Structural and Electrochemical Characterization of Ethylenediaminated Single-Walled Carbon Nanotubes Prepared from Fluorinated SWCNTs

Abstract

We prepared ethylenediaminated single-walled carbon nanotubes (SWCNTs) from fluorinated SWCNTs by substituting fluorine groups with ethylenediamine groups. The ethylenediaminated SWCNTs were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman scattering spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area measurement by nitrogen adsorption, contact angle measurement, zeta potential analysis, and thermogravimetry. In addition, the properties of 30 wt % sulfuric acid aqueous electrolyte-based electric double-layer supercapacitors (EDLSCs) with free-standing ethylenediaminated SWCNT electrodes were investigated. The degree of ethylenediamine functionalization was 0.603 mmol/g and 1.46 μmol/m2, and the specific surface area was ∼413.3 m2/g. From HRTEM observation, isolated nanotubes disentangled from the bundled SWCNTs were present in many observed areas, and the structures retained a nanotube skeleton. The properties of the EDLSCs with the ethylenediaminated SWCNT electrodes included an average specific capacitance of 94 F/g at a low scan rate of 10 mV/s and an energy density of 2.6 Wh/kg at a power density of 0.24 kW/kg. The EDLSCs exhibited an average specific capacitance of 67 F/g at a high scan rate of 1000 mV/s and an energy density of 1.3 Wh/kg at a power density of 24 kW/kg, values that were superior to those of carboxylated SWCNT electrodes.

Defluorination-assisted nanotube-substitution reaction with ammonia gas for synthesis of nitrogen-doped single-walled carbon nanotubes

“…To begin with, highly crystalline SWCNTs (hc-SWCNTs) (150 mg) were synthesized by the arc discharge method, purified by oxidation in air and a subsequent acid treatment, and finally annealed at 1200°C (see Supplementary Data) [39,40]. After being annealed, the hc-SWCNTs were placed in a polytetrafluoroethylene (PTFE) tube (inner diameter of 6.0 mm).…”

“…Subsequently, they were subjected to thermal annealing at 250°C for 1 h in a nitrogen flow (20 mL/min). The fluorinated SWCNTs were characterized using XPS [39,41]. Fig.…”

“…The peaks labeled N1 (398.5 eV), N3 (399.9 eV), and N4 (401.2 eV) corresponded to the binding energies of the doped nitrogen atoms and were attributed to pyridinic-, pyrrolic-, and graphitic-type nitrogen bonds, respectively [13,47]. The peak N2 (399.3 eV) was attributed to the C tube -NH-bonds between the carbon atoms (C tube ) of the nanotube frame and amines, which corresponded to the nitrogen atoms in a free primary amine (C tube -NH 2 ) [39,48]. Furthermore, the peak N5 at 402.7 eV was attributed to the pyridine-N-oxide bond [13,[49][50][51].…”

“…They confirmed that the major products of the thermal decomposition process were carbonyl fluoride (COF 2 ) (for decomposition below 300°C) and CF 4 (for decomposition above 300°C) [36]. There have also been few reports on the products formed during the thermal decomposition of fluorinated SWCNTs [36][37][38][39]. Mickelson investigated the products of the thermal decomposition of fluorinated SWCNTs (synthesized by laser vaporization) with a stoichiometry of CF 0.5 in vacuum at temperatures of up to 800°C using variable-temperature pyrolysis-electron ionization mass spectroscopy.…”

“…They confirmed that the major products of the thermal decomposition process were CF 4 and COF 2 . In a previous study, we had subjected fluorinated SWCNTs (synthesized by arc discharge) with a stoichiometry of CF 0.41 to defluorination via thermal treatments at temperatures of 350-600°C in an inert atmosphere [39]. We found that most of the modified fluorine groups desorbed in the form of carbon fluoride compounds such as CF 2 , CHF 2 , CF 3 , and CF 4 .…”