Maximizing Photoelectrochemical Performance in Metal-Oxide Hybrid Composites via Amorphous Exsolution-A New Exsolution Mechanism for Heterogeneous Catalysis

Exsolution generates metal nanoparticles anchored within crystalline oxide supports, ensuring efficient exposure, uniform dispersion, and strong nanoparticle-perovskite interactions. Increased doping level in the perovskite is essential for further enhancing performance in renewable energy applications; however, this is constrained by limited surface exsolution, structural instability, and sluggish charge transfer. Here, hybrid composites are fabricated by vacuum-annealing a solution containing SrTiO3 photoanode and Co cocatalyst precursors for photoelectrochemical water-splitting. In situ transmission electron microscopy identifies uniform, high-density Co particles exsolving from amorphous SrTiO3 films, followed by film-crystallization at elevated temperatures. This unique process extracts entire Co dopants with complete structural stability, even at Co doping levels exceeding 30%, and upon air exposure, the Co particles embedded in the film oxidize to CoO, forming a Schottky junction at the interface. These conditions maximize photoelectrochemical activity and stability, surpassing those achieved by Co post-deposition and Co exsolution from crystalline oxides. Theoretical calculations demonstrate in the amorphous state, dopant─O bonds become weaker while Ti─O bonds remain strong, promoting selective exsolution. As expected from the calculations, nearly all of the 30% Fe dopants exsolve from SrTiO3 in an H2 environment, despite the strong Fe─O bond's low exsolution tendency. These analyses unravel the mechanisms driving the amorphous exsolution.

Fabrication of Heterostructural FeNi3-Loaded Perovskite Catalysts by Rapid Plasma for Highly Efficient Photothermal Reverse Water Gas Shift Reaction

Metal-semiconductor heterostructured catalysts have attracted great attention because of their unique interfacial characteristics and superior catalytic performance. Exsolution of nanoparticles is one of the effective and simple ways for in-situ growth of metal nanoparticles embedded in oxide surfaces and their favorable dispersion and stability. However, both high-temperature and a reducing atmosphere are required simultaneously in conventional exsolution, which is time-consuming and costly, and particles often agglomerate during the process. In this work, Ca0.9Ti0.8Ni0.1Fe0.1O3-δ (CTNF) is exposed to dielectric blocking discharge (DBD) plasma at room temperature to fabricate alloying FeNi3 nanoparticles from CTNF perovskite. FeNi3-CTNF has outstanding catalytic activity for photothermal reverse water gas shift reaction (RWGS). At 350 °C under full-spectrum irradiation, the carbon monoxide (CO) yield of FeNi3-CTNF (10.78 mmol g-1 h-1) is 11 times that of pure CaTiO3(CTO), and the CO selectivity is 98.9%. This superior catalytic activity is attributed to the narrow band gap, photogenerated electron migration to alloy particles, and abundant surface oxygen vacancies. The carbene pathway reaction is also investigated through in-situ Raman spectroscopy. The present work presents a straightforward method for the exsolution of nanoalloys in metal-semiconductor heterostructures for photothermal CO2 reduction.

Improving the Oxygen Evolution Reaction: Exsolved Cobalt Nanoparticles on Titanate Perovskite Catalyst

Perovskites are an important class of oxygen evolution reaction (OER) catalysts due to highly tunable compositions and adaptable characteristics. However, perovskite-based catalysts can have limited atom utilization efficiency due to large particle size, resulting in low mass activity. Herein, Cobalt nanoparticles are exsolved from La0.2+2x Ca0.7-2x Ti1-x Cox O3 perovskite and applied in OER. Upon reduction in the 5% H2 /N2 atmosphere at 800 °C for 2 h, the Co exsolved perovskite catalyst (R-LCTCo0.11) exhibits optimal OER performance. The mass activity of R-LCTCo0.11 reaches ≈1700 mA mg-1 at an overpotential of 450 mV, which is 17 times and 3 times higher than that of LCTCo0.11 (97 mA mg-1 ) and R-Mix (560 mA mg-1 ) catalysts respectively, surpassing the benchmark catalyst RuO2 (42.7 mA mg-1 of oxide at η = 470 mV). Electrochemical impedance spectroscopy (EIS) data reveals that R-LCTCo0.11 has the lowest charge transfer resistance (Rct  = 58 Ω), demonstrating the highest catalytic and kinetic activity for OER. Furthermore, this catalyst shows high stability during an accelerated durability test of 10 h electrolysis and 1000 cycles cyclic voltammetry (CV). This work demonstrates that nanoparticle exsolution from a doped perovskite is an effective strategy for improving the atom utilization efficiency in OER.

Recent Advances in Iridium-based Electrocatalysts for Acidic Electrolyte Oxidation

Ongoing research to develop advanced electrocatalysts for the oxygen evolution reaction (OER) is needed to address demand for efficient energy conversion and carbon-free energy sources. In the OER process, acidic electrolytes have higher proton concentration and faster response than alkaline ones, but their harsh strongly acidic environment requires catalysts with greater corrosion and oxidation resistance. At present, iridium oxide (IrO2 ) with its strong stability and excellent catalytic performance is the catalyst of choice for the anode side of commercial PEM electrolysis cells. However, the scarcity and high cost of iridium (Ir) and the unsatisfactory activity of IrO2 hinder industrial scale application and the sustainable development of acidic OER catalytic technology. This highlights the importance of further research on acidic Ir-based OER catalysts. In this review, recent advances in Ir-based acidic OER electrocatalysts are summarized, including fundamental understanding of the acidic OER mechanism, recent insights into the stability of acidic OER catalysts, highly efficient Ir-based electrocatalysts, and common strategies for optimizing Ir-based catalysts. The future challenges and prospects of developing highly effective Ir-based catalysts are also discussed.

