Realizing an Asymmetric Supercapacitor Employing Carbon

Subscriber access provided by Kaohsiung Medical University

Energy, Environmental, and Catalysis Applications

Realizing an Asymmetric Supercapacitor Employing Carbon Nanotubes Anchored to MnO Cathode and FeO Anode 3

4

3

4

Ankit Kumar, Debasish Sarkar, Soham Mukherjee, Satish Patil, D. D. Sarma, and Ashok K. Shukla ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b16639 • Publication Date (Web): 15 Nov 2018 Downloaded from http://pubs.acs.org on November 17, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Realizing an Asymmetric Supercapacitor Employing Carbon Nanotubes Anchored to Mn3O4 Cathode and Fe3O4 Anode Ankit Kumar,† Debasish Sarkar,*,† Soham Mukherjee, Satish Patil, D. D. Sarma and Ashok Shukla* Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru-560012, India. Keywords: Pseudocapacitive materials; carbon nanotubes; metal-hexacyanoferrate complex; asymmetric supercapacitor; high-power density; cycling stability Abstract A facile route to anchor pseudocapacitive materials on multi-walled Carbon Nanotubes (CNTs) to realize high-performance electrode materials for Asymmetric Supercapacitors (ASCs) is reported. The anchoring process is developed subsequent to direct decomposition of metalhexacyanoferrate complex on the CNT surface. Transmission electron microscopy (TEM) analysis reveals that the nanoparticles (NPs) are discretely attached over CNT surface without forming a uniform layer, thus making nearly entire NP surface available for electrochemical reactions. Accordingly, CNT-Mn3O4 nanocomposite cathode shows significantly improved capacitive performance as compared to pristine CNT electrode, validating the efficacy of designing the composite electrode. With CNT-Fe3O4 nanocomposite as paired anode, the hybrid ASC delivers a specific capacitance of 135.2 F/g at a scan rate of 10 mV/s within a potential window of 0-1.8V in the aqueous electrolyte and retains almost 100% of its initial capacitance after 15000 cycles. The serially connected ASCs can power commercial LEDs and mobile phones reflecting their potential in next-generation storage applications. ___________________________________________________________________________ 1 ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

*Authors to whom correspondence should be addressed: E-mail addresses: [email protected] , [email protected] (D. Sarkar), Tel: +91 (080) 2293 2945, and [email protected] (A. Shukla), Tel: +91 (080) 2293 2795. †Authors

contributed equally to this work.

TOC Graphic

2 ACS Paragon Plus Environment

Page 2 of 28

Page 3 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Introduction In recent years, energy usage across the globe has started shifting towards renewable and related sustainable energy sources to counter global proliferation of greenhouse gas emissions arising due to excessive usage of fossil fuels. Accordingly, a quantum leap in the development of high-performance storage devices looks inevitable owing to the intermittent nature of alternative energy resources, like sun and wind. In this regard, supercapacitors (SCs) or ultracapacitors have gained attention owing to their superfast energy uptake and delivery capabilities as well as ultra-long cycle life with extremely stable performance as compared to batteries.1-3 But SCs lag behind traditional batteries in terms of energy storage capacity,2, 4 which restricts their usage in applications like electric traction and modern electronic gadgets. Therefore, enhancing energy density of SCs on par with the conventional batteries without sacrificing inherent traits of the former, namely high-power density and cycle life, remains a challenge. Pseudocapacitors based on transition-metal oxides, hydroxides and nitrides exhibit enormous potential in designing high-performance electrodes with high charge storage capability akin to batteries in addition to long cycle-life and high power-density of carbonbased electrical double layer capacitors (EDLCs). 2, 4-5 However, poor electronic conductivity of metal oxides severely affects their rate capability and power density, which limit their usage. Accordingly, several innovative attempts have been expended in this regard, like designing nano-structured electrodes,

1-3, 6

devising core-shell electrode concepts,

7-8

and fabricating

composite electrode materials, 5, 9-10 to enhance the conductivity of pseudocapacitive materials. Furthermore, assembling asymmetric supercapacitors (ASCs) with pseudocapacitive materials would extend their operating potential window even in aqueous electrolytes and hence their energy density. 3, 7-8



Page 4 of 28

In the literature, Manganese (II, III) oxide (Mn3O4) has been investigated extensively as a potential cathode material for next-generation ASCs due to its high and stable redox activity over a wide potential window, low cost owing to its natural abundance and environmental compatibility. 10-12 However, its poor electronic conductivity affects its overall performance in ASCs, which can be enhanced by fabricating Mn3O4-carbon composites with carbon as the conductive counterpart. 5, 12-13 In this context, carbon nanotubes (CNTs) could be considered as the synergic counterpart for oxide pseudocapacitors in realizing composite electrode materials owing to their outstanding electronic conductivity, high tensile-strength, high chemical-stability and high aspect-ratio providing large active-surface-area,

14-17

albeit

suffering from poor electrochemical activity that has been impeding its use as an active material in SCs. In the light of the foregoing, it is desirable to attach redox active nanomaterials with the CNTs to realise composite electrode materials that would combine the inherent positive traits of individual component materials. In this communication, a facile method is reported to anchor Mn3O4 and Fe3O4 nanoparticles on multi-walled CNTs to realise respective positive and negative electrode materials for a high-performance ASC. Magnetite (Fe3O4) has gained wide attention as anode material for SCs due to its high theoretical capacitance, high-electronic conductivity, natural abundance and environmental compatibility. Both CNT-Mn3O4 and CNT-Fe3O4 composites are obtained by a similar sol-gel method, thus making the process versatile for electrode fabrication. When the anodes and cathodes are assembled together, the CNT-Fe3O4//CNTMn3O4 hybrid ASC exhibits stable electrochemical behaviour between 0-1.8V in an aqueous electrolyte, delivering an energy density as high as 37 Wh/kg and a power density of about 10 kW/kg with a cycle life over 15000 cycles with no loss in capacitance.


