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A La0.9Ce0.1Mn0.8Ni0.1Cu0.1O3 (LCMNCu) perovskite nanomaterial with in situ-exsolved metallic nanoparticles (Re-LCMNCu) was fabricated successfully and acted as a catalyst for methanol steam reforming. Due to the fine and uniform NiCu alloy nanoparticles (∼35 nm) exsolved from the ceramic substrate, Re-LCMNCu displayed a stable conversion of methanol above 99% at 350 °C and maintained a hydrogen production rate of 285 mmol h–1 gcat–1 for 60 h, with a negligible amount of CO in the outlet gas. The NiCu alloy played an important role in catalytic activity, and the optimal prereduction treatment condition for catalyst activation was determined to be 6 h. Upon further examination, the NiCu alloy partially embedded into the substrate ensured high catalytic performance and the synergy between the NiCu alloy, CeO2 promoter, and perovskite substrate with more oxygen vacancies improved the catalytic activity of Re-LCMNCu catalysts. [ABSTRACT FROM AUTHOR]

We have developed a general route for combining Ni, Fe, Co, Cu, and Pd in a nanoparticle using the exsolution mechanism from LaFe0.7Ni0.1Co0.1Cu0.05Pd0.05O3 perovskite oxide precursors. The strong adherence of the nanoparticles to the support yields attractive catalytic properties for dry methane reforming, such as coke resistance and thermal sintering suppression. The reduction of the precursors at 700 and 900 °C yielded NiCoCuPd or NiFeCoCuPd nanoparticles with a size-dependent phase transition from a complex concentrated alloy to phase-separated heterostructures. Our findings indicate that smaller concentrated alloy nanoparticles (∼10 nm) are more effective for methane activation than larger (>20 nm) phase-separated nanoparticles. [ABSTRACT FROM AUTHOR]

Ammonia has emerged as a promising fuel for solid oxide fuel cells (SOFCs) owing to its high energy density, high hydrogen content, and carbon-free nature. Herein, the electrocatalytic potential of a novel Ni-doped SFM double-perovskite (Sr 1.9 Fe 0.4 Ni 0.1 Mo 0.5 O 6-δ ) is studied, for the first time, as an alternative anode material for symmetrical direct-ammonia SOFCs. Scanning and transmission electron microscopy characterization has revealed the exsolution of Ni-Fe nanoparticles (NPs) from the parent Sr 2 Fe 1.5 Mo 0.5 O 6 under anode conditions, and X-ray diffraction has identified the FeNi 3 phase after exposure to ammonia at 800 °C. The active-exsolved NPs contribute to achieving a maximal ammonia conversion rate of 97.9% within the cell's operating temperatures (550-800 °C). Utilizing 3D-printed symmetrical cells with SFNM-GDC electrodes, the study demonstrates comparable polarization resistances and peak power densities of 430 and 416 mW cm -2 for H 2 and NH 3 fuels, respectively, with long-term stability and a negligible voltage loss of 0.48% per 100 h during ammonia-fed extended galvanostatic operation. Finally, the ammonia consumption mechanism is elucidated as a multistep process involving ammonia decomposition, followed by hydrogen oxidation. This study provides a promising avenue for improving the performance and stability of ammonia-based SOFCs for potential applications in clean energy conversion technologies.

An advanced materials solution utilizing the concept of "smart catalysts" could be a game changer for today's automotive emission control technology, enabling the efficient use of precious metals via their two-way switching between metallic nanoparticle forms and ionic states in the host perovskite lattice as a result of the cyclical oxidizing/reducing atmospheres. However, direct evidence for such processes remains scarce; therefore, the underlying mechanism has been an unsettled debate. Here, we use advanced scanning transmission electron microscopy to reveal the atomic-scale behaviors for a LaFe 0.95 Pd 0.05 O 3 -supported Ir-Pd-Ru nanocatalyst under fluctuating redox conditions, thereby proving the reversible dissolution/exsolution for Ir and Ru but with a limited occurrence for Pd. Despite such selective dissolution during oxidation, all three elements remain cooperatively alloyed in the subsequent reduction, which is a key factor in preserving the catalytic activity of the ternary nanoalloy while displaying its self-regenerating functionality and control of particle agglomeration.

