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Vol. 8. Issue 5.
Pages 4227-4238 (September - October 2019)
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Vol. 8. Issue 5.
Pages 4227-4238 (September - October 2019)
DOI: 10.1016/j.jmrt.2019.07.033
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Fabrication of manganese oxide@nitrogen doped graphene oxide/polypyrrole (MnO2@NGO/PPy) hybrid composite electrodes for energy storage devices
Sivalingam Ramesha, Hemraj M. Yadavb, K. Karuppasamyc, Dhanasekaran Vikramanc, Hyun-Seok Kimc, Joo-Hyung Kimd,
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Corresponding authors.
, Heung Soo Kima,
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Corresponding authors.
a Department of Mechanical, Robotics and Energy Engineering, Dongguk University-Seoul, Pildong-ro 1 gil, Jung-gu, Seoul 04620, Republic of Korea
b Department of Energy Engineering, Dongguk University-Seoul, Pildong-ro 1 gil, Jung-gu, Seoul 04620, Republic of Korea
c Division of Electronics and Electrical Engineering, Dongguk University-Seoul, Pildong-ro 1 gil, Jung-gu, Seoul 04620, Republic of Korea
d Department of Mechanical Engineering, Inha University, Inha-ro 100, Nam-gu, Incheon 22212, Republic of Korea
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The highly efficient hydrothermal chemical reaction was used to synthesis the manganese oxide@nitrogen doped graphene oxide/polypyrrole (MnO2@NGO/PPy) composites as a high capacitance electrode material for supercapacitors. The prepared composites structural and surface properties were confirmed by spectral and electron microscopic studies, respectively. The electrochemical cyclic voltammetric analysis carried out for MnO2@NGO and MnO2@NGO/PPy electrodes using potassium hydroxide electrolyte. The improved capacitance of 480 F.g−1 exhibited for MnO2@NGO/PPy hybrid electrode compared with 360 F.g-1 for MnO2@NGO electrode at 0.5 A. g−1 current density. The better cycling and rate retention properties exposed for MnO2@NGO/PPy hybrid electrode. Hence, the observed results suggested that MnO2@NGO/PPy electrodes offer promising uses for the high-performance supercapacitor.

