Perovskite Metal Oxides Research Articles

Enhanced performance of La1-xFeO3-δ oxygen carrier via A-site cation defect engineering for chemical looping dry reforming of methane

Chemical looping is a process-intensification tool that focuses on the fields of fossil fuel combustion, CO2 capture, hydrocarbon valorization, energy storage, and other energy-related and environmental-related areas. Perovskite-structured LaFeO3, a typical oxygen storage material, shows great potential for chemical looping partial oxidation and H2O/CO2 splitting. Here, we report a simple and efficient strategy to enhance catalytic activity by tuning A-site cation defects in perovskites via a sol-gel method. Systematically studies show that A-site cation defects affect both the physical and chemical properties. With the A-site cation defect engineering, the crystallite size of the La1-xFeO3-δ perovskites is reduced. The catalytic performance for CH4 oxidation and CO2 splitting is enhanced with increasing oxygen vacancy concentration. The La0.93FeO3-δ oxygen carrier exhibits the highest catalytic performance with 88% CO selectivity and 90% methane conversion at 750 °C. In addition, the La0.93FeO3-δ shows higher stability in the successive CH4 partial oxidation/CO2 splitting redox cycles, with almost unchanged CH4 conversion and CO selectivity. All these results demonstrate that the strategy of adjustment of different molar ratios of A/B site in perovskite metal oxides can effectively regulate the oxygen vacancy concentration.

Ultrafast synthesized LaFeO3-based oxides for highly sensitive n-propanol sensor

Metal-organic frameworks (MOFs) have been used as sacrificial templates to fabricate porous metallic oxides. However, its usage is limited in preparing rare earth perovskite-type oxides, which are usually synthesized by sol-gel method. Herein, sol-gel route was employed to construct the uniform La/Fe MOFs, completed in several seconds at room temperature. The fabricated LaFeO3/La2O3, LaFeO3 and LaFeO3/Fe2O3 have porous structure, and the LaFeO3 possesses the largest specific surface area of 18.16 m2/g. Besides, abundant oxygen species exist on the surface of LaFeO3/La2O3 and LaFeO3, with percentages of 68.13 % and 64.15 % in O 1 s spectra, respectively. Benefit from the morphology structure and elements states, the LaFeO3-based sensor exhibits an ultra-high response of 258.4–100 ppm n-propanol, and the LaFeO3/La2O3-based sensor possesses the detection limit of 0.16 ppm, at a quite low working temperature of 100 ℃. This work provided a facile, universal, and adjustable approach to design perovskite metal oxides for ultra-sensitive detection of various gases.

Multifunctional Hybrid Interfacial Layers for High-Performance Inverted Perovskite Solar Cells.

Challenges remain hindering the performance and stability of inverted perovskite solar cells (PSCs), particularly for the nonstable interface between lead halide perovskite and charge extraction metal oxide layer. Herein, a simple yet scalable interfacial strategy to facilitate the assemble of high-performance inverted PSCs and scale-up modules is reported. The hybrid interfacial layer containing self-assembly triphenylamine and conjugated poly(arylamine) simultaneously improves the chemical stability, charge extraction, and energy level alignment of hole-selective interface, meanwhile promoting perovskite crystallization. Consequently, the correspondent inverted PSCs and modules achieve remarkable power conversion efficiencies (PCEs) of 24.5% and 20.7% (aperture area of 19.4 cm2 ), respectively. The PSCs maintain over 80% of its initial efficiency under one-sun equivalent illumination of 1200 h. This strategy is also effective to perovskite with various bandgaps, demonstrating the highest PCE of 19.6% for the 1.76-eV bandgap PSCs. Overall, this work provides a simple yet scalable interfacial strategy for obtaining state-of-the-art inverted PSCs and modules.

Probing the Local Electronic Structure in Metal Halide Perovskites through Cobalt Substitution.

