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.

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.

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.

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.

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.

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.

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.

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.

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+ .

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.

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.

Local Electric Field Induced by Atomic-Level Donor-Acceptor Couple of O Vacancies and Mn Atoms Enables Efficient Hybrid Capacitive Deionization.

Transition metal oxides suffer from slow salt removal rate (SRR) due to inferior ions diffusion ability in hybrid capacitive deionization (HCDI). Local electric field (LEF) can efficiently improve the ions diffusion kinetics in thin electrodes for electrochemical energy storage. Nevertheless, it is still a challenge to facilitate the ions diffusion in bulk electrodes with high loading mass for HCDI. Herein, this work delicately constructs a LEF via engineering atomic-level donor (O vacancies)-acceptor (Mn atoms) couples, which significantly facilitates the ions diffusion and then enables a high-performance HCDI. The LEF boosts an extended accelerated ions diffusion channel at the particle surface and interparticle space, resulting in both remarkably enhanced SRR and salt removal capacity. Convincingly, the theoretical calculations demonstrate that electron-enriched Mn atoms center coupled with an electron-depleted O vacancies center is formed due to the electron back-donation from O vacancies to adjacent Mn centers. The resulted LEF efficiently reduce the ions diffusion energy barrier. This work sheds light on the effect of atomic-level LEF on improving ions diffusion kinetics at high loading mass application and paves the way for the design of transition metal oxides toward high-performance HCDI applications.

Challenges and Opportunities of Transition Metal Oxides as Electrocatalysts.

As a sustainable energy technology, electrocatalytic energy conversion and storage has become increasingly prominent. The oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CO2 RR) are the key steps in the industrial applications of energy conversion and storage. Compared to the widely used precious metal catalysts, less-noble transition metal oxides (TMOs) and TMO-like materials have attracted broad attention as electrocatalysts in the above reactions. In this concept, we summarize the challenges and opportunities of some typical TMOs in electrocatalysis, and modification strategies of TMOs as electrocatalysts are discussed.

C-H Activation by Iron-Vanadium Bimetallic Oxide Cluster Anions FeV3 O10 - and FeV5 O15 - : A Comparison with Scandium-Vanadium Oxide Clusters.

Late transition metal-bonded atomic oxygen radicals (LTM-O⋅- ) have been frequently proposed as important active sites to selectively activate and transform inert alkane molecules. However, it is extremely challenging to characterize the LTM-O⋅- -mediated elementary reactions for clarifying the underlying mechanisms limited by the low activity of LTM-O⋅- radicals that is inaccessible by the traditional experimental methods. Herein, benefiting from our newly-designed ship-lock type reactor, the reactivity of iron-vanadium bimetallic oxide cluster anions FeV3 O10 - and FeV5 O15 - featuring with Fe-O⋅- radicals to abstract a hydrogen atom from C2 -C4 alkanes has been experimentally characterized at 298 K, and the rate constants are determined in the orders of magnitude of 10-14 to 10-16  cm3 molecule-1 s-1 , which are four orders of magnitude slower than the values of counterpart ScV3 O10 - and ScV5 O15 - clusters bearing Sc-O⋅- radicals. Theoretical results reveal that the rearrangements of the electronic and geometric structures during the reaction process function to modulate the activity of Fe-O⋅- . This study not only quantitatively characterizes the elementary reactions of LTM-O⋅- radicals with alkanes, but also provides new insights into structure-activity relationship of M-O⋅- radicals.

Efficient non-fullerene organic solar cells employing aqueous solution-processed MoO3as a hole-transporting layer.

Organic solar cell (OSC) has drawn considerable interest in recent decades owing to their advantages of light weight, flexible, large area and potentially low-cost. Employing an appropriate hole-transporting layer (HTL) into an OSC device has been proved as an efficient method to obtain high efficiency OSC due to the enhancement of the hole transporting and extraction of the device. In this work, aqueous solution-processed MoO3(s-MoO3) thin films were employed as HTLs to construct non-fullerene PM6:Y6 OSCs. The s-MoO3thin film was prepared by using an aqueous solution process from an isopolymolybdate [NH4]6Mo7O24.4H2O precursor followed by thermal annealing treatment to convert the precursor to MoO3. The s-MoO3HTL based PM6:Y6 device demonstrates a power conversion efficiency of 15.75%, which is 38% improved than that of the device with thermally evaporated-MoO3as HTL and 8% improved than that of the device with PEDOT:PSS as HTL. The enhancement of the device performance could be attributed to the enhanced hole mobility and better band matching of the s-MoO3HTL. Moreover, the s-MoO3HTL based PM6:Y6 device exhibited higher device stability than those of the reference devices. Our finding indicates that this s-MoO3film has great potential as efficient HTL for high performance non fullerene OSCs.

Rational design principles for giant spin Hall effect in 5d-transition metal oxides.

Spin Hall effect (SHE), a mechanism by which materials convert a charge current into a spin current, invokes interesting physics and promises to empower transformative, energy-efficient memory technology. However, fundamental questions remain about the essential factors that determine SHE. Here, we solve this open problem, presenting a comprehensive theory of five rational design principles for achieving giant intrinsic SHE in transition metal oxides. Arising from our key insight regarding the inherently geometric nature of SHE, we demonstrate that two of these design principles are weak crystal fields and the presence of structural distortions. Moreover, we discover that antiperovskites are a highly promising class of materials for achieving giant SHE, reaching SHE values an order of magnitude larger than that reported for any oxide. Additionally, we derive three other design principles for enhancing SHE. Our findings bring deeper insight into the physics driving SHE and could help enhance and externally control SHE values.

A Facile Strategy To Construct Au@VxO2x+1 Nanoflowers as a Multicolor Electrochromic Material for Adaptive Camouflage.

Transition metal oxides (TMOs) are promising inorganic electrochromic materials (ECMs) that can be widely used in electronic displays and adaptive camouflage. However, there are still huge challenges for TMOs to simultaneously achieve multicolor transformation capability and good cycling stability. Herein, we assemble Au-modified (0.01 wt %) VxO2x+1 (x > 2) nanoflowers (Au@VxO2x+1 NFs) composed of two-dimensional porous nanosheets containing two valences states of vanadium (V4+ and V5+). The Au@VxO2x+1 NFs exhibits outstanding electrochromic performance with five reversible color transformations (orange, yellow, green, gray, and blue) at a voltage less than 1.5 V and excellent cycling stability (2000 cycles without significant decay). To the best of our knowledge, this is the first time that a single vanadium oxide ECM, rather than a device, realizes five color changes. This work provides a feasible way for the efficient preparation of multicolor electrochromic TMOs. The newly developed Au@VxO2x+1 NFs demonstrate the potential application in adaptive camouflage.

Concentration Gradient Induced Delithiation Failure of MoO3 for Li-Ion Batteries.

Electric vehicle manufacturers worldwide are demanding superior lithium-ion batteries, with high energy and power densities, compared to gasoline engines. Although conversion-type metal oxides are promising candidates for high-capacity anodes, low initial Coulombic efficiency (ICE) and poor capacity retention have hindered research on their applications. In this study, the ICE of conversion-type MoO3 is investigated, with a particular focus on the delithiation failure. A computational modeling predicts the concentration gradient of Li+ in MoO3 particles. The highly delithiated outer region of the particle forms a layer with low electronic conductivity, which impedes further delithiation. A comparative study using various sizes of MoO3 particles demonstrated that the electrode failure during delithiation is governed by the concentration gradient and the subsequent formation of a resistive shell. The proposed failure mechanism provides critical guidance for the development of conversion-type anode materials with improved electrochemical reversibility.