Delving into the dissimilarities in electrochemical performance and underlying mechanisms for sodium and potassium ion storage in N-doped carbon-encapsulated metallic Cu_(2)Se nanocubes

The large volumetric variations experienced by metal selenides within conversion reaction result in inferior rate capability and cycling stability,ultimately hindering the achievement of superior electrochemical performance.Herein,metallic Cu_(2)Se encapsulated with N-doped carbon(Cu_(2)Se@NC)was prepared using Cu_(2)O nanocubes as templates through a combination of dopamine polymerization and hightemperature selenization.The unique nanocubic structure and uniform N-doped carbon coating could shorten the ion transport distance,accelerate electron/charge diffusion,and suppress volume variation,ultimately ensuring Cu_(2)Se@NC with excellent electrochemical performance in sodium ion batteries(SIBs)and potassium ion batteries(PIBs).The composite exhibited excellent rate performance(187.7 mA h g^(-1)at 50 A g^(-1)in SIBs and 179.4 mA h g^(-1)at 5 A g^(-1)in PIBs)and cyclic stability(246,8 mA h g^(-1)at 10 A g^(-1)in SIBs over 2500 cycles).The reaction mechanism of intercalation combined with conversion in both SIBs and PIBs was disclosed by in situ X-ray diffraction(XRD)and ex situ transmission electron microscope(TEM).In particular,the final products in PIBs of K_(2)Se and K_(2)Se_(3)species were determined after discharging,which is different from that in SIBs with the final species of Na_(2)Se.The density functional theory calculation showed that carbon induces strong coupling and charge interactions with Cu_(2)Se,leading to the introduction of built-in electric field on heterojunction to improve electron mobility.Significantly,the theoretical calculations discovered that the underlying cause for the relatively superior rate capability in SIBs to that in PIBs is the agile Na~+diffusion with low energy barrier and moderate adsorption energy.These findings offer theoretical support for in-depth understanding of the performance differences of Cu-based materials in different ion storage systems.

Hydrogen generation from ammonia electrolysis on bifunctional platinum nanocubes electrocatalysts

The ammonia electrolysis is a highly efficient and energy-saving method for ultra-pure hydrogen generation, which highly relies on electrocatalytic performance of electrocatalysts. In this work, high-quality platinum(Pt) nanocubes(Pt-NCs) with 4.5 nm size are achieved by facile hydrothermal synthesis. The physical morphology and structure of Pt-NCs are exhaustively characterized, revealing that Pt-NCs with special {100} facets have excellent uniformity, good dispersity and high crystallinity. Meanwhile, the electrocatalytic performance of Pt-NCs for ammonia electrolysis are carefully investigated in alkaline solutions, which display outstanding electroactivity and stability for both ammonia electrooxidation reaction(AEOR) and hydrogen evolution reaction(HER) in KOH solution. Furthermore, a symmetric Pt-NCs||Pt-NCs ammonia electrolyzer based on bifunctional Pt-NCs electrocatalyst is constructed, which only requires 0.68 V electrolysis voltage for hydrogen generation. Additionally, the symmetric Pt-NCs||Pt-NCs ammonia electrolyzer has excellent reversible switch capability for AEOR at anode and HER at cathode, showing outstanding alternating operation ability for ammonia electrolysis.

Enhanced photoluminescence of CdSe quantum dots by the coupling of Ag nanocube and Ag film

The coupling of local surface plasmon （LSP） of nanoparticle and surface plasmon （SP） mode produced by metal film can lead to the enhanced electromagnetic field, which has an important application in enhancing the fluorescence of quantum dots （QDs）. Herein, the Ag nanocube and Ag film are used to enhance the fluorescence of CdSe QDs. The enhancement is found to relate to the sizes of the Ag nanocube and the thickness of the Ag film. Moreover, we also present the fluorescence enhancement caused by only SP. The result shows that the coupling between metal nanoparticles and metal film can realize larger field enhancement. Numerical simulation verifies that a nanocube can localize a strong electric field around its comer. All the results indicate that the fluorescence of QDs can be efficiently improved by optimizing the parameters of Ag film and Ag cubes.

Optical binding forces between plasmonic nanocubes： A numerical study based on discrete-dipole approximation

Plasmonic nanocubes are ideal candidates in realizing controllable reflectance surfaces, unidirectional nanoantennas and other plasmon-associated applications. In this work, we perform full-wave calculations of the optical forces in threedimensional gold nanocube dimers. For a fixed center-to-center separation, the rotation of the plasmonic nanocube leads to a slight shift of the plasmonic resonance wavelength and a strong change in the optical binding forces. The effective gap and the near field distribution between the two nanocubes are shown to be crucial to this force variation. We further find that the optical binding force is dominated by the scattering process while the optical forces in the wavevector direction are affected by both scattering and absorption, making the former relatively more sensitive to the rotation of(an effective gap between) the nanocubes. Our results would be useful for building all-optically controllable meta-surfaces.

