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Enhancement Performance of Carbon Electrode for Supercapacitors by
Quinone Derivatives Loading via Solvent-free Method
Nutcharin Tisawat a, Chanatip Samart a,b, Panichakorn Jaiyong a, Richard A. Bryce c, Khanin
Nuengnoraj d, Narong Chanlek e, Suwadee Kongparakul a,b*
a Department of Chemistry, Faculty of Science and Technology, Thammasat University,
Pathumthani 12120, Thailand
b Bioenergy and Biochemical Refinery Technology Program, Faculty of Science and
Technology, Thammasat University 12120, Thailand
c Division of Pharmacy & Optometry, School of Health Sciences, Faculty of Biology, Medicine
& Health, University of Manchester, Manchester M13 9PT, UK
d School of Bio-Chemical Engineering and Technology, Sirindhorn International Institute of
Technology, Thammasat University, Pathumthani 12120, Thailand
e Synchrotron Light Research Institute (Public Organization), 111 University Avenue, Muang
District, Nakhon Ratchasima 3000, Thailand
*Corresponding Author. E-mail: [email protected] or [email protected] (S. Kongparakul)
Tel: +662-564-4440 ext 2418; Fax: +662-564-4483
ABSTRACT
Activated carbon (AC) from coconut shell, surface area of 764.09 cm2/g, was functionalized with
various quinone derivatives (anthraquinone (AQ), 9,10-phenanthrenequinone (PQ) or
tetrachlorohydroquinone (TCHQ)) via a sublimation method for supercapacitor application. The
properties of modified activated carbons were characterized by X-ray diffraction (XRD),
scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) spectroscopy,
X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption. The results showed
a supercapacitor containing AC modified with 16%wt. AQ achieved higher specific capacitance
than other quinone derivatives which performed specific capacitance about 485 F g-1 at a current
density of 1.0 A g-1, resistance of 2.25 Ω and exhibited high cyclability which loss specific
capacitance of 1.2% after 1000 charge-discharge cycles. The experimental data is in good
agreement with the computational results of quinone adsorption on graphene surface; the lowest
interaction energy (IE) of -28.0 kcal mol-1 was obtained for AQ loading model. The modified AC
successfully prepared by a solvent-free method which could be further developed as low-cost
and environmentally friendly electrode materials for high-performance supercapacitors.
Keywords: Supercapacitor, Quinone derivatives, Sublimation, Solvent-free method
1. Introduction
Supercapacitor is an important part of most electronic devices for using as an energy storage.
In addition, they are used for short-term power backup supply which able to rapid charge and
discharge. However, the major drawback of supercapacitor is low charge storage compare to a
traditional battery. The supercapacitor electrodes are usually made of high surface area porous
carbon materials. Previous literatures implemented to reduce their cost based on the research and
development of carbon-based electrodes from biomass and an enhancement of their energy
density including the long-term stability. Various biomass resources such as bamboo1-3, mud-
stone and lignin4, orange-peel5, coconut shell6, lignin7, etc. have been used for porous carbon
preparation and applied as high-performance supercapacitors. It can be prepared by pyrolysis and
activation method, microwave-assisted method, electrospinning and hydrothermal method.
Among these, coconut shell has great potential since it composed of cellulose and hemicellulose
and easily to produce bunch amount of porous carbons. It has the merits of eco-friendly, low
cost, abundant as a sustainable biomass resource. However, those activated carbons derived from
coconut shell always show a specific surface area below 1800 m2 g−1 with micropores size less
than 2 nm leading to low specific capacitance and poor rate capability for energy storage
applications.
