Carbon Nanotube/Graphene Supercapacitors Containing 

Manganese Oxide Nanoparticles

by Matthew Ervin, Vinay Raju, Mary Hendrickson, 

and Thomas Podlesak

ARL-TR-6289 December 2012

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Army Research Laboratory 

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ARL-TR-6289 December 2012 

Carbon Nanotube/Graphene Supercapacitors Containing 

Manganese Oxide Nanoparticles 

Matthew Ervin and Vinay Raju 

Sensors and Electronic Devices Directorate, ARL 

Mary Hendrickson and Thomas Podlesak 

Command, Power, and Integration Directorate, CERDEC 

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Carbon Nanotube/Graphene Supercapacitors Containing Manganese Oxide 

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Matthew Ervin, Vinay Raju, Mary Hendrickson, and Thomas Podlesak

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14. ABSTRACT

Supercapacitors are of interest because they are energy storage devices with greater power density than batteries. 

Unfortunately, supercapacitors have significantly lower energy densities than batteries, which limit the applications for 

supercapacitors. The addition of pseudocapacitance, that is, chemical reactions similar to those in batteries but which behave 

electrically like a capacitance, can be used to increase the energy density of supercapacitors. This work focuses on increasing 

the capacitance of carbon nanotube (CNT)- or graphene-based supercapacitors by adding pseudocapacitive manganese oxide

nanoparticles. A number of methods have been investigated for fabrication of CNT/graphene/manganese oxide composites. 

Manganese oxide nanoparticle pseudocapacitance has been successfully incorporated into CNT/graphene-based 

supercapacitors. Further optimization of the composite compositions and electrode fabrication methods is still required to 

optimize the energy densities of these devices.

15. SUBJECT TERMS

Supercapacitor, CNT, graphene, manganese oxide, pseudocapacitance

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Matthew Ervin

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iii

Contents 

List of Figures iv

1. Introduction 1

2. Results 2

2.1 GO/Manganese Acetate Solution Preparation .................................................................2

2.2 G/MnOx NP Synthesis Method Investigation .................................................................3

2.2.1 Dry Mixing/Grinding ..........................................................................................3

2.2.2 Solution Mixing Synthesis ..................................................................................3

2.2.3 Freeze-dry Synthesis ...........................................................................................4

2.2.4 Hydrothermal Processing ....................................................................................5

2.2.5 Spray Dry Processing ..........................................................................................6

2.3 Capacitor Performance ....................................................................................................7

2.3.1 Capacitor Evaluation ...........................................................................................7

2.3.2 Capacitance Increasing with Cycling ..................................................................8

2.3.3 Morphology Change with Cycling ......................................................................9

2.3.4 Mechanically Unstable Electrodes ......................................................................9

2.3.5 Greater Capacitance at Slower Scan Rate .........................................................10

2.3.6 Electrolyte Effects .............................................................................................11

2.3.7 Pseudocapacitance Results ................................................................................12

3. Conclusions 12

4. References 14

List of Symbols, Abbreviations, and Acronyms 15

Distribution List 16
iv

List of Figures 

Figure 1. TGA at 1 °C/min of MnAc demonstrating that it decomposes below 300 °C. The 

mass lost indicates that Mn3O4 may be the resulting species. ...................................................2

Figure 2. SEM image of ball milled MnAc (3 mole %) with multi-wall carbon nanotubes 

(MWCNTs) annealed at 370 °C. The resulting material is rather inhomogeneous and the 

MnOx NPs do not appear to be well associated with the MWCNTs (Mn370C303). ...............3

Figure 3. SEM image of ball milled MnAc (3 mole %) with MWCNTs annealed at 370 °C. 

The resulting material is rather inhomogeneous and the MnOx NP do not appear to be 

well associated with the MWCNTs (Mnsoln370107). .............................................................4

Figure 4. SEM of rGO coated with MnOx nanoparticles fabricated through freeze-dry 

method (VNRA1).......................................................................................................................5

Figure 5. Hydrothermally produced MnOx NPs on CNTs (left) and rGO (right) 

(MnHTCNT204, MnHTG205). .................................................................................................5

Figure 6. SEM images of reduced, drop-cast GO solution (left) and reduced, spray-dried GO 

solution (right) (MHE23502 and MHE23802). .........................................................................6

Figure 7. SEM of MnOx NPs formed on rGO using spray dry process (SDGO14, SDGO09). .....7

