LaCoO3 Perovskite Research Articles

Study of LaCoO3 Across Insulator–Metallic Phase Transition

The standard solid-state reaction method was used to prepare perovskite LaCoO3 crystal successfully. The crystal structure was confirmed by means of powder X-ray diffraction. An investigation of the electrical properties shows an interesting temperature dependence. The real and imaginary parts of the dielectric constant show maximum at 533 K and minimum at 548 K. This indicates an Insulating-Metallic phase transition. It was found that the activation energy \(\Delta E_{a}\) in the semiconducting region was about 0.80 eV. The grain resistance shows an inverse dependence on temperature justify negative temperature coefficient of resistance exhibit. The crystal exhibits non-Debye type dielectric relaxation.

Enhanced Ferromagnetism Induced by Chemical Doping and Epitaxial Strain in La0.8Sr0.2CoO3 Films

The perovskite LaCoO3 and La0.8Sr0.2CoO3 thin films were synthesized successfully by a polymer-assisted deposition method. The structural characterization and thermal decomposition measurements indicate that appropriately increasing the annealing temperature is helpful in improving the film crystallinity. Compared with LaCoO3 films, the Curie temperature is enhanced to a higher temperature in La0.8Sr0.2CoO3 films, which is attributed to the changes in both the valence state and spin state induced by the chemical doping. In addition, a broad transition temperature region is observed in La0.8Sr0.2CoO3 films, revealing the existence of inhomogeneous ground states in this system.

Nanoscale Engineering of Structurally Stable Nd-Substituted LaCoO3 as An Electrode Material for Supercapacitors

Perovskite oxides have recently emerged as a novel class of electrochemical materials owing to their amazing reversible redox capabilities and enriched electrical characteristics, rich oxygen vacancies, and highly stable structure. Herein, the impact of Nd-substitution on the morphological and electrochemical features of Nd-doped LaCoO3 nanoparticles has been studied. A facile and cost-effective sol-gel process routed via auto-ignition was used for sample synthesis. The development of pure single-phase cubic LaCoO3 perovskite and its structural stability throughout the series was confirmed via X-ray diffraction. The transformation from sponge-like structure to grains-like morphology was evident by a field-emission scanning electron microscope. Cyclic voltammetry measurements revealed a surface redox and intercalation pseudo-capacitive nature of the samples. It is outcome that La0.95Nd0.05CoO3 at 6 A g−1 of current density exhibits paramount power (5788.8 W kg−1) and energy (0.975 Wh kg−1) densities. All the revealed consequences had inferred La0.95Nd0.05CoO3 (x = 0.05) as a potential candidate for electrode material in supercapacitors.

Highly efficient LaMO3 (M = Co, Fe) perovskites catalyzed Fenton's reaction for degradation of direct blue 86

Perovskite-structured catalysts LaMO3 (M = Co, Fe) were successfully synthesized and attempted to catalyze hydrogen peroxide (H2O2) for the degradation of Direct Blue 86 (DB86), a carcinogenic phthalocyanine dye. The heterogeneous Fenton-like reaction revealed that the oxidative power of the LaCoO3-catalyzed H2O2 (LaCoO3/H2O2) process was higher than that of LaFeO3/H2O2. When LaCoO3 was calcined at 750 °C for 5 h, 100 mg/L of DB86 could be completely degraded within 5 min via LaCoO3/H2O2 system under H2O2 0.0979 mol/L, initial pH 3.0, LaCoO3 0.4 g/L, and 25 °C. The oxidative LaCoO3/H2O2 system has a low activation energy (14.68 kJ/mol) for DB86 degradation, indicating that it is a fast reaction process with highly favorable at high reaction temperatures. For the first time, a cyclic reaction mechanism of catalytic LaCoO3/H2O2 system was proposed based on the evidence of coexisting CoII and CoIII on the LaCoO3 surface and the presence of HO• radicals (major), O2•- radicals (minor), and 1O2 (minor). LaCoO3 perovskite catalyst was reusable and still maintained reactive with a satisfactory degradation efficiency within 5 min even after five consecutive uses. This study shows that the as-prepared LaCoO3 is a highly efficient catalyst for phthalocyanine dye degradation.