Owing to the unique chemical and electronic properties arising from 3d-electrons, substitution with transition metal ions is one of the key routes for engineering new functionalities into materials. While this approach has been used extensively in complex metal oxide perovskites, metal halide perovskites have largely resisted facile isovalent substitution. In this work, it is demonstrated that the substitution of Co2+ into the lattice of methylammonium lead triiodide imparts magnetic behavior to the material while maintaining photovoltaic performance at low concentrations. In addition to comprehensively characterizing its magnetic properties, the Co2+ ions themselves areutilizedas probes to sense the local electronic environment of Pb in the perovskite, thereby revealing the nature of their incorporation into the material. A comprehensive understanding of the effect of transition metal incorporation is provided, thereby opening the substitution gateway for developing novel functional perovskite materials and devices for future technologies.

Mechanical, optoelectronic and thermoelectric properties of the transition metal oxide perovskites YScO3 and LaScO3: First principle calculation

In this paper, we report a density functional theory (DFT) calculation study based on the full potential linear augmented plane wave (FP-LAPW) to discuss the mechanical stability as well as the optoelectronic and thermoelectric properties of two proposed orthorhombic transition metal oxide perovskites, namely, YScO3 and LaScO3. We found that our proposed perovskites are mechanically stable and elastically anisotropic materials. Also, they present promising thermal barrier coating (TBC) due to their high mechanical parameters. The topology of the band structure is of a wide energy gap insulator character for our compounds. We tested several functionals to recover the observed band gaps; especially the Eg band gap of LaScO3 has been a challenging problem with conventional exchange-correlation (XC) functionals used in the DFT calculations. Thus, the Yukawa-screened hybrid XC YS-PBE0 successfully gives Eg = 5.78 eV which is in good agreement with the experimental value of 5.8 eV. With DF-PT (perturbation theory) taking into account the lattice vibration, we found that our compounds have a high dielectric constant. We also calculated the main optical properties and found that both compounds have a large optical Eg, very small reflectivity, and could absorb light in the UV region and therefore, making them promising host materials for UV applications and ideal for optoelectronic devices.

Accessible chemical space for metal nitride perovskites.

Building on the extensive exploration of metal oxide and metal halide perovskites, metal nitride perovskites represent a largely unexplored class of materials. We report a multi-tier computational screening of this chemical space. From a pool of 3660 ABN3 compositions covering I-VIII, II-VII, III-VI and IV-V oxidation state combinations, 279 are predicted to be chemically feasible. The ground-state structures of the 25 most promising candidate compositions were explored through enumeration over octahedral tilt systems and global optimisation. We predict 12 dynamically and thermodynamically stable nitride perovskite materials, including YMoN3, YWN3, ZrTaN3, and LaMoN3. These feature significant electric polarisation and low predicted switching electric field, showing similarities with metal oxide perovskites and making them attractive for ferroelectric memory devices.

Homogeneously Nitrogen Doped BaLa4Ti4O15Extending Visible Light Responsive Range for Photocatalytic Oxygen Evolution

Homogeneous nitrogen doping is a promising strategy for narrowing the band gap of layered metal oxides without altering the crystal structures and microstructures of precursors. In this work, BaLa4Ti4O15, a (111) plane-type layered perovskite metal oxide with a band gap of about 3.77 eV, was doped with nitrogen by a thermal treatment in an ammonia atmosphere. The nitrogen dopants are homogeneously distributed in the layered perovskite framework, resulting in an extended band-to-band visible light absorption edge up to 600 nm, corresponding to a band gap of 2.07 eV. It is worth noting that the nitrogen doping process has trivial impact on the crystal structure, microstructure, and chemical states of the BaLa4Ti4O15, which minimizes the side effect of photogenerated carrier separation and surface chemical reaction. BaLa4Ti4O15–xNy exhibited efficient photocatalytic water oxidation activity under visible light. This work highlights the usefulness of homogeneous doping for tuning wide band gap layered metal oxides.

