In this work, a porous Co3O4 anode material with capsule–shaped morphology is prepared by a simple solvothermal method and subsequent heat treatment process in air. The as–synthesized CoCO3 precursor ...and Co3O4 sample are systematically studied and analyzed by a series of testing technologies, such as XRD, FTIR, FESEM, (HR)TEM, TGA, XPS and N2 adsorption/desorption measurement. As negative materials in Li–ion batteries, the Co3O4 active material exhibits high charge/discharge specific capacity, good rate performance and satisfactory cycle stability. The excellent electrochemical properties are inevitably related to the structural characteristics of the electrode material itself, including regular morphology, rich pore structure, large specific surface area, high crystallinity, nanoscale particle size, etc.
2D amorphous transition metal oxides (a‐TMOs) heterojunctions that have the synergistic effects of interface (efficiently promoting the separation of electron−hole pairs) and amorphous nature ...(abundant defects and dangling bonds) have attracted substantial interest as compelling photocatalysts for solar energy conversion. Strategies to facilely construct a‐TMOs‐based 2D/2D heterojunctions is still a big challenge due to the difficulty of preparing individual amorphous counterparts. A generalized synthesis strategy based on supramolecular self‐assembly for bottom–up growth of a‐TMOs‐based 2D heterojunctions is reported, by taking 2D/2D g‐C3N4 (CN)/a‐TMOs heterojunction as a proof‐of‐concept. This strategy primarily depends on controlling the cooperation of the growth of supramolecular precursor and the coordinated covalent bonds arising from the tendency of metal ions to attain the stable configuration of electrons, which is independent on the intrinsic character of individual metal ion, indicating it is universally applicable. As a demonstration, the structure, physical properties, and photocatalytic water‐splitting performance of CN/a‐ZnO heterojunction are systematically studied. The optimized 2D/2D CN/a‐ZnO exhibits enhanced photocatalytic performance, the hydrogen (432.6 µmol h−1 g−1) and oxygen (532.4 µmol h−1 g−1) evolution rate are 15.5 and 12.2 times than bulk CN, respectively. This synthetic strategy is useful to construct 2D a‐TMOs nanomaterials for applications in energy‐related areas and beyond.
A generalized synthesis strategy for the bottom–up growth of amorphous transition metal oxides (a‐TMOs) 2D/2D heterojunctions with large contact area via covalent interfacial interaction is provided. A number of 2D/2D CN/a‐TMOs heterojunctions, such as CN/a‐FeOx, CN/a‐CuOx, CN/a‐MnOx, CN/a‐CoOx, and CN/a‐ZnO are successfully synthesized, which has a large and perfect order−disorder interface. Particularly, 2D/2D CN/a‐ZnO heterojunction exhibit boosted photocatalytic hydrogen and oxygen evolution.
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•On-going progresses and chanllenges of Transition metal compounds in SCs was reviewed.•The strategies on improving the electrochemcial behaviors of TMCs were deeply discussed.•The ...charge storage mechanisms of SCs are catagorized to solve the confusion about pseudocapacitor and battery.•The perspectives about the future directions of TMCs were subjectively present.
Supercapacitors (SCs), as an attractive energy storage device, have drawn great interests on basis of large power density, fast charging/discharging capability and good cycling performance. Transition metal compounds (TMCs) have promised as electrode materials of supercapacitors to raise the insufficient energy density by the reverse reaction among their multiple oxidation states. To further the rational design of TMCs-based electrode materials, this review looks into advances and challenges in their applications of SCs. The witnessed active TMCs including transition metal oxides, transition metal hydroxides, and their derivatives, are selectively and individually discussed in detail. To deeply illuminate the mechanistic understanding into charge storage, fundamentals of supercapacitors have been categorized into three typical types including electric double layer, pseudocapacitive and asymmetrical storage, where battery-type and pseudocapacitive electrodes are also distinguished by giving two crucial criterions. As a dynamically advancing research frontier for energy storage, we therefore provide a relatively long perspective to identify great opportunities and obstacles in the practical scale up of SCs.
