Oxide Research Articles

Modeling of Nanomaterials for Supercapacitors: Beyond Carbon Electrodes.

Capacitive storage devices allow for fast charge and discharge cycles, making them the perfect complements to batteries for high power applications. Many materials display interesting capacitive properties when they are put in contact with ionic solutions despite their very different structures and (surface) reactivity. Among them, nanocarbons are the most important for practical applications, but many nanomaterials have recently emerged, such as conductive metal-organic frameworks, 2D materials, and a wide variety of metal oxides. These heterogeneous and complex electrode materials are difficult to model with conventional approaches. However, the development of computational methods, the incorporation of machine learning techniques, and the increasing power in high performance computing now allow us to tackle these types of systems. In this Review, we summarize the current efforts in this direction. We show that depending on the nature of the materials and of the charging mechanisms, different methods, or combinations of them, can provide desirable atomic-scale insight on the interactions at play. We mainly focus on two important aspects: (i) the study of ion adsorption in complex nanoporous materials, which require the extension of constant potential molecular dynamics to multicomponent systems, and (ii) the characterization of Faradaic processes in pseudocapacitors, that involves the use of electronic structure-based methods. We also discuss how recently developed simulation methods will allow bridges to be made between double-layer capacitors and pseudocapacitors for future high power electricity storage devices.

Hypoeutectic Liquid Metal Printing of 2D Indium Gallium Oxide Transistors.

2D native surface oxides formed on low melting temperature metals such as indium and gallium offer unique opportunities for fabricating high-performance flexible electronics and optoelectronics based on a new class of liquid metal printing (LMP). An inherent property of these Cabrera-Mott 2D oxides is their suboxide nature (e.g., In2O3-x), which leads high mobility LMP semiconductors to exhibit high electron concentrations (ne >1019cm-3) limiting electrostatic control. Binary alloying of the molten precursor can produce doped, ternary metal oxides such as In-X-O with enhanced electronic performance and greater bias-stress stability, though this approach demands a deeper understanding of the native oxides of alloys. This work presents an approach for hypoeutectic rapid LMP of crystalline InGaOx (IGO) at ultralow process temperatures (180°C) beyond the state of the art to fabricate transistors with 10X steeper subthreshold slope and high mobility (≈18cm2Vs-1). Detailed characterization of IGO crystallinity, composition, and morphology, as well as measurements of its electronic density of states (DOS), show the impact of Ga-doping and reveal the limits of doping induced amorphization from hypoeutectic precursors. The ultralow process temperatures and compatibility with high-k Al2O3 dielectrics shown here indicate potential for 2D IGO to drive low-power flexible transparent electronics.

The enhanced nonlinear absorption, nonlinear refraction and optical limiting properties of Bi2WO6/ZnO composites

The Bi2WO6/ZnO (BWO/ZnO) composites were synthesized by using a hydrothermal method. Then, the BWO/ZnO composites were poured into methyl methacrylate through polymerization to make the BWO/ZnO/PMMA organic glasses (OGs) with different amounts. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to investigate the crystal structures and morphology size of BWO/ZnO composites. The nonlinear absorption (NLA), nonlinear refraction (NLR) and optical limiting (OL) properties were systematically investigated by using the Z-scan technique at 532 nm. The BWO/PMMA and BWO/ZnO/PMMA OGs may transform from saturable absorption (SA) to reverse saturable absorption (RSA) by varying the input energy. The NLA, NLR and OL performances of the BWO/ZnO/PMMA OGs are superior to those of the BWO/PMMA OGs and other bismuth-based metal oxides. The synergistic interaction of BWO and ZnO plays a crucial role in the BWO/ZnO/PMMA OGs. The NLA mechanisms were analyzed using an energy-level model.

