Graphene Nickel Research Articles

High power density microbial fuel cell with flexible 3D graphene–nickel foam as anode

The structure and electrical conductivity of anode play a significant role in the power generation of microbial fuel cells (MFCs). In this study, we developed a three-dimensional (3D) reduced graphene oxide-nickel (denoted as rGO-Ni) foam as an anode for MFC through controlled deposition of rGO sheets onto the nickel foam substrate. The loading amount of rGO sheets and electrode surface area can be controlled by the number of rGO loading cycles. 3D rGO-Ni foam anode provides not only a large accessible surface area for microbial colonization and electron mediators, but also a uniform macro-porous scaffold for effective mass diffusion of the culture medium. Significantly, at a steady state of the power generation, the MFC device with flexible rGO-Ni electrodes produced an optimal volumetric power density of 661 W m(-3) calculated based on the volume of anode material, or 27 W m(-3) based on the volume of the anode chamber. These values are substantially higher than that of plain nickel foam, and other conventional carbon based electrodes (e.g., carbon cloth, carbon felt, and carbon paper) measured in the same conditions. To our knowledge, this is the highest volumetric power density reported for mL-scale MFC device with a pure strain of Shewanella oneidensis MR-1. We also demonstrated that the MFC device can be operated effectively in a batch-mode at least for a week. These new 3D rGO-Ni electrodes show great promise for improving the power generation of MFC devices.

Electrochemically reduced graphene oxide–nickel nanocomposites for urea electrolysis

Urea has been demonstrated as a stable, non-toxic, and non-flammable hydrogen carrier for long-term sustainable energy supply. Electrocatalytic oxidation using nickel catalysts has been used as an effective approach for hydrogen production via urea electrolysis. In this work, graphene–nickel nanocomposites were synthesized through one-step electrochemical reduction process and developed as electrocatalysts for hydrogen production through urea electro-oxidation. The graphene–nickel nanocomposites diminished the surface blockage effect observed with other catalysts during the oxidation of urea, and enhanced the current density of this reaction. The improved electrochemical performance of the urea electrolysis process using graphene–nickel nanocomposites as the electrocatalysts shows potential for future applications in hydrogen production and fuel cells.

Magnetic loading of graphene–nickel nanoparticle hybrid for electrochemical sensing ofcarbohydrates

Graphene–nickel nanoparticle hybrid was prepared by the one-step far infrared-assisted reduction of graphene oxide and nickel (II) ions using hydrazine. It was loaded on the surface of a magnetic electrode for electrochemical sensing. The feasibility and performance of the novel electrode were demonstrated by measuring carbohydrates using cyclic voltammetry and amperometry. It demonstrated that nickel nanoparticles decorated on graphene sheets exhibited higher electrocatalytic activity toward the oxidation of carbohydrates while graphene improved the electron transduction. The synergistic effect significantly enhanced the current response of carbohydrates.

Far-Infrared-Assisted Preparation of a Graphene-Nickel Nanoparticle Hybrid for the Enrichment of Proteins and Peptides

A new approach based on far infrared-assisted in situ reduction was developed for the facile one-step preparation of graphene-nickel nanoparticle hybrid by refluxing a mixture solution containing graphene oxide, nickel(II) sulfate, and hydrazine over an far-infrared heater. The reduction time was as short as 20 min. The structure of the material was investigated by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy, vibrating sample magnetometery, and Fourier transform infrared spectroscopy. Magnetic investigations indicate that the grapheme-nickel nanoparticle hybrid exhibits ferromagnetic behavior at room temperature. Meanwhile, the hybrid was successfully employed in the enrichment and identification of proteins and peptides in combination with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry based on its excellent magnetic responsibility, high dispersibility, large surface area, and hydrophobicity, indicating great promise for a wide range of applications.