Figure 8. Representative CV scan of a rGO/MnOx NP electrode in 0.5 M K2SO4. .......................7

Figure 9. Depiction of 1200 CV cycles of a spray-dried MWCNT/MnOx NP electrode made 

with Kynar 761 binder. The red trace is the first cycle (MHE23403). ......................................8

Figure 10. SEM image of MWCNT/MnOx NP electrode after 9000 CV cycles showing 

MnOx NP platelet formation. (MHE20001). .............................................................................9

Figure 11. SEM of spray-dried rGO nanosphere electrode with 20% SWCNT as binder 

(MHE24303). ...........................................................................................................................10

Figure 12. Plot of capacitance observed as a function of scan rate (MHE25406). .......................11

Figure 13. CV curves of a rGO/MnOx NP electrode in K2SO4 (left), NaCl (middle), and 

CaCl2 (right) (MHE25402, 04, 05). .........................................................................................11
1

1. Introduction 

Supercapacitors have several advantages over conventional batteries, including higher specific 

power (~2 orders of magnitude higher), higher cycle life (millions of charge/discharge cycles), 

rapid charge/discharge times (seconds to minutes), high efficiencies (up to 98%), and good 

performance in extreme heat and cold (1). Increasing supercapacitor energy and power densities 

will make them more useful for portable power applications. Two materials being studied for 

supercapacitor electrodes are single-wall carbon nanotubes (SWCNTs) and graphene (G). 

Extremely large double-layer capacitances may be obtainable if these materials can be assembled 

in a manner that optimizes the electrode surface area that is accessible to the electrolyte. 

Solution-based processing was chosen for this work as it is manufacturable and it does not 

impose significant thermal and chemical constraints on the underlying current collector as direct 

growth on the current collector would. When carbon nanotubes (CNTs) or G are deposited from 

solution, they typically do so in bundles or as stacked sheets. Our previous work (2) indicates 

that this bundling or restacking is detrimental to the resulting accessible surface area and 

therefore reduces the double-layer capacitance. 

In this work, the addition of manganese oxide nanoparticles (NPs) to the CNTs or G surfaces has 

been investigated to see if it increases the capacitances of these materials. Approaches to deposit 

the NPs onto the CNTs/G before electrode fabrication, as opposed to electrochemically 

depositing the NPs onto an existing CNT/G electrode, were investigated as there was a 

possibility that deposition onto existing CNT/G electrodes would prevent the incorporation of 

NPs within the CNT bundles or between stacked G sheets. This is important since the inclusion 

of NPs is, in part, desirable as it may prevent the tight bundling/restacking of the CNTs/G, thus 

increasing the accessible surface area, which would increase the specific double-layer 

capacitance of these materials. In addition, manganese oxide is known to have pseudocapacitive 

properties (3). That is, it supports fast redox reactions that behave like a capacitance. Such 

redox-based capacitance would impart an additional pseudocapacitance contribution to the 

specific capacitances of the CNT/G electrodes. The CNT/G material, in turn, increases the 

electrical conductivity of the manganese oxide (MnOx), which increases the electrochemical 

utility of this material. 

A number of fabrication methods for combining CNT or G with MnOx NPs are investigated 

here. While incorporation of MnOx NPs may increase energy density through increased 

accessible surface area and pseudocapacitive contributions, the NPs may also reduce the power 

density by reducing the electrode electronic conductivity, and it may reduce the cycle life 
2

through the incorporation of redox reactions. Characterization of these materials has uncovered 

a number of issues that will need to be addressed in a practical device. 

2. Results

2.1 GO/Manganese Acetate Solution Preparation

Numerous electrodes were made using CNTs in powder form and graphene oxide (GO) solution 

obtained from commercial sources (Helix Material Solutions and Cheaptubes.com, respectively). 

The benefit of working with GO is that it is water soluble and once the electrode has been 

fabricated, the GO can be thermally reduced to graphene (G, or rGO). Typically, 225 °C 

overnight (in air) has been used to thermally reduce the GO used here. The thermal conversion 

of manganese acetate (MnAc) (obtained from Sigma Aldrich) has been used to produce the 

MnOx NPs used here (3). Higher temperatures (300 °C/1 h/in air) have typically been used to 

convert the MnAc to MnOx. Thermal gravimetric analysis (TGA) was used to determine that the 

MnAc decomposes below 300 °C, as shown in figure 1. The amount of mass lost indicates that 

Mn3O4 may be the resulting species. The electrode materials produced were examined with 

scanning electron microscopy (SEM). 