Symmetrical solid oxide cells (SSOCs) have recently gained significant attention for their potential in energy conversion due to their simplified cell configuration, cost-effectiveness, and excellent reversibility. However, previous research efforts have mainly focused on improving the electrode performance of perovskite-type electrodes through different doping strategies, neglecting microstructural optimization. This work presents novel approaches for the nanostructural tailoring of (La 0.8 Sr 0.2 ) 0.95 Fe 1- x Ti x O 3-δ (LSFT x , x = 0.2 and 0.4) electrodes using a single-step spray-pyrolysis deposition process. By incorporating these electrodes into a Ce 0.9 Gd 0.1 O 1.95 (CGO) porous backbone or employing a nanocomposite architecture with nanoscale particle size, we achieved significant improvements in the polarization resistance ( R ) compared with traditional screen-printed electrodes. To further boost the fuel oxidation performance, a Ni-doping strategy, coupled with meticulous microstructural optimization, was implemented. The exsolution of Ni nanoparticles under reducing conditions resulted in remarkable p ) compared with traditional screen-printed electrodes. To further boost the fuel oxidation performance, a Ni-doping strategy, coupled with meticulous microstructural optimization, was implemented. The exsolution of Ni nanoparticles under reducing conditions resulted in remarkable R p values as low as 0.34 and 0.11 Ω cm 2 in air and wet H 2 at 700 °C, respectively. Moreover, an electrolyte-supported cell with symmetrical electrodes demonstrated a stable maximum power density of 617 mW cm -2 at 800 °C. These findings highlight the importance of combining electrode composition optimization with advanced morphology control in the design of highly efficient and durable SSOCs.

Exsolution has emerged as a promising method for generating metallic nanoparticles, whose robustness and stability outperform those of more conventional deposition methods, such as impregnation. In general, exsolution involves the migration of transition metal cations, typically perovskites, under reducing conditions, leading to the nucleation of well-anchored metallic nanoparticles on the oxide surface with particular properties. There is growing interest in exploring alternative methods for exsolution that do not rely on high-temperature reduction via hydrogen. For example, utilizing electrochemical potentials or plasma technologies has shown promising results in terms of faster exsolution, leading to better dispersion of nanoparticles under milder conditions. To avoid limitations in scaling up exhibited by electrochemical cells and plasma-generation devices, we proposed a method based on pulsed microwave (MW) radiation to drive the exsolution of metallic nanoparticles. Here, we demonstrate the H 2 -free MW-driven exsolution of Ni nanoparticles from lanthanum strontium titanates, characterizing the mechanism that provides control over nanoparticle size and dispersion and enhanced catalytic activity and stability for CO 2 hydrogenation. The presented method will enable the production of metallic nanoparticles with a high potential for scalability, requiring short exposure times and low temperatures.

Nanoparticle (NP) exsolution from perovskite-based oxides matrix upon reduction has emerged as an ideal platform for designing highly active catalysts for energy and environmental applications. However, the mechanism of how the material characteristics impacts the activity is still ambiguous. In this work, taking Pr 0.4 Sr 0.6 Co 0.2 Fe 0.7 Nb 0.1 O 3 thin film as the model system, we demonstrate the critical impact of the exsolution process on the local surface electronic structure. Combining advanced microscopic and spectroscopic techniques, particularly scanning tunneling microscopy/spectroscopy and synchrotron-based near ambient X-ray photoelectron spectroscopy, we find that the band gaps of both the oxide matrix and exsolved NP decrease during exsolution. Such changes are attributed to the defect state within the forbidden band introduced by oxygen vacancies and the charge transfer across the NP/matrix interface. Both the electronic activations of oxide matrix and the exsolved NP phase lead to good electrocatalytic activity toward the fuel oxidation reaction at elevated temperature.

The process of exsolution for the synthesis of strongly anchored metal nanoparticles (NPs) on host oxide lattices has been proposed as a promising strategy for designing robust catalyst-support composite systems. However, because conventional exsolution processes occur in harsh reducing environments at high temperatures for long periods of time, the choice of support materials and dopant metals are limited to those with inherently high thermal and chemical stability. Herein, we report the exsolution of a series of noble metal catalysts (Pt, Rh, and Ir) from metal oxide nanofibers (WO 3 NFs) supports in an entirely ambient environment induced by intense pulsed light (IPL)-derived momentary photothermal treatment (>1000 °C). Since the exsolution process spans an extremely short period of time (<20 ms), unwanted structural artifacts such as decreased surface area and phase transition of the support materials are effectively suppressed. At the same time, exsolved NPs (<5 nm) with uniform size distributions could successfully be formed. To prove the practical utility of exsolved catalytic NPs functionalized on WO 3 NFs, the chemiresistive gas sensing characteristics of exsolved Pt-decorated WO 3 NFs were analyzed, exhibiting high durability (>200 cyclic exposures), enhanced response ( R air / R S target gas. Altogether, we successfully demonstrated that ultrafast exsolution within a few milliseconds could be induced in ambient conditions using the IPL-derived momentary photothermal treatment and contributed to expanding the practical viability of the exsolution-based synthetic approaches for the production of highly stable catalyst systems.gas > 800 @ 1 ppm/350 °C), and selectivity toward H 2 S target gas. Altogether, we successfully demonstrated that ultrafast exsolution within a few milliseconds could be induced in ambient conditions using the IPL-derived momentary photothermal treatment and contributed to expanding the practical viability of the exsolution-based synthetic approaches for the production of highly stable catalyst systems.

