Ultralight graphene–amorphous carbon (AC) hierarchical foam (G-ACHF) was synthesized by chemical vapor deposition at 1065 °C, close to the melting point of copper. The high temperature leads to the hierarchical structure with an inner layer of graphene and an outer layer of AC. The inner graphene layer with high conductivity and integrity provides high sensitivity. The outer AC layer helps to enhance its durability and mechanical resiliency. The hierarchical structure recovers without damaging the structural integrity after a large strain of 90%. The electrical resistance of G-ACHF remains stable after 200 cycles of compression to a strain level of 50%. The fluctuation of the resistance value remains within ±3%, showing its stability in sensing performance. The pressure sensitivity of G-ACHF reaches as high as ∼11.47 Pa–1. Finite element simulation reveals that the stress borne by the key position of G-ACHF is 47% lower than that of graphene foam without the AC layer, proving that the AC layer can disperse the stress effectively. With a very low density of 1.17 × 10–3 g cm–1, the reversibly compressible G-ACHF strain sensor material exhibits its promising application potential in lightweight and wearable devices.Keywords: graphene−amorphous carbon hierarchical foam; high-temperature chemical vapor deposition; reversibly compressible; strain sensor; ultralight;

A template-free graphene foam-supported Ni nanoparticle (GFN) composite was prepared by a hydrothermal method, followed by a calcination process. Phase, composition and morphology of the composites were characterized by XRD, Raman spectroscopy, FTIR, XPS, FESEM, and TEM. GFN exhibited a well-defined and interconnected three-dimensional (3D) network structure without template, and Ni nanoparticles were uniformly dispersed on the graphene nanosheets and attached via C–Ni covalent bonds. The microwave absorption (MA) properties of the samples were also investigated with a vector network analyzer. Based on the 3D structure of graphene foam, due to interfacial effects (graphene/Ni/wax) and the synergistic effect between graphene and Ni nanoparticles, GFN showed the most remarkable MA properties, compared with the graphene foam-supported NiO nanoparticles composite (GFNO), pure graphene foam (GF) and pure Ni nanoparticles. When the thickness of the GFN/wax sample was 3.4 mm and the content of GFN in the sample was only 1 wt%, the maximum reflection loss of GFN could reach −49 dB at 11.5 GHz. This high reflection loss was a result of the multiple reflections and attenuations of electromagnetic waves within the 3D structure of the graphene foam, the interfacial polarization and the better impedance matching characteristics of GFN. Hence, a template-free graphene foam-supported Ni nanoparticle composite with strong absorption and lightweight properties showed a promising future in microwave absorption applications.

•Platinum nanoparticles (PtNPs) loaded holey RGO framework (Pt/HGF) is synthesized.•Pt/HGF is used for freestanding counter electrodes of DSSC and methanol oxidation.•PCE of Pt/HGF-DSSC (5.55%) is better than Pt-DSSC (5.19%) and Pt/G-DSSC (5.12%).•Pt/HGF deliver better methanol oxidation catalytic activity and stability than Pt/G.Platinum nanoparticles (PtNPs)-loaded holey reduced graphene oxide framework (Pt/HGF) has been synthesized as freestanding counter electrodes (CEs) of dye sensitized solar cells (DSSCs) and methanol oxidation catalysts. PtNPs (∼2.5 nm) are uniformly incorporated into holey reduced graphene oxide framework by a solvothermal treatment. Pt/HGF possesses high specific surface area (340.65 m2 g−1). Its charge transfer resistance (RCT) at the I−/I3− electrolyte/CE interface reaches 1.61 Ω cm2, lower than that of pure Pt (2.99 Ω cm2) and PtNPs loaded non-hole reduced graphene oxide (Pt/G, 2.37 Ω cm2), and its RCT at the methanol electrolyte/electrode interface (0.75 Ω cm2) is much lower than that of Pt/G (3.14 Ω cm2), showing good electrocatalytic activity for I−/I3− redox reaction and methanol oxidation reaction (MOR). The assembled Pt/HGF-DSSC achieves a photoelectric conversion efficiency of 5.55% and a short-circuit current density (Jsc) of 12.27 mA cm−2, better than those of Pt-DSSC (5.19%, 10.50 mA cm−2) and Pt/G-DSSC (5.12%, 11.12 mA cm−2). In methanol oxidation test, Pt/HGF delivers better electrocatalytic activity and stability than Pt/G. Thus, high electrocatalytic activity and efficient electron/ion transport are achieved by Pt/HGF due to the synergistic effect of well dispersed PtNPs, hierarchical holey structure, and framework, and it may serve as an alternative of pure Pt for DSSC-CEs and MOR catalysts.Download high-res image (439KB)Download full-size image

The effects of cupric ions on the corrosion behavior of aluminum alloy 5A02 in ethylene glycol–water solutions were studied by potentiodynamic polarization, electrochemical noise (EN), and complementary techniques including scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). A positive corrosion potential and increased corrosion current were observed due to the deposition of copper. The results demonstrate that the main corrosion type was pitting and the increasing cupric ion concentration augmented the pitting density. The pits became larger and deeper as a result of the embedment of copper into the surface of the alloy. Cupric ions were preferentially deposited at the defects around the secondary phase, leading to the formation of Al–Cu microgalvanic couples, which increased the corrosion rate. The corrosion rate gradually reached a stable value as the concentration of cupric ions was increased beyond 10 mmol/L.

