LaCoO3 Perovskite Research Articles

Praseodymium induced symmetry switching and electrochemical characteristics of LaCoO3 nanostructures

A comparative study of the crystal structures and electrochemical characteristics of bulk and nanoscale La1-xPrxCoO3 (x = 0, 0.3 and 0.6) perovskites is made using synchrotron x-ray diffraction, cyclic voltammetry, and galvanostatic charge/discharge methods. It is shown that the sol-gel synthesized nano structures and bulk LaCoO3 exhibit different crystal structures, viz., rhombohedral [a = b = 5.4401 Å, c = 13.134 Å (on hexagonal axes), Z = 6, R3‾c] and monoclinic [am = 5.3865 Å, bm = 5.4482 Å, cm = 7.6365 Å, βm = 89.010°, Z = 4, I2/a], respectively. The evidence for CoO6 octahedra distortion in bulk LaCoO3 is also gathered from the three distinct Raman active modes at 518, 646, and 688 cm−1 emerging due to the Jahn-Teller effect, which, in-turn, reduces the crystal symmetry for achieving structure stabilization. This amounts to changes in Co–O bond lengths and Co–O–Co bond angles with promotion of t2g electron to eg level simultaneously for Co3+(3d6) to attain an intermediate spin state (S = 1) or higher. However, Pr-insertion induces phase transition to orthorhombic in both but with space group Pnma in nanostructures and equivalent Pbnm in bulk. The substitution effect on the specific capacitance (C) is opposite in nature, i.e., while ‘C’ decreases from 149 to 12 F/g in nano structures, it increases from 0.4 to 4 F/g in bulk with increase in Pr-content from x=0 to 0.6. A galvanostatic charge-discharge test of pristine nano LaCoO3 performed at a constant scan rate of 50 mVs−1 reveals electrode electrochemical stability by retaining 96 % of specific capacitance ∼82.5 F/g for 2000 cycles at least. The variation in the crystal structure and bond length and/or angle plays a key role in controlling the electrochemical performance of Pr-substituted LaCoO3 perovskites.

Insights into the role of A/B-site substitution in chemical looping gasification of cotton stalk for enhanced syngas production over La-Co-O based perovskite oxygen carriers

Biomass chemical looping gasification (BCLG) is an emerging technology for efficient and clean utilization of cotton stalk (CS) to produce high-quality syngas. Among various oxygen carriers, perovskite oxides are holding an ever-increasing position in BCLG due to their unique structural properties and compositional flexibilities. However, research on perovskite-type oxygen carriers mostly focused on Fe-based oxides, and there is little in-depth investigation of Co-based perovskite and the role of A/B site substitution in the BCLG process. Herein, the LaCoO3 perovskite is selected as the basic oxygen carrier, and Sr, Fe are further doped on the A/B-site to form LaCo1-xFexO3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) and La1-ySryCoO3 (y = 0, 0.2, 0.4, 0.6, 0.8) series. Effects of perovskite type, gasification temperature, steam volume fraction and oxygen carrier mass fraction of the BCLG performance are investigated. Results indicate that La0.6Sr0.4CoO3 and LaCo0.2Fe0.8O3 exhibit enhanced syngas production with the maximum of 1.304 m3/kg and 1.188 m3/kg, respectively, and outstanding cyclic stability at optimal reaction conditions. Further characterizations including H2-TPR, XPS and EPR analysis reveal that Sr substitution facilitate the formation of oxygen vacancies and adsorbed oxygen species, while Fe doping leads to the increasing concentration of oxygen vacancies and surface lattice oxygen species. Combined with the experimental and characterization results, it is deduced that the oxygen vacancies which promote the adsorption of reactants and accelerate the migration of bulk lattice oxygen, play the key role in the enhanced BCLG performance.

