nanoparticles in defect engineered layered perovskite oxides for efficient CO_(2) electrolysis

Solid oxide electrolysis cell(SOEC) could be a potential technology to afford chemical storage of renewable electricity by converting water and carbon dioxide.In this work,we present the Ni-doped layered perovskite oxides,(La_(4)Sr_(n-4))_(0.9)Ti_(0.9n)Ni_(0.1n)O_(3n+2) with n=5,8,and 12(LSTNn) for application as catalysts of CO_(2) electrolysis with the exsolution of Ni nanoparticles through a simple in-situ growth method.It is found that the density,size,and distribution of exsolved Ni nanoparticles are determined by the number of n in LSTNn due to the different stack structures of TiO_6 octahedra along the c axis.The Ni doping in LSTNn significantly improved the electrochemical activity by increasing oxygen vacancies,and the Ni metallic nanoparticles afford much more active sites.The results show that LSTNn cathodes can successfully be manipulated the activity by controlling both the n number and Ni exsolution.Among these LSTNn(n=5,8,and 12),LSTN8 renders a higher activity for electrolysis of CO_(2) with a current density of 1.50A cm^(-2)@2.0 V at 800℃ It is clear from these results that the number of n in(La_(4)Sr_(n-4))_(0.9)Ti_(0.9n)Ni_(0.1n)O_(3n+2)with Ni-doping is a key factor in controlling the electrochemical performance and catalytic activity in SOEC.

Boosting oxygen reduction activity and CO_(2) resistance on bismuth ferrite-based perovskite cathode for low-temperature solid oxide fuel cells below 600℃

Developing efficient and stable cathodes for low-temperature solid oxide fuel cells(LT-SOFCs) is of great importance for the practical commercialization.Herein,we propose a series of Sm-modified Bi_(0.7-x)Sm_xSr_(0.3)FeO_(3-δ) perovskites as highly-active catalysts for LT-SOFCs.Sm doping can significantly enhance the electrocata lytic activity and chemical stability of cathode.At 600℃,Bi_(0.675)Sm_(0.025)Sr_(0.3)FeO_(3-δ)(BSSF25) cathode has been found to be the optimum composition with a polarization resistance of 0.098 Ω cm^2,which is only around 22.8% of Bi_(0.7)Sr_(0.3)FeO_(3-δ)(BSF).A full cell utilizing BSSF25 displays an exceptional output density of 790 mW cm^(-2),which can operate continuously over100 h without obvious degradation.The remarkable electrochemical performance observed can be attributed to the improved O_(2) transport kinetics,superior surface oxygen adsorption capacity,as well as O_(2)p band centers in close proximity to the Fermi level.Moreover,larger average bonding energy(ABE) and the presence of highly acidic Bi,Sm,and Fe ions restrict the adsorption of CO_(2) on the cathode surface,resulting in excellent CO_(2) resistivity.This work provides valuable guidance for systematic design of efficient and durable catalysts for LT-SOFCs.

Boosting the oxygen evolution reaction through migrating active sites from the bulk to surface of perovskite oxides

The oxygen evolution reaction (OER) dominates the efficiency of electrocatalytic water splitting owing to its sluggish kinetics.Perovskite oxides (ABO_(3)) have emerged as promising candidates to accelerate the OER process owing to their high intrinsic activities and tailorable properties.Fe ions in perovskite oxides have been proved to be a highly catalytic element for OER,while some Fe-based perovskites such as SrTi_(0.8)Fe_(0.2)O_(3-δ)(STF) and La_(0.66)Ti_(0.8)Fe_(0.2)O_(3-δ)(LTF) exhibit inferior OER activity.Yet the essential reason is still unclear and the effective method to promote the activity of such perovskite is also lacking.Herein,an in-situ exsolution strategy was proposed to boost the OER by migrating Fe from the bulk to the surface.Significantly enhanced OER activity was achieved on STF and LTF perovskites with surfacedecorated oxygen vacancies and Fe nanoparticles.In addition,theoretical calculation confirmed that the oxygen vacancies and Fe nanoparticle on surface could lower the overpotential of OER by facilitating the adsorption of OH^(-).From this study,migration of the active elements in perovskite is found to be an effective strategy to increase the quantity and activity of active sites,providing new insights and understanding for designing efficient OER catalysts.