Page 5 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Experimental Synthesis of CNT-Mn3O4 and CNT-Fe3O4 nanocomposites Mn3O4 nanoparticles were anchored on the CNT by decomposing Mn-hexacyanoferrate complex directly on the CNT surface. At first, CNT surface was chemically functionalized with hydroxyl, carboxyl, and carbonyl groups by refluxing in concentrated nitric acid. The functional groups not only help CNT dispersion, but also serve as anchoring sites for Mnhexacyanoferrate complex, which after reduction nucleates Mn3O4 on CNT surface. Mn3O4 synthesis was initiated by mixing 30 ml MnCl2.4H2O aqueous solution in 15 ml CNT solution under mechanical stirring for 30 min followed by ultrasonication for 15 min. Subsequently, 30 ml aqueous K3Fe(CN)6 solution was added to the above mixture and stirred for 3h to obtain Mn-hexacyanoferrate-CNT complex, which was then washed copiously until the pH of the solution became neutral. Finally, Mn-hexacyanoferrate-CNT complex was decomposed with slow addition of 1M NaOH solution under continuous stirring for 3h to realise Mn3O4-CNT nanocomposite as black precipitate, which was then filtered and washed with deionized water followed by overnight drying in vacuum oven at 90°C. The detailed chemical process for synthesis for Mn3O4 is summarized below.

K 3 Fe(CN)6 + MnCl2  KMnFe(CN)6 + 2KCl

(1)

KMnFe(CN)6 + 2NaOH  Mn(OH) 2 + KNa 2 Fe(CN)6

(2)

Mn(OH) 2  MnO + H 2 O

(3)

2MnO + O 2  2MnO 2

(4)

2MnO+MnO 2  Mn 3O 4

(5)



Similarly, CNT-Fe3O4 nanocomposite was synthesized using FeCl3.6H2O as the iron precursor. However, in this synthesis, the vacuum dried sample was further annealed in Ar atmosphere at 450°C for 2h. Fabrication of electrodes with nanocomposites and the ASC To prepare the electrodes for electrochemical characterization, individual nanocomposites were mixed with polyvinylidene difluoride (PVDF) and activated carbon in percent ratio of 75:5:20 followed by adding an appropriate amount of di-methyl formamide (DMF) to form a slurry. The slurry was then evenly pasted over properly-cleaned Ni-foam substrate followed by drying overnight in an air oven at 80°C. The mass density of active materials was estimated by calculating the weight difference of the Ni-foam substrate before and after the slurry casting of electroactive materials and was around 2 mg/cm2 for CNT-Mn3O4 and 3 mg/cm2 for CNTFe3O4 electrodes. The ASC was assembled by sandwiching a polypropylene-mesh separator in-between the electrolyte-soaked cathode and anode followed by encapsulation with poly-ethylene terephthalate (PET) film to avoid any electrolyte leakage. Based on charge-balance calculations, the mass ratio between cathode (CNT-Mn3O4) and anode (CNT-Fe3O4) materials was about 1.00:1.40 in the ASC cell (see Supporting information). Characterization of as-prepared materials Morphology, structure and composition of different electrode materials were characterized using field emission SEM (FESEM, FEI, Quanta FEG 650), TEM (TEM, JEOL JEM-2100F) and XRD (XRD, PANalytical Empyrean X-ray Diffractometer). Chemical states for different ionic species in the samples were identified by using X-ray photo-electron spectroscopy (XPS) technique. Brunauer–Emmett–Teller (BET) surface area and porosities for composite materials were measured using N2 adsorption/desorption method. Electrochemical characterization for 6 ACS Paragon Plus Environment

Page 6 of 28

Page 7 of 28

individual electrode material was carried out on a software-controlled conventional threeelectrode electrochemical work station (AutoLab PGSTAT 302N) comprising as prepared samples as working electrodes, a Pt foil as counter electrode and an Ag/AgCl reference electrode in 1M aqueous Na2SO4 solution. Electrochemical impedance spectroscopy (EIS) on individual electrodes and assembled ASC were performed in the same electrochemical cell in the frequency range between 10 mHz and 100 kHz with an operating ac field amplitude of 5 mV. Results and discussion Structural and morphological characterization of CNT-Mn3O4 nanocomposite

(c)

(b)

 CNT

(002)

(a)

(100)

Intensity (arb. unit)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CNT-Mn3O4

Mn3O4 (JCPDS No. 24-0734) 20

30

40

50

2 (degree)

(d)

60

70

(f )

(e)

Figure 1. (a) XRD pattern of the as synthesized CNT-Mn3O4 nanocomposites compared with the standard pattern of Mn3O4 (JCPDS No. 24-0734); (b) FESEM image of CNT-Mn3O4 nanocomposite drop casted on Si substrate; TEM images of (c) pristine CNT and (d) CNTMn3O4 nanocomposite; (e) and (f) depict high resolution TEM images of the CNT-Mn3O4 nanocomposite.



Page 8 of 28

Crystallographic identity of the synthesized composite material is studied using XRD technique and corresponding pattern is shown in Figure 1a. The diffraction pattern consists of peaks that can be indexed to the reference diffraction peaks of tetragonal hausmannite phase of Mn3O4 (JCPDS No. 24-0734)5,

9-10

and the diffraction peaks of CNT at 25.8° and 42.9°,

corresponding to (002) and (100) planes of graphitized carbon, respectively.9,

14

Sharp

diffraction peaks of Mn3O4 suggest excellent crystallinity and phase purity of the synthesized nanoparticles. Figure 1b depicts the FESEM image of CNT-Mn3O4 nanocomposite where no agglomeration of Mn3O4 particles is observed. Anchoring of Mn3O4 nanoparticles on CNT can be better understood after comparing the TEM images of bare CNT (Figure 1c) and CNTMn3O4 nanocomposite shown in Figure 1d as well as in Figure S1 (Supporting information). Figure 1e zooms into Figure 1d to depict the anchoring of nanoparticles at multi-walled CNT surfaces as also to show the efficacy of the synthetic procedure. It is noteworthy that the distribution of NPs on CNTs is discrete, thus making most of the NP surface available for electrochemical reactions, which would otherwise remain inaccessible in case of continuous NP covering on CNTs. After analysing several TEM images, the size of the Mn3O4 NPs is estimated to be between 15-20 nm. The high resolution TEM (HRTEM) image depicted in Figure 1f shows well aligned lattice planes with inter-planar spacing of 0.249 nm that perfectly matches with the spacing of (211) lattice planes of tetragonal Mn3O4.


