Like an electrochemical battery, a capacitor is used to store energy. Some electrochemical batteries can indeed be relatively efficient; however, charge time is still their primary limiting factor for their usage as a replacement to fossil fuel in industrial and commercial applications. High capacity batteries require more time for charging.
This is one of the reasons behind the slow adoption of electrically powered vehicles. On the other hand, the charging rate of capacitors is much higher, but they can store only less energy.
Supercapacitors or ultracapacitors can hold very large amount of electrical charge when compared to standard capacitors. Hence, they are ideal to be used a substitute for electrochemical batteries in various commercial and industrial applications.
Supercapacitors can function in very low temperatures at which many types of electrochemical batteries stop working. For these benefits, supercapacitors are already being utilized in flashlights and emergency radios, where energy can be generated kinetically, followed by subsequent storage in a supercapacitor for the device to utilize.
Structure of Capacitors and Supercapacitors
A traditional capacitor consists of two conductive material layers isolated by an insulator. The amount of charge that can be hold by a capacitor depends on the distance between the two conductors, their surface area, and the dielectric constant of the insulator.
On the other hand, supercapacitors do not consist of a solid insulator, but have two conductive plates in a cell that are coated with a porous material, normally activated carbon. The cells are submerged in an electrolyte solution.
The porous material will preferably have a very large surface area, thus enabling the supercapacitor to achieve very high levels of charge because its capacitance is decided by the surface area of the porous material as well as the distance between the two layers.
Drawbacks of Supercapacitors
Although supercapacitors can store much higher energy when compared to standard capacitors, they are not capable enough to withstand high voltage. Moreover, their production cost is also on the higher side and their scalability in industry is currently narrowing the application options because energy efficiency is negated against cost efficiency.
In a research paper, UCLA scientists demonstrated their ability to fabricate supercapacitors from graphene through the use of a simple DVD LightScribe writer on a home PC. This new technique employs a commercially available laser device instead of a highly sophisticated atomic force microscope used in thermochemical nanolithography.
Advantages of Graphene
Although the relative surface area of activated carbon is much higher, graphene, a form of carbon, has considerably more. If the relative surface area of a conductive material used in a supercapacitor is much higher, then the material can more efficiently store electrostatic charge. Moreover, graphene is lighter as it is made up of one single atomic layer.
Moreover, since graphene is actually just graphite, it is eco-friendly when compared to other forms of energy storage. Another important factor to be considered is the efficiency of the supercapacitor.
Researchers were able to fabricate supercapacitors that can store 150 F/g. However, some have proposed that the theoretical upper limit for graphene-based supercapacitors is 550 F/g, which is a much higher value when compared to existing technology.
Future for Graphene-Based Supercapacitors
Graphene's inherit mechanical strength and elastic properties coupled with advantages of graphene based supercapacitors such as lightweight dimensions and minimal production costs make the technology featuring these supercapacitors to be available within the next five to ten years.
Moreover, graphene-based or hybrid supercapacitors will find use in a variety of applications due to advances in energy storage limits for supercapacitors.
Supercapacitors are already being used in some vehicles and their usage in mobile telephones and other mobile electronic devices is expected within the next few years. The use of supercapacitors allows these electronic devices to be charged at a much faster rate and last for a much longer time.
Other current and potential applications of supercapacitors are as power backup supplies for industrial purposes or even for homes. Businesses can make investments in power backup solutions which can store large amount of energy at high voltages to offer adequate power for production. The availability of a fuel cell vehicle that can store high levels of electrical energy can be used to power homes in the occurrence of a power outage.
The adoption of advanced energy storage and recovery solutions is expected to increase in the coming years if the energy density and efficiency of supercapacitors increase and the production expenses decrease.
Although graphene-based supercapacitors will not be a practical solution until some time in the future, it is necessary to advance the technology to achieve it.
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