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.

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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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Carbon-coated lithium iron phosphate supported on a titanium nitride nanowire network was designed as the electrode material for a lithium-ion supercapacitor.

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In this study, the polypyrrole-titania nanotube hybrid has been synthesized for an electrochemical supercapacitor application. The highly ordered and independent titania nanotube array is fabricated by an electro-oxidation of titanium sheet through an electrochemical anodization process in an aqueous solution containing ammonium fluoride, phosphoric acid and ethylene glycol. The polypyrroletitania nanotube hybrid is then prepared by electrodepositing the conducting polypyrrole into well-aligned titania nanotubes through a normal pulse voltammetry deposition process in an organic acetonitrile solution containing pyrrole monomer and lithium perchlorate. The morphology and microstructure of polypyrrole-titania nanotube hybrid are characterized by scanning electron microscopy, infrared spectroscopy and Raman spectroscopy. The electrochemical capacitance performance is determined by cyclic voltammetry and charge/discharge measurement. It indicates that the polypyrrole film can been uniformly deposited on both surfaces of titania nanotube walls, demonstrating a heterogeneous coaxial nanotube structure. The specific capacitance of polypyrrole-titania nanotube hybrid is determined to be 179 Fg −1 based on the polypyrrole mass. The specific energy and specific power are 7.8 Wh kg −1 and 2.8 kW kg −1 at a constant charge/discharge current of 1.85 mA cm −2 , respectively. The retained specific capacitance still keeps 85% of the initial capacity even after 200 cycle numbers.This result demonstrates the satisfying stability and durability of PPy-TiO 2 nanotube hybrid electrode in a cyclic charge/discharge process. Such a composite electrode material with highly ordered and coaxial nanotube hybrid structure can contribute high energy storage for supercapacitor applications.

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