N-doped GO
hybrid composites
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In the recent decades, supercapacitors have been considering as the most significant energy storage devices because of their high power density, long cycling stability and low cost fabrication process [1]. The requirement of high power density supercapacitors for handy electronic devices has directed to study numerous active electrode materials, which are including conducting polymer and nanostructured carbon based metal oxide materials [1–4]. Supercapacitors are classified into two categories depend on their storage properties through the electrochemical reaction such as double layer capacitance and pseudo capacitance, whereas the first case stored the energy between the electrode and electrolyte and the latter case used the electro sorption of surface by redox reactions [2,5,6]. Recently, research has been extended to focus the development of next generation portable electronics using supercapacitors with environmental friendly materials [7,8]. The active electrode materials are need to be offered the rapid reversible and electron transfer mechanism between the electrolyte and electrode in the electrochemical analysis which are prerequisite for high-performance supercapacitor charging-discharging properties [8–10]. Carbon and their derivative materials are broadly considered as the active electrode materials for electrochemical applications, because of their large surface area, charge carrier mobility, and excellent conductivity [8,11,12]. Among them, graphene oxide (GO) is an excellent conductivity and electrocatalytic material and numerous research groups are elaborately studied their uses in supercapacitor and sensor applications [13,14]. GO materials have been synthesized through the hydrothermal, nitrogen plasma, chemical vapor deposition, arc discharge, and ammonization processes [15–19]. Further to develop the GO based materials activity, electron donating or withdrawal atoms, such as nitrogen (N), boron, sulphur, and oxygen atoms, are used to dope with GO to achieve the superior electrochemical properties [20,21]. The nitrogen doped GO (NGO) materials were prepared through the chemical modification process via “N” atom doping into GO matrix for supercapacitors [22,23]. Moreover, the selective d-block metals and their oxides such as manganese dioxide (MnO2), cobalt oxide, zirconium oxide, nickel oxide, ferrous oxide, vanadium oxide, and tin oxide have been used as the well-established active electrodes for high capacitance supercapacitors owing to their pseudo capacitive behavior [17,19,23–25]. In particular, MnO2, having high theoretical capacitance and lesser toxicity, is an excellent electrode material for electrochemical applications. The nanocrystalline structured MnO2 has constructed with octahedral structure and it can be produced the different morphological properties and crystallographic structure to tune the electrochemical properties via composites formation or doping process [26–28]. The highly active carbon nanotube (CNT)/MnOx composites were prepared by electrodeposition process with superior capacitance properties [29]. Furthermore, the conductive polymers such as polythiophene, polydiaminodiphenyl sulphone, polyaniline, polypyrrole (PPy), and their derivatives are widely used as the active electrodes for supercapacitor applications [24,30,31]. In situ chemically derived CNT/polypyrrole/MnO2 composites cyclic voltammetric (CV) curves revealed the specific capacitance of 281 F.g-1 at 200 mV.s-1, with an excellent stability of 88% retention up to 10000 cycles [32]. Self-assembled reduced-GO/MnO2/PPy film produced the better capacitance properties by CV analysis for supercapacitors. Recently, numerous studies have been conducted to study the synergistic properties of MnO2 and PPy in the hybrid composite for its excellent specific capacitance and cyclic stability [7,32,33]. The nitrogen doped carbon derivatives with PPy nanocomposite materials enhanced the specific capacitance and cyclic stability for the high-performance supercapacitor [15,34–36]. Hence, in this work is focused to synthesis the MnO2@NGO and MnO2@NGO/PPy as the electrode materials for supercapacitor applications. The prepared hybrid composite electrodes structurally confirmed by various spectral and microscopic analyses. The detailed electrochemical measurements such as CV, galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) were used to establish the supercapacitance properties of prepared hybrid composites.


Graphite flakes, manganese (III) acetate dehydrate (Mn(CH3COO)2), potassium permanganate (KMnO4), sulfuric acid (H2SO4), pyrrole, ammonium hydroxide (NH4OH), sodium nitrate (NaNO3), ferric chloride (FeCl3), hydrogen peroxide (H2O2), potassium hydroxide (KOH), N-methyl-2-pyrrolidone, and polytetrafluorethylene (PTFE) chemicals were purchased from the Aldrich Chemical, South Korea.

2.2Nitrogen doped graphene oxide (NGO) synthesis

The GO materials was synthesized by an improved Hummers method with the slight modification as reported in the previous works [13,37]. In brief, the 30 g of graphite flakes, 300 mL of H2SO4, and 7 g of NaNO3 were mixed in the conical flask with an ice bath at 0 °C. Then, KMnO4 (6 g) was added, and the bath solution was temperature raised to 50 °C with continuous stirring for 12 h. The resultant product was filtered, and washed using ethanol and water several times. Finally, the GO was dried in vacuum oven at 50 °C for 24 h. For NGO preparation, 3 g of as-prepared GO was dispersed in 300 mL of water by using sonication for 4 h to obtain a homogeneous solution. Then, the GO solution was filtered by using millipore filter, and dried in oven at 95 °C for 12 h. The purified GO solution and 10 mL of urea (1 g) and ammonia (1 g) were mixed, and stirred constantly at 95 °C for 12 h with uniform dispersion. The resulted solution was dry in oven at 180 °C for 12 h, and purified by using ethanol solvent. After that, the resulted product was subjected to calcination at 200 °C for another 12 h, and the final NGO product was collected, used for further experiments.

