Carbon nanofibers (CNFs) show a high electrical conductivity but a reduced specific surface area that limits their use as electrode materials for supercapacitors. In this work, amorphous CNFs, with a relatively high electrical conductivity are easily activated in KOH, using certain KOH/CNF weight ratios. Activation does not produce any important change in the shape, surface roughness, diameter, graphene sheet size, and electrical conductivity of starting nanofibers. However, activation leads to new micropores and larger surface areas as well as a higher content of basic oxygen groups. They clearly enhanced the specific capacitance, attaining values higher than those reported for other activated CNFs. In this study, the effects of micropore size and oxygen content on the specific capacitance are discussed for three electrolytes: H 2 SO 4 , KOH, and (CH 3 CH 2 ) 4 NBF 4 . Moreover, a good cycle life is found for the most activated CNFs.

Microchannelled 3D architectures composed of multiwall carbon nanotubes (MWCNTs) surface decorated with Pt nanoparticles and chitosan (CHI) are prepared by an ice segregation induced self-assembly (ISISA) process. The microchannelled structures are highly porous (specific gravity ∼10-2) and exhibit excellent electron conductivity (2.5 S·cm-1) thanks to both the high content of MWCNTs (up to 89 wt %) and their interconnection. The Pt/MWCNT/CHI 3D architectures provide remarkable performance as anodes for a direct methanol fuel cell (DMFC).

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Ultrasmall porous anatase mesocrystals show good electrochemical performance and good capabilities for enzyme immobilization and photocatalytic degradation of contaminants. These materials are potential candidates for energy storage devices, photocatalysis, enzyme immobilization, and, when properly functionalized, could be used for photoelectrochemistry and healthcare applications.

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High-temperature cubic spinels were obtained by thermal treatment at 1100 °C of the corresponding LiCo y Mn 2-y O 4 (0 e y e 1) spinels. The samples were characterized by X-ray powder diffraction, thermogravimetric analysis, electron paramagnetic resonance (EPR) spectroscopy, and electrical and electrochemical measurements. The lattice parameter of the new phases in the 0.3 < y e 1 range is larger compared to the starting ones. The EPR spectra of the new compounds are also different from the starting ones. The electrical conductivity of the new phases depends on the Co content. For y > 0.65 the sharp increase in conductivity observed is associated with a change in electron hopping from Mn 3+ /Mn 4+ ions to Co 2+ /Co 3+ ones. At high temperatures, the conductivity is explained in terms of phonon-assisted polaron hopping among either Mn 3+ /Mn 4+ or Co 2+ /Co 3+ nearest neighbors. At low temperatures electron hopping beyond the nearest neighbors accounts for the conductivity. The electrochemical behavior of the new compounds as positive electrodes was analyzed. The discharge curves show both the 4 and 5 V plateau due to the Mn 4+ /Mn 3+ and Co 4+ /Co 3+ reduction, respectively. Differences in electrochemical characteristics compared to the starting samples are found. From electrochemical and thermogravimetric measurements, the oxidation states of the transition metal ions and the chemical composition of the high-temperature samples are estimated.

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In the last two decades cathodic materials for rechargeable lithium batteries have been extensively studied because these batteries show elevated potential, high energy density, long shelf-life, and safety. 1,2 Among the cathodic materials investigated LiMn 2 O 4 -based spinels are promising candidates to replace LiCoO 2 , which is the material currently used in commercial lithium batteries. In fact, the low cost of the manganese compounds together with their acceptable environmental requirement make these compounds suitable for cathodic materials. [3][4][5][6][7][8][9][10][11][12][13][14][15] It is worth noting that the positive electrodes (cathodes) of the lithium batteries are normally composites in which, besides the active electrode material (LiCoO 2 , LiMn 2 O 4 , etc.), a polymer and a good electronic conductor are usually added. So, it seems that a detailed knowledge of the composites is needed for improving their electrochemical response as positive electrodes. Carbon black (CB) is generally chosen because of its good electronic conductivity which assures an efficient electronic transport through the composite. The efficiency in electronic transport is required because the deinsertion/insertion of Li ϩ ions in the active material is accompanied by oxidation/reduction of some of its elements (Mn, Co, etc.). Moreover, it seems that CB favors a good absorption of the liquid electrolyte by the composite, and hence, a good contact between Li ϩ ions and the particles of the active material. The polymer, which is normally an insulating material from the electrical point of view, can be used as a binder for improving handling of the composite. 1,2 In binary composites formed of a polymer and a good electronic conductor such as CB, graphite, etc., the relative content of the components and, specially, their distribution within the composite are responsible for the electrical conductivity found. [16][17][18][19][20][21][22] In ternary composites formed of LiMn 2 O 4 , CB, and a polymer, the relative content of the three compounds would be the parameter more strongly affecting the electrical conductivity as well as the electrochemical response of the composites. However, this point has not been analyzed in detail so far.In this work we have prepared composites from physical mixtures of LiMn 2 O 4 , CB, and polyvinylidenefluoride (PVDF). The content in PVDF was kept constant, and we analyzed how the electrical conductivity and the discharge capacity were changed as a function of the relative content in LiMn 2 O 4 and CB. The significant variation found in both conductivity and capacity is discussed in terms of the microstructure of the composites as followed by scanning electron microscopy (SEM). ExperimentalComposites of different composition were prepared by mixing and grinding the three components, LiMn 2 O 4 , polyvinylidenefluoride (PVDF), and carbon black (CB), in an agate mortar. Cylindrical and parallelepiped pellets of the composites as well as of the individual components were obtained by cold pressing at ...