{One-step synthesis of mesoporous carbon/ iron sulfide nanocomposite for supercapacitors}


doi:10.5599/jese.572  55 

J. Electrochem. Sci. Eng. 9(1) (2019) 55-62; DOI: http://dx.doi.org/10.5599/jese.572 

 
Open Access: ISSN 1847-9286 

www.jESE-online.org 
Original scientific paper 

In-situ synthesis of mesoporous carbon/iron sulfide 
nanocomposite for supercapacitors 

Xiaolong Yu, Bogang Li  

College of Materials Science and Engineering, Sichuan University, Chengdu 610065, China 

Corresponding author: E-mail libogang@scu.edu.cn  

Received: August 7, 2018; Revised: October 20, 2018; Accepted: October 21, 2018 
 

Abstract 
Mesoporous C@FexSy composite as a negative electrode for supercapacitors was 
synthesized via a one-step hydrothermal treatment followed by an electrodeposition 
process and its electrochemical properties were studied. Compared with bare carbon 
sphere, the electrochemical performance of C@FexSy composite was significantly improved, 
with a high specific capacitance (267.45 F/g), good rate performance (201.08 F/g at 2.5 
A/g), and superior cycling stability (almost no capacitance degradation after 1000 cycles). 
The results show that the obtained C@FexSy composite is a promising negative electrode 
material for supercapacitors. 

Keywords 
Carbonaceous materials; porous structure; hydrothermal treatment; electrochemical properties; 
energy storage 

 

Introduction 

Supercapacitors have attracted tremendous attention in recent years owing to their high power 

density, short charging time, and good stability [1–3]. Carbonaceous materials have been widely 

adopted as negative electrode materials for supercapacitors because of their low cost, good 

electrical conductivity, and long cycle lifetime. However, carbonaceous materials exhibit limited 

double-layer capacitance, which limits further development of high energy density supercapacitors 

[4,5]. One of the effective approaches to enhance the energy density of supercapacitors is to 

improve the specific capacitance of carbonaceous materials [6–8]. 

Carbon spheres (CS) with their large surface area, high porosity, and fine pore size is a promising 

carbonaceous material for supercapacitors. Nevertheless, the low capacitance of CS limits its 

practical applications [9,10]. To improve the capacitance, researchers have recently focused on 

developing new negative electrode materials by activation pretreatment, doping modification, and 

loading of metal-base materials [5,11–13]. Among the metal-base materials, Fe-based materials are 

http://dx.doi.org/10.5599/jese.
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J. Electrochem. Sci. Eng. 9(1) (2019) 55-62 MESOPOROUS CARBON/IRON SULFIDE NANOCOMPOSITE 

56  

promising candidates because of their suitable working window in negative potential, abundance, 

low cost, large theoretical capacitance, and nontoxicity [14–17]. Fe-based materials are combined 

with carbonaceous materials to explore an effective method to prepare composites; this not only 

could improve the rate performance of Fe-based materials, but also enhance the specific 

capacitance of carbonaceous materials. 

In this work, CS was grown in situ on nickel foam (NF) using a one-step hydrothermal process, 

and iron sulfide was selected as Fe-based material. A new approach was found to synthesize 

C@FexSy composite by using the cyclic voltammetry (CV) electrochemical deposition method to 

introduce iron sulfide onto CS. The electrical performance of C@FexSy was investigated, and the 

results indicated that the C@FexSy composite exhibited a significantly improved electrochemical 

performance than bare CS. The findings of this study would open up new possibilities for the design 

of carbon-based composites for high-performance supercapacitors. 

Experimental  

Materials 

Commercial NF was used as the current collector. Anhydrous dextrose, FeCl3·6H2O, thiourea, and 

the other reagents in this experiment were used without further purification. Deionized water was 

used to prepare solutions. 

