Morphology-Conserved Transformations of Metal-Based Precursors to Hierarchically Porous Micro-/Nanostructures for Electrochemical Energy Conversion and Storage

To meet future market demand, developing new structured materials for electrochemical energy conversion and storage systems is essential. Hierarchically porous micro-/nanostructures are favorable for designing such high-performance materials because of their unique features, including: i) the prevention of nanosized particle agglomeration and minimization of interfacial contact resistance, ii) more active sites and shorter ionic diffusion lengths because of their size compared with their large-size counterparts, iii) convenient electrolyte ingress and accommodation of large volume changes, and iv) enhanced light-scattering capability. Here, hierarchically porous micro-/nanostructures produced by morphology-conserved transformations of metal-based precursors are summarized, and their applications as electrodes and/or catalysts in rechargeable batteries, supercapacitors, and solar cells are discussed. Finally, research and development challenges relating to hierarchically porous micro-/nanostructures that must be overcome to increase their utilization in renewable energy applications are outlined.

Two-Dimensional Metal Oxide Nanomaterials for Next-Generation Rechargeable Batteries

The exponential increase in research focused on two-dimensional (2D) metal oxides has offered an unprecedented opportunity for their use in energy conversion and storage devices, especially for promising next-generation rechargeable batteries, such as lithium-ion batteries (LIBs) and sodium-ion batteries (NIBs), as well as some post-lithium batteries, including lithium-sulfur batteries, lithium-air batteries, etc. The introduction of well-designed 2D metal oxide nanomaterials into next-generation rechargeable batteries has significantly enhanced the performance of these energy-storage devices by providing higher chemically active interfaces, shortened ion-diffusion lengths, and improved in-plane carrier-/charge-transport kinetics, which have greatly promoted the development of nanotechnology and the practical application of rechargeable batteries. Here, the recent progress in the application of 2D metal oxide nanomaterials in a series of rechargeable LIBs, NIBs, and other post lithium-ion batteries is reviewed relatively comprehensively. Current opportunities and future challenges for the application of 2D nanomaterials in energy-storage devices to achieve high energy density, high power density, stable cyclability, etc. are summarized and outlined. It is believed that the integration of 2D metal oxide nanomaterials in these clean energy devices offers great opportunities to address challenges driven by increasing global energy demands.

Advances and Challenges in Metal Sulfides/Selenides for Next-Generation Rechargeable Sodium-Ion Batteries

Rechargeable sodium-ion batteries (SIBs), as the most promising alternative to commercial lithium-ion batteries, have received tremendous attention during the last decade. Among all the anode materials for SIBs, metal sulfides/selenides (MXs) have shown inspiring results because of their versatile material species and high theoretical capacity. They suffer from large volume expansion, however, which leads to bad cycling performance. Thus, methods such as carbon modification, nanosize design, electrolyte optimization, and cut-off voltage control are used to obtain enhanced performance. Here, recent progress on MXs is summarized in terms of arranging the crystal structure, synthesis methods, electrochemical performance, mechanisms, and kinetics. Challenges are presented and effective ways to solve the problems are proposed, and a perspective for future material design is also given. It is hoped that light is shed on the development of MXs to help finally find applications for next-generation rechargeable batteries.

Controllable structure transitions of Mn3O4 nanomaterials and their effects on electrochemical properties

Mn₃O₄ with purposely tuned different morphologies, crystal structures and sizes is synthesized using a hydrothermal method with varying processing temperatures, together with the help of a surfactant. Systematic investigations, both by experimental and computational studies, into these Mn₃O₄ nanomaterials were conducted in order to find the most suitable morphology and a compatible electrolyte for energy storage applications. The Mn₃O₄ nanofibers with a tunnel size of 1.83 Å in the crystal structure show much higher volumetric capacitance (188 F cm^-3 at a scan rate of 1 mV s^-1 of cyclic voltammetry test) than two other morphologies/crystal structures, when using 1 M LiCl aq. as the electrolyte. It is demonstrated in this work that crystal morphology and particle size play important roles in determining the capacitance of an electrode material. In addition, the detailed structures, especially the atomic arrangements within the crystalline structure, are crucial in order to choose the most suitable electrolyte.