Insights into the interface of NiCo2O4 spinel /LaCoO3 perovskite nano-composite for CO and soot oxidation

In the quest for the development of thermally stable, highly active and low-cost catalysts for use in catalyzed diesel particulate filter, nano-composites are new areas of research. Therefore, we reported the easy synthesis of spinel NiCo2O4/perovskite LaCoO3 nano-composite, and its individual oxides NiCo2O4 and LaCoO3 for comparison. The detailed insights into the physio-chemical characteristics of formed NiCo2O4/ LaCoO3 nano-composite were done based on various characterization analysis such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR), N2 physiosorption, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The characterization analysis of NiCo2O4/LaCoO3 revealed the successful formation of a chemical interface possessing strong interfacial interaction, resulting in desirable physicochemical characteristics such as small crystallite size, abundant mesoporosity, high specific surface area and activation of surface lattice oxygen. Owing to the desirable characteristics, the activity results over NiCo2O4/LaCoO3 nano-composite showed the excellent CO oxidation performance and high soot oxidation activity, recyclability and thermal stability. This work mainly attempts to emphasize the effectiveness of the facile, inexpensive and conventionally used precipitation method for the successful formation of highly efficient nano-composites.

Influence of LaCoO3 perovskite oxides prepared by different method on the catalytic combustion of ethyl acetate in the presence of NO

Effect of preparation methods, including selective etching (LCO-E), sol–gel (LCO-S) and co-precipitation (LCO-C), on the physicochemical properties of LaCoO3 and its catalytic activity for removal ethyl acetate (EA) are investigated. The physicochemical properties of these LaCoO3 materials are characterized by XRD, N2 physicosorption, SEM, HR-TEM, H2-TPR O2-TPD, EPR and in situ DRIFTS. The preparation methods have a strong influence for LaCoO3 perovskites on crystalline size, surface area, redox ability, oxygen mobility, Co3+ content and the catalytic activity from the highest to the lowest value were LCO-E > LCO-S > LCO-C. In particular, we found that NO plays different roles in the reaction depending on the reaction temperature below or above 160 ℃, where the oxidation of NO to NO2 occurs or not. This directs a new strategy to simultaneously remove EA and NO, and even to pollutants with more complicated compositions. Moreover, it is found that the presence of small amount of water can significantly improve the reaction activity. The presence of excess water severely occupies the active sites, resulting in the decrease of activity. A mechanism for the removal of NO and EA in the presence of water is proposed.

Stability enhancing of perovskite LaCoO3 by compositing with oxygen doped MoS2 in Fenton-like reactions

Perovskite materials are reported to be effective in peroxymonosulfate (PMS) based Fenton-like reactions, the leaching rates of chalcogenide materials in perovskite materials are however serious, thus leading to bad performance in long-term stability. In this study, an O-doped MoS2 is synthesized to composite with LaCoO3, and the high catalytic activity of LaCoO3 is well preserved with greatly decreased Co leaching. During the BPA degradation with PMS as oxidant, ∼100% degradation can be achieved in 20 min and this degradation efficiency can be maintained for ∼45 h in a simulated fixed bed reactor, which is almost 3 times longer than the pure LaCoO3. With the compositing of O-doped MoS2, the leached Co was greatly decreased and the dominated reactive oxidation species (ROS) transformed from SO4•– into O2•– with longer lifespan, thus resulting in the better stability. This study could promote the application of perovskite materials in the real industrial wastewater treatment.

Interface engineering for bismuth tungstate and lanthanum cobaltate towards promoted sulfamethoxazole photocatalytic oxidation

Diversified photocatalysts with high catalytic activity and durability are urgently needed for antibiotics degradation upon environmental remediation. Herein, we devised a unique catalyst, LB-2 (LaCoO3:Bi2WO6=1:2, mole ratio), which constitute of by ultrathin aurivillius perovskite Bi2WO6 (BWO) nanosheets growing on classical perovskite LaCoO3 (LCO) nanofibers. The novel complex catalyst exhibited outstanding catalytic activity and superior stability for sulfamethoxazole (SMX) degradation. The degradation efficiency of LB-2 for SMX achieved 91.3% and the efficiency still remained at 76% after cycling experiments, indicating the excellent stability of LB-2. Probable synergistic mechanisms between Bi2WO6 and LaCoO3 were investigated by active species capture experiments and electron spin resonance (ESR). In addition, possible products of different routes of SMX degradation were presented based on high performance liquid chromatography-tandem mass spectrometry (HPLC/MS). This investigation proposes the application of composite chalcogenide oxides in the photocatalytic degradation of SMX, and confirmed that the heterojunction interface between chalcogenide oxides is the key to enhance the performance according to the experimental and mechanistic investigation.