Synthesis of carbon spheres 

The CS was prepared by hydrothermal treatment. NF (2×4 cm2) was treated with hydrochloric 

acid (3 mol/L), acetone, and absolute ethanol in an ultrasound bath for 10 min, respectively, and 

then washed with deionized (DI) water. Anhydrous dextrose (10.8 g) was dispersed in 60 ml of DI 

water and stirred at 25 C until a clear solution was obtained. The solution was transferred into a 

100 ml Teflon-lined autoclave. A piece of NF was placed vertically in the Teflon-lined stainless-steel 

autoclave, soaked in the solution, at 180 C for 4 h. Subsequently, CS precursors were formed on 

the NF. Then, the product was washed with DI water followed by vacuum drying at 60 C for 12 h 

and heat treatment at 800 C for 1 h in a N2 atmosphere to remove oxygen-containing groups on 

the surface of the CS. 

Synthesis of C@FexSy composite 

C@FexSy was obtained through an electrochemical deposition method. The experiment was 

carried out using an electrochemical workstation with a three-electrode cell. CS grown on NF was 

used as the working electrode, and a platinum plate and a saturated calomel electrode (SCE) were 

used as the counter electrode and the reference electrode, respectively. FeCl3·6H2O (1, 1.5, 2, 2.5, 

and 3 mmol) and thiourea (5 mmol) dissolved in 100 ml DI water was used as the deposition bath. 

The deposition process was carried out via CV at 5 mV/s for 6 cycles in the voltage range of -1.2 to 

0.2 V. The as-prepared C@FexSy composites with 1, 1.5, 2, 2.5, and 3 mmol of FeCl3·6H2O are 

henceforth referred to as C@FexSy-1, C@FexSy-1.5, C@FexSy-2, C@FexSy-2.5, and C@FexSy-3, 

respectively. The as-prepared C@FexSy-n (n = 1, 1.5, 2, 2.5, and 3) was then carefully rinsed with DI 

water and dried in a vacuum oven at 60 C for 12 h. 

Characterization and electrochemical measurements 

The morphology and the microstructure were observed by scanning electron microscopy (SEM, 

Hitachi, S-4800). The crystal structure was characterized using an X-ray diffraction (XRD, Rigaku) 

system with Cu K irradiation. The chemical composition of the sample was investigated by X-ray 



X. Yu and B. Li J. Electrochem. Sci. Eng. 9(1) (2019) 55-62 

doi:10.5599/jese.572 57 

photoelectron spectroscopy (XPS, ESCALAB 250Xi, Thermo Scientific). The structure of C@FexSy-2 

was further explored by Raman spectroscopy (Renishaw Invia RM200). The Brunauer-Emmett-Teller 

(BET; Gemini VII) specific surface areas of the samples were determined from N2 adsorption data in 

the relative pressure ranging from 0.1 to 1.0. 

Electrochemical characterization was carried out using a CHI 660D electrochemical workstation 

(Chenhua, Shanghai) at 25 C. The electrochemical characterization includes CV, galvanostatic 

charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS), using a three-electrode 

cell with 3.0 M KOH as the electrolyte, materials grown on NF (1×1 cm2) as the working electrode, 

Hg/HgO as the reference electrode, and Pt foil as the counter electrode. CV was performed in the 

voltage window from -1 V to 0 V at scan rates of 5, 10, 20, 30, and 50 mV/s. GCD was carried out 

between -0.95-0 V at current densities of 0.25, 0.5, 1.0, 1.5, 2.0, and 2.5 A/g. EIS was evaluated in 

the frequency range of 105 to 0.01 Hz. The DC potential and the AC amplitude for EIS measurements 

are -0.01 V and 5 mV, respectively. 

Results and discussion 

Morphology and structural analysis 

The SEM images of CS and C@FexSy-2 are presented in Figure 1. Highly dense CSs are distributed 

on the NF substrate (Figure 1a). These CSs exhibit smooth surfaces and they are connected with 

each other. This provides high volumetric specific surface area and good mass transport property, 

which are useful for supercapacitor application. The size distribution of the carbon particles is within 

the range of 1-2 μm. Figure 1b shows that the C@FexSy-2 composite maintains the spherical 

structure, and many FexSy nanoparticles are dispersed on the surface of the carbon particles. This 

provides a large surface area for easy diffusion of the electrolyte toward the electrode surface and 

contributes to the enhancement of specific capacitance. 

