Hierarchially porous carbon particles for electrochemical applications
View Patent ↗Hierarchically porous graphitic carbon particles are prepared by an aerosol process using a aqueous solution of a carbon precursor compound in which different sized particles or clusters of silicon oxide species are dispersed. The aerosol is heated to evaporate the solvent. The solid residue is carbonized and non-carbon species removed to obtain small porous particles of graphitic carbon. The interconnected, different size pores in the small carbon particles make them very useful as electrode materials in electrochemical devices, such as supercapacitors, in which efficient ion transport through the pores or the particles is required.
1. A method of making nanometer size graphitic carbon particles having interconnected micropores and mesopores, the method comprising:
forming a colloidal dispersion of liquid water droplets in a stream of inert gas, the liquid water droplets comprising an aqueous solution of a carbohydrate and a transition metal compound for promoting carbonization of the carbohydrate, the aqueous solution containing silica particles as templates for the mesopores and orthosilicate clusters as templates for the micropores, the ratio of silica particles and orthosilicate clusters being selected to yield a desired proportion of mesopores and micropores;
heating the stream to evaporate the water and to form solid particles of the dissolved and dispersed constituents;
collecting the solid particles from the stream;
heating the collected particles to carbonize the carbon compound to form graphite particles containing the metal and template materials;
and removing the metal promoter and silicon-containing material from the graphite particles to form porous, generally spherical graphite particles with diameters in the range of fifty to three hundred nanometers and with micropores up to about 2 nanometers in largest dimension interconnected with mesopores of about two to twenty nanometers in largest dimension, and the porous graphite particles have a BET surface area of about 1500 m 2 g −1 or higher.
2. A method as recited in claim 1 in which the liquid droplets are formed from an aqueous solution of a carbohydrate and a transition metal compound with dispersed silica particles and dispersed clusters of ethyl orthosilicate.
3. A method as recited in claim 1 in which the liquid droplets are formed from an aqueous solution of sucrose and nickel nitrate with dispersed silica particles and dispersed clusters of ethyl orthosilicate.
4. A method as recited in claim 2 in which the liquid droplets are carried in a stream of nitrogen and the stream is heated to a temperature of about 450° C. for a time to evaporate the solvent and form solid particles of the dissolved and dispersed constituents.
5. A method as recited in claim 4 in which the solid particles are carbonized at a temperature of about 900° C. in a nitrogen atmosphere to form the porous graphite particles.