200

400

600

(b)

Intensity (arb. units)

O 1s Mn 3s

Mn 2p1/2

C 1s

Mn 3p


(a)

0

800

C-O

p3/2

282

284

11.8 eV 620

630

640

650

660

670

Binding energy (eV)

286

288

290

292

294

Binding energy (eV) Mn 2p

p1/2

O-C=O -* transitions

680


(c)

C 1s

C-C defects on nanotube structure

Binding energy (eV) Intensity (arb. units)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Mn 2p3/2

Page 9 of 28

(d)

O22

O 1s isolated OH, C=O, O-C=O C-O-C, C-O-OH, C-OH

528

530

532

534

536

538

Binding energy (eV)

Figure 2. X-ray photoelectron spectroscopy (XPS) spectra of the as synthesized CNT-Mn3O4 nanocomposite, (a) survey spectrum and the core-level spectra of (b) C1s, (c) Mn 2p, (d) O1s. Formation of the Mn3O4 phase is further confirmed using XPS analysis and Figure 2a shows the survey scan for the CNT-Mn3O4 nanocomposite, where the peaks corresponding to Mn, C and O are seen clearly. The C1s core-level spectrum shown in Figure 2b can be deconvoluted into different peaks centred on 284.6 eV, 285.6 eV, 287.0 eV, 288.7 eV and 291.3 eV. The most resolved peak at 284.6 eV can be assigned to C-C bonds of sp2-hybridized carbon atoms.14, 18 The peak at 285.6 eV can be attributed to the defects in the nanotube structure, whereas the peaks at 287.0 eV and 288.7 eV correspond to carbon atoms coordinated to different oxygen containing groups (C-O, O-C=O).14, 18-19 Moreover, the π-π* transition loss peak can also be observed at 291.3 eV 19. In the Mn 2p core-level spectrum shown in Figure 2c, a 2p3/2-2p1/2 doublet can be observed at 642.7 eV and 654.5 eV, with a spin-orbit splitting of 11.8 eV, which are in good agreement with those reported for Mn3O4 previously.5, 9, 18, 20



The O1s core-level spectra, shown in Figure 2d, is broad and asymmetric, and can be deconvoluted into three peaks centred at 530.0 eV, 531.5 eV and 533.6 eV, suggesting the presence of three different oxygen species. The peak around 530.0 eV can be attributed to MnO bond in Mn3O4, while the latter peaks confirms the presence of some hydroxyl (531.5 eV) and carboxylic (533.6 eV) functional groups onto the CNT surface, probably arising during functionalization of CNTs.14, 19, 21 These analyses collectively suggest the successful formation of CNT-Mn3O4 composites through the synthetic procedure adapted here. Additionally, typeIV N2 adsorption/desorption isotherm (Figure S2a, Supporting information) suggests mesoporous structure of the nanocomposite, with Brunauer–Emmett–Teller (BET) surface area of 163.6 m2/g and pore volume of 0.3287 cm3/g. However, the corresponding Barrett–Joyner– Halenda (BJH) pore size distribution remains within 1-8 nm. Electrochemical characterization of the CNT-Mn3O4 nanocomposite electrode Electrochemical properties of as-prepared CNT-nanoparticle composites along with asobtained bare-CNTs were investigated using three-electrode electrochemical cell with an Ag/AgCl reference electrode and a Pt counter electrode in 1M Na2SO4 aqueous electrolyte.

1.0

2 1

CNT

0 -1 -2 CNT-Mn3O4

-3 0.0

0.2

0.4

0.6

CNT CNT-Mn3O4

(b)

0.8

0.4 0.2

0 1.0

10 0 -10 10 mV/s 15 mV/s 20 mV/s

-20 -30

0.0

0.2

0.4

30 mV/s 40 mV/s 50 mV/s 100 mV/s

0.6

0.8

Potential (V) vs Ag/AgCl

6

CPEDL

Rel

4

200

400

600

0

CPEP

800 1000 1200

Rct

0

Time (s) Potential (V) vs Ag/AgCl

Current density (A/g)

20

8

2 0.0

0.8

(d)

CNT CNT-Mn3O4

10

0.6

Potential (V) vs Ag/AgCl 30

(c)

12

-Z'' (Ohm)

(a)

(e)

0.28 A/g 0.56 A/g 0.84 A/g 1.12 A/g 1.68 A/g 2.80 A/g 4.20 A/g

0.8 0.6 0.4 0.2 0.0 0

500

1000

1500

2

4

6

8

CPEW

10

12

Z' (Ohm)

2000

Time (s)


Specific capacitance (F/g)

3



4

350

(f )

300

600 500

250

400

200

300 200

150

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5


Areal capacitance (mF/cm2)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 28

Page 11 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. (a) Comparison of cyclic voltammograms (CVs) for pristine CNT and CNT-Mn3O4 nanocomposite electrodes at a scan rate of 10 mV/s, (b) GCD curves of the electrodes at a current density of 1.12 A/g, (c) shows the Nyquist plots for both of the electrodes comparing their Rel and Rct values based on the fittings using the equivalent circuit as shown in the inset; (d) CV curves of the CNT-Mn3O4 nanocomposite electrode at varying scan rates; (e) shows GCD curves at varying current densities, and (f) variation of areal and specific capacitances as a function of load current densities for the composite electrode. Figure 3a shows the comparison of cyclic voltammetry (CV) data for CNT-Mn3O4 and bareCNT electrodes obtained at a scan rate of 10 mV/s within the potential window of 0-0.8 V. It is observed that CNT-Mn3O4 composite electrode shows enhanced current density along with larger CV loop area in relation to the bare-CNT electrode, suggesting striking improvement in electrochemical performances of the composite electrode. Moreover, the CV data for CNTMn3O4 electrode is more rectangular in relation to the bare-CNT electrode which further reflects higher reversibility for the former electrode. The galvanostatic charge-discharge (GCD) data for the electrodes are also compared within the same potential window of 0-0.8 V at a current density of 1.12 A/g as shown in Figure 3b. The GCD profiles for the electrodes are almost linear with discharge profiles perfectly symmetrical to the charge profiles, without any significant iR-drop. Significantly enlarged GCD profile for the CNT-Mn3O4 electrode with almost 7 times longer discharge time as compared to the bare-CNT electrode further suggests improvement in the charge storage capacity post-combination of Mn3O4 nanoparticles with CNT. Such a striking improvement in the capacitive performance of the composite electrode can be ascribed to the synergistic combination of pseudocapacitive properties of Mn3O4, resulting from the surface or near-surface based fast faradaic reactions, along with the electrical double layer capacitance of bare-CNT electrode. The faradaic reactions for Mn3O4 electrode can be represented as follows: 5, 22 11 ACS Paragon Plus Environment


MnO x (OH) y   Na    e   Na  MnO x (OH) y

Page 12 of 28

(6)