NiO@ZnO composite bimetallic nanocrystalline decorated TiO2-CsPbI3 photo-anode surface modifications for perovskite-sensitized solar cell applications

In this work, we fabricated a novel NiO@ZnO modification of TiO2-CsPbI3 photoanode-based Perovskite solar cells (PSCs). A facile hydrothermal synthesis is adopted for the preparation of NiO@ZnO-modified TiO2-CsPbI3 composite. The as-prepared NiO@ZnO modified TiO2-CsPbI3 composite is characterized by XRD, HR-TEM, SAED, FE-SEM with EDAX, AFM, XPS, FT-IR, UV-Vis, and Tauc plot analysis. UV-Vis spectra show that visible light absorption of the NiO@ZnO modified TiO2-CsPbI3 bilayer photoanode was more effective than NiO/ZnO modified TiO2-CsPbI3. XRD analysis showed the formation of NiO@ZnO in the TiO2-CsPbI3 in cubic crystalline nature. Morphological analyses were performed using FESEM, HRTEM, SAED, and AFM which revealed the formation of NiO@ZnO-modified TiO2-CsPbI3 with a multi-crystalline surface. EDAX and XPS analyses confirmed the presence of Ni, Zn, O, Ti, Cs, Pb, and I elements in the NiO@ZnO-modified TiO2-CsPbI3 composite. FT-IR spectra of perovskite metal oxide and hydroxide stretching vibrations peaks appeared at 920 and 3450 cm−1. The band gap was found to be 2.47 eV for NiO@ZnO-modified TiO2-CsPbI3 by using a Tauc plot. Finally, the photoanode-based PSCs were optimized by adding NiO@ZnO and TiO2-CsPbI3 composite, giving a high efficiency of 8.73%. We confirm that NiO@ZnO-modified TiO2-CsPbI3 bilayer photoanode-based PSCs show a better performance than NiO and ZnO-modified TiO2-CsPbI3.

Raman study of BiFeO3 nanostructures using different excitation wavelengths: Effects of crystallite size on vibrational modes

Bismuth ferrite (BiFeO3) is a perovskite metal oxide well known because of its multifunctional properties. In this study, we report Raman analysis of BiFeO3 nanostructures synthesized using the sol–gel method at different annealing conditions. The synthesis was conducted at two different annealing temperatures of 500 °C and 600 °C, and three different annealing rates of 2, 5, and 10 °C/min. The crystallite sizes and particle sizes were evaluated for the obtained nanostructures using X-ray diffraction and scanning electron microscopy. Raman scattering study was conducted for the prepared BiFeO3 samples at different excitation wavelengths in the visible and near-infrared region (457 nm, 532 nm, 633 nm, and 785 nm). The variations in the features of the Raman modes with different excitation wavelengths and annealing conditions were examined in detail. Resonant Raman scattering was observed when the excitation energy was comparable to or greater than the bandgaps of the BiFeO3 nanostructures, where the intensities of the A1-3, E-3, and E-4 vibrational modes increased. The variations in the relative intensities and areas of the A1-2 and A1-1 modes with the crystallite size were correlated with the occurrence of size-dependent magnetic properties in BiFeO3.

Evolution of electronic band reconstruction in thickness-controlled perovskite SrRuO$$_3$$ thin films

Transition metal perovskite oxides display a variety of emergent phenomena which are tunable by tailoring the oxygen octahedral rotation. SrRuO$_3$, a ferromagnetic perovskite oxide, is well-known to have various atomic structures and octahedral rotations when grown as thin films. However, how the electronic structure changes with the film thickness has been hardly studied. Here, by using angle-resolved photoemission spectroscopy and electron diffraction techniques, we study the electronic structure of SrRuO$_3$ thin films as a function of the film thickness. Different reconstructed electronic structures and spectral weights are observed for films with various thicknesses. We suggest that octahedral rotations on the surface can be qualitatively estimated via comparison of intensities of different bands. Our observation and methodology shed light on how structural variation and transition may be understood in terms of photoemission spectroscopy data.

