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Freestanding, thin, and bendable electrodes for supercapacitors are fabricated by filtering DNA-dispersed double walled carbon nanotubes ͑DWNTs͒ into a thin film and thermally treating the film in argon. We found that DNA has the ability to disperse the strongly bundled DWNTs and is converted to phosphorus-enriched carbons, which give rise to strong redox peaks at around 0.4 V. The combination of the large capacitance from the DNA-derived carbons and the high electrical conductivity of carbon nanotubes allow DWNT/DNA films to be used as a potential electrode material for supercapacitors. © 2009 American Institute of Physics. ͓doi:10.1063/1.3271768͔Biomolecule-engineered nanosized active materials targeted for energy storage devices have attracted lots of attention because of their high charge rate capability and large storage capacity.1,2 Supercapacitors have several advantages over lithium ion batteries, such as higher power density and higher efficiency, due to simple ion adsorption on their electrodes.3 It is well known that the electrochemical performance of the supercapacitor strongly depends on the morphology, texture, and composition of the electrode material. 3Among the many types of active materials, carbon nanotubes have been studied as a potential candidate for achieving a high performance supercapacitor due to both their intrinsically high electrical conductivity and their nanosized diameter. [4][5][6] However, presently available carbon nanotube samples are in a bundled structure and contain metallic impurities that limit the capacitance of carbon nanotube-based supercapacitors. To solve these problems, we used high purity ͑99%͒ double walled carbon nanotubes ͑DWNTs͒ prepared by a catalytic chemical vapor deposition and subsequent oxidation process.7 Their high purity relative to residual catalyst particles has been confirmed by diamagnetic susceptibility experiments.8 In addition, we have chosen single stranded DNA ͑ssDNA͒ for dispersing the strongly bundled DWNTs, and we have confirmed the dispersion state of the tubes in an aqueous ssDNA solution using optical spectroscopy. Then, the filtered DWNT/DNA films were thermally treated at 600°C in argon in order to convert the insulating ssDNA into porous carbon materials. We have found that the freestanding DWNT-derived thin electrodes thus prepared exhibited two times more capacitance than a pure DWNT film, due to the evolution of the pseudocapacitance from the phosphorous-containing functional groups. We also found that these films were mechanically strong enough to show flexibility. This is due to their intrinsic morphology, such as the small diameter and the long length of the nanotubes, which also made them easy to fabricate.We used high purity and crystalline ͓shown by the absence of the Raman D band in Fig. 1͑c͔͒ DWNTs in which nanotubes with an outer diameter of approximately 1.6 nm were packed in hexagonal arrays ͓Fig. 1͑a͔͒ within largersized bundles ͓Fig. 1͑b͔͒. By dispersing the DWNTs ͑ap-proximately 20 mg͒ in an aqueous solution ͑10 ml͒ w...

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The crystal structures of three cobaloxime complexes with different axial base ligands have been analyzed by X-ray analysis at room temperature. I: (2-Cyanoethyl)bis(dimethylglyoximato)((S)-phenylalaninol)cobalt(III); the crystal is orthorhombic, the space group being P212121, Z = 4 with a = 9.416(3), b = 27.184(3), c = 9.184(3) Å. II: (2-Cyanoethyl)bis(dimethylglyoximato)((S)-phenyl-alanine methyl ester)cobalt(III); the crystal is monoclinic, the space group being P21, Z = 4 with a = 14.376(2), b = 11.988(2), c = 14.874(1) Å, and β = 101.05(1)°. III: (2-Cyanoethyl)bis(dimethylglyoximato)(methyldiphenylphosphine)cobalt(III); the crystal is monoclinic, the space group being P21/n, Z = 4 with a = 11.558(4), b = 15.542(3), c = 14.393(5) Å, and β = 91.02(4)°. The structures were refined by the full-matrix least-squares method to final R values of 0.041, 0.052, and 0.044 for 2340, 3287, and 4400 observed reflections, respectively. The photoisomerization rates of I, II, and III in the solid state were obtained from the changes in the IR spectra. The rate of I was insignificantly small, but the rates of II and III were calculated to be 0.1 × 10−4 and 1.9 × 10−4 s−1, respectively, assuming first-order kinetics. The 2-cyanoethyl groups in the three complex crystals take perpendicular conformations to their cobaloxime planes. The 2-cyanoethyl group of I makes a hydrogen bond with the N–H group of the neighboring molecule. The non-reactivity of I may be brought about by the hydrogen bond.

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