Different oxidation routes for lattice oxygen recovery of double-perovskite type oxides LaSrFeCoO6 as oxygen carriers for chemical looping steam methane reforming

Double-perovskite type oxide LaSrFeCoO_6(LSFCO) was used as oxygen carrier for chemical looping steam methane reforming(CL-SMR) due to its unique structure and reactivity. Two different oxidation routes,steam-oxidation and steam-air-stepwise-oxidation, were applied to investigate the recovery behaviors of the lattice oxygen in the oxygen carrier. The characterizations of the oxide were determined by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), hydrogen temperature-programmed reduction(H_2-TPR) and scanning electron microscopy(SEM). The fresh sample LSFCO exhibits a monocrystalline perovskite structure with cubic symmetry and high crystallinity, except for a little impurity phase due to the antisite defect of Fe/Co disorder. The deconvolution distribution of XPS patterns indicated that Co,and Fe are predominantly in an oxidized state(Fe^(3+) and Fe^(2+)) and(Co^(2+) and Co^(3+)), while O 1s exists at three species of lattice oxygen, chemisorbed oxygen and physical adsorbed oxygen. The double perovskite structure and chemical composition recover to the original state after the steam and air oxidation, while the Co ion cannot incorporate into the double perovskite structure and thus form the CoO just via individual steam oxidation. In comparison to the two different oxidation routes, the sample obtained by steam-oxidation exhibits even higher CH_4 conversion, CO and H_2 selectivity and stronger hydrogen generation capacity.

Effect of Preparation Method on Catalytic Properties of Double Perovskite Oxides LaSrFeMo_0.9Co_0.1O₆for Methane Combustion

The double perovskite oxides LaSrFeMo0.9Co0.1O6 was prepared by co-precipitation method and sol-gel method. The title catalysts were calcined at 800°C and characterized by XRD H2-TPR, SEM and TG-DTA techniques. The catalytic activity was evaluated for methane combustion. The specific surface area of them was calculated by BET model. The samples exhibit significant catalytic activity for methane combustion at 800°C. Upon calcination at 800°C, the LaSrFeMo0.9Co0.1O6 prepared by sol-gel method retains a specific surface area of 24 m2.g-1 and shows an excellent activity for methane combustion (the conversion of 10% and 90% are obtained at 505°C and 660°C, respectively).

Phase Behavior and Crystal Structure of Perovskite-Type Rare Earth Complex Oxides

Several compounds of rare earth complex oxides containing manganese and titanium were synthesized in Ar, and their crystal structures were analyzed by powder X-ray diffraction data and Rietveld method. Structures of A 0.67 Ln 0.33 Mn 0.33 Ti 0.67 O3 （A=Ca or Sr and Ln=rare earth） were found to have orthorhombic symmetry with the space group Pnma, and their interatomic distances and bond angles were obtained. This space group was also derived from electron microscopic study. Electrical conductivity of Ca 0.67 Ln 0.33 Mn 0.33 Ti 0.67 O3 for several rare earth elements showed a semiconducting property with the activation energy of 0.4 eV. Some of these compounds of the strontium system show the antiferromagnetic properties below 10 K.

Preparation and properties of K_2NiF_4-type perovskite oxides La_2NiO_4 catalysts for steam reforming of ethanol

The performance of La2NiO4 perovskite catalysts,prepared using a citric acid complexation method,for the steam reforming of ethanol was studied.The catalysts were characterized by X-ray diffractometry(XRD),specific surface area measurements(BET),thermogravimetric analysis(TGA)and scanning electron microscopy(SEM).The experimental results show that the calcination temperature and the amount of citric acid(CA)have a significant influence on the characteristics of the catalysts and their catalytic activity.Among the catalysts tested,the La2NiO4 catalyst calcined at 700 ℃withn(La):n(Ni):n(CA)of 2:1:3 exhibits the best activity and excellent stability as well as very low coke formation.

Comparison of LaFeO_3,La_(0.8)Sr_(0.2)FeO_3,and La_(0.8)Sr_(0.2)Fe_(0.9)CO_(0.1)O_3 perovskite oxides as oxygen carrier for partial oxidation of methane

LaFeO 3, La 0.8 Sr 0.2 FeO 3, 和 La 0.8 Sr 0.2 Fe 0.9 公司 0.1 O 3 perovskite 氧化物被连续流动反应和顺序的氧化还原作用反应作为为当气体的氧不在时的甲烷的部分氧化的氧搬运人调查。甲烷被 perovskite 氧化物的氧种类当气体的氧不在时与高选择氧化到 syngas。顺序的氧化还原作用反应表明在氧化还原作用反应的结构的稳定性和连续的氧供应在 La 0.8 Sr 0.2 Fe 0.9 公司 0.1 O 3 氧化物，当时 LaFeO 3 和 La 0.8 Sr 0.2 FeO 3 展出了优秀结构的稳定性和连续的氧供应。

