Rubik's cube PBA frameworks for optimizing the electrochemical performance in alkali metal-ion batteries.

PBA frameworks have stood out among metal-organic frameworks because of their easy preparation, excellent stability, porous structures, and rich redox properties. Unfortunately, their non-ideal conductivity and significant volume expansion during cycling prevent more widespread application in alkali-metal-ion (Li+, Na+, and K+) batteries. By changing the type and molar ratio of metal ions, Rubik's PBA frameworks with infinite structural variations were obtained in this study, just like the Rubik's cube undergoes infinite changes during the rotation. X-ray adsorption fine structure measurements have documented the existence and determined the coordination environment of the metal ions in the Rubik's PBA framework. Benefiting from the more stable Rubik's cube structures with diverse composition, enhanced conductivity, and greater adsorption capacity, the obtained Rubik's cubes CoM-PBA anodes, especially CoZn-PBA deliver the enhanced cycling and rate performance in all the alkali-metal-ion batteries. The findings are supported by density functional theory calculations. Ex-situ X-ray photoelectron spectroscopy, and in-situ X-ray diffraction measurements were undertaken to explore the storage mechanism of CoZn-PBA anodes. Our results further demonstrate that the Rubik's cube PBA framework-based materials could be widely applied in the field of alkali-metal-ion batteries.

Covalent organic frameworks and their composites for rechargeable batteries.

Covalent organic frameworks (COFs), characterized by well-ordered pores, large specific surface area, good stability, high precision, and flexible design, are a promising material for batteries and have received extensive attention from researchers in recent years. Compared with inorganic materials, COFs can construct elastic frameworks with better structural stability, and their chemical compositions and structures can be precisely adjusted and functionalized at the molecular level, providing an open pathway for the convenient transfer of ions. In this review, the energy storage mechanism and unique superiority of COFs and COF composites as electrodes, separators and electrolytes for rechargeable batteries are discussed in detail. Special emphasis is placed on the relationship between the establishment of COF structures and their electrochemical performance in different batteries. Finally, this review summarizes the challenges and prospects of COFs and COF composites in battery equipment.

Layered (AlO)2OH·VO3 composite superstructures for ultralong lifespan aqueous zinc-ion batteries.

The unique superstructures electrode materials are of dominant significance for improving the performance of aqueous zinc-ion batteries (AZIBs). In this work, using nano MIL-96 (Al) as the precursor, a series of the layered (AlO)2OH·VO3 composite superstructures with different morphologies and V-oxide contents were prepared by combining calcination and hydrothermal synthesis. Among which, the HBC650·V4 superstructure is composed of the amorphous Al2O3/C, V-oxide, and the fluffy structure of (AlO)2OH, thus the superstructure can enhance the stability, increase the active center, and shorten Zn2+ diffusion, respectively. It is commendable that, the HBC650·V4 superstructure exhibits a high specific capacity of 180.1 mAh·g-1 after 300 cycles at 0.5 A·g-1. Furthermore, the capacity retention can be as high as 99.6 % after 5000 cycles at a high current density of 5.0 A·g-1, showing superior long cycling stability. Importantly, the in-situ XRD patterns and ex-situ analysis revealed the structural changes and reaction mechanisms of the HBC650·V4 superstructure during Zn2+ insertion/extraction. Therefore, the HBC650·V4 superstructure prepared using Al-MOF exhibits the advanced AZIBs performance. The preparation of nano-MOF into multifunctional superstructures through innovative strategies will be development trend in this field, which opens a new way to design AZIBs cathode materials.

Recent advance of nanomaterials modified electrochemical sensors in the detection of heavy metal ions in food and water.