To improve the energy storage performance, an incorporation of organic molecules with
redox kinetics to the inexpensive high-surface-area conductive substrates can store additional
energy by electrochemical reactions. Quinone derivatives are one of the most interesting
molecules according to their redox performance. For example, PQ (9,10-phenanthrenequinone),
PYT (pyrene-4,5,9,10-tetraone) and AQ (anthraquinone) were polymerized and grafted over
Ketjenblack for lithium batteries with high power densities8 or 2,5-bis (pro-2-ny-1-ylamino)
cyclohexa-2,5-diene-1,4-dione (HBU-281) was loaded over AC by physical mixing for
supercapacitor electrode9. Furthermore, the addition of redox active quinone/phenol additives
such as redox reaction of pyrocatechol/o-quinone pair could enhance the capacitance of
pyridinic-N carbonaceous capacitive system which increased the electrode capacitance by up to
512 F g-1 at 1.0 A g-1 and performed an excellent cyclability10.
However, there are many steps and chemical reagents required for this method. It has been
reported that the electrochemical performance of a composite electrode consisting of
carbon/quinone derivative via either electrochemically grafted lithium ion battery or physical
mixing was comparable11. However, the major limitation of carbon materials is charge
accumulate via electric double layer (EDL) mechanism which depends on electrostatic between
electrode and electrolyte interface. The electrochemical properties of carbon electrode for
supercapacitor can be improved by combination of redox material to enhance charge storage via
pseudocapacitance behavior which perform electron transfer through redox reaction12. The
objective of this work is to enhancement the performance of carbon electrode for supercapacitors
by loading of quinone derivatives (anthraquinone (AQ), 9,10-phenanthrenequinone (PQ) or
tetrachlorohydroquinone (TCHQ)) over activated carbon from coconut shell via solvent-free
method. The physical/chemical properties and electrochemical performance will be discussed.
2. Experimental
Materials
Activated carbon (AC) from coconut shell was provided from Carbokarn Co., Ltd. (Thailand).
Anthraquinone (AQ), 9,10-phenanthrenequinone (PQ), tetrachlorohydroquinone (TCHQ) and
polytetrafluoroethylene (PTFE, 60wt% in water) were supplied from Sigma-Aldrich. Sulfuric
acid, AR grade (>98%) was purchased from Acros. All chemicals were used without
purification.
Preparation of quinone/AC.
Quinone derivatives were loaded over activated carbon by a sublimation method. Activated
carbon (0.5 g) was placed in a sealed Schlenk tube and pretreated by vacuum drying at 150C for
4 h. The required amount of quinone was added into an opened-end glass ampule, the topped
with quartz wool and transferred into the Schlenk tube, vacuumed for 20 min, heated up to
desired temperature and sublimed at proper temperature (150-250C) for 5 h. The quinone/AC
products were kept in dry place for further use as a composite electrode. The optimum
sublimation condition of AQ/AC, PQ/AC, and TCHQ/AC are 250C, 220C and 240C for 5h,
respectively using the same pretreatment method as described above (see detail in Supporting
Table S1).
Characterizations
Nitrogen adsorption/desorption isotherms at −196 °C were recorded using a volumetric V-Sorb
2800P instrument (Gold APP Instruments Corporation China). Surface area and the pore
characteristic has been analyzed by the Barrett-Joyner-Halenda (BJH) and Brunauer-Emmett-
Teller (BET) methods, respectively. The surface morphology and elemental distribution were
investigated by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-
EDX) (JEOL, JSM-5410LV and ISIS300) at accelerating voltage of 20 KV. X-ray diffraction
(XRD) analyses were carried out using an X-ray diffractometer (PANalytical X'Pert Pro) at room
temperature with Cu K𝛼 radiation in the 2 range of 10–50 and a scanning rate of 1.5 min−1. X-
ray photoelectron spectra (XPS) were recorded using (ULVAC-PHI, PHI 500 Versa Probe II)
with Al K X-ray radiation as the X-ray source for excitation. The elemental composition of
quinone modified activated carbons was provided by the analysis of the C1s, O1s, and Cl2p
spectra. The sensitivity of the machine was 0.01–0.5% (atomic percent). Attenuated total
reflection Fourier transform infrared spectrometry (ATR-FTIR, Perkin Elmer, USA) was used
for identifying the functional group of the samples by recording the wavenumbers from 4000 to
600 cm-1.