Metal oxide Perovskite-Carbon composites as electrocatalysts for zinc-air batteries. Optimization of ball-milling mixing parameters

Zn-air batteries (ZABs) are promising electrochemical devices to store energy. Metal oxide perovskites mixed with carbon materials are highlighted as interesting materials for this application because of their appropriate bifunctional performance in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The interaction between both components of the electrocatalyst is important in the bifunctional electrocatalytic activity, and the mixing method plays an important role in this interaction. Then, different mixing methods have been studied in this work (ball-milling, mortar and manual shaking). The use of different physicochemical techniques such as temperature programmed desorption (TPD), temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) in the materials characterization, allows us to conclude that the mixing method strongly influences the particle size and the interaction between both components, which determine the final electrocatalytic activity. The materials prepared by ball-milling displayed the best performance. Herein, the experimental conditions were optimized to obtain electrocatalysts with enhanced electrocatalytic activity for ORR and OER. Low rotating speed, air atmosphere and low ball-milling time generate electrocatalysts with a small nanoparticle size, more homogeneous and with a higher interaction between both components, which enhances electron transfer, and consequently, the overall oxygen-involved reactions. The best electrocatalyst obtained was studied as air-electrode in a Zn-air battery and it was compared to a commercial Pt/C electrocatalyst, obtaining higher cyclability (55.2 vs 51.7 %) for 30 h, and higher energy density at 5 mA/cm2 (764 mAh/g vs 741 mAh/g).

A facile approach to improve the methane catalytic performance of LaCoO3 perovskite

Some series of LaCoO3 perovskite metal oxide catalysts were modified with different molar amounts of transition metal Co and Fe, namely LaCoO3-xCo and LaCoO3-yFe. They were applied to methane catalytic combustion, and the effects of Co and Fe doping on the defect structure mechanism of LaCoO3 crystal growth and on the performance of methane catalytic combustion were investigated, respectively. The results showed that hydrothermal addition of Co and Fe could both significantly improved the performance of LaCoO3 catalyst for methane catalytic combustion, with the best catalytic methane activity at x=2 and y=7, the T50 was 425 ℃ and 397 ℃, the T90 was 480 ℃ and 457 ℃, respectively. The performance of the hydrothermally modified catalysts were investigated by characterization techniques such as BET, XRD, SEM and XPS, and it turned out that the excellent activity was mainly due to the significantly enhanced oxygen migration rate and the altered LaCoO3 crystal growth mechanism constructing surface defects during the hydrothermal process. In conclusion, this study provides an efficient and simple method for the synthesis of methane combustion catalysts.

High-Performance Perovskite Bifunctional Electrocatalysts for Oxygen Reduction Reaction and Oxygen Evolution Reaction

Perovskite structured earth-abundant metal oxides are attractive candidates as bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolytes. Herein, we present a series of perovskite electrocatalysts (La0.65Sr0.3)zFeO3−δ with different A-site cation deficiencies through a simple and scalable solid-state synthesis method. Their electrocatalytic activities toward ORR and OER are studied by rotating disk electrode and rotating-ring disk electrode techniques in an alkaline electrolyte. Two obvious oxygen reduction potential regions are first reported in this work for these perovskites; the electron transfer number during ORR in the first oxygen reduction potential region is ∼2 and that in the second region is ∼4, indicating two different ORR mechanisms in these two potential regions. Among these perovskites, (La0.65Sr0.3)1.00FeO2.95 exhibits the highest electrocatalytic activity for ORR in the first ORR potential region with an onset potential of 0.72 V, a potential of 0.6 V at −1 mA cm–2, and a Tafel slope of 60.4 mV dec–1 in 0.1 M KOH. For OER in the alkaline electrolyte, (La0.65Sr0.3)0.89FeO2.9 with the highest A-site cation deficiency is proved to be the most active catalyst among these perovskites, which is mainly caused by its highest surface oxygen vacancy content. As a result, our work could provide guidance in the further development of easily prepared, scalable, and earth-abundant perovskite metal oxides.

