NASA has developed a novel hybrid supercapacitor system utilizing vertical graphene as an electrode material grown directly on collector metals using a plasma enhanced chemical vapor de - position. Supercapacitors are an alternative to batteries for energy storage, offering high power density and rapid charging time. Nanomaterials such as carbon nanotubes and graphene offer high surface area and porosity to construct the electrodes. Vertical graphene grown directly on a collector metal substrate enables construction of a supercapacitor. The key to the hybrid supercapacitor technology is the growth of vertical graphene directly onto an inexpensive metal substrate without the use of bulk graphene, catalysts, or binders, resulting in increased power density. Adding the metal oxide or electrically conducting polymer to the vertical graphene adds redox (reduction and oxidation) capacitance, thus increasing the overall performance of the device.
The electrodes are soaked in electrolyte, separated by a separator membrane, and packaged into a cell assembly to form an electrochemical double layer supercapacitor. Its capacitance can be enhanced by a redox capacitance contribution through the addition of metal oxide to the porous structure of vertical graphene, or coating the vertical graphene with an electrically conducting polymer. Vertical graphene offers high surface area and porosity, does not necessarily have to be grown in a single layer, and can consist of two to ten layers. A variety of collector metals can be used, such as silicon, nickel, titanium, copper, germanium, tungsten, tantalum, molybdenum, and stainless steel.
Supercapacitors are superior to batteries in that they can provide high power density (in units of kw/kg) and the ability to charge and discharge in a matter of seconds. Aside from its excellent power density, a supercapacitor also has a longer lifecycle and can undergo many more charging sequences in its lifespan than batteries. This long lifecycle means that supercapacitors last for longer periods of time, which alleviates environmental concerns associated with the disposal of batteries.
These supercapacitors have potential applications in electric automobile power sources; renewable energy storage; energy and environmental design; consumer electronic products; power delivery solutions for forklifts, robots, buses, trolleys, and light rail; and computer memory backup devices.