A study on dramatically enhanced capacitance of graphene-decorated hierarchically porous nickelian heterogenite for energy storage application

The eminent theoretical capacitance of metal oxide or hydroxide resulting from the Faradaic redox reaction makes them attractive to high performance energy storage devices. Unfortunately, the poor conductivity and dispersion could limit their practical application. Although incorporating with conductive materials such as graphene has proved to be an effective method to solve the above problems, the role of the graphene is not clear yet. This work provides a systematic study on graphene-decorated porous nickelian heterogenite ((Ni,Co)OOH). The dispersion of particles and conductivity is found to be significantly improved by the graphene-decoration, resulting in great enhancements of electrochemical properties. The contributed capacitance value of (Ni,Co)OOH in (Ni,Co)OOH-rGO-10 h (decorated with 10 h reduced graphene oxide) is 1045 F g(-1), 3.5 times higher than that in the pure sample (296 F g(-1)). This is the best enhancement to our knowledge. A model is also proposed to illustrate that this enhancement in capacitance is attributed to extra and deeper redox reactions, which are due to the improvement of conductivity and dispersion by the incorporation of graphene. Therefore, the graphene-decorating is an essential and important way to improve the capacitance of metal oxidehydroxide. (C) 2013 Elsevier Ltd. All rights reserved.