Synthesis of CuO/NiO nanostructured hybrid electrode for supercapacitors

Supercapacitors employing copper metal oxides have garnered significant interest due to their substantial theoretical capacity and expansive active surface area. However, the performance of pure copper oxide electrode materials cannot meet the high demands currently placed on supercapacitors. In this study, a convenient, efficient, two-step electrodeposition method was utilized to develop micro/nanostructures of CuO/NiO on nickel foam. The synthetic strategy optimizes the capacitive performance of the composite by adjusting the deposition parameters during the growth of the NiO film.The CuO/NiO electrode can provide an area ratio capacitance of up to 1435.62 mF/cm2, the addition of NiO improves the area capacitance of the electrode material and the capacitance retention after cycling. In addition, the CuO/NiO composite material has been used to prepare solid-state symmetric supercapacitors, the device can reach a maximum energy and power density of 31.89 μWh/cm2 and 2099.76 μW/cm2, respectively. These results suggest that CuO/NiO electrodes exhibit promising potential as energy storage electrode materials.

Minimal doping approach to activate lattice oxygen participation in K2WO4 electrocatalysts for oxygen evolution reaction

Understanding oxygen redox processes is pivotal for advancing oxygen evolution catalysts, critical in electrochemical devices for renewable fuel synthesis. Thermodynamic instability of high entropy metal oxides can interfere with oxygen redox reactions via electrochemical reconstruction. Transforming a W5N4 pre-catalyst into thermodynamically stable K2WO4 through electrochemical treatment in KOH, and incorporating minimal Fe doping, modifies the oxygen evolution reaction (OER) pathway towards oxygen redox activity, significantly influenced by the pH of the electrolyte. The Fe-doped K2WO4 catalyst demonstrates superior OER performance, achieving 10 mA/cm^2 at an overpotential of merely 181 mV (without iR compensation) and sustaining a lifetime of 1200 h at 1000 mA/cm2. Electrochemical methods and DFT calculations confirmed Fe doping creates oxygen vacancies and increases electron density near the Fermi level, enhancing the OER pathway. This methodology offers a versatile approach to adapt high entropy catalysts for broad electrochemical energy conversion applications, highlighting its potential for innovation in renewable energy technologies.

How the Interplay between SnO2 and Zn(II) Porphyrins Impacts on the Electronic Features of Gaseous Acetone Chemiresistors.

Herein, the integration of SnO2 nanoparticles with two Zn(II) porphyrins─Zn(II) 5,10,15,20-tetraphenylporphyrin (ZnTPP) and its perfluorinated counterpart, Zn(II) 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (ZnTPPF20)─was investigated for the sensing of gaseous acetone at 120 °C, adopting three Zn-porphyrin/SnO2 weight ratios (1:4, 1:32, and 1:64). For the first time, we were able to provide evidence of the correlation between the materials' conductivity and these nanocomposites' sensing performances, obtaining optimal results with a 1:32 ratio for ZnTPPF20/SnO2 and showcasing a remarkable detection limit of 200 ppb together with a boosted sensing signal with respect to bare SnO2. To delve deeper, the combination of experimental data with density functional theory calculations unveiled an electron-donating behavior of both porphyrins when interacting with tin dioxide semiconductor, especially for the nonfluorinated one. The study suggested that the interplay between electrons injected, from the porphyrins' highest occupied molecular orbital to SnO2 conduction band, and the latter's available electronic states has a dramatic impact to boost the chemiresistive sensing. Indeed, we highlighted that the key lies in preventing the full saturation of SnO2 electronic states concomitantly increasing the materials' conductivity: in this respect, the best compromise turned out to be the perfluorinated porphyrin. A further corroboration of our findings was obtained by illuminating the sensors during measurements with light-emitting diode (LED) light. Actually, we demonstrated that it does not have any impact on improving the sensing behavior, most probably due to the electronic oversaturation and scattering caused by LED excitation in porphyrins. Lastly, the most effective hybrids (1:32 ratio) were physicochemically characterized, confirming the physisorption of the macrocycles onto the SnO2 surface. In conclusion, herein, we underscore the feasibility of customizing the porphyrin chemistry and porphyrin-to-SnO2 ratio to enhance the gaseous sensing of bare metal oxides, providing valuable insights for the engineering of highly performing light-free chemiresistors.

Tuning the Local Environment of Pt Species at CNT@MO2-x (M = Sn and Ce) Heterointerfaces for Boosted Alkaline Hydrogen Evolution.