 

 
Figure 1. (a) SEM image of the carbon spheres/NF. (b) SEM image of C@FexSy-2/NF. 

The XRD patterns of CS and C@FexSy-2 (Figure 2a) showed similar characteristics. A broad 

diffraction peak is observed at approximately 2 = 23 besides peaks of Ni, corresponding to (002) 

plane of graphitic structure. The decreased peaks for C@FexSy-2 indicate the amorphous nature of 

FexSy. Figure 2b shows the Raman spectrum of the CS and C@FexSy-2 samples. Both of them exhibit 

two characteristic peaks at 1345 and 1597 cm-1, corresponding to D peak from amorphous structure 

of carbon and G peak from graphitic structure of carbon, respectively[18,19]. The ID/IG ratio of 

C@FexSy-2 is 0.97, a little higher than 0.90 of CS, which indicates the C@FexSy-2 has a small number 

of defects. The XPS data of C@FexSy-2 are shown in Figure 2c-d. The peaks at approximately 723 eV 



J. Electrochem. Sci. Eng. 9(1) (2019) 55-62 MESOPOROUS CARBON/IRON SULFIDE NANOCOMPOSITE 

58  

(Fe 2p1/2), 713 eV (Fe 2p3/2) and 164 eV in the Fe 2p spectra and the S 2p spectra are assigned to 

amorphous iron sulfide [20,21]. These results are in good agreement with the SEM observations and 

further confirm the presence of C@FexSy-2 on the composite electrode. 
 

 
Figure 2. (a) XRD patterns of CS/NF and C@FexSy-2/NF electrode. (b) Raman spectra of CS and 

C@FexSy-2. (c)-(d) Fe 2p and S 2p XPS spectra of C@FexSy-2, respectively. 

The nitrogen adsorption-desorption isotherms and Brunauer-Joyner-Halenda (BJH) pore 

diameter distribution of C@FexSy-2 are shown in Figure 3. The sample exhibits a typical type IV 

isotherm and shows a hysteresis loop at medium relative pressure (Figure 3a), which reveals the 

existence of relatively mesoporous pores. The hysteresis loop exhibits H2 type characteristics, 

indicating that the sample has a wide pore size distribution. The BET surface area of C@FexSy-2 is 

117.74 m2/g. The BJH pore diameter distribution of C@FexSy-2 (Figure 3b) shows that the pore 

diameter distribution is within the range of 5-10 nm, which further demonstrates that the sample 

has a mesoporous structure. From the above results, it is evident that the C@FexSy-2 electrode 

material has a high specific surface area, and the mesoporous structure could facilitate infiltration 

of the electrolyte and shorten electron and ion transport distances during energy storage. This 

would increase the surface utilization of the active material and improve the capacitance of the 

electrode material. 
 



X. Yu and B. Li J. Electrochem. Sci. Eng. 9(1) (2019) 55-62 

doi:10.5599/jese.572 59 

 
Figure 3. (a) BET of C@FexSy-2. (b) Pore diameter distribution of C@FexSy-2. 

Electrochemical performance analysis 

The electrochemical performance of the composites was estimated by CV and GCD 

measurements. Figure 4a shows the GCD curves of CS and C@FexSy-n (n = 1, 1.5, 2, 2.5, and 3) at a 

current density of 0.25 A/g. The charge/discharge curves are nearly linear in shape, indicating ideal 

electrical double-layer capacitive behavior. The symmetric triangle characteristics reveal the excel-

lent electrochemical reversibility of the samples with high Coulombic efficiency. The C@FexSy-2 

sample exhibited the longest charge-discharge time, and hence, the largest specific capacitance. The 

specific capacitance derived from galvanostatic tests can be determined using the following 

equation [22]: 






I t
C

m V
 (1) 

where C is the specific capacitance, I is the discharge current (A), ∆t is the discharge time, m is the 

mass of active materials loaded on the working electrode, and ∆V is the potential window. 
 

