Carbon nanotube-graphene composite

A system for preparing a carbon nanotube-graphene composite, the system comprising:

• a reaction chamber configured to receive a graphite substrate that includes stacked graphene sheets;
• a chemical reservoir configured to direct a carbon nanotube chemical vapor deposition catalyst or a precursor thereof to the reaction chamber;
• a gas source configured to direct to the reaction chamber:
• a reductant gas;
• an oxidant gas;
• an inert gas;
• and a chemical vapor deposition feedstock suited for carbon nanotube deposition;
• a pressure sensor configured to measure a pressure in the reaction chamber;
• a heater configured to heat the reaction chamber to in a range from about 550° C. to about 1000° C.;
• a temperature sensor configured to measure a temperature in the reaction chamber;
• and
• a controller coupled to the reaction chamber, the chemical reservoir, the gas source, the pressure sensor, the heater, and the temperature sensor, where the controller is programmable to:
• provide a graphite substrate that includes stacked graphene sheets to the reaction chamber;
• provide a carbon nanotube chemical vapor deposition catalyst to the reaction chamber,
• insert the carbon nanotube chemical vapor deposition catalyst between at least a portion of the stacked graphene sheets of the graphite substrate;
• employ the heater and the temperature sensor to heat the carbon nanotube chemical vapor deposition catalyst in contact with a chemical vapor deposition feedstock provided by the gas source to a temperature selected to grow the carbon nanotubes;
• grow the carbon nanotubes from the heated carbon nanotube chemical vapor deposition catalyst between the stacked graphene sheets of the graphite substrate for a period of time sufficient to separate at least a portion of the stacked graphene sheets of the graphite substrate with the carbon nanotubes;
• and
• employ the temperature sensor to monitor a reduction in temperature of the carbon nanotubes and the separated graphene sheets to provide the carbon nanotube-graphene composite.

A capacitor device, comprising:

• a first electrode;
• a second electrode;
• a first carbon nanotube-graphene composite conductively coupled to the first electrode;
• a second carbon nanotube-graphene composite conductively coupled to the second electrode,
• wherein the first and second carbon nanotube graphene composites each include:
• an array of graphene sheets arranged in a substantially graphitic structure;
• and
• a collection of carbon nanotubes disposed between at least a portion of the stacked graphene sheets, wherein the carbon nanotubes separate the portion of the stacked graphene sheets by a distance of at least about 10 nanometers.