Enhancing the Electrochemical Performance in Symmetrical Solid Oxide Cells through Nanoengineered Redox-Stable Electrodes with Exsolved Nanoparticles

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 (La0.8Sr0.2)0.95Fe1-xTixO3-δ (LSFTx, x = 0.2 and 0.4) electrodes using a single-step spray-pyrolysis deposition process. By incorporating these electrodes into a Ce0.9Gd0.1O1.95 (CGO) porous backbone or employing a nanocomposite architecture with nanoscale particle size, we achieved significant improvements in the polarization resistance (Rp) 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 Rp values as low as 0.34 and 0.11 Ω cm2 in air and wet H2 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.

Strongly-Interacted NiSe2 /NiFe2 O4 Architectures Built Through Selective Atomic Migration as Catalysts for the Oxygen Evolution Reaction

The interactions between the catalyst and support are widely used in many important catalytic reactions but the construction of strong interaction with definite microenvironments to understand the structure-activity relationship is still challenging. Here, strongly-interacted composites are prepared via selective exsolution of active NiSe2 from the host matrix of NiFe2 O4 (S-NiSe2 /NiFe2 O4 ) taking advantage of the differences of migration energy, in which the NiSe2 possessed both high dispersion and small size. The characteristics of spatially resolved scanning transmission X-ray microscopy (STXM) coupled with analytical Mössbauer spectra for the surface and bulk electronic structures unveiled that this strongly interacted composite triggered more charge transfers from the NiSe2 to the host of NiFe2 O4 while stabilizing the inherent atomic coordination of NiFe2 O4 . The obtained S-NiSe2 /NiFe2 O4 exhibits overpotentials of 290 mV at 10 mA cm-2 for oxygen evolution reaction (OER). This strategy is general and can be extended to other supported catalysts, providing a powerful tool for modulating the catalytic performance of strongly-interacted composites.

Microwave-Driven Exsolution of Ni Nanoparticles in A-Site Deficient Perovskites

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 H2-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 CO2 hydrogenation. The presented method will enable the production of metallic nanoparticles with a high potential for scalability, requiring short exposure times and low temperatures.

Electronic Activation during Nanoparticle Exsolution for Enhanced Activity at Elevated Temperature

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_0.4Sr_0.6Co_0.2Fe_0.7Nb_0.1O₃ 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.

Insights into the Contribution of Oxidation-Reduction Pretreatment for Mn0.2Zr0.8O2-δ Catalyst of CO Oxidation Reaction

A Mn_0.2Zr_0.8O_2-δ mixed oxide catalyst was synthesized via the co-precipitation method and studied in a CO oxidation reaction after different redox pretreatments. The surface and structural properties of the catalyst were studied before and after the pretreatment using XRD, XANES, XPS, and TEM techniques. Operando XRD was used to monitor the changes in the crystal structure under pretreatment and reaction conditions. The catalytic properties were found to depend on the activation procedure: reducing the CO atmosphere at 400-600 °C and the reaction mixture (O₂ excess) or oxidative O₂ atmosphere at 250-400 °C. A maximum catalytic effect characterized by decreasing T₅₀ from 193 to 171 °C was observed after a reduction at 400 °C and further oxidation in the CO/O₂ reaction mixture was observed at 250 °C. Operando XRD showed a reversible reduction-oxidation of Mn cations in the volume of Mn_0.2Zr_0.8O_2-δ solid solution. XPS and TEM detected the segregation of manganese cations on the surface of the mixed oxide. TEM showed that Mn-rich regions have a structure of MnO₂. The pretreatment caused the partial decomposition of the Mn_0.2Zr_0.8O_2-δ solid solution and the formation of surface Mn-rich areas that are active in catalytic CO oxidation. In this work it was shown that the introduction of oxidation-reduction pretreatment cycles leads to an increase in catalytic activity due to changes in the origin of active states.

Exsolution Modeling and Control to Improve the Catalytic Activity of Nanostructured Electrodes

In situ exsolution for nanoscale electrode design has attracted considerable attention because of its promising activity and high stability. However, fundamental research on the mechanisms underlying particle growth remains insufficient. Herein, cation-diffusion-determined exsolution is presented using an analytical model based on classical nucleation and diffusion. In the designed perovskite system, the exsolution trend for particle growth is consistent with this diffusion model, which strongly depends on the initial cation concentration and reduction conditions. Based on the experimental and theoretical results, a highly Ni-doped anode and an electrochemical switching technique are employed to promote exsolution and overcome growth limitations. The optimal cell exhibits an outstanding maximum power density of 1.7 W cm^-2 at 900 °C and shows no evident degradation when operating at 800 °C for 240 h under wet H₂ . This study provides crucial insights into the developing and tuning of heterogeneous catalysts for energy-conversion applications.