As one of the main pollutants, heavy metal ions can accumulate in the human body and cause a cascade of damage. Electrochemical sensors provide great prospects for tracing heavy metal ions because of their properties of high sensitivity, low detection limits and fast response. Electrode surface modification materials play a key role in enhancing the performance of electrochemical sensors. Herein, we summarize in detail the recent work on electrochemical sensors modified by carbon nanomaterials (graphene and its derivatives, carbon nanofibers and carbon nanotubes), metal nanomaterials (gold, silver, bismuth and iron), complexes (MOFs, ZIFs and MXenes) and their composites for the detection of heavy metal ions (mainly include Cd(II), Hg(II), Pb(II), As(III), Cu(II) and Zn(II)) in food and water. The synthetic strategies, mechanisms, innovations, advantages, challenges and prospects of various electrode modification nanomaterials for the detection of heavy metal ions in food and water are discussed.

Space-Confined Metal Ion Strategy for Carbon Materials Derived from Cobalt Benzimidazole Frameworks with High Desalination Performance in Simulated Seawater.

Various metal ions with different valence states (Mg2+ , Al3+ , Ca2+ , Ti4+ , Mn2+ , Fe3+ , Ni2+ , Zn2+ , Pb2+ , Ba2+ , Ce4+ ) are successfully confined in quasi-microcube shaped cobalt benzimidazole frameworks using a space-confined synthesis strategy. More importantly, a series of derived carbon materials that confine metal ions are obtained by high-temperature pyrolysis. Interestingly, the derived carbon materials exhibited electric double-layer and pseudocapacitance properties because of the presence of metal ions with various valence states. Moreover, the presence of additional metal ions within carbon materials may create new phases, which can accelerate Na+ insertion/extraction and thus increase electrochemical adsorption. Density functional theory results showed that carbon materials in which Ti ions are confined exhibit enhanced insertion/extraction of Na+ resulting from the presence of the characteristic anatase crystalline phases of TiO2 . The Ti-containing materials have an impressive desalination capacity (62.8 mg g-1 ) in capacitive deionization (CDI) applications with high cycling stability. This work provides a facile synthetic strategy for the confinement of metal ions in metal-organic frameworks and thus supports the further development of derived carbon materials for seawater desalination by CDI.

Embedding Atomically Dispersed Iron Sites in Nitrogen-Doped Carbon Frameworks-Wrapped Silicon Suboxide for Superior Lithium Storage.

Silicon suboxide (SiOx ) has attracted widespread interest as Li-ion battery (LIB) anodes. However, its undesirable electronic conductivity and apparent volume effect during cycling impede its practical applications. Herein, sustainable rice husks (RHs)-derived SiO2 are chosen as a feedstock to design SiOx /iron-nitrogen co-doped carbon (Fe-N-C) materials. Using a facile electrospray-carbonization strategy, SiOx nanoparticles (NPs) are encapsulated in the nitrogen-doped carbon (N-C) frameworks decorating atomically dispersed iron sites. Systematic characterizations including high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure (XAFS) verify the existence of Fe single atoms and typical coordination environment. Benefiting from its structural and compositional merits, the SiOx /Fe-N-C anode delivers significantly improved discharge capacity of 799.1 mAh g-1 , rate capability, and exceptional durability, compared with pure SiO2 and SiOx /N-C, which has been revealed by the density functional theory (DFT) calculations. Additionally, the electrochemical tests and in situ X-ray diffraction (XRD) analysis reveal the oxidation of Lix Si phase and the storage mechanism. The synthetic strategy is universal for the design and synthesis of metal single atoms/clusters dispersed N-C frameworks encapsulated SiOx NPs. Meanwhile, this work provides impressive insights into developing various LIB anode materials suffering from inferior conductivity and huge volume fluctuations.

Effect of Solvothermal Temperature on Morphology and Supercapacitor Performance of Ni-MOF.

A series of Ni-MOF materials were synthesized via a simple hydrothermal method and can be employed as electrodes for supercapacitors (SCs). Different temperatures were selected to unveil the effect of temperature on the formation, structure, and electrochemical performance of Ni-MOF-x (x = 60, 80, 100, and 120). Ni-MOF-80 possessed a larger specific surface area with a cross-network structure formed on its surface. The synthesized Ni-MOF electrode delivered a specific capacity of 30.89 mA h g-1 when the current density reached 1 A g-1 in a three-electrode system. The as-fabricated Ni-MOF materials could be further designed and are expected to deliver satisfactory performance in practice.

