Both polypyrrole-titanium nitride (PPy-TiN) and polypyrrole-titania (PPy-TiO 2 ) nanotube hybrids have been prepared by incorporating electroactive polypyrrole into well-aligned titanium nitride and titania nanotube arrays through a normal pulse voltammetry deposition process. Microstructure characterization shows that the polypyrroles have been fully coated on the titanium nitride and titania nanotube arrays to form coaxial heterogenous nanohybrids. The galvanostatic charge-discharge measurements indicate that the PPy-TiN and PPy-TiO 2 nanotube hybrids have specific capacitances of 1265 and 382 F g À1 at a current density of 0.6 A g À1 . Both nanotube hybrids have similar cyclability, exhibiting stable capacitances of 459 and 72 F g À1 after 2000 cycles at a high current density of 15 A g À1 . The highly conductive titanium nitride substrate can promote the electrochemical capacitance of polypyrrole more significantly, as compared to the titania semiconductor, contributing to a higher supercapacitance performance of PPy-TiN. This indicates that PPy-TiN nanotube hybrids can be more suitable to act as supercapacitor electrode materials.
Carbon quantum dots modified polypyrrole/titania (CQDs-PPy/TiO 2 ) nanotube hybrid was designed as supercapacitor electrode material for an energy storage. CQDs-PPy/TiO 2 was prepared by incorporating CQDs-hybridized PPy into well-aligned titania nanotube array. CQDs-PPy/TiO 2 exhibited a highly-ordered heterogeneous coaxial nanotube structure. CQDs hybridizing modification could well improve the electrical conductivity of PPy. The charge transfer resistance decreased from 22.4 mΩ cm −2 to 9.3 mΩ cm −2 and the ohmic resistance decreased from 0.817 for to 0.154 Ω cm −2 when PPy/TiO 2 was converted into CQDs-PPy/TiO 2 nanotube hybrid. The specific capacitance was accordingly enhanced from 482 F g −1 (or 161 mF cm -2 ) for PPy/TiO 2 to 849 F g −1 (or 212 mF cm -2 ) for CQDs-PPy/TiO 2 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 high current density of 20 A g −1 .The effective incorporation CQDs into PPy could simultaneously increase electrochemical capacitance and cycle stability of PPy, leading to a superior electrochemical performance. A flexible solid-state supercapacitor based on CQDs-PPy nanohybrid exhibited the stable capacitive performance at both planar and bending state. CQDs-hybridized PPy presented the promising application as supercapacitor electrode material for energy storage.
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