Phase transformation induced capacitance activation for 3D graphene-CoO nanorod pseudocapacitor

Yun Guang Zhu, Ye Wang, Yumeng Shi, Zhi Xiang Huang, Lin Fu, Hui Ying Yang*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

88 Scopus citations


Development of a pseudocapacitor over the integration of metal oxide on carbonaceous materials is a promising step towards energy storage devices with high energy and power densities. Here, a self-assembled cobalt oxide (CoO) nanorod cluster on three-dimensional graphene (CoO-3DG) is synthesized through a facile hydrothermal method followed by heat treatment. As an additive-free electrode, CoO-3DG exhibits good electrochemical performance. Compared with CoO nanorod clusters grown on Ni foam (i.e., CoO-Ni, ≈680 F g-1 at 1 A g-1 and ≈400 F g-1 at 20 A g-1), CoO-3DG achieves much higher capacitance (i.e., ≈980 F g-1 at 1 A g -1 and ≈600 F g-1 at 20 A g-1) with excellent cycling stability of 103% retention of specific capacitance after 10 000 cycles. Furthermore, it shows an interesting activation process and instability with a redox reaction for CoO. In addition, the phase transformation from CoO nanorods to Co3O4 nanostructures was observed and investigated after charge and discharge process, which suggests the activation kinetics and the phase transformable nature of CoO based nanostructure. These observations demonstrate phase transformation with morphological change induced capacitance increasement in the emergent class of metal oxide materials for electrochemical energy storage device. An ex situ method demonstrates that the capacity increase of cobalt oxide nanorod cluster on 3D graphene (CoO-3DG) pseudocapacitors is due to phase transformation from nanorods to nanoflowers with a valence change of Co. This evidence could help to understand the activation process phenomenon in metal oxide pseudocapacitors.

Original languageEnglish (US)
Article number1301788
JournalAdvanced Energy Materials
Issue number9
StatePublished - Jun 24 2014
Externally publishedYes


  • activation process
  • cobaltous oxide
  • phase transformation
  • pseudo-capacitor
  • three-dimensional graphene

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • General Materials Science


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