Supported nanoparticles fabricated by an ex-solution process from perovskite scaffolds serve promising capabilities for various thermal and electrochemical reactions. Although the size distribution of the nanoparticles plays a crucial role in catalysis, it remains difficult to control in ex-solution due to the lack of understanding of their underlying energetic factors. Here, we investigate the impact of B-site doping in two different types of perovskite hosts (A2+B4+O3 and A3+B3+O3) on the size distribution of ex-solved nanoparticles. By incorporating non-reducible ions at the B-site, we observe the variations in nanoparticles' sizes and densities using model cleaved surfaces of ceramic pellets. Density functional theory calculations help correlate the observed experimental results with the computed energetic descriptors, providing deeper insights into the particle ex-solution and enabling the description of particle density via a first-order nucleation model. Furthermore, we utilize the tailored ex-solution materials as catalysts for N2O decomposition, and it exhibits a volcano-plot relationship between the catalytic activity and size distribution of ex-solution particles. It suggests that our findings can provide an alternative way to optimizing catalytic active sites for various environmental and energy applications.

Surface cation segregation, specifically strontium (Sr), has been identified as a primary factor contributing to the performance degradation of perovskite-based oxide electrodes used in various energy conversion devices. However, due to the complex chemistry and structure of the perovskite oxide surfaces, the mechanisms behind surface segregation and its impact on electrode activity are only partially understood. Moreover, this phenomenon occurs during perovskite synthesis, further complicating the situation. To address this issue, this study implements a controlled approach using a model thin film system composed of SrTi0.5Fe0.5O3-δ (STF50) with a stoichiometric surface and atomically flat terraces, enabling detailed examination. The evolution of surface structure, composition, and oxygen exchange kinetics are observed as a function of temperature and time. By integrating experiments and ab initio simulations, we tackle several fundamental questions, including the evaluation of reactivity for pristine perovskite oxide surface before surface segregation and the correlation between surface segregation at the surface with oxygen exchange kinetics. Our comprehensive analysis clearly reveals that the decline in performance of the perovskite oxide electrodes is primarily attributed to the detrimental effects of Sr-deficiency on the surface, thereby resolving longstanding debates in the field.

Rational engineering of the surfaces of heterogeneous catalysts (especially the surfaces of supported metals) can endow intriguing catalytic functionalities for electrochemical reactions. However, it often requires complicated steps, and even if it does not, breaking the trade-off between activity and stability is quite challenging. Herein, we present a strategy for reconstructing supported catalysts via in situ growth of metallic nanolayers from the perovskite oxide support. When Ru-coated LaFe0.9Co0.1O3 is thermally reduced, the CoFe nanoalloy spontaneously migrates onto the Ru and greatly increases the physicochemical stability of Ru in alkaline water electrolysis. Benefiting from an 81% reduction in Ru dissolution after decoration, it operates for over 200 h without noticeable degradation. Furthermore, the underlying Ru modifies the electronic structure and surface adsorption properties of the CoFe overlayer toward reaction intermediates, synergistically catalyzing both the oxygen evolution reaction and the hydrogen evolution reaction. Specifically, the mass activity of the oxygen evolution reaction is 64.1 times greater than that of commercial RuO2. Our work highlights a way to protect inherently unstable Ru from dissolution while allowing it to influence surface kinetics from the subsurface sites in heterogeneous catalysts.

It is indicated that water can be an active motif for nanoparticle ex-solution. Yet, only a handful of studies are available, if possible, limited to the elemental composition of Ba(Co,Fe,Zr,Y)O3-delta as a mother oxide. Here we prove the versatility of water-mediated ex-solution by expanding the perovskite palettes. Among these, our selected composition (i.e., Ag ex-solved Ba0.95Ag0.05Co0.8Nb0.1Ta0.1O3-delta, e-BACNT) is demonstrated as an oxygen electrode material for protonic ceramic electrochemical cells, promoting efficient reversible fuel-power generation. Thereby, a peak power density of similar to 1.81 W cm-2 and water-splitting current density of similar to 2.93 A cm-2 at 1.3 V and 650 degrees C are achieved within a single cell. Apart from its notable cell performances, this work unveils new opportunities for creating functional metal-oxide heterointerfaces.