Accordingly, the nanoparticle structure of Mn3O4 results in a significantly enhanced electroactive surface area for faradaic reactions and shortened ion-diffusion path length, together with the CNTs serving as highly conducting scaffold for poorly-conducting but highly-pseudocapacitive Mn3O4 nanoparticles. This in effect helps in achieving compelling capacitive performance for the composite electrode material. For further confirmation of enhanced electrochemical performance of the composite electrode material, electrochemical impedance spectroscopy (EIS) is carried out within the frequency range of 10 mHz to 100 kHz. The Nyquist plots for individual electrodes as depicted in Figure 3c suggest that the electrodes behave as resistors at high frequencies, while these act as pure capacitors at lower frequencies. In the frequency dependent region, the resistance of an electrode can increase owing to several factors. However, it is observed from Figure 3c that the low frequency part of the Nyquist plot for the composite electrode is almost vertical and indeed more parallel to the -Z″ axis as compared to that for the bare-CNT electrode. This suggests a complete invariance of the system resistance (real part Z′) with frequency. These arguments further establish a higher stability for the composite electrode material. The Nyquist plots are fitted using equivalent circuit (inset to Figure 3c) comprising various resistances and constant phase elements (ZCPE).23-24 Here, constant phase elements are used instead of simple capacitors for allowing distribution of capacitance values which is more relevant for surface charge storage in materials with disordered surface structure (for details see Supporting information and Table S1). From the fitting, the ohmic resistance (Rel) values are estimated to be 0.791 Ω for bare-CNT and 1.179 Ω for the CNT-Mn3O4 composite electrodes, respectively. Interestingly, the charge transfer resistance (Rct) calculated from the diameter of the semicircle in the mid-frequency range of the Nyquist plots is 0.634 Ω for the composite electrode, a value


Page 13 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


smaller than ~1 Ω obtained for the bare-CNT electrode, thus suggesting improved chargetransfer kinetics after combining pseudocapacitive Mn3O4 nanoparticles with highly conducting CNTs. Figure 3d represents the CV data for the CNT-Mn3O4 composite electrode obtained at varying scan rates within the potential window of 0 - 0.8 V. Semi-rectangular shape of the CV data even at higher scan rates can be attributed to the pseudocapacitive behaviour of Mn3O4 nanoparticles. It has been estimated that the composite electrode achieves a specific capacitance as high as 453 F/g at a scan rate of 10 mV/s with an active mass loading of 2 mg/cm2. The composite electrode outperforms many of the other nanostructured Mn3O4 electrodes as well as manganese oxide based hybrid electrodes at similar scan rates, namely Mn3O4 nanocubes (338 F/g),25 Mn3O4/MWCNT (379 F/g),26 Mn3O4/NGP (350 F/g),11 Graphene/Mn3O4 composite (110 F/g),18 MnO2-CNT (223 F/g),27 and MnO2/ZnO core-shell NRs (230 mF/cm2).28 At a scan rate of 100 mV/s, the electrode shows ~61% capacitance retention, which decreases gradually with increasing mass loading of CNT-Mn3O4 composite (Figure S3, Supporting information). The triangular shapes of the GCD data (Figure 3e) with symmetrical charge-discharge profiles observed at varying current densities suggest higher reversibility of the composite electrode owing to the pseudocapacitive properties of Mn3O4 supported by fast electron transport through CNTs. The specific capacitance values calculated from the discharge data are plotted in Figure 3f as a function of load current-densities. It can be observed that the composite electrode exhibits a capacitance value of about 304 F/g (equivalent to an aerial capacitance of 608 mF/cm2) at a load current-density of 0.28 A/g. The electrode can retain almost 60% of its initial capacitance as the current increases from 0.28 A/g to 4.2 A/g, suggesting good rate capability of the electrode. The capacitance values at varying current-densities are also found to be higher as compared to other manganese oxide based nanostructured electrode materials reported in the literature.10-11, 13 ACS Paragon Plus Environment

26, 29

Such an improved


capacitive performance for the CNT-Mn3O4 electrode supports the efficacy of designing composite materials over individual components. We have also checked the cycling stability of CNT-Mn3O4 composite over 16000 CV cycles (Figure S4, Supporting information) which shows ~100% capacitance retention during the process, suggesting excellent stability of the electrode material, which is better than the cycling performance for several Mn3O4-based electrodes reported in the literature.10-11, 26 Characterization of CNT-Fe3O4 nanocomposite anode and the assembled ASC

(a)

(b)

(c)

Intensity (arb. unit)

(002)

 CNT

Fe3O4

CNT-Fe3O4

Fe3O4 (JCPDS No. 65-3107) 40

50

2 (degree)

60

70 15

Fe2+ oct

Fe 2p Fe3+ oct Fe3+ tet Fe2+ sat

710

715

Fe3+ sat

720

725

730

Binding energy (eV)

735


(d)

30

10

(e)

5 0 -5 10 mV/s 15 mV/s 20 mV/s

-10 -15

-0.9

-0.6

30 mV/s 40 mV/s 50 mV/s 100 mV/s


20


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 28

-0.3


-0.9

(f )

0.2 A/g 0.4 A/g 0.6 A/g 0.8 A/g 1.0 A/g 1.5 A/g 2.0 A/g 3.0 A/g

-0.6

-0.3 0

600

1200

1800

2400

3000

Time (s)

Figure 4. (a) XRD pattern for the CNT-Fe3O4 nanocomposite electrode material along with the standard spectrum for Fe3O4 (JCPDS No. 65-3107); (b) TEM image of CNT-Fe3O4 nanocomposite showing Fe3O4 NPs anchored of on the CNT surface; (c) high resolution TEM image depicting well resolved lattice fringes; (d) Fe 2p core-level XPS spectrum for CNTFe3O4 nanocomposite, (e) CV curves for CNT-Fe3O4 nanocomposite electrode at varying scan rates, and (f) shows the GCD curves at varying current densities. To study the feasibility of CNT-Mn3O4 as positive electrode for an ASC, an ASC with CNTMn3O4 as positive electrode and CNT-Fe3O4 as negative electrode is designed. CNT-Fe3O4 is 14 ACS Paragon Plus Environment