2.3Synthesis of MnO2@NGO and MnO2@NGO/PPy composites2.3.1Pyrrole to polypyrrole (Oxidative polymerization)

Firstly, 6 g of pyrrole, and 1.5 g of FeCl3 and 10 mL of H2O2 were mixed into 100 mL of double distilled water in the flask, and stirred for 4 h at room temperature. Then, solution mixture was allowed to oxidative polymerization by heating process at 90 °C for 2 h. After that, the resultant product of pyrrole monomer polymerized polypyyrole was collected.

2.3.2MnO2@NGO composites

Synthesized NGO (0.6 g), Mn(CH3COO)2 (0.01 M) and KMnO4 (0.01 M) were, liquefied solutions using millipore water, poured into 500 mL three-neck vessel. Then, 25 mL of NH4OH solution was added, and allowed to stir continuously at 95 °C for 12 h. Thereafter, the whole reaction solution was transferred into 300 mL teflon-lined autoclave, and heated at 180 °C for 12 h. The resultant product was cleansed using millipore water, and the samples dried at 95 °C. The collected composite was further annealed for 10 h at 450 °C in vacuum furnace, and purified by water and ethanol solutions. Finally, the MnO2@NGO composites was collected and kept in desiccator for further use.

2.3.3MnO2@NGO/PPy hybrid composites

For the synthesis of MnO2@NGO/PPy hyrbid composites, as-synthesized NGO (0.6 g), polymerized polypyrrole, Mn(CH3COO)2 (0.01 M) and KMnO4 (0.01 M) were mixed into 500 mL three-neck vessel. Then, the above mentioned similar procedure was followed to prepare the MnO2@NGO/PPy hybrid composites. The MnO2@NGO/PPy hybrid composite was collected and stored in vacuum desiccator for further analysis and characterization.

2.4Fabrication of working electrodes and electrochemical measurements

For the supercapacitor working electrode fabrication, the prepared MnO2@NGO and MnO2@NGO/PPy hybrid composites were used. Initially, the prepared composites, carbon black and PVDF with the weight ratio of 70:20:10 were used to make slurry using N-methyl-2-pyrrolidone as solvent. The resultant slurry was coated onto nickel wire foam and then dried at 95 °C for 24 h.

The electrochemical studies were executed in a symmetrical three-electrode using Versa STAT3 electrochemical workstation, Princeton, USA. The prepared MnO2@NGO and MnO2@NGO/PPy composites working electrodes were used to characterize CV, GCD, and EIS analyses. CV studies performed at different scan rates such as 10, 30, 50, 70, 90, and 100 mV.s-1 with the potential range of 0.0 - 0.5 V. GCD analysis measured at various current density such as 0.5, 1.0, 1.5, 2.0, and 2.5 A.g-1 with the constant potential range of 0.0 - 0.5 V. EIS analysis carried out in the frequency range 0.1 Hz - 100 kHz with open circuit potential for supercapacitors.

2.5Materials characterization

The prepared composites were characterized by RM200 confocal Raman spectroscopy with the spectral range of 0-3500 cm-1. X-ray diffraction (XRD) patterns of the composite were acquired by Rijeka Rotaflex (RU-200B), with Cu Kα radiation. The morphological properties of the composites were characterized using Hitachi S-4800 scanning electron microscopy (SEM) and JEM-2010 F field emission transmission electron microscopy (FE-TEM). The elemental composition of the prepared composites were studied by X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi, USA).

3Results and discussion

MnO2@NGO and MnO2@NGO/PPy composites were successfully prepared by hydrothermal reaction. Schematic structure for the preparation of MnO2@NGO/PPy composites is illustrated in the Fig. 1.

Fig. 1.

Schematic preparation of MnO2@NGO/PPy hybrid composites by the simple hydrothermal process.

