3 research outputs found
Influence of the Boron Precursor and Drying Method on Surface Properties and Electrochemical Behavior of Boron-Doped Carbon Gels
Two
series of B-doped carbon gels were prepared by the polymerization
of resorcinol and formaldehyde in water using either boric acid or
phenyl boronic acid as dopants. Both organic hydrogels were dried
by four methods: supercritical, freeze, microwave oven, and vacuum
oven drying. The effects of the boron precursor and drying method
on the surface characteristics were studied by N<sub>2</sub> and CO<sub>2</sub> adsorption at â196 and 0 °C, respectively, immersion
calorimetry into benzene and water, temperature-programmed desorption
coupled with mass spectrometry, X-ray photoelectron spectroscopy,
and thermogravimetric analysis. Electrochemical characterization was
carried out in a three-electrode cell, using Ag/AgCl as a reference
electrode and a Pt wire as a counter electrode. The surface area obtained
from immersion calorimetry into benzene was more realistic than that
yielded by the BrunauerâEmmettâTeller (BET) equation.
The hydrophobicity of the samples decreased linearly with a higher
oxygen content. In addition, the oxygen content of the B-doped carbon
gels increased linearly with a higher B content, and the interfacial
or areal capacitance decreased linearly with a larger surface area.
The capacitance was increased by B addition because of the pseudocapacitance
effects of the higher oxygen content of the samples. The cryogel and
vacuum-dried xerogel obtained from the boric acid series, Bc and Bv,
respectively, showed the largest gravimetric and volumetric capacitances,
around 140 F/g and 95 F/cm<sup>3</sup>, respectively
Carbon Xerogel Microspheres and Monoliths from ResorcinolâFormaldehyde Mixtures with Varying Dilution Ratios: Preparation, Surface Characteristics, and Electrochemical Double-Layer Capacitances
Carbon xerogels in
the form of microspheres and monoliths were
obtained from the solâgel polymerization of resorcinol and
formaldehyde in the presence of potassium carbonate as catalyst, using
water as solvent and two different molar dilution ratios. The objectives
of this study were as follows: to investigate the effect of the dilution
ratio, polymerization reaction time, and temperature on the rheological
properties of the sols used to prepare the carbon xerogel microspheres
and monoliths; and to determine the influence of their preparation
methods and shapes on their surface characteristics and electrochemical
double-layer (EDL) capacitance. An increase in the molar dilution
ratio produced a decrease in the apparent activation energy of the
solâgel transition. Carbon xerogel microspheres were steam-activated
at different burnoff percentages. The morphology, surface area, porosity,
and surface chemistry of samples were determined. The main difference
between the carbon xerogel microspheres and monoliths was that the
latter are largely mesoporous. Better electrochemical behavior was
shown by carbon xerogels in monolith than in microsphere form, but
higher gravimetric and volumetric capacitances were found in activated
carbon xerogel microspheres than in carbon xerogel monoliths
Activated-carbon cloth supports umbilical-cord stromal stem cells growth and differentiation
Activated-carbon cloth supports umbilical-cord stromal stem cells growth and differentiation. Oral communication presented on the World conference on Carbon in Rio de Janeiro on July 17th of 2013