Exsolution of Ru Nanoparticles on BaCe0.9 Y0.1 O3-δ Modifying Geometry and Electronic Structure of Ru for Ammonia Synthesis Reaction Under Mild Conditions

Green ammonia is an efficient, carbon-free energy carrier and storage medium. The ammonia synthesis using green hydrogen requires an active catalyst that operates under mild conditions. The catalytic activity can be promoted by controlling the geometry and electronic structure of the active species. An exsolution process is implemented to improve catalytic activity by modulating the geometry and electronic structure of Ru. Ru nanoparticles exsolved on a BaCe_0.9 Y_0.1 O_3-δ support exhibit uniform size distribution, 5.03 ± 0.91 nm, and exhibited one of the highest activities, 387.31 mmol_NH3  g_Ru ^-1  h^-1 (0.1 MPa and 450 °C). The role of the exsolution and BaCe_0.9 Y_0.1 O_3-δ support is studied by comparing the catalyst with control samples and in-depth characterizations. The optimal nanoparticle size is maintained during the reaction, as the Ru nanoparticles prepared by exsolution are well-anchored to the support with in-plane epitaxy. The electronic structure of Ru is modified by unexpected in situ Ba promoter accumulation around the base of the Ru nanoparticles.

Electrochemical Activation Applied to Perovskite Titanate Fibers to Yield Supported Alloy Nanoparticles for Electrocatalytic Application

Active bi-metallic nanoparticles are of key importance in catalysis and renewable energy. Here, the in situ formation of bi-metallic nanoparticles is investigated by exsolution on 200 nm diameter perovskite fibers. The B-site co-doped perovskite fibers display a high degree of exsolution, decorated with NiCo or Ni₃ Fe bi-metallic nanoparticles with average diameter about 29 and 35 nm, respectively. The perovskite fibers are utilized as cathode materials in pure CO₂ electrolysis cells due to their redox stability in the CO/CO₂ atmosphere. After in situ electrochemical switching, the nanoparticles exsolved from the perovskite fiber demonstrate an enhanced performance in pure CO₂ electrolysis. At 900 °C, the current density of solid oxide electrolysis cell (SOEC) with 200 µm YSZ electrolyte supported NiFe doped perovskite fiber anode reaches 0.75 Acm^-2 at 1.6 V superior to the NiCo doped perovskite fiber anode (about 1.5 times) in pure CO₂ . According to DFT calculations (PBE-D3 level) the superior CO₂ conversion on NiFe compared to NiCo bi-metallic species is related to an enhanced driving force for C-O cleavage under formation of CO chemisorbed on the nanoparticle and a reduced binding energy of CO required to release this product.

A novel exsolution technique-twice lasers: rapidly aroused explosive exsolution of nanoparticles to boost electrochemical performance

The exsolution of nanoparticles (NPs) on material surfaces exhibits good performance with great potential in the field of catalysis. In this study, a method with twice lasers treatment (TLT) is proposed for the first time to rapidly promote the exsolution of Co NPs to the surface of (La_0.7Sr_0.3)_0.93Ti_0.93Co_0.07O₃(LSTC) by laser rapid heating to enhance the electrochemical performance of the LSTC. The entire process from precursor powder-stable perovskite crystal structure-Co NPs exsolution on the LSTC surface takes only ≈36 s by TLT. The Co NPs exsolution was confirmed by x-ray diffractometer, scanning electron microscopy and high-resolution transmission electron microscopy. After TLT, a large number of Co NPs reached 75 particlesμm^-2appeared on the surface of LSTC with the onset potential of 1.38 V, the overpotential of 214 mV, and the Tafel slope of 81.14 mV dec^-1, showing good catalytic activity and long-term stability. The novel process of using TLT to rapidly induce exsolution of NPs enables the rapid preparation of nanoparticle-decorated perovskite materials with better electrochemical properties, thus enriching exsolution technology and opening a new avenue for surface science research.

Ultrafast Ambient-Air Exsolution on Metal Oxide via Momentary Photothermal Effect

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 (WO₃ 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 WO₃ NFs, the chemiresistive gas sensing characteristics of exsolved Pt-decorated WO₃ NFs were analyzed, exhibiting high durability (>200 cyclic exposures), enhanced response (R_air/R_gas > 800 @ 1 ppm/350 °C), and selectivity toward H₂S 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.

Ni/(R2O3,CaO) Nanocomposites Produced by the Exsolution of R1.5Ca0.5NiO4 Nickelates (R = Nd, Sm, Eu): Rare Earth Effect on the Catalytic Performance in the Dry Reforming and Partial Oxidation of Methane

In order to clarify the role of R₂O₃ in the metal-oxide catalysts derived from complex oxide precursors, a series of R_1.5Ca_0.5NiO₄ (R = Nd, Sm, Eu) complex oxides was obtained. A significant systematic increase in the orthorhombic distortion of the R_1.5Ca_0.5NiO₄ structure (K₂NiF₄ type, Cmce) from Nd to Eu correlates with a corresponding decrease in their ionic radii. A reduction of R_1.5Ca_0.5NiO₄ in the Ar/H₂ gas mixture at 800 °C causes a formation of dense agglomerates of CaO and R₂O₃ coated with spherical 25-30 nm particles of Ni metal. The size of metal particles and oxide agglomerates is similar in all Ni/(R₂O₃,CaO) composites in the study. Their morphology is rather similar to the products of redox exsolution obtained by the partial reduction of complex oxides. All obtained composites demonstrated a significant catalytic activity in the dry reforming (DRM) and partial oxidation (POM) of methane at 700-800 °C. A systematic decrease in the DRM catalytic activity of composites from Nd to Eu could be attributed to the basicity reduction of R₂O₃ components of the composite catalysts. The maximum CH₄ conversion in POM reaction was observed for Ni/(Sm₂O₃,CaO), while the maximum selectivity was demonstrated by Nd₂O₃-based composite. The possible reasons for the observed difference are discussed.

