We found a giant Seebeck effect in semiconducting single-wall carbon nanotube (SWCNT) films, which exhibited a performance comparable to that of commercial Bi 2 Te 3 alloys. Carrier doping of semiconducting SWCNT films further improved the thermoelectric performance. These results were reproduced well by first-principles transport simulations based on a simple SWCNT junction model. These findings suggest strategies that pave the way for emerging printed, allcarbon, flexible thermoelectric devices.

We present protocols to prepare high-purity metallic single-wall carbon nanotubes (SWCNTs) with three basic colors, cyan, magenta, and yellow, through density gradient centrifugations. Addition of deoxycholate sodium salts as a co-surfactant could improve separation capability for metallic SWCNTs in centrifugations. We applied the improved separation protocols to the SWCNTs with different average diameters (1.34, 1.0, and 0.84 nm), and obtained the metallic SWCNTs with cyan, magenta, and yellow colors. Their optical/conductive characteristics were revealed, and conductive color films were formed from the metallic SWCNTs.

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Recently published research from the National Renewable Energy Laboratory (NREL) reports that biohybrid hydrogen electrodes comprising metallic single-walled carbon nanotube (SWNT) networks and the hydrogenase from Clostridium acetobutylicum achieved a new activity record for hydrogenase-based electrode electrocatalysis. These results demonstrate that hydrogenase/ SWNT electrodes have the potential to provide a cheaper but equally efficient alternative to the precious metal catalysts, such as platinum, for application in photoelectrochemical or fuel cells. The high-performance hydrogen electrodes are based on the [FeFe]-hydroge-nase from C. acetobutylicum immobilized onto SWNT networks. The researchers prepared the electrodes with varying ratios of metallic (m-) and semiconducting (s-) SWNTs to explore the role of SWNT electronic structure in the biohybrid electrodes. Although most hydrogenase/SWNT electrodes showed improved performance in comparison to the hydrogenase immobilized directly to bulk carbon, high current densities up to 12 mA cm-2 (at-1 V vs. SHE) were achieved with hydrogenase immobilized on SWNT networks with high m-SWNT content. Using electrochemical methods, NREL researchers showed that m-SWNTs contribute to increased electrode electroactive surface available for hydrog-enase binding and improve electronic coupling between the electrode and the hydrogenase redox sites.

We report across-bandgap p-type and n-type control over the Seebeck coefficients of semiconducting single-wall carbon nanotube networks through an electric double layer transistor setup using an ionic liquid as the electrolyte. All-around gating characteristics by electric double layer formation upon the surface of the nanotubes enabled the tuning of the Seebeck coefficient of the nanotube networks by the shift in gate voltage, which opened the path to Fermi-level-controlled three-dimensional thermoelectric devices composed of one-dimensional nanomaterials.

Studies on confined water are important not only from the viewpoint of scientific interest but also for the development of new nanoscale devices. In this work, we aimed to clarify the properties of confined water in the cylindrical pores of single-walled carbon nanotubes (SWCNTs) that had diameters in the range of 1.46 to 2.40 nm. A combination of x-ray diffraction (XRD), nuclear magnetic resonance, and electrical resistance measurements revealed that water inside SWCNTs with diameters between 1.68 and 2.40 nm undergoes a wet-dry type transition with the lowering of temperature; below the transition temperature T(wd), water was ejected from the SWCNTs. T(wd) increased with increasing SWCNT diameter D. For the SWCNTs with D = 1.68, 2.00, 2.18, and 2.40 nm, T(wd) obtained by the XRD measurements were 218, 225, 236, and 237 K, respectively. We performed a systematic study on finite length SWCNT systems using classical molecular dynamics calculations to clarify the effect of open ends of the SWCNTs and water content on the water structure. It was found that ice structures that were formed at low temperatures were strongly affected by the bore diameter, a = D - σ(OC), where σ(OC) is gap distance between the SWCNT and oxygen atom in water, and the number of water molecules in the system. In small pores (a < 1.02 nm), tubule ices or the so-called ice nanotubes (ice NTs) were formed irrespective of the water content. On the other hand, in larger pores (a > 1.10 nm) with small water content, filled water clusters were formed leaving some empty space in the SWCNT pore, which grew to fill the pore with increasing water content. For pores with sizes in between these two regimes (1.02 < a < 1.10 nm), tubule ice also appeared with small water content and grew with increasing water content. However, once the tubule ice filled the entire SWCNT pore, further increase in the water content resulted in encapsulation of the additional water molecules inside the tubule ice. Corresponding XRD measurements on SWCNTs with a mean diameter of 1.46 nm strongly suggested the presence of such a filled structure.

Single-wall carbon nanotubes (SWCNTs) exhibit resonant absorption localized in specific spectral regions. To expand the light spectrum that can be utilized by SWCNTs, we have encapsulated squarylium dye into SWCNTs and clarified its microscopic structure and photosensitizing function. X-ray diffraction and polarization-resolved optical absorption measurements revealed that the encapsulated dye molecules are located at an off center position inside the tubes and aligned to the nanotube axis. Efficient energy transfer from the encapsulated dye to SWCNTs was clearly observed in the photoluminescence spectra. Enhancement of transient absorption saturation in the S1 state of the semiconducting SWCNTs was detected after the photoexcitation of the encapsulated dye, which indicates that ultrafast (<190 fs) energy transfer occurred from the dye to the SWCNTs.