Elsevier

Applied Surface Science

Volume 470, 15 March 2019, Pages 882-892
Applied Surface Science

Full Length Article
Fluoroalkylated nanoporous carbons: Testing as a supercapacitor electrode

https://doi.org/10.1016/j.apsusc.2018.11.141Get rights and content

Highlights

  • The one-stage route was proposed to functionalize carbon by hydrofluorocarbons.

  • 0.11–0.72 mmol g−1 of the F-containing thermostable groups are grafted.

  • Formation of CF3, CF2, and CF groups are proved by ss-19F NMR, XPS, ATR studies.

  • Fluoralkylation develops the mesoporosity of micro-mesoporous carbon solids.

  • Fluoralkylation increases the surface capacitance in KOH solution by 40%.

Abstract

The surface of microporous Norit® GAC 830 W carbon was fluoroalkylated by heating in 1,1,1,2-tetrafluoroethane and 1,1,1,2,2-pentafluoroethane at 400 and 500 °C. Elemental analysis, FTIR ATR spectroscopy, and TG studies showed the presence of ∼0.1–0.7 mmol g−1 of the fluorine-containing groups. Nitrogen adsorption measurements and quenched solid density functional theory simulations proved an increase in the mesoporosity. By combining the results of solid-state 19F NMR and XPS analyses, we determined the functionalization of the carbon surface with single bondCF, single bondCF3, and double bondCF2 fluorine-containing groups. Supercapacitor electrodes prepared from these materials were subjected to the charge-discharge tests and electrical impedance measurements. During galvanostatic cycling in the aqueous 30% KOH, they showed an enhanced charge capacitance compared to the parent (830 W) and the reference (Supra 30) carbons. These observations suggest that the fluoroalkylated surface and the modified microporous structure have an additive effect on capacitance parameters of carbon electrodes studied in symmetric, negative and positive modes. The fluoroalkylation caused an increase in the surface capacitance up to 38%. Herein, we demonstrate the fluoroalkylation is a simple way to increase a capacitance of carbon electrodes.

Introduction

This decade has witnessed a significant increase in the consumption of energy storage devices, including supercapacitors (SC). They play an important role in the energy storage and conversion systems. However, the recognized drawbacks of the existing commercial recharging devices are their still low energy storage capacities. This parameter depends on an electrode material for the most. Recently, with the increasing volume of scientific activity in this field, researchers have focused on the improvement of electrode materials for SC. Conductive carbons as an electrode material for SCs provide beneficial properties: large specific surface areas, high conductivities, and high electrochemical stabilities in addition to their environment-friendly sustainable sources and inexpensive production [1]. In particular, for such purpose were proposed surface-doped advanced activated carbons and/or graphene [2], [3].

Numerous studies were carried out through electrode material fine-tuning, considering conducting polymers [4], [5], [6] and different forms of carbon [7], [8], [9]. Besides, a large diversity of carbonaceous materials has been proposed and studied. Now, they seem to be the most proper for application in SC [10]. An actual task of current studies is enchaining of their electrochemical properties. One of the convenient methods for such purpose is the surface doping with fluorine [11]. Typically, innovative fluorinated carbon materials possess the potential of providing a hydrophobic surface while maintaining chemical passivity and advanced porosity [12], [13]. On this background, tuning C/F ratio with fluorine groups fixed to carbon and increasing the stability of such fluorine groups are of great importance for the preparation of fluorinated carbon materials of different structural origin having advanced macroscale properties, for example, tribological, mechanical and electromagnetic, including capacitive ones [14], [15], [16], [17], [18], [19], [20].

When Liu et al. introduced the fluorinated carbon CFx cathodes in 2014 [21], their improved properties have attracted lots of attention and currently, the use of the fluorinated carbons remains one of the most prominent ways of material-mediated low capacity problem-solving.

Technically, direct fluorination of carbon materials and the thermal decomposition of fluorinated polymers are known techniques of fluorocarbons preparation. Their application results in the carbon surface coverage with groups that have high amphiphobicity and high resistance to oxidation [12], [13], [21], [22], [23].

Considering fluorinated polymers, it is clear that in contrast to expensive and poorly soluble polytetrafluorethylene [22], the use of polyvinylidene fluoride, which is a cheaper polymer well soluble in organic solvents, could be much more effective.

Indeed, one can effectively produce fluorinated carbon materials for selective adsorption and electrochemical applications [24], [25], [26], [27], [28], [29], [30], [23] by thermal, radiative, chemical and mechanochemical carbonization of polyvinylidene fluoride [24], [25], [26], [27], [28], [29], [30], [23], [31], [32], [33], [34], [35]. Despite this apparent success, there are several drawbacks. For example, the de(hydro)fluorination lowers the fluorine content in the prepared fluorinated carbons [27], [30], [31], [36], [37] while evaporation of polymer chains causes unwanted gases production [38]. Practically all known methods used for the preparation of fluorinated carbons materials are faced with serious technical difficulties and strictly speaking are tedious. In particular, they require the use of free fluorine or plasma. Here we propose a simple and effective direct fluoroalkylation technique for the functionalization of the inner surface of nanoscale porous carbons, which is described in [39]. We characterize these materials as a new class of fluorinated carbons (Fluocar® F materials) and demonstrate their utility as supercapacitor electrodes with an improved capacitance.

