New frontiers in the world of supercapacitors

In the world of materials science, electrode materials are rapidly being developed in institutions across the world which can serve multiple purposes, in particular to serve as smaller and highly efficient supercapacitors.

Supercapacitors are capable of providing short sharp bursts of energy in comparison to regular capacitors; normal capacitors store generally up to 10-fold more charge than supercapacitors but can only supply their energy in smaller, consistent surges.  Previously, one of the major shortcomings of supercapacitors had been the fact that they store far less energy than regular capacitors.

Recently, a single-surface material has been devised by a team led by Dr. James Tour at Rice University, consisting of a hybrid of graphene/carbon nanotubes. This has made the news and cheekily been dubbed “James’ bond”.

The carbon nanotubes protruding from the graphene sheets give this material higher surface area which is advantageous for their application. The covalent bonds that exist between the graphene sheets and the nanotubes also gives the structure more stability. The high surface area helps overcome one of the biggest setbacks in the field of supercapacitors which is the fact that they are not capable of storing a lot of energy.

The process of creating this material is unique because the catalyst used in the process actually grows the carbon nanotubes onto the graphene surface, bottom upwards. This differs from other hybrid systems because in other cases of hybrid systems, they generally transfer the nanotubes onto the surface of the sheets, which makes the structure more unstable. The uniformity in their electron dispersion makes this carbon/graphene hybrid a seamless material which gives it a high surface area.

Another similar and slighly more recent study has been carried out by a team at the Dalian Institute of Chemistry in China. 

Unlike the protruding carbon nanotube from graphene sheets structure produced by the Rice Institute researchers, the Team at the Dalian Institute created a partially graphitized activated carbon structure, made of carbon and then graphitized. The material has a microporous structure which gives it an increased surface area. 

Partially graphitized activated carbon is also a hybrid system, where catalysts and heat treatment caused the graphitization of carbon structure – so rather than weaving carbon tubes onto a graphene structure, they partially graphitized some of the carbon present within the structure. One of the unique parts of the study was the usage of shells from Ginkgo seeds as the starting ingredient in the process of creating the material. 

Chemisroption characterization enabled the analysis of “the specific surface area and the porous texture of the activated carbons”, as well as the pore size distributions. This showed that the formation of the pores contributes to the increased surface area of the material. 

Both these developments have been able to devise materials with higher surface area which enables the storage of power in higher density; this leads to longer life cycles of the supercapacitors. Though both newly developed materials take different approaches in their development, both strive towards making supercapacitors more efficient.

Reference

Jiang L et al. High rate performance activated carbons prepared from ginkgo shells for electrochemical supercapacitors. Carbon (2013), http://dx.doi.org/10.1016/j.carbon.2012.12.085

Yan Z et al. Three-Dimensional Metal Graphene Nanotube Multifunctional Hybrid Materials. ACS Nano (2012), http://dx.doi.org/10.1021/nn3015882