Electrochemical measurements
Electrochemical analyses were performed on a potentiostat/galvanostat instrument (VerSa
STAT3, Princeton Applied research) with 1.0M H2SO4 electrolyte at 25C in a three-electrode
system (Ag/AgCl as a reference electrode, Pt as counter electrode, modified carbon composites
as working electrode). The working electrode was fabricated by mixing 80%wt. active material,
10%wt. carbon black and 10wt% polytetrafluoroethylene (PTFE: 60% disperse in H2O),
sonicated the mixture for 10 min and dried at 80C for 2 h. The mixture was grinded in agate
mortar until homogeneous and pressed on stainless steel mesh no.150. Cyclic voltammetry (CV)
was conducted in the potential range of -0.4 – 1.0 V vs. Ag/AgCl and scan rate of 10-125 mV s−1
for ten cycles. The galvanostatic charge-discharge (GCD) was investigated at current density
range of 1-7 A g-1. The electrochemical impedance spectroscopy (EIS, frequency range of 1-105
Hz) and self-discharge were recorded using Autolab M204 (Metrohm). A cyclability test was
conducted at a current density of 1.0 A g−1 for 1000 cycles in 1.0M H2SO4 electrolyte.
Computational modeling
To investigate the molecular interaction between quinones noncovalently bound to pristine
graphene (C96H24), the energies of the optimized models were computed using B97D density
functional with def2-TZVPP basis set. All complex models were optimized at B97D/def2-SVP
level of theory using Gaussian 09 program13. The interaction energy (IE) was calculated
according to Eq (1) with counterpoise correction of basis set superposition error.
IE = Ecomplex + (Egraphene Equinone) …………(1)
3. Results and Discussion
The physical and chemical characteristics of pristine AC and quinone modified AC are
illustrated in Figure 1 and summarized in Table 1. SEM images of AC show irregular shapes of
granular AC including visible pores with a diameter less than 1.0 μm. After sublimation, fine
particles (particle size < 0.5 μm) were deposited and well distributed over the AC surface as
illustrated in SEM-EDX, especially, TCHQ/AC samples where Cl element related to chloride
group in the chemical structure of TCHQ. N2 adsorption-desorption isotherms of AC revealed
type IV isotherm which represented to porous structure and continuous 3D networks. (see
morphology, elementary mapping and N2 adsorption-desorption isotherms in Figures S1-S2,
ESI). The amount of quinone loading significantly affected to the pore characteristic of AC. In
this work, the amount of quinone loading was in the range of 0-30% wt. BET surface area (SBET)
decreased when increased in % quinone loading. According to the IUPAC classification, AQ/AC
samples significantly changed the N2 adsorption-desorption isotherms from type IV isotherm to
type I isotherm which associated with non-porous material behavior14.
Figures 1c-e show XPS survey spectra and high-resolution XPS C1s spectrum of AQ/AC
and Cl2p spectrum of TCHQ/AC. XPS wide scan spectra contain the peaks of carbon (C1s and
Auger peak of C KLL), oxygen (O1s peak and Auger line of O LMM) and chlorine (Cl2p
doublet, Cl2p peak and Auger peak of Cl LMM). All peaks precisely coincide with the binding
energies given in the XPS database15-16. The core level high resolution XPS analyses showed that
the peak of carbon (C) is mainly found at 284.5 eV, 284.9 eV, 286.8 V which are assigned to sp2
C (C=C), sp3 C (C-C) and C–O (hydroxyl and epoxy), respectively17-20. New particular peak of
C=O (carbonyl) at 287.6 eV has been observed after quinones loading which indicated to the
presence of quinone entirely in the quinone/AC composites. The peak of oxygen (O) is mainly
found in O1s which represents O-C=O (531.6 eV), C-O (533.6 eV) and C=O (533.5 eV) which
also supports the results of C1s spectra. The peak of chlorine (Cl) is mainly found in Cl2p which
represents chloride (Cl2p3/2 at 197.8 eV and Cl2p1/2 at 199.1 eV) and organic Cl (Cl2p3/2 at 200.1
eV and Cl2p1/2 at 201.9 eV). It is clearly observed for TCHQ/AC sample, the chloride-containing
composites. The full XPS characterization both wide scan and deconvolution of core level
spectrum of each sample is presented in Figure S3-S6 (ESI).