Cuprous Chloride Nanocubes Grown on Copper Foil for Pseudocapacitor Electrodes

In this paper, for the first time, we report the synthesis of nanoscale cuprous chloride(Cu Cl) cubic structure by a facile hydrothermal route. A possible mechanism for the growth of those nanostructures is proposed based on the experimental results. It is discovered that the existence of HCl could affect the surface of Cu Cl nanocubes. This unique cube-like nanostructure with rough surface significantly enhances the electroactive surface areas of Cu Cl, leading to a high special capacitance of 376 m F cm-2at the current density of 1.0 m A cm-2. There is still a good reversibility with cycling efficiency of 88.8 % after 2,000 cycles, demonstrating its excellent long-term cycling stability and might be the promising candidates as the excellent electrode material.

Facile Synthesis of Porous Zn–Sn–O Nanocubes and Their Electrochemical Performances

Porous Zn–Sn–O nanocubes with a uniform size were synthesized through a facile aqueous solution route combined with subsequent thermal treatment. The chemical composition, morphology, and microstructure of Zn–Sn–O nanocubes, which have significant effects on the lithium storage performances, were easily tuned by adjusting the calcination temperature in preparation processes of ZnSn(OH)6solid nanocubes. Further studies revealed that porous Zn–Sn–O nanocubes prepared at 600 °C exhibited a good rate capability and a high reversible capacity of 700 m Ah g^(-1)at a current density of 200 m Ag^(-1)after 50 cycles, which may be a great potential as anode materials in Lithium-ion batteries.

Controllable Synthesis of Ag Nanocubes via a Polyol Method

The controllable synthesis of uniform silver nanocubes with high purity is pivotal for the fundamental study of self-assembly and further research on the hollow nanostructures,gold nanocages for instance.Here,Ag nanocubes of different sizes were synthesized by an improved polyol method.With addition of HCl solution,Ag nanocubes with size about 100 nm were obtained under an air atmosphere.And Ag nanocubes with size around50 nm can be produced in a short time under Argon atmosphere with the presence of NaHS instead of HCl.Meanwhile,uniform Ag nanocubes with size larger than 100 nm were also synthesized successfully via adjusting experiment parameters.Results of transmission electron microscopy(TEM)combined with selected area electron diffraction(SAED)show that the Ag nanocubes are single crystalline with six(200)surface plane.In the UV-Vis-NIR optical absorption spectrum,the diple moment resonance absorption peak is changed in the range of 420—500nm with the increase of Ag nanocubes size.

Core-shell-structured Co@Co4N nanoparticles encapsulated into MnO-modified porous N-doping carbon nanocubes as bifunctional catalysts for rechargeable Zn–air batteries

Designing the highly catalytic activity and durable bifunctional catalysts toward oxygen reduction/evolution reaction(ORR/OER) is paramount for metal–air batteries. Metal–organic frameworks(MOFs)-based materials have attracted a great deal of attention as the potential candidate for effectively catalyzing ORR/OER due to their adjustable composition and porous structure. Herein, we first introduce the Mn species into zeolitic-imidazole frameworks(ZIFs) and then further pyrolyze the Mn-containing bimetallic ZIFs to synthesize core-shell-structured Co@Co4N nanoparticles embedded into MnO-modified porous N-doped carbon nanocubes(Co@Co4N/MnO–NC). Co@Co4N/MnO–NC exhibits the outstanding catalytic activity toward ORR and OER which is attributed to its abundant pyridinic/graphitic N and Co4N,the optimized content of MnO species, highly dispersed catalytic sites and porous carbon matrix. As a result, the Co@Co4N/MnO–NC-based Zn–air battery exhibits enhanced performances, including the high discharge capacity(762 mA h gZn-1), large power density(200.5 mW cm-2), stable potential profile over 72 h, low overpotential(<1.0 V) and superior cycling life(2800 cycles). Moreover, the belt-shaped Co@Co4N/MnO–NC cathode-based Zn–air batteries are also designed which exhibit the superb electrochemical properties at different bending/twisting conditions.