Mesoporous NiS2 Nanospheres Anode with Pseudocapacitance for High-Rate and Long-Life Sodium-Ion Battery

It is of great importance to exploit electrode materials for sodium-ion batteries (SIBs) with low cost, long life, and high-rate capability. However, achieving quick charge and high power density is still a major challenge for most SIBs electrodes because of the sluggish sodiation kinetics. Herein, uniform and mesoporous NiS₂ nanospheres are synthesized via a facile one-step polyvinylpyrrolidone assisted method. By controlling the voltage window, the mesoporous NiS₂ nanospheres present excellent electrochemical performance in SIBs. It delivers a high reversible specific capacity of 692 mA h g^-1 . The NiS₂ anode also exhibits excellent high-rate capability (253 mA h g^-1 at 5 A g^-1 ) and long-term cycling performance (319 mA h g^-1 capacity remained even after 1000 cycles at 0.5 A g^-1 ). A dominant pseudocapacitance contribution is identified and verified by kinetics analysis. In addition, the amorphization and conversion reactions during the electrochemical process of the mesoporous NiS₂ nanospheres is also investigated by in situ X-ray diffraction. The impressive electrochemical performance reveals that the NiS₂ offers great potential toward the development of next generation large scale energy storage.

Preparation of PPy-Coated MnO2 Hybrid Micromaterials and Their Improved Cyclic Performance as Anode for Lithium-Ion Batteries

MnO₂@PPy core-shell micromaterials are prepared by chemical polymerization of pyrrole on the MnO₂ surface. The polypyrrole (PPy) is formed as a homogeneous organic shell on the MnO₂ surface. The thickness of PPy shell can be adjusted by the usage of pyrrole. The analysis of SEM, FT-IR, X-ray photoelectron spectroscopy (XPS), thermo-gravimetric analysis (TGA), and XRD are used to confirm the formation of PPy shell. Galvanostatic cell cycling and electrochemical impedance spectroscopy (EIS) are used to evaluate the electrochemical performance as anode for lithium-ion batteries. The results show that after formation of MnO₂@PPy core-shell micromaterials, the cyclic performance as anode for lithium-ion batteries is improved. Fifty microliters of PPy-coated caddice-clew-like MnO₂ has the best cyclic performances as has 620 mAh g^-1 discharge specific capacities after 300 cycles. As a comparison, the discharge specific capacity of bare MnO₂ materials falls to below 200 mAh g^-1 after 10 cycles. The improved lithium-storage cyclic stability of the MnO₂@PPy samples attributes to the core-shell hybrid structure which can buffer the structural expansion and contraction of MnO₂ caused by the repeated embedding and disengagement of Li ions and can prevent the pulverization of MnO₂. This experiment provides an effective way to mitigate the problem of capacity fading of the transition metal oxide materials as anode materials for (lithium-ion batteries) LIBs.

Chemical synthesis of hierarchical NiCo2S4 nanosheets like nanostructure on flexible foil for a high performance supercapacitor

In this study, hierarchical interconnected nickel cobalt sulfide (NiCo₂S₄) nanosheets were effectively deposited on a flexible stainless steel foil by the chemical bath deposition method (CBD) for high-performance supercapacitor applications. The resulting NiCo₂S₄ sample was characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and electrochemical measurements. XRD and X-ray photoelectron spectroscopy (XPS) results confirmed the formation of the ternary NiCo₂S₄ sample with a pure cubic phase. FE-SEM and HR-TEM revealed that the entire foil surface was fully covered with the interconnected nanosheets like surface morphology. The NiCo₂S₄ nanosheets demonstrated impressive electrochemical characteristics with a specific capacitance of 1155 F g⁻¹ at 10 mV s⁻¹ and superior cycling stability (95% capacity after 2000 cycles). These electrochemical characteristics could be attributed to the higher active area and higher conductivity of the sample. The results demonstrated that the interconnected NiCo₂S₄ nanosheets are promising as electrodes for supercapacitor and energy storage applications.