Supported nanoparticles incorporating catalytically attractive nonmetal elements have gained significant attention as a promising strategy for enhancing catalytic activity in various industrial applications. This study presents an innovative one-pot synthesis method for fabricating hybrid catalysts, which simultaneously modifies surface properties through the precipitation of nanoparticles with the concurrent incorporation of nonmetal elements. The underlying concept is to synchronize the temperature required for particle formation with that of nonmetal incorporation by adjusting the oxygen chemical potential of the host oxide. As a case study, Ir- and Ru-doped WO3 are selected as the starting material, with phosphorus (P) as the representative nonmetal for surface functionalization. Notably, the hybrid catalyst, composed of amorphous (Ir,Ru)Px particles dispersed on P-rich WO2.9 sheets, is synthesized through a single heat treatment at 500 °C, avoiding undesirable sintering of the host material. When used as a hydrogen evolution catalyst, this material exhibits outstanding mass activity, durability, compared to state-of-the-art Pt/C catalysts. Density functional theory calculations further reveal that the superior performance of the hybrid catalysts attributes to improved water dissociation and favorable adsorption and desorption of key reaction intermediates. This novel synthesis strategy offers considerable potential for advancing diverse areas of heterogeneous catalysis.

In this study, we identify the local structures of ex-solved nanoparticles using machine-learned potentials (MLPs). We develop a method for training machine-learned potentials by sampling local structures of heterointerface configurations as a training set with its efficacy tested on the Ni/MgO system, illustrating that the error in interface energy is only 0.004 eV/Å2. Using the developed scheme, we train an MLP for the Ni/La0.5Ca0.5TiO3 ex-solution system and identify the local structures for both exo- and endo-type particles. The established model aligns well with the experimental observations, accurately predicting a nucleation size of 0.45 nm. Lastly, the density functional theory calculations on the established atomistic model verify that the kinetic barrier for the dry reforming of methane are substantially reduced by 0.49 eV on the ex-solved catalysts compared to that on the impregnated catalysts. Our findings offer insights into the local structures, growth mechanisms, and underlying origin of the catalytic properties of ex-solved nanoparticles.

Ex-solution catalysts containing spontaneously formed metal nanoparticles socketed on the surface of reservoir oxides have recently been employed in various research fields including catalysis and sensing, due to the process efficiency and outstanding chemical/thermal stability. However, since the ex-solution process accompanies harsh reduction heat treatment, during which many oxides undergo phase decomposition, it restricts material selection and further advancement. Herein, we propose an elaborate design principle to uniformly functionalize ex-solution catalysts at porous oxide frameworks via an electrospinning process. As a case study, we selected the ex-solved La0.6Ca0.4Fe0.95Co0.05-xNixO3-δ (x = 0, 0.025 and 0.05) and SnO2 nanofibers as ex-solution hybrids and main frameworks, respectively. We confirmed superior dimethyl sulfide (C2H6S) gas sensing characteristics with excellent long-cycling stability. In particular, the high catalytic activities of ex-solved CoNiFe ternary nanoparticles, strongly socketed on reservoir oxide, accelerate the spillover process of O2 to dramatically enhance the response toward sulfuric analytes with exceptional tolerance. Altogether, our contribution represents an important stepping-stone to a rational design of ex-solved particle-reservoir oxide hybrids functionalized on porous oxide scaffolds for a variety of applications.

Deformable semi-solid liquid metal particles (LMP) have emerged as a promising substitute for rigid conductive fillers due to their excellent electrical properties and stable conductance under strain. However, achieving a compact and robust coating of LMP on fibers remains a persistent challenge, mainly due to the incompatibility of conventional coating techniques with LMP. Additionally, the limited durability and absence of initial electrical conductivity of LMP restrict their widespread application. In this study, we propose a solution process that robustly and compactly assembles mechanically durable and initially conductive LMP on fibers. Specifically, we present a shearing-based deposition of polymer-attached LMP followed by additional coating with CNT-attached LMP to create bi-layer LMP composite with exceptional durability, electrical conductivity, stretchability, and biocompatibility on various fibers. The versatility and reliability of this manufacturing strategy for 1D electronics are demonstrated through the development of sewn electrical circuits, smart clothes, stretchable biointerfaced fiber, and multifunctional fiber probes.

