Air-Stable High-Entropy Layered Oxide Cathode with Enhanced Cycling Stability for Sodium-Ion Batteries.

O3-type layered oxides have been extensively studied as cathode materials for sodium-ion batteries due to their high reversible capacity and high initial sodium content, but they suffer from complex phase transitions and an unstable structure during sodium intercalation/deintercalation. Herein, we synthesize a high-entropy O3-type layered transition metal oxide, NaNi0.3Cu0.05Fe0.1Mn0.3Mg0.05Ti0.2O2 (NCFMMT), by simultaneously doping Cu, Mg, and Ti into its transition metal layers, which greatly increase structural entropy, thereby reducing formation energy and enhancing structural stability. The high-entropy NCFMMT cathode exhibits significantly improved cycling stability (capacity retention of 81.4% at 1C after 250 cycles and 86.8% at 5C after 500 cycles) compared to pristine NaNi0.3Fe0.4Mn0.3O2 (71% after 100 cycles at 1C), as well as remarkable air stability. Finally, the NCFMMT//hard carbon full-cell batteries deliver a high initial capacity of 103 mAh g-1 at 1C, with 83.8 mAh g-1 maintained after 300 cycles (capacity retention of 81.4%).

Defective Tungsten Oxides with Stacking Faults for Proton Exchange Membrane Green-Hydrogen Generation.

Defects can introduce atomic structural modulation and tailor performance of materials. Herein, it demonstrates that semiconductor WO3 with inert electrocatalytic behavior can be activated through defect-induced tensile strains. Structural characterizations reveal that when simply treated in Ar/H2 atmosphere, oxygen vacancies will generate in WO3 and cause defective structures. Stacking faults are found in defects, thus modulating electronic structure and transforming electrocatalytic-inert WO3 into highly active electrocatalysts. Density functional theory (DFT) calculations are performed to calculate *H adsorption energies on various WOx surfaces, revealing the oxygen vacancy composition and strain predicted to optimize the catalytic activity of hydrogen evolution reaction (HER). Such defective tungsten oxides can be integrated into commercial proton exchange membrane (PEM) electrolyser with comparable performance toward Pt-based PEM. This work demonstrates defective metal oxides as promising non-noble metal catalysts for commercial PEM green-hydrogen generation.

An Active Strategy to Reduce Residual Alkali for High-Performance Layered Oxide Cathode Materials of Sodium-Ion Batteries.

Residual alkali is one of the biggest challenges for the commercialization of sodium-based layered transition metal oxide cathode materials since it can even inevitably appear during the production process. Herein, taking O3-type Na0.9Ni0.25Mn0.4Fe0.2Mg0.1Ti0.05O2 as an example, an active strategy is proposed to reduce residual alkali by slowing the cooling rate, which can be achieved in one-step preparation method. It is suggested that slow cooling can significantly enhance the internal uniformity of the material, facilitating the reintegration of Na+ into the bulk material during the calcination cooling phase, therefore substantially reducing residual alkali. The strategy can remarkably suppress the slurry gelation and gas evolution and enhance the structural stability. Compared to naturally cooled cathode materials, the capacity retention of the slowly cooled electrode material increases from 76.2% to 85.7% after 300 cycles at 1 C. This work offers a versatile approach to the development of advanced cathode materials toward practical applications.

Recent Development on Transition Metal Oxides-Based Core-Shell Structures for Boosted Energy Density Supercapacitors.

