Pyrolytic carbon has been widely used in electrochemical energy storage devices due to its favorable thermal and electrical properties. Phenol-formaldehyde resin (PFR) is a popular carbon precursor for synthesizing pyrolytic carbon nanostructures. However, the carbonization of PFR always produces non-graphitic carbon and results in deteriorated electrode performance. It is thus crucial to develop practical techniques for improving the graphitization degree of PFR-derived carbon. Graphene has also demonstrated superior potential as an energy-storage electrode material owing to its large surface area and high electrical conductivity favorable for storage and transportation of ions and electrons.
Inspired by the “yolk/egg white/egg shell” structure of an egg, a joint research group of Prof. Huai-Ping Cong from the Hefei University of Technology and Prof. Shu-Hong Yu from the University of Science and Technology of China have combined these materials into one core–dual shell polystyrene (PS)/PFR/graphene oxide (GO) spheres by using PS spheres as the organic core (yolk), a PFR coating as the inner shell (egg white), and GO nanosheets as the outer protective shell (egg shell). In their report in ChemNanoMat, they show that these graphene-wrapped hollow carbon spheres (HCSs) can be fabricated by removing the PS core and simultaneously carbonizing PFR and GO to form interior and thin outer shells. Meanwhile, transition metal ion (Fe3+) catalysis was employed during carbonization to convert PFR into graphitic carbon, giving the graphene-wrapped graphitic HCSs (G-graphitic HCS).
With its beneficial structure, the G-graphitic HCS has enhanced integrity, higher electric and ionic conductivity, and more active sites for the adsorption and storage of ions, which are beneficial for advanced energy storage devices including rechargeable Li/Na batteries and supercapacitors. In addition to its low cost and multifunctional properties for electrochemical energy storage, the bioinspired design concept and the facile synthetic methodology could also help inspire the rational design of other key enabling materials for electrochemical devices.

Material Views, 2016-08-01, Source: http://www.materialsviews.com/bioinspired-hollow-spheres-energy-storage/