CuOx supported LaCoO3 perovskite for the photoassisted reverse water gas shift reaction at low temperature

CuOx/LaCoO3 systems have been studied for the rWGS reaction under thermal assisted photocatalytic conditions within low temperature range of 180–330 ºC. CuOx species deposited from chemical reduction method over LaCoO3 homogeneously covered the perovskite surface. The reduction pretreatment before reaction leads to the partial Co reduction and the complete reduction of Cu. A significant improvement on CO production has been attained upon Cu incorporation. In addition, upon UV–vis irradiation the CO production is also enhanced. Best results have been obtained for 5 wt% Cu. The highest synergistic effect was observed for the lowest temperature, for which catalytic contribution is negligible. Thus, a good compromise is attained at 300 ºC for which a CO production of 5.45 mmol/h·g and 92 % selectivity, showing a good synergistic effect between thermo and thermo-photocatalytic activity.

Kinetics of N2O decomposition over bulk and supported LaCoO3 perovskites

For the first time, kinetic data on the decomposition of N2O over mixed oxide LaCoO3 with a perovskite structure have been obtained. Bulk LaCoO3 synthesized using microwave activation exhibited an increased intrinsic reaction rate with a 30 kJ mol–1 lower activation energy. Perovskite samples supported on ZrO2-La demonstrated lower intrinsic reaction rates due to the lower content of the LaCoO3 phase, but the activation energies were also lower by 50–80 kJ mol–1.

Correlating atomic-scale structural and compositional details of Ca-doped LaCoO3 perovskite nanoparticles with activity and stability towards the oxygen evolution reaction

Developing efficient oxygen evolution reaction (OER) electrocatalysts requires a thorough understanding of structure–activity-stability relationships, ideally at the atomic scale. Herein, we employed atom probe tomography and transmission electron microscopy to reveal compositional and structural changes on LaCoO3 and Ca-doped LaCoO3 surfaces during OER. We reveal that the topmost surfaces of pristine perovskite are terminated by the A-site element (La). After OER, amorphous La(OH)3 is formed on the surfaces of LaCoO3, which leads to significant activity deterioration. For Ca-doped LaCoO3, enhanced intercalation and penetration of hydroxide ions, along with the appearance of Co3+/4+ redox couple, are observed, contributing to its enhanced OER activity and stability. Our study demonstrates how atomic-scale compositional and structural details of electrocatalyst surfaces deepen our understanding of their activity and stability.

Interface engineering assisted La1-xSrxCoO3/FeOOH heterostructure as a high-performance electrocatalyst for oxygen evolution reaction

Perovskite oxides play a crucial role as catalysts in the oxygen evolution reaction (OER) owing to their distinctive structure and diverse physical and chemical characteristics. Currently, enhancing the electronic structure and specific surface area of the perovskite surface through strategic regulation poses a significant challenge in the advancement of perovskite catalyst development. Here, we propose a novel method for enhancing the OER activity of LaCoO3 (LCO) perovskite through atomic doping and interface engineering. The La0.6Sr0.4CoO3–FeOOH (Fe-LSCO) composite exhibits a notable enhancement in electrocatalytic performance, manifesting a low overpotential of 296.3 mV for the oxygen evolution reaction (OER) at a current density of 10 mA cm−2, while maintaining a high level of activity for a duration of 120 h. The enhanced activity of Fe-LSCO can be attributed to oxygen vacancy defects and the increase of the active site caused by A-site-doping and amorphous nanosheets of FeOOH, which synergistic effect reduces the energy barrier for water dissociation. The highly disordered surface and high surface energy of amorphous FeOOH render it highly active. This study presents a viable interface engineering approach for manipulating the reconstruction of the active phase in high-performance perovskite-based electrocatalytic materials.