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.

Exsolution-Driven Surface Transformation in the Host Oxide

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_0.65Fe_0.35O₃ during Fe⁰ 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.

Galvanic Restructuring of Exsolved Nanoparticles for Plasmonic and Electrocatalytic Energy Conversion

There is a growing need to control and tune nanoparticles (NPs) to increase their stability and effectiveness, especially for photo- and electrochemical energy conversion applications. Exsolved particles are well anchored and can be re-shaped without changing their initial location and structural arrangement. However, this usually involves lengthy treatments and use of toxic gases. Here, the galvanic replacement/deposition method is used, which is simpler, safer, and leads to a wealth of new hybrid nanostructures with a higher degree of tailorability. The produced NiAu bimetallic nanostructures supported on SrTiO₃ display exceptional activity in plasmon-assisted photoelectrochemical (PEC) water oxidation reactions. In situ scanning transmission electron microscopy is used to visualize the structural evolution of the plasmonic bimetallic structures, while theoretical simulations provide mechanistic insight and correlate the surface plasmon resonance effects with structural features and enhanced PEC performance. The versatility of this concept in shifting catalytic modes to the hydrogen evolution reaction is demonstrated by preparing hybrid NiPt bimetallic NPs of low Pt loadings on highly reduced SrTiO₃ supports. This powerful methodology enables the design of supported bimetallic nanomaterials with tunable morphology and catalytic functionalities through minimal engineering.

In Situ Exsolution Catalyst: An Innovative Approach to Develop Highly Selective and Sensitive Gas Sensors

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_0.43Ca_0.37Co_0.06Ti_0.94O_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.

A-site deficient La0.52Sr0.28Ti0.94Ni0.06O3by low-pulsed electric current treatment: achieved exsolution of B-site Ni nanoparticles and significant improvement of electrocatalytic properties

Perovskite materials with exsolved nanoparticles have a wide range of applications in energy conversion systems owing to their unique basal plane active sites and excellent catalytic properties. The introduction of A-site deficiency can help the formation of highly mobile oxygen vacancies and remarkably enhance the reducibility of Ni nanoparticles, thus significantly increasing electronic conductivity and catalytic activity simultaneously. Herein, we adopt pulsed electric current (PEC) treatment, a novel approach instead of the long-time high-temperature reduction technique, and for the first time review that the exsolution of minuscule Ni nanoparticles (8-20 nm) could be facilitated on Ni-doped La_0.52Sr_0.28Ti_0.94Ni_0.06O₃(LSTN) anodes with A-site deficiency. Encouragingly, finding that low PEC can successfully lead to nanoparticle exsolution and show a significantly improved oxygen evolution reaction performance of LSTN-PEC (LSTN after PEC treatment) possessing A-site deficiency, the onset potential of LSTN-PEC (500 V) (LSTN after PEC treatment with 500 V-4 Hz-90 s) was advanced by 0.173 V, theR_ctvalue was reduced by 82.38 Ω·cm², and the overpotential was also reduced by 73 mV.

A Flexible Method to Fabricate Exsolution-Based Nanoparticle-Decorated Materials in Seconds

Decorating metallic nanoparticles on the surface of oxide support is a promising approach to tailor the catalytic activity of perovskite. Here, for the first time using thermal shock to rapidly fabricate nanoparticle-decorated materials (NDMs) is proposed. Low-cost and size-tailorable carbon paper is used as the heating source during the thermal shock. It is reported that by thermal shock technique, only ≈13 s including heating and treating time is needed to fabricate the exsolution-based NDMs (the fastest method to date). Benefitted by the sufficiently provided driving force and the short treating time, as compared to the product prepared by the conventionally furnace-based method, higher particle density and smaller particle size of the exsolved catalysts are acquired for the thermal shock fabricated NDM, giving rise to a fascinating improvement (12-fold) of the electrochemical performance. This work develops a new technique to rapidly fabricate NDMs in an economic and high-throughput manner, profoundly improving the flexibility of the application of exsolution-based materials in electrochemical devices.

Realizing Simultaneous Detrimental Reactions Suppression and Multiple Benefits Generation from Nickel Doping toward Improved Protonic Ceramic Fuel Cell Performance

Anode-supported protonic ceramic fuel cells (PCFCs) are highly promising and efficient energy conversion systems. However, several challenges need to be overcome before these systems are used more widely, including the poor sintering of recently developed proton-conducting oxides and the decreased proton conductivity due to detrimental reactions between the nickel from anode and the electrolyte occurring during high-temperature co-sintering. Herein, a Ni doping strategy to increase the electrolyte sintering, suppress the detrimental phase reactions, and generate stable Ni nanoparticles for enhanced performance is proposed. A nickel-doped perovskite oxide is developed with the nominal composition of Ba(Zr_0.1 Ce_0.7 Y_0.1 Yb_0.1 )_0.95 Ni_0.05 O_{3- δ} . Acting as a sintering aid, such a small amount of nickel effectively improves the sintering of the electrolyte. Concomitantly, reactions between nickel and the Ni-doped ceramic phase are suppressed, turning detrimental phase reactions into benefits. The nickel doping further promotes the formation of Ni nanoparticles, which enhance the electrocatalytic activity of the anode toward the hydrogen oxidation reaction and improve the charge transfer across the anode-electrolyte interface. As a result, highly efficient PCFCs are developed. The innovative anode developed in this work also shows favorable activity toward ammonia decomposition, making it highly promising for use in direct ammonia fuel cells.