XPS also performed to investigate the elemental composition and functional groups of
quinone/AC. The result reveals that the atomic concentration of O increased related to the
amount of AQ or PQ over AC. For TCHQ/AC, the elemental content of Cl increased with an
increasing in TCHQ amount. These results suggested to the effective loading of AQ, PQ or
TCHQ on the carbon framework via sublimation method, however, high amount of quinone
loading could be fully filled the into the pore and covered the AC surface which led to non-
porous material as mentioned above.
Figure 1 (a, b) SEM images of pristine activated carbon and quinone/AC, respectively (Insets
show high magnification images of the samples), (c) XPS survey spectra (Inset shows zoom in of
Cl2p region for TCHQ/AC sample), (d) deconvolution of core level spectrum of C1s of AQ/AC,
and (e) deconvolution of core level spectrum of Cl2p of TCHQ/AC, respectively.
Table 1 BET surface area, total pore volume and the elemental composition of pristine AC and
quinone modified AC.
Samples Quinonea SBET Vtot Atomic concentrationb (%)
(%) m2 g-1 cm3 g-1 C1s O1s Cl2p
AC 0 764 0.43 90.89 9.11 0
AQ/AC 3 458 0.26 89.43 10.21 0.35
8 312 0.18 88.20 11.41 0.38
16 254 0.15 87.65 12.09 0.26
27 24 0.03 86.05 13.42 0.53
PQ/AC 2 599 0.35 89.52 10.17 0.32
4 556 0.33 89.00 10.64 0.36
12 547 0.30 88.74 11.05 0.22
28 446 0.25 88.13 11.43 0.45
TCHQ/AC 2 692 0.40 88.89 10.14 0.97
6 637 0.38 87.57 11.96 0.47
12 566 0.31 84.69 13.51 1.80
30 432 0.24 87.95 10.11 1.94
a Weight of quinone (%) in quinone/AC composite by gravimetric calculation.
b Atomic concentration (%) was determined by XPS elemental analysis.
Figure 2 illustrates the FTIR spectra of pristine AC and AC after sublimation with quinone.
All the samples feature two peaks located at 1327 and 1554 cm-1, which are typical vibration
modes of carbonaceous materials. The band between 3500 - 3800 cm-1 attributed to phenolic -
OH, the bands at 2977 cm−1 and 2885 cm−1 attributed to C-H aliphatic stretching of C–H and
δC–H (= stretching and δ =bending) in aromatic structure, respectively. The shoulder at 1554
cm−1 assigned to the C=C stretching vibration in aromatic ring and the other peaks at 1230, 1046,
and 879 are characteristics of C-O, C–OH stretching vibration, and out-of-plane C–H bending
vibration, respectively. The quinone loaded AC samples show a strong band in their main
characteristic peak of quinonyl group (C=O stretching vibration) at 694 cm-1 which assigned to
the ring breathing frequency21-22. The results identified the presence quinone functional groups
over the AC surface.
Figure 2 FTIR spectra of pristine AC and quinone/AC.
From Figure 3, XRD patterns of pristine quinones (AQ, PQ, and TCHQ) clearly showed the
sharp diffraction peaks which indicated crystallinity of substance due to its π-π stacking between
the anthracene ring layers23, on the other hands, XRD pattern of the pristine AC exhibited C(002)
broadened diffraction peak (2θ of 15-30) which attributed to the amorphous carbon structures
and the graphite structure of AC present broad diffraction peak around 2θ of 40-50 which
represent to C (101) and the diffraction peak 2θ of 26.61 referred to oxygen functional group
such as ketone and chromene which typically surface functional groups present in activated
carbons24-25. After AC has been sublimed with quinones, the XRD patterns illustrate both
overlapped broad peak and sharp peak which can be ascribed to quinones/AC. Therefore, this
XRD result suggested that the quinone derivative was preferable to hold inside the porous carbon
with a less-crystalline structure. A similar XRD observation has been reported previously for
loading of 1,5-dichloroanthraquinone (DCAQ) over AC beads and the adsorption of AQ on
carbon nanotube, respectively26-27.