Review of magnetocaloric effect in perovskite-type oxides

We survey the magnetocaloric effect in perovskite-type oxides (including doped ABO 3-type manganese oxides, A3B2O7-type two-layered perovskite oxides, and A2B'B''O6-type ordered double-perovskite oxides). Magnetic entropy changes larger than those of gadolinium can be observed in polycrystalline La1-xCaxMnO3 and alkali-metal (Na or K) doped La0.8Ca0.2MnO3 perovskite-type manganese oxides. The large magnetic entropy change produced by an abrupt reduction of magnetization is attributed to the anomalous thermal expansion at the Curie temperature. Considerable magnetic entropy changes can also be observed in two-layered perovskites La1.6Ca1.4Mn2O7 and La2.5-xK0.5+xMn2O7+δ (0 < x < 0.5), and double-perovskite Ba2Fe1+xMo1-xO6 (0 ≤ x ≤ 0.3) near their respective Curie temperatures. Compared with rare earth metals and their alloys, the perovskite-type oxides are lower in cost, and they exhibit higher chemical stability and higher electrical resistivity, which together favor lower eddy-current heating. They are potential magnetic refrigerants at high temperatures, especially near room temperature.

Partial Oxidation of Methane Over the Perovskite Oxides

Ba0.5Sr0.5Co0.8Fe0.2O3-?and Ba0.5Sr0.5Co0.8Ti0.2O3- oxides were synthesized by a combined EDTA-citrate complexing method. The catalytic behavior of these two oxides with the perovskite structure was studied during the reaction of methane oxidation. The pre-treatment with methane has different effect on the catalytic activities of both the oxides. The methane pre-treatment has not resulted in the change of the catalytic activity of BSCFO owing to its excellent reversibility of the perovskite structure resulting from the excellent synergistic interaction between Co and Fe in the oxide. However, the substitution with Ti on Fe-site in the lattice makes the methane pre-treatment have an obvious influence on the activity of the formed BSCTO oxide.

Reviewing perovskite oxide sites influence on electrocatalytic reactions for high energy density devices

Batteries,fuel cells,and supercapacitors are electrochemical devices already on the market and still need a boost in kinetics to match the high energy density demand of applications.Perovskites have attracted the scientific community's attention in the last decade due to their electrocatalytic activity,chemical and structural properties,tunability,low cost,and scalability.Efforts have been made to understand the active sites and the operational mechanisms in perovskite oxides to shape them as an electrocatalyst in advanced energy devices.Understanding the role of perovskites is the key to engineering more controlled and efficient electrocatalysts via chemical synthesis,and there is still much to do.This review highlights the use of perovskites in different energy storage and conversion systems.The A,B,and A&B doping-site effects are analyzed to understand the opportunities and challenges related to this class of materials.In addition,the synthesis methods and the properties related to the doping site are described and summarized.

Perovskite Oxides in Catalytic Combustion of Volatile Organic Compounds:Recent Advances and Future Prospects

Volatile organic compounds are a kind of important indoor and outdoor air pollutants.In recent years,more and more attention has been paid to the ways of volatile organic compound elimination because of its potential long-term effects on human health.Among the various available methods for volatile organic compound elimination,the catalytic combustion is the most attractive method due to its high efficiency,low cost,simple operation,and easy scale-up.Perovskite oxides,as a large family of metal oxides with their A-site mainly of lanthanide element and/or alkaline earth metal element and B-site of transition metal element,have been extensively investigated as active and stable catalysts for volatile organic compound removal reactions due to their abundant compositional elements,high thermal/chemical stability,and compositional/structural flexibility.The catalytic performance of perovskite oxides is strongly depended on its material composition,morphology,and surface/bulk properties,while the doping,tailored synthesis route,and composite construction may have a significant effect on the bulk(oxygen vacancy concentration,lattice structure),surface(oxygen species,defect)properties,and particulate morphology,consequently the catalytic activity and stability for volatile organic compound removal.Herein,a comprehensive review about the recent advances in perovskite oxides for volatile organic compound elimination reactions based on catalytic combustion is presented from different aspects with a special emphasis on the material design strategies,such as compositional tuning,morphology control,nanostructure building,hybrid construction,and surface modification.At last,some perspectives are presented on the development and design of perovskite oxide-based catalysts for volatile organic compound removal applications by highlighgting the critical issues and challenges.

