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.

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Nature provides a wide range of entities and/or systems with different functions that may serve as a source of bioinspiration for material chemists. Actually, materials exhibiting a 3D porous texture (combining pores at different scales, from macro-to meso-up to micropores) mimic the hierarchical structure of different systems found in living organisms (e.g., the blood circulation or the respiratory system in mammalians). Structural organization at different scales is ultimately responsible for the outstanding properties offered by hierarchical materials (not only as stationary phases in separation and catalytic processes, [1] but also as electrodes in fuel cells and capacitors)[2] because they offer not only large surface areas, but also accessibility to such a surface.A number of synthetic routes have been explored by using different carbonaceous precursors [3] and either exo or endo templates to modulate the porous texture of the resulting carbon structures.[4] Recent efforts have also been focused on the preparation of porous carbon composites containing graphitic carbon entities (e.g., carbon nanotubes [5] and nanohorns, [6] or even graphene oxide [7] ) the challenge of which is double and resides in 1) the achievement of a homogenous dispersion of these entities throughout the monolith structure and 2) the preservation of high surface areas. Baumann and co-workers have recently performed a quite extensive and stimulating work on single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) synthesized by resorcinol-formaldehyde polycondensation.[5] Particularly interesting in terms of conductivity and surface area were those composites based on DWCNTs, although the authors expressed the convenience of substituting the surfactants used for carbon-nanotube (CNT) dispersion.[5d]Ionic liquids (ILs) [8] and deep eutectic solvents (DESs, a new class of ILs obtained by complexion of quaternary ammonium salts with hydrogen-bond donors, such as acids, amines, and alcohols) [9] have lately been the solvent of choice in a number of chemical processes because of special features: for example, they are nonreactive with water, nonvolatile, and biodegradable as well as excellent solvents for a wide variety of solutes, such as different substrates, enzymes, and even microorganisms of catalytic and biocatalytic interest.[10] Of particular interest for the purpose of this work are those processes for which the capability both as solvents for CNT dispersion [11] and structure-directing agents in the synthesis of different materials [12] was demonstrated. Actually, ILs and DESs have been used as solvents for preparation of CNT-based carbon composites [13] and even as carbonaceous precursors of both nontextured and textured carbons. [14] In particular, we have recently described the preparation of DESs based on mixtures of resorcinol and choline chloride, the rupture of which (via resorcinol polycondensation and subsequent segregation of choline chloride) resulted in the formation of bimodal porous ca...

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Synthetic approaches based on deep eutectic solvents allow the preparation of phophate‐functionalized carbon monoliths with a hierarchical structure. Both functionalization and hierarchy—combining macropores and high surface areas while preserving high monolith densities—are critical for the ahievement of remarkable energy densities in supercapacitor cells.

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