Exsolution synthesizes self-assembled metal nanoparticle catalysts via phase precipitation. An overlooked aspect in this method thus far is how exsolution affects the host oxide surface chemistry and structure. Such information is critical as the oxide itself can also contribute to the overall catalytic activity. Combining X-ray and electron probes, we investigated the surface transformation of thin-film SrTi 0.65 Fe 0.35 O 3 during Fe 0 exsolution. We found that exsolution generates a highly Fe-deficient near-surface layer of about 2 nm thick. Moreover, the originally single-crystalline oxide near-surface region became partially polycrystalline after exsolution. Such drastic transformations at the surface of the oxide are important because the exsolution-induced nonstoichiometry and grain boundaries can alter the oxide ion transport and oxygen exchange kinetics and, hence, the catalytic activity toward water splitting or hydrogen oxidation reactions. These findings highlight the need to consider the exsolved oxide surface, in addition to the metal nanoparticles, in designing the exsolved nanocatalysts.

The gas sensing characteristics of oxide semiconductors can be enhanced by loading noble metal or metal oxide catalysts. The uniform distribution of nanoscale catalysts with high thermal stability over the sensing materials is essential for sensors operating at elevated temperatures. An in situ exsolution process, which can be applied to catalysts, batteries, and sensors, provides a facile synthetic route for developing second-phase nanoparticles with uniform distribution, excellent thermochemical stability, and strong adhesion to the mother phase. In this study, we investigated the effect of Co-exsolved nanoparticles on the gas sensing characteristics of La 0.43 Ca 0.37 Co 0.06 Ti 0.94 O 3- d (LCCoT). The amount and size of the Co-exsolved nanoparticles on the surface of the perovskite mother phase were adjusted depending on the reduction temperature of the exsolution process. The LCCoT with Co-exsolved nanoparticles prepared by reduction at 700 °C exhibited a response (resistance ratio) of 116.3 to 5 ppm ethanol at 350 °C, which was 10-fold higher than the response of a sensor without exsolution. The high gas response was attributed to the catalytic effect promoted by the uniformly distributed Co-exsolved nanoparticles and the formation of p-n junctions on the sensing surface during reduction. Additionally, we demonstrated the catalytic effect of Co-exsolved nanoparticles using a proton transfer reaction-quadrupole mass spectrometer. By controlling the amount and distribution of exsolved nanoparticles on semiconductor chemiresistors, a new pathway for designing high-performance gas sensors with enhanced thermal stability can be achieved.

Perovskites are promising alternative materials for conventional Ni-based cermet anodes, benefitting from their mixed ionic and electronic conductivity properties and good structure stability. However, they generally show a commonplace electrochemical catalytic activity. Here, a novel anode material La 0.52 Sr 0.28 Ti 0.8 Co 0.1 Fe 0.1 O 3-δ (LSTCF) is successfully synthesized, and we report that the electrochemical performance of LSTCF can be commendably tuned by gas treatment, deriving from the exsolution of the impressively well-distributed Co-Fe alloy nanocatalyst with splendid catalytic activity for hydrogen electrochemical oxidation. At 900 °C, a power density value of 897 mW cm -2 is achieved by the treated LSTCF anode when using hydrogen as fuel, which is almost three times higher than that of the fresh anode. Moreover, we show that the nanoparticle-modified LSTCF perovskite also exhibits fascinating electrochemical catalytic activity at low temperatures.