Super helical Au/TiO2 nanocomposites were synthesized using plasmid DNA and incorporated into photoanode of dye-sensitized solar cells (DSSCs). The performance of photoanode films and DSSCs was investigated. Plasmid DNA can not only support as bio scaffold to synthesize Au/TiO2 nanocomposites, but also act as an effective reducing agent under ultraviolet (UV) irradiation. Compared with TiO2-only DSSCs, the light harvesting (LH), corresponding photocurrent and power conversion efficiency (PCE) of DSSCs were enhanced by incorporating of mechanically mixed Au-TiO2 NPs and Au/TiO2 nanocomposites. Compared to the TiO2-only DSSCs samples (5.12%), the PCE of DSSCs with mechanically mixed Au-TiO2 nanoparticles (NPs) (6.41%) increased by 25.20%, and DSSCs with Au/TiO2 nanocomposites (8.17%) increased by 59.57%. The best PCE (8.24%) of DSSCs was obtained with the incorporation of Au/TiO2 nanocomposites. Two reasons were presented for the best performance of DSSCs with Au/TiO2 nanocomposites. Firstly, the localized surface plasmon resonance (LSPR) effect of Au NPs enhanced the absorption visible light. Secondly, the super helical structure of Au/TiO2 nanocomposites provided a path for the transmission of photoelectrons.

•Graphene oxide (GO) is introduced into sol-gel system to prepare protective films.•GO is covalently functionalized with silanol of silane coupling agents.•Layered GO promotes cross-linking reaction and provides good barrier property.•The sol-gel film with 0.5 mg/ml GO shows good corrosion protective properties.Graphene oxide (GO) was introduced into sol-gel systems to enhance the corrosion protective properties of the obtained film on AA2024-T3 aluminum alloy. The characterization of morphology, microstructure and component of the films indicated that GO covalently reacted with silanol groups from hydrolyzed 3-glycidoxypropyl-trimethoxysilane (GPTMS) monomer, forming silane functionalized GO (SGO) by COSi covalent bonds. Corrosion protective properties of the films were evaluated through electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and immersion tests studies. The results showed that the addition of GO improved the corrosion protective properties of sol-gel film distinctly by providing the good barrier property of layered GO and enhancing the cross-linking density of the film. The significant improvement of GO on sol-gel film mainly focused on the resistance and capacitance of film itself. The optimal concentration of GO addition was 0.5 mg mL−1, at which the film was uniform and showed good corrosion protective properties in 0.05 M NaCl aqueous solution. The corrosion current density of the sol-gel film with 0.5 mg mL−1 GO was one order magnitude smaller than that of sol-gel film without GO. The protection efficiency of the film was up to 99.45%.

Mesoporous NiCo2O4 nanoneedles were directly grown on three dimensional (3D) graphene-nickel foam which was prepared by chemical vapor deposition, labeled as NCO/GNF. The structure and morphology of NCO/GNF were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, element mapping and Raman spectroscopy. The NCO/GNF was employed as electrodes for supercapacitor and methanol electro-oxidation. When used for supercapacitor, the NiCo2O4 nanoneedles exhibit hi exhibit high specific capacitance (1588 F g−1 at 1 A g−1), high power density and energy density (33.88 Wh kg−1 at 5 kW kg−1) as well as long cycling stability. In methanol electro-oxidation, the NiCo2O4 nanoneedles deliver high electro-oxidation activity (93.3 A g−1 at 0.65 V) and electro-oxidation stability. The good electrochemical performance of NiCo2O4 nanoneedles is attributed to the 3D structure with large specific area, high conductivity and fast ions/electrons transport.

BaTiO3-CoxFe3-xO4 (x is regulated by the R value, R = M (FeCl2•4H2O)/M (CoCl2•6H2O), the molar ratio of FeCl2•4H2O to CoCl2•6H2O) core-shell particles were synthesized by facile homogeneous coprecipitation method utilizing urea as pH adjuster and air as oxidizer. The morphology, microstructure and the chemical compositions of the core-shell particles were characterized by TEM, XRD and EDX, respectively. The results showed that a compact, continuous and pure spinel structure CoxFe3-xO4 shell was formed on the surface of BaTiO3 particles after the homogeneous coprecipitation processes at low temperature (<100 °C). The results of vibrating sample magnetometer (VSM) showed that with the R value increasing from 1.5 to 4, the saturation magnetization and coercivity of the BaTiO3-CoxFe3-xO4 core-shell particles increased from 16.2 emu/g to 38.7 emu/g and 136.6 Oe to 386.5 Oe, respectively. The magnetism of BaTiO3-CoxFe3-xO4 core-shell particles can be controlled by regulating the R.

The structure and mechanical property of Dabryanus scale were investigated. Environmental Scanning Electron Microscopy (ESEM) and Transmission Electron Microscopy (TEM) were used to observe the scale structure. The scale has a discrete osseous layer which is composed of boat-like unit (due to the shape). The osseous layer is embedded into fibrillary layer, and the largest thickness ratio of osseous layer to fibrillary layer is about 7, much higher than those of other reported fish scales. Nanoindentation test was used to investigate mechanical property of the scale. Elastic modulus (Er) and hardness (H) of Dabryanus scale are much lower than those of other reported fish scales. Scale models were proposed and the principles of materials mechanics were used to analyze the mechanical properties of the Dabryanus scale. The boat-like unit in osseous layer makes the scale flexible while keeping a high thickness ratio of osseous layer to fibrillary layer, which increases the flexibility and protection capacity of the scale This study may provide new strategy for the design of flexible armor or flexible devices.