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.

Mechanical and chemical degradations of high-capacity anodes, resulting from lithiationinduced stress accumulation, volume expansion and pulverization, and unstable solidelectrolyte interface formation, represent major mechanisms of capacity fading, limiting the lifetime of electrodes for lithium-ion batteries. Here we report that the mechanical degradation on cycling can be deliberately controlled to finely tune mesoporous structure of the metal oxide sphere and optimize stable solid-electrolyte interface by high-rate lithiationinduced reactivation. The reactivated Co 3 O 4 hollow sphere exhibits a reversible capacity above its theoretical value (924 mAh g À 1 at 1.12 C), enhanced rate performance and a cycling stability without capacity fading after 7,000 cycles at a high rate of 5.62 C. In contrast to the conventional approach of mitigating mechanical degradation and capacity fading of anodes using nanostructured materials, high-rate lithiation-induced reactivation offers a new perspective in designing high-performance electrodes for long-lived lithium-ion batteries.

The performance of graphene field-effect transistors is limited by the drastically reduced carrier mobility of graphene on silicon dioxide (SiO2) substrates. Here we demonstrate an ultrasensitive ultraviolet (UV) phototransistor featuring an organic self-assembled monolayer (SAM) sandwiched between an inorganic ZnO quantum dots decorated graphene channel and a conventional SiO2/Si substrate. Remarkably, the room-temperature mobility of the chemical-vapor-deposition grown graphene channel on the SAM is an order-of-magnitude higher than on SiO2, thereby drastically reducing electron transit-time in the channel. The resulting recirculation of electrons (in the graphene channel) within the lifetime of the photogenerated holes (in the ZnO) increases the photoresponsivity and gain of the transistor to ∼10(8) A/W and ∼3 × 10(9), respectively with a UV to visible rejection ratio of ∼10(3). Our UV photodetector device manufacturing is also compatible with current semiconductor processing, and suitable for large volume production.

We report a simple, efficient and versatile method for assembling metal oxide nanomaterial-graphene core-shell structures. An ultraviolet photodetector fabricated from the ZnO nanoparticle-graphene core-shell structures showed high responsivity and fast transient response, which are attributed to the improved carrier transport efficiency arising from graphene encapsulation.

Chemical doping of nitrogen into graphene can significantly enhance the reversible capacity and cyclic stability of the graphene-based lithium ion battery (LIB) anodes, and first principles calculations based on density functional theory suggested that pyridinic-N shows stronger binding with Li with reduced energy barrier for Li diffusion and thus is more effective for Li storage than pyrrolic and graphitic-N. Here, we report a novel and rapid (~30 seconds) process to fabricate nitrogen-doped graphene (NGr) by simultaneous thermal reduction of graphene oxide with ammonium hydroxide. The porous NGr with dominant pyridinic N atoms displays greatly enhanced reversible capacities, rate performance and exceptional cyclic stability as compared with pristine graphene. The reversible discharge capacity of the NGr electrode cycled between 0.01-3 V can reach 453 mA h g(-1) after 550 cycles at a charge rate of 2 A g(-1) (~5.4 C), and 180 mA h g(-1) after 2000 cycles at a high charge rate of 10 A g(-1) (~27 C) without any capacity fading. When charged within 0.01-1.5 V, the NGr anode still exhibits high reversible capacities of 224 mA h g(-1) and 169 mA h g(-1) after 700 cycles and 800 cycles at a charge rate of 1 A g(-1) and 5 A g(-1), respectively. Ex situ X-ray photoelectron spectroscopy (XPS) analysis of the NGr electrode upon lithiation and delithiation indicated that the pyridinic-N dominates the capacity enhancement at 3 V, while the pyrrolic-N contributes primarily to Li ion storage below 1.5 V.