Graphene gel for high rate, large capacity supercapacitors

An innovative principle is developed to spontaneously convert reduced graphene oxide into highly conducting gel having no practical size limit, and it can be engineered in three dimensions on demand. The gel overcomes the bottleneck of high-rate capability in large areal capacity supercapacitors.

Article  |  Fall 2014

The use of different sorts of gels has become common, including contact lenses, hair gels, wound-healing hydrogels, and even edible gels. Interestingly, a one-atom-thick web of carbon and graphene can also be transformed into a new sort of porous hydrogel that can greatly conduct electricity. Thus, the general concept of hard electronic components should be revisited by the creation of conductive gel-like graphene materials.

Despite selective efforts in previous research to make gels out of chemically-converted graphene (reduced graphene oxide), its arbitrary large-scale production with tailored structure via minimal processing steps remains a formidable technological challenge.

Professor Sang Ouk Kim’s lab has invented a surprisingly simple and versatile graphene gelation principle capable of producing micrometer-thick three-dimensional shape-engineered hydrogels with no practical size limit. They show that just simple immersion of an arbitrarily-shaped zinc (Zn) frame in aqueous graphene oxide (GO) dispersion spontaneously generates graphene hydrogel films at Zn surfaces. This site-specific gelation enables a wide-range controllability of three-dimensional gel structures in porous morphology as well as the macroscopic object scale according to customized purposes.

They also reported that the gel is an excellent candidate for energy storage if it is used as a supercapacitor electrode. In general, a fast charging/discharging rate (or power density) is hardly compatible with large areal capacity (or energy density) for energy devices. While thin supercapacitor electrodes with facile electrolyte transports are favorable for high rate capacity, thick electrodes are desired for large areal capacity. The three-dimensional controllability of their graphene gel morphology optimizes the aqueous electrolyte transport within sufficiently thick gel structures. Consequently, the fundamental challenge to attain large areal capacity without sacrificing rate capability is successfully addressed.

Their gelation principle has much broader significance as it could be straightforwardly used for creating layered nanocomposites for synergistic properties. Irrespective of the shape, size, and chemical character, any nanomaterials dispersible in aqueous GO solution can be inserted between graphene layers during layer-by-layer gelation. They also exhibited that the gel can be transferred over any porous platform like fabrics and metallic foam, which could be used in different areas of research such as fabric electronics and energy storage/conversion.

This article (entitled “Three-dimensional shape-engineered, interfacial gelation of reduced graphene oxide for high rate, large capacity supercapacitors”) was published in Advanced Materials as the cover article.

Reference: “Three-dimensional shape engineered, interfacial gelation of reduced graphene oxide for high rate, large capacity supercapacitors.” UN Maiti, J Lim, KE Lee, WJ Lee, SO Kim Advanced Materials 26,615-619, 2014.

Additional links for more information:

http://onlinelibrary.wiley.com/doi/10.1002/adma.201303503/full

http://snml.kaist.ac.kr/