Effect of highly dispersed Co3O4 on the catalytic performance of LaCoO3 perovskite in the combustion of lean methane

In this work, a series of nano LaCoO3 perovskite catalysts were effectively synthesized by a sol-gel method through modulating the La/Co molar ratio. These catalysts were characterized by ICP, XRD, N2 sorption, H2-TPR, O2-TPD, and XPS, and their catalytic performance in the lean methane combustion were then investigated. The results indicate that highly dispersed Co3O4 nanoparticles on the LaCoO3 perovskite catalysts are beneficial to the activation of CH4 at a low temperature, while the La-Co-perovskite bulk phase can provide a large amount of lattice oxygen, which can enhance the reaction rate of methane combustion and the catalytic stability at a high temperature. Through altering the La/Co molar ratio, the dispersion of Co3O4 nanoparticles in the La-Co-perovskite catalyst can be effectively modulated, to achieve the concurrence of low-temperature activity and high-temperature stability in the lean methane combustion. In particular, the La0.9CoO3 perovskite catalyst with a La/Co molar ratio of 0.9 exhibits excellent performance in lean methane combustion, with a light-off temperature of 382 °C at a space velocity of 30000 mL/(g·h); in addition, the methane conversion holds above 95% even after 72 h on stream. These results should be helpful for the development of low-cost, high-activity and high-stability catalysts for lean methane combustion.

Oxygen vacancies engineering of Fe doped LaCoO3 perovskite catalysts for efficient H2S selective oxidation

Fe-doped LaCoO3 perovskite catalysts synthesized via a facile citric acid-assisted sol-gel route have been applied for the H2S selective oxidation. The as-synthesized LaFexCo1−xO3 perovskites exhibit a randomly macroporous structure formed by the accumulation of nanoparticles. Characterization studies reveal that appropriate Fe substitution effectively enhances the formation of oxygen vacancies, and thus improves the lattice oxygen mobility and H2S adsorbability, respectively. The obtained LaFe0.4Co0.6O3 exhibited remarkable catalytic activity, with the H2S conversion and sulfur yield of 100% at 190 °C. A combined approach of in-situ FT-IR and in-situ Raman experiments disclosed that the plausible reaction pathway of H2S selective oxidation over LaFexCo1−xO3 perovskites follows the Mars-van Krevelen mechanism. The density functional theory calculations revealed that Fe-doping improves the formation of oxygen vacancy and enhances the adsorption of H2S. This study offers new insights for the design of highly efficient perovskites for the selective oxidation of H2S.

Exploration of magnetic characteristics in perovskite LaCoO3 by particle swarm optimization combined with Monte Carlo method

In this paper, the new method combined with Monte Carlo simulation and particle swarm optimization is presented to explore the magnetic characteristics of perovskite LaCoO3 described by Ising model. We use the particle swarm optimization to obtain the appropriate physical parameters, such as Jab, Jaa and further adopt the Monte Carlo simulation to calculate the magnetization M, the magnetic susceptibility χ, the entropy S, the internal energy U of system under the influence of the anisotropy D and magnetic field h. The phase diagrams and the hysteresis loops are given. These results are also compared with the relevant theoretical and experimental results.

CeO2 supported MOFs derived LaBxFeyO3 (B=Mn, Co) perovskite catalysts for degradation of toluene.

In this work, LaCoO3 and LaMnO3 perovskites with the higher specific surface area were synthesized using MOFs as precursor, then, the composite catalysts CeO2-LaCoxFeyO3 and CeO2-LaMnxFeyO3 were prepared by using CeO2 as support and Fe element doping LaCoO3 and LaMnO3, respectively. The as-prepared samples were characterized by XRD, SEM, XPS, H2-TPR, and N2 physisorption techniques. Subsequently, toluene was used as the probe molecule for volatile organic compounds (VOCs) to test the catalytic activity of these as-prepared catalysts. The results show that the initial reaction temperature for toluene oxidation on supported perovskite catalysts is lower. Among which, CeO2-LaCo0.25Fe0.75O3 (T90=215 °C, T90: the temperature corresponding to 90% conversion of toluene) and CeO2-LaMn0.25Fe0.75O3 (T90=205 °C) catalysts show the best catalytic performance. Therefore, the supported perovskite prepared in this study has the advantages of high specific surface area, abundant oxygen vacancies, and excellent oxygen mobility, which makes it exhibit better performance in VOCs catalytic oxidation.