Retarded saturation of the areal capacitance using 3D-aligned MnO2 thin film nanostructures as a supercapacitor electrode

The supercapacitive properties of manganese oxide (MnO₂) thin films electrodeposited on three-dimensionally (3D) aligned inverse-opal nickel nanostructures are investigated. Compared to conventional planar or two-dimensionally (2D) aligned nanostructures, 3D-aligned nanostructures can provide considerably increased and controllable contacts between the electrode and electrolyte. As a result, saturation of the areal capacitance with the electrode thickness and associated decrease of the specific capacitance, C_sp, become much slower than those of the planar and 2D-aligned electrode systems. While, for planar MnO₂ electrodes, the C_sp of a 60-cycle electrodeposited electrode is only the half of the 10-cycle electrodeposited one, the value of the 3D-nanostructured electrode remains unchanged under the same condition. The maximum C_sp value of 864 F g⁻¹, and C_sp retention of 87.7% after 5000 cycles of galvanostatic charge-discharge are obtained. The voltammetric response is also improved significantly and the C_sp measured at 200 mV s⁻¹ retains 71.7% of the value measured at 10 mV s⁻¹. More quantitative analysis on the effect of this 3D-aligned nanostructuring is also performed using a deconvolution of the capacitive elements in the total capacitance of the electrodes.

Facile synthesis of ultrathin Ni-MOF nanobelts for high-efficiency determination of glucose in human serum

Ultrathin Ni-MOF nanobelts, [Ni₂₀(C₅H₆O₄)₂₀(H₂O)₈]·40H₂O(Ni-MIL-77 NBs), were synthesized by a facile one-pot solution process and can be used as an efficient catalyst electrode for glucose oxidation under alkaline conditions. Electrochemical measurements demonstrate that the NB/GCE, when used as a non-enzymatic glucose sensor, offers superior analytical performances with a wide linear range (from 1 μM to 500 μM), a low detection limit (0.25 μM, signal-to-noise = 3), and a response sensitivity of 1.542 μA mM^-1 cm^-2. Moreover, it can also be applied for glucose detection in human blood serum with the relative standard deviation (RSD) of 7.41%, showing the high precision of the sensor in measuring real samples.

Functional Hybrid Materials Based on Manganese Dioxide and Lignin Activated by Ionic Liquids and Their Application in the Production of Lithium Ion Batteries

Kraft lignin (KL) was activated using selected ionic liquids (ILs). The activated form of the biopolymer, due to the presence of carbonyl groups, can be used in electrochemical tests. To increase the application potential of the system in electrochemistry, activated lignin forms were combined with manganese dioxide, and the most important physicochemical and morphological-microstructural properties of the novel, functional hybrid systems were determined using Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), scanning electron microscopy (SEM), zeta potential analysis, thermal stability (TGA/DTG) and porous structure analysis. An investigation was also made of the practical application of the hybrid materials in the production of lithium ion batteries. The capacity of the anode (MnO₂/activated lignin), working at a low current regime of 50 mA·g-1, was ca. 610 mAh·g-1, while a current of 1000 mA·g-1 resulted in a capacity of 570 mAh·g-1. Superior cyclic stability and rate capability indicate that this may be a promising electrode material for use in high-performance lithium ion batteries.