As the most promising hydrogen evolution reaction (HER) electrocatalysts, platinum (Pt)-based catalysts still struggle with sluggish kinetics and expensive costs in alkaline media. Herein, we accelerate the alkaline hydrogen evolution kinetics by optimizing the local environment of Pt species and metal oxide heterointerfaces. The well-dispersed PtRu bimetallic clusters with adjacent MO2-x (M = Sn and Ce) on carbon nanotubes (PtRu/CNT@MO2-x) are demonstrated to be a potential electrocatalyst for alkaline HER, exhibiting an overpotential of only 75 mV at 100 mA cm-2 in 1 M KOH. The excellent mass activity of 12.3 mA μg-1Pt+Ru and specific activity of 32.0 mA cm-2ECSA at an overpotential of 70 mV are 56 and 64 times higher than those of commercial Pt/C. Experimental and theoretical investigations reveal that the heterointerfaces between Pt clusters and MO2-x can simultaneously promote H2O adsorption and activation, while the modification with Ru further optimizes H adsorption and H2O dissociation energy barriers. Then, the matching kinetics between the accelerated elementary steps achieved superb hydrogen generation in alkaline media. This work provides new insight into catalytic local environment design to simultaneously optimize the elementary steps for obtaining ideal alkaline HER performance.

Insulated π-Conjugated Azido Scaffolds for Stepwise Functionalization via Huisgen Cycloaddition on Metal Oxide Surfaces.

In organic-inorganic hybrid devices, fine interfacial controls by organic components directly affect the device performance. However, fabrication of uniformed interfaces using π-conjugated molecules remains challenging due to facile aggregation by their strong π-π interaction. In this report, a π-conjugated scaffold insulated by covalently linked permethylated α-cyclodextrin moiety with an azido group is synthesized for surface Huisgen cycloaddition on metal oxides. Fourier-transformed infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy confirm the successful immobilization of the insulated azido scaffold on ZnO nanowire array surfaces. Owing to the highly independent immobilization, the scaffold allows rapid and complete conversion of the surface azido group in Huisgen cycloaddition reactions with ethynyl-terminated molecules, as confirmed by FT-IR spectroscopy monitoring. Cyclic voltammetry analysis of modified indium tin oxide substrates shows the positive effects of cyclic insulation toward suppression of intermolecular interaction between molecules introduced by the surface Huisgen cycloaddition reactions. The utility of the scaffold for heterogeneous catalysis is demonstrated in electrocatalytic selective O2 reduction to H2O2 with cobalt(II) chlorin modified fluorine doped tin oxide electrode and photocatalytic H2 generation with iridium(III) dye-sensitized Pt-loadedTiO2 nanoparticle. These results highlight the potential of the insulated azido scaffold for a stepwise functionalization process, enabling precise and well-defined hybrid interfaces.

In-situ 4D-STEM Study of Chemo-Mechanical Interactions during Metal Oxidation

In-situ 4D-STEM Study of Chemo-Mechanical Interactions during Metal Oxidation

High Frequency Breakdown Characteristics of Alumina Filler Content Epoxy Resin

Power electronic transformers have high insulation frequency and compact insulation structure, and insulation performance is one of the main factors restricting their further development. Epoxy resin is an important insulating material in the electrical industry, its thermal conductivity and mechanical properties can not meet the needs of high-frequency transformers, usually metal oxide (Al2O3, etc.) is added to form composite insulation material. It is of great reference value for the insulation design of power electronic transformer to study the insulation performance of composite insulation materials with different filler content ratio under high-frequency AC. The effects of power supply frequency and alumina filler content on the breakdown performance of the composite were investigated experimentally. The results show that the breakdown voltage of pure epoxy resin decreases exponentially with frequency. At any filler content, the breakdown voltage of epoxy resin decreases with the increase of frequency, and the decreasing trend gradually slows down when the frequency increases from 50Hz to 1000Hz, and the decreasing trend gradually increases when the frequency increases to 2000Hz. The breakdown voltage of epoxy resin showed a down-rise-down trend with the increase of filler content, and the effect of filler content on breakdown voltage gradually weakened with the increase of frequency.