In recent years, nanomaterials exploration and synthesis have played a crucial role in advancing energy storage research, particularly in supercapacitor development. Researchers have diversified materials, including metal oxides, chalcogenides, and composites, as well as carbon materials, to enhance energy and power density. Balancing energy density with electrochemical stability remains challenging, driving intensified efforts in advancing electrode materials. This review focuses on recent progress in designing and synthesizing core-shell materials tailored for supercapacitors. The core-shell architecture offers advantages such as increased surface area, redox active sites, electrical conductivity, ion diffusion kinetics, specific capacitance, and cyclability. The review explores the impact of core and shell materials, specifically transition metal oxides (TMOs), on supercapacitor electrochemical behavior. Metal oxide choices, such as cobalt oxide as a preferred core and manganese oxide as a shell, are discussed. The review also highlights characterization techniques for assessing structural, morphological, and electrochemical properties of core-shell materials. Overall, it provides a comprehensive overview of ongoing TMOs-based core-shell material research for supercapacitors, showcasing their potential to enhance energy storage for applications ranging from gadgets to electric vehicles. The review outlines existing challenges and future opportunities in evolving TMOs-based core-shell materials for supercapacitor advancements, holding promise for high-efficiency energy storage devices.

New Suggestion of Highly Durable Electrode Design for Ordered Mesoporous Ni-Mn Binary Transition Metal Oxide Anode Material in Lithium-Ion Batteries.

Anode materials storing large-scale lithium ions gradually decrease electrochemical performance due to severe volume changes during cycling. Therefore, there is an urgent need to develop anode materials with high electrochemical capacity and durability, without deterioration arising due to the volume changes during the electrochemical processes. To date, mesoporous materials have received attention as anode materials due to their ability to mitigate volume expansion, offer a short pathway for Li+ transport, and exhibit anomalous high capacity. However, the nano-frameworks of transition metal oxide collapse during conversion reactions, demanding an improvement in nano-framework structure stability. In this study, ordered mesoporous nickel manganese oxide (m-NMO) is designed as an anode material with a highly durable nanostructure. Interestingly, m-NMO showed better cycle performance and higher electrochemical capacity than those of nickel oxide and manganese oxide. Operando small-angle X-ray scattering and ex situ transmission electron microscopic results confirmed that the binary m-NMO sustained a highly durable nanostructure upon cycling, unlike the single metal oxide electrodes where the mesostructures collapsed. Ex situ X-ray absorption spectroscopy proved that nickel and manganese showed different electrochemical reaction voltages, and thus undergoes sequential conversion reactions. As a result, both elements can act as complementary nano-propping buffers to maintain stable mesostructure.

Carbon Nanosheets-Based Supercapacitor Materials: Recent Advances and Prospects.

The need for inexpensive and ecologically sustainable energy storage technologies is rising rapidly along with the severity of the world's environmental challenges as well as with the rising demand for portable electronics and hybrid vehicles. Supercapacitors have drawn a lot of attentions lately in this regard because of their ultrahigh power density, outstanding electrochemical stability, and environmental friendliness. Due to various advantages, carbon materials are the choice of designer for developing commercial electrodes for various applications including devising supercapacitors. Two-dimensional (2D) carbon nanosheets (CNSs) with a large surface area and excellent electronic transport properties have fired up the interest of researchers due to their unique properties and potential applications in energy storage. Such engineered 2D porous CNS may significantly improve the energy storage performance of supercapacitor by enabling fast ion transport and charge transfer kinetics. This article summarizes the most recent and significant advances in the area of activated, porous, graphene-based various CNSs and their composites with a special focus on their use as supercapacitor electrodes. A succinct overview about their syntheses and key characterizations regarding their different structural aspects have been discussed. The present challenges and prospects in using CNS in supercapacitor applications are highlighted.

Neuromorphic learning with Mott insulator NiO.

Habituation and sensitization (nonassociative learning) are among the most fundamental forms of learning and memory behavior present in organisms that enable adaptation and learning in dynamic environments. Emulating such features of intelligence found in nature in the solid state can serve as inspiration for algorithmic simulations in artificial neural networks and potential use in neuromorphic computing. Here, we demonstrate nonassociative learning with a prototypical Mott insulator, nickel oxide (NiO), under a variety of external stimuli at and above room temperature. Similar to biological species such as Aplysia, habituation and sensitization of NiO possess time-dependent plasticity relying on both strength and time interval between stimuli. A combination of experimental approaches and first-principles calculations reveals that such learning behavior of NiO results from dynamic modulation of its defect and electronic structure. An artificial neural network model inspired by such nonassociative learning is simulated to show advantages for an unsupervised clustering task in accuracy and reducing catastrophic interference, which could help mitigate the stability-plasticity dilemma. Mott insulators can therefore serve as building blocks to examine learning behavior noted in biology and inspire new learning algorithms for artificial intelligence.