Selective Photocatalytic Reduction of CO2 to Syngas Over Tunable Metal-Perovskite Interface

The extensive emission of CO₂ results in critical environmental issues, such as global warming. Photocatalytic CO₂ conversion is a meaningful route to convert CO₂ into useful chemicals. However, the highly selective reduction of CO₂ with the avoidance of hydrogen evolution is still challenging. Herein, the photocatalytic reduction CO₂ to synthesis gas (syngas) was achieved on a metal Ag socketed perovskite LaFeO₃ (LFO) catalytic interface prepared by an in-situ exsolution method. The conduction band of Ag-exsolved LFO is more negative than LFO, benefiting efficient CO₂ reduction. By tuning the dopant Ag cation in the lattice to nanoparticles pinned on the surface, the CO formation rate was improved around five-fold from 0.51 to 2.41 μmol g^-1  h^-1 . Meanwhile, the H₂ /CO molar ratio also showed strong dependence on the modality of Ag at the metal-perovskite interface. The design offers a promising pathway for transforming CO₂ to valuable chemicals based on efficient photocatalysts design.

Manipulating Electrocatalytic Activity of Perovskite Oxide Through Electrochemical Treatment

Perovskite oxides are widely used in electrochemical cells, profiting from their excellent accommodation of different elements and structure stability. Here, it is reported that when rapidly exceeding the electrochemical stability window of a perovskite oxide through electrochemical treatment, nanoparticles can dynamically exsolve from the perovskite lattice, yielding a nanoparticle decorated material (NDM) with fascinating particle population and distribution. It is reported that as compared to the NDM produced by chemical gas reduction, electrochemical treatment fabricated NDM shows much better electrochemical performance. At 900 °C, a peak power density (PPD) of 896 mW cm^-2 (more than tenfold enhancement) is obtained for a yttrium stabilized zirconia (YSZ) electrolyte-supported symmetrical cell with La_0.43 Ca_0.37 Ti_0.8 Co_0.1 Fe_0.1 O_{3- δ} (LCTCF) electrode after electrochemical treatment for several minutes, while it only reaches to 210 mW cm^-2 after chemical gas treatment for tens of hours using humidified hydrogen as fuel. The study establishes a new fairyland for tuning the performance of-but not limited to-the electrochemical cells.

Plasma Driven Exsolution for Nanoscale Functionalization of Perovskite Oxides

Perovskite oxides with dispersed nanoparticles on their surface are considered instrumental in energy conversion and catalytic processes. Redox exsolution is an alternative method to the conventional deposition techniques for directly growing well-dispersed and anchored nanoarchitectures from the oxide support through thermochemical or electrochemical reduction. Herein, a new method for such nanoparticle nucleation through the exposure of the host perovskite to plasma is shown. The applicability of this new method is demonstrated by performing catalytic tests for CO₂ hydrogenation over Ni exsolved nanoparticles prepared by either plasma or conventional H₂ reduction. Compared to the conventional thermochemical H₂ reduction, there are plasma conditions that lead to the exsolution of a more than ten times higher Ni amount from a lanthanum titanate perovskite, which is similar to the reported values of the electrochemical method. Unlike the electrochemical method, however, plasma does not require the integration of the material in an electrochemical cell, and is thus applicable to a wide range of microstructures and physical forms. Additionally, when N₂ plasma is employed, the nitrogen species are stripping out oxygen from the perovskite lattice, generating a key chemical intermediate, such as NO, rendering this technology even more appealing.

Active Exsolved Metal-Oxide Interfaces in Porous Single-Crystalline Ceria Monoliths for Efficient and Durable CH4 /CO2 Reforming

Dry reforming of CH₄ /CO₂ provides an attractive route to convert greenhouse gas into syngas; however, the resistance to sintering and coking of catalyst remains a fundamental challenge at high operation temperatures. Here we create active and durable metal-oxide interfaces in porous single-crystalline (PSC) CeO₂ monoliths with in situ exsolved single-crystalline (SC) Ni particles and show efficient dry reforming of CH₄ /CO₂ at temperatures as low as 450 °C. We show the excellent and durable performance with ≈20 % of CH₄ conversion and ≈30 % of CO₂ conversion even in a continuous operation of 240 hours. The well-defined active metal-oxide interfaces, created by exsolving SC Ni nanoparticles from PSC Ni_x Ce_1-x O₂ to anchor them on PSC CeO₂ scaffolds, prevent nanoparticle sintering and enhance the coking resistance due to the stronger metal-support interactions. Our work would enable an industrially and economically viable path for carbon reclamation, and the technique of creating active and durable metal-oxide interfaces in PSC monoliths could lead to stable catalyst designs for many challenging reactions.

