Xuefan Jiang

Preparation of Fe3O4 with high specific surface area and improved capacitance as a supercapacitor

Here, we report for the first time a facile ultrasonic synthesis of Fe3O4 nanoparticles using FeCl3 and the organic solvent ethanolamine (ETA). The intermediate of the ETA-Fe(II) complex produces Fe3O4 after hydrolysis and hydrothermal treatment. The moderate reduction of ETA and ultrasound play an important role in the synthesis of superfine Fe3O4 particles with a very high specific surface area (165.05 m(2) g(-1)). The Fe3O4 nanoparticles were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), high-resolution transmission electron microscopy (HRTEM), and ultraviolet-visible absorption spectroscopy (UV-vis). Fe3O4 as an electrode material was fabricated into a supercapacitor and characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge measurements. The as-synthesized Fe3O4 exhibits remarkable pseudocapacitive activities including high specific capacitance (207.7 F g(-1) at 0.4 A g(-1)), good rate capability (90.4 F g(-1) at 10 A g(-1)), and excellent cycling stability (retention 100% after 2000 cycles). This novel synthetic route towards Fe3O4 is a convenient and potential way of producing a secondary energy material which is expected to be applicable in the synthesis of other metal oxide nanoparticles.

Composite structure and properties of Mn3O4/graphene oxide and Mn3O4/graphene

Colloidal Mn3O4 nanocrystals supported by graphene oxide (GO) and reduced graphene oxide (RGO) (Mn3O4/GO and Mn3O4/RGO nanocomposites) have been fabricated through a facile synthetic route with ultrasonic-assisted in ethanol amine (ETA)-water system. It is proposed that in the formation mechanism of these intriguing nanocomposites, investigated by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), ultraviolet-visible absorption spectroscopy (UV-vis), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, the manganese ions are anchored on GO nanosheets (GOs) or enwrapped in curved RGO nanosheets (RGOs), followed by the nucleation and growth of Mn3O4 nanoparticles in ethanol ETA-water system via hydrolysis and oxidation, which in turn results in the exfoliation of GOs or RGOs. Based on the surface properties of GO and RGO, this work firstly explains how the synergetic compositing structure of Mn3O4/GO and Mn3O4/RGO nanocomposites plays a very important role in their properties for electrochemical capacitors (ECs) or lithium ion batteries (LIBs). The opinions we put forward may be readily extended to a strong basis for other classes of hybrids based on GOs or RGOs to make a wise choice between the ECs and LIBs applications.

Bicontinuous Structure of Li3V2(PO4)3 Clustered via Carbon Nanofiber as High-Performance Cathode Material of Li-Ion Batteries

In this work, the composite structure of Li3V2(PO4)3 (LVP) nanoparticles with carbon nanofibers (CNF) is designed. The size and location of LVP particles, and the degree of graphitization and diameter of carbon nanofibers, are optimized by electrospinning and heat treatment. The bicontinuous morphologies of LVP/CNF are dependent on the carbonization of PVP and simultaneous growing of LVP, with the fibers shrunk and the LVP crystals grown toward the outside. LVP nanocystals clustered via carbon nanofibers guarantee improving the diffusion ability of Li(+), and the carbon fiber simultaneously guarantees the effective electron conductivity. Compared with the simple carbon-coated LVP and pure LVP, the particle-clustered structure guarantees high rate capability and long-life cycling stability of NF-LVP as cathode for LIBs. At 20 C rate in the range 3.0-4.3 V, NF-LVP delivers the initial capacity of 122.6 mAh g(-1) close to the theoretical value of 133 mAh g(-1), and maintains 97% of the initial capacity at the 1000th cycle. The bead-like structure of cathode material clustered via carbon nanofibers via electrospinning will be further applied to high-performance LIBs.

In situ preparation of SnO2@polyaniline nanocomposites and their synergetic structure for high-performance supercapacitors

This method for the synthesis of SnO2@polyaniline starts from primary SnO crystals. SnO is produced through ultrasonication in the presence of ethanolamine (ETA), while polyaniline (PANI) is polymerized in situ. The tunable ratio of the inorganic component and the polymer substrate in the SnO2@PANI nanocomposite plays an important role in the morphology and electrochemical performance. The nanocomposites were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and Fourier transformation infrared spectroscopy (FT-IR). SnO2@PANI, as an electrode material, was fabricated into a supercapacitor and characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge measurements. A nanocomposite of SnO2@PANI (SP-2) with a high specific surface area (91.63 m2 g−1), exhibited remarkable pseudocapacitive activity, including a high specific capacitance (335.5 F g−1 at 0.1 A g−1), good rate capability (108.8 F g−1 at 40 A g−1) and excellent cycling stability (no capacitance loss after 10 000 cycles). The in situ oxidation and polymerization route of the synthesis of the SnO2@PANI nanocomposite is potentially a convenient way of producing secondary energy materials, which is expected to be applicable to the synthesis of other metal oxide@polymer nanocomposites.

Large-scale preparation of shape controlled SnO and improved capacitance for supercapacitors: from nanoclusters to square microplates

Here, we first provide a facile ultrasonic-assisted synthesis of SnO using SnCl2 and the organic solvent of ethanolamine (ETA). The moderate alkalinity of ETA and ultrasound play very important roles in the synthesis of SnO. After the hydrolysis of the intermediate of ETA-Sn(II), the as-synthesized SnO nanoclusters undergo assembly, amalgamation, and preferential growth to microplates in hydrothermal treatment. The as-synthesized SnO was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible absorption spectroscopy (UV-vis) and X-ray diffraction (XRD). To explore its potential applications in energy storage, SnO was fabricated into a supercapacitor electrode and characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge measurements. The as-synthesized SnO exhibits remarkable pseudocapacitive activity including high specific capacitance (208.9 F g(-1) at 0.1 A g(-1)), good rate capability (65.8 F g(-1) at 40 A g(-1)), and excellent cycling stability (retention 119.3% after 10,000 cycles) for application in supercapacitors. The capacitive behavior of SnO with various crystal morphologies was observed by fitted EIS using an equivalent circuit. The novel synthetic route for SnO is a convenient and potential way to large-scale production of microplates which is expected to be applicable in the synthesis of other metal oxide nanoparticles.