Discerning the role of a site cation in ACoO3 perovskites for boosting Co3+/Co2+ redox cycle for pollutant degradation: DFT calculation, mechanism and toxicity evolution

The degradation of persistent and refractory pollutants, particularly plastic and resins manufacturing wastewater, poses a significant challenge due to their high toxicity and high concentrations. This study developed a novel hybrid ACoO3 (A = La, Ce, Sr)/PMS perovskite system for the treatment of multicomponent (MCs; ACN, ACM and ACY) from synthetic resin manufacturing wastewater. Synthesized perovskites were characterized by various techniques i.e., BET, XRD, FESEM with EDAX, FTIR, TEM, XPS, EIS, and Tafel analysis. Perovskite LaCoO3 exhibited the highest degradation of MCs i.e., ACN (98.7%), ACM (86.3%), and ACY (56.4%), with consumption of PMS (95.2%) under the optimal operating conditions (LaCoO3 dose 0.8 g/L, PMS dose 2 g/L, pH 7.2 and reaction temperature 55 °C). The quantitative contribution (%) of reactive oxygen species (ROS) reveals that SO4•− are the dominating radical species, which contribute to ACN (58.3% for SO4•− radicals) and ACM degradation (46.4% for SO4•− radicals). The tafel plots and EIS spectra demonstrated that perovskites LaCoO3 have better charge transfer rates and more reactive sites that are favorable for PMS activation. Further, four major degradation pathways were proposed based on Fukui index calculations, as well as GC-MS characterization of intermediate byproducts. Based on a stability and reusability study, it was concluded that LaCoO3 perovskites are highly stable, and minimal cobalt leaching occurs (0.96 mg/L) after four cycles. The eco-toxicity assessment performed using QSAR model indicated that the byproducts of the LaCoO3/PMS system are non-toxic nature to common organism (i.e., fish, daphnids and green algae). In addition, the cost of the hybrid LaCoO3/PMS system in a single cycle was estimated to be $34.79 per cubic meter of resin wastewater.

Study of structural and magnetic properties of Sn-doped cobaltite perovskite LaCoO3: experimental and DFT approach

Study of structural and magnetic properties of Sn-doped cobaltite perovskite LaCoO3: experimental and DFT approach

Supported LaCoO3 perovskite-like oxides for N2O decomposition: The key role of the support nature and LaCoO3 content

In this work a detailed comparison of the N2O decomposition catalytic performance of LaCoO3 perovskite-like mixed oxides supported over different commercial materials was conducted. Zirconia-, silica- and γ-alumina-based supports were studied. Zirconia-based supports turned out to be the most applicable because of the formation of the pure LaCoO3 perovskite phase on their surface. Among these supports, ZrO2-La revealed to possess the best activity owing to the highest Co2+/Co3+ (0.82) and Oads./OL (0.67) ratios on its surface. The raw of activities was as follows: LaCoO3(20 %)/ZrO2-La > LaCoO3(20 %)/ZrO2 > LaCoO3(20 %)/ZrO2-W. When the LaCoO3 content in LaCoO3/ZrO2-La was 20 wt%, the maximum of activity was observed – 94.78 mmol(N2O)/[g(cat.)·h] at 450 °C. This fact was in accordance with the highest Co2+/Co3+ (0.82) and Oads./OL (0.67) ratios at the 20 wt% LaCoO3 content. Coordinatively unsaturated Co2+, forming Lewis acid-base pairs, were proposed to be the active sites of the zirconia-based LaCoO3 catalysts in the N2O decomposition.

Non-PGM hollow fibre-based after-treatment for emission control under real diesel engine exhaust gas conditions

Hollow fibre (HF)-based technologies for emission control, as an alternative to the traditional monolithic technology, offers a promising route to the uptake of non-PGM catalytic systems. In this work, a series of Cu-doped LaCoO3 perovskites were investigated as potential non-PGM Diesel Oxidation Catalysts (DOC). Two HF-based modules, comprising single-channel (i.e., 1CM) and four-channel (i.e., 4CM) HFs respectively, were impregnated with the best catalyst candidate, and their performance was tested under real exhaust gas conditions, using a single-cylinder diesel engine. Compared to the 1CM, the 4CM demonstrated enhanced CO conversion, and reduced performance towards Total Hydrocarbon (THC) conversion. Overall, these findings reveal the influence of HF morphology on catalytic performance, and in turn, will contribute towards the refinement of HF-based technology for emission control, as well as enabling the transition towards non-PGM catalytic systems.

