Yibing Xie

Electrochemical capacitance of polypyrrole–titanium nitride and polypyrrole–titania nanotube hybrids

Both polypyrrole–titanium nitride (PPy–TiN) and polypyrrole–titania (PPy–TiO2) 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–TiO2 nanotube hybrids have specific capacitances of 1265 and 382 F g−1 at a current density of 0.6 A g−1. Both nanotube hybrids have similar cyclability, exhibiting stable capacitances of 459 and 72 F g−1 after 2000 cycles at a high current density of 15 A g−1. 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.

Preparation and electrochemical capacitance of graphene/titanium nitride nanotube array

Two kinds of graphene composite electrode materials were synthesized on a titanium nitride nanotube array (TiN NTA) and a nickel foam (NF) substrate by a simple adsorption–reduction process, forming a graphene/titanium nitride (G/TiN) NTA and graphene/nickel foam (G/NF). Both the chemical reduction method and the thermal reduction method were used to convert graphene oxide into graphene, forming a G/TiN NTA and thermal reduction graphene/titanium nitride (TRG/TiN) NTA. The morphology and microstructure of the G/TiN NTA, G/NF and TRG/TiN NTA were characterized by scanning electron microscopy, Raman spectra and X-ray diffraction analysis. The electrochemical performance of G/TiN NTA, G/NF and TRG/TiN NTA were investigated by electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge–discharge measurements. The specific capacitances of G/NF and G/TiN NTA were 198.7 and 333.7 F g−1, respectively, at a current density of 1 A g−1 with respect to the mass of graphene. TiN NTA was more suitable as a substrate material for the graphene composite electrode and G/TiN NTA achieved a higher capacitance performance. Additionally, the specific capacitance of G/TiN NTA and TRG/TiN NTA was 230.7 and 197.9 F g−1, respectively, at a current density of 4 A g−1. This indicated that the chemical reduction method was effective for producing graphene composite electrodes with a higher capacitive performance. An all-solid-state flexible supercapacitor was also constructed using two symmetric G/TiN NTA electrodes and a gel electrolyte of polyvinyl alcohol–potassium hydroxide–potassium iodide, achieving an energy density of 34.2 W h kg−1 and a power density of 11.3 kW kg−1.

SERS performance of graphene oxide decorated silver nanoparticle/titania nanotube array

A graphene oxide (GO) decorated silver nanoparticle/titania nanotube array (Ag/TiO2 NTA) has been designed as a surface-enhanced Raman scattering (SERS) substrate for the sensitive detection of organic molecules. Anatase TiO2 NTA was synthesized by controlled anodic oxidation and annealing treatment processes. Ag/TiO2 NTA was formed by depositing silver nanoparticles (Ag NPs) on the surface of anatase TiO2 NTA through the polyol process. GO/Ag/TiO2 NTA was prepared by decorating GO on the surface of Ag/TiO2 NTA through an impregnation process. Methyl blue (MB) was used as the probe molecule to evaluate the adsorption capability and SERS activity of the as-prepared SERS substrates. The adsorption ratio of MB was increased from 25.2% for Ag/TiO2 NTA up to 38.0% for GO/Ag/TiO2 NTA, presenting an obvious improvement of the adsorption capability. The analytical enhancement factor was increased from 1.06 × 104 for Ag/TiO2 NTA up to 3.67 × 104 for GO/Ag/TiO2 NTA, presenting an obvious improvement of SERS detection performance. The GO/Ag/TiO2 NTA substrate accordingly achieved a very low detection limit of 1.0 × 10−9 M MB. GO/Ag/TiO2 NTA also exhibited good adsorption capability to bisphenol A (BPA) with a weak affinity, presenting a SERS detection limit of 5 × 10−7 M BPA. Moreover, GO/Ag/TiO2 NTA was able to achieve self-cleaning functionality through photocatalytic degradation of organic molecules adsorbed on the SERS substrate under solar light irradiation. GO/Ag/TiO2 NTA having good adsorption capability, self-cleaning properties, reproducibility and cycleability contributed to a promising application for sensitive and recyclable SERS detection.