Morphology and Structure Engineering in Nanofiber Reactor: Tubular Hierarchical Integrated Networks Composed of Dual Phase Octahedral CoMn2 O4 /Carbon Nanofibers for Water Oxidation

1D hollow nanostructures combine the advantages of enhanced surface-to-volume ratio, short transport lengths, and efficient 1D electron transport, which can provide more design ideas for the preparation of highly active oxygen evolution (OER) electrocatalysts. A unique architecture of dual-phase octahedral CoMn₂ O₄ /carbon hollow nanofibers has been prepared via a two-step heat-treatment process including preoxidation treatment and Ostwald ripening process. The hollow and porous structures provide interior void spaces, large exposed surfaces, and high contact areas between the nanofibers and electrolyte and the morphology can be engineered by adjusting the heating conditions. Due to the intimate electrical and chemical coupling between the oxide nanocrystals and integrated carbon, the dual-phase octahedral CoMn₂ O₄ /carbon hollow nanofibers exhibit excellent OER activity with overpotentials of 337 mV at current density of 10 mA cm^-2 and Tafel slope of 82 mV dec^-1 . This approach will lead to the new perception of design issue for the nanoarchitecture with fine morphology, structures, and excellent electrocatalytic activity.

Stabilization of Garnet/Liquid Electrolyte Interface Using Superbase Additives for Hybrid Li Batteries

To improve the solid-electrolyte/electrode interface compatibility, we have proposed the concept of hybrid electrolyte by including a small amount of liquid electrolyte in between. In this work, n-BuLi, a superbase, has been found to significantly improve the cycling performance of LiFePO₄/Li hybrid cells containing Li₇La₃Zr_1.5Ta_0.5O₁₂ (LLZT) and conventional carbonate-based liquid electrolyte. The modified cells have been cycled for 400 cycles at 100 and 200 μA cm^-2 at room temperature, indicating excellent solid/liquid electrolyte interface stability. The role of n-BuLi may be 3-fold: to retard the decomposition reaction of LE, to suppress the Li⁺/H⁺ exchange, and to lithiate the garnet/LE interface, inhibiting side reactions and enhancing interfacial lithium-ion transport.

Electrochemical performance of Ti3C2Tx MXene in aqueous media: towards ultrasensitive H2O2 sensing

An extensive characterization of pristine and oxidized Ti₃C₂T_x (T: =O, -OH, -F) MXene showed that exposure of MXene to an anodic potential in the aqueous solution oxidizes the nanomaterial forming TiO₂ layer or TiO₂ domains with subsequent TiO₂ dissolution by F^- ions, making the resulting nanomaterial less electrochemically active compared to the pristine Ti₃C₂T_x. The Ti₃C₂T_x could be thus applied for electrochemical reactions in a cathodic potential window i.e. for ultrasensitive detection of H₂O₂ down to nM level with a response time of approx. 10 s. The manuscript also shows electrochemical behavior of Ti₃C₂T_x modified electrode towards oxidation of NADH and towards oxygen reduction reactions.

Top-Down Strategy to Synthesize Mesoporous Dual Carbon Armored MnO Nanoparticles for Lithium-Ion Battery Anodes

To overcome inferior rate capability and cycle stability of MnO-based materials as a lithium-ion battery anode associated with the pulverization and gradual aggregation during the conversion process, we constructed robust mesoporous N-doped carbon (N-C) protected MnO nanoparticles on reduced graphene oxide (rGO) (MnO@N-C/rGO) by a simple top-down incorporation strategy. Such dual carbon protection endows MnO@N-C/rGO with excellent structural stability and enhanced charge transfer kinetics. At 100 mA g^-1, it exhibits superior rate capability as high as 864.7 mAh g^-1, undergoing the deep charge/discharge for 70 cycles and outstanding cyclic stability (after 1300 cyclic tests at 2000 mA g^-1; 425.0 mAh g^-1 remains, accompanying merely 0.004% capacity decay per cycle). This facile method provides a novel strategy for synthesis of porous electrodes by making use of highly insulating materials.

In Situ Atom Probe Deintercalation of Lithium-Manganese-Oxide

Atom probe tomography is routinely used for the characterization of materials microstructures, usually assuming that the microstructure is unaltered by the analysis. When analyzing ionic conductors, however, gradients in the chemical potential and the electric field penetrating dielectric atom probe specimens can cause significant ionic mobility. Although ionic mobility is undesirable when aiming for materials characterization, it offers a strategy to manipulate materials directly in situ in the atom probe. Here, we present experimental results on the analysis of the ionic conductor lithium-manganese-oxide with different atom probe techniques. We demonstrate that, at a temperature of 30 K, characterization of the materials microstructure is possible without measurable Li mobility. Also, we show that at 298 K the material can be deintercalated, in situ in the atom probe, without changing the manganese-oxide host structure. Combining in situ atom probe deintercalation and subsequent conventional characterization, we demonstrate a new methodological approach to study ionic conductors even in early stages of deintercalation.

