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Electrocatalytic nitrate reduction to ammonia (NO3RR) is very attractive for nitrate removal and ammonia production in industrial processes. However, the nitrate reduction reaction is characterized by intense hydrogen competition at strong reduction potentials, which greatly limits the Faraday efficiency at strong reduction potentials. Herein, we reported an AuxCu single-atom alloy aerogels (AuxCu SAAs) with three-dimensional network structure with significant nitrate reduction performance of Faraday efficiency (FE) higher than 90% over a wide potential range (0 ~ -1 VRHE). The FE of the catalyst was close to 100% at a high reduction potential of -0.8 VRHE, accompanying with NH3 yield reaching 6.21 mmol h-1 cm-2. More importantly, the catalyst maintained a long-term operation over 400 h at 400 mA cm-2 for the NO3RR using a continuous flow system in a H-cell. Experimental and theoretical analysis demonstrate that the catalyst can lower the energy barrier for the hydrogenation reaction of *NO2, leading to a rapid consumption of the generated *H, facilitate the hydrogenation process of NO3RR, and inhibit the competitive HER at high overpotentials, which efficiently promotes the nitrate reduction reaction, especially in industrial applications.

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Electrochemical nitrate reduction reaction (NO3-RR) is a promising low-carbon and environmentally friendly approach for the production of ammonia (NH3). Herein, we develop a high-temperature quenched copper (Cu) catalyst with the aim of inducing nonequilibrium phase transformation, revealing the multiple defects (distortion, dislocations, vacancies, etc.) presented in Cu, which lead to low overpotential for NO3-RR and high efficiency for NH3 production. Further loading a low content of iridium (Ir) species on the Cu surface improves the reactivity and ammonia selectivity. The resultant CuIr electrode exhibits a Faradaic efficiency of 93% and a record yield of 6.01 mmol h-1 cm-2 at -0.22 VRHE exceeding those of state-of-the-art NO3-RR catalysts. Detailed investigations have demonstrated that the synergistic effect between multiple defects and Ir decoration effectively regulate the d-band center of copper, change the adsorption state of the catalyst surface, and promote the adsorption and reduction of intermediates and reactants. The strong H* adsorption ability of the Ir element provides more active hydrogen for the generation of ammonia, promoting the reduction of nitrate to NH3.

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Aqueous zinc-iodine batteries (AZIBs) are highly appealing for energy requirements owing to their safety, cost-effectiveness, and scalability. However, the inadequate redox kinetics and severe shuttling effect of polyiodide ions impede their commercial viability. Herein, several Zn-MOF-derived porous carbon materials are designed, and the further preparation of iron-doped porous carbon (Fe-N-C, M9) with varied Fe doping contents is optimized based on a facile self-assembly/carbonization approach. M9, with atomic Fe coordinated to nitrogen atoms, is employed as an efficient cathode host for AZIBs. Functional modifications of porous carbon hosts involving the doping species and levels are investigated. The adsorption tests, in situ Raman spectroscopy, and in situ UV-vis results demonstrate the adsorption capability and charge-discharge mechanism for the iodine species. Furthermore, experimental findings and theoretical analyses have proven that the redox conversion of iodine is enhanced through a physicochemical confinement effect. This study offers basic principles for the strategic design of single-atom dispersed carbon as an iodine host for high-performance AZIBs. Flexible soft-pack battery and wearable microbattery applications also have implications for future long-life aqueous battery designs.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

RESUMEN

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.

RESUMEN

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.

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RESUMEN

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.

RESUMEN

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.

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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.

RESUMEN

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: .

RESUMEN

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.