Oestrone removal by anodic oxidation using different mixed metal oxide anodes and graphite cathode

ABSTRACT In this study, the removal of oestrone (E1), one of the endocrine disrupting compounds (EDCs) that strongly affects the life activities of organisms in the receiving water environment and is naturally secreted by many organisms and enters water resources, was investigated by the anodic oxidation (AO) process using titanium (Ti) anode and different metal oxide (MMO) anodes (Ti/Pt, Ti/IrO2, Ti/RuO2, Ti/IrO2-Ta2O5 and Ti/IrO2-RuO2-SnO2) and graphite cathode. Batch experiments showed removal efficiencies between 86.1 and 92.3%. The highest removal efficiency was obtained at the Ti/Pt anode using an applied current of 1.5 A (28 mA/cm2 current density), an initial pH of 8.3, an initial E1 concentration of 20 mg/L, an oxidation time of 160 min and an electrolyte concentration of 0.1 M Na2SO4. Different E1 concentrations (5 mg/L, 10 mg/L, 20 mg/L) were investigated. After 160 min, the removals were 97.9%, 95.5% and 92.4%, with degradation rates (k) of 0.0235, 0.0186 and 0.0158 min−1 and high R2 values. The specific energy consumption was also calculated to be in the range of 396–412 kWh/m3 and the lowest SEC value was obtained at an initial E1 concentration of 20 mg/L.

Binary transition metal oxide: A novel and efficient catalyst for the synthesis of boron nitride nanotubes

AbstractA novel binary transition metal oxide (NiFe2O4) nanosphere catalyst with a diameter of 500 nm has been synthesized by the hydrothermal reaction, which can efficiently catalyze the formation of hexagonal boron nitride nanotubes (BNNTs) with high‐yield and large aspect ratio. Based on the temperature dependence of the product phase composition and microstructure, combined with results generated using single‐component catalysts, the BNNTs formation process can be summarized as follows: NiFe2O4 reacts with NH3 to generate Fe0.64Ni0.36, which dissolves to form a liquid‐phase Ni‐Fe alloy at high temperatures, where the B component in the precursor and the N atom formed by the decomposition of NH3 diffuse on the surface of the Ni‐Fe alloy; when the concentration of B and N exceed the saturation threshold, hollow BNNTs containing catalyst at the tips are precipitated. The formation process is dominated by a vapor‐liquid‐solid mechanism with tip‐growth mode, where the synergistic catalytic effect of the Ni‐Fe binary system promotes a high yield of large aspect ratio BNNTs.

Selective degradation of pollutants in the Mn-NG/PMS system: The crucial role of surface reactive Mn(IV) species

The combination of transition metal oxides with carbon-based materials is a promising strategy for constructing efficient catalysts for peroxymonosulfate (PMS) activation to degrade aqueous organic contaminants. However, the complex heterostructure of the composites often hinders the identification of the actual reactive species responsible for pollutant degradation. In this study, we integrate Mn3O4 into N-doped graphite (NG) to elucidate the mechanisms involved in the Mn-NG composite mediated PMS activation process. The Mn-NG/PMS system shows excellent performance in oxidizing bisphenol A (BPA) over a wide pH range (3.4 to 9.4) and in the presence of co-existing substrates. Mn sites in Mn3O4 are responsible for the activation of PMS, and the NG matrix enhances the dispersion of Mn in the Mn-NG composite. Multiple experimental results indicate that free radicals (i.e., hydroxyl radicals (HO•) and sulfate radicals (SO4•−)) are not generated, and surface reactive Mn(IV) is proposed as the primary reactive species for BPA oxidation. This study provides new insights into understanding the role of Mn oxides in carbon-based composites in PMS activation for degradation of organic pollutants.