Development of MOF-derived Co3O4 microspheres composed of fiber stacks for simultaneous electrochemical detection of Pb2+ and Cu2.

As an ideal transition metal oxide, Co3O4 is a P-type semiconductor with excellent electrical conductivity, non-toxicity and low cost. This work reports the successful construction of Co3O4 materials derived from metal-organic frameworks (MOFs) using a surfactant micelle template-solvothermal method. The modified electrodes are investigated for their ability to electrochemically detect Pb2+ and Cu2+ in aqueous environments. By adjusting the mass ratios of alkaline modifiers, the morphological microstructures of Co3O4-X exhibit a transition from distinctive microspheres composed of fiber stacks to rods. The results indicate that Co3O4-1(NH4F/CO(NH2)2 = 1:0) has a distinctive microsphere structure composed of stacked fibers, unlike the other two materials. Co3O4-1/GCE is used as the active material of the modified electrode, it shows the largest peak response currents to Pb2+ and Cu2+, and efficiently detects Pb2+ and Cu2+ in the aqueous environment individually and simultaneously. The linear response range of Co3O4-1/GCE for the simultaneous detection of Pb2+ and Cu2+ is 0.5-1.5 µM, with the limits of detection (LOD, S/N = 3) are 9.77 nM and 14.97 nM, respectively. The material exhibits a favorable electrochemical response, via a distinctive Co3O4-1 microsphere structure composed of stacked fibers. This structure enhances the number of active adsorption sites on the material, thereby facilitating the adsorption of heavy metal ions (HMIs). The presence of oxygen vacancies (OV) can also facilitate the adsorption of ions. The Co3O4-1/GCE electrode also exhibits excellent anti-interference ability, stability, and repeatability. This is of great practical significance for detecting Pb2+ and Cu2+ in real water samples and provides a new approach for developing high-performance metal oxide electrochemical sensors derived from MOFs.

Electrochemical Sensors Based on Transition Metal Materials for Phenolic Compound Detection.

Electrochemical sensors have been recognized as crucial tools for monitoring comprehensive chemical information, especially in the detection of a significant class of molecules known as phenolic compounds. These compounds can be present in water as hazardous analytes and trace contaminants, as well as in living organisms where they regulate their metabolism. The sensitive detection of phenolic compounds requires highly efficient and cost-effective electrocatalysts to enable the development of high-performance sensors. Therefore, this review focuses on the development of advanced materials with excellent catalytic activity as alternative electrocatalysts to conventional ones, with a specific emphasis on transition metal-based electrocatalysts for the detection of phenolic compounds. This research is particularly relevant in diverse sectors such as water quality, food safety, and healthcare.

Nanostructured Transition Metal Oxides on Carbon Fibers for Supercapacitor and Li-Ion Battery Electrodes: An Overview.

Nowadays, owing to the new technological and industrial requirements for equipment, such as flexibility or multifunctionally, the development of all-solid-state supercapacitors and Li-ion batteries has become a goal for researchers. For these purposes, the composite material approach has been widely proposed due to the promising features of woven carbon fiber as a substrate material for this type of material. Carbon fiber displays excellent mechanical properties, flexibility, and high electrical conductivity, allowing it to act as a substrate and a collector at the same time. However, carbon fiber's energy-storage capability is limited. Several coatings have been proposed for this, with nanostructured transition metal oxides being one of the most popular due to their high theoretical capacity and surface area. In this overview, the main techniques used to achieve these coatings-such as solvothermal synthesis, MOF-derived obtention, and electrochemical deposition-are summarized, as well as the main strategies for alleviating the low electrical conductivity of transition metal oxides, which is the main drawback of these materials.