Ordered porous and uniform electric-field-strength micro-supercapacitors by 3D printing based on liquid-crystal V2O5 nanowires compositing carbon nanomaterials.

The design of electrode internal structure plays an important role in improving the performance of micro-supercapacitors (MSCs). However, the complexity of the program hinders the development and application of Three-dimensional(3D)-printed MSCs. Herein, printable inks were prepared by using vanadium pentoxide nanowires as active materials, carbon nanotubes as collector and conductive agent, graphene oxide as adhesive, scaffold and water retaining agent. Benefiting from the liquid-crystal properties of materials and 3D printing technology as well as the adjustment of the materials proportion, onion-like structures with ordered porous layered structure and uniform electric-field-strength MSCs were constructed. The 3D-printed MSC has fine area capacitance (34.68 mF cm-2) and area energy density (1.73 µWh cm-2 at a current density of 0.24 mA cm-2). Therefore, using the unique characteristics of materials to build an efficient 3D printing strategy is expected to provide a feasible solution for the construction of various MSCs and other high-energy storage systems.

Hollow mesoporous carbon nanospheres space-confining ultrathin nanosheets superstructures for efficient capacitive deionization.

In this work, we propose a novel strategy to fabricate nickel silicate nanoflakes inside hollow mesoporous carbon spheres (Ni3Si2O5(OH)4/C). Hollow mesoporous carbon spheres (HMCSs) can well regulate and limit the growth of Ni3Si2O5(OH)4 nanosheets, which obviously enhance the structural stability and conductivity of the composites. The core-shell Ni3Si2O5(OH)4/C superstructure has been proven to possess an extremely excellent electrosorption capacity of 28.7 mg g-1 at 1.2 V under a NaCl concentration of 584 mg L-1 for capacitive deionization (CDI). This outstanding property can be attributed to the core-shell superstructure with ultrathin Ni3Si2O5(OH)4 nanosheets as the stable core and mesoporous carbon as the conductive shell. This work will provide a direction for the application of core-shell superstructure carbon-based nanomaterials as high-performance electrode materials for CDI.

Synthesis of truncated octahedral zinc-doped manganese hexacyanoferrates and low-temperature calcination activation for lithium-ion battery.

Owing to their open three-dimensional framework structure, Prussian blue analogues (PBAs) have attracted increasing interest as anode materials for future lithium-ion batteries (LIBs). However, some disadvantages, such as inferior stability and short cycle life, hinder its utilization significantly. Hence, we develop a simple method to prepare a unique truncated octahedral ZnMnFe-PBA with exposed {111} crystal facets. The doping of Zn into Mn-based PBA enhances structural stability and improves the electronic conductivity. Meanwhile, low-temperature calcination not only improves the electrochemical activity but also preserves the porosity to enable mass transfer. When the ratio of Mn:Zn is 90:10 and the calcination temperature is 100 °C, sample Z10-100 displays high capacity and excellent cycle life (∼510.6 mA h g-1 at 0.1 A g-1, 168.9 mA h g-1 after 5000 cycles at 1.0 A g-1 with 99.9% capacity retention). The significant improvements in cycle stability and cycle life are attributable to transition metal ion doping and effective low-temperature calcination activation, which provide a facile approach for the synthesis of low-cost and efficient electrode materials.

Construction of SiOx/nitrogen-doped carbon superstructures derived from rice husks for boosted lithium storage.