3.1Structural studies

Raman scattering is an important tool to validate the carbon based hybrid composites materials [8]. For the confirmation of NGO formation, Raman spectrum inserts in the Fig. 2a. From the pure NGO Raman spectrum, two prominent peaks represent D (disordered carbon atoms) and G (sp2 carbon atoms) mode of vibrations at 1342 cm-1 and 1579 cm-1, respectively along with the 2D peak at 2684 cm-1 are established the formation. Fig. 2a-b show the Raman spectral curves of MnO2@NGO and MnO2@NGO/PPy composites, respectively. For MnO2@NGO (Fig. 2a), the Raman scattering peak observes at 644 cm-1 which belongs to Ag mode vibrations of octahedral crystalline nature of MnO2 in the composite [38]. In addition, the small hump exhibits at around 359 cm-1 due to bending mode of vibration of α-MnO2. There is no separate mode of vibrations exhibited for NGO in MnO2@NGO. For MnO2@NGO composites (Fig. 2b), Raman peaks are at 193,479, 528, 625 ad 692 cm-1 due to metal-oxygen bonding which consisted with the previous literature [39]. Also, there is no additional peaks due PPy and NGO separately exhibited. These observations may be due to dominant behavior of MnO2 structure [13].

Fig. 2.

Raman scattering spectra of (a) MnO2@NGO (inset: pure NGO spectrum) and (b) MnO2@NGO/PPy hybrid composites.


Fig. 3 depicts the XRD patterns of MnO2@NGO and MnO2@NGO/PPy hybrid composites. The observed XRD results are revealed the tetragonal phase polycrystalline structured MnO2 (JCPDS: 44-0141) [40,41]. The XRD peaks are at 12.62°, 26.98°, 28.92°, 36.24°, 37.49°, 38.48°, 40.25°, 42.45°, 45.54°, 47.72°, 51.11°, 55.62°, 62.89°, 65.65° and 69.73° corresponds to the (110), (220), (310), (400), (211), (330) (420), (301), (321), (510), (411), (600), (521), (002) and (541) planes, respectively, for the tetragonal MnO2 in the MnO2@NGO composites. The observed diffraction peaks at 23.5° and 25.5° represents the disordered stacked NGO sheets in the MnO2@NGO composites [13]. For MnO2@NGO/PPy hybrid composites, the peaks are at 18.05°, 28.40°, 31.02°, 33.03°, 36.12°, 38.26°, 40.56°, 44.44°, 50.24°, 53.92°, 55.32°, 56.34°, 58.68°, 60.13°, 64.68°, 66.47° and 73.79° corresponds to the (200), (310), (200), (103), (400), (211), (330), (321), (510), (411), (600), (431), (321), (521), (002), (112) and (730) lattices planes of α-MnO2 tetragonal structure. The observed results are indexed with tetragonal structured manganese oxide (JCPDS: 44-0141 and 24-0734). The observed XRD peak at 29.02° is might be originated from PPy [42]. Also, the low intensity peak NGO peaks are exhibited at 21.65° and 23.5° which are shifted low diffraction angle for MnO2@NGO/PPy hybrid composites compared with MnO2@NGO composites. Hence, the inclusion of PPy with MnO2@NGO matrix for MnO2@NGO/PPy composites is evidently proved by XRD results. In addition, no other impurity related results are observed in the XRD results further supported the purity of the prepared composites.

Fig. 3.

XRD patterns of (a) MnO2@NGO, and (b) MnO2@NGO/PPy hybrid composites.


Furthermore, the elemental composition of MnO2@NGO and MnO2@NGO/PPy hybrid composites confirmed by XPS analysis. Fig. 4a-e show the XPS characteristics peaks of selective element binding energy for MnO2@NGO composites and survey spectrum. Fig. 4a depicts the C 1s element peaks in the range of 283, 291 and 295 eV corresponds to sp2 and sp3 C-C and O-C = O, respectively from NGO of MnO2@NGO composites (Fig. 4a) [43]. Fig. 4b reveals the broad O 1s characteristic peak at 529 eV due to metal-oxygen bond for the MnO2@NGO composites. N 1s characteristics peaks originates with weak signal from the graphitic N of NGO (Fig. 4c). The Mn 2p characteristics peaks of 2p3/2 and 2p1/2 states are at 641 and 654 eV, respectively with the energy difference between the two states is 13 eV [12]. The survey spectrum of MnO2@NGO composites confirms the presence of C, O, N and Mn elements (Fig. 4d).