Zinc doping effect on the structural and electrochemical properties of LaCoO3 perovskite as a material for hybrid supercapacitor electrodes

In the present study, a series of LaCo1−xZnxO3 (0 ≤ x ≤ 0.1) perovskite-type oxides was successfully synthesized via the sol-gel process followed by thermal treatment. The zinc doping effect on the structure, the surface chemical composition, morphology, porosity, as well as the electrochemical properties of LaCoO3 has been investigated, for the first time, for potential use as a material for supercapacitor electrodes. We infer from the results that the LaCo0.95Zn0.05O3 electrode provides the best specific capacitance (300.47 F/g); this is almost four times higher compared to the undoped electrode (75.36 F/g). The electrode material also shows an excellent capacitance retention of 85.73% after 5000 cycles at 5 A/g. In addition, a hybrid supercapacitor with high energy density was constructed by combining LaCo0.95Zn0.05O3 with activated carbon. The LaCo0.95Zn0.05O3//activated carbon hybrid device offers a high energy density of 36.12 Wh.kg−1 at a power density of 390.35 W.kg−1. The device is characterized by an outstanding retention of capacitance of 81% after being subjected to 5000 successive charge-discharge cycles.

Oxygen vacancy engineering for tuning the catalytic activity of LaCoO3 perovskite

Herein, we attempted to engineer oxygen vacancies on the surface of LaCoO3 perovskite through simple post-treatments (acid or reductive thermal treatments). Acid treatment induces oxygen vacancies through the selective etching of the La cations, whereas thermal treatment in a reducing atmosphere generates oxygen vacancies by directly removing lattice oxygen. The characterization results confirm that the number of surface oxygen vacancies, which are crucial in various catalytic oxidation reactions, considerably increases in the LaCoO3 catalysts treated with acid or reducing gas. Acid treatment enriches the oxygen vacancies while maintaining the structure of the LaCoO3 catalysts, which can not be achieved through reductive thermal treatment. Therefore, the acid treatment is considered a promising technique for oxygen vacancy engineering of perovskite catalysts for tuning their catalytic activities. Furthermore, the catalytic activities of the posttreated LaCoO3 catalysts for CO oxidation were evaluated and are noted to be considerably better than those of the pristine LaCoO3 catalyst due to their abundant oxygen vacancies. Consequently, we conclude that the oxygen vacancies of perovskite catalysts can be effectively engineered via two simple methods and play a significant role in CO oxidation.

Small polaron hopping conduction mechanism and enhanced thermoelectric power factor in the perovskite LaCoO3 ceramic.

Among the various thermoelectric oxide materials, perovskites offer more flexibility to adjust the interdependent thermoelectric parameters for an improved thermoelectric performance. In this work, we investigated the effect of A-site cation deficiency and Sr-substitution on the thermoelectric properties of the LaCoO3 ceramic synthesized via a solid-state reaction. A rhombohedral crystal structure with the R3̄c space group was revealed through Rietveld refinement of the XRD data. XPS analysis further confirmed the presence of multiple oxidation states of Co, and the mechanism of charge transport involving these multivalent cations was described using the small polaron hopping model. The La deficiency and Sr-substitution were found to increase the electrical conductivity in the LCO1 and LCO2 compositions, which resulted in a significant increase in the thermoelectric power factor. It was found that the increase in electrical conductivity of LCO1 and LCO2 was caused by a substantial reduction in the activation energy barrier for small polaron hopping conduction and an increase in fractional polaron concentration. The maximum power factor value of 78 μW m-1 K-2 was observed for the LCO2 composition at 403 K.

Ca substitution improves the catalytic activity of perovskite LaCoO3 toward toluene: comprehension of electronic structure alteration.

For perovskite La1-xCaxCoO3 (Ca-x, x = 0-0.3), Ca-0.2 with the closest O p band center to the Fermi level, displays the best catalytic activity for toluene oxidation. The O p band center determines the reducibility and active oxygen content. This finding is beneficial for the design of highly active perovskite catalysts.

Magnetic Field-Enhanced Electrocatalytic Oxygen Evolution on a Mixed-Valent Cobalt-Modulated LaCoO3 Catalyst.

Extensive efforts to enhance the oxygen evolution reaction (OER) catalytic performance of transition metal oxides mainly concentrate on the extrinsic morphology tailoring, lattice doping, and electrode interface optimizing. Nevertheless, little room is left for performance improvement using these methods and an obvious gap still exists compared to the precious metal catalysts. In this work, a novel "mixed-valent cobalt modulation" strategy is presented to enhance the electrocatalytic OER of perovskite LaCoO3 (LCO) oxide. The valence transition of cobalt is realized by ethylenediamine post reduction procedure at room temperature, which further induces the variation of magnetic properties for LCO catalyst. The optimized LCO catalyst with Co2+ /Co3+ of 1.98 % exhibits the best OER activity, and the overpotential at 10 mA cm-2 current density is decreased by 170 mV compared pristine LCO. Impressively, the ferromagnetic LCO catalyst can perform magnetic OER enhancement. By application of an external magnetic field, the overpotential of LCO at 10 mA cm-2 can be further decreased by 20 mV compared to that of under zero magnetic field, which arises from the enhanced energy states of electrons and accelerated electron transfer process driven by magnetic field. Our findings may provide a promising strategy to break the bottleneck for further enhancement of OER performance.