Modest Oxygen-Defective Amorphous Manganese-Based Nanoparticle Mullite with Superior Overall Electrocatalytic Performance for Oxygen Reduction Reaction

Manganese-based oxides have exhibited high promise as noncoinage alternatives to Pt/C for catalyzing oxygen reduction reaction (ORR) in basic solution and a mix of Mn^3+/4+ valence is believed to be vital in achieving optimum ORR performance. Here, it is proposed that, distinct from the most studied perovskites and spinels, Mn-based mullites with equivalent molar ratio of Mn³⁺ and Mn⁴⁺ provide a unique platform to maximize the role of Mn valence in facile ORR kinetics by introducing modest content of oxygen deficiency, which is also beneficial to enhanced catalytic activity. Accordingly, amorphous mullite SmMn₂ O_5-δ nanoparticles with finely tuned concentration of oxygen vacancies are synthesized via a versatile top-down approach and the modest oxygen-defective sample with an Mn³⁺ /Mn⁴⁺ ratio of 1.78, i.e., Mn valence of 3.36 gives rise to a superior overall ORR activity among the highest reported for the family of Mn-based oxides, comparable to that of Pt/C. Altogether, this study opens up great opportunities for mullite-based catalysts to be a cost-effective alternative to Pt/C in diverse electrochemical energy storage and conversion systems.

MCNTs@MnO2 Nanocomposite Cathode Integrated with Soluble O2-Carrier Co-salen in Electrolyte for High-Performance Li-Air Batteries

Li-air batteries (LABs) are promising because of their high energy density. However, LABs are troubled by large electrochemical polarization during discharge and charge, side reactions from both carbon cathode surface/peroxide product and electrolyte/superoxide intermediate, as well as the requirement for pure O₂. Here we report the solution using multiwall carbon nanotubes (MCNTs)@MnO₂ nanocomposite cathode integrated with N,N'-bis(salicylidene)ethylenediaminocobalt(II) (Co^II-salen) in electrolyte for LABs. The advantage of such a combination is that on one hand, the coating layer of δ-MnO₂ with about 2-3 nm on MCNTs@MnO₂ nanocomposite catalyzes Li₂O₂ decomposition during charge and suppresses side reactions between product Li₂O₂ and MCNT surface. On the other hand, Co^II-salen works as a mobile O₂-carrier and accelerates Li₂O₂ formation through the reaciton of (Co^III-salen)₂-O₂^2- + 2Li⁺ + 2e^- → 2Co^II-salen + Li₂O₂. This reaction route overcomes the pure O₂ limitation and avoids the formation of aggressive superoxide intermediate (O₂^- or LiO₂), which easily attacks organic electrolyte. By using this double-catalyst system of Co-salen/MCNTs@MnO₂, the lifetime of LABs is prolonged to 300 cycles at 500 mA g^-1 (0.15 mA cm^-2) with fixed capacity of 1000 mAh g^-1 (0.30 mAh cm^-2) in dry air (21% O₂). Furthermore, we up-scale the capacity to 500 mAh (5.2 mAh cm^-2) in pouch-type batteries (∼4 g, 325 Wh kg^-1). This study should pave a new way for the design and construction of practical LABs.