 
Figure 4. (a) GCD curves of CS and C@FexSy-n (n = 1, 1.5, 2, 2.5, and 3) at a current density of 

0.25 A/g. (b) Specific capacitances of CS and C@FexSy-n based on the GCD curves. (c) CV curves 
of CS and C@FexSy-2 at a scan rate of 20 mV/s. 



J. Electrochem. Sci. Eng. 9(1) (2019) 55-62 MESOPOROUS CARBON/IRON SULFIDE NANOCOMPOSITE 

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As plotted in Figure 4b, all the C@FexSy samples exhibit a higher specific capacitance than the CS 

electrode (158.01 F/g); C@FexSy-2 has the highest specific capacitance of 267.45 F/g at 0.25 A/g. It 

is considered that the loading mass of FexSy affected the capacitance, and C@FexSy-2 has the 

optimum loading mass. The reason might be that FexSy deposited on the surface of CS provides a 

porous structure, which further increases the specific surface area of the electrode material and 

thus enhances the capacitance. However, owing to the poor conductivity of Fe-base materials, when 

the loading mass of FexSy further increases, the capacitance of the electrode material decreases. 

Figure 4c shows the CV curves of CS and C@FexSy-2 at a scan rate of 20 mV/s. As expected, the 

C@FexSy-2 composite shows a much higher capacitance than CS. 

The electrochemical performance of C@FexSy-2 for supercapacitor applications was investigated 

in KOH solution with a three-electrode system. As shown in Figure 5a, CV test was carried out at 

various scan rates of 5-50 mV/s. The quasi-rectangular shape of the CV curves with an obvious hump 

shape indicates the effect of electrical double-layer capacitance. Moreover, the rectangular shape 

of the curve even at a high scan rate of 50 mV/s suggests the outstanding capacitive behavior and 

high ionic conductivity of C@FexSy-2. The inconspicuous redox peaks may be induced by FexSy. These 

results demonstrate that C@FexSy-2 provides numerous accessible pores and paths for ion transfer. 

Figure 5b-c show the discharge curves of C@FexSy-2 and CS at different current densities. All the 

curves exhibited excellent linear response, implying the ideal electric double-layer capacitive 

behavior of the samples. It is evident from Figure 5d that C@FexSy-2 has a much higher capacitance 

than CS at all current densities. Remarkably, the C@FexSy-2 electrode exhibited capacitance 

retention of 75 % when the current density was increased from 0.25 to 2.5 A/g, indicating its 

outstanding rate capability. 

The cycling stability of C@FexSy-2 was evaluated for 1000 cycles at a high charging-discharging 

current density of 2.5 A/g. As shown in Figure 5e, the C@FexSy-2 electrode does not show 

capacitance degradation, and the charge/discharge curves in the last ten cycles are almost identical 

to those in the first ten cycles. After 1000 cycles, the capacitance retention of the C@FexSy-2 

electrode is even 103 % of the initial capacitance, indicating its superior cyclic performance. The 

reason for the slight increase in the capacitance may be the gradual entry of the electrolyte into the 

inner micropores of the C@FexSy-2 electrode after several cycles, which increases the contact area 

of the electrode and electrolyte, thus enhancing the capacitance. 

EIS was used to gain a deep understanding of the rate capability of the C@FexSy-2 electrode. 

