Krzysztof Kierzek

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.

Electrochemical Characteristics of Discrete, Uniform, and Monodispersed Hollow Mesoporous Carbon Spheres in Double-Layered Supercapacitors

Core-shell-structured mesoporous silica spheres were prepared by using n-octadecyltrimethoxysilane (C18TMS) as the surfactant. Hollow mesoporous carbon spheres with controllable diameters were fabricated from core-shell-structured mesoporous silica sphere templates by chemical vapor deposition (CVD). By controlling the thickness of the silica shell, hollow carbon spheres (HCSs) with different diameters can be obtained. The use of ethylene as the carbon precursor in the CVD process produces the materials in a single step without the need to remove the surfactant. The mechanism of formation and the role played by the surfactant, C18TMS, are investigated. The materials have large potential in double-layer supercapacitors, and their electrochemical properties were determined. HCSs with thicker mesoporous shells possess a larger surface area, which in turn increases their electrochemical capacitance. The samples prepared at a lower temperature also exhibit increased capacitance as a result of the Brunauer-Emmett-Teller (BET) area and larger pore size.

Nanoconfinement induced formation of core/shell structured mesoporous carbon spheres coated with solid carbon shell.

A novel method for the fabrication of core/shell structured mesoporous carbon spheres with solid shell using a template method has been presented. The unique molecular nanostructures are characterized by XRD, TEM, TGA, and nitrogen adsorption/desorption measurement. The formation mechanism of the mesostructured carbon spheres with a carbon shell is proposed according to the experimental results. Nanoconfinement effect, occurring in the core/shell structured template, is believed to play a key role in mediating the formation of these hierarchical carbon mesostructures, with SnO2 as a template and C2H4 as a carbon source of a mesoporous carbon core. This synthesis method is simple, straightforward, and suitable for the preparation of various nanostructures that are unique scaffolds in catalytic and electrochemical applications.

Facile synthesis of porous iron oxide/graphene hybrid nanocomposites and potential application in electrochemical energy storage

A facile and efficient method is used to synthesize porous iron oxide coated with graphene as electrode materials for lithium-ion batteries and supercapacitors. Graphene encapsulation of porous Fe2O3 and Fe3O4 nanorods is directly carried out from FeOOH@GO colloids by taking advantage of an electrostatic self-assembly method, owing to the positively-charged surface of FeOOH and the negatively-charged surface of GO. The combination of graphene and porous iron oxide brings about multifunctional features of the electrode materials as follows: (1) enhanced electrical conductivity makes the electrodes the current collectors; (2) reinforced softness of the electrodes accommodates the large volume changes during charge–discharge cycles; (3) improved high specific surface area of the electrodes increases the accessibility of the active electrode materials to electrolyte; (4) the pores formed by graphene and iron oxide particles facilitate ion transportation; (5) iron oxide particles separate graphene and prevent their restacking or agglomeration, and vice versa, thus improving the immersion and splitting of electrolyte into and out of the electroactive material. Consequently, the porous iron oxide/graphene hybrid nanocomposites deliver a good performance in the electrochemical energy storage for lithium-ion batteries and supercapacitors.

Effect of PAN Oxidation on the Electrochemical Lithium Insertion/Deinsertion Behavior of Resultant Carbons

The effect of polyacrylonitrile (PAN) oxidation on the properties and electrochemical lithium insertion/deinsertion behavior of carbons produced in the temperature range of 1000–1150°C has been assessed. Air-treatment at 220 and 240°C modifies essentially the carbonization behavior of polymer leading to materials with developed microporosity and enhanced oxygen content in contrast to practically nonporous pristine PAN-based carbon. The extent of the modification increases with the oxidation depth and decreases with HTT. Galvanostatic charge/discharge reveals typical hard carbons characteristics of all the materials. PAN-based carbon heat-treated at 1050°C represents most promising anodic performance. It gives reversible capacity () near 420 mAh g−1 with a reasonable coulombic efficiency during cycling of ~99% and a moderate low voltage capacity of 100 mAh g−1. Extensive oxidation enhances overall 1st discharge cycle capacity to 870 mAh g−1 and to 560 mAh g−1; however, large irreversible capacity () and poor cycleability are serious drawbacks of all carbons from oxidized PAN. Pyrolytic carbon coating using methane CVD at 830°C is effective in suppressing by about 30% but the cycleability remains nonacceptable.

New synthesis method of sword-sheath structured carbon nanotubes

Here, we report a facile method to synthesize a novel material-mesoporous carbon nanowires trapped in carbon nanotubes forming sword-sheath structures (MCW@CNT). They are fabricated by combining surfactant-templating self-assembly method and chemical vapor deposition in AAO template. Both of the sword and the sheath are formed by graphitic layers analogous to multiwalled carbon nanotubes. The formation of this sword-sheath structure resulted in the enhancement of specific surface area. Uniform SnO2 nanoparticles were deposited in the inner space of carbon nanotubes. The electrochemical properties of the SnO2-MCW@CNTs composites as anode materials for lithium batteries were investigated.