Hierarchically porous graphene as a lithium-air battery electrode.

The lithium-air battery is one of the most promising technologies among various electrochemical energy storage systems. We demonstrate that a novel air electrode consisting of an unusual hierarchical arrangement of functionalized graphene sheets (with no catalyst) delivers an exceptionally high capacity of 15000 mAh/g in lithium-O(2) batteries which is the highest value ever reported in this field. This excellent performance is attributed to the unique bimodal porous structure of the electrode which consists of microporous channels facilitating rapid O(2) diffusion while the highly connected nanoscale pores provide a high density of reactive sites for Li-O(2) reactions. Further, we show that the defects and functional groups on graphene favor the formation of isolated nanosized Li(2)O(2) particles and help prevent air blocking in the air electrode. The hierarchically ordered porous structure in bulk graphene enables its practical applications by promoting accessibility to most graphene sheets in this structure.

Atomic Origins of the Self-Healing Function in Cement-Polymer Composites.

Motivated by recent advances in self-healing cement and epoxy polymer composites, we present a combined ab initio molecular dynamics and sum frequency generation (SFG) vibrational spectroscopy study of a calcium-silicate-hydrate/polymer interface. On stable, low-defect surfaces, the polymer only weakly adheres through coordination and hydrogen bonding interactions and can be easily mobilized toward defected surfaces. Conversely, on fractured surfaces, the polymer strongly anchors through ionic Ca-O bonds resulting from the deprotonation of polymer hydroxyl groups. In addition, polymer S-S groups are turned away from the cement-polymer interface, allowing for the self-healing function within the polymer. The overall elasticity and healing properties of these composites stem from a flexible hydrogen bonding network that can readily adapt to surface morphology. The theoretical vibrational signals associated with the proposed cement-polymer interfacial chemistry were confirmed experimentally by SFG vibrational spectroscopy.

Fabrication of Periodic Gold Nanocup Arrays Using Colloidal Lithography.

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing in combination with new nanofabrication techniques. A plasmon is a quantum of charge density oscillation that lends nanoscale metals such as gold and silver unique optical properties. In particular, gold and silver nanoparticles exhibit localized surface plasmon resonances-collective charge density oscillations on the surface of the nanoparticle-in the visible spectrum. Here, we focus on the fabrication of periodic arrays of anisotropic plasmonic nanostructures. These half-shell (or nanocup) structures can exhibit additional unique light-bending and polarization-dependent optical properties that simple isotropic nanostructures cannot. Researchers are interested in the fabrication of periodic arrays of nanocups for a wide variety of applications such as low-cost optical devices, surface-enhanced Raman scattering, and tamper indication. We present a scalable technique based on colloidal lithography in which it is possible to easily fabricate large periodic arrays of nanocups using spin-coating and self-assembled commercially available polymeric nanospheres. Electron microscopy and optical spectroscopy from the visible to near-infrared (near-IR) was performed to confirm successful nanocup fabrication. We conclude with a demonstration of the transfer of nanocups to a flexible, conformal adhesive film.

Manipulating surface reactions in lithium-sulphur batteries using hybrid anode structures.

Lithium-sulphur batteries have high theoretical energy density and potentially low cost, but significant challenges such as severe capacity degradation prevent its widespread adoption. Here we report a new design of lithium-sulphur battery using electrically connected graphite and lithium metal as a hybrid anode to control undesirable surface reactions on lithium. Lithiated graphite placed in front of the lithium metal functions as an artificial, self-regulated solid electrolyte interface layer to actively control the electrochemical reactions and minimize the deleterious side reactions, leading to significant performance improvements. Lithium-sulphur cells incorporating this hybrid anodes deliver capacities of >800 mAh g(-1) for 400 cycles at a high rate of 1,737 mA g(-1), with only 11% capacity fade and a Coulombic efficiency >99%. This simple hybrid concept may also provide scientific strategies for protecting metal anodes in other energy-storage devices.