RESUMEN
A soft-hard template-assisted method toward the unconventional free-standing ordered mesoporous carbon sheets (OMCSs) with uniform hexagonal morphology is developed by applying MgAl-layered double hydroxide (MgAl-LDH) as the hard template, triblock copolymer F127 as the soft template, and phenolic resols as the carbon sources. It is found that the surface of MgAl-LDH can induce the morphology variation of resol-F127 monomicelles, leading to the formation of vertically or horizontally aligned mesopore arrays in the OMCSs, which can in turn determine their electrochemical energy storage behaviors in supercapacitors with different configurations. In an all-solid-state supercapacitor with two face-to-face electrodes, an OMCS with vertical mesopores manifests the best performance among the samples. By contrast, in a micro-supercapacitor with in-plane film-like electrodes, an OMCS with horizontal mesopores delivers higher energy/power densities than the other OMCSs, which are also comparable to the state-of-the-art supercapacitors based on ordered mesoporous carbons. The achievement of uniform carbon sheets with orientation-adjustable mesopore arrays can help elucidate their electrochemical storage mechanism and allow the optimization of the performances according to the device configuration, thus providing a powerful tool for the manipulation of energy storage devices on the nanoscale.
RESUMEN
Monodisperse spherical silica particles, with solid cores and mesoporous shells (SCMS), were synthesized at various temperatures using a one-pot method utilizing a cationic surfactant template. The temperature of the synthesis was found to significantly affect the diameters of both the cores (ca. 170-800 nm) and shells (ca. 11-80 nm) of the particles, which can be tailored for specific applications that require a high specific surface area of the nanocarriers (mesoporous shells) and simultaneously their mechanical robustness for, e.g., facile isolation from suspensions (dense cores). The applied method enabled the formation of the relatively thick mesoporous shells at conditions below room temperature. Radially ordered pores with narrow distributions of their sizes in 3-4 nm range were found in the shells. The adsorption ability of the SCMS particles was studied using rhodamine 6G as a model dye. Decolorization of the dye solution in the presence of the SCMS particles was correlated with their structure and specific surface area and reached its maximum for the particles synthesized at 15 °C. The presented strategy may be applied for the fine-tuning of the structure of SCMS particles and the enhancement of their adsorption capabilities.
RESUMEN
A facile method to fabricate hierarchically structured fiber composites is described based on the electrospinning of a dope containing nickel and manganese nitrate salts, citric acid, phenolic resin, and an amphiphilic block copolymer. Carbonization of these fiber mats at 800 °C generates metallic Ni-encapsulated NiO/MnOx/carbon composite fibers with average BET surface area (150 m(2)/g) almost 3 times higher than those reported for nonporous metal oxide nanofibers. The average diameter (â¼900 nm) of these fiber composites is nearly invariant of chemical composition and can be easily tuned by the dope concentration and electrospinning conditions. The metallic Ni nanoparticle encapsulation of NiO/MnOx/C fibers leads to enhanced electrical conductivity of the fibers, while the block copolymers template an internal nanoporous morphology and the carbon in these composite fibers helps to accommodate volumetric changes during charging. These attributes can lead to lithium ion battery anodes with decent rate performance and long-term cycle stability, but performance strongly depends on the composition of the composite fibers. The composite fibers produced from a dope where the metal nitrate is 66% Ni generates the anode that exhibits the highest reversible specific capacity at high rate for any composition, even when including the mass of the nonactive carbon and Ni(0) in the calculation of the capacity. On the basis of the active oxides alone, near-theoretical capacity and excellent cycling stability are achieved for this composition. These cooperatively assembled hierarchical composites provide a platform for fundamentally assessing compositional dependencies for electrochemical performance. Moreover, this electrospinning strategy is readily scalable for the fabrication of a wide variety of nanoporous transition metal oxide fibers.