Figure 1. TGA at 1 °C/min of MnAc demonstrating that it decomposes below 300 °C. 

The mass lost indicates that Mn3O4 may be the resulting species.
3

2.2 G/MnOx NP Synthesis Method Investigation

2.2.1 Dry Mixing/Grinding

Dry mixing and grinding of CNTs with MnAc was attempted as described by Yi Lin (4). After 

baking the dry mixture, SEM imaging indicated there was insufficient mixing of the materials 

and that using more than 5 mole % of MnAc may be useful, as can be seen in figure 2.

Figure 2. SEM image of ball milled MnAc (3 mole %) with multiwall carbon nanotubes (MWCNTs) annealed at 370 °C. 

The resulting material is rather inhomogeneous and the 

MnOx NPs do not appear to be well associated with the 

MWCNTs (Mn370C303).

2.2.2 Solution Mixing Synthesis

In order to obtain a more thorough mixing of the CNTs and MnAc, a mixing of these materials in 

solution was attempted. A mass ratio of 18:82 MnAc:MWCNT was suspended in ethanol (the 

MnAc dissolves, but the MWCNTs are merely suspended). The resulting suspension was 

immediately drop cast after ultrasonication and the resulting deposit was baked at 370 °C. As 

can be seen in figure 3, 10-nm NPs are associated with the MWCNTs, but there are also 

agglomerated MnOx NPs. The lack of complete mixing of the materials is likely due to 

separation during the dropcasting.
4

Figure 3. SEM image of ball milled MnAc (3 mole %) with 

MWCNTs annealed at 370 °C. The resulting material 

is rather inhomogeneous and the MnOx NP do not 

appear to be well associated with the MWCNTs 

(Mnsoln370107).

2.2.3 Freeze-dry Synthesis

In an effort to prevent the segregation of the MnAc from the carbon during evaporation of the 

solution, a freeze dry method was used. In addition, a water solution of GO was used for the 

carbon source since the GO is actually in solution and not merely suspended as the MWCNTs

above were. Next, 2 mg of GO and 3.3 mg of MnAc were dissolved in 3 ml of water. This 

solution was flash frozen by depositing it drop wise into liquid nitrogen. The resulting ice 

crystals were freeze dried at 10–3torr. After baking to reduce the GO to rGO and convert the 

MnAc to MnOx, the resulting powder was imaged with the SEM. Figure 4 shows there are small 

MnOx NPs coating the rGO. While successful in producing NP-coated graphene, it was difficult 

to collect sufficient material for further electrode processing, so additional synthesis methods 

were attempted.
5

Figure 4. SEM of rGO coated with MnOx nanoparticles fabricated 

through freeze-dry method (VNRA1).

2.2.4 Hydrothermal Processing

Next, 2 to 1 solutions (by mass) of MnAc and CNTs or GO were hydrothermally treated at 

200 °C for 14 h and the resulting MnOx NP decorated materials are seen in figure 5.

Figure 5. Hydrothermally produced MnOx NPs on CNTs (left) and rGO (right) (MnHTCNT204, MnHTG205).

For subsequent hydrothermal syntheses, a MnAc and GO solution was mixed with trace amounts

of potassium hydroxide (KOH) using a procedure described by Wang (5). The fabrication 

process involved stirring 0.4 mmol MnAc solution, 0.9 mmol KOH solution, and GO solution 

(1 mg/mL) and heating at 180 °C for 14 h in a Teflon-coated autoclave. The solution was then 

deposited onto current collectors by dropcasting. These electrodes were then baked at 300 °C for 

1 h to ensure that the MnAc was converted to MnOx NPs. 
6

2.2.5 Spray Dry Processing

The final synthesis method investigated was spray drying, which was done with the assistance of 

Prof. Hongwei Qiu of Stevens Institute of Technology. As it turns out, spray drying has some 

interesting effects on the GO all by itself even before MnAc is incorporated. In spray drying, the 

GO solution is aerosolized and the droplets are dried with a hot carrier gas. The surface tension 

of the drying droplets, crumples the GO sheets up into nanospheres. Figure 6 shows the flat 

uncrumpled appearance of drop cast GO solution and the crumpled morphology of the spray 

dried GO solution. The crumpled morphology is of interest for further investigation since it may 

result in more surface area and greater ionic conductivity (porosity) in the electrodes produced 

this method. On the other hand, the crumpled morphology will increase the electrical resistivity 

due to reduced contact between adjacent rGO sheets in the final electrode. 