A Strategy for Anode Recovery and Upgrading by In Situ Growth of Iron-Based Oxides on Microwave-Puffed Graphite.

Faced with the increasing volume of retired lithium-ion batteries (LIBs), recycling and reusing the spent graphite (SG) is of great significance for resource sustainability. Here, a facile method for transforming the SG into a carbon framework as well as loading Fe2O3 to form a composite anode with a sandwich structure is proposed. Taking advantage of the fact that the layer spacing of the spent graphite naturally expands, impurities and intercalants are eliminated through microwave thermal shock to produce microwave-puffed graphite (MPG) with a distinct three-dimensional structure. Based on the mechanism of microwave-induced gasification intercalation, a Fe2O3-MPG intercalation compound (Fe2O3-MPGIC) anode material was constructed by introducing iron precursors between the framework layers and subsequently converting them into Fe2O3 through annealing. The Fe2O3-MPGIC anode exhibits a high reversible capacity of 1000.6 mAh g-1 at 200 mA g-1 after 100 cycles and a good cycling stability of 504.4 mAh g-1 at 2000 mA g-1 after 500 cycles. This work can provide a reference for the feasible recycling of SG and development of high-performance anode materials for LIBs.

Facile Fabrication of Large-Area CuO Flakes for Sodium-Ion Energy Storage Applications.

CuO is recognized as a promising anode material for sodium-ion batteries because of its impressive theoretical capacity of 674 mAh g-1, derived from its multiple electron transfer capabilities. However, its practical application is hindered by slow reaction kinetics and rapid capacity loss caused by side reactions during discharge/charge cycles. In this work, we introduce an innovative approach to fabricating large-area CuO and CuO@Al2O3 flakes through a combination of magnetron sputtering, thermal oxidation, and atomic layer deposition techniques. The resultant 2D CuO flakes demonstrate excellent electrochemical properties with a high initial reversible specific capacity of 487 mAh g-1 and good cycling stability, which are attributable to their unique architectures and superior structural durability. Furthermore, when these CuO flakes are coated with an ultrathin Al2O3 layer, the integration of the 2D structures with outer nanocoating leads to significantly enhanced electrochemical properties. Notably, even after 70 rate testing cycles, the CuO@Al2O3 materials maintain a high capacity of 525 mAh g-1 at a current density of 50 mA g-1. Remarkably, at a higher current density of 2000 mA g-1, these materials still achieve a capacity of 220 mAh g-1. Moreover, after 200 cycles at a current density of 200 mA g-1, a high charge capacity of 319 mAh g-1 is sustained. In addition, a full cell consisting of a CuO@Al2O3 anode and a NaNi1/3Fe1/3Mn1/3O2 cathode is investigated, showcasing remarkable cycling performance. Our findings underscore the potential of these innovative flake-like architectures as electrode materials in high-performance sodium-ion batteries, paving the way for advancements in energy storage technologies.

Investigating the Electrochemical Performance of MnFe2O4@xC Nanocomposites as Anode Materials for Sodium-Ion Batteries.

Transition metal oxides (TMOs) are important anode materials in sodium-ion batteries (SIBs) due to their high theoretical capacities, abundant resources, and cost-effectiveness. However, issues such as the low conductivity and large volume variation of TMO bulk materials during the cycling process result in poor electrochemical performance. Nanosizing and compositing with carbon materials are two effective strategies to overcome these issues. In this study, spherical MnFe2O4@xC nanocomposites composed of MnFe2O4 inner cores and tunable carbon shell thicknesses were successfully prepared and utilized as anode materials for SIBs. It was found that the property of the carbon shell plays a crucial role in tuning the electrochemical performance of MnFe2O4@xC nanocomposites and an appropriate carbon shell thickness (content) leads to the optimal battery performance. Thus, compared to MnFe2O4@1C and MnFe2O4@8C, MnFe2O4@4C nanocomposite exhibits optimal electrochemical performance by releasing a reversible specific capacity of around 308 mAh·g-1 at 0.1 A·g-1 with 93% capacity retention after 100 cycles, 250 mAh·g-1 at 1.0 A g-1 with 73% capacity retention after 300 cycles in a half cell, and around 111 mAh·g-1 at 1.0 C when coupled with a Na3V2(PO4)3 (NVP) cathode in a full SIB cell.