Fig. 4.

XPS results of the MnO2@NGO composite. (a) C 1s, (b) O 1s, (c) N 1s and (d) Mn 2p binding energy and (e) survey spectrum.


Fig. 5 shows the characteristic XPS peaks for MnO2@NGO/PPy hybrid composites. The C 1s element peaks (Fig. 5a) are observed, with the improved intensity compared with MnO2@NGO, at 284, 288, 291 and 294 eV binding energy corresponds to C-C (sp2), C-N, C-C (sp3) and O-C = O, respectively, from the NGO of MnO2@NGO/PPy hybrid composites [13,43]. The broad oxygen (O 1s) peak at 529 eV represents the characteristic metal-oxygen bonds with the shoulder peak of 531 eV due to -OH group of NGO for the hybrid composites are shown in Fig. 5b. N 1s characteristics peaks are exhibited in the range of 397 and 407 eV, which originated from pyrrolic N and graphitic N (Fig. 5c) by PPy and NGO, respectively [44]. These results are confirmed the PPy incorporation with MnO2@NGO matrix. Mn 2p characteristics peaks are at 641 and 653 eV corresponds to the 2p3/2 and 2p1/2, respectively with the energy difference between the two states is 12 eV [12]. The survey spectrum of MnO2@NGO/PPy composites confirms the presence of all the elements (Fig. 5d). From the Raman, XRD and XPS results, the formation of MnO2@NGO and MnO2@NGO/PPy composites is proved by the simple hydrothermal reaction.

Fig. 5.

XPS results of the MnO2@NGO/PPy hybrid composites. (a) C 1s, (b) O 1s, (c) N 1s and (d) Mn 2p binding energy and (e) survey spectrum.

3.2Surface properties

The surface morphological properties of prepared nanocomposites are validated by FE-SEM measurements. Fig. 6 shows the FE-SEM images of MnO2@NGO composites with their EDX profile. FE-SEM images indicated that constitutes of cauliflower like morphology due to agglomeration of smaller grains (Fig. 6a-b). The higher magnification FE-SEM images are visibly shown the established larger size grains by the agglomeration of spherically shaped smaller grains (Fig. 6c-d). The agglomeration can be created due to addition of NGO with MnO2. The observed spherical shaped grain sizes are in the range of ˜20-30 nm. The composition of MnO2@NGO composites extracted for broad range of FE-SEM surface (Fig. 6e) and their EDX profile is included in the Fig. 6f. The observed elemental compositions are confirmed the formation of MnO2@NGO matrix. Fig. 7 shows FE-SEM micrographs and EDX profile of MnO2@NGO/PPy hybrid composites. The inhomogeneous sizes of grains are observed with hillocks structure for MnO2@NGO/PPy hybrid composites (Fig. 7a-b). The surface constitutes of spherically shaped protruding grains from the surface, as shown in Fig. 7c-d, due to inclusion of PPy with MnO2@NGO in the MnO2@NGO/PPy hybrid composites. In addition, the morphology clearly exhibits the larger surface area of MnO2 nanoparticles decorated NGO/PPy matrix. The porosity of the hybrid can be broadly improved due the NGO/PPy interaction with the controlled nanoscale sized MnO2 particles. Based on the nanostructured morphologies, the large surface area of the decorated MnO2 nanoparticles is structurally organized of NGO/PPy polymer chains that greatly enhance the high specific capacitance in the MnO2@NGO/PPy hybrid composite. Fig. 7f shows EDX spectrum of large area FE-SEM surface (Fig. 7e) for MnO2@NGO/PPy hybrid composites. The observed elemental compositions are confirmed the formation of MnO2@NGO/PPy hybrid composites.

Fig. 6.

