Xian-Zhu Fu

Facile Preparation of Monodisperse, Impurity-Free, and Antioxidation Copper Nanoparticles on a Large Scale for Application in Conductive Ink

Monodisperse copper nanoparticles with high purity and antioxidation properties are synthesized quickly (only 5 min) on a large scale (multigram amounts) by a modified polyol process using slightly soluble Cu(OH)2 as the precursor, L-ascorbic acid as the reductant, and PEG-2000 as the protectant. The resulting copper nanoparticles have a size distribution of 135 ± 30 nm and do not suffer significant oxidation even after being stored for 30 days under ambient conditions. The copper nanoparticles can be well-dispersed in an oil-based ink, which can be silk-screen printed onto flexible substrates and then converted into conductive patterns after heat treatment. An optimal electrical resistivity of 15.8 μΩ cm is achieved, which is only 10 times larger than that of bulk copper. The synthesized copper nanoparticles could be considered as a cheap and effective material for printed electronics.

Comparative study of LiMnPO4 cathode materials synthesized by solvothermal methods using different manganese salts

The effects of anions on the particle size, phase impurity, crystal structural, and crystal growth orientation of olivine LiMnPO4 prepared via the solvothermal synthesis method are systematically studied. LiMnPO4 cannot be obtained for the precursor containing NO3− anions due to its strong oxidizing ability in acid environment. The SO42− anion may facilitate the growth of high-index planes of the LiMnPO4 crystals owing to its higher charge number. The Ac− anion with larger volume may have a significant atomic-scale template effect, thus the particle size of LiMnPO4 is greatly limited and the crystal growth is inclined to the equilibrium state. The LiMnPO4 samples, prepared from MnSO4, MnCl2 and Mn(Ac)2, deliver an initial capacity of 145, 129 and 81 mAh g−1, respectively. Among them, the sample synthesized from MnCl2 can maintain 91% of its initial capacity after 200 cycles at 2 C, due to its high purity and crystal orientation growth with ac planes.

Electro-deposition of CoNi2S4 flower-like nanosheets on 3D hierarchically porous nickel skeletons with high electrochemical capacitive performance

Ternary cobalt nickel sulfide (CoNi2S4) flower-like nanosheets are directly grown on three dimensional (3D) hierarchically porous nickel skeletons by one-step electro-deposition. The resultant 3D porous Ni/CoNi2S4 composites could serve as binder-free integrated electrodes for supercapacitors, which exhibit higher capacitance than those of 3D porous Ni/Co9S8, 3D porous Ni/Ni3S2, Ni foam/CoNi2S4 and smooth Ni/CoNi2S4 electrodes. Furthermore, the 3D porous Ni/CoNi2S4 electrodes demonstrate better electrochemical reversibility and excellent rate capability. The super electrochemical capacitive behavior might be attributed to the highly interconnected conductive networks of 3D hierarchically porous Ni scaffold supported CoNi2S4 flower-like nanosheets with a large specific area and highly active sites.

Urchin-like Pd@CuO–Pd yolk–shell nanostructures: synthesis, characterization and electrocatalysis

Novel urchin-like Pd@CuO–Pd yolk–shell nanostructures are synthesized through subsequent oxidation of Pd@Cu2O truncated octahedron core–shell precursors with a PdCl42− aqueous solution. The permeable hierarchical CuO shells are constructed by a radially standing 1D single-crystalline nanothorn with Pd nanoparticles. The Pd nanocube cores are encapsulated and confined in the void space of the urchin-like shells. The urchin-like yolk–shell Pd@CuO–Pd nanostructures demonstrate excellent electrocatalytic activity and selectivity for glucose oxidation. Enzyme-free glucose biosensors based on the urchin-like yolk–shell Pd@CuO–Pd electrocatalysts display a higher sensitivity (665.9 μA cm−2 mM−1) than those of the CuO nanoparticles (455.8 μA cm−2 mM−1), Cu2O nanoparticles (220.4 μA cm−2 mM−1), Pd@Cu2O truncated octahedra (179.1 μA cm−2 mM−1), Pd mixtures (65.5 μA cm−2 mM−1) and Pd nanocubes (1.42 μA cm−2 mM−1). The outstanding electrocatalytic performance of the urchin-like Pd@CuO–Pd yolk–shell nanostructures might be ascribed to two reasons: the unique hierarchical yolk–shell structures provide highly exposed active sites and act as an individualized nanoreactor to enhance the mass diffusion and transport of reactants at the electrode/electrolyte interface. Moreover, the nanocomposite of metal oxide semiconductor CuO and noble metal Pd would result in a synergetic effect to improve the electrocatalysis.

Electrochemical fabrication of Ni(OH)2/Ni 3D porous composite films as integrated capacitive electrodes

Ni(OH)2 coated on Ni porous films are facilely fabricated by anode oxidation of 3D hierarchical porous Ni films which are prepared through a hydrogen bubble template electro-deposition method. The highly porous nickel films function as effective 3D conductive network current collectors and scaffolds to in situ form a thin layer of Ni(OH)2 active material. The electrochemical capacitive performances are investigated by cyclic voltammetry (CV) and the galvanostatic charge–discharge technique in 6 M KOH electrolyte. The 3D porous Ni(OH)2/Ni integrated electrodes demonstrate a much higher specific capacity of 828 mF cm−2 than 126 mF cm−2 for the smooth Ni(OH)2/Ni electrode at a current density of 10 mA cm−2. The 3D porous Ni(OH)2/Ni integrated electrodes also display a good capacity retention of 95% after 1000 cycles. The superior capacitive properties of 3D porous Ni(OH)2/Ni electrodes might result from the thin layer Ni(OH)2 active materials in situ formed on the highly 3D porous Ni metallic current collector with large surface area, low contact resistance between Ni(OH)2 active material and Ni current collector, and fast electron/ion conduction.