Formation and Growth of Silver Nanocubes upon Nanosecond Pulsed Laser Irradiation: Effects of Laser Intensity and Irradiation Time

Silver nanoparticles (AgNPs) were fabricated by repetitive irradiation of near ultraviolet (UV) nanosecond laser pulses (355 nm, 5 ns) in an aqueous solution of silver nitrate in the absence of stabilizing agents. A broad absorption peak was observed in the visible region showing the formation of a variety of AgNPs in the solution. Among the variety of products, it was found that silver nanocubes (AgNCs) grew in size with longer laser irradiation time. The size of AgNCs also increased with higher laser intensity. The average size of AgNCs, investigated by a scanning electron microscope (SEM) was in the range of 75 - 200 nm. The number of reduced atoms in AgNCs as a function of laser intensity showed that the AgNCs are apparently produced by a four photon process, implying that the formation of dimer silver atoms is essential for the formation.

A Solvothermal Route to Cu_2O Nanocubes and Cu Nanoparticles

Cu2O nanocubes and Cu nanoparticles were prepared by reducing Cu（ Ⅱ ） salt with ethanol as the reducing agent and solvent in the presence of multidentate ligand poly（vinylpyrrolidone） （PVP） under different conditions. The morphologies and the crystalline structures of the products were characterized by using scanning electron microscopy （SEM）, transmission electron microscopy（TEM）, selected-area electron diffraction（ SAED）, and powder X-ray diffraction（XRD）. In particular, the influences of the solvothennal reaction temperature and alkalinity on the products were investigated. A lower temperature and a lower alkali concentration favor the formation of the Cu2O phase, whereas a higher temperature and a higher alkali concentration generally lead to the formation of the Cu phase.

Synthesis of monodisperse palladium nanocubes and their catalytic activity for methanol electrooxidation

The single crystalline palladium nanocubes with an average size of 7 nm were prepared in the presence of poly （vinyl pyrrolidone） （PVP） and KBr using the polyol method. The as-prepared Pd nanocubes were highly uniform in both size and shape. The ordered packing structures including monolayer and multilayer can be fabricated via the rate-controlled evaporation of solution solvent. The electrochemical catalytic activity of these Pd nanocubes towards methanol oxidation was found to be higher than that of spherical Pd nanoparticles of similar size.

Enhanced detection of ppb-level NO_(2)by uniform Pt-doped ZnSnO_(3)nanocubes

ZnSnO_(3) nanocubes(ZSNCs)with various Pt concentrations(i.e.,1 at%,2 at%,and 5 at%)were synthesized by a simple one-pot hydrothermal method.The microstructures of pure and Pt-doped ZSNCs were characterized by X-ray diffractometry,scanning electron microscopy,transmission electron microscopy,energy-dispersive X-ray spectroscopy,and X-ray photoelectron spectroscopy.Results showed that the pure ZSNCs have a perovskite structure with a side length of approximately 600 nm;this length was reduced to 400 nm after Pt doping.Following doping,PtO_(x)(PtO and PtO_(2)) nanoparticles with a diameter of approximately 5 nm were uniformly coated on the surface of the ZSNCs.Systematic investigation of the gas-sensing abilities of the nanocubes showed that the Pt-doped ZSNCs have excellent sensing properties toward nitrogen dioxide(NO_(2)) gas in the operating temperature range of 75-175℃.Among the sensors prepared,that based on 1 at%Pt-doped ZSNCs exhibited the best response of 16.0 toward 500 ppb NO_(2) at 125℃;this response is over 11 times higher compared with that of pure ZSNCs.The enhanced NO_(2) sensing mechanism of the Pt-doped ZSNCs may be attributed to the synergistic effects of catalytic activity and chemical sensitization by Pt doping.

Fabrication and Investigation on Double-Hollow Shell CoFe Oxide@TiO_(2) Nanocube with Superior Electromagnetic Properties

Electromagnetic wave absorbing materials are urgently required in the fields of medicine,communication,and military.However,the thickness,weight,narrow effective bandwidth,and weak absorbing ability of the materials restrict their further application.In this work,a double-layer hollow nanocube with a dielectric titanium dioxide(TiO_(2))shell and a magnetic CoFe oxide inner shell is prepared.Prussian blue(PB)is prepared by the hydrothermal method,and used as the template to prepare PB@CoFe PB analogue(PBA).After selective etching and further calcination,hollow CoFe oxide particles are obtained.The obtained particles are then coated with SiO_(2)and TiO_(2),respectively,and the intermediate layer is dislodged to obtain the final CoFe oxide@TiO_(2)with the hollow double shell structure.The obtained double-layer hollow structure can effectively capture the incident electromagnetic waves,and increase the propagation path.Moreover,the obvious enhancement of interface polarization and the improvement of impedance matching enhance the wave absorbing ability of the material.The analysis results show that,the structure is stable and the dispersion is good.The maximum reflection loss(RL)at 10 GHz is as high as-46.1 dB with the sample thickness of 1.6 mm.The light-weight and high-efficiency CoFe oxide@TiO_(2)absorber is promised to be used in commercial and military aerospace fields.