Figure 5f shows the Nyquist plots of C@FexSy-2 and CS. It can be seen that the Nyquist plot is mainly 

composed of two parts: a semicircle in the high frequency range and a vertical line in the low 

frequency region. The inset in Figure 5f shows the magnified portion of the Nyquist plot near the 

origin, providing more details on the electrode impedance behavior. The x-intercept of the high 

frequency semicircle provides the value of equivalent series resistance (Rs) of the electrochemical 

system [23,24]. It is observed that the Rs values of C@FexSy-2 and CS are 0.60 and 0.71 Ω, 

respectively. The diameter of the high frequency semicircle corresponds to the charge transfer 

resistance (Rct). The Rct of C@FexSy-2 and CS was calculated to be 0.12 and 0.50 Ω, respectively. As 

for C@FexSy-2, the low resistances are associated with FexSy nanoparticles on the carbon substrate, 

which provide a larger electrolyte/electrode interface, facilitating the electrode material wetting 

and the ion transfer. The Nyquist plot of C@FexSy-2 exhibits an obvious Warburg 45° line region, 

corresponding to the semi-infinite ion diffusion resistance, which reflects a lower ion diffusion rate 

within the porous C@FexSy-2 electrode [25,26]. In the low-frequency region, the straight line 

represents the good capacitive behavior of the electrode and the more parallel to the virtual axis, 



X. Yu and B. Li J. Electrochem. Sci. Eng. 9(1) (2019) 55-62 

doi:10.5599/jese.572 61 

the closer to the double-layer capacitance [27]. The Nyquist plot in the low frequency range of 

C@FexSy-2 shows a less vertical line, which is an indication that C@FexSy-2 has diffusion-controlled 

faradaic processes due to the higher contribution of Warburg impedance [28-30]. 
 

 
Figure 5. (a) CV curves of C@FexSy-2 at different scan rates. (b)-(c) GCD curves of C@FexSy-2 

and CS at different current densities, respectively. (d) Specific capacitance of C@FexSy-2 and CS 
at different discharge current densities. (e) Cycling performance of the C@FexSy-2 electrode at 

a current density of 2.5 A/g. (f) Electrochemical impedance spectra of C@FexSy-2 and CS. 

Conclusions 

In this study, a mesoporous negative electrode C@FexSy composite was successfully fabricated 

on NF using a hydrothermal method followed by an electrodeposition treatment. The 

electrochemical performance of the C@FexSy-2 electrode was significantly higher than that of bare 



J. Electrochem. Sci. Eng. 9(1) (2019) 55-62 MESOPOROUS CARBON/IRON SULFIDE NANOCOMPOSITE 

62  

CS. The hybrid electrode demonstrated a high specific capacitance (up to 267.45 F/g), good rate 

performance (201.08 F/g at 2.5 A/g), and superior cycling stability (almost no capacitance 

degradation after 1000 cycles). The excellent electrochemical behavior could be attributed to the 

unique hybrid electrode design and the enhancement in the surface area. The present study 

provides an adaptable method for novel design of negative electrode materials for supercapacitors, 

extending the potential applications of carbon-based devices. 

Acknowledgements: The authors greatly appreciate the support of Xinyue Huang, Xingye Tong, and 
Xiaoming Tu. 

References 

[1] X. Yuan, B. Tang, Y. Sui, S. Huang, J. Qi, Y. Pu, F. Wei, Y. He, Q. Meng, P. Cao, Journal of Materials Science: 
Materials in Electronics 3 (2018) 1-13. 

[2] P. Simon, Y. Gogotsi, Nature Materials 7 (2008) 845-854. 
[3] S. Liu, L. Wang, C. Zheng, C. Qidi, M. Feng, Y. Yu, ACS Sustainable Chemistry & Engineering 5 (2017) 9903-

9913. 
[4] B. Lv, P. Li, Y. Liu, S. Lin, B. Gao, B.-Z. Lin, Applied Surface Science 437 (2017) 169-175. 
[5] N. Syarif, IA. Tribidasari, W. Wibowo, Journal of Electrochemical Science & Engineering 3(2) (2013) 37-45. 
[6] H. Zhang, X. Zhang, Y. Ma, Electrochimica Acta 184 (2015) 347-355. 
[7] X. Yang, H. Ma, G. Zhang, Langmuir : The ACS Journal of Surfaces and Colloids 33 (2017) 3975-3981.  
[8] J. Pang, W. Zhang, H. Zhang, J. Zhang, H. Zhang, G. Cao, M. Han, Y. Yang, Carbon 132 (2018) 280-293. 
[9] T. Liu, L. Zhang, W. You, J. Yu, Small 14 (2018) 1702407. 

