High volumetric energy density combined with high power density is highly desired for electrical double-layer capacitors. Usually the volumetric performance is improved by compressing carbon material to increase density but at the much expense of power density due to the deviation of the compressed porous structure from the ideal one. Herein the authors report an efficient approach to increase the density and optimize the porous structure by collapsing the carbon nanocages via capillarity. Three samples with decreasing sizes of meso- and macropores provide us an ideal model system to demonstrate the correlation of volumetric performance with porous structure. The results indicate that reducing the surplus macropores and, more importantly, the surplus mesopores is an efficient strategy to enhance the volumetric energy density while keeping the high power density. The optimized sample achieves a record-high stack volumetric energy density of 73 Wh L−1 in ionic liquid with superb power density and cycling stability.

Electrochemical energy storage (EES) devices combining high energy density with high power density are necessary for addressing the growing energy demand and environmental crisis. Nickel oxide (NiO) is a promising electrode material for EES owing to the ultrahigh theoretical specific capacity, but the practical values are far below the theoretical limit to date, with inferior rate and cycling performances. Herein, we report the novel mesostructured NiO/Ni composites, which consist of hetero-NiO/Ni components at nanoscale while displaying 3D porous architectures at mesoscale, with adjustable metallic Ni content in a wide range. The unique mesostructure boosts the EES performance of NiO to its theoretical limit with the ultrahigh specific capacity, high rate capability and stability. The superior performance is well correlated with the synergism of the high accessibility to electrolyte, short solid-state ion diffusion length, and much enhanced conductivity of the mesostructured NiO/Ni composites. This study demonstrates a new strategy likely applicable to other transition metal oxides in maximizing their potential in energy storage, i.e. by constructing the similar mesostructured metal-oxide/metal composites.

Iron/nitrogen/carbon (Fe/N/C) catalyst is so far the most promising non-precious metal electrocatalyst for oxygen reduction reaction (ORR) in acidic medium, whose performance depends closely on the synthesis chemistry. Herein, we report a MnOx-induced strategy to construct the Fe/N/C with highly exposed Fe–Nx active sites, which involves the uniform spreading of polyaniline on hierarchical N-doped carbon nanocages by a reactive-template polymerization, followed by the successive iron incorporation and polyaniline pyrolysis. The resulting Fe/N/C demonstrates an excellent ORR performance, including an onset potential of 0.92 V (vs. RHE), four electron selectivity, superb stability and immunity to methanol crossover. The excellent performance is well correlated with the greatly enhanced surface active sites of the catalyst stemming from the unique MnOx-induced strategy. This study provides an efficient approach for exploring the advanced ORR electrocatalysts by increasing the exposed active sites.

•Hierarchical LiNixCoyO2 (h-LNCO) mesostructures are facilely synthesized.•h-LNCO owns exposed (110) planes, small particle size and porous structure.•h-LNCO exhibits high capacity, superior cyclability and rate capability.•The superior performance of h-LNCO results from the unique mesostructure.Lithium ion batteries (LIBs) with enhanced performance to commercial ones are urgently demanded in portable electric devices. Herein, we demonstrate an efficient strategy to improve the electrochemical performance of a dominant commercial cathode material (LiCoO2) by constructing 3D hierarchical LiNixCoyO2 (h-LNCO). The h-LNCO presents porous spherical-shaped morphology at mesoscale while comprises interconnected primary nanoparticles at nanoscale. Such a unique morphology endows the h-LNCO with porous structure for easy penetration of electrolyte, relatively small size of primary particles with short Li+ ions diffusion length and abundant exposed surface in favor of Li+ intercalation/deintercalation. The synergism of these merits makes the h-LNCO exhibit superior electrochemical properties with high capacity, superior cyclability and rate capability, much better than the solid granular LNCO counterparts and commercial LiCoO2. This strategy of constructing porous hierarchical mesostructures could be extended to other electrode materials for electrochemical energy storage.