Figure 6. SEM images of reduced, drop-cast GO solution (left) and reduced, spray-dried GO solution (right)

(MHE23502 and MHE23802).

When MnAc is included with GO in the spray-dried solution, a good mixture of the MnOx NP 

and rGO sheets results, as can be seen in figure 7. The figure shows 5- to 10-nm NPs on the 

rGO.
7

Figure 7. SEM of MnOx NPs formed on rGO using spray dry process (SDGO14, SDGO09).

2.3 Capacitor Performance

2.3.1 Capacitor Evaluation

Electrodes were fabricated by drop casting solutions containing the GO/CNT/MnAc materials 

onto titanium (Ti) or stainless steel current collectors and then annealing them to reduce the GO 

or convert the MnAc to MnOx as needed. Testing was performed using cyclic voltammetry 

(CV) and electrochemical impedance spectroscopy (EIS) on a potentiostat typically using a 

three-electrode setup with a large excess of electrolyte. In a later experiment, a two electrode 

setup was used with fabricated button cells. The CV scan rate for the majority of the testing was 

20 mV/s, except where noted. The voltage range of scan was 0 to 0.7 V (versus the silver/silver 

chloride electrode when using the three electrode mode). The electrolyte typically used in this 

study was 0.5 M potassium sulfate (K2SO4). A typical CV obtained is seen in figure 8.

Figure 8. Representative CV scan of a rGO/MnOx NP electrode in 0.5 M K2SO4.
8

The specific capacitance is calculated from a three electrode measurement using

CV Current/(Scan Rate*Mass of Sample) = Capacitance (F/g) (1)

where the current is measured as half the difference between the oxidation and reduction currents 

near the center of the CV curve near where this value is a minimum to avoid overstating the 

capacitance. In a two electrode (button cell) measurement, the specific capacitance is calculated 

in the same manner, but the mass of both electrodes is included and the result is multiplied by 

four to report it in the three electrode standard as is observed in the literature.

2.3.2 Capacitance Increasing with Cycling

A MnOx NP decorated MWCNT material was made using a spray-dry process. This electrode 

material was deposited onto a current collector from an n-methylpyrrolidone (NMP) suspension 

that also contained polyvinylidene fluoride (PVDF) binder. When this electrode was cycled for 

1200 cycles, the capacitance was observed to increase from 29.2 to 42.8 mF, as shown in figure

9. After subtracting out the capacitance expected from the MWCNTs alone, the specific 

capacitance of the MnOx NPs was calculated to increase from 8.3 to 31.8 F/g. It is believed that 

this increase is due to the conversion of the MnOx from its initially synthesized phase believed to 

be Mn3O4 to the more electrochemically active birnessite phase (6).

Figure 9. Depiction of 1200 CV cycles of a spray-dried MWCNT/MnOx NP electrode made with 

Kynar 761 binder. The red trace is the first cycle (MHE23403).
9

2.3.3 Morphology Change with Cycling 

Unfortunately, the capacitance does not always increase with cycling. Often, it decreases for 

various reasons. There may be a potential issue with the MnOx dissolving during part of the CV 

cycle and then redepositing later in the cycle. Figure 10 shows the morphology of the MnOx NP 

after 9000 cycles. In this case, the capacitance was still increasing, but the significant changes in 

morphology could be an issue in a practical device. Since the MnOx dissolves during part of the 

CV cycle, it is possible that the electrodes tested in a three electrode mode using a large excess 

of electrolyte could lose a significant amount of Mn to the electrolyte. However, making a 

button cell with a limited amount of electrolyte was not successful in increasing the measured 

capacitance, so this may not be a serious issue with the measurements made here.

Figure 10. SEM image of MWCNT/MnOx NP electrode after 

9000 CV cycles showing MnOx NP platelet formation.

(MHE20001).

2.3.4 Mechanically Unstable Electrodes

The hydrothermal method used mixed KOH with MnAc and GO. The KOH seemed to have 

formed crystals on some of the dropcast electrodes. Here, KOH crystals were formed in the 

electrode and created an unstable electrode mass by absorbing moisture from the air. Dissolution 

of the KOH crystals also resulted in the electrode deteriorating in the electrolyte, producing 

falling capacitance readings. 