Cation-Exchange-Induced Metal and Alloy Dual-Exsolution in Perovskite Ferrite Oxides Boosting the Performance of Li-O2 Battery

A temperature-controlled cation-exchange approach is introduced to achieve a unique dual-exsolution in perovskite La_0.8 Fe_0.9 Co_0.1 O_3-δ where both CoFe alloy and Co metal are simultaneously exsolved from the parent perovskite, forming an alloy and metal co-decorated perovskite oxide. Mossbauer spectra show that cation exchange of Fe atoms in CoFe alloy and Co cations in the perovskite is the key to the co-existence of Co metal and CoFe alloy. The obtained composite exhibits an enhanced catalytic activity as Li-O₂ battery cathode catalysts with a specific discharge capacity of 6549.7 mAh g^-1 and a cycling performance of 215 cycles without noticeable degradation. Calculations show that the combination of decorated CoFe alloy and Co metal synergistically modulated the discharge reaction pathway that improves the performance of Li-O₂ battery.

Cation Ordering and Exsolution in Copper-Containing Forms of the Flexible Zeolite Rho (Cu,M-Rho; M=H, Na) and Their Consequences for CO2 Adsorption

The flexibility of the zeolite Rho framework offers great potential for tunable molecular sieving. The fully copper-exchanged form of Rho and mixed Cu,H- and Cu,Na-forms have been prepared. EPR spectroscopy reveals that Cu2+ ions are present in the dehydrated forms and Rietveld refinement shows these prefer S6R sites, away from the d8r windows that control diffusion. Fully exchanged Cu-Rho remains in an open form upon dehydration, the d8r windows remain nearly circular and the occupancy of window sites is low, so that it adsorbs CO2 rapidly at room temperature. Breakthrough tests with 10 % CO2 /40 % CH4 mixtures show that Cu4.9 -Rho is able to produce pure methane, albeit with a relatively low capacity at this pCO2 due to the weak interaction of CO2 with Cu cations. This is in strong contrast to Na-Rho, where cations in narrow elliptical window sites enable CO2 to be adsorbed with high selectivity and uptake but too slowly to enable the production of pure methane in similar breakthrough experiments. A series of Cu,Na-Rho materials was prepared to improve uptake and selectivity compared to Cu-Rho, and kinetics compared to Na-Rho. Remarkably, Cu,Na-Rho with >2 Cu cations per unit cell exhibited exsolution, due to the preference of Na cations for narrow S8R sites in distorted Rho and of Cu cations for S6R sites in the centric, open form of Rho. The exsolved Cu,Na-Rho showed improved performance in CO2 /CH4 breakthrough tests, producing pure CH4 with improved uptake and CO2 /CH4 selectivity compared to that of Cu4.9 -Rho.

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.

Tailoring Electrochemical Performance of Perovskite Anodes through In Situ Exsolution of Nanocatalysts

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_0.52Sr_0.28Ti_0.8Co_0.1Fe_0.1O_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.

Performance and Limitations of Nickel-Doped Chromite Anodes in Electrolyte-Supported Solid Oxide Fuel Cells

Ni-doped chromite anodes were integrated into electrolyte-supported cells (ESC) with 5×5 cm2 size and investigated in fuel cell mode with H2 /H2 O fuel gas. Both a stoichiometric and a nominally A-site deficient chromite anode material showed promising performance at 860 °C approaching the ones of state-of-the-art Ni/Gd-doped ceria (CGO) anodes. While the difference in polarization resistance was small, an increased ohmic resistance of the perovskite anodes was observed, which is related to their limited electronic conductivity. Increasing the chromite electrode thickness was shown to enhance performance and stability considerably. Degradation increased with current density, suggesting its dependency on the electrode potential, and could be reversed by redox cycling. Sulfur poisoning with 20 ppm hydrogen sulfide led to rapid voltage drops for the chromite anodes. It is discussed that Ni nanoparticle exsolution facilitates hydrogen dissociation to the extent that it is not rate-limiting at the investigated temperature unless an insufficiently thick electrode thickness is employed or sulfur impurities are present in the feed gas.

Emergence and Future of Exsolved Materials

Supported nanoparticle systems have received increased attention over the last decades because of their potential for high activity levels when applied to chemical conversions, although, because of their nanoscale nature, they tend to exhibit problems with long-term durability. Over the last decade, the discovery of the so-called exsolution concept has addressed many of these challenges and opened many other opportunities to material design by providing a relatively simple, single-step, synthetic pathway to produce supported nanoparticles that combine high stability against agglomeration and poisoning with high activity across multiple areas of application. Here, the trends that define the development of the exsolution concept are reviewed in terms of design, functionality, tunability, and applicability. To support this, the number of studies dedicated to both fundamental and application-related studies, as well as the types of metallic nanoparticles and host or support lattices employed, are examined. Exciting future directions of research are also highlighted.