Exposure Surface Active Sites of Perovskite‐Type LaFeO3 Gas Sensors by Selectively Dissolving La Cations for Enhancing Gas Sensing Properties to Acetone

AbstractWhile perovskite metal oxide semiconductors (MOS) gas sensors have great potential for detecting various hazardous gases, the surface enrichment of inactive A‐sites severely limits their ability to obtain excellent gas sensing properties. Herein, one simple and facile citric acid etching method is reported with the aim of significantly improving the acetone sensing properties of perovskite LaFeO3 (LFO) by surface structure optimization. Structural characterization shows that citric acid selectively solubilized the A‐site cations and inhibits the occurrence of La segregation on the surface without destroying the perovskite structure, thus increasing the exposure of the active site Fe. At the operating temperature of 200 °C, the response of etched LFO for 20 ppm acetone reaches 50, which is almost 12 times higher than that of pristine LFO sample. Meanwhile, the etched LFO samples also exhibit low detection limits (50 ppb), good selectivity, and stability. The enhanced gas sensitivity is attributed to near‐perfect surface metal ion ratio (La/Fe atomic ratio = 0.97) and abundant oxygen species concentration. This work provides an avenue to enhance the acetone sensing properties and beyond by intentional structural modification, which not only has great scientific meaning, but also valuable potential for industrial and domestic applications.

RGO/ReO3 nano composite modified electrode for the ultra-sensitive determination of dopamine and uric acid

Development of suitable modified electrode in generating the electrochemical signals from dopamine (DA), uric acid (UA) and ascorbic acid (AA) has remained challenging issue even after decades of research in the related field. Under the present investigation the perovskite type metal oxide nano particle has been used in the form of composite with the reduced graphene oxide (rGO) as the active material for sensing. The superior electrical conductivity of Rhenium oxide (ReO3) combined with the adsorptive and conducting nature of rGO has been utilised in enhancing the electrochemical responses form the molecules. Thin films of Nafion was used over the rGO/ReO3 composite materials for stabilization of the modification. The electron transfer property of the molecules has been evaluated from the cyclic voltammetry and electrochemical impedance measurements. The standard electron transfer rate constants have been obtained from the Laviron formulations of the cyclic voltammetry measurements. Simultaneous electrochemical response has been obtained from the three molecules over the rGO/ReO3 nano composite modified electrode, the analytical method has been developed with the detection limit (S/N = 3) of 0.08 nM, 0.06 μM and 0.89 μM for DA, UA and AA respectively. For simultaneous determination however, the determination of DA and UA has been proposed and the interference test was carried out through simultaneous detection of the signals of the molecules. The analytical method has been applied for the detection of analytical signals of DA and UA in synthetic serum samples through spiked recovery test.

Rational synthesis of rare-earth lanthanum molybdate covered reduced graphene oxide nanocomposites for the voltammetric detection of Moxifloxacin hydrochloride

Recently, perovskite structure-based metal oxide nanomaterials and their composites opted for electrocatalyst because of its excellent conductivity, unique, and favored electronic structure. In this attempt, herein we prepared the rare earth mixed metal molybdate covered reduced graphene oxide La2(MoO4)3@rGO nanocomposites by a simple hydrothermal method for the sensitive detection of Moxifloxacin hydrochloride (MOF) in pharmaceutical and human urine samples. The various physicochemical analysis such as SEM, TEM, XRD and Raman spectroscopy confirms the successful formation of (La2(MoO4)3@rGO) nanocomposites. Furthermore, the electroanalytical performance of La2(MoO4)3@rGO modified glassy carbon electrode (La2(MoO4)3@rGO/GCE) was analyzed using the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) which shows excellent results with a wide range of 1.0 × 10−8 M to 6.0 × 10−4 M and the detection limit of 2.84 × 10−9 M towards the MOF detection. Furthermore, the developed sensor expressed good selectivity, repeatability, stability and reproducibility. Finally, the real sample analysis of the developed sensor was tested in the MOF tablets and human urine samples, which shows the appreciable recoveries.

Accurate and Efficient Approximate Quasiparticle DFT‐1/2 Band Structure Calculations of Transition Metal Oxide Perovskites

The transition metal oxide perovskites are materials intensively studied due to their diversity of chemical and physical properties, as well as their potential for wide applications. From the theoretical point of view of ab initio calculations of quasiparticle (QP) energies and band structures, they remain a challenge. Herein, the performance of the low computational cost ab initio DFT‐1/2 approximate QP method is assessed for the nonmagnetic transition metal oxide perovskites, including 3d , , 4d , and 5d and . The results with experiments and a large set with other QP calculations are compared. It is demonstrated that the DFT‐1/2 method presents a remarkable accuracy for these materials, opening an avenue to study more complex systems.