Another potential reason for an electrode material losing electrical contact with the current 

collector is due to insufficient binder. In much of this work, a binder material was not used to 

avoid any complications that would result if it coated the surface of the electrode materials. 

However, electrochemical deterioration was observed when testing many electrodes, sometimes

due to a detachment of the electrode material from the current collector. When necessary 

electrodes were made using a PVDF binder, but the formulation has not been optimized. The 
10

CNT and G materials have such large surface areas that more binder than is typically used to 

make electrodes is likely required to obtain adequate mechanical robustness. 

2.3.5 Greater Capacitance at Slower Scan Rate

Since redox reaction based pseudocapacitance is slower than the double-layer capacitance 

contribution, it is worthwhile to measure how the capacitance changes with the scan rate. The 

electrode used was made from spray-dried powder from a solution that had 100 mg of GO and 

145 mg of MnAc in 50 ml of water, which should yield >10 mole % Mn:C. This spray-dried 

GO/Mn Ac powder was baked at 275 °C for 4 h. Then, 1.06 mg of the reduced/converted 

powder was mixed with 0.37 mg of SWCNTs in NMP. The SWCNTs were added to improve 

the electrical conductivity between the MnOx NP covered G nanospheres and bind the electrode 

materials together. Figure 11 shows a similar electrode made without the MnOx NPs. 

Figure 11. SEM of spray-dried rGO nanosphere electrode 

with 20% SWCNT as binder (MHE24303).

The resulting suspension was dropcast onto a Ti current collector. The capacitance as a function 

of scan rate is plotted in figure 12. At the slowest scan rate measured, 2 mV/s, the capacitance 

was measured to be 135 F/g. 
11

Figure 12. Plot of capacitance observed as a function of scan rate (MHE25406).

2.3.6 Electrolyte Effects

MnOx containing electrodes are typically used with neutral (pH) electrolytes. In order to 

investigate the effect of the electrolyte on the capacitance observed, the same spray-dried 

rGO/MnOx NP with SWCNT electrode as above was tested at a 2 mV/s scan rate in three 

different electrolytes: 0.5 M K2SO4, 1 M sodium chloride (NaCl), and 1 M calcium chloride

(CaCl2). The qualitative CV behavior of the three electrolytes can be seen in figure 13. Before 

taking these CVs, the electrode was cycled in 0.5 M K2SO4 for 200 cycles until its capacitance 

stabilized. Then it was tested in the three electrolytes in succession. The observed capacitances 

were 85.7 F/g in K2SO4, 97.8 F/g in NaCl, and 153 F/g in CaCl2 electrolyte. These results are 

considered reliable, and not inflated by a leakage current, because the phase angle as measured 

using electrochemical impedance spectroscopy is ‒80° at the lowest frequency (10 mHz) 

measured, and so there is not a significant leakage current contributing to the measured 

capacitance.

Figure 13. CV curves of a rGO/MnOx NP electrode in K2SO4 (left), NaCl (middle), and CaCl2 (right) 

(MHE25402, 04, 05).
12

2.3.7 Pseudocapacitance Results 

In the above electrolyte study, a specific capacitance of 84 F/g was obtained at 20 mV/s in CaCl2

electrolyte. This is the combination of the double-layer capacitance of the SWCNTs and rGO 

combined with the pseudocapacitance of the MnOx NPs. Extracting the pseudocapacitance of 

the MnOx NPs is somewhat difficult and requires some approximations. If I assume that the GO 

has a C7O3 stoichiometry and the MnAc converts to MnO2 and that the rGO contributes 50 F/g 

(based on a similar electrode with no MnOx) and the SWCNTs contribute 35 F/g (based on 

previous work), I then calculate the MnOx NPs are contributing 108 F/g of pseudocapacitance. 

This is a reasonable result when compared to the literature for MnOx electrodes (3), but is it 

lower than some reports in the literature for MnOx/G or CNT electrodes. The measured 

pseudocapacitance is presumably higher at the slower scan rate of 2 mV/s, but I do not have 

sufficient data to calculate that value at this time. 