Progress of Exsolved Metal Nanoparticles on Oxides as High Performance (Electro)Catalysts for the Conversion of Small Molecules

Utilizing electricity and heat from renewable energy to convert small molecules into value-added chemicals through electro/thermal catalytic processes has enormous socioeconomic and environmental benefits. However, the lack of catalysts with high activity, good long-term stability, and low cost strongly inhibits the practical implementation of these processes. Oxides with exsolved metal nanoparticles have recently been emerging as promising catalysts with outstanding activity and stability for the conversion of small molecules, which provides new possibilities for application of the processes. In this review, it starts with an introduction on the mechanism of exsolution, discussing representative exsolution materials, the impacts of intrinsic material properties and external environmental conditions on the exsolution behavior, and the driving forces for exsolution. The performances of exsolution materials in various reactions, such as alkane reforming reaction, carbon monoxide oxidation, carbon dioxide utilization, high temperature steam electrolysis, and low temperature electrocatalysis, are then summarized. Finally, the challenges and future perspectives for the development of exsolution materials as high-performance catalysts are discussed.

Toward Controlling Filament Size and Location for Resistive Switches via Nanoparticle Exsolution at Oxide Interfaces

Memristive devices are among the most prominent candidates for future computer memory storage and neuromorphic computing. Though promising, the major hurdle for their industrial fabrication is their device-to-device and cycle-to-cycle variability. These occur due to the random nature of nanoionic conductive filaments, whose rupture and formation govern device operation. Changes in filament location, shape, and chemical composition cause cycle-to-cycle variability. This challenge is tackled by spatially confining conductive filaments with Ni nanoparticles. Ni nanoparticles are integrated on the bottom La_0.2 Sr_0.7 Ti_0.9 Ni_0.1 O_{3- δ} electrode by an exsolution method, in which, at high temperatures under reducing conditions, Ni cations migrate to the perovskite surface, generating metallic nanoparticles. This fabrication method offers fine control over particle size and density and ensures strong particle anchorage in the bottom electrode, preventing movement and agglomeration. In devices based on amorphous SrTiO₃ , it is demonstrated that as the exsolved Ni nanoparticle diameter increases up to ≈50 nm, the ratio between the ON and OFF resistance states increases from single units to 180 and the variability of the low resistance state reaches values below 5%. Exsolution is applied for the first time to engineer solid-solid interfaces extending its realm of application to electronic devices.

Shaping a Doped Perovskite Oxide with Measured Grain Boundary Defects to Catalyze Bifunctional Oxygen Activation for a Rechargeable Zn-Air Battery

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 ABO₃-type La_0.7Sr_0.3CoO_3-δ, a marginally higher ionic radius of Pd⁴⁺ than Co³⁺ enables partial deportation of Pd⁴⁺ 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 O₂ 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/cm². 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.

Exsolution of Catalytically Active Iridium Nanoparticles from Strontium Titanate

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 SrTiO₃ perovskite is reported and their growth preliminary probed by in situ electron microscopy. Upon reduction of SrIr_0.005Ti_0.995O₃, 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_0.005Ti_0.995O₃ is compared to the activity of a commercial catalyst with 1% loading (1% Ir/Al₂O₃). 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.

Metal Nanoparticle Exsolution on a Perovskite Stannate Support with High Electrical Conductivity

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_0.2Ba_0.7Sn_0.9Ni_0.1O_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 ABO₃ 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.

Endogenous Nanoparticles Strain Perovskite Host Lattice Providing Oxygen Capacity and Driving Oxygen Exchange and CH4 Conversion to Syngas

Particles dispersed on the surface of oxide supports have enabled a wealth of applications in electrocatalysis, photocatalysis, and heterogeneous catalysis. Dispersing nanoparticles within the bulk of oxides is, however, synthetically much more challenging and therefore less explored, but could open new dimensions to control material properties analogous to substitutional doping of ions in crystal lattices. Here we demonstrate such a concept allowing extensive, controlled growth of metallic nanoparticles, at nanoscale proximity, within a perovskite oxide lattice as well as on its surface. By employing operando techniques, we show that in the emergent nanostructure, the endogenous nanoparticles and the perovskite lattice become reciprocally strained and seamlessly connected, enabling enhanced oxygen exchange. Additionally, even deeply embedded nanoparticles can reversibly exchange oxygen with a methane stream, driving its redox conversion to syngas with remarkable selectivity and long term cyclability while surface particles are present. These results not only exemplify the means to create extensive, self-strained nanoarchitectures with enhanced oxygen transport and storage capabilities, but also demonstrate that deeply submerged, redox-active nanoparticles could be entirely accessible to reaction environments, driving redox transformations and thus offering intriguing new alternatives to design materials underpinning several energy conversion technologies.

Compositional Engineering of a La1-xBaxCoO3-δ-(1-a) BaZr0.9Y0.1O2.95 (a = 0.6, 0.7, 0.8 and x = 0.5, 0.6, 0.7) Nanocomposite Cathodes for Protonic Ceramic Fuel Cells

Compositionally engineered a La1-xBaxCoO3-δ-(1-a) BaZr0.9Y0.1O2.95 (a = 0.6, 0.7, 0.8 and x = 0.5, 0.6, 0.7) (LBZ) nanocomposite cathodes were prepared by oxidation driven in situ exsolution of a single-phase material deposited on a BaZr0.9Y0.1O2.95 electrolyte. The processing procedure of the cathode was optimized by reducing the number of thermal treatments as the single-phase precursor was deposited directly on the electrolyte. The exsolution and firing of the cathodes occurred in one step. The electrochemical performance of symmetrical cells with the compositionally engineered cathodes was investigated by impedance spectroscopy in controlled atmospheres. The optimized materials processing gave web-like nanostructured cathodes with superior electrochemical performance for all compositions. The area specific resistances obtained were all below 12 Ω·cm2 at 400 °C and below 0.59 Ω·cm2 at 600 °C in 3% moist synthetic air. The resistances of the nominal 0.6 La0.5Ba0.5CoO3-δ-0.4 BaZr0.9Y0.1O2.95 and 0.8 La0.5Ba0.5CoO3-δ-0.2 BaZr0.9Y0.1O2.95 composite cathodes were among the lowest reported for protonic ceramic fuel cells cathodes in symmetrical cell configuration with ASR equal to 4.04 and 4.84 Ω·cm2 at 400 °C, and 0.21 and 0.27 Ω·cm2 at 600 °C, respectively.

