Scientists at the University of California, San Diego discovered a method to increase the amount of electric charge that can be stored in graphene, in a research that may provide a better understanding of how to improve the energy storage ability of capacitors for potential applications in cars, wind turbines, and solar power.
The team attempted to introduce more charge into a capacitor electrode using graphene as a model material for their tests. The idea is that increased charge leads to increased capacitance, which translates to increased energy storage.
Instead of trying to avoid graphene defects, the scientists used the defects and charged them for energy storage. They used a method called argon-ion based plasma processing, in which graphene samples are bombarded with positively-charged argon ions. During this process, carbon atoms are taken out of the graphene layers and leave behind holes containing positive charges ― the aforementioned charged defects. Exposing the graphene samples to argon plasma increased the capacitance of the materials three-fold. The experiment showed that the scientists were not only able to increase capacitance by using the defects, but also to control the kind of charged defects they introduced.
Using Raman spectroscopy and electrochemical measurements, the team was able to characterize the types of defects that the argon plasma processing introduced into the graphene lattices. The results revealed the formation of extended defects known as “armchair” and “zigzag” defects (named after the shape of the configurations of missing carbon atoms). Also, electrochemical tests helped the team discover a new length scale that measures the distance between charges.They believe that this new length scale will be important for electrical applications, since it can provide a basis for how small electrical devices can be made.