Figure 3 XRD pattern of pristine AC, pristine quinone derivatives and quinone/AC.
Electrochemical properties of the quinone/AC composites
The effect of quinone types and the amount of quinones (2-30%wt) on electrochemical
properties was carried out employing a three-electrode system in 1.0 M H2SO4 electrolyte. Cyclic
voltammetry (CV) and galvanostatic charge/discharge (GCD) have been carried out at a scan rate
of 0.1 V s-1 and a current density of 1.0 A g-1, respectively.
Figure 4 displays a series of voltammograms at various scan rates from 0.01 V s-1 to
0.125 V s-1 and a series of galvanostatic charge–discharge curves at various current density from
1.0 A g-1 to 7 A g-1. Generally, an increasing in the scan rate refer to an increasing in the
electronic field which will alter both faradaic and non-faradaic processes. From Figure 4(a), the
shift of voltammograms has been observed with the increase of scan rate where cathodic peak
shifted towards the negative potential and the anodic peak shifted towards positive potential. The
results implied to a diffusion controlled redox process. The anodic current (Ipa) to cathodic
current (Ipc) linearly increased with an increasing in the scan rate as shown in Figure 4(c),
moreover, the ratio of Ipa /Ipc was in the range of 0.91-1.17 which not unity and corresponds to a
quasi-reversible system28. The GCD profiles by variation of current density, Figure 4(b),
illustrates the symmetric charge-discharge at high currents with low IR drops which indicated to
the excellent coulombic efficiency and the low IR drops indicated to the minimal diffusion29. The
comparison of capacity based on active quinone loading (mAh per gram of quinone loading),
Figure 4(d), revealed that AQ/AC performed higher capacity, however, the electrode tends to
degrade earlier at high currents compare to the rate capabilities of the PQ/AC and TCHQ/AC
electrodes. The high active surface area particularly exhibited the great capacity response with
excellent rate stability which allows for the shortened electron pathways from the electrolyte to
the current collector. As presented in Table 1, SBET of AQ/AC quite lower than that of PQ/AC
and TCHQ/AC. Furthermore, as the scan rate increases, the diffusion of electrolyte ion into the
internal structure of porous electrode became more difficulty (diffusion limitation) which led to
the capacity decay. Therefore, the active species loading, and surface area of the electrode are the
important factors to improve the electrode performance.
Figure 4 (a) Cyclic voltammetric evolution of quinone/AC at varying scan rates from 0.01 to
0.125 V s-1 (where a1 is AQ/AC, a2 is PQ/AC and a3 is TCHQ/AC), (b) Galvanostatic charge–
discharge curves of quinone/AC at varying current density from 1.0 to 7.0 A g-1 (where b1 is
AQ/AC, b2 is PQ/AC and b3 is TCHQ/AC), (c) Dependence of peak current on square root of
scan rate from cyclic voltammograms of (a1)-(a3), and (d) Comparison of capacity of quinone/AC
samples at different current density.
Figure S7 (ESI) clearly shows redox peak for AQ/AC electrodes which informed to
pseudocapacitor behavior, whereas the CV of PQ/AC and TCHQ/AC show weak redox peak.