Reversible Exsolution of Dopant Improves the Performance of Ca2Fe2O5 for Chemical Looping Hydrogen Production

Hydrogen (H₂) is a clean energy carrier and a major industrial feedstock, e.g., to produce ammonia and methanol. High-purity H₂ can be produced efficiently from methane (CH₄) using chemical looping-based approaches. In this work, we report on the development of a calcium-iron-based oxygen carrier (Ca₂Fe₂O₅) doped with Ni or Cu and investigate its redox performance for H₂ production when CH₄ is used as the fuel. The experimental results suggest that the rapid formation of metallic Ni or Cu through exsolution promotes the reducibility of Ca₂Fe₂O₅ with CH₄. It was found that the reversible exsolution of Ni or Cu nanoparticles and their reincorporation in the Ca₂Fe₂O₅ structure is key to avoid particle sintering and deactivation. Having the potential of converting a larger fraction of steam to H₂ than pure iron oxide in addition to its higher reactivity with CH₄, the doped calcium-iron-based oxygen carrier is a promising material for chemical looping H₂ production.

A Highly Efficient and Robust Perovskite Anode with Iron-Palladium Co-exsolutions for Intermediate-Temperature Solid-Oxide Fuel Cells

The low performance and insufficient catalytic activity of perovskite anodes hinder their further application in intermediate-temperature solid-oxide fuel cells (IT-SOFCs). A novel La_0.8 Sr_0.2 Fe_0.9 Nb_0.1 Pd_0.04 O_3-δ (LSFNP) anode material has been developed with Fe-Pd co-exsolutions for IT-SOFCs. Fe⁰ and Pd⁰ metallic nanoparticles are confirmed to exsolve on the surface of the perovskite anode during operation under a hydrogen atmosphere. The introduced Pd exsolutions promote the charge-transfer process slightly and the H₂ -adsorption ability of the La_0.8 Sr_0.2 Fe_0.9 Nb_0.1 O_3-δ (LSFN) parent anode significantly, as metallic Pd is a conductor with excellent catalytic activity and an absorber of hydrogen that can absorb a large amount of H₂ by forming unstable chemical bonds. A single cell with the LSFNP anode exhibits high output performance (maximum power density of 287.6 mW cm^-2 at T=800 °C by using humidified H₂ as the fuel), excellent redox stability, and considerable coking and sulfur tolerances. After the introduction of Pd exsolutions, the increase in the electrochemical performance is more significant under low H₂ concentrations and at low temperatures with a maximum power density ratio of the LSFNP anode cell/LSFN anode cell reaching 18 under 5 % H₂ /argon at T=650 °C. Pd-decorated LSFNP is a high-performance, redox-stable, coking-tolerant, and sulfur-tolerant anode material for IT-SOFCs, making Pd exsolution a reliable nanodecoration strategy to improve the low kinetics of perovskite anodes.

Niobium Doped Lanthanum Strontium Ferrite as A Redox-Stable and Sulfur-Tolerant Anode for Solid Oxide Fuel Cells

The Nb-doped lanthanum strontium ferrite perovskite oxide La_0.8 Sr_0.2 Fe_0.9 Nb_0.1 O_3-δ (LSFNb) is evaluated as an anode material in a solid oxide fuel cell (SOFC). The effects of Nb partial substitution in the crystal structure, the electrical conductivity, and the valence of Fe ions are studied. LSFNb exhibits good structural stability in a severe reducing atmosphere at 800 °C, suggesting that high-valent Nb can effectively promote the stability of the lattice structure. The concentration of Fe²⁺ increases after Nb doping, as confirmed by X-ray photoelectron spectroscopy. The maximum power density of a thick Sc-stabilized zirconia (ScSZ) electrolyte-supported single cell reached 241.6 mW cm^-2 at 800 °C with H₂ as fuel. The cell exhibited excellent stability for 100 h continuous operation without detectable degeneration. Scanning electron microscopy clearly revealed exsolution on the LSFNb surface after operation. Meanwhile, LSFNb particles agglomerated significantly during long-term stability testing. Impedance spectra suggested that both the LSFNb anode and the (La_0.75 Sr_0.25 )_0.95 MnO_3-δ /ScSZ cathode underwent an activation process during long-term testing, through which the charge transfer ability increased significantly. Meanwhile, low-frequency resistance (R_L ) mainly attributed to the anode (80 %) significantly increased, probably due to the agglomeration of LSFNb particles. The LSFNb anode exhibits excellent anti-sulfuring poisoning ability and redox stability. These results demonstrate that LSFNb is a promising anode material for SOFCs.