Structural Manipulation of Functional Metal Oxides by In-Situ TEM

Structural Manipulation of Functional Metal Oxides by In-Situ TEM

Enabling long-distance hydrogen spillover in nonreducible metal-organic frameworks for catalytic reaction

Hydrogen spillover is an extraordinary effect in heterogeneous catalysis and hydrogen storage, which refers to the surface migration of metal particle-activated hydrogen atoms over the solid supports. Historical studies on this phenomenon have mostly been limited to reducible metal oxides where the long-distance proton-electron coupled migration mechanism has been established, yet the key question remains on how to surmount short-distance and defect-dependent hydrogen migration on nonreducible supports. By demerging hydrogen migration and hydrogenation reaction, here we demonstrate that the hydrogen spillover in nonreducible metal-organic frameworks (MOFs) can be finely modulated by the ligand functional groups or embedded water molecules, enabling significant long-distance (exceed 50 nm) movement of activated hydrogen. Furthermore, using sandwich nanostructured MOFs@Pt@MOFs as catalysts, we achieve highly selective hydrogenation of N-heteroarenes via controllable hydrogen spillover from Pt to MOFs-shell. We anticipate that this work will enhance the understanding of hydrogen spillover and shed light on de novo design of MOFs supported catalysts for many important reactions involving hydrogen.

Electrolysis of CuCl/HCl aqueous system in Cu–Cl thermochemical cycle for green hydrogen production: Investigations on alternative to platinum anode

The ICT-OEC Cu–Cl cycle is a six-step thermochemical copper-chlorine (Cu–Cl) closed-loop cycle to produce green hydrogen via water splitting. One of the critical steps in this cycle involves the electrolysis of CuCl to generate copper (Cu) and cupric chloride (CuCl2). Using platinum as the anode material in this system is economically disadvantageous and expensive. Consequently, this work investigates the feasibility of alternative anode materials to replace platinum. Mixed Metal Oxide (MMO) coated on Ti mesh (MMO mesh) and Pt coated on Ti mesh (Pt mesh) were evaluated as suitable anode alternatives to pure Pt sheet based on their performance metrics at different voltages. The integration of MMO mesh for a 100-h Time on Stream (TOS) study at a mini-pilot scale demonstrated promising current density and efficiency values. However, performance variations were observed over prolonged operation, potentially due to changes in membrane resistance. After 100 h, the MMO mesh remained undamaged, indicating its durability for extended use. Characterization studies revealed the electrodeposited copper to have a dendritic structure with an FCC phase. The findings suggest that MMO mesh and Pt mesh are viable alternatives to platinum at operating voltages above 0.7 V in this system.

Spin Symmetry Breaking‐Induced Hubbard Gap Near‐Closure in N‐Coordinated MnO2 for Enhanced Aqueous Zinc‐Ion Battery Performance

AbstractTransition metal oxides (TMOs) are promising cathode materials for aqueous zinc ion batteries (ZIBs), however, their performance is hindered by a substantial Hubbard gap, which limits electron transfer and battery cyclability. Addressing this, we introduce a heteroatom coordination approach, using triethanolamine to induce axial N coordination on Mn centers in MnO2, yielding N‐coordinated MnO2 (TEAMO). This approach leverages the change of electronegativity disparity between Mn and ligands (O and N) to disrupt spin symmetry and augment spin polarization. This enhancement leads to the closure of the Hubbard gap, primarily driven by the intensified occupancy of the Mn eg orbitals. The resultant TEAMO exhibit a significant increase in storage capacity, reaching 351 mAh g−1 at 0.1 A g−1. Our findings suggest a viable strategy for optimizing the electronic structure of TMO cathodes, enhancing the potential of ZIBs in energy storage technology.

Surface-Enhanced Infrared Absorption Spectroscopy by Resonant Vibrational Coupling with Plasmonic Metal Oxide Nanocrystals.