The spin-state effect on the redox performance of LaCoO3 perovskites

LaCoO3 is well-known for its unique thermally induced transition of Co3+ (3d6) ions from a low spin (LS) state to a higher spin state of intermediate spin (IS) state or high spin (HS) state, due to a delicate balance between crystal-field splitting and Hund’s coupling. In this work, we try to stabilize all possible spin states in the same initial structural model and further investigate the spin-state effect on the redox performance of LaCoO3. We find that an initial model of pseudocubic with R3¯c tilting octahedra was effective in stabilizing all possible spin states. The oxygen vacancy formation values of LS > HS + LS > HS > IS indicate that the IS state is the most optimal spin state in oxygen vacancy formation, which results from a weakened Co-O bonding energy by eg orbital occupation. The oxygen migration barriers of LS > IS > HS + LS > HS show that oxygen migration is easier in the relatively loose structure and thus LS structure is the most unfavorable in oxygen migration. Combining the oxygen vacancy formation and migration results, we conclude that the higher spin states of IS and HS are more beneficial than LS in oxygen conduction. Our results confirm the influence of the spin-state effect on oxygen conduction and show that spin-state regulation is a good strategy for improving the redox performance of perovskites.

A theoretical study of electronic, magnetic, magnetocaloric and thermoelectric of perovskite LaCoO3 compound with high spin

ABSTRACT The electronic and thermoelectric properties of the perovskite LaCoO3 compound were studied using first-principles calculations. However, Monte Carlo calculation (MC) combined with the Metropolis algorithm, calculates the magnetic and magneto-caloric properties. The partial moment of the Cobalt atom (Co) and exchange coupling interactions for Co-d orbital at high spin (HS: S = 2), show values µCo = 2.54 μ B , J 1 Co − Co = 2.39 meV , J 2 Co − Co = 0.9 meV , respectively. The calculated Curie temperature value (TC) is 100 K, which agrees with the experimental results, such as the LaCoO3 metallic perovskite has a secondary Ferro-Para magnetic transition around TC. The evolutions in magnetic and magnetocaloric (MEC) properties with external magnetic fields were also studied. Finally, thermoelectric properties are examined.

Visible-light photoelectric performance and bending stability of flexible LaCoO3/Mica thin films

New energy sources such as solar energy have been developed and utilized due to the shortage of non-renewable energy, and photoelectric materials have attracted more attention, accordingly. Moreover, flexible optoelectronic devices are crucial in the fields of wearable artificial intelligence, portable energy, and smart medical care. At present, photoelectric devices based on traditional perovskite cobalt oxide rigid films have problems such as inability to bend and deformation, which limits their application environment. Here, natural mica with atomically flat surface, high thermal stability, high transparency and good mechanical flexibility was selected as the substrate for preparing a series of LaCoO3 flexible photoelectric films. These films exhibit excellent photoelectric properties and flexible properties. More importantly, the flexible film still has fast response speed and reproducible light response after 500 bending cycles. It reveals that all-inorganic perovskite LaCoO3 is a promising candidate for designing high-performance, flexible and wearable optoelectronic devices.

Ultra-efficient decontamination via functionalized reactive electrochemical membrane for peroxymonosulfate activation: High water flux with extremely low energy consumption

A perovskite LaCoO3 functionalized Ti4O7 reactive electrochemical membrane (REM) was developed for electro-enhanced peroxymonosulfate (PMS) activation (E-REM-PMS), addressing limitations in wastewater treatment efficiency, reusability, and interference resistance. It achieved 100% carbamazepine (CBZ) removal at a rate constant of 39.69 min−1, 233 and 23 times of electro-REM (E-REM) system without PMS and REM-PMS system without electricity. In-situ Fourier transform infrared spectroscopy (FTIR) highlighted the promotion of electro-activation on PMS, while density functional theory (DFT) calculations elucidated mechanism differences under three adsorption configurations. 1O2 (2.97×10−9 M), SO4•− (2.09×10−11 M) and •OH (7.36×10−12 M) dominated the E-REM-PMS system, consistent with sequence of reactive species by DFT results. Continuous treatment of pharmaceutical wastewater confirmed 100% CBZ removal and 60%-70% TOC mineralization at ultrahigh water flux (642.86 L/m2·h) with minimal energy consumption (0.01 kWh/m3·order). This work proposed a high-performance and anti-fouling REM, offering an efficient and economical solution for wastewater treatment.

