Inverse Opal Carbon Research Articles

Inverse Opal Carbons Derived from a Polymer Precursor as Electrode Materials for Electric Double-Layer Capacitors

Self-standing and macroporous carbon materials were prepared by using silica opals (colloidal crystal) as a template. Poly(furfuryl alcohol) was synthesized in the interstice of the silica colloidal crystals, followed by carbonization at . The silica templates were etched off to give inverse opal carbons. The inverse opal carbons were characterized by scanning electron micrograph (SEM), reflection spectroscopy, elemental analysis, infrared spectroscopy, X-ray diffraction, direct current conductivity, and -adsorption/desorption experiments. The SEM images and the reflection spectra indicated periodic porous structures that were negative structures of the silica opal templates. The inverse opal carbons were hard carbons, mainly consisting of amorphous incompletely graphitized structures, and have electronic conductivity of . The nitrogen adosorption/desorption experiments clarified that the carbons have large -BET (Brunauer-Emmett-Teller) specific surface area resulting from a lot of mesopores, in addition to macropores based on the silica templates. Electric double-layer charging and discharging of the carbons were studied in a tetraethylammonium tetrafluoroborate/propylene carbonate solution. The electric double-layer gravimetric capacitance and the coulombic efficiency of the inverse opal carbon electrodes in the solution increased with a decrease in the diameter of the silica spheres used for the opal templates and became superior to those of a typical activated carbon.

A colorful oil-sensitive carbon inverse opal

A colorful oil-sensitive carbon inverse opal was fabricated by using poly(St–MMA–AA) colloidal crystals as a template. The color shift upon adsorption of oil was reversible, and was easily visible with the naked eye. The peak positions showed a linear relationship with the refractive indices of the oils. In particular, different oils could be distinguished by the color of the carbon inverse opal with a pore size of 240 nm. The response time of the carbon inverse opal was less than 30 s, which is faster than traditional oil sensors. Moreover, the as-prepared carbon inverse opal showed good oil-sensing stability under cyclic adsorption experiments, which suggests that it is a promising and economical alternative to traditional oil-sensing materials, providing a new approach to in situ oil monitoring and detection.

Structures and Characterization of Inverse Opal Carbons and the Properties as Electrode Materials

not Available.

Thermal properties of carbon inverse opal photonic crystals

The thermal conductivity of thin-wall glassy carbon and graphitic carbon inverse opals, fabricated by templating of silica opal has been measured in the temperature range 10–400 K using transient pulse method. The heat flow through 100 Å-thick layers of graphite sheets tiled on spherical surfaces of empty overlapping spheres arrayed in face-centered-cubic lattices has been analyzed in term of anisotropy factor. Taking into account high anisotropy factor in graphite, γ=342, we found that the thermal conductivity of inverse opal prepared by chemical vapor deposition infiltration is limited by heat flow across the graphitic layers in bottleneck, κ⊥=3.95 W/m K. The electronic contribution to the thermal conductivity, κ e(300 K) =3.7×10 −3 W/m K is negligible comparing to the measured value, κ (300 K) =0.33 W/m K. The obtained phonon mean free path, l=90 nm is comparable with the graphite segments between hexagonal array of interconnections.

Inside Front Cover: Photonic Crystal Structures as a Basis for a Three‐Dimensionally Interpenetrating Electrochemical‐Cell System (Adv. Mater. 13/2006)

AbstractThe inside cover shows an SEM image of a 3D‐interpenetrating electrochemical cell with submicrometer features, as reported by Stein and coworkers on p. 1750. The pores of an inverse‐opal carbon electrode are coated with a conformal layer of a polymer separator and infiltrated with vanadia to form the opposite electrode after lithiation. The idealized scheme illustrates lithium‐ion transport between the electrodes through the polymer membrane.

Pore size dependence of field emission from nanoscale porous carbon

Carbon inverse opals with three-dimensional nanoporous structures are fabricated by a template method using synthetic opals formed by the sedimentation of SiO2 spheres. The pore size of the carbon inverse opals ranges widely from about 74 nm to 550 nm depending on the diameter of the SiO2 spheres. These nanoporous structures of carbon exhibit excellent characteristics as electron emitters. As the pore size of porous carbon decreases, the effective emission area of field emission increases. The main emitter sites of porous carbon are interpreted to be the edges formed in the boundary of the neighboring pores. The emission characteristics have drastically improved upon heat treatment at high temperatures (about 2760 °C).

Molecular Simulation of Novel Carbonaceous Materials for Hydrogen Storage

We predict by using molecular simulation that a novel class of carbonaceous materials called graphitic carbon inverse opal (GCIO) provides an excellent absorbent for hydrogen storage at room temperature. Simulation results based on well-calibrated force fields show that the gravimetric delivery amount of hydrogen at T ) 298 K and p ) 30.25 MPa achieves up to 5.9 wt % when the diameter of the spherical cavity in the GCIO materials is 1.78 nm. The corresponding volumetric delivery capacity of hydrogen reaches up to 50 kg/m 3 , very close to the target set by the Department of Energy (DOE). A major advantage of the GCIO materials is that their mass-production is technically accessible, which makes them a good candidate for inexpensive storage of hydrogen in future automobile vehicles.

Preparation and Electronic Properties of Nanoporous Carbon Inverse Opal

Carbon inverse opals with three-dimensional nanoporous structures are fabricated by a template method using synthetic opals formed by the sedimentation of SiO2 spheres. The pore size of the carbon inverse opals ranges widely from approximately 11 nm to 1 µm depending on the diameter of the SiO2 spheres. The nanostructure size and the degree of graphitization of carbon are also controlled by the change in pyrolysis technique. X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) observations of the carbon inverse opals prepared by pyrolysis at a heat-treatment temperature (HTT) of 2800°C revealed that the graphite layers are formed in the area surrounding the pore and the degree of graphitization depends on the pore size. The electronic properties of the carbon inverse opals are dependent on pore size and the conditions of pyrolysis and are interpreted to be influenced by weak localization effect by taking into consideration the degree of graphitization depending on pore size.

Carbon structures with three-dimensional periodicity at optical wavelengths

Porous carbons that are three-dimensionally periodic on the scale of optical wavelengths were made by a synthesis route resembling the geological formation of natural opal. Porous silica opal crystals were sintered to form an intersphere interface through which the silica was removed after infiltration with carbon or a carbon precursor. The resulting porous carbons had different structures depending on synthesis conditions. Both diamond and glassy carbon inverse opals resulted from volume filling. Graphite inverse opals, comprising 40-angstrom-thick layers of graphite sheets tiled on spherical surfaces, were produced by surface templating. The carbon inverse opals provide examples of both dielectric and metallic optical photonic crystals. They strongly diffract light and may provide a route toward photonic band-gap materials.