Cyclic production of biocompatible few-layer graphene ink with in-line shear-mixing for inkjet-printed electrodes and Li-ion energy storage

The scalable production of two-dimensional (2D) materials is needed to accelerate their adoption to industry. In this work, we present a low-cost in-line and enclosed process of exfoliation based on high-shear mixing to create aqueous dispersions of few-layer graphene, on a large scale with a Yw ~ 100% yield by weight and throughput of ϕ ~ 8.3 g h−1. The in-line process minimises basal plane defects compared to traditional beaker-based shear mixing which we attribute to a reduced Reynolds number, Re ~ 105. We demonstrate highly conductive graphene material with conductivities as high as σ ∼ 1.5 × 104 S m−1 leading to sheet-resistances as low as Rs ∼ 2.6 Ω □−1 (t ∼ 25 μm). The process is ideal for formulating non-toxic, biocompatible and highly concentrated (c ∼ 100 mg ml−1) inks. We utilise the graphene inks for inkjet printable conductive interconnects and lithium-ion battery anode composites that demonstrate a low-rate lithium storage capability of 370 mAh g−1, close to the theoretical capacity of graphite. Finally, we demonstrate the biocompatibility of the graphene inks with human colon cells and human umbilical vein endothelial cells at high c ∼ 1 mg ml−1 facilitating a route for the use of the graphene inks in applications that require biocompatibility at high c such as electronic textiles.publishedVersio

Efficient hydrolytic hydrogen evolution from sodium borohydride catalyzed by polymer immobilized ionic liquid‐stabilized platinum nanoparticles

Platinum nanoparticles stabilized by imidazolium‐based phosphine‐decorated Polymer Immobilized Ionic Liquids (PPh2‐PIIL) catalyze the hydrolytic evolution of hydrogen from sodium borohydride with remarkable efficiency, under mild conditions. The composition of the polymer influences efficiency with the catalyst based on a polyethylene glycol modified imidazolium monomer (PtNP@PPh2‐PEGPIILS) more active than its N‐alkylated counterpart (PtNP@PPh2‐N‐decylPIILS). The maximum initial TOF of 169 moleH2.molcat−1.min−1 obtained at 30 °C with a catalyst loading of 0.08 mol% is among the highest to be reported for the aqueous phase hydrolysis of sodium borohydride catalyzed by a PtNP‐based system. Kinetic studies revealed that the apparent activation energy (Ea) of 23.9 kJ mol−1 for the hydrolysis of NaBH4 catalyzed by PtNP@PPh2‐PEGPIILS is significantly lower than that of 35.6 kJ mol−1 for PtNP@PPh2‐N‐decylPIILS. Primary kinetic isotope effects kH/kD of 1.8 and 2.1 obtained with PtNP@PPh2‐PEGPIILS and PtNP@PPh2‐N‐decylPIILS, respectively, for the hydrolysis with D2O support a mechanism involving rate determining oxidative addition or σ‐bond metathesis of the O−H bond. Catalyst stability and reuse studies showed that PtNP@PPh2‐PEGPIILS retained 70 % of its activity across five runs; the gradual drop in conversion appears to be due to poisoning of the catalyst by the accumulated metaborate product as well as the increased viscosity of the reaction mixture

Nitrogen ion irradiation of Au(110) : Photoemission spectroscopy and possible crystal structures of gold nitride

Photoemission spectroscopy demonstrates the formation of a surface gold nitride upon irradiation of a Au(110) surface with 500 eV nitrogen ions at room temperature. After irradiation two N1s peaks are observed at binding energies of 396.7±0.2 eV and 397.7±0.2 eV along with a broadening of the Au4d5/2 line. Changes in valence-band spectra are also observed, including an additional density of states at 1.6 eV binding energy and new states at ~3.1 eV. Annealing experiments indicate that the two N1s lines are associated with nitrogen compounds of differing thermal stability, possibly due to the formation of more than one nitride phase. To further investigate the properties of gold nitride we have undertaken ab initio pseudopotential calculations on the most likely nitride stoichiometry, Au3N, and identified a novel triclinic crystal structure of a significantly lower energy than the anti-ReO3 expected from a simple consideration of the periodic table, although the latter structure is also found to be stable. The triclinic structure is determined to be metallic, of importance to possible applications

Photoemission spectroscopy of clean and potassium-intercalated carbon onions

Hollow onionlike carbon (OLC), generated by annealing nanodiamond at 2140 K, has been studied by core-level and valence-band photoemission spectroscopy. Upon intercalation with potassium, core and valence states of the OLC show an almost rigid shift to higher binding energies, and the density of states at the Fermi level (EF) is observed to increase. An asymmetric broadening of the C1s line from the OLC as intercalation proceeds indicates an increase in electron-hole pair excitations. Both core and valence-band spectra are consistent with charge transfer from the intercalated potassium to the OLC, and support the conclusion that the electronic structure of the carbon onions bears strong similarity to that of graphite, although differences do exist. In consequence the conclusion can be drawn that these species behave as graphite ``nanocrystals'' rather than as large fullerene molecules

Quantum mechanical ab initio calculations of the structural, electronic and optical properties of bulk gold nitrides

In the present work, the atomic and the electronic structures of Au3N, AuN and AuN2 are investigated using first-principles density-functional theory (DFT). We studied cohesive energy vs. volume data for a wide range of possible structures of these nitrides. Obtained data was fitted to a Birch-Murnaghan third-order equation of state (EOS) so as to identify the most likely candidates for the true crystal structure in this subset of the infinite parameter space, and to determine their equilibrium structural parameters. The analysis of the electronic properties was achieved by the calculations of the band structure and the total and partial density of states (DOS). Some possible pressure-induced structural phase transitions have been pointed out. Further, we carried out GW0 calculations within the random-phase approximation (RPA) to the dielectric tensor to investigate the optical spectra of the experimentally suggested modification: Au3N(D0_9). Obtained results are compared with experiment and with some available previous calculations.Comment: 12 Pages, 11 Figures, 2 Table

Gold film with gold nitride-A conductor but harder than gold

The formation of surface nitrides on gold films is a particularly attractive proposition, addressing the need to produce harder, but still conductive, gold coatings which reduce wear but avoid the pollution associated with conventional additives. Here we report production of large area gold nitride films on silicon substrates, using reactive ion sputtering and plasma etching, without the need for ultrahigh vacuum. Nanoindentation data show that gold nitride films have a hardness ~50% greater than that of pure gold. These results are important for large-scale applications of gold nitride in coatings and electronics