Page 15 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


chosen as anode because of its high capacitive performance as anode material and easy synthesis. In fact, CNT-Fe3O4 nanocomposite are prepared following the same procedure as used for synthesising CNT-Mn3O4 composite simply by replacing the manganese precursor with the iron precursor, FeCl3.6H2O, making the synthesis versatile for preparing both positive and negative electrode materials. XRD analyses (Figure 4a and Figure S5, Supporting information) reveal that the synthesis results in a mixture of Fe2O3 and Fe3O4 nanoparticles, which after reduction by CNT during high-temperature anneal gives rise to the phase-pure Fe3O4 nanoparticles. The XRD data for the resultant sample can be best indexed with the Bragg planes of Fe3O4 (JCPDS No. 65-3107). Attachment of Fe3O4 nanoparticles with CNTs is confirmed through TEM analysis (Figure 4b); the HRTEM image shown in Figure 4c exhibits well resolved lattice fringes with spacing of 0.25 nm referring to the (311) planes of Fe3O4. To substantiate the phase purity of CNT-Fe3O4 sample, XPS analyses are performed as shown in Figures 4d and S6 (Supporting information). In Fe 2p core-level XPS spectrum (Figure 4d), two dominant peaks around binding energy values of 711 eV and 724.7 eV correspond to Fe 2p3/2 and Fe 2p1/2, respectively. On deconvoluting the spectrum, the lowest binding energy peak observed at 710.2 eV is ascribed to the Fe2+ ions in octahedral site (Fe2+oct) with corresponding satellite peak at 716.5 eV. However, the Fe3+ octahedral (Fe3+oct) and Fe3+ tetrahedral (Fe3+tet) species are found at binding energies of 711 eV and 713.1 eV, respectively, which are in good agreement with literature.30-31 The fitting also suggests 2+/3+ ratio as almost 0.5 for the Fe 2p3/2 transition as expected for stoichiometric Fe3O4. Further, the CNT-Fe3O4 nanocomposite exhibits a BET surface area of 90.5 m2/g and total pore volume of 0.3831 cm3/g, with BJH pore size distribution within 2-10 nm (Figure S2b, Supporting information), indicating mesoporous microstructure. Figure 4e depicts the CV data of the CNT-Fe3O4 composite electrode at varying scan rates, where semi-rectangular nature of the CV loops suggests dominance of pseudocapacitive properties for Fe3O4 over the EDLC behaviour of CNT. Pseudocapacitive



Page 16 of 28

charge storage in Fe3O4 is governed by the redox reaction between Fe3+ and Fe2+ ions with simultaneous intercalation of sulphate ions ( SO 24 ) so as to balance the extra charge inside iron oxide layers and can be described as follows:32-33 2Fe 2+ O + SO 24  (Fe3+ O) + SO 24 (Fe3+ O) + + 2e 

(7)

It is found that the CNT-Fe3O4 electrode exhibits a specific capacitance of about 373 F/g (equivalent to 1165 mF/cm2) at a scan rate of 10 mV/s within the potential window of -0.2 V and -0.9 V, which is higher than many other Fe3O4 based electrode materials at a similar scan rate reported in the literature, namely 270 F/g for Fe3O4-rGO,34 135 F/g for Fe3O4-CNF composite,33 232 F/g (@ 5 mV/s) for Fe3O4/Fe2O3 core-shell NWs,35 255 F/g for Fe2O3-CNT sponge,16 and 64.5 F/g (≈ 277 mF/cm2) for N-Fe2O3 NR electrodes.3 Symmetric and perfecttriangular like GCD curves at varying load current-densities (Figure 4f) further suggest pseudocapacitive charge storage in CNT-Fe3O4 nano-composites. The composite material achieves a specific capacitance of ~330 F/g at a current density of 0.2 A/g and retains ~ 52% of its initial capacitance at a current density of 3 A/g. Moreover, compelling cycling stability for CNT-Fe3O4 composite can be observed with almost 100% capacitance retention even after 16000 CV cycles (Figure S4, Supporting information).


Page 17 of 28

3

-1

30

80

20

70

10

1.2

1.4

1.6

Cell potential (V)

0

200

1.8

0

8

(e)

4 0 -4

10 mV/s 15 mV/s 20 mV/s

-8 0.0

0.4

0.8

1.2

400

600

800

1000

Time (s)

30 mV/s 40 mV/s 50 mV/s 100 mV/s

1.6

Cell potential (V)


40

90



50

1.0

2.0

V

(d)

0.8

1.5

Cell potential (V)

100

60

1.0

1 .8

110

0.5

V

0.0

V

0.8

1 .4

0.4

V

0.0

V

-0.4


V

-0.8

0.5 0.0

-2 -4

1.0

1 .6

Cell potential (V)

1 .8 V

1 .6 V

1 .4 V

1 .2 V

0

(c) 1.5

1 .2

-2

1 1 .0 V

0

2

0 .8 V

2

2.0

(b)

1 .0


(a)

0 .8


4

Energy density (Wh/kg)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2.0

160

(f )

140 120 100 80 60

0

20

40

60

80

100

Scan rate (mV/s)

Figure 5. (a) Comparison of CV curves for the CNT-Fe3O4 anode and CNT-Mn3O4 cathode within their respective potential windows at a scan rate of 10 mV/s; (b) CV curves and (c) GCD curves recorded at different potential windows ranging from 0.8-1.8V for the assembled CNTFe3O4//CNT-Mn3O4 hybrid ASC; (d) shows the evolution of specific capacitance and energy density of the ASC with increasing potential window; (e) CV curves for the ASC recorded at varying scan rates within the potential window of 0-1.8V, and (f) shows the variation of the calculated specific capacitance with scan rates. Figure 5a shows comparison of CV data for CNT-Fe3O4 anode and CNT-Mn3O4 cathode within their respective potential windows before assembling the ASC. To establish a stable operating potential window for the ASC, the CV data as well as corresponding GCD curves at different potential windows are recorded and the data are depicted in Figures 5b and 5c, respectively. It can be observed that the ASC demonstrates stable electrochemical behaviour with excellent reversibility within the potential window extended up to 1.8 V; notably, coulombic efficiency drops to about 81% above this voltage (Figure S7, Supporting information). For a quantitative analysis of the efficacy in assembling the ASC, specific capacitance and energy densities are 17 ACS Paragon Plus Environment