NOx Storage and Reduction (NSR) Performance of Sr-Doped LaCoO3 Perovskite Prepared by Glycine-Assisted Solution Combustion

Here, we successfully synthesized Sr-doped perovskite-type oxides of La1−xSrxCo1−λO3−δ, “LSX” (x = 0, 0.1, 0.3, 0.5, 0.7), using the glycine-assisted solution combustion method. The effect of strontium doping on the catalyst structure, NO to NO2 conversion, NOx adsorption and storage, and NOx reduction performance were investigated. The physicochemical properties of the catalysts were studied by XRD, SEM-EDS, N2 adsorption–desorption, FTIR, H2-TPR, O2-TPD, and XPS techniques. The NSR performance of LaCoO3 perovskite was improved after Sr doping. Specifically, the perovskite with 50% of Sr doping (LS5 sample) exhibited excellent NOx storage capacity within a wide temperature range (200–400 °C), and excellent stability after hydrothermal and sulfur poisoning. It also displayed the highest NOx adsorption–storage capacity (NAC: 1889 μmol/g; NSC: 1048 μmol/g) at 300 °C. This superior performance of the LS5 catalyst can be attributed to its superior reducibility, better NO oxidation capacity, increased surface Co2+ concentration, and, in particular, its generation of more oxygen vacancies. FTIR results further revealed that the LSX catalysts primarily store NOx through the “nitrate route”. During the lean–rich cycle tests, we observed an average NOx conversion rate of over 50% in the temperature range of 200–300 °C, with a maximum conversion rate of 61% achieved at 250 °C.

In-situ reconstruction of LaCoO3-Co3O4 hetero-interface over lanthanum modified Co3O4 nanocatalyst for improved catalytic activity and sintering resistance in methane combustion

Nanoparticles-based catalysts still suffer from deactivation due to sintering and structural collapse through long-time running at high reaction temperature. Developing simple strategy for improving the sintering resistance of nanoparticles is of great importance for fabrication of durable heterogeneous catalysts. In this work, lanthanum was used to prevent Co3O4 nanoparticles from sintering with restricting growth of nanocrystals by in-situ generation of LaCoO3 perovskite phase during thermal ageing process, further building LaCoO3-Co3O4 hetero-interface with strong interfacial effect. Specifically, the Co3O4 nanocatalyst was loaded with different amount of La by traditional impregnation method and a series of characterizations were carried out to explore the physical and chemical properties of the as-prepared catalysts, including XRD, Raman, BET, SEM, HRTEM, XPS, H2-TPR and O2-TPD. It was found that 5 wt% La-Co3O4 has the highest catalytic activity in CH4 combustion and the value of T90 (temperature of 90% methane conversion) between fresh and aged was only 9 ºC, while this value was 108 ºC over pure Co3O4 sample. The Raman, XPS, H2-TPR and O2-TPD results exhibited that the synergistic effect between Co3O4 and LaCoO3 could not only induce lattice distortion in Co3O4 with more defects and adsorbed oxygen species, enhanced oxygen mobility and reducibility, but also significantly suppress the growth of Co3O4 nanocrystals during thermal ageing treatment.

Enhanced photocatalytic activities of LaCoO3 perovskite nanostructures for degrading cationic and anionic dyes

Sustainable and cost-effective technologies are crucial for addressing environmental pollution issues. Perovskite photocatalysts have gained increased attention as a potential solution which could be accounted to their tuneable structural characteristics, flexible bandgap, and superior catalytic properties. In this study, we synthesized Lanthanum Cobaltite (LaCoO3) perovskite nanostructures via co-precipitation for photocatalytic purposes. Morphological analysis revealed LaCoO3 nanoparticles with an average size of ∼33 nm whose crystalline characteristics were investigated as a function of annealing temperatures. We found that the pure and crystalline LaCoO3 phase formed after the post-annealing process at 600°C. Photocatalytic studies showed that the degradation potential of LaCoO3 was significantly improved when hydrogen peroxide (H2O2) was added as co-catalyst system. We achieved degradation efficiencies of up to 91% and 85% for MB and methyl orange (MO), respectively. LaCoO3/H2O2 exhibited excellent photocatalytic potential for degrading both anionic and cationic organic dyes for environmental remediation applications.