Silicon sub-oxides (SiOx) are increasingly becoming a prospective anode material for lithium-ion batteries (LIBs). Nevertheless, inferior electrical conductivity and drastic volume fluctuation upon cycling significantly hamper the electrochemical performance of SiOx. In this work, rice husks (RHs)-derived pitaya-like SiOx/nitrogen-doped carbon (SNC) superstructures have been prepared by a simple electrospray-carbonization approach. SiOx nanoparticles (NPs) are well-dispersed in a spherical nitrogen-doped carbon (NC) matrix. The carbon frameworks discourage the aggregation of SiOx NPs, facilitating the kinetics for ion diffusion and charge transfer, and maintaining structural stability upon cycling, thus bringing about improved electrochemical performance. When the optimized SNC superstructures with SiOx content of 64.3% are utilized as LIBs anodes, a stable specific capacity of 622.8 mA h g-1 after 100 cycles at 0.1 A g-1, and an excellent long cycle performance of 190.1 mA h g-1 after 5000 cycles at 5 A g-1 are obtained. This effective and universal synthetic strategy for fabricating controllable superstructures offers insights into the development of high-performance LIBs.

Rational Design and General Synthesis of Multimetallic Metal-Organic Framework Nano-Octahedra for Enhanced Li-S Battery.

Metal-organic frameworks (MOFs), which consist of central metal nodes and organic linkers, constitute a fast growing class of crystalline porous materials with excellent application potential. Herein, a series of Mn-based multimetallic MOF (bimetallic and trimetallic MIL-100) nano-octahedra are prepared by a facile one-pot synthetic strategy. The types and proportions of the incorporated elements can be tuned while retaining the original topological structure. The introduction of other metal ions is verified at the atomic level by combining X-ray absorption fine structure experiments and theoretical calculations. Furthermore, these multimetallic Mn-based MIL-100 nano-octahedra are utilized as sulfur hosts to prepare cathodes for Li-S batteries. The MnNi-MIL-100@S cathode exhibits the best Li-S battery performance among all reported MIL-100@S composite cathode materials, with a reversible capacity of ≈708.8 mAh g-1 after 200 cycles. The synthetic strategy described herein is utilized to incorporate metal ions into the MOF architecture, of which the parent monometallic MOF nano-octahedra cannot be prepared directly, thus rationally generating novel multimetallic MOFs. Importantly, the strategy also allows for the general synthesis and study of various micro-/nanoscale MOFs in the energy storage field.

Silicon oxide-protected nickel nanoparticles as biomass-derived catalysts for urea electro-oxidation.

The urea electro-oxidation reaction (UOR) is explored as a new technique for energy conversion and the removal of urea via electrochemical means in wastewater. Nickel (Ni) nanoparticles grown on nanosheets were prepared by a facile hydrothermal reaction and a subsequent calcination process of silicon oxide/nitrogen-doped carbon (SiOx/NC) as the precursor, in which SiOx/NC with a natural three-dimensional (3D) interconnected structure was obtained from bamboo leaves. The nickel/silicon oxide/nitrogen-doped carbon (Ni/SiOx/NC, denoted as Y) obtained at 900 °C (Y3), exhibits the most optimal catalytic properties for the UOR with a low potential of 1.384 V vs. RHE at 10 mA cm-2. The protective role of SiOx was also explored via the partial etching of SiOx (Y3-NaOH), and the results show that the overpotential of the curve increased rapidly after long-term test. The findings indicate that full exploitation of the comprehensive advantages of biomass materials is beneficial for alleviating the problems encountered in the development of energy-related technologies.

Geometric analysis of shape transition for two-layer carbon-silicon nanotubes.

The two-layer nanotubes consisted of carbon atoms on the outside layer and silicon atoms on the inside layer (CNT@SiNT) show a series of diversity in the shape transitions, for instance transforming from a circle through an oval to a rectangle. In this paper, we investigate this geometric change from three perspectives. In the first aspect, we stationary time, followed by quantize in the three-dimensional Z-axis of nanotubes. In the second aspect, we stationary Z-axis, followed by quantize in the time. Finally, we tracked distance of nanotubes flattest section and roundest section. At the stationary time, the overall image of different Z-axis distance distributions is similar to a plan view of multiple ice creams, regardless of whether CNT or SiNT are on the same Z-axis, their slice plans are circle or rectangle of the projection of the Z-axis section on the XOY plane. In the stationary Z-axis, the nanotubes periodically change from a circle to an oval, and then from an oval to a rectangle at different times. Most remarkably, the distance value of deformation which we track the flattest and roundest is a constant value, and in the same distance period, there is only one roundest circle and one longest rectangle at different section and different time. The geometric analysis provided theoretical reference for the preparation of various devices and semiconductor nano-heterojunctions.

