Electrochemical capacitance of a carbon quantum dots-polypyrrole/titania nanotube hybrid

A carbon quantum dots modified polypyrrole/titania (CQDs-PPy/TiO2) nanotube hybrid was designed as a supercapacitor electrode material for energy storage. CQDs-PPy/TiO2 was prepared by incorporating CQDs-hybridized PPy into a well-aligned titania nanotube array. CQDs-PPy/TiO2 exhibited a highly-ordered heterogeneous coaxial nanotube structure. A CQDs hybridized modification could improve the electrical conductivity of PPy. The charge transfer resistance decreased from 22.4 mU cm(-2) to 9.3 mU cm(-2) and the ohmic resistance decreased from 0.817 to 0.154 Omega cm(-2) when PPy/TiO2 was converted into the CQDs-PPy/TiO2 nanotube hybrid. The specific capacitance was accordingly enhanced from 482 F g(-1) (or 161 mF cm(-2)) for PPy/TiO2 to 849 F g(-1) (or 212 mF cm(-2)) for CQDs-PPy/TiO2 at a current density of 0.5 A g(-1). The capacitance retention was slightly increased from 78.5% to 89.3% after 2000 cycles at a high current density of 20 A g(-1). The effective incorporation of CQDs into PPy could simultaneously increase the electrochemical capacitance and cycle stability of PPy, leading to a superior electrochemical performance. A flexible solid-state supercapacitor based on the CQDs-PPy nanohybrid exhibited the stable capacitive performance in both planar and bent states. CQDs-hybridized PPy presented promising applications as a supercapacitor electrode material for energy storage.