One-dimensional alloyed InxAl1−xN nanostructures are successfully synthesized through a chemical reaction of InCl3, AlCl3 and NH3. By tuning the vapour pressure ratio of InCl3 to AlCl3, their morphologies evolve from nanocones, to nanocolumns, nanobrushes, and back to nanocones, with composition regulation in the range of 0 < x < 5 at%.

Prediction and design of various nanomaterials is a long-term dream in nanoscience and nanotechnology, which depends on the deep understanding on the growth mechanism. Herein, we report the successful prediction on the growth of AlN nanowires by nitriding Al69Ni31 alloy particles across the liquid-solid (β) phase region (1133–1638°C) based on the phase-equilibrium-dominated vapor-liquid-solid (PED-VLS) mechanism proposed in our previous study. All predictions about the growth of AlN nanowires, the evolutions of lattice parameters and geometries of the coexisting Al-Ni alloy phases are experimentally confirmed quantitatively. The preconditions for the applicability of the PED-VLS mechanism are also clarified. This progress provides the further evidence for the validity of the PED-VLS mechanism and demonstrates a practical guidance for designing and synthesizing different nanomaterials according to corresponding phase diagrams based on the insight into the growth mechanism.纳米材料的预测和设计是纳米科学与技术领域的长期梦想, 该梦想的实现有赖于对生长机理的深刻理解. 本文基于我们前期研究揭示 的相平衡主导的气-液-固(VLS)生长机理, 成功地预测了在1133~1638°C温区内通过氮化Al69Ni31合金颗粒生长AlN纳米线的过程, 有关AlN纳米 线的生长、共存Al-Ni合金相的晶格参数及形貌演变等预测均得到了定量化实验结果的证实, 并界定了相平衡主导的VLS生长机理的适用条件. 本文为相平衡主导的VLS生长机理的有效性提供了进一步的实验证据, 同时展示了在生长机理的指导下根据相图设计和制备纳米材料的一个 实例.

Exploring cheap and stable electrocatalysts to replace Pt for the oxygen reduction reaction (ORR) is now the key issue for the large-scale application of fuel cells. Herein, we report an alloyed Co–Mo nitride electrocatalyst supported on nitrogen-doped carbon nanocages (NCNCs) which combines the merits of cobalt nitride and molybdenum nitride, showing high activity comparable to that of cobalt nitride and progressively enhanced stability with the increase in the Mo ratio. The typical Co0.5Mo0.5Ny/NCNCs catalyst demonstrates excellent ORR performance in acidic medium with a high onset potential of 808 mV vs RHE, superior stability (>80% retention after 100 h of continuous testing in 0.5 mol L–1 H2SO4), a dominant four-electron catalytic process, and good immunity to methanol crossover. Together with the convenient and scalable preparation as well as the low cost, the alloyed Co–Mo nitride electrocatalyst shows great potential in application for fuel cells. This study also suggests a promising strategy to develop non-precious-metal ORR electrocatalysts in acidic medium: i.e., to construct the alloyed compounds by combining substances with respective high activity and high stability.Keywords: acidic medium; alloyed Co−Mo nitride; electrocatalysts; nonprecious metal; oxygen reduction reaction

Patterned arrays of Si- or Mg-doped AlN nanocones were synthesized via chemical vapor deposition. The field emission properties of the AlN nanocones were enhanced with Si-doping but deteriorated with Mg-doping, which demonstrated the great potential of doping in tuning the properties of field emitters.

Composition regulation of semiconductors can engineer their bandgaps and hence tune their properties. Herein, we report the first synthesis of ternary ZnxCd1−xS semiconductor nanorods by superionic conductor (Ag2S)-mediated growth with [(C4H9)2NCS2]2M (M = Zn, Cd) as single-source precursors. The compositions of the ZnxCd1−xS nanorods are conveniently tuned over a wide range by adjusting the molar ratio of the corresponding precursors, leading to tunable bandgaps and hence the progressive evolution of the light absorption and photoluminescence spectra. The nanorods present well-distributed size and length, which are controlled by the uniform Ag2S nanoparticles and the fixed amount of the precursors. The results suggest the great potential of superionic conductor-mediated growth in composition regulation and bandgap engineering of chalcogenide nanowires/nanorods.

