Nanosized core–shell structured graphene–MnO2 nanosheet arrays as stable electrodes for superior supercapacitors

Directly fabricating vertically standing graphene–manganese dioxide (MnO2) nanoparticle hybrids as electrode materials remains a challenge, especially so without the use of organic binders. Such hybrids should exhibit high electrochemical performance and high stability. To address this challenge, we report a strategy for fabricating nanosized core–shell graphene–MnO2 nanosheet arrays (G–MnO2 NAs) for use as electrodes for supercapacitors. The as-grown MnO2 nanosheets are transformed into core–shell G–MnO2 nanoparticles by plasma-enhanced chemical vapor deposition. The in situ formed graphene layers act as binders and frameworks, and provide integrity and stability to the overall nanosheet. The resulting core–shell nanoparticles exhibit a high specific surface area and long-term cycling stability. The synergistic effect of the vertically standing intercalated architecture and in situ formed graphene provides a short ion diffusion pathway and a high conductivity. The G–MnO2 NAs exhibit a high specific capacitance of 1176 F g−1 at 2 mV s−1, and a long cycling lifetime with negligible capacitance loss after 10000 cycles. This process for the in situ formation of graphene may be useful for improving the electrochemical performance of other metal oxide-based electrodes.