Geometry and temperature effects of the interfacial thermal conductance in copper– and nickel–graphene nanocomposites

Graphene has excellent mechanical, electrical and thermal properties. Recently, graphene–metal composites have been proposed as a means to combine the properties of metals with those of graphene, leading to mechanically, electrically and thermally functional materials. The understanding of metal–graphene nanocomposites is of critical importance in developing next-generation electrical, thermal and energy devices, but we currently lack a fundamental understanding of how their geometry and composition control their thermal properties. Here we report a series of atomistic simulations, aimed at assessing the geometry and temperature effects of the thermal interface conductance for copper– and nickel–graphene nanocomposites. We find that copper–graphene and nickel–graphene nanocomposites have similar thermal interface conductances, but that both cases show a strong performance dependence on the number of graphene layers between metal phases. Single-graphene-layer nanocomposites have the highest thermal interface conductance, approaching ∼500 MW m−2 K−1. The thermal interface conductance reduces to half this value in metal–bilayer graphene nanocomposites, and for more than three layers of graphene the thermal interface conductances further reduces to ∼100 MW m−2 K−1 and becomes independent with respect to the number of layers of graphene. This dependence is attributed to the relatively stronger bonding between the metal and graphene layer, and relatively weaker bonding between graphene layers. Our results suggest that designs combining metal with single graphene layers provide the best thermal properties.

Three dimensional nickel–graphene core–shell electrodes

The annealing of nickel-coated porous carbon structures results in a new three dimensional nanostructured graphene encapsulated nickel core–shell electrode. A highly interdependent and dynamic process is observed that results in the complete reversal of the spatial orientations of the two component system after the annealing process. We examine the mechanism of carbon diffusion and observe unexpected morphological changes of the nickel in response to carbon crystallization. The new nickel–graphene core–shell electrode demonstrates excellent electrochemical properties with promising applications in micro-batteries and biosensors.

Atomistic simulation of a graphene-nanoribbon–metal interconnect * * Contribution of the National Institute of Standards and Technology, an agency of the US government. Not subject to copyright in the USA.

We report a molecular statics simulation of the physical processes responsible for binding and lattice distortions in a nanoscale electrical interconnect with realistic boundary conditions. The interconnect consists of a graphene ribbon interfaced with the (111) crystallographic surfaces (over 11 000 atoms overall) of two nickel electrodes. We quantify the graphene lattice distortions by mapping strains, as well as out-of-plane atomic displacements on a grid, throughout the simulated interconnect. The results suggest strongly localized graphene lattice distortions at the edges and strains that do not exceed 0.5% elsewhere. Such strains are not expected to affect the electrical properties of the graphene nanoribbon interconnect. A stand-alone graphene nanoribbon is simulated in order to identify the effect of electrodes partially supporting the graphene nanoribbon. Our results indicate that the electrodes reduce the in-plane strains induced by the nanoribbon edges, while causing rippling of the graphene lattice. The average graphene–nickel intersurface separation and the cohesive energy for the top-fcc configuration are calculated at ∼2.13 Å and 68.22 meV Å−2. In order to describe the interatomic interactions in the simulation, we utilize a set of accurate atomistic potentials for graphene on a nickel surface. The approach is based on the modified embedded atom method (MEAM) for the C–C and Ni–Ni interactions, and a Morse-type potential, which takes the surface configuration into account, for the Ni–C interactions. Our focus is on the Ni-(111) crystallographic surface interfaced with graphene in top-fcc, top-hcp, and hcp–fcc initial configurations. The interactions were validated by calculating the equilibrium binding energy and intersurface distance. The resulting binding energies and equilibrium intersurface separations obtained are in very good agreement with previous experimental and ab initio data obtained by use of density functional theory (DFT).

Synthesis and characterization of graphene–nickel oxide nanostructures for fast charge–discharge application

Graphene–metal oxide composites as anode materials for Li-ion batteries have been investigated extensively, but these attempts are mostly limited to moderate rate charge–discharge applications. Here, graphene–nickel oxide nanostructures have been synthesised using a controlled hydrothermal method, which enabled in situ formation of NiO with a coralloid nanostructure on graphene. Graphene/NiO (20%), graphene/NiO (50%) and pure NiO show stable discharge capacities of 185 mAh/g at 20 C (1 C = 300 mA/g), 450 mAh/g at 1 C, and 400 mAh/g at 1 C, respectively. High rate capability and good stability in prolonged charge–discharge cycling permit the application of the material in fast charging batteries for upcoming electric vehicles. To the best of our knowledge such fast rate performance of graphene/metal oxide composite as anode and such stability for pure NiO as anode have not been reported previously.