calculated for different potential windows and are plotted in Figure 5d. It is observed that the capacitance increases significantly from 66 F/g to 104.6 F/g as the potential window is increased from 0.8 V to 1.8 V. Meanwhile, the energy density of the ASC (calculated using E = 1/2CV2, C being the capacitance for the voltage window V) increased almost 800%, suggesting the efficacy of assembling the ASC. Figure 5e depicts the CV data for the ASC at different potential scan rates within the potential window of 0-1.8 V, where the semirectangular shape of the CV data results from the pseudocapacitive properties of individual electrode materials. The shape of the curves does not change much with increasing scan rate, suggesting good reversibility for the electrode materials. The capacitance values calculated from the CV data, plotted in Figure 5f, show that the CNT-Fe3O4//CNT-Mn3O4 ASC delivers a specific capacitance as high as 135.2 F/g at a scan rate of 10 mV/s that is larger than many other metal oxides or carbon-based ASCs, viz. 115 F/g for ZnO/α-Fe2O3//ZnO/C core-shell NR ASC,36 78 F/g for Activated carbon nano-fibre//Graphene/MnO2 ASC,37 70 F/g for MWNTα-Fe2O3//MWNT ASC,15 15 F/g for MWCNT based SSC,15 92 F/g (at 5 mV/s) for Fe2O3//MnO2 ASC,38 and 40 F/g for Graphene//MnO2 NW-Graphene ASC.39 The ASC retains almost 56% of its capacitance at a scan rate of 100 mV/s, suggesting good rate capability for the device. It is interesting to note that the GCD curves, shown in Figure 6a, are triangular in shape and charge profiles are almost symmetrical to the corresponding discharge profiles with small iR-drop. This suggests excellent reversibility for the assembled device that in turn would result in excellent cycle life for the device. The Nyquist plot for the ASC (Figure 6b) exhibits an ohmic resistance of 0.833 Ω, further suggesting low internal resistance of the electrode materials together with good conductivity of the electrolyte. The vertical line parallel to the Z″ axis in the low frequency region of the Nyquist plot corresponds to the diffusion-controlled charge-transfer processes in the system.


Page 18 of 28

Page 19 of 28

The long-term cycle life of the ASC is investigated by monitoring over 15000 CV cycles at a scan rate of 100 mV/s and corresponding capacitance retention data is plotted in Figure 6c. It is seen that the capacitance increases for the first few thousand cycles and then becomes almost constant for 10000 cycles and retains almost 100% of its initial capacitance, suggesting excellent cycling stability for the ASC reported in this study. Interestingly, semi-rectangular shape of the CV data for the ASC (inset to Figure 6c) is maintained even after 15000 cycles without significant change in loop area, further establishing good reversibility of the electrode

0.11 A/g 0.22 A/g 0.33 A/g 0.44 A/g 0.55 A/g 0.66 A/g 1.11 A/g 1.66 A/g

1.6 1.2 0.8

15

(b)

10

5

0.4

Rel = 0.833  Rct = 2.197 

0.0 0

500

1000

1500

2000

2500

0

3000

0

5

102 This work

V2O5-CNT//

101

15

8 4

1 st 5000 th 10000 th 15000 th

0 -4 -8 0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

Cell potential (V)

0

0

3000

6000

9000

12000

15000

Number of cycles

(g)

Fe2O3-CNT// MnO2-CNT ASC

Graphene Hydrogel// MnO2 ASC

MnO2-C ASC MnO2@

3D graphene SSC

M

W

CN

r-GO SSC

10

50

(e)

(d)

(c)

100

Z' (Ohm)

Time (s) CNT/PANI // CNT/MnO2/Graphene ASC

10

150


(a)

-Z'' (Ohm)

Cell potential (V)

2.0

Capacitance retention (%)

materials in the ASC device within the operating potential window.

Energy density (Wh/kg)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


T

SS

C

PEDOT//MnO2 Gr ASC a M n phen e/ / O 2 /G r ap he ne AS C

(f)

0

101

102

103

104

105

106

Power density (W/kg)

Figure 6. (a) GCD curves of the assembled CNT-Fe3O4//CNT-Mn3O4 hybrid ASC recorded at varying load current densities; (b) Nyquist plot for the assembled ASC along with the data fitted using equivalent circuit model shown in the inset of Figure 3c; (c) long term cycling performance of the ASC investigated at a scan rate of 100 mV/s ( inset to figure shows a few intermediate CV loops); (d) Ragone plot for the ASC gathered using GCD data at varying current densities, the energy and power density values reported for other ASCs are also included for comparison; as application of ASC devices: (e) shows a single ASC powering a 19 ACS Paragon Plus Environment


Red LED, while (f) shows the tandem ASC device lighting a Blue LED and (g) demonstrates three series-connected ASC devices employed for charging a Samsung mobile phone. Energy and power densities for the ASC are calculated using the GCD data shown in Figure 6a to compare the performance of the assembled ASC within the energy-power landscape of various other ASCs already reported in the literature. The Ragone plot, shown in Figure 6d, reveals that the CNT-Fe3O4//CNT-Mn3O4 hybrid ASC can deliver an energy density of around 37 Wh/kg at a load current of 0.11 A/g. Interestingly, the ASC can retain an energy density of 31.4 Wh/kg as the load current increases by 15 times and exhibits a maximum power density as high as 10.3 kW/kg, suggesting excellent rate capability for the device. Such a compelling energy-power performance for the present device can easily outperform many transition-metal oxide based and/or carbon-based symmetric SCs (SSCs) and hybrid ASCs reported in the literature,

3, 15, 29, 35, 38-46

including MWCNT-based SSC (6 Wh/kg),15 MnO2 on 3D Graphene

based SSC (6.8 Wh/kg),41 r-GO based SSC (3.1 Wh/kg),42 Graphene Hydrogel//MnO2 ASC (14.9 Wh/kg),29 Graphene//MnO2/Graphene ASC (7 Wh/kg),39 Fe2O3-CNT//MnO2-CNT ASC (19.2 Wh/kg),40 CNT/PANI//CNT/MnO2/Graphene ASC (24.8 Wh/kg),43 V2O5/CNT//MnO2C ASC (16 F/g),44 and PEDOT//MnO2 ASC (13.5 Wh/kg).46 To validate the feasibility of the present ASC in practical applications, some electronic systems are charged with the ASCs. After a single charge for 10s with a current of 50 mA, a single ASC cell (1.8 V) can light-up a commercial red LED for more than 2 min (Figure 6e), while two series-connected ASCs (3.6 V) can light up a commercial blue LED for almost 5 min (Figure 6f). Moreover, a tandem device with three ASCs connected in series can charge a commercial mobile phone (Samsung J5) for almost 1.5 min after a single charge for 15s with a current of 100 mA (Figure 6g and Movie S1, Supporting information). Accordingly, aforesaid observations do manifest the potential of the ASC reported in this study for powering electronic devices. Conclusions 20 ACS Paragon Plus Environment