MnS–MnO heterogeneous nanocube@N,S-doped carbon as a highly efficient bifunctional water splitting electrocatalyst

A stable,efficient,and economical bifunctional electrolytic catalyst would be incredibly beneficial for the development of hydrogen production by electrocatalytic water splitting.In this study,we synthesized a novel MnS–MnO heterogeneous nanocube@N,S-doped carbon(MnS–MnO@NSC).MnS–MnO nanocubes possess rich heterogeneous interfaces and plentiful catalytic active sites to promote electrochemical reactions,while the N,S-doped carbon shell possesses excellent conductivity and catalytic properties and protects the nanocubes.MnS–MnO@NSC exhibited excellent electrochemical properties as an effective bifunctional electrocatalyst for the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)in KOH solution.In the HER,the overpotential was as low as 124 mV at a current density of 10 mA·cm^(-2)while in the OER,it was only 340 mV at 100 mA·cm^(-2)under the same conditions.In addition,a MnS–MnO@NSC||MnS–MnO@NSC electrolyzer exhibited almost comparable activity and higher steadiness than those exhibited by the state-of-the-art Pt/C||RuO_(2)/C system for full water splitting in KOH solution.

B and Fe co-doped Co_(2)P hollow nanocubes for nitrate electroreduction to ammonia

Nitrate(NO_(3)^(−))electroreduction reaction(NO_(3)^(−)RR)provides an attractive and sustainable route for NO_(3)^(−)pollution mitigation or energy-saved ammonia(NH3)synthesis.In this work,high-quality B and Fe co-doped Co_(2) P hollow nanocubes(B/Fe-Co_(2) P HNCs)are successfully synthesized though simultaneous boronation-phosphorization treatment,which reveal outstanding selectivity,activity,stability for the NO_(3)^(−)to NH_(3) conversion in neutral electrolyte because of big surface area,fast mass transport,superhydrophilic surface,and optimized electronic structure.B/Fe-Co_(2) P HNCs can achieve the high NH3 yield rate(22.67 mg h^(−1) mg_(cat)^(−1))as well as Faradaic efficiency(97.54%)for NO_(3)^(−)RR,greatly outperforming most of non-precious metal based NO_(3)^(−)RR electrocatalysts.

In situ construction of surface defects of carbon-doped ternary cobalt-nickel-iron phosphide nanocubes for efficient overall water splitting

The ternary cobalt-nickel-iron phosphide nanocubes (P-Co0.9Ni0.9Fe1.2 NCs) with high intrinsic activity, conductivity, defect concentration and optimized ratio have been realized through a facile phosphorization treatment using ternary cobalt-nickel-iron nanocubes of Prussian blue analogs (PBA) as a precursor. The scanning electron microscopy and transmission electron microscopy results show that the P-Co0.9Ni0.9Fe1.2 NCs maintain a cubic structure with a rough surface, implying the rich surface defects as exposed active sites. The thermal phosphorization of the ternary PBA precursor not only provids carbon doping but also leads to the in situ construction of surface defects on the NCs. The carbon doping from the PBA precursor lowers the charge transfer resistance and optimizes the electronic transformation. The synergistic effect among the ternary metal ions and rich defects contributes to the enhanced electrocatalytic performance . The P-Co0.9Ni0.9Fe1.2NCs achieve low overpotentials of -200.7 and 273.1 mV at a current density of 10 mA cm^-2 for the hydrogen evolution reaction and the oxygen evolution reaction, respectively. The potential of overall water splitting reaches 1.52 V at a current density of 10 mA cm^-2. The longterm stability of the electrocatalysts was also evaluated. This work provides a facile method to design efficient transitionmetal- based bifunctional electrocatalysts for overall water splitting.