MnO2/g-C3N4 nanocomposite with highly enhanced supercapacitor performance

A novel sandwich-like MnO₂/g-C₃N₄ nanocomposite (NC) based on the integration of high-density MnO₂ nanorods (NRs) onto the surfaces of two-dimensional (2D) g-C₃N₄ sheets has been successfully fabricated through a facile soft chemical route at low temperature. The MnO₂/g-C₃N₄ NC electrode enhanced the supercapacitor (SC) performance, benchmarked against both the bare MnO₂ NRs electrode and the MnO₂/graphene oxide (GO) NC electrode, exhibiting high specific capacitance of 211 F/g at a current density of 1 A/g, with good rate capacity and cycling stability. The sandwich-like hybrid structure, the unique 2D structure of the g-C₃N₄ sheets and the presence of nitrogen in the g-C₃N₄ all contributed to the promising SC performance of the MnO₂/g-C₃N₄ NC. This work demonstrated the advantages of the g-C₃N₄ sheets over the commonly-used GO sheets in the design of novel hybrid composite for enhanced capacitance performance of MnO₂-based electrochemical SCs, and the results could be extended to other electrode materials for SCs.

Heterogeneously-Catalyzed Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid with MnO2

A simple non-precious-metal catalyst system based on costeffective and ubiquitously available MnO₂ , NaHCO₃ , and molecular oxygen was used to convert 5-hydroxymethylfurfural (HMF) to 2,5-difurandicarboxylic acid (FDCA) as a bioplastics precursor in 91 % yield. The MnO₂ catalyst could be recovered by simple filtration and reused several times. The present system was also applicable to the aerobic oxidation of other biomass-derived substrates and the gram-scale oxidation of HMF to FDCA, in which 2.36 g (86 % yield) of the analytically pure FDCA could be isolated.

Tuning the Morphologies of MnO/C Hybrids by Space Constraint Assembly of Mn-MOFs for High Performance Li Ion Batteries

Morphology controllable fabrication of electrode materials is of great significance but is still a major challenge for constructing advanced Li ion batteries. Herein, we propose a novel space constraint assembly approach to tune the morphology of Mn(terephthalic acid) (PTA)-MOF, in which benzonic acid was employed as a modulator to adjust the available MOF assembly directions. As a result, Mn(PTA)-MOFs with microquadrangulars, microflakes, and spindle-like microrods morphologies have been achieved. MnO/C hybrids with preserved morphologies were further obtained by self-sacrificial and thermal transformation of Mn(PTA)-MOFs. As anodes for Li ion batteries, these morphologies showed great influence on the electrochemical properties. Owing to the abundant porous structure and unique architecture, the MnO/C spindle-like microrods demonstrated superior electrochemical properties with a high reversible capacity of 1165 mAh g^-1 at 0.3 A g^-1, excellent rate capability of 580 mAh g^-1 at 3 A g^-1, and no considerable capacity loss after 200 cycles at 1 A g^-1. This strategy could be extended to engineering the morphology of other MOF-derived functional materials in various structure-dependent applications.

NiCo₂O₄-Based Supercapacitor Nanomaterials

In recent years, the research on supercapacitors has ushered in an explosive growth, which mainly focuses on seeking nano-/micro-materials with high energy and power densities. Herein, this review will be arranged from three aspects. We will summarize the controllable architectures of spinel NiCo₂O₄ fabricated by various approaches. Then, we introduce their performances as supercapacitors due to their excellent electrochemical performance, including superior electronic conductivity and electrochemical activity, together with the low cost and environmental friendliness. Finally, the review will be concluded with the perspectives on the future development of spinel NiCo₂O₄ utilized as the supercapacitor electrodes.