Limited levels of UV exposure can be beneficial to the human body. However, the UV radiation present in the atmosphere can be damaging if levels of exposure exceed safe limits which depend on the ...individual the skin color. Hence, UV photochromic materials that respond to UV light by changing their color are powerful tools to sense radiation safety limits. Photochromic materials comprise either organic materials, inorganic transition metal oxides, or a hybrid combination of both. The photochromic behavior largely relies on charge transfer mechanisms and electronic band structures. These factors can be influenced by the structure and morphology, fabrication, composition, hybridization, and preparation of the photochromic materials, among others. Significant challenges are involved in realizing rapid photochromic change, which is repeatable, reversible with low fatigue, and behaving according to the desired application requirements. These challenges also relate to finding the right synergy between the photochromic materials used, the environment it is being used for, and the objectives that need to be achieved. In this review, the principles and applications of photochromic processes for transition metal oxides and hybrid materials, photocatalytic applications, and the outlook in the context of commercialized sensors in this field are presented.
Herein, the fundamentals of UV photochromism for transition metal oxides and organic materials are presented. The recent applications of UV photochromic materials consisting of oxides or composite of oxides and organic materials, known as hybrids, are comprehensively discussed. The review concludes with a summary of applications, challenges, and future pathways for this field.
The metal–insulator transition (MIT) in correlated materials is a novel phenomenon that accompanies a large change in resistivity, often many orders of magnitude. It is important in its own right but ...its switching behavior in resistivity can be useful for device applications. From the material physics point of view, the starting point of the research on the MIT should be to understand the microscopic mechanism. Here, an overview of recent efforts to unravel the microscopic mechanisms for various types of MITs in correlated materials is provided. Research has focused on transition metal oxides (TMOs), but transition metal chalcogenides have also been studied. Along the way, a new class of MIT materials is discovered, the so‐called relativistic Mott insulators in 5d TMOs. Distortions in the MO6 (M = transition metal) octahedron are found to have a large and peculiar effect on the band structure in an orbital dependent way, possibly paving a way to the orbital selective Mott transition. In the final section, the character of the materials suitable for applications is summarized, followed by a brief discussion of some of the efforts to control MITs in correlated materials, including a dynamical approach using light.
The metal–insulator transition (MIT) is one of the most fascinating phenomena observed in correlated materials, with its switching behavior under various environmental perturbations leading to high potential for novel devices. The microscopic mechanisms of MITs in various correlated materials discovered through spectroscopic investigations are reviewed. Possible ways to control MITs in correlated materials are also discussed based on the findings.
Potassium‐ion batteries have been regarded as the potential alternatives to lithium‐ion batteries (LIBs) due to the low cost, earth abundance, and low potential of K (−2.936 vs standard hydrogen ...electrode (SHE)). However, the lack of low‐cost cathodes with high energy density and long cycle life always limits its application. In this work, high‐energy layered P2‐type hierarchical K0.65Fe0.5Mn0.5O2 (P2‐KFMO) microspheres, assembled by the primary nanoparticles, are fabricated via a modified solvent‐thermal method. Benefiting from the unique microspheres with primary nanoparticles, the K+ intercalation/deintercalation kinetics of P2‐KFMO is greatly enhanced with a stabilized cathodic electrolyte interphase on the cathode. The P2‐KFMO microsphere presents a highly reversible potassium storage capacity of 151 mAh g−1 at 20 mA g−1, fast rate capability of 103 mAh g−1 at 100 mA g−1, and long cycling stability with 78% capacity retention after 350 cycles. A full cell with P2‐KFMO microspheres as cathode and hard carbon as anode is constructed, which exhibits long‐term cycling stability (>80% of retention after 100 cycles). The present high‐performance P2‐KFMO microsphere cathode synthesized using earth‐abundant elements provides a new cost‐effective alternative to LIBs for large‐scale energy storage.