Rapid and durable oxygen reduction reaction enabled by a perovskite oxide with self-cleaning surface

The growth of electrochemically inert segregation layers on the surface of solid oxide fuel cell cathodes has become a bottleneck restricting the development of perovskite-structured oxygen reduction catalysts.Here,we report a new discovery in which enriched Ba and Fe ions on the near-surface of Nd_(1/2)Ba_(1/2)Co_(1/3)Fe_(1/3)Mn_(1/3)O_(3-δ)spontaneously agglomerate into dispersed Ba_(5)Fe_(2)O_(8) nanoparticles and maintain a highly active and durable perovskite structure on the surface.This unique surface selfcleaning phenomenon is related to the low average potential energy of Ba_(5)Fe_(2)O_(8),which is grown on the near-surface layer.The electrochemically inert Ba_(5)Fe_(2)O_(8) segregation layer on the near-surface of the perovskite catalyst achieves self-cleaning by regulating the formation energy of enriched metal oxides.This self-cleaned perovskite surface exhibits an ultrafast oxygen exchange rate,high catalytic activity for the oxygen reduction reaction,and good adaptability to the actual working conditions of solid oxide fuel cell stacks.This study paves a new way for overcoming the stubborn problem of perovskite catalyst surface deactivation and enriches the scientific knowledge of surface catalysis.

Adjusting oxygen vacancies in perovskite LaCoO_(3)by electrochemical activation to enhance the hydrogen evolution reaction activity in alkaline condition

Developing highly-active,earth-abundant non-precious-metal catalysts for hydrogen evolution reaction(HER)in alkaline solution would be beneficial to sustainable energy storage.Perovskite oxides are generally regarded as low-active HER catalysts,due to their inapposite hydrogen adsorption and water dissociation.Here,we report a detailed study on perovskite LaCoO_(3)epitaxial thin films as a model catalyst to significantly enhance the HER performance via an electrochemical activation process.As a result,the overpotential for the activation films to achieve a current density of 0.36 m A/cm^(2)is 238 m V,reduced by more than 200 m V in comparison with that of original samples.Structural characterization revealed the activation process dramatically increases the concentration of oxygen vacancies(Vo)on the surface of LaCoO_(3).We established the relationship between the electronic structure induced by Vo and the enhanced HER activity.Further theoretical calculations revealed that the Vo optimizes the hydrogen adsorption and dissociation of water on the surface of LaCoO_(3)thin films,thus improving the HER catalytic activity.This work may promote a deepened understanding of perovskite oxides for HER mechanism by Vo adjusting and a new avenue for designing highly active electrochemical catalysts in alkaline solution.

Spontaneous decoration of ionic compounds at perovskite interfaces to achieve 23.38% efficiency with 85% fill factor in NiO_X-based perovskite solar cells

Inorganic hole transport materials, particularly NiO_X, have shown considerable promise in boosting the efficiency and stability of perovskite solar cells. However, a major barrier to commercialization of NiO_X-based perovskite solar cells with positive-intrinsic-negative architectures is their direct contact with the absorbing layer, which can lead to losses of photovoltage and fill factor. Furthermore, highly positive under-coordinated Ni cations degrade the perovskite at the interface. Here, we address these issues with the use of an ionic compound(QAPyBF_(4)) as an additive to passivate defects throughout the perovskite layer and improve carrier conduction and interactions with under-coordinated Ni cations. Specifically,the highly electronegative inorganic anion [BF_(4)]~- interacts with the NiO_x/perovskite interface to passivate under-coordinated cations(Ni^(≥3+)). Accordingly, the decorated cells achieved a power conversion efficiency of 23.38% and a fill factor of 85.5% without a complex surface treatment or NiO_X doping.

In operando-formed interface between silver and perovskite oxide for efficient electroreduction of carbon dioxide to carbon monoxide

Electrochemical carbon dioxide(CO_(2))reduction(ECR)is a promising technology to produce valuable fuels and feedstocks from CO_(2).Despite large efforts to develop ECR catalysts,the investigation of the catalytic performance and electrochemical behavior of complex metal oxides,especially perovskite oxides,is rarely reported.Here,the inorganic perovskite oxide Ag-doped(La_(0.8)Sr_(0.2))_(0.95)Ag_(0.05)MnO_(3-δ)(LSA0.05M)is reported as an efficient electrocatalyst for ECR to CO for the first time,which exhibits a Faradaic efficiency(FE)of 84.3%,a remarkable mass activity of 75Ag^(-1)(normalized to the mass of Ag),and stability of 130 h at a moderate overpotential of 0.79 V.The LSA0.05M catalyst experiences structure reconstruction during ECR,creating the in operando-formed interface between the perovskite and the evolved Ag phase.The evolved Ag is uniformly distributed with a small particle size on the perovskite surface.Theoretical calculations indicate the reconstruction of LSA0.05M during ECR and reveal that the perovskite-Ag interface provides adsorption sites for CO_(2) and accelerates the desorption of the*CO intermediate to enhance ECR.This study presents a novel high-performance perovskite catalyst for ECR andmay inspire the future design of electrocatalysts via the in operando formation of metal-metal oxide interfaces.