Symmetry broken configurations within a long-range atomic arrangement exhibit new physical properties, and distinctive strategies are needed to resuscitate the localized symmetry by introducing measured defects, which can be attractive in displaying enhanced catalytic activities for energy applications. Our hypothesis is validated by introducing lattice defects due to the strain originating from a slightly higher doped grain boundary (GB) than at the interconnected grains of perovskite oxide. When Pd is doped at the B-site of ABO 3 -type La 0.7 Sr 0.3 CoO 3-δ , a marginally higher ionic radius of Pd 4+ than Co 3+ enables partial deportation of Pd 4+ to the GB. Consequently, the GB unit cell is relatively expanded with a higher interplanar spacing, as observed by microscopic analysis. When the Pd concentration is increased, oxygen vacancy sites are reduced and both metallic Pd and PdO x are exsolved at the perovskite oxide surface. With the Pd/Co ratio of 0.05, the defects originating from the Pd-modulated GB can be maximized to 1.29 ± 0.21% which enhances the bifunctional O 2 activation ability by lowering the combined overpotential of oxygen evolution and reduction reactions (OER/ORR) to 0.91 V, duly corroborated by computational studies. The fabricated rechargeable Zn-air battery has a specific capacity of 740 mA·h/g Zn (851 mW·h/g Zn ) when discharge is performed at 10 mA/cm 2 . Galvanostatic charge-discharge cycling with a 1 h cycle time shows 60 h stable performance. The OER/ORR bifunctional activity is found to be strongly correlated to the repositioned lattice symmetry at the perovskite GB.

The search for new functional materials that combine high stability and efficiency with reasonable cost and ease of synthesis is critical for their use in renewable energy applications. Specifically in catalysis, nanoparticles, with their high surface-to-volume ratio, can overcome the cost implications associated with otherwise having to use large amounts of noble metals. However, commercialized materials, that is, catalytic nanoparticles deposited on oxide supports, often suffer from loss of activity because of coarsening and carbon deposition during operation. Exsolution has proven to be an interesting strategy to overcome such issues. Here, the controlled emergence, or exsolution, of faceted iridium nanoparticles from a doped SrTiO 3 perovskite is reported and their growth preliminary probed by in situ electron microscopy. Upon reduction of SrIr 0.005 Ti 0.995 O 3 , the generated nanoparticles show embedding into the oxide support, therefore preventing agglomeration and subsequent catalyst degradation. The advantages of this approach are the extremely low noble metal amount employed (∼0.5% weight) and the catalytic activity reported during CO oxidation tests, where the performance of the exsolved SrIr 0.005 Ti 0.995 O 3 is compared to the activity of a commercial catalyst with 1% loading (1% Ir/Al 2 O 3 ). The high activity obtained with such low doping shows the possibility of scaling up this new catalyst, reducing the high cost associated with iridium-based materials.

In situ exsolution of metal nanoparticles (NPs) is emerging as an alternative technique to deliver thermally stable and evenly dispersed metal NPs, which exhibit excellent adhesion with conducting perovskite oxide supports. Here we provide the first demonstration that Ni metal NPs with high areal density (∼175 μm -2 ) and fine size (∼38.65 nm) are exsolved from an A-site-deficient perovskite stannate support (La 0.2 Ba 0.7 Sn 0.9 Ni 0.1 O 3-δ (LBSNO)). The NPs are strongly anchored and impart coking resistance, and the Ni-exsolved stannates show exceptionally high electrical conductivity (∼700 S·cm -1 ). The excellent conductivity is attributed to conduction between delocalized Sn 5s orbitals along with structural improvement toward ABO 3 stoichiometry in the stannate support. We also reveal that experimental conditions with strong interaction must be optimized to obtain Ni exsolution without degrading the perovskite stannate framework. Our finding suggests a unique process to induce the formation of metal NPs embedded in stannate with excellent electrical properties.

Hydrogen (H 2 ) is a clean energy carrier and a major industrial feedstock, e.g., to produce ammonia and methanol. High-purity H 2 can be produced efficiently from methane (CH 4 ) using chemical looping-based approaches. In this work, we report on the development of a calcium-iron-based oxygen carrier (Ca 2 Fe 2 O 5 ) doped with Ni or Cu and investigate its redox performance for H 2 production when CH 4 is used as the fuel. The experimental results suggest that the rapid formation of metallic Ni or Cu through exsolution promotes the reducibility of Ca 2 Fe 2 O 5 with CH 4 . It was found that the reversible exsolution of Ni or Cu nanoparticles and their reincorporation in the Ca 2 Fe 2 O 5 structure is key to avoid particle sintering and deactivation. Having the potential of converting a larger fraction of steam to H 2 than pure iron oxide in addition to its higher reactivity with CH 4 , the doped calcium-iron-based oxygen carrier is a promising material for chemical looping H 2 production.