Facile Synthesis of Nanoporous Pt-Y alloy with Enhanced Electrocatalytic Activity and Durability

Recently, Pt-Y alloy has displayed an excellent electrocatalytic activity for oxygen reduction reaction (ORR), and is regarded as a promising cathode catalyst for fuel cells. However, the bulk production of nanoscaled Pt-Y alloy with outstanding catalytic performance remains a great challenge. Here, we address the challenge through a simple dealloying method to synthesize nanoporous Pt-Y alloy (NP-PtY) with a typical ligament size of ~5 nm. By combining the intrinsic superior electrocatalytic activity of Pt-Y alloy with the special nanoporous structure, the NP-PtY bimetallic catalyst presents higher activity for ORR and ethanol oxidation reaction, and better electrocatalytic stability than the commercial Pt/C catalyst and nanoporous Pt alloy. The as-made NP-PtY holds great application potential as a promising electrocatalyst in proton exchange membrane fuel cells due to the advantages of facile preparation and excellent catalytic performance.

Intermartensitic Transformation and Enhanced Exchange Bias in Pd (Pt) -doped Ni-Mn-Sn alloys

In this work, we studied the phase transitions and exchange bias of Ni50−xMn36Sn14Tx (T = Pd, Pt; x = 0, 1, 2, 3) alloys. An intermartensitic transition (IMT), not observed in Ni50Mn36Sn14 alloy, was induced by the proper application of negative chemical pressure by Pd(Pt) doping in Ni50−xMn36Sn14Tx (T = Pd, Pt) alloys. IMT weakened and was suppressed with the increase of applied field; it also disappeared with further increase of Pd(Pt) content (x = 3 for Pd and x = 2 for Pt). Another striking result is that exchange bias effect, ascribed to the percolating ferromagnetic domains coexisting with spin glass phase, is notably enhanced by nonmagnetic Pd(Pt) addition. The increase of unidirectional anisotropy by the addition of Pd(Pt) impurities with strong spin-orbit coupling was explained by Dzyaloshinsky-Moriya interactions in spin glass phase.

Extremely large magnetoresistance in the antiferromagnetic semimetal GdSb

Semimetals with extremely large magnetoresistance have attracted significant interest because of their possible nontrivial electronic structures, unusual transport properties, and also deep connections to high-energy physics. In this paper, we synthesize the GdSb single crystal and systematically characterize its crystal structure, magnetism, and electric transport properties. It is found that this compound crystallizes in the NaCl-type structure with a space group Fmm and experiences an antiferromagnetic phase transition at 23.4 K. Electric transport measurements reveal that this compound is metallic, in which spin disorders induced a resistivity anomaly emerging around its magnetic transition temperature. Intriguingly, obvious resistivity plateaus are observed at low temperatures, when the compound is subjected to the external magnetic field, showing an extremely large magnetoresistance effect up to 12 100% at 2 K and 9 T. Through the Hall resistivity measurement and first-principles band structure calculations, GdSb is believed to be a multi-band and compensated semimetal, in which the total carrier concentrations of electrons and holes are almost comparable. The electron–hole compensation and ultrahigh mobility of GdSb can contribute to the large magnetoresistance in this compound.

Modulated multiferroic properties of MnWO4 via chemical doping

Here we prepare polycrystalline Mn1−xNixWO4 ceramics with x = 0, 0.02, 0.04, 0.06 for investigating their magnetic, ferroelectric, and multiferroic properties. The Ni2+-substitution gradually expands the lattice and modifies the magnetic performance with increasing x, resulting in a strong modulation of electric properties of those samples. For Mn0.96Ni0.04WO4, ferroelectric polarization is observed in the whole temperature regime below TAF2, and is well modified by an external magnetic field, which is discussed under the framework of a spin-current model in this manuscript.

Evidence of s -wave superconductivity in the noncentrosymmetric La 7 Ir 3

Superconductivity in noncentrosymmetric compounds has attracted sustained interest in the last decades. Here we present a detailed study on the transport, thermodynamic properties and the band structure of the noncentrosymmetric superconductor La 7 Ir 3 (Tc ~ 2.3 K) that was recently proposed to break the time-reversal symmetry. It is found that La7Ir3 displays a moderately large electronic heat capacity (Sommerfeld coefficient γn ~ 53.1 mJ/mol K2) and a significantly enhanced Kadowaki-Woods ratio (KWR ~32 μΩ cm mol2 K2 J−2) that is greater than the typical value (~10 μΩ cm mol2 K2 J−2) for strongly correlated electron systems. The upper critical field Hc2 was seen to be nicely described by the single-band Werthamer-Helfand-Hohenberg model down to very low temperatures. The hydrostatic pressure effects on the superconductivity were also investigated. The heat capacity below Tc reveals a dominant s-wave gap with the magnitude close to the BCS value. The first-principles calculations yield the electron-phonon coupling constant λ = 0.81 and the logarithmically averaged frequency ωln = 78.5 K, resulting in a theoretical Tc = 2.5 K, close to the experimental value. Our calculations suggest that the enhanced electronic heat capacity is more likely due to electron-phonon coupling, rather than the electron-electron correlation effects. Collectively, these results place severe constraints on any theory of exotic superconductivity in this system.