Perovskites with Enriched Oxygen Vacancies as a Family of Electrocatalysts for Efficient Nitrate Reduction to Ammonia.

Electrochemical nitrate reduction to ammonia (NRA) provides an efficient, sustainable approach to convert the nitrate pollutants into value-added products, which is regarded as a promising alternative to the industrial Haber-Bosch process. Recent studies have shown that oxygen vacancies of oxide catalysts can adjust the adsorption energies of intermediates and affect their catalytic performance. Compared with other metal oxides, perovskite oxides can allow their metal cations to exist in abnormal or mixed valence states, thereby resulting in enriched oxygen vacancies in their crystal structures. Here, the catalytic activities of perovskite oxides toward NRA catalysis with respect to the amount of oxygen vacancies are explored, where four perovskite oxides with different crystal structures (including cubic LaCrO3 , orthorhombic LaMnO3 and LaFeO3 , hexagonal LaCoO3 ) are chosen and investigated. By combining X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy and electrochemical measurements, it is found that the amount of oxygen vacancies in these perovskite oxides surprisingly follow the same order as their activities toward NRA catalysis (LaCrO3 <LaMnO3 <LaFeO3 <LaCoO3 ). Further theoretical studies reveal that the existence of oxygen vacancies in LaCoO3 perovskite can decrease the energy barriers for reduction of *HNO3 to *NO2 , leading to its superior NRA performance.

Electrochemical activation construction of LaCo1-x-yNixFeyO3 promoted by optimized lattice Ni doping toward water oxidation

Iron sites with high intrinsic activity for oxygen evolution reaction (OER) can effectively enhanced the performance of perovskite oxide as electrocatalyst for water electrolysis. However, doping of iron in perovskite LaCoO3 remains a challenge owing the strong Co–O bond and robust structure of LaCoO3. Herein, the lattice doping of Ni in LaCoO3 has been adopted to promote the interaction between iron ions and Co site in LaCoO3. Firstly, molten salt of Ni(NO3)2 provides free-moving Ni ions to substitute Co sites in the lattice of LaCoO3 forming LaCo1-xNixO3 at the optimized Ni doping condition. Then, iron ions can easily be absorbed to LaCo1-xNixO3 due to the strong interaction between Ni and Fe by electrochemical activation at room temperature. The prepared LaCo1-x-yNixFeyO3 nanoparticles keep the coarse surface for maximizing the exposure of active sites. The high-valence Co and oxygen vacancy from LaCo1-x-yNixFeyO3 contribute to the better intrinsic activity for OER, demonstrating the overpotential of ƞ10 of approximately 315 mV and good stability. The strategy of by introducing the lattice doping of other metal ion can realize the facile and effective construction of iron doped perovskite oxide for water oxidation.

PtPd nanoparticles on LaCoO3 with ruthenium in the interfaces for CO oxidation

In this work, trimetallic Pt-Pd-Ru nanoparticles (NPs) loaded on LaCoO3 perovskite were prepared by using LaCo0.9PtxPdyRu0.1-x-yO3 as precursor through citrate complexing sol-gol method and characterized by N2 adsorption/desorption, XRD, H2 Temperature-programmed reduction, XPS, CO-TPD, ICP-OES and TEM techniques. The special structure of the trimetallic catalyst and its catalytic performance for CO oxidation were investigated. The results demonstrated that Pt, Ru and Pd ions were successfully incorporated into the lattice of LaCoO3 to form with perovskite structure. After the reduction treatment, the catalyst Pt-Pd-Ru/LaCoO3 was obtained, which exhibited special structure of Pt surface, Pd sub-surface and Ru interface. The trimetallic Pt-Pd-Ru/LaCoO3 displayed the highest activity and best stability for CO oxidation as compared with corresponding bimetallic and monometallic catalysts. The significant improvement on the catalytic activity was ascribed to the combination of the oxygen vacancies on the surface of LaCoO3 and the highly dispersed NPs. The excellent stability was owing to the special metal-support interaction, that is the Pt-Pd in the NPs are connected and adhered to the support of LaCoO3 by the Ru species in the interface.