Mesoporous Mn-Sn bimetallic oxide nanocubes as long cycle life anodes for Li-ion half/full cells and sulfur hosts for Li-S batteries

Mesoporous Mn-Sn bimetallic oxide （BO） nanocubes with sizes of 15-30 run show outstanding stable and reversible capacities in lithium ion batteries CLIBs）, reaching 856.8 mAh.g-1 after 400 cycles at 500 mA·g^-1 and 506 mAh·g^-1 after 850 cycles at 1,000 mA·g^-1. The prelimLnary investigation of the reaction mechanism, based on X-ray diffraction measurements, indicates the occurrence of both conversion and alloying-dealloying reactions in the Mn-Sn bimetallic oxide electrode. Moreover, Mn-Sn BO//LiCoO2 Li-ion full cells were successfully assembled for the first time, and found to deliver a relatively high energy density of 176.25 Wh·kg^-1 at 16.35 W·kg^-1 （based on the total weight of anode and cathode materials）. The superior long-term stability of these materials might be attributed to their nanoscale size and unique mesoporous nanocubic structure, which provide short Li^＋ diffusion pathways and a high contact area between electrolyte and active material. In addition, the Mn-Sn BOs could be used as advanced sulfur hosts for lithium-sulfur batteries, owing to their adequate mesoporous structure and relatively strong chemisorption of lithium polysulfide. The present results thus highlight the promising potential of mesoporous Mn-Sn bimetallic oxides for application in Li-ion and Li-S batteries.

Origin of strong and narrow localized surface plasmon resonance of copper nanocubes

Inexpe nsive copper nano particles are generally thought to possess weak and broad localized surface plasm on resonance(LSPR).The,present experimental and theoretical studies show that tailoring the Cu nanoparticle to a cubic shape results in a single intense,narrow,and asymmetric LSPR line shape,which is even superior to round-shaped gold nanoparticles.In this study,the dielectric function of copper is decomposed into an interband transition component and a free-electron component.This allows interband transition-induced plasmon damping to be visualized both spectrally and by surface polarization charges.The results reveal that the LSPR of Cu nanocubes originates from the comer mode as it is spectrally separated from the interb and transitions.In additi on,the interband tran sitions lead to severe damping of the local electromagnetic field but the cubic corner LSPR mode survives.Cu nanocubes display an extinction coefficient comparable to the dipole mode of a gold nanosphere with the same volume and show a larger local electromagnetic field enhancement These results will guider-development of in expensive plasmonic copper-based nano materials.

Mesoporous Ag nanocubes synthesized via selectively oxidative etching at room temperature for surface- enhanced Raman spectroscopy

Silver nanocubes enriched with {100} facets have been extensively used for surface-enhanced Raman scattering. Herein, we report a new water-phase synthesis method for weU-defined Ag nanocubes with tunable sizes via a two-step procedure at room temperature. First, irregularly shaped Ag nanoparticles （INPs） were prepared by reducing silver ammonia solution using ethylal. Second, the agglomerated INPs were selectively etched with HNO3 and C1- to yield {100} facet-rich mesoporous Ag nanocubes. The mechanism of Ag-nanocube formation and growth was investigated in detail by elucidating the involved chemical reactions and physical changes at each step during the synthesis. The addition of C1- anions was responsible for facilitating Ag nanoparticle growth by removing surface-adsorbed Ag＋ species, thereby eliminating inter-particle repulsive forces. This agglomeration was found crucial for the subsequent selective oxidation of Ag nanoparticles because the protective agent used, polyvinylpyrrolidone （PVP）, was the most effective one for adsorption on the surfaces of Ag nanoparticles of size greater than approximately 50 nm. Importantly mesopores were found inside the Ag nanocubes; this can be attributed to the unavoidable imperfect packing during the agglomeration of INPs. The newly prepared Ag nanocubes were further used to enhance the Raman signal of rhodamine 6G, which is capable of reducing the detection limitation to 10-16 mol·L-1.

Metal-organic framework-derived CoSn/NC nanocubes as absorbers for electromagnetic wave attenuation

Metal-organic framework-derived composites have been widely used in electromagnetic wave(EMW)absorption,but the traditional synthetic strategy greatly limits the structure and species of MOFs.This research provided a solvent-free method to synthesize Co-MOF and its derivatives.Using CoSnO_(3)as the precursor,the preparation of Co-MOF is achieved by bridging the cobalt(II)ion of CoSnO_(3)and the 2-methylimidazole skeleton.The CoSn/N-doped carbon(CoSn/NC)composites derived from CoSnO_(3)-MOF(Co-MOF with CoSnO_(3)as Co source)retain the original morphology of CoSnO_(3).Besides,the polarization effect produced by the N-doped carbon layers also benefits the excellent EMW absorption performance of the CoSn/NC composites.It is reflected in the minimum reflection loss(RL)of-48.2 dB at 2.2 mm and the effective bandwidth(EBA)of 5.84 GHz.This work provides a new channel to the construction of Co-MOFs,which could be extended to other Co-based oxides and vastly expand the species of MOFs based on metallic Co.