No abstract

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.

In this study, we have employed infrared (IR) absorption spectroscopy, visible Raman spectroscopy, and x-ray absorption near edge structure (XANES) to quantify the hydrogen (H) content in hydrogenated amorphous carbon (a-C:H) films. a-C:H films with a hydrogen content varying from 29 to 47 at. % have been synthesized by electron cyclotron resonance chemical vapor deposition at low substrate temperatures (< 1 2 0 °C) applying a wide range of bias voltage, Vb, (-300 V < Vb < +100 V). With the application of high negative Vb, the a-C:H films undergo a dehydrogenation process accompanied by a sharp structural modification from polymer-to fullerenelike films. The trend in the H content derived from elastic recoil detection analysis (ERDA) is quantitatively reproduced from the intensity of the C -H bands and states in the IR and XANES spectra, respectively, as well as from the photoluminescence (PL) background drop in the Raman spectra. Using the H contents obtained by ERDA as reference data, semiquantitative expressions are inferred for the amount of bonded hydrogen as a function of the experimental spectroscopic parameters, i.e., the integrated area of the IR C -H stretching band at about 2900 cm-1, the PL background in visible Raman spectra, and the XANES intensity of the o-*-CH peak.