Figure 5(a) illustrates the AQ-composite electrode consisting 16 wt% of AQ loading reached
oxidation peak current of 0.009 A, 3 times larger than pristine activated carbon which presents a
quasi-rectangular shape, the electrical double-layer (EDL) characteristic. Figures 5(b) shows
cyclic voltammetry (CV) curves of AQ/AC at a constant current of 1.0 A g-1. At 16 wt% of AQ
loading exhibited longer discharge time than the other ratios and achieved highest specific
capacitance about 485 F g-1 whilst 28 wt% of PQ loading, 30 wt% of TCHQ loading and pristine
AC provided specific capacitance about 161 F g-1,143 F g-1, and 98 F g-1, respectively as shown
in Figure S7 (ESI). The quinone/AC samples with high specific capacitance for each quinone
loading have been selected and further characterized for cyclability testing and electrochemical
impedance, as presented in Figure 5(c) – (d). After 1,000 charge-discharge cycles, AQ/AC
performed highest cyclability with capacitance loss of 1.2%. It can be implied to the advantage
of employing AQ group with pristine carbon that works primarily by EDL characteristic. EIS
measurement in Figure 5(d) shows a semicircle which ascribed to the charge transfer resistance
and constant phase element of the electrodes, and a sloping line following the semicircle which
reflected to the diffusion of ions in the porous electrode. The results demonstrated that all
quinone/AC electrodes possess lower resistances than pristine AC electrode which usually come
from pore tortuosity of AC structure30. From Table 2, the bulk solution resistance (Rs) values are
slightly different with related to a similar diffusion resistance, however, the charge transfer
resistance at electrode-electrolyte (Rct) of quinone/AC was lower than that of pristine AC where
AQ/AC showed lowest Rct value. This result revealed the improvement of conductivity by
quinone loading over pristine AC and demonstrate good properties for supercapacitor
application. Therefore, a possibility of physicochemical transport model was (i) electric double
layer (EDL) formation at the electrode/electrolyte interface, (ii) charge transport in the electrode,
and (iii) ion electrodiffusion. Figure 3(e) shows Ragone plot of all quinone/AC electrodes31. The
energy density in terms of the amount of working material varied from 2 to 8 Wh kg-1
corresponding to a power density from 111 to 265 W kg-1 (detail in Table S2, ESI). The
comparison of quinone/AC electrode characteristics from this work compare to various energy
deliveries or storage systems is presented in Figure S8 (ESI).
Figure 5 (a) CV of AQ/AC electrodes at a scan rate of 0.01 V s-1, (b) GCD of AQ/AC electrodes
at a current density of 1.0 A g-1, (c) Cyclability of supercapacitor, (d) Nyquist plots (The inset
shows the equivalent circuit of a supercapacitor containing double layer capacitor C , charge
transfer resistance Rct, series resistance Rs, and Warburg element W), and (e) Ragone plot of
quinone/AC supercapacitors at various amount of quinones.
Table 2 Resistance value of composite electrode.
Sample Rs (Ω) Rct (Ω)
AC 0.93 16.04
AQ/AC (16%wt.) 1.08 2.25
PQ/AC (28%wt.) 1.45 4.79
TCHQ/AC (30%wt.) 0.98 6.37
At acidic media, two protonation reaction directly affords hydroquinone QH2 as product
(Q + 2H+ +2e- QH2). The quinone derivatives undergo reversible two-electron reduction
during charge-discharge process where AQ was reduced into anthrahydroxyquinone (AHQ), PQ
was reduced into 9,10-phenanthrenehydroquinone (PHQ), and TCHQ was oxidized into
tetrachloro benzoquinone (TCBQ). Therefore, quinone and hydroxyl could enhance the carbon
materials capacity. The theoretical capacity (mAh g of quinone-1) can be calculated by Faraday’s
law32 as presented in Figure 6(a). It was found that the capacity of quinone/AC electrodes were
lower than the theoretical capacity where AQ/AC performed higest capacity with capacity loss of
2.8% for 1000 cycles. The results implied to the stability of AQ/AC electrode was better than
that of the other electrodes.
Self-discharge is an essentially characteristic to measure the voltage drop in the charged
capacitor after a period with no load condition. The prepared electrodes were charged to 1.0 V
with constant current of 10 mA and the charging source was disconnected, and recorded the
voltage drop during the discharge time in the open circuit system. In particular, there is three
self-discharge mechanisms in supercapacitors which are self-discharge due to overvoltage, self-
discharge due to faradaic reactions and self-discharge due to ohmic leakage33. In Figure 6(b),
AQ/AC and AC show the voltage decay whilst voltages of PQ/AC and TCHQ/AC initially
slightly increased after discharged and then slowly voltage decay due to non-uniformly charged
and time dependent charge re-distribution in the porous electrodes. The quinone/AC electrodes
overcome the self- discharge due to faradaic reactions according to the presence of quinone
moieties which are chemically active molecules via redox reaction over the potential range of
study. These redox processes causing self-discharge are diffusion controlled. According to the
experimental results, the equivalent circuit model is presented in Figure 6(c) where C is double
layer capacitor, Rct is charge transfer resistance, Rs is series resistance, and W is Warburg
element).