Page 20 of 28

Page 21 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


A facile and versatile method is reported for synthesizing both positive and negative electrode materials comprising CNT-nanoparticle composites to realize a high-performance ASC. CNTMn3O4 and CNT-Fe3O4 composites are prepared by simply changing the precursors for Mn and Fe ions keeping other reaction conditions unaltered, thus making the process scalable and viable for industrial level fabrication of electrode materials. The assembled ASC has attractive specific capacitance and energy-power densities within a potential window of 0-1.8 V in an aqueous electrolyte and exhibits almost 100% capacitance retention during 15000 cycles, which is rarely observed in aqueous medium. Moreover, the ASCs can power various LEDs and charge mobile phones suggesting their potential for applications as power source in widerange electronic gadgets. It is noteworthy that further improvement in the device performance is highly likely as the engineering parameters are not yet fully optimized. ASSOCIATED CONTENT Supporting Information. Additional details including calculation methods of different electrochemical performance parameters, TEM image of Mn3O4 anchored on CNT, N2 adsorption/desorption curves for surface area analyses, description of equivalent circuit for fitting Nyquist plots and fitting parameters, capacitance retention at different mass loadings of CNT-Mn3O4, cycling performance of individual electrode materials, XRD pattern of the sample obtained after decomposing Fe-hexacyanoferrate complex, XPS analyses of CNTFe3O4 composite, GCD analyses for the assembled ASC, and a movie on charging mobile phone with tandem ASCs. AUTHOR INFORMATION Corresponding authors: *Email: [email protected] and [email protected], Tel: +91 (80) 2293 2945 (D. Sarkar). 21 ACS Paragon Plus Environment


E-mail: [email protected], Tel: +91 (80) 2293 2795 (A. Shukla). Author contributions †Authors

contributed equally to this work.

Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS DS acknowledges the financial support from the Department of Science and Technology, Government of India, through an INSPIRE Faculty Award (IFA-14 MS-32). DDS thanks ‘Jamsetji Tata Trust’ for support. AKS & SP acknowledge financial support from UKRI Global Challenge Research Fund Project, SUNRISE (EP/P032591/1). REFERENCES (1) Simon, P.; Gogotsi, Y. Materials for Electrochemical Capacitors. Nat. Mater. 2008, 7 (11), 845-854. (2) Sarkar, D.; Khan, G. G.; Singh, A. K.; Mandal, K. High-Performance Pseudocapacitor Electrodes Based on α-Fe2O3/MnO2 Core–Shell Nanowire Heterostructure Arrays. J. Phys. Chem. C 2013, 117 (30), 15523-15531. (3) Lu, X.; Zeng, Y.; Yu, M.; Zhai, T.; Liang, C.; Xie, S.; Balogun, M.-S.; Tong, Y. OxygenDeficient Hematite Nanorods as High-Performance and Novel Negative Electrodes for Flexible Asymmetric Supercapacitors. Adv. Mater. 2014, 26 (19), 3148-3155. (4) Simon, P.; Gogotsi, Y.; Dunn, B. Where Do Batteries End and Supercapacitors Begin? Science 2014, 343 (6176), 1210-1211.


Page 22 of 28

Page 23 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(5) Xiong, T.; Lee, W. S. V.; Huang, X.; Xue, J. M. Mn3O4/Reduced Graphene Oxide based Supercapacitor with Ultra-Long Cycling Performance. J. Mater. Chem. A 2017, 5 (25), 1276212768. (6) Sarkar, D.; Shukla, A.; Sarma, D. D. Substrate Integrated Nickel–Iron Ultrabattery with Extraordinarily Enhanced Performances. ACS Energy Lett. 2016, 1 (1), 82-88. (7) Singh, A. K.; Sarkar, D. Substrate-Integrated Core-Shell Co3O4@Au@Cuo Hybrid Nanowires as Efficient Cathode Materials for High-Performance Asymmetric Supercapacitors with Excellent Cycle Life. J. Mater. Chem. A 2017, 5 (41), 21715-21725. (8) Sarkar, D.; Pal, S.; Mandal, S.; Shukla, A.; Sarma, D. D. α-Fe2O3-Based Core-ShellNanorod–Structured Positiveand Negative Electrodes for a High-Performance α-Fe2O3/C//αFe2O3/MnOx Asymmetric Supercapacitor. J. Electrochem. Soc. 2017, 164 (12), A2707-A2715. (9) Lee, G.; Kim, D.; Yun, J.; Ko, Y.; Cho, J.; Ha, J. S. High-Performance All-Solid-State Flexible Micro-Supercapacitor Arrays with Layer-by-Layer Assembled MWNT/MnOx Nanocomposite Electrodes. Nanoscale 2014, 6 (16), 9655-9664. (10) Subramani, K.; Jeyakumar, D.; Sathish, M. Manganese hexacyanoferrate derived Mn3O4 nanocubes-reduced graphene oxide nanocomposites and their charge storage characteristics in supercapacitors. Phys. Chem. Chem. Phys. 2014, 16 (10), 4952-4961. (11) Feng, J.-X.; Ye, S.-H.; Lu, X.-F.; Tong, Y.-X.; Li, G.-R. Asymmetric Paper Supercapacitor Based on Amorphous Porous Mn3O4 Negative Electrode and Ni(OH)2 Positive Electrode: A Novel and High-Performance Flexible Electrochemical Energy Storage Device. ACS Appl. Mater. Interfaces 2015, 7 (21), 11444-11451. (12) Hu, Y.; Guan, C.; Feng, G.; Ke, Q.; Huang, X.; Wang, J. Flexible Asymmetric Supercapacitor based on Structure-Optimized Mn3O4/Reduced Graphene Oxide Nanohybrid Paper with High Energy and Power Density. Adv. Funct. Mater. 2015, 25 (47), 7291-7299.