P2‐type K0.65Fe0.5Mn0.5O2 microspheres as high‐energy cathodes for K‐ion batteries are first fabricated via a scalable facile self‐templated method. They achieve high capacity (151 mAh g−1 at 20 mA g−1), fast rate capability, and stable long‐term cycling performance with 78% capacity retention after 350 cycles. This low‐cost K‐ion cathode with earth‐abundant elements provides a promising choice for the large‐scale energy storage.
A binary transition metal oxides MnCo2O4 with hierarchical porous sphere structure (MnCo2O4 PSs) electrode material for supercapacitor was prepared by a moderate methanol solvothermal and calcination ...method. The MnCo2O4 PSs presents a large specific surface area (213.2 m2 g−1). Hierarchical porous sphere is beneficial for forming conductive networks and furnishing more electrochemically active sites. Amazingly, the MnCo2O4 PSs exhibits brilliant electrochemical properties that a relatively high specific capacitance of 1044 F g−1 and remarkable cycling stability (133.3% retention after 10000 cycles) are owned. A mimetic asymmetric supercapacitor (ASC) was constructed by the MnCo2O4 PSs and the starch-derived carbon foam material (SCF) as positive and negative electrode, respectively. The MnCo2O4 PSs//SCF ASC shows excellent specific energy (42.27 Wh kg−1) at the specific power of 400 W kg−1 under the optimal output potential difference of 1.6 V and long-term cycling stability. Herein, the MnCo2O4 PSs electrode material prepared in this work is a distinguished candidate material for supercapacitor.
•MnCo2O4 materials with hierarchical porous sphere were prepared.•MnCo2O4 electrode exhibits excellent cycling stability of 133.3% retention after 10000 cycles.•Supercapacitors with MnCo2O4 show high energy density of 42.27 Wh kg−1.
The development of efficient and cost-effective electrocatalysts for hydrogen evolution reaction (HER) is an urgent requirement but formidable challenge. In this work, Co and Mn were introduced into ...self-supported nickel-vanadium layered double hydroxide (NiV–LDH) to modulate electronic structure. The introduced Co and Mn can induce electron transfer among various cations to modulate the electronic structure, exerting a positive influence on the catalytic activity of HER. As a results, the samples with Co (NiVCo–LDH) and Mn (NiVMn–LDH) exhibits excellent HER activity. To achieve a current density of 10 mA cm–2 in 1.0 M KOH, NiVCo–LDH and NiVMn–LDH requiring overpotential of 135 mV and 123 mV, respectively. In contrast, NiV–LDH needed an overpotential of 198 mV to reach the same current density. The ideal performance of NiVCo–LDH and NiVMn–LDH offer a potential application in non-noble metal-based industrial electrolytic water splitting to produce high-purity hydrogen.
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•The surface degradation process of the lithium-layered transition metal oxide cathode is revealed by an operando Raman spectroscopy study.•The degradation process is visualized by ...Raman mapping with the spectral window of ∼600 cm−1.•The degradation process not only involves the structural changes, but also the growth and merging between the degenerated layers on charge–discharge.•The present study offers crucial information to counter the capacity decay of the NMC batteries.
The well-defined layered structure for Li+ (de)intercalation of transition metal oxide cathodes plays a crucial role in delivering high capacity for lithium-ion batteries. Therefore, structural deformations of the layered structure are often considered as the evidence of deterioration in the battery performance and stability. In this study, the surface degradation mechanism of the layered LiNi1/3Co1/3Mn1/3O2 cathode is examined on charge–discharge using an operando Raman cell. We revealed the surface degradation process of the cathode with the A1g Raman spectral window (∼600 cm−1) in the voltage range of 2.8–4.35 V, and proposed the nucleation-merging mechanism. The spectral shifts and mappings have been compared between the early-stage and later-stage cycles (≥15 cycles). It has been identified that the degradation process not only involves the structural changes (i.e., nucleation of the degenerated layers), but also the growth/merging between the degenerated layers during charge and discharge. This observation provides key information on how the reconstructed surface can expand during cycling.
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