Preparation of carbon-coated lithium iron phosphate/titanium nitride for a lithium-ion supercapacitor

Carbon-coated lithium iron phosphate (C-LiFePO4) supported on a titanium nitride (TiN) substrate was designed as the electrode material for a lithium-ion supercapacitor for an energy storage application. C-LiFePO4 nanoparticles were prepared via a hydrothermal synthesis and carbonization treatment process. TiN nanowires were prepared using an anodization oxidation and nitridization process. A C-LiFePO4/TiN nanowire network was synthesized by loading C-LiFePO4 nanoparticles onto TiN nanowires through a chemical bath deposition method. The surface morphology and microstructure of C-LiFePO4/TiN were characterized using scanning electron microscopy, X-ray diffraction and Raman spectrum analysis. The lithium-ion insertion–extraction behavior of the C-LiFePO4/TiN in a Li2SO4 aqueous electrolyte was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements. C-LiFePO4/TiN exhibited a high capacitance of 972 F g−1 at the current density of 1.0 A g−1, presenting a capacity improvement of 210% when compared with 314 F g−1 for LiFePO4/TiN. The C-LiFePO4/TiN nanowire network also exhibited good cycle stability and high rate capability, presenting a promising application of the lithium-ion supercapacitor.

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 mΩ cm−2 to 9.3 mΩ cm−2 and the ohmic resistance decreased from 0.817 to 0.154 Ω 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.

Fabrication and supercapacitor behavior of phosphomolybdic acid/polyaniline/titanium nitride core-shell nanowire array

Phosphomolybdic acid (PMo12) with reversible electron shuttling is a potential electrode material. Possessing good solubility limits its applications in energy storage. A novel and efficient phosphomolybdic acid/polyaniline/titanium nitride core–shell nanowire array (PMo12/PANI/TiN NWA) was synthesized as a supercapacitor electrode. FT-IR and Raman spectra showed that PMo12 was well incorporated into PANI and the structures of PANI and PMo12 were completely retained. PMo12/PANI/TiN NWA displayed core–shell nanowire array morphology with narrow diameters and oriented perpendicular to the substrate, benefiting ion diffusion and electron transportation. The PMo12/PANI/TiN NWA electrode exhibited a higher specific capacitance of 469 F g−1 at 1 A g−1 compared with PANI/TiN NWA electrode. PMo12/PANI/TiN supercapacitor could achieve a specific capacitance of 69 F g−1 and an energy density of 21.6 W h kg−1 at a current density of 0.5 A g−1 and an output voltage of 1.5 V. The effects of PMo12 incorporated in PANI and the immobilization mechanism of PMo12 are proposed and discussed.

Capacitive performance of ruthenium-coordinated polypyrrole

Ruthenium coordinated polypyrrole electrodeposited on a carbon paper substrate is developed as an active electrode material for supercapacitors. PPy–Ru(12) was formed by electrochemical polymerization of the ruthenium chloride coordinated pyrrole monomer with a saturation coordination time of 12 h. The capacitance of PPy declined from 249 at 1.0 A g−1 to 102 F g−1 at 20.0 A g−1 with a capacitance retention of 40.9%. The capacitance of PPy–Ru(12) declined from 618 at 1.0 A g−1 to 301 F g−1 at 20.0 A g−1 with a capacitance retention of 48.7%, presenting higher rate capability. The coordination process could induce bipolarons to improve the electrochemical conductivity and rate capability. The capacity retention ratio highly increased from 79.4% for PPy to 91.4% for PPy–Ru(12) after 2000 cycles at 20.0 A g−1, presenting the superior cycling stability of PPy–Ru(12). The coordination reaction between the pyrrole monomer and RuCl3 led to the formation of a tetrahedral structure that restrained volume swelling or shrinking of PPy during the charge–discharge process, accordingly causing improved electrochemical cycling stability. In addition, the all-solid-state PPy–Ru(12) supercapacitor showed a capacitance of 122 F g−1 at 2.0 A g−1 and a capacity retention ratio of 82.8% after 500 cycles. This PPy–Ru(12) with good capacitive performance and electrochemical stability presents promising application as a supercapacitor electrode material.