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

Correction for 'Facile synthesis of ultrathin Ni-MOF nanobelts for high-efficiency determination of glucose in human serum' by Xiao Xiao et al., J. Mater. Chem. B, 2017, 5, 5234-5239, DOI: .

Porous pyrrhotite Fe7S8 nanowire/SiOx/nitrogen-doped carbon matrix for high-performance Li-ion-battery anodes.

Iron sulfides, known as attractive anode materials for rechargeable lithium-ion batteries, have been extensively studied. Nevertheless, low electrical conductivity and huge volume expansion of iron sulfides hinder its practical applications. Herein, a novel method was developed to synthesize ternary porous Fe7S8 nanowires/SiOx/nitrogen-doped carbon matrix by facile hydrothermal method and subsequent sulfidation derived from bamboo leaves. The SiOx/nitrogen-doped carbon matrix can ensure the growth of nanowires, maintain the structural stability, improve the conductivity and provide improved capacity of Fe7S8. The 3D matrix structure and porous properties of Fe7S8 nanowires effectively relieve the volume change upon the insertion/extraction of Li+. The Fe7S8/SiOx/nitrogen-doped carbon anode exhibited a superior discharge capacity of 1060.2 mA h g-1 at 200 mA g-1 along with good long cycling performance of 415.8 mA h g-1 at the 1000th cycle at 5 A g-1. The facile strategy for preparing ternary Fe7S8 composites with superb LIB electrochemical performances demonstrates a great potential in electrochemical energy storage.

Facile one-pot generation of metal oxide/hydroxide@metal-organic framework composites: highly efficient bifunctional electrocatalysts for overall water splitting.

In situ growth of Co3O4 nanocubes on the surface of Co-MOF is an effective way to adjust the surface electron structure of electrocatalysts and increase extra active sites for the OER, the HER and overall water splitting. A facile one-pot hydrothermal method can be extended to the preparation of other metal oxide/hydroxide@MOF composites.

Synthesis of Co0.5 Mn0.1 Ni0.4 C2 O4 ⋠n H2 O Micropolyhedrons: Multimetal Synergy for High-Performance Glucose Oxidation Catalysis.

Owing to the synergy between metals, trimetal oxalate micropolyhedrons have been synthesized by means of a room-temperature coprecipitation strategy. The effect of their nanoscale size on their electrochemical performance toward glucose oxidation was investigated. In particular, the Co0.5 Mn0.1 Ni0.4 C2 O4 ⋅n H2 O micropolyhedrons illustrated prominent electrocatalytic activity for the glucose oxidation reaction. Additionally, the Co0.5 Mn0.1 Ni0.4 C2 O4 ⋅n H2 O micropolyhedrons, when used as an electrode material, illustrated an excellent lower limit of detection (1.5 µm), a wide detection concentration range (0.5-5065.5 µm), and a high sensitivity (493.5 µA mm-1 cm-2 ). Further analysis indicated that the effectively improved conductivity may have been due to the small size of the materials, and it was easier to form a flat film when Nafion was coated onto the glassy carbon electrode.

FeO x -Based Materials for Electrochemical Energy Storage.

Iron oxides (FeO x ), such as Fe2O3 and Fe3O4 materials, have attracted much attention because of their rich abundance, low cost, and environmental friendliness. However, FeO x , which is similar to most transition metal oxides, possesses a poor rate capability and cycling life. Thus, FeO x -based materials consisting of FeO x , carbon, and metal-based materials have been widely explored. This article mainly discusses FeO x -based materials (Fe2O3 and Fe3O4) for electrochemical energy storage applications, including supercapacitors and rechargeable batteries (e.g., lithium-ion batteries and sodium-ion batteries). Furthermore, future perspectives and challenges of FeO x -based materials for electrochemical energy storage are briefly discussed.