•Novel 3D hierarchical carbon nanocages with high pore volume, network geometry and good conductivity.•High-loading confinement of ~80 wt% sulfur inside the nanocages.•Much alleviated polysulfides dissolution due to the confinement.•The high-rate performance for the high-sulfur-loading carbon-sulfur composites.•Well established correlation between the high performance and unique structure.Lithium–sulfur batteries are hindered by the low utilization of sulfur, short cycle life and poor rate capability which are severe challenges today. Herein we report a new kind of carbon–sulfur composites by infusing sulfur into the novel hierarchical carbon nanocages (hCNC) with high pore volume, network geometry and good conductivity. The designed S@hCNC composite with a high sulfur loading of 79.8 wt% presents the large capacity, high-rate capability and long cycle life, which could shorten the charging time for mobile devices from hours to minutes. The excellent performance derives from the unique mesostructure of hCNC that enables the encapsulation of high-loading sulfur inside the carbon nanocages to alleviate polysulfide dissolution, meanwhile much enhance the electron conduction and Li-ion diffusion.

Here we report the construction of CsI–AlN hybrid nanostructures by evaporating CsI onto preformed AlN nanocone arrays. The field emission performances of the hybrid samples are much improved due to the lower work function, better conductivity and more emission sites, depending on the size and density of the CsI nanoparticles. But the performance gradually decays after ca. 45 min stable emission due to the instability of CsI during field emission which has been neglected to date. The results suggest that further effort to prevent the loss of Cs species to improve the stability of CsI-decorated hybrid nanostructures is required for practical applications.

A convenient template- and surfactant-free strategy has been developed to prepare porous hierarchical Ni nanostructures by directly calcining the nickel-based flower-like precursor in Ar. The precursor is preformed by refluxing the solution of nickel nitrate and the co-precipitators of hexamethylenetetramine and oxalic acid at 100 °C for 6 h. The unique Ni nanostructures are composed of porous sheets of several nanometers in thickness with a wide pore size distribution of 5–100 nm, with a Brunauer–Emmett–Teller specific surface area up to 24.5 m2 g−1. The formation process has been in situ examined by thermogravimetry–differential scanning calorimetry–mass spectroscopy, which illuminates the continuous generation of Ni species with the simultaneous release of gaseous species from decomposition and/or reduction of the precursor. Coupled with the good soft ferromagnetism, the porous Ni nanostructures with high surface area have great potential as a magnetically separable catalyst, as demonstrated in the excellent performance for the selective hydrogenation of acetophenone to 1-phenylethanol at 100 °C.

A convenient in situ chloride-generated route was pursued to synthesize chromium silicide (CrSi2) nanomaterials in this study, and the influence of growth conditions on the morphologies of CrSi2 products was examined in an optimized growth apparatus. Various morphologies of CrSi2 including nanowire bundles, nanobelts and cattail hassock-like microdisks have been controllably synthesized through the concentration regulation of gaseous Cr and Si sources on the nucleation and growth stages by changing the growth temperature and the precursor diffusion manner. The morphological evolution of CrSi2 nanostructures could be attributed to the growth habits of the CrSi2 crystal under different conditions as well as the electrostatic interactions among their exposed polar faces on the basis of the experimental results. The field emission behavior of the CrSi2 nanostructures shows low turn-on fields of 3.6–5.3 V μm−1 at an anode–cathode distance of 400 μm, suggesting their potential application in field emission devices.