Figure 6 (a) Theoretic capacity of quinones by Faraday’s law, (b) self-discharge of electrodes,
and (c) model of equivalent circuit.
To confirm the stability of quinone molecules physically interacted on the carbon surface,
the quantum chemical study based on density functional theory (DFT) has been carried out (see
detail in Supplementary Table S3) using the graphene (Gr) model of 120 atoms in size. For all
models studied, the interaction energy (IE) for TCHQ/Gr is -19.6 kcal mol-1 and its weighted IE
regarding its molar mass is -23.3 kcal mol-1. Both AQ/Gr and PQ/Gr have the lower IE of -28
kcal mol-1 with the staggered conformation of AQ with respect to carbon atoms of Gr sheet
(Figure 7). From our computational results, we suggest that either AQ or PQ could be better
stabilized on the Gr surface than TCHQ. The same amount of IE for AQ/Gr and PQ/Gr is due to
the same fashion of aromaticity and the charge-redistribution process of PQ compared with AQ.
However, PQ slightly differs from AQ only at the position of the two carbonyl groups. This
could affect the preferred coordinated position of the co-cations, resulting in the different
electrochemical performance as reported in previous literature34. Our model of AQ/Gr well
agreed with our experimental data from which the highest performance and long-term stability of
electrode. We highlight strong correlation between the computed interaction energy of
quinone/carbon framework and the performance of a fabricated electrode.
Figure 4 Optimized configuration of anthraquinone (AQ) on graphene (Gr) surface: (a) top view
and (b) side view.
4. Conclusions
Activated carbon (AC) from coconut shell, surface area of 764.09 cm2 g-1, was successfully
functionalized with various quinone derivatives (AQ, PQ or TCHQ) via sublimation method for
supercapacitor application. High loading amount of quinone effected to the pore structure of AC.
The supercapacitor containing AC modified AQ (AQ/AC) achieved higher specific capacitance
than other quinone derivates loaded over AC. At 25% wt. of AQ loaded over AC, the
supercapacitor performed specific capacitance about 485 F g-1 at current density of 1.0 A g-1,
resistance of 2.25 Ω and exhibited high cyclability which loss specific capacitance 1.18% after
1000 charge-discharge cycles, however rapidly decay of self-discharge has been observed. Our
experimental data is in good agreement with the computational results of quinone adsorption on
graphene surface; the lowest interaction energy (IE) of -28.0 kcal mol-1 was obtained for AQ
loading model. Hence, the modified AC successfully prepared by a solvent-free method which
could be further developed as low-cost and environmentally friendly electrode materials for
high-performance supercapacitors.
Supporting information.
Supplementary Figures S1–S8
Supplementary Tables S1–S3
AUTHOR INFORMATION
Corresponding Author
(S.K.) E-mail: [email protected]
Author Contributions
NT conceived the experiments, synthesized and characterized the composites based on
discussion with SK. CS and SK provided instrument and laboratory equipment. NC characterized
XPS. PJ and RB simulated the molecular modeling. KN measured EIS and SDC. SK wrote the
manuscript, responded to the reviewer, revised and finalized the manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGEMENTS
The authors gratefully acknowledge the financial supported by Energy Promotion and
Conservation Fund and National Science and Technology Development Agency (P-17-50509)
and Thammasat University Research Fund under the TU Research Scholar, contract no.
2/49/2561. Instrument support from Center of Scientific Equipment for Advanced Science
Research, Office of Advanced Science and Technology, Thammasat University. XPS
measurement from the SUT-NANOTEC-SLRI joint research facility at the Synchrotron Light
Research Institute (Public Organization). The assistance given by IT Services and the use of the
Computational Shared Facility at The University of Manchester; the Science Cloud Project at
Department of Computer Science, Faculty of Science and Technology, Thammasat University
and National e-Science Infrastructure Consortium.
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