Papers by Keyword: Carbon Aerogels

Abstract: Organic aerogels were prepared by sol-gel polycondensation of resorcinol and formaldehyde using sodium carbonate as a catalyst and dried under ambient pressure. Carbon aerogels were obtained by the dried organic aerogels carbonized under nitrogen atmosphere at high temperature. The pore structures and surface characteristic of the carbon aerogels obtained were investigated by N₂ adsorption isotherms, scanning electron microscope (SEM). Through controlling the concentrations of the main ingredients (resorcinol and formaldehyde), catalyst concentration, we can find out the best concentration which the specific surface area can reach the highest. In this experiment the highest specific surface area was 1645m²/g. In addition, the results show that catalyst for the cross link effect between colloidal microspheres is greater than the growth of the colloid itself, and the effect of water solvent plays an important role in the density of carbon aerogel.

Abstract: The electrochemical performances of resorcinol–formaldehyde-based carbon aerogels can be significantly enhanced by nitric acid activation.FT-IR spectra and SEM images reveal the constitution and morphology of samples .The electrochemical performances of materials were tested by cyclic voltammetry,galvanostatic charge/discharge test ,electrochemical impedance spectroscopy and cyclic test. The results show that activation does not influence the molecular structure of carbon aerogels,which maintains their nano-porous structure. Activation increases the specific capacitance by 50% and improves the conductivity of carbon aerogels,resulting in fenfect cycling stability. So nitric acid activated carbon aerogels is an ideal electrode material for supercapacitors.

Abstract: To improve the controllability of the fabrication of carbon aerogels, the effects of the concentration of the reactant (RF%) on the structural properties of organic resorcinol formaldehyde (RF) gel and the effects of the carbonization temperature on nanostructure of carbon aerogels were discussed. The concentration of the reaction was turned from 5%,10%,20%,30%,40%,50%,55% and 60% to prepare the samples. The RF aerogels were carbonized at temperature of 700, 900 and 1050. The shrinkage and nitrogen gas adsorption were measured. Experimental results showed that the structural stability of the organic RF aerogel can be improved by decreasing the shrink in drying process and increasing the condensation of reactant in the starting solution to a certain value, such as 55%. The ordered pore size distribution of carbon aerogels with less structure defects is able to be produced through the effective particle fusing at the carbonization temperature as high as 1050.

Abstract: The purpose of this paper is to develop feasible composite electrodes with a long cycle life and large specific capacitance and to investigate optimal ratio between aniline and carbon aerogels (CA) materials. The characterization of the composite electrode materials was studied by using scanning electron microscopy (SEM), electrochemical impedance spectroscopy, cyclic voltammetry (CV) and the constant charge-discharge. The specific capacitance of the composite electrode materials, measured using cyclic voltammetry at scan rate of 1mV•s^-1, was found to be 1139.66F•g^-1. For a simple supercapcitor, the highest specific capacitance (127.53 F•g^-1 at 30mA) is obtained at ratio between aniline and CA is 1:4.

Abstract: Carbon aerogels were modified by ammonia solution assisted by microwave radiation in order to obtain materials with good dispersion stability in water and satisfactory electrical conductivity simultaneously. Several techniques were used to characterize the materials including FTIR, Raman spectroscopy, Zeta potential, Four-Point Probe and nitrogen adsorption. The results revealed that the dispersion stability of carbon aerogels in water got better and electrical conductivity of carbon aerogels increased at first and then decreased with the increase of microwave heating time, which were closely associated with oxygen surface groups and degree of graphitization and pore structure. As a good template, the modified carbon aerogels with good dispersion stability and electrical conductivity were used to synthesize LiFePO₄ composites, and the improved electrochemical properties of these composites were characterized by means of Four-Point Probe and galvanostatic charging/discharging.

Abstract: This study used carbon aerogels (CA) and phenolic resin in fixed proportations to produce nano high polymer resin, and used poly ehtylene oxide (PEO) as the modifying agent for phenolic resin to improve the mechanical properties of phenolic resin and promote the surface conductivity. The prepared nano high polymer resin and carbon cloth were made into nano-prepreg by using ultrasonic impregnation method, and a nano-prepreg composite material was prepared by using hot compacting and cut to test pieces to measure its mechanical properties and surface conductivity as well as the influence of temperature-humidity environment (85°C/168hr and 85°C/85%RH/168hr) on mechanical properties. The result showed that the surface conductivity increased by 64.55%, the tensile strength at room temperature increased by 35.7%, the flexural strength increased by 18.4%, and the impact strength increased by 101%. In hot environment (85°C/168hr), the tensile strength decreased by 23.8%, the flexural strength increased by 3.1%, and the impact strength increased by 84.6%. In high temperature-high humidity environment (85°C/85% RH/168hr), the tensile strength decreased by 29.6%, the flexural strength decreased by 17%, and the impact strength increased by 95.7%.Introduction

Abstract: We use carbon aerogels and nanofoams as conductive, ultraporous platforms onto which ultrathin (<5-nm thick) conformal poly(o-methoxyaniline) coatings are applied using self-limiting electrodeposition. The electroactive polymer coating is incorporated to increase the overall chargestorage capacity of the resulting hybrid electrode structure. Nitrogen-sorption techniques are used to characterize the carbon nanoarchitecture pore structure before and after application of the polymer coating. The subtle modifications of the carbon nanoarchitecture with the polymer coating are correlated with the resulting electrochemical properties, as determined by cyclic voltammetry and electrochemical impedance spectroscopy.

Abstract: Carbon aerogels are very promising substrates for electrocatalyst deposition involved in fuel cells. Their advantage over high surface area carbon blacks currently used, is the porous monolithic structure yielding large pore volumes with controlled pore sizes. By changing the synthesis parameters, it is possible to adjust their multi-scale structure which is strongly related to the electrochemical performances. The aim of the lecture is to give a survey of information about the multi-scale structure that can be obtained by small and wide angle X-ray scattering (SAXS and WAXS) techniques combined with contrast variation (CV). To this end, a series of SAXS experiments on carbon aerogels are described and the analysis of the experimental data is explained. Particular attention is paid to the determination of the specific surface area, SSAXS, and to the reasons why WAXS curves combined to SAXS ones make this determination more pertinent. The physical meaning of similarity or difference between SSAXS and surface area determined by gas adsorption, SADS, is discussed and information obtained by using contrast variation (CV) is described for two carbon aerogels prepared in different conditions.

Abstract: RF (Resorcinol-Formaldehyde) aerogels and carbon aerogels were prepared through the sol-gel method following the routes of polymerization, gelation, supercritical drying and pyrolysis processes. The influence of fabrication parameters on the textural structure of the samples, e.g., specific surface area, pore size, and pore size distribution, etc., were systematically investigated. With a decrease in the R/F molar ratio, or an increase in the catalyst content within a limited range, the porosity of the nanostructure materials increases. The optimal temperature of pyrolysis for RF aerogel was investigated by TGA (Thermogravimetric Analysis).