Morphological regulation of nanomaterials is essential for their properties and potential applications, and many strategies have been developed. The great influence of anions on the morphologies of nanomaterials was discovered recently by being adsorbed selectively on a specific crystalline plane of material to tune its growth habit. In this work, the effect of anions on the morphologies of In(OH)3 nanostructures was studied and a series of In(OH)3 nanostructures have been obtained by controlling the species and concentrations of the presenting anions in hydrothermal system. In(OH)3 nanocubes and nanorods were obtained by using indium chloride as indium source, whereas nanoflakes were produced in the indium nitrate case. Moreover, adding appropriate amount of sodium halides into the hydrothermal reaction could convert nanoflakes into nanocubes and nanorods, while adding sodium nitrate into the hydrothermal system of indium nitrate could lead to the formation of superstructures constructed by aligned nanoflakes. By calcining these In(OH)3 nanostructures, porous In2O3 nanostructures with inherited morphologies were obtained. The gas sensors fabricated by these porous In2O3 nanostructures exhibited excellent and morphology-dependent sensitivities for ethanol vapor, implying their great potential in ethanol detection.

Herein we report the synthesis of vertically aligned AlN nanostructures on conductive substrates through the chemical reaction between AlCl3 and NH3 in the temperature range of 650–850 °C. The morphologies of the AlN nanostructures could be controllably modulated from cone-like to rod-like geometries by increasing the reaction temperature. The formation mechanism of the AlN nanostructures on the nitrified Ti substrates has been discussed based on the analysis of the intermediate products. The field emission (FE) property of AlN nanocones grown on the nitrified Ti substrate is better than that for AlN nanocones on Si substrate. The improvement of FE property can be attributed to the lower resistance between AlN nanocones and the nitrified Ti substrate because the conductive titanium nitride film can directly contact with AlN emitters while a high-resistive silica layer would easily form between Si substrate and AlN nanocones. These results indicate that the deposition of nanoscale filed emitters on conductive substrates is an effective way to improve the FE behavior, and may find potential applications in FE devices.Highlights► AlN nanocone arrays are promising field emitters. ► The substrates cannot influence the morphologies of AlN products. ► AlN products can evolve from cone-like to rod-like geometries with temperature. ► AlN nanocones on conductive substrate show better field emission properties. ► Better performance arising from better electrical contact.

A convenient hydrothermal method has been developed for the controllable synthesis of various nanostructures of manganese oxides and their derivatives through modified redox reactions between Mn2+ and the combinative oxidizer of KBrO3/KX (X = Cl, Br, I). The morphologies and oxidation states of the products could be modulated simply by changing the anions in KX to regulate the oxidizability of the combinative oxidizer. With KBrO3/KBr as the oxidizer, potassium manganese oxide (KMO) nanowires are obtained owing to the appropriate oxidizability of the oxidizer as well as the assistance of ion-intercalated effect. The KMO nanowires exhibit the electrochemical capacitance of about 134.2 F g−1 at the scan rate of 10 mV s−1 and superior cycling stability as revealed by cyclic voltammetry and charge/discharge measurements, implying their potential application in supercapacitors for electrical storage.

The application of one-dimensional AlN nanostructures as field emitters is still difficult because of their poor conductivity and tendency toward easy oxidization and hydrolyzation. In this study, by coating preformed AlN nanocone arrays, we successfully prepared AlN-based core–shell nanostructures of AlN–C, AlN–CN, and AlN–BCN, as confirmed by characterization using electron microscopy, Raman spectroscopy, and compositional analysis. The field-emission performances of the core–shell nanostructures were effectively enhanced compared to that of the pristine AlN arrays, in the order AlN–BCN > AlN–CN > AlN–C > AlN, because of the enhanced conductivity, the lower work function arising from the coating layer, and the synergetic effect between the inner core and the outer shell. The thickness of the coating layer is also an important factor influencing the field emission, and a thin coating layer is preferred for optimization. The results indicate that the construction of core–shell nanostructures can efficiently improve the field-emission performance of AlN-based nanocones, which is a promising route for the practical application of AlN-based field emitters.

