Spencer M. Scott

Highly thermally conductive and mechanically strong graphene fibers.

A superior mix of big and small Graphene is often described as an unrolled carbon nanotube. However, although nanotubes are known for their exceptional mechanical and conductivity properties, the same is not true of graphene-based fibers. Xin et al. intercalated small fragments of graphene into the gaps formed by larger graphene sheets that had been coiled into fibers. Once annealed, the large sheets provided pathways for conduction, while the smaller fragments helped reinforce the fibers. The result? Superior thermal and electrical conductivity and mechanical strength. Science, this issue p. 1083 Intercalated graphene sheets form compact, ordered fibers with enhanced thermal conductivity and mechanical properties. Graphene, a single layer of carbon atoms bonded in a hexagonal lattice, is the thinnest, strongest, and stiffest known material and an excellent conductor of heat and electricity. However, these superior properties have yet to be realized for graphene-derived macroscopic structures such as graphene fibers. We report the fabrication of graphene fibers with high thermal and electrical conductivity and enhanced mechanical strength. The inner fiber structure consists of large-sized graphene sheets forming a highly ordered arrangement intercalated with small-sized graphene sheets filling the space and microvoids. The graphene fibers exhibit a submicrometer crystallite domain size through high-temperature treatment, achieving an enhanced thermal conductivity up to 1290 watts per meter per kelvin. The tensile strength of the graphene fiber reaches 1080 megapascals.

Synthesis of ZnO quantum dot/graphene nanocomposites by atomic layer deposition with high lithium storage capacity

Zinc oxide, as an inexpensive anode material, has attracted less attention than other metal oxides due to its poor cycling stability. A rational design of ZnO nanostructures with well-controlled particle sizes and microstructures is essential in order to improve their stability and performance as electrodes for lithium ion batteries (LIBs). Here, we demonstrate a simple approach via atomic layer deposition (ALD) to synthesize ZnO quantum dots (QDs) on graphene layers, in which the size of the ZnO QDs can be controlled from 2 to 7 nm by ALD cycles. A strong relationship between size and electrochemical performance is observed, in which smaller sized QDs on graphene display enhanced electrochemical performance. A high reversible specific capacity of 960 mA h g−1 is achieved at a current density of 100 mA g−1 for 2 nm ZnO QDs, approaching to the theoretical value of ZnO as the LIB anode. The greatly enhanced cycling stability and rate performance of the ALD ZnO QD/graphene composite electrode can be attributed to the well-maintained structural integrity without pulverization upon electrochemical charge/discharge for ZnO QDs with the grain size below a critical value.

Advanced phase change composite by thermally annealed defect-free graphene for thermal energy storage

Organic phase change materials (PCMs) have been utilized as latent heat energy storage and release media for effective thermal management. A major challenge exists for organic PCMs in which their low thermal conductivity leads to a slow transient temperature response and reduced heat transfer efficiency. In this work, 2D thermally annealed defect-free graphene sheets (GSs) can be obtained upon high temperature annealing in removing defects and oxygen functional groups. As a result of greatly reduced phonon scattering centers for thermal transport, the incorporation of ultralight weight and defect free graphene applied as nanoscale additives into a phase change composite (PCC) drastically improve thermal conductivity and meanwhile minimize the reduction of heat of fusion. A high thermal conductivity of the defect-free graphene-PCC can be achieved up to 3.55 W/(m K) at a 10 wt % graphene loading. This represents an enhancement of over 600% as compared to pristine graphene-PCC without annealing at a comparable loading, and a 16-fold enhancement than the pure PCM (1-octadecanol). The defect-free graphene-PCC displays rapid temperature response and superior heat transfer capability as compared to the pristine graphene-PCC or pure PCM, enabling transformational thermal energy storage and management.

Facile low temperature solid state synthesis of iodoapatite by high-energy ball milling

The apatite structure-type has been proposed as a potential waste form for the immobilization of long-lived fission products, such as I-129; however, it is difficult to synthesize iodoapatite without significant iodine loss due to its high volatility. In this study, we report a facile low temperature (∼50 °C) solid-state method for successfully synthesizing lead-vanadate iodoapatite by high-energy ball milling (HEBM) of constituent compounds: PbI2, PbO and V2O5. As-milled iodoapatite is in the form of an amorphous matrix embedded with nanocrystals and can be readily crystallized by subsequent thermal annealing at a low temperature of 200 °C with minimal iodine loss. Rietveld refinement of the X-ray diffraction patterns indicates that the thermally-annealed iodoapatite is iodine deficient with an iodine concentration of ∼4.2 at%. Thermal gravimetric analysis (TGA) indicates that low temperature annealing greatly improves the thermal stability and iodine confinement. This novel approach, using HEBM and thermal annealing, is a very promising method for synthesizing advanced materials that can confine highly volatile radionuclides, such as I-129, which pose significant challenges for the successful disposal of high-level nuclear waste.

Microstructure control of macroscopic graphene paper by electrospray deposition and its effect on thermal and electrical conductivities

Macroscopic graphene paper is fabricated by an electrospray deposition approach, and the microstructure can be controlled from highly porous to highly compact geometries by varying deposition parameters including graphene colloid concentration and deposition rate. Free-standing graphene films can be separated from substrates via a simple water exfoliation method in which the surface properties of graphene films and substrates control film exfoliation. Specifically, water exfoliation can be achieved when the contact angle of substrates is 64° or below. Thermal and electrical conductivities of the macroscopic graphene paper upon thermal annealing are measured, enabling the establishment of the process-microstructure-property correlation beneficial for further development and property manipulation of graphene-based materials.