Capacitors made using the hydrothermal method from the literature did not yield specific 

capacitances higher than what could be achieved with rGO alone. It is possible that the 180 F/g 

for MnOx reported when using the hydrothermal method is in error as they used a very low 

MnOx loading on their G and their observed capacitance could be entirely due to the G (5). 

3. Conclusions 

In this work, a number of synthesis methods have been investigated for making MnOx NPs on 

CNT/G electrodes for achieving increased double-layer capacitance as well as adding 

pseudocapacitance to CNT/G electrodes. Some methods (dry/solution mixing) were abandoned 

as they did not result in sufficient mixing of the MnOx and G/CNTs. Another (freeze drying) 

was abandoned due to the difficulty in making sufficient material on a laboratory scale. Both 

hydrothermal processing and spray drying appear to be promising methods for coating G/CNTs 

with NPs. 

In all of the methods, the decomposition of MnAc to MnOx was used to produce the MnOx NPs. 

Electrodes made with these composite materials were found to increase in capacitance with 

electrochemical cycling, which is believed to convert the initial MnOx phase to a more active 

phase, and it is also observed to change the morphology of the MnOx deposits. As is typical 

with supercapacitors, the capacitance was observed to increase as the CV scan rate was 

decreased. The electrolyte used was also found to significantly affect the observed capacitance 

with CaCl2, yielding almost twice the capacitance as K2SO4. A specific capacitance of 108 F/g 

was calculated for the pseudocapacitance of the MnOx phase at 20 mV/s with more expected at 

slower scan rates. This is comparable to what has been reported in the literature for MnOx; 
13

however, there have been reports of significantly higher specific capacitances for MnOx/G or 

CNT composite electrodes in the literature. 

In future work, the best ratio of MnOx:G/CNT should be determined. In much of the reported 

MnOx:G/CNT composite electrode work, the G/CNT is merely an additive that increases the 

electrical conductivity of the MnOx. The energy and power requirements of the ultimate 

application are liable to determine the optimum ratio of materials. In addition, additional 

synthesis routes for producing the most electrochemically active MnOx phase should be 

investigated. Finally, more electrode fabrication process optimization is required to prevent 

electrode deterioration that is sometimes seen. 
14

4. References 

1. Pandolfo, G.; Hollenkamp, A. F. J. Power Sources 157, 11–27 (2006). 

2. Ervin, M. H.; Mailly, B.; Palacios, T. Electrochemical Double Layer Capacitance of 

Metallic and Semiconducting SWCNTs and Single-Layer Graphene. ECS Transactions

2012, 41 (22), 153–160. 

3. Xu, F.; Kang, B.; Li, B.; Du, H. Recent Progress on Manganese Dioxide Based 

Supercapacitors. Journal Material Research 2010, 25 (8) 1421–1432. 

4. Lin, Yi; Watson, K. A.; Fallbach, M. J.; Ghose, S.; Smith, J. G. Jr; Delozier, D. M.; Cao, W.; 

Crooks, R. E.; Connell, J. W. Rapid, Solventless, Bulk Preparation of Metal Nanoparticledecorated Carbon Nanotubes. ACS Nano 2009, 3, 871–884.

5. Wang, D.; Li, Y.; Wang, Q.; Wang, T. Facile Synthesis of Porous Mn3O4 NanocrystalGraphene Nanocomposites for Electrochemical Supercapacitors. Journal Inorganic 

Chemistry 2012, 628–635.

6. Inoue, R.; Nakashima, Y.; Tomono, K.; Nakayama, M. Electrically Rearranged BirnessiteType MnO2 by Repetitive Potential Steps and Its Pseudocapacitive Properties. Journal of 

the Electrochemical Society 2012, 159 (4), A445–A451. 
15

List of Symbols, Abbreviations, and Acronyms 

CaCl2 calcium chloride 

CNTs carbon nanotubes 

CV cyclic voltammetry 

EIS electrochemical impedance spectroscopy 

G or rGO graphene 

GO graphene oxide 

K2SO4 potassium sulfate 

KOH potassium hydroxide 

MnAc manganese acetate 

MnOx manganese oxide 

MWCNTs multi-wall carbon nanotubes 

NaCl sodium chloride 

NMP n-methylpyrrolidone 

NPs nanoparticles 

PVDF polyvinylidene fluoride 

SEM scanning electron microscopy 

SWCNTs single-wall carbon nanotubes 

TGA thermal gravimetric analysis 

Ti titanium 
16

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