Regulation of excitation energy transfer in Sb-alloyed Cs_(4)MnBi_(2)Cl_(12) perovskites for efficient CO_(2) photoreduction to CO and water oxidation toward H_(2)O_(2)

Lead(Pb)-free halide perovskites have recently attracted increasing attention as potential catalysts for CO_(2) photoreduction to CO due to their potential to capture solar energy and drive catalytic reaction.However,issues of the poor charge transfer still remain one of the main obstacles limiting their performance due to the overwhelming radiative and nonradiative charge-carrier recombination losses.Herein,Pb-free Sb-alloyed all-inorganic quadruple perovskite Cs_(4)Mn(Bi_(1-x)Sb_(x))_(2)Cl_(12)(0≤x≤1)is synthesized as efficient photocatalyst.By Sb alloying,the undesired relaxation of photogenerated electrons from conduction band to emission centers of[MnCl6]^(4-)is greatly suppressed,resulting in a weakened PL emission and enhanced charge transfer for photocatalyst.The ensuing Cs_(4)Mn(Bi_(1-x)Sb_(x))_(2)Cl_(12) photocatalyst accomplishes efficient conversion of CO_(2)into CO,accompanied by a surprising production of H_(2)O_(2),a high valueadded product associated with water oxidation.By optimizing Sb^(3+) concentration,a high CO evolution rate of 35.1μmol g^(-1)h^(-1)is achieved,superior to most other Pb and Pb-free halide perovskites.Our findings provide new insights into the mixed-cation alloying strategies for improved photocatalytic performance of Pb-free perovskites and shed light on the rational design of robust band structure toward efficient energy transfer.

卷取温度对DP钢热轧板表面氧化影响的研究

Si含量0.5%左右的DP钢在成品工序常发生表面色差类缺陷,原因之一为热轧期间表面氧化铁皮残留在酸洗阶段难以彻底去除,而影响酸洗效率的原因中包含了热轧板氧化层组成、厚度等,这些受到热轧终轧温度、卷取温度、冷却速率等工艺参数的影响。从卷取温度对DP钢热轧板表面氧化的影响入手,重点研究不同卷取温度下DP钢热轧板表面氧化层厚度、富Si层厚度以及氧化层构成等,通过SEM和XRD检验手段证明降低卷取温度可以降低氧化层和富Si层厚度,并改善氧化层构成,有利于提高酸洗效率。

Ca_(2)Fe_(2)O_(5)催化剂对半焦基DC-SOFC性能的影响

半焦与CO_(2)的气化反应速率是影响半焦燃料基DC-SOFC电池性能的关键。为提高半焦的CO_(2)气化反应性,采用柠檬酸溶胶-凝胶法制备了具有钙钛矿结构的Ca_(2)Fe_(2)O_(5)催化剂,用SEM、XRD、XPS、低温氮气吸脱附等分析手段研究了Ca_(2)Fe_(2)O_(5)催化剂的形貌和结构,采用热重分析实验研究Ca_(2)Fe_(2)O_(5)催化剂对半焦燃料的CO_(2)气化反应催化活性;在Ag-GDC|YSZ|GDC-Ag电解质支撑电池系统上,研究了添加Ca_(2)Fe_(2)O_(5)催化剂对半焦燃料基DC-SOFC输出性能的影响。结果表明,随着催化剂焙烧温度的提高,Ca_(2)Fe_(2)O_(5)催化剂晶粒尺寸逐渐增大、比表面积降低,750℃焙烧的催化剂具有良好的分散性、颗粒尺寸约为0.1μm,在半焦的CO_(2)气化反应中催化作用最好;相较于CaO和Fe2O3,Ca_(2)Fe_(2)O_(5)催化剂结构中吸附氧浓度更高,在半焦的CO_(2)气化反应中表现出更为优异的催化活性;Ca_(2)Fe_(2)O_(5)催化剂的循环稳定性取决于催化剂结构的热稳定性,其循环使用时活性降低主要归因于半焦燃料中无机灰分的包裹。催化剂对DC-SOFC输出性能影响表明,当半焦中添加10%的Ca_(2)Fe_(2)O_(5)催化剂时,电池的峰值功率密度从15.3 mW/cm^(2)增大到23.7 mW/cm^(2);EIS分析表明阳极传质阻力是影响DC-SOFC输出性能和燃料利用率的主要因素,降低灰分、催化剂累积带来的传质阻力可有效提高电池寿命和燃料利用率。