[10] J.-G. Wang, H. Liu, H. Sun, W. Hua, H. Wang, X. Liu, B. Wei, Carbon 127 (2017) 85-92. 
[11] D. Iglesias, E. Senokos, B. Aleman, L. Cabana, C. Navío, R. Marcilla, M. Prato, J. J. Vilatela, S. Marchesan, 

ACS Applied Materials & Interfaces 10 (2018) 5760-5770. 
[12] X. Xia, Y. Zhang, Z. Fan, D. Chao, Q. Xiong, J. Tu, H. Zhang, H. Jin Fan, Y. X Xia, D. Zhang, J. Chao, Fan, Q. X 

Xia, J. Xiong, Tu, Z. H Fan, Zhang, Advanced Energy Materials 5 (2014) 1-9. 
[13] J. Tang, J. Wang, L. Shrestha, S. Hossain, Z. Alothman, Y. Yamauchi, K. Ariga, ACS Applied Materials & 

Interfaces 9 (2017) 18986-18993. 
[14] J. Ma, X. Guo, Y. Yan, H. Xue, H. Pang, Advanced Science 5 (2018) 1700986. 
[15] Y. Zhang, R. Lin, Y. Fu, X. Wang, X. Yu, J. Li, Y. Zhu, S. Tan, Z. Wang, Materials Letters (2018) 9-12. 
[16] Y. Zhong, J. Liu, Z. Lu, H. Xia, Materials Letters 166 (2015) 223-226. 
[17] M.A. Azam, R.N.A.R. Seman, M.A. Mohamed, Advances in Natural Sciences: Nanoscience and 

Nanotechnology 7(4) (2017) 1-10. 
[18] J. Wu, H. Xu, J. Zhang, Acta Chimica Sinica 72(3) (2014) 301-318. 
[19] T. Jawhari, A. Roid, J. Casado, Carbon 33(11) (1995) 1561-1565. 
[20] J. Feng, L.T. Peckler, A.J. Muscat, Crystal Growth & Design 15 (2015) 3565-3572. 
[21] V. Sridhar, H. Park, Journal of Alloys and Compounds 732 (2017) 799-805. 
[22] N. Zhang, C. Fu, D. Liu, Y. Li, H. Zhou, Y. Kuang, Electrochimica Acta 210 (2016) 804-811. 
[23] J.-G. Wang, Y. Yang, Z.-H. Huang, F. Kang, Carbon 61 (2013) 190-199. 
[24] H. Yoo, J. Hyun Jang, J. Heon Ryu, Y. Park, S. M. Oh, Journal of Power Sources 267 (2014) 411-420. 
[25] J.-G. Wang, Z. Zhang, X. Zhang, X. Yin, X. Li, X. Liu, F. Kang, B. Wei, Nano Energy 39 (2017) 647-653.  
[26] J. Gao, X. Wang, Y. Zhang, J. Liu, Q. Lu, M. Liu, Electrochimica Acta 207 (2016) 266-274. 
[27] W. Zhang, C. Xu, C. Ma, G. Li, Y. Wang, K. Zhang, F. Li, C. Liu, Advanced Materials 29(36) (2017) 1701677. 
[28] M.R. Lukatskaya, B. Dunn, Y. Gogotsi, Nature Communications 7 (2016) 12647. 
[29] J. Liu, J. Wang, C. Xu, H. Jiang, C. Li, L. Zhang, Advanced Science 5(1) (2018) 1700322. 
[30] X. Du, C. Wang, M. Chen, Y. Jiao, The Journal of Physical Chemistry C 113(6) (2009) 2643-2646. 

 
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