Section snippets

Materials

Norit® granular activated carbon 830 W (designated “830 W”) prepared by carbonization and activation of natural coal was supplied by Electrochemservice (the official distributor of Norit® in Ukraine) and used as an initial material. DLC Supra 30 (designated “Supra 30”) activated carbon was selected as a known reference material for electrochemical studies [40]. Deashed 830 W was repeatedly washed with HCl, HF, and double-distilled water (DDW). In this study, all required acids and salts were

Results and discussion

According to Table 1, elemental analysis revealed the addition from 0.09 to 0.72 mmol g−1 of F, higher for more elevated temperatures of fluoroalkylation as expected. We suppose that the highest F content is due to an intensive thermal decomposition of carboxylic (Cb) surface groups that promote the HFC homolysis.

The remaining ash content in the parent 830 W was found to be ∼1.9 mass%. After fluoroalkylation, it was noticeably reduced to 0.2–0.3 mass% and will have a negligible influence on the

Conclusions

We propose a novel direct method of fluoroalkylation for chemical modification of nanoporous carbon electrode materials as a perspective way to improve supercapacitors. The materials obtained this way all possess excellent thermal and chemical stability. The surface fluoroalkylation at 400–500 °C provides up to ∼ 2 mass% of grafted fluorine, which is approx. 1 mmol g−1 of F (mostly in form of CFx-groups). The treatment temperature had a direct influence on the resulting textural parameters and

Acknowledgments

All authors express their gratitude to entrepreneur Vasyl Prusov for the labware. V.V.L. thanks to the National Scholarship Programme of the Slovak Republic managed by Slovak Academic Information Agency (SAIA), n.o., and funded by the Ministry of Education, Science, Research and Sport of the Slovak Republic, grants in 2015, ID number 14511, and in 2017, ID number 20917; and International Visegrad Fund for scholarship ID number 51810574 in 2018. O.Yu.B. thanks to the National Scholarship

Conflict of interest

A. Zaderko, V. Prusov, and V. Diyuk are listed as inventors of the World patent publication WO/2016/072959, Method for carbon material surface modification by the fluorocarbons and derivatives.

References (58)

  • X. Liang et al.

    Facile synthesis and spectroscopic characterization of fluorinated graphene with tunable C/F ratio via Zn reduction

    Appl. Surf. Sci.

    (2017)
  • S.-E. Lee et al.

    Effect of fluorination on the mechanical behavior and electromagnetic interference shielding of MWCNT/epoxy composites

    Appl. Surf. Sci.

    (2016)
  • M.-J. Jung et al.

    The surface chemical properties of multi-walled carbon nanotubes modified by thermal fluorination for electric double-layer capacitor

    Appl. Surf. Sci.

    (2015)
  • V.K. Abdelkader-Fernández et al.

    Degree of functionalization and stability of fluorine groups fixed to carbon nanotubes and graphite nanoplates by CF4 microwave plasma

    Appl. Surf. Sci.

    (2015)
  • S. Shiraishi et al.

    Chapter 17 – Application of Carbon Materials Derived from Fluorocarbons in an Electrochemical Capacitor

  • M.-H. Kim et al.

    Fluorinated activated carbon with superb kinetics for the supercapacitor application in nonaqueous electrolyte

    Colloids. Surf. A. Physicochem. Eng. Asp.

    (2014)
  • S.M. Hong et al.

    Preparation of porous carbons based on polyvinylidene fluoride for CO2 adsorption: a combined experimental and computational study

    Micropor. Mesopor. Mater.

    (2016)
  • V. Ruiz et al.

    Effect of the thermal treatment of carbon-based electrodes on the electrochemical performance of supercapacitors

    J. Electroanal. Chem.

    (2008)
  • S.S. Chebotaryov et al.

    Modification of X-ray excited photoelectron and C KVV Auger spectra during radiative carbonization of poly(vinylidene fluoride)

    Phys. E Low Dimens. Syst. Nanostruct.

    (2007)
  • D. Schopf et al.

    In situ processing of fluorinated carbon—lithium fluoride nanocomposites

    Mater. Des.

    (2018)
  • M. Senna et al.

    Fluorine incorporation into SnO2 nanoparticles by co-milling with polyvinylidene fluoride

    Solid State Sci.

    (2014)
  • S.S. Chebotaryov et al.

    Radiative defluorination of poly (vinylidene fluoride) under soft X-ray radiation

    Rad. Phys. Chem.

    (2006)
  • B.P. Bakhmatyuk

    High-energy-density electrode on the basis of activated carbon material for hybrid supercapacitors

    Electrochim. Acta

    (2015)
  • V.E. Diyuk et al.

    Functionalization of activated carbon surface with sulfonated styrene as a facile route for solid acids preparation

    Mater. Chem. Phys.

    (2016)
  • Y.S. Lee et al.

    Surface properties of fluorinated singlewalled carbon nanotubes

    J. Fluorine Chem.

    (2003)
  • Y.M. Shulga et al.

    XPS study of fluorinated carbon multi-walled nanotubes

    J. Electron Spectros. Relat. Phenomena

    (2007)
  • D.D. Chronopoulos et al.

    Chemistry, properties, and applications of fluorographene

    Appl. Mater. Today

    (2017)
  • B.Y. Venhryn et al.

    The effect of ultrasonic and HNO3 treatment of activated carbon from fruit stones on capacitive and pseudocapacitive energy storage in electrochemical supercapacitors

    Ultrason. Sonochem.

    (2013)
  • B.P. Bakhmatyuk et al.

    Influence of chemical modification of activated carbon surface on characteristics of supercapacitors

    J. Power Sources

    (2008)
  • Cited by (0)

    View full text