A review on transition metal oxides based photocatalysts for degradation of synthetic organic pollutants.

This review provides insight into the current research trend in transition metal oxides (TMOs)-based photocatalysis in removing the organic colouring matters from water. For easy understanding, the research progress has been presented in four generations according to the catalyst composition and mode of application, viz: single component TMOs (the first-generation), doped TMOs/binary TMOs/doped binary TMOs (the second-generation), inactive/active support-immobilized TMOs (the third-generation), and ternary/quaternary compositions (the fourth-generation). The first two generations represent suspended catalysts, the third generation is supported catalysts, and the fourth generation can be suspended or supported. The review provides an elaborated comparison between suspended and supported catalysts, their general/specific requirements, key factors controlling degradation, and the methodologies for performance evaluation. All the plausible fundamental and advanced dye degradation mechanisms involved in each generation of catalysts were demonstrated. The existing challenges in TMOs-based photocatalysis and how the researchers approach the hitch to resolve it effectively are discussed. Future research trends are also presented.

Disproportionation of Co2+ in the Topochemically Reduced Oxide LaSrCoRuO5.

Complex transition-metal oxides exhibit a wide variety of chemical and physical properties which are a strong function the local electronic states of the transition-metal centres, as determined by a combination of metal oxidation state and local coordination environment. Topochemical reduction of the double perovskite oxide, LaSrCoRuO6 , using Zr, yields LaSrCoRuO5 . This reduced phase contains an ordered array of apex-linked square-based pyramidal Ru3+ O5 , square-planar Co1+ O4 and octahedral Co3+ O6 units, consistent with the coordination-geometry driven disproportionation of Co2+ . Coordination-geometry driven disproportionation of d7 transition-metal cations (e.g. Rh2+ , Pd3+ , Pt3+ ) is common in complex oxides containing 4d and 5d metals. However, the weak ligand field experienced by a 3d transition-metal such as cobalt leads to the expectation that d7+ Co2+ should be stable to disproportionation in oxide environments, so the presence of Co1+ O4 and Co3+ O6 units in LaSrCoRuO5 is surprising. Low-temperature measurements indicate LaSrCoRuO5 adopts a ferromagnetically ordered state below 120 K due to couplings between S=1 /2 Ru3+ and S=1 Co1+ .

Unlocking Spin Gates of Transition Metal Oxides via Strain Stimuli to Augment Potassium Ion Storage.

Transition metal oxides (TMOs) are key in electrochemical energy storage, offering cost-effectiveness and a broad potential window. However, their full potential is limited by poor understanding of their slow reaction kinetics and stability issues. This study diverges from conventional complex nano-structuring, concentrating instead on spin-related charge transfer and orbital interactions to enhance the reaction dynamics and stability of TMOs during energy storage processes. We successfully reconfigured the orbital degeneracy and spin-dependent electronic occupancy by disrupting the symmetry of magnetic cobalt (Co) sites through straightforward strain stimuli. The key to this approach lies in the unfilled Co 3d shell, which serves as a spin-dependent regulator for carrier transfer and orbital interactions within the reaction. We observed that the opening of these 'spin gates' occurs during a transition from a symmetric low-spin state to an asymmetric high-spin state, resulting in enhanced reaction kinetics and maintained structural stability. Specifically, the spin-rearranged Al-Co3O4 exhibited a specific capacitance of 1371 F g-1, which is 38 % higher than that of unaltered Co3O4. These results not only shed light on the spin effects in magnetic TMOs but also establish a new paradigm for designing electrochemical energy storage materials with improved efficiency.

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

Transition 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.