Modified Calcium Manganites for Thermochemical Energy Storage Applications

CaAl0.2Mn0.8O3-δ (CAM28) and CaTi0.2Mn0.8O3-δ (CTM28) are perovskite metal oxides developed for high-temperature thermochemical energy storage (TCES) applications, e.g., in support of air Brayton power generation. Previous reports for these compounds focus on the equilibrium non-stoichiometry (δ) as a function of temperature and oxygen partial pressure (pO2) and the endotherm (or exotherm) accompanying changes in δ resulting from thermal reduction (or re-oxidation). Herein, we report results for elemental substitution and doping (Al, Co, Fe, La, Sr, Ti, Y, Zn, and Zr) of calcium manganites (CM) that establish the preference for CAM28 and CTM28. Techniques employed include conventional (screening and equilibrium) and ballistically heated multi-cycle thermogravimetric analysis (TGA), conventional and high temperature (in-situ) X-ray diffraction (XRD), and differential scanning calorimetry (DSC). Forward-looking results for A-site Y-doped materials, e.g., Ca0.9Y0.1MnO3-δ (CYM910), establish a route to increasing the reduction enthalpy relative to CAM28 and CTM28, albeit at the expense of increased reduction temperatures and raw materials costs. A thermodynamic model presented for CAM28, but extendable to related materials, provides values for the reaction enthalpy and extent of reduction as a function of temperature and oxygen partial pressure for use in design efforts. Taken as a whole, the results support the choice of Al-doped CaMnO3-δ as a low-cost material for TCES in a high temperature air Brayton application, but point the way to achieving higher stored energy densities that could lead to overall cost savings.

Electronic Engineering of ABO3 Perovskite Metal Oxides Based on d0 Electronic‐Configuration Metallic Ions toward Photocatalytic Water Splitting under Visible Light

Particulate photocatalytic water splitting is considered as one of the most promising and low‐cost routes toward green hydrogen production, toward which developing a semiconductor photocatalyst with a wide visible light response and high charge transfer velocity is the key issue. Metal oxides based on d 0‐configuration metal ions, especially those with the perovskite structure, are a group of ideal candidates toward photocatalytic water splitting, benefitting from their high structural stability, suitable conduction band minimum (CBM), and high carrier mobility. However, the main problems staggering the development of highly efficient photocatalysts are from the rather big bandgap of these d 0‐configuration metal oxides to cause limited UV light response and from the flexibly changed valence state of the d 0‐configuration metal cations in the B site of the perovskite structure. Various strategies are developed to address these problems, and the summary on electronic engineering strategies of the d 0‐metal‐based perovskite metal oxides toward visible light response and stable photocatalytic performance in this review is focused on. Finally, the construction of the photocatalytic overall water splitting (OWS) system based on these perovskite semiconductors is discussed and outlooked.

Highly thin film with aerosol-deposited perovskite quantum dot/metal oxide composite for perfect color conversion and luminance enhancement

Erstwhile, displays using down-converting color changing medium utilized color filters as an essential part of clarifying the trade-off between true colors and transmittance. In this study, we report the development of a novel, smart process for producing thin luminescent films that completely convert colors and enhance light intensity. Highly dense films are prepared by the co-deposition of perovskite quantum dots and metal oxide particles as color conversion layers and scattering agents, respectively. These layers can be directly deposited on blue organic light-emitting diodes using ultrasonic-assisted aerosol deposition (UAD). This method can allow displays using a down-conversion system to streamline the process due to absence of color filters. Using this method, films can be a minimum of 3 µm thick for complete conversion of blue light, a quarter that of inkjet-printed films. We demonstrate 7,353 cd m-2 in green and 411 cd m-2 in red converted emissions with no blue light leakage. Furthermore, the developed technique was shown to be compatible with versatile patterning processes. For example, UAD may be combined with a fine-metal shadow mask to produce a pattern of 30-μm-diameter dots. Even without using a mask, the method still produces a pattern of 13 μm wide lines. This system provides a new approach that may serve as an alternative to inkjet printing.