3D Reticular Li1.2Ni0.2Mn0.6O2 Cathode Material for Lithium-Ion Batteries

In this study, a hard-templating route was developed to synthesize a 3D reticular Li_1.2Ni_0.2Mn_0.6O₂ cathode material using ordered mesoporous silica as the hard template. The synthesized 3D reticular Li_1.2Ni_0.2Mn_0.6O₂ microparticles consisted of two interlaced 3D nanonetworks and a mesopore channel system. When used as the cathode material in a lithium-ion battery, the as-synthesized 3D reticular Li_1.2Ni_0.2Mn_0.6O₂ exhibited remarkably enhanced electrochemical performance, namely, superior rate capability and better cycling stability than those of its bulk counterpart. Specifically, a high discharge capacity of 195.6 mA h g^-1 at 1 C with 95.6% capacity retention after 50 cycles was achieved with the 3D reticular Li_1.2Ni_0.2Mn_0.6O₂. A high discharge capacity of 135.7 mA h g^-1 even at a high current of 1000 mA g^-1 was also obtained. This excellent electrochemical performance of the 3D reticular Li_1.2Ni_0.2Mn_0.6O₂ is attributed to its designed structure, which provided nanoscale lithium pathways, large specific surface area, good thermal and mechanical stability, and easy access to the material center.

Tuning the oxidation state of manganese oxide nanoparticles on oxygen- and nitrogen-functionalized carbon nanotubes for the electrocatalytic oxygen evolution reaction

The oxidation state of manganese oxide nanoparticles can be more easily changed when using nitrogen-functionalized carbon nanotubes as the support.

Synthesis and ORR electrocatalytic activity of mixed Mn–Co oxides derived from divalent metal-based MIL-53 analogues

Four mixed Mn–Co oxides were synthesized from multivariant MIL-53 precursors and showed superior ORR activities in alkaline media.

MnOOH nanorods as high-performance anodes for sodium ion batteries

MnOOH nanorods, which were prepared using a hydrothermal method, have been used for the first time as anode materials for sodium ion batteries.

High-performance carbon-coated mesoporous LiMn2O4 cathode materials synthesized from a novel hydrated layered-spinel lithium manganate composite

High-performance carbon-coated mesoporous LiMn₂O₄ cathode materials have been synthesized from a novel hydrated layered-spinel lithium manganate composite.

Facile synthesis of 3D porous Co3V2O8 nanoroses and 2D NiCo2V2O8 nanoplates for high performance supercapacitors and their electrocatalytic oxygen evolution reaction properties

Porous Co₃V₂O₈ nanoroses and NiCo₂V₂O₈ nanoplates served as effective electrocatalysts in the oxygen evolution reaction and as electrodes of supercapacitors.

Chemically Integrated Inorganic-Graphene Two-Dimensional Hybrid Materials for Flexible Energy Storage Devices

State-of-the-art energy storage devices are capable of delivering reasonably high energy density (lithium ion batteries) or high power density (supercapacitors). There is an increasing need for these power sources with not only superior electrochemical performance, but also exceptional flexibility. Graphene has come on to the scene and advancements are being made in integration of various electrochemically active compounds onto graphene or its derivatives so as to utilize their flexibility. Many innovative synthesis techniques have led to novel graphene-based hybrid two-dimensional nanostructures. Here, the chemically integrated inorganic-graphene hybrid two-dimensional materials and their applications for energy storage devices are examined. First, the synthesis and characterization of different kinds of inorganic-graphene hybrid nanostructures are summarized, and then the most relevant applications of inorganic-graphene hybrid materials in flexible energy storage devices are reviewed. The general design rules of using graphene-based hybrid 2D materials for energy storage devices and their current limitations and future potential to advance energy storage technologies are also discussed.

Porous CuO nanotubes/graphene with sandwich architecture as high-performance anodes for lithium-ion batteries

Constructing a porous conductive framework represents a promising strategy for designing high-performance anodes for Li-ion batteries. Here, porous CuO nanotubes/graphene with hierarchical architectures were fabricated by simple annealing of copper nanowires/graphene hybrids synthesized by a microwave-assisted process. In these nanoarchitectures, the embedded porous CuO nanotubes can prevent restacking of the graphene sheets, whereas graphene can increase the electrical conductivity of CuO. Moreover, these two components constitute a sandwich-like interlaced framework that favors ion diffusion, as well as promoting better electron transport. As a result, the as-prepared nanohybrid exhibits a high specific capacity of 725 mA h g^-1 and a capacity retention of ∼81% after 250 cycles, as well as outstanding rate performance in comparison to those of bare CuO or a CuO-CNT (carbon nanotubes) hybrid.