Chemical looping reforming coupled with CO2 splitting is a promising CO2 utilization method that produces a valuable fuel. Here, we present a novel perovskite oxide with the composition of La0.6Ca0.4Fe0.95M0.05O3-delta (M = Ni, Co, Ni-Co) that functions both as an oxygen carrier and as a redox catalyst. Using a multi technique approach with HR-TEM, XRD, XAS, and Mossbauer spectroscopy, we find that alloy nanoparticles spontaneously form on the surface of Ni-Co doped carriers in a CH4 atmosphere, and as they are repeatedly exposed to CO2 and CH4 during the chemical loop, Fe atoms move back and forth between the inside (as Fe cations in the lattice) and the outside (as a part of metallic alloy) of the host scaffold. Eventually, the co-doped samples become highly reactive towards both gases and have excellent coking and redox stability, demonstrating record-level syngas yield (total similar to 10 mmol/g) at 850 degrees C, over 50 redox cycles.

An universal oxygen-electrode, compatible to both oxygen- and proton-conducting solid oxide electrochemical cells (O-SOCs and H-SOCs, respectively), as well as for electricity and hydrogen production purpose is showcased.

Ex-solution catalysts, in which a host oxide is decorated with confined metallic nanoparticles, have exhibited breakthrough activity in various catalytic reactions. However, catalysts prepared by conventional ex-solution processes are limited by the low surface area of host oxides, the limited solubility of dopants, and the incomplete conversion of doped cations into metal catalysts. Here, the design of the host oxide structure is reconceptualized using a metal-organic framework (MOF) as an oxide precursor that can absorb a large quantity of ions while also promoting ex-solution at low temperatures (400-500 °C). The MOF-derived metal oxide host can readily incorporate metal cations, from which catalytic nanoparticles can be uniformly ex-solved owing to the short diffusion length in the nano-sized oxides. The distinct ex-solution behaviors of Pt, Pd, and Rh, and their bimetallic combinations are investigated. The MOF-driven mesoporous ZnO particles functionalized with PdPt catalysts ex-solved at 500 °C show benchmark-level of acetone oxidation activity as well as acetone-sensing characteristics by accelerating both oxygen chemisorption and acetone dissociation. Their findings provide a new route for the preparation of highly active catalysts by engineering the architecture and composition of the host oxide to facilitate the ex-solution process rationally.

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.

The lack of bifunctional features of perovskite oxide toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) significantly limits its use as a cathode catalyst for rechargeable Zn-air batteries (ZABs). Thus far, numerous techniques to disperse additional catalysts on a perovskite host have been suggested to overcome this problem; however, cost-effectiveness and catalyst lifespan remain unsatisfactory. Herein, we present cobalt-based-nanoparticle-decorated Sr0.95Nb0.1Co0.7Fe0.2O3-delta (S0.95NCF) by a simple ex-solution method and use it as a novel air-electrode catalyst. We successfully implemented the socketed nanoparticles with various compositions at different reduction temperatures, achieving notably enhanced activity towards OER and ORR. More importantly, the newly designed catalyst exhibits record-high charge/discharge durability over 500 h (or 1500 consequent cycles) when used as the ZABs cathode. Our findings provide essential guidelines for designing heterostructured electrocatalysts for future energy devices, in which multifunctionality is desirable.

Metal oxides possessing distinctive physical/chemical properties due to different crystal structures and stoichiometries play a pivotal role in numerous current technologies, especially heterogeneous catalysis for production/conversion of high-valued chemicals and energy. To date, many researchers have investigated the effect of the structure and composition of these materials on their reactivity to various chemical and electrochemical reactions. However, metal oxide surfaces evolve from their initial form under dynamic reaction conditions due to the autonomous behaviors of the constituent atoms to adapt to the surrounding environment. Such nanoscale surface phenomena complicate reaction mechanisms and material properties, interrupting the clarification of the origin of functionality variations in reaction environments. In this review, the current findings on the spontaneous surface reorganization of metal oxides during reactions are categorized into three types: 1) the appearance of nano-sized second phase from oxides, 2) the (partial) encapsulation of oxide atoms toward supported metal surfaces, and 3) the oxide surface reconstruction with selective cation leaching in aqueous solution. Then their effects on each reaction are summarized in terms of activity and stability, providing novel insight for those who design metal-oxide-based catalytic materials.

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

Schematics of water-mediated ex-solution and accordingly nano-engineered protonic ceramic fuel cell furnished with the water-mediated ex-solution on a cathode and H 2 ex-solution on an anode.

Isovalent doping is a practical solution for ensuring surface stability of Sr-containing perovskite oxides for solid oxide fuel cell O2-electrodes under actual operating conditions.

Tuning of the cation–oxygen bond strength effectively promotes B-site ex-solution in a perovskite, thereby boosting the catalytic activity of CO oxidation.