The A-site and B-site regulation of LaCoO3 nanofiber based on electrospinning for boosting photocatalytic CO2 conversion

Photocatalytic CO2 reduction with perovskite can effectively address both energy and environmental issues. Nevertheless, it remains challenging to prepare photocatalysts with suitable hollow tubular structures in rational. Herein, the La1-xSrxCo1-δFeδO3 nanofiber with a hollow tubular structure was fabricated through an electrospinning method. The hollow nanofiber structure was constructed by doping Sr atoms in the A-site and Fe atoms in the B-site of LaCoO3 perovskite. The characterization of TEM proved that the hollow tubular structural La1-xSrxCo1-δFeδO3 nanofiber exhibited an external diameter of about 95 nm and an internal diameter of about 50 nm. The hollow tubular structural La1-xSrxCo1-δFeδO3 nanofiber showed superior carrier separation ability which could exhibit significant advantages for photocatalytic CO2 reduction. The CH3OH generation rate over the optimized La0.8Sr0.2Co0.7Fe0.3O3 nanofiber could reach 5.25 µmol⋅g−1⋅h−1. This work highlighted an electrospinning strategy to build a hollow tubular structural La1-xSrxCo1-δFeδO3 nanofiber for enhancing photoreduction CO2.

Electricity-pulse-sparked rapid combustion of diesel soot on conductive LaCoO3 catalysts

In coping with the rapid emission of massive soot particles during the cold starts of diesel vehicles, achieving rapid catalytic soot combustion at low temperatures is a formidable challenge. Herein, we developed an electricity-pulse-sparked catalysis (EPSC) strategy on a conductive LaCoO3 perovskite catalyst, creating instantaneous soot combustion. As soon as 800 J of electricity pulse is applied, approximately 80 % of soot is combusted within 1 min at <300 °C, exhibiting the higher reaction rates (180−1300 µmol gcat−1 s−1) and energy efficiencies (18−100 gsoot kWh−1) than previously reported results for catalytic soot combustion. Moreover, the EPSC eliminates the gap of contact between soot and catalyst that is a longstanding bottleneck for the specific solid (soot)-solid (catalyst)-gas (O2) reaction, which can be synchronized with the frequently engine start/stop operations, demonstrating potential to address the challenges of soot emissions for hybrid powers.

Hydrogen-Driven Low-Temperature Topotactic Transition in Nanocomb Cobaltite for Ultralow Power Ionic-Magnetic Coupled Applications.

We reversibly control ferromagnetic-antiferromagnetic ordering in an insulating ground state by annealing tensile-strained LaCoO3 films in hydrogen. This ionic-magnetic coupling occurs due to the hydrogen-driven topotactic transition between perovskite LaCoO3 and brownmillerite La2Co2O5 at a lower temperature (125-200 °C) and within a shorter time (3-10 min) than the oxygen-driven effect (500 °C, tens of hours). The X-ray and optical spectroscopic analyses reveal that the transition results from hydrogen-driven filling of correlated electrons in the Co 3d-orbitals, which successively releases oxygen by destabilizing the CoO6 octahedra into CoO4 tetrahedra. The transition is accelerated by surface exchange, diffusion of hydrogen in and oxygen out through atomically ordered oxygen vacancy "nanocomb" stripes in the tensile-strained LaCoO3 films. Our ionic-magnetic coupling with fast operation, good reproducibility, and long-term stability is a proof-of-principle demonstration of high-performance ultralow power magnetic switching devices for sensors, energy, and artificial intelligence applications, which are keys for attaining carbon neutrality.