Coupling between plasmonic resonances and molecular vibrations in nanocrystals (NCs) offers a promising approach for detecting molecules at low concentrations and discerning their chemical identities. Metallic NC superlattices can enhance vibrational signals under far-field detection by generating a myriad of intensified electric field hot spots between the NCs. Yet, their effectiveness is limited by the fixed electron concentration dictated by the metal composition and inefficient hot spot creation due to the large mode volume. Doped metal oxide NCs, such as tin-doped indium oxide (ITO), could overcome these limitations by enabling broad tunability of resonance frequencies in the mid-infrared range through independent variation of size and doping concentration. This study investigates the potential of close-packed ITO NC monolayers for surface-enhanced infrared absorption by quantifying trends in the coupling between their plasmon modes and various molecular vibrations. We show that maximum vibrational signal intensity occurs in monolayers composed of larger, more highly doped NCs, where the plasmon resonance peak lies at higher frequency than the molecular vibration. Using finite element and mutual polarization methods, we establish that near-field enhancement is stronger on the low-frequency side of the plasmon resonance and for more strongly coupled plasmonic NCs, thus rationalizing the design rules we experimentally uncovered. Our results can guide the development of optimal metal oxide NC-based superstructures for sensing target molecules or modifying their chemical properties through vibrational coupling.

P2-Type Na0.84Li0.1Ni0.27Mn0.63O2-Layered Oxide Na-Ion Battery Cathode: Structural Insights and Electrochemical Compatibility with Room-Temperature Ionic Liquids.

Modern technologies that can replace state-of-the-art Li-ion batteries (LIBs), such as Na-ion batteries (NIBs), are currently driving new advancements in energy storage research. Developing functional active materials having sustainable features and enhanced performances able to assess their exploitation in the large-scale market represents a major challenge. Rationally designed P2-type layered transition metal (TM) oxides can enable high-energy NIB cathodes, where the tailored composition directly tunes the electrochemical and structural properties. Such positive electrodes need stable electrolytes, and exploration of unconventional room-temperature ionic liquid (RTIL)-based formulations paves the route toward safer options to flammable organic solvents. Notwithstanding the fact that Li+ doping in these materials has been proposed as a viable strategy to improve structural issues, an in-depth understanding of structure-property relationship as well as electrochemical testing with innovative RTIL-based electrolytes is still missing. Herein, we propose the solid-state synthesis of P2-Na0.84Li0.1Ni0.27Mn0.63O2 (NLNMO) cathode material, which exhibits promising structural reversibility and superior capacity retention upon cycling when tested in combination with RTIL-based electrolytes (EMI-, PYR14-, and N1114-FSI) compared to the standard NaClO4/PC. As unveiled from DFT calculations, lattice integrity is ensured by the reduced Jahn-Teller distortion upon Na removal exerted by Mn4+ and Li+ sublattices, while the good redox reversibility is mainly associated with the electrochemically active Ni2+/Ni3+/Ni4+ series burdening the charge compensation upon desodiation. By declaring the electrochemical compatibility of the P2-NLNMO cathode with three RTIL-based electrolytes and dissecting the role of Li/Ni/Mn sublattices in determining the electrochemical behavior, our comprehensive study enlightens the potential application of this electrode/electrolyte setup for future high-energy NIB prototype cells.

Full prediction of band potentials in semiconductor materials

A machine learning (ML) framework to predict the physical band potentials for a range of semiconductor materials, from metal sulfide, oxide, and nitride, to oxysulfide and oxynitride, is hereby described. A valence band maximum (VBM) model was established via the transfer learning of a relatively large dataset of 2D materials (1382 samples, but with incorrect VBM potentials) to a much smaller dataset of physically measured VBM for bulk 3D materials (87 samples) on a crystal graph convolutional neural network. This gave predictions with experimental accuracy for a wide range of materials (RMSE = 0.27 eV), which is a 3-fold improvement compared with ML trained on the physical dataset without transfer learning (RMSE = 0.75 eV). When combined with the bandgap prediction model (RMSE = 0.29 eV), a full prediction of conduction and valence band potentials can be made, which to the best of our knowledge, is the first for any ML framework. The variation of band potentials across low-index surfaces was predicted correctly and verified with reported physical potentials. In fact, the framework is able to capture variation in band potentials associated with minor atomic position alterations. Based on this, a general trend between surface atomic displacement and VBM shift is observed across various semiconductor materials. The model is not yet able to cope with major rearrangement of atomic sequence on surface layers, i.e., surface reconstructions., since it was not trained with such data but can be easily done so with specifically designed dataset. As an example application, the ML framework was used for the screening of potential photocatalytic materials for visible light water splitting. A total of 824 materials was successfully identified, including those experimentally-verified in the literature.