(a-d) FE-SEM images with different magnifications; (e) large area FE-SEM surface and (f) their EDX profile for MnO2@NGO composite.

Fig. 7.

(a-d) FE-SEM images with different magnifications; (e) large area FE-SEM surface and (f) their EDX profile for MnO2@NGO/PPy hybrid composites.


FE-TEM analysis employed to confirm the nanoscale grains in the prepared composites. Fig. 8 shows the different magnifications of the FE-TEM images for MnO2@NGO composites. The higher magnification FE-TEM images confirmed the rod and sheet like grains (Fig. 8c-e). FE-TEM results revealed the well-defined sheet like nanostructures with different sizes in the range of 30–40 nm diameter and 10-20 nm thickness. Fig. 8f confirms the ring SAED pattern for due to the polycrystalline structure of MnO2 in the MnO2@NGO matrix. Moreover, Fig. 9a-e represents the different magnifications of the FE-TEM results for MnO2@NGO/PPy hybrid composites. These images are clearly confirmed the surface modification in MnO2@NGO due to incorporation of PPy for MnO2@NGO/PPy. The nano-disc like segregated grains are dispensed over the surface of the composites (Fig. 9c-e). The observed interlayer distance of ˜0.12 nm is related due to (310) lattice plane of nanocrystalline MnO2 in the MnO2@NGO/PPy hybrid composite.

Fig. 8.

(a-e) FE-TEM images with different magnifications and (f) their SAED pattern for MnO2@NGO composites.

Fig. 9.

(a-e) FE-TEM images with different magnifications and (f) their SAED pattern for MnO2@NGO/PPy hybrid composites.

3.3Electrochemical studies

The pristine MnO2, NGO and PPy electrodes supercapacitor results were reported in the previous literatures [13,32,45]. In order to study the supercapacitor properties of MnO2@NGO and MnO2@NGO/PPy electrodes, CV, GCD, and EIS analyses were carried out using three-electrode configuration with 5 M KOH aqueous solution as an electrolyte. For the measurements, the Pt wire used as the counter electrode, Ag/AgCl used as the reference electrode and prepared composites such as, MnO2@NGO and MnO2@NGO/PPy used as the working electrodes. The specific capacitance of MnO2@NGO and MnO2@NGO/PPy composites electrodes were calculated by the reported procedure [3,23]. The electrochemical results of MnO2@NGO composites electrode are provided in the Fig. 10. Fig. 10a shows CV results with the different scan rates such as 10, 30, 50, 70, 90, and 100 mV/s using the potential range of 0 - 0.5 V. CV curves showed the redox peaks due to their pseudo capacitance behavior for MnO2@NGO. The peak current values are increased with increase of scan rate. Fig. 10b shows GCD curves for MnO2@NGO composites with different current density values 0.5-2.5 A. g-1. For low current density, the rectangle like broad charge-discharge behavior is exhibited due to their high capacitance properties. The rectangle behavior GCD curve width is decreased with increase of current density. The estimated MnO2@ NGO electrode specific capacitances values are at 360, 185, 160, 131, 90, and 70 F.g-1 for the current density of 0.5, 1, 1.5, 2, and 2.5 A. g-1, respectively (Fig. 10c). The high capacitance retention behavior with 90% is observed after 6000 cycles for MnO2@NGO composites electrode (Fig. 10d).

Fig. 10.

Electrochemical analysis of the MnO2@NGO composites. (a) CV with different scan rate, (b) charge-discharge, (c) current densities versus specific capacitance and (d) cyclic stability curves.