Enhanced Reduction of Graphene Oxide on Recyclable Cu Foils to Fabricate Graphene Films with Superior Thermal Conductivity

Large-area freestanding graphene films are facilely fabricated by reducing graphene oxide films on recyclable Cu foils in H2-containing atmosphere at high temperature. Cu might act as efficient catalysts for considerably improved reduction of graphene oxide according to the SEM, EDS, XRD, XPS, Raman and TGA results. Comparing to the graphene films with ~30 μm thickness reduced without Cu substrate at 900 °C, the thermal conductivity and electrical conductivity of graphene films reduced on Cu foils are enhanced about 140% to 902 Wm−1K−1 and 3.6 × 104 S/m, respectively. Moreover, the graphene films demonstrate superior thermal conductivity of ~1219 Wm−1K−1 as decreasing the thickness of films to ~10 μm. The graphene films also exhibit excellent mechanical properties and flexibility.

One-Step Preparation of Silver Hexagonal Microsheets as Electrically Conductive Adhesive Fillers for Printed Electronics

A facile one-step solution-phase chemical reduction method has been developed to synthesize Ag microsheets at room temperature. The morphology of Ag sheets is a regular hexagon more than 1 μm in size and about 200 nm in thickness. The hexagonal Ag microsheets possess a smoother and straighter surface compared with that of the commercial Ag micrometer-sized flakes prepared by ball milling for electrically conductive adhesives (ECAs). The function of the reagents and the formation mechanism of Ag hexagonal microsheets are also investigated. For the polyvinylpyrrolidone (PVP) and citrate facet-selective capping, the Ag atoms freshly reduced by N2H4 would orientationally grow alone on the {111} facet of Ag seeds, with the synergistically selective etching of irregular and small Ag particles by H2O2, to form Ag hexagonal microsheets. The hexagonal Ag microsheet-filled epoxy adhesives, as electrically conductive materials, can be easily printed on various substrates such as polyethylene terephthalate (PET), epoxy, glass, and flexible papers. The hexagonal Ag microsheet filled ECAs demonstrate lower bulk resistivity (approximately 8 × 10(-5) Ω cm) than that of the traditional Ag micrometer-sized-flake-filled ECAs with the same Ag content of 80 wt % (approximately 1.2 × 10(-4) Ω cm).

Facile fabrication of reduced graphene oxide encapsulated copper spherical particles with 3D architecture and high oxidation resistance

Reduced graphene oxide nano-sheets encapsulated copper spherical particles (Cu@rGO) were obtained through a simple electrostatic self-assembly process followed by chemical reduction. The oxidation resistance of Cu spherical particles was considerably enhanced by the coating of rGO nano-sheets. XRD results show that the core–shell structured Cu@rGO did not exhibit any sign of oxidation in air after storage at room temperature for 70 days or after heat treatment at 130 °C for 1.5 h. Furthermore, the rGO wrapped on the surface of Cu particles could transfer the two-dimensional rGO nano-sheets into three-dimensional (3D) networks. The Cu@rGO particles with 3D structure might have promising potential applications in thermal management, electrically conductive interconnection, electrodes, etc.

Facile synthesis of flexible graphene–silver composite papers with promising electrical and thermal conductivity performances

Free-standing and flexible graphene–silver (GE–Ag) composite paper has been successfully fabricated through an evaporation of graphene oxide–AgNO3 aqueous aerosol followed by a chemical reduction. The size, thickness and shape of the GE–Ag paper can be tuned according to the Teflon substrate used. The GE–Ag paper presents the advantages of good flexibility, high electrical conductivity (159 Ω per sq) and good thermal conductivity in the vertical direction (3.3 W mK−1), which are more optimal than the pure GE paper.

Core–shell Cu@rGO hybrids filled in epoxy composites with high thermal conduction

Due to the increased power density of electronic devices, the heat originated from the core components increases the working temperature of the devices, enormously degrading their reliability and shortening their lifespan. So, effective heat dissipation from high-power electronic devices has become an urgent and complex problem. Herein, we report epoxy-based composites with an enhanced thermal conductivity by using reduced graphene oxide encapsulated copper sphere (Cu@rGO) hybrids as fillers. The Cu@rGO hybrid exhibits a 3D structure with high oxidation resistance. The obtained polymer composites exhibit a high thermal conductivity (7 W m−1 K−1), as the loading of the Cu@rGO hybrids is 80 wt%, which is 2.6 times higher than that of the polymer composites filled with only Cu spheres. The high thermal conductivity might be attributed to the synergistic effects between spherical Cu and rGO nano-sheets, which enhanced the oxidation resistance of copper and increased the thermal transfer path, along with the reduced interfacial thermal resistance between Cu and epoxy resins. In addition, the Cu@rGO/epoxy composites reveal a decreased thermal expansion coefficient (CTE), an increased glass transition temperature (Tg), and an enhanced shear strength. This unique 3D core–shell Cu@rGO structure and its epoxy composites with high thermal conductivity and dimensional stability could be suitable as excellent thermal interface materials in advanced electronic packaging techniques.