Quantum Spin Exchange Interactions Trigger O†p Band Broadening for Enhanced Aqueous Zinc-Ion Battery Performance.

The pressing demand for large-scale energy storage solutions has propelled the development of advanced battery technologies, among which zinc-ion batteries (ZIBs) are prominent due to their resource abundance, high capacity, and safety in aqueous environments. However, the use of manganese oxide cathodes in ZIBs is challenged by their poor electrical conductivity and structural stability, stemming from the intrinsic properties of MnO2 and the destabilizing effects of ion intercalation. To overcome these limitations, our research delves into atomic-level engineering, emphasizing quantum spin exchange interactions (QSEI). These essential for modifying electronic characteristics, can significantly influence material efficiency and functionality. We demonstrate through density functional theory (DFT) calculations that enhanced QSEI in manganese oxides broadens the O p band, narrows the band gap, and optimizes both proton adsorption and electron transport. Empirical evidence is provided through the synthesis of Ru-MnO2 nanosheets, which display a marked increase in energy storage capacity, achieving 314.4 mAh g-1 at 0.2 A g-1 and maintaining high capacity after 2000 cycles. Our findings underscore the potential of QSEI to enhance the performance of TMO cathodes in ZIBs, pointing to new avenues for advancing battery technology.

Octahedral/Tetrahedral Vacancies in Fe3 O4 as K-Storage Sites: A Case of Anti-Spinel Structure Material Serving as High-Performance Anodes for PIBs.

Potassium-ion batteries (PIBs) have attracted more and more attention as viable alternatives to lithium-ion batteries (LIBs) due to the deficiency and uneven distribution of lithium resources. However, it is shown that potassium storage in some compounds through reaction or intercalation mechanisms cannot effectively improve the capacity and stability of anodes for PIBs. The unique anti-spinel structure of magnetite (Fe3 O4 ) is densely packed with thirty-two O atoms to form a face-centered cubic (fcc) unit cell with tetrahedral/octahedral vacancies in the O-closed packing structure, which can serve as K+ storage sites according to the density functional theory (DFT) calculation results. In this work, carbon-coated Fe3 O4 @C nanoparticles are prepared as high-performance anodes for PIBs, which exhibit high reversible capacity (638 mAh g-1 at 0.05 A g-1 ) and hyper stable cycling performance at ultrahigh current density (150 mAh g-1 after 9000 cycles at 10 A g-1 ). In situ XRD, ex-situ Fe K-edge XAFS, and DFT calculations confirm the storage of K+ in tetrahedral/octahedral vacancies.

Amorphous Vanadium Oxide Nanosheets with Alterable Polyhedron Configuration for Fast-Charging Lithium-Ion Batteries.

Transition metal oxides with high theoretical capacities are promising anode materials for lithium-ion batteries (LIBs). However, the sluggish reaction kinetics remain a bottleneck for fast-charging applications due to its slow Li+ migration rate. Herein, a strategy is reported of significantly reducing the Li+ diffusion barrier of amorphous vanadium oxide by constructing a specific ratio of the VO local polyhedron configuration in amorphous nanosheets. The optimized amorphous vanadium oxide nanosheets with a ratio ≈1:4 for octahedron sites (Oh ) to pyramidal sites (C4v ) revealed by Raman spectroscopy and X-ray absorption spectroscopy (XAS) demonstrate the highest rate capability (356.7 mA h g-1 at 10.0 A g-1 ) and long-term cycling life (455.6 mA h g-1 at 2.0 A g-1 over 1200 cycles). Density functional theory (DFT)calculations further verify that the local structure (Oh :C4v = 1:4) intrinsically changes the degree of orbital hybridization between V and O atoms and contributes to a higher intensity of electron occupied states near the Fermi level, thus resulting in a low Li+ diffusion barrier for favorable Li+ transport kinetics. Moreover, the amorphous vanadium oxide nanosheets possess a reversible VO vibration mode and volume expansion rate close to 0.3%, as determined through in situ Raman and in situ transmission electron microscopy.