The supercapacitor results of MnO2@NGO/PPy hybrids composites electrode are given in the Fig. 11. Fig. 11a displays the CV curves recorded using different scan rate such as 10, 30, 50, 70, 90, and 100 mV/s for the potential range of 0 - 0.5 V. As analogous to the MnO2@NGO, MnO2@NGO/PPy hybrids is produced the pseudo capacitance behavior of CV curves with Faradaic redox peaks. The peak current values are increased with increase of scan rate (Fig. 11a). Fig. 11b shows GCD curves for MnO2@NGO/PPy hybrid composites with different current density values 0.5-2.5 A. g-1. For low current density, the rectangle like broad charge-discharge behavior is exhibited due to their high capacitance properties. The rectangle behavior GCD curve width is decreased with increase of current density. The estimated MnO2@NGO/PPy electrode specific capacitances values are at 480, 340, 245, 186, and 120 F.g-1 for the current density of 0.5, 1, 1.5, 2, and 2.5 A. g-1, respectively (Fig. 11c). The capacitance values are decreased with increase of current density because of the fast diffusion of electrolyte ions provided by surface of the electrode materials without interior reaction of the electrode [12,46]. The improved specific capacitance values of 480 F.g-1 is recognized for MnO2@NGO/PPy hybrid composites by the synergetic effect of PPy, MnO2 and NGO network structure. The superior capacitance retention behavior with 95% is observed after 6000 cycles for MnO2@NGO/PPy hybrid composites electrode (Fig. 11d). The observed results reveals the electrode performance depends on the active materials of MnO2@NGO and MnO2@NGO/PPy composites.

Fig. 11.

Electrochemical analysis of the MnO2@NGO/PPy hybrid composites. (a) CV with different scan rate, (b) charge-discharge, (c) current densities versus specific capacitance and (d) cyclic stability curves.


EIS measurements were carried out in the three-electrode system in the presence of 5 M KOH as an electrolyte. The Nyquist plot represents the resistive and capacitive behavior of composites. In the Nyquist results, the real axis intercepts represent the series resistance (Rs), the contact resistance (Rct), and the intrinsic properties of the composite electrode materials in an electrolyte. The smaller Rs and semi-circle are represented the higher conductivity and lower Rct, respectively which can be increased the capacitance behavior. Fig. 12a-b show the EIS results of the MnO2@NGO and MnO2@NGO/PPy hybrid composites. The estimated Rs and Rct values are at 20 Ω and Rct = 80 Ω for MnO2@NGO composite and 10 Ω and 60 Ω for MnO2@NGO/PPy composite electrodes, respectively. The observed Rs and Rct values are represented the increased electrochemical behaviour due to the synergetic effect between the MnO2@NGO and PPy materials. The observed semicircle for the MnO2@NGO and MnO2@NGO/PPy electrodes represents the Faradaic reactions or charge transfer present in the active surface of electrode.

Fig. 12.

EIS profiles for (a) MnO2@NGO and (b) MnO2@NGO/PPy hybrid composites.


In summary, the MnO2@NGO and MnO2@NGO/PPy hybrid composites were synthesized via simple hydrothermal reactions as the electrode materials for supercapacitor applications. Raman, XRD and XPS results confirmed the formation of MnO2@NGO and MnO2@NGO/PPy hybrid composites. The sheet like dispensed nanograins exhibited for PPy modified MnO2@NGO surface. The hybrid composite electrodes displayed the higher capacitance of ˜360 and ˜ 480 F.g-1 for MnO2@NGO and MnO2@NGO/PPy hybrids, respectively, at 0.5 A. g-1 current density with the excellent cyclic stability up to 6,000 cycles. Hence, the MnO2@NGO and MnO2@NGO/PPy hybrid composite results suggests the capability to use as the efficient electrode materials for the high performance supercapacitors.

Conflicts of interest

The authors declare no conflicts of interest.


The research was fully supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF-2017R1D1A1B03028368, NRF-2017M3A9E2063256), under the Ministry of Education; and also fully supported by the framework of the 2017 international cooperation program (GRDC Joint Research) through the National Research Foundation by the Ministry of Science and ICT of Korea (Grant no: 2017K1A4A3013662).

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Copyright © 2019. Dongguk University-Seoul, Pildong-ro 1 gil, Jung-gu, Seoul 04620, Republic of Korea.
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