Influence of KOH followed by oxidation pretreatment on the electrochemical performance of phenolic based activated carbon fibers

https://doi.org/10.1016/j.jelechem.2007.09.003Get rights and content

Abstract

Oxygen treatment after KOH corrosion of phenolic-based activated carbon fibers was conducted to explore the influence of oxygen functional groups on the performance of capacitors fabricated with the carbon fibers. Scanning electron microscopy analysis shows that KOH corrosion can increase the surface roughness. The result of temperature programmed desorption shows that the amount of surface oxygen functional groups increases with the extent of oxygen treatment after KOH corrosion, and reaches a maximum at 250 °C; the increase is contributed mainly by the formation of carbonyl- or quinone-type groups. The performance of the capacitors was tested in 7 M KOH using potential sweep cyclic voltammetry and constant current charge–discharge cycling. The results reveal that the specific capacitance increases from 163.5 F g−1 to 280.7 F g−1 at a current density of 50 mA g−1 with increasing the amount of oxygen functional groups. The oxygen functional groups can improve the wet ability of carbon surface and causes the quick faradic charge transfer reaction, which decreases the total resistance, and results in the enhancement of specific capacitance at high current density.

Introduction

Phenolic based activated carbon fibers (ACFs) have several merits over traditional granular activated carbons. ACFs have high specific surface area and adsorption–desorption rate [1], [2]. Therefore, the use of ACFs in polarizable electrodes has been paid great attention [3]. ACFs have been considered as the suitable material for the polarizable electrodes of the electric double layer capacitors (EDLCs) with high capacitance, working voltage, reliability and low leakage current [4], [5].

It is well known that pore structures of carbon electrodes affect the performance of the resulting capacitors [6], [7], [8], [9]. The effects of the specific surface area and the pore size distribution of the carbon electrodes have been discussed. Apart from that, geometric heterogeneity e.g. roughness, and the chemical characteristics e.g. the distribution of heteroatom on carbon surface could also influence the capacitor performance [10], [11], [12], [13]. It was reported that the presence of the carbonyl- or quinone-type functional groups may induce double-layer formation, faradic current and surface polarity of the resulting EDLCs [14], [15]. For increasing the capacitance of EDLCs, the surface functional groups were introduced on the surface of activated carbon fibers through many methods such as gaseous oxidation with oxidizing gases, chemical oxidation in HNO3 or H2SO4 solutions, electrochemical oxidation and cold plasma modification, etc. [16], [17], [18]. In the present study, KOH corrosion followed by oxygen treatment of ACFs was employed for achieving high capacitance of EDLCs. The performance of EDLCs fabricated using the resulting ACFs was examined. The surface morphology and oxygen functional groups were characterized using scanning electron microscopy (SEM) and a temperature programmed desorption (TPD) technique, in attempt to elucidate the effects of the morphology and oxygen functional groups during the course of double layer formation at the electrolyte-carbon interface in 7 M KOH/H2O electrolyte.

Section snippets

Preparation of ACFs

The phenolic resin was dissolved in methanol, and then dried by using a vacuum evaporation at 80 °C. The resulting phenolic resin was spun, stabilized in an acidic solution [19], [20], and then carbonized in nitrogen at 900 °C for 30 min. The ACF was prepared by activating the carbon fiber (CF) in a stream of CO2 at 900 °C for 4 h.

The original ACF was denoted ACF and the fibers oxidized at different temperatures for 3 h were denoted ACF-T (thermal treatment temperature). Chemical corrosion was

Structural characteristics of ACFs

The SBET and pore structural parameters of ACF, ACF-T, ACF-KOH and ACF-KOH-T are given in Table 1. From Table 1 it can be seen that for ACF-T series SBET and pore volume increase slightly with increasing oxidation temperature. The burn-off of these samples also increases with increasing oxidation temperature, indicating that carbon gasification plays a dominant role in these cases. For ACF-KOH and ACF-KOH-T series SBET and pore volume do not change obviously with increasing oxidation

Conclusions

The present work has demonstrated that the capacitance of ACFs in 7 M KOH can be enhanced with KOH corrosion followed by oxygen treatment at 250 °C. Heat treatment in air at 150–300 °C for 3 h had slight influence on the SBET and surface oxygen functional groups. KOH corrosion can increase the surface roughness of ACFs. The amount of surface oxygen functional groups increases with the extent of oxygen treatment after KOH corrosion, and reaches the maximum at 250 °C; the increase is contributed

References (34)

  • I. Mochida et al.

    Carbon

    (2000)
  • J. Alcaňiz-Monge et al.

    Carbon

    (1997)
  • I. Tanahashi et al.

    Carbon

    (1990)
  • K. Miura et al.

    Carbon

    (2000)
  • D. Lozano-Castelló et al.

    Carbon

    (2003)
  • T. Morimoto et al.

    J. Power Sources

    (1996)
  • D. Qu et al.

    J. Power Sources

    (1998)
  • Y. Kibi et al.

    J. Power Sources

    (1996)
  • T. Pajkossy et al.

    J. Electroanal. Chem.

    (1996)
  • T. Pajkossy

    Solid State Ionics

    (1997)
  • H.K. Song et al.

    Electrochem. Acta

    (1999)
  • Y.R. Nian et al.

    J. Electroanal. Chem.

    (2003)
  • C.T. Hsieh et al.

    Carbon

    (2002)
  • A. Yoshida et al.

    Carbon

    (1990)
  • C.L. Liu et al.

    Mater. Chem. Phys.

    (2005)
  • C. Moreno-Castilla et al.

    Carbon

    (1995)
  • Y. Otake et al.

    Carbon

    (1993)
  • Cited by (49)

    • One-dimensional hierarchical porous carbon nanofibers with cobalt oxide in a hollow channel for electrochemical applications

      2022, Journal of Alloys and Compounds
      Citation Excerpt :

      As shown in Fig. 3d, the deconvoluted spectra of the N1s region showed two strong peaks at 398.4 eV and 400.7 eV (N5), corresponding to the binding energy of pyridinic-N and pyrrolic-N [27]. The peaks of the O1s spectral (Fig. 3e) curves at 530.5 eV, 532.0 eV, and 533.2 eV were fitted to Co–O in cobalt spinel oxide, surface adsorbed oxygen, and hydroxyl oxygen species [15,26]. TEM analysis with SAED and EDS elemental mapping was performed to confirm the presence and distribution of Co3O4 NPs in the carbon matrix.

    • Crumpled graphene oxide/spinel cobalt oxide composite based high performance supercapacitive energy storage device

      2021, Journal of Energy Storage
      Citation Excerpt :

      The vertical line at low frequency region states the domination of capacitive behaviour through the formation of electrochemical double layer. At this point, the total resistance of the electrochemical cell (Rt) which is also denoted as the equivalent series resistance (ESR) can be calculated through extrapolation of the capacitive line in the low frequency region of the real impedance axis [46]. The value of Rt should be as small as possible to reduce the energy losses during charge cycling.

    View all citing articles on Scopus
    View full text