Controllable synthesis of well-shaped nanocrystals is of significant importance for understanding the surface-related properties as well as for the exploration of potential applications. Herein, CeO2 nanorods and nanocubes were selectively synthesized using cerium(III) chloride and cerium(III) nitrate as precursor, respectively. Counter anions of the cerium source were crucial to the shapes of the resulting products. Intriguingly, the as-synthesized nanorods could be converted into nanocubes by the addition of an appropriate amount of NO3− ions into the hydrothermal reaction. The NO3− ions are considered as both a capping agent and an oxidizer during the formation of CeO2 nanocubes. Moreover, the influences of several others anions are investigated. Br−, I−, and SO42− ions have similar roles to Cl− ions, which lead to the formation of nanorods. The introduction of BrO3− ions can bring on the generation of irregular nanoparticles because they can function as an oxidizer but not a capping agent. The anion-induced controllable growth process is simple and low cost, which makes this strategy potentially useful for the preparation of other faceted nanostructures.

Hollow nanostructures have attracted increasing attention due to the unique properties and potential applications in many fields such as drug delivery, biomedical agents, energy storage, and reaction containers. In this paper, we report the preparation of cerium fluoride (CeF3) hollow nanostructures including nanocages, nanorings, nanococoons, and circular hollow disks through a facile hydrothermal process. The morphologies (hollow or solid) and cross sections (hexagonal or circular) of as-prepared nanostructures are dependent on the hydrothermal temperatures. All the precursors including KBrO3, Ce(IV) ions, H2SO4, and organic reducer (for example, citric acid or malonic acid), are necessary agents for the formation of CeF3 hollow nanostructures. On the basis of these experimental results, it is proposed that the growth microenvironment of CeF3 products is controlled by the Belousov−Zhabotinsky oscillating reaction, and the obtained hollow nanostructures could be regarded as the replicas of spatial patterns formed in the unstirred bromate−citric acid−Ce(IV)−H2SO4 oscillating system. The strong and uniform blue light emission of CeF3 hollow nanostructures implies their potential applications in light-emitting devices.

An in situ generated template method has been developed via the simple reaction of AlCl 3 with NH 3 for the synthesis of AlN hollow nanospheres with diameters of 80−400 nm and shell thickness of ∼15 nm. On the basis of the detailed characterization on the intermediate compounds, the preparation process has been elucidated which includes the first formation of the AlCl 3· xNH 3@AlN core−shell nanostructures followed by the decomposition of the inner compound around 1100 °C. This reaction route successfully extended the traditional CVD reaction of AlCl 3 with NH 3 from producing solid AlN powder to preparing AlN hollow nanospheres.

A convenient hydrothermal method has been developed for the controllable synthesis of various nanostructures of manganese oxides and their derivatives through modified redox reactions between Mn2+ and the combinative oxidizer of KBrO3/KX (X = Cl, Br, I). The morphologies and oxidation states of the products could be modulated simply by changing the anions in KX to regulate the oxidizability of the combinative oxidizer. With KBrO3/KBr as the oxidizer, potassium manganese oxide (KMO) nanowires are obtained owing to the appropriate oxidizability of the oxidizer as well as the assistance of ion-intercalated effect. The KMO nanowires exhibit the electrochemical capacitance of about 134.2 F g−1 at the scan rate of 10 mV s−1 and superior cycling stability as revealed by cyclic voltammetry and charge/discharge measurements, implying their potential application in supercapacitors for electrical storage.

Here we report the construction of CsI–AlN hybrid nanostructures by evaporating CsI onto preformed AlN nanocone arrays. The field emission performances of the hybrid samples are much improved due to the lower work function, better conductivity and more emission sites, depending on the size and density of the CsI nanoparticles. But the performance gradually decays after ca. 45 min stable emission due to the instability of CsI during field emission which has been neglected to date. The results suggest that further effort to prevent the loss of Cs species to improve the stability of CsI-decorated hybrid nanostructures is required for practical applications.

Patterned arrays of Si- or Mg-doped AlN nanocones were synthesized via chemical vapor deposition. The field emission properties of the AlN nanocones were enhanced with Si-doping but deteriorated with Mg-doping, which demonstrated the great potential of doping in tuning the properties of field emitters.