Purification of single-walled carbon nanotubes by capillary electrophoresis (CE) is demonstrated. Real-time Raman spectroscopy of the separation process and single-wavelength UV/vis detection show the ability of CE to provide high-resolution separations of nanotube fractions with baseline separation. AFM images of collected fractions demonstrate that separations are based on tube length. The separation method is suggested to be based on alignment of the nanotubes along the separation field.

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Electrochemical impedance spectroscopy ͑EIS͒ was used as a diagnostics tool for direct methanol fuel cell ͑DMFC͒ single cells and stacks, capable of separating individual contributions to the overall polarization of fuel cells under load. Anode impedance spectra were interpreted assuming porous electrode model and a reaction mechanism involving one adsorbed intermediate. No evidence of methanol transport limitations was found at the anode under operating conditions tailored for portable applications of DMFCs. Anode experiments revealed substantial poisoning of the electrode by methanol-derived surface species ͑CO͒ and negative order of methanol oxidation in methanol concentration. Because of the clear indication of the presence of adsorbed species at the cathode, the cathode process was assumed to be a combination of oxygen reduction reaction and methanol oxidation occurring in parallel. The porosity and oxygen transport effects were included for the cathode in order to adequately describe the impedance spectra. In addition to divulging methanol crossover, the cathode spectra provided an indication of nonequipotentiality of the cathode, flooding of the cathode backing, flooding/dry-out of the cathode catalyst layer, and hindering of oxygen transport in the cathode backing by crossover methanol. The ability of EIS to reveal these phenomena proved to be highly useful in the identification of performance issues in individual cells of a six-cell DMFC stack.High fuel energy content and no need for the fuel reforming make the direct methanol fuel cell ͑DMFC͒ a highly promising power source, especially for portable electronics applications, including mobile phones, laptop computers, battery chargers, small auxiliary power units, etc. 1-5 The last decade has brought significant progress in the fundamental DMFC research, especially in the anode and cathode electrocatalysis, membrane-electrode structure optimization, and cell design. [6][7][8] The research in these areas has proven crucial to the recent acceleration in DMFC hardware development, stack prototyping, and system integration. 9,10 At the same time, however, there has been a growing need for new and powerful diagnostic techniques, capable of providing more comprehensive information on the performance of DMFCs and their individual components.Until recently, DMFC diagnostics has been practically limited to the use of various dc electrochemical techniques, such as potential and current step. The information generated by these techniques is usually only about the sum of various cell polarizations, which is difficult or impossible to break down into individual polarization contributions. Contrary to the dc techniques, electrochemical impedance spectroscopy ͑EIS͒ is based on the resonance with individual processes occurring in the electrochemical system and, if used skillfully, it can provide insight into these processes. In the EIS experiment, a small sinusoidal electrical perturbation is applied to a linearly responding system under study on top of a bias polarizati...

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