(13) Huang, S.-Z.; Cai, Y.; Jin, J.; Liu, J.; Li, Y.; Yu, Y.; Wang, H.-E.; Chen, L.-H.; Su, B.-L. Hierarchical Mesoporous Urchin-Like Mn3O4/Carbon Microspheres with Highly Enhanced Lithium Battery Performance by In-Situ Carbonization of New Lamellar Manganese Alkoxide (Mn-DEG). Nano Energy 2015, 12, 833-844. (14) Sathiya, M.; Prakash, A. S.; Ramesha, K.; Tarascon, J. M.; Shukla, A. K. V2O5-Anchored Carbon Nanotubes for Enhanced Electrochemical Energy Storage. J. Am. Chem. Soc. 2011, 133 (40), 16291-16299. (15) Zhao, X.; Johnston, C.; Grant, P. S. A Novel Hybrid Supercapacitor with a Carbon Nanotube Cathode and an Iron Oxide/Carbon Nanotube Composite Anode. J. Mater. Chem. 2009, 19 (46), 8755-8760. (16) Cheng, X.; Gui, X.; Lin, Z.; Zheng, Y.; Liu, M.; Zhan, R.; Zhu, Y.; Tang, Z. ThreeDimensional α-Fe2O3/Carbon Nanotube Sponges as Flexible Supercapacitor Electrodes. J. Mater. Chem. A 2015, 3 (42), 20927-20934. (17) Masarapu, C.; Zeng, H. F.; Hung, K. H.; Wei, B. Effect of Temperature on the Capacitance of Carbon Nanotube Supercapacitors. ACS Nano 2009, 3 (8), 2199-2206. (18) Lee, J. W.; Hall, A. S.; Kim, J.-D.; Mallouk, T. E. A Facile and Template-Free Hydrothermal Synthesis of Mn3O4 Nanorods on Graphene Sheets for Supercapacitor Electrodes with Long Cycle Stability. Chem. Mater. 2012, 24 (6), 1158-1164. (19) Datsyuk, V.; Kalyva, M.; Papagelis, K.; Parthenios, J.; Tasis, D.; Siokou, A.; Kallitsis, I.; Galiotis, C. Chemical Oxidation of Multiwalled Carbon Nanotubes. Carbon 2008, 46 (6), 833840. (20) Gao, S.; Geng, K. Facile Construction of Mn3O4 Nanorods Coated by a Layer of NitrogenDoped Carbon with High Activity for Oxygen Reduction Reaction. Nano Energy 2014, 6, 4450.


Page 24 of 28

Page 25 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(21) Sarkar, D.; Singh, A. K. Mechanism of Nonvolatile Resistive Switching in ZnO/α-Fe2O3 Core–Shell Heterojunction Nanorod Arrays. J. Phys. Chem. C 2017, 121 (23), 12953-12958. (22) Hu, C.-C.; Tsou, T.-W. The Optimization of Specific Capacitance of Amorphous Manganese Oxide for Electrochemical Supercapacitors using Experimental Strategies. J. Power Sources 2003, 115 (1), 179-186. (23) Pokrzywinski, J.; Keum, J. K.; Ruther, R. E.; Self, E. C.; Chi, M.; Meyer Iii, H.; Littrell, K. C.; Aulakh, D.; Marble, S.; Ding, J.; Wriedt, M.; Nanda, J.; Mitlin, D. Unrivaled Combination of Surface Area and Pore Volume in Micelle-templated Carbon for Supercapacitor Energy Storage. J. Mater. Chem. A 2017, 5 (26), 13511-13525. (24) Brezesinski, T.; Wang, J.; Senter, R.; Brezesinski, K.; Dunn, B.; Tolbert, S. H. On the Correlation between Mechanical Flexibility, Nanoscale Structure, and Charge Storage in Periodic Mesoporous CeO2 Thin Films. ACS Nano 2010, 4 (2), 967-977. (25) Luo, Y.; Yang, T.; Li, Z.; Xiao, B.; Zhang, M. High Performance of Mn3O4 Cubes for Supercapacitor Applications. Mater. Lett. 2016, 178, 171-174. (26) Mondal, C.; Ghosh, D.; Aditya, T.; Sasmal, A. K.; Pal, T. Mn3O4 Nanoparticles Anchored to Multiwall Carbon Nanotubes: A Distinctive Synergism for High-Performance Supercapacitors. New J. Chem. 2015, 39 (11), 8373-8380. (27) Xia, H.; Wang, Y.; Lin, J.; Lu, L. Hydrothermal Synthesis of MnO2/CNT Nanocomposite with a CNT Core/Porous MnO2 Sheath Hierarchy Architecture for Supercapacitors. Nanoscale Research Letters 2012, 7 (1), 33. (28) Zilong, W.; Zhu, Z.; Qiu, J.; Yang, S. High Performance Flexible Solid-State Asymmetric Supercapacitors from MnO2/ZnO Core-Shell Nanorods//Specially Reduced Graphene Oxide. J. Mater. Chem. C 2014, 2 (7), 1331-1336.



Page 26 of 28

(29) Gao, H.; Xiao, F.; Ching, C. B.; Duan, H. High-Performance Asymmetric Supercapacitor Based on Graphene Hydrogel and Nanostructured MnO2. ACS Appl. Mater. Interfaces 2012, 4 (5), 2801-2810. (30) Wilson, D.; Langell, M. A. XPS Analysis of Oleylamine/Oleic Acid Capped Fe3O4 Nanoparticles as a Function of Temperature. Appl. Surf. Sci. 2014, 303, 6-13. (31) Poulin, S.; França, R.; Moreau-Bélanger, L.; Sacher, E. Confirmation of X-ray Photoelectron Spectroscopy Peak Attributions of Nanoparticulate Iron Oxides, Using Symmetric Peak Component Line Shapes. J. Phys. Chem. C 2010, 114 (24), 10711-10718. (32) Zhu, J.; Tang, S.; Xie, H.; Dai, Y.; Meng, X. Hierarchically Porous MnO2 Microspheres Doped with Homogeneously Distributed Fe3O4 Nanoparticles for Supercapacitors. ACS Appl. Mater. Interfaces 2014, 6 (20), 17637-17646. (33) Mu, J.; Chen, B.; Guo, Z.; Zhang, M.; Zhang, Z.; Zhang, P.; Shao, C.; Liu, Y. Highly Dispersed Fe3O4 Nanosheets on One-Dimensional Carbon Nanofibers: Synthesis, Formation Mechanism, and Electrochemical Performance as Supercapacitor Electrode Materials. Nanoscale 2011, 3 (12), 5034-5040. (34) Qi, T.; Jiang, J.; Chen, H.; Wan, H.; Miao, L.; Zhang, L. Synergistic Effect of Fe3O4/reduced Graphene Oxide Nanocomposites for Supercapacitors with Good Cycling Life. Electrochim. Acta 2013, 114, 674-680. (35) Tang, X.; Jia, R.; Zhai, T.; Xia, H. Hierarchical Fe3O4@Fe2O3 Core–Shell Nanorod Arrays as High-Performance Anodes for Asymmetric Supercapacitors. ACS Appl. Mater. Interfaces 2015, 7 (49), 27518-27525. (36) Sarkar, D.; Das, S.; G, S.; Pal, B.; Rensmo, H.; Shukla, A.; Sarma, D. D. A Cost-Effective and

High-Performance

Core-Shell-Nanorod-Based

ZnO/α-Fe2O3//ZnO/C

Supercapacitor. J. Electrochem. Soc. 2017, 164 (6), A987-A994.


Asymmetric

Page 27 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(37) Fan, Z.; Yan, J.; Wei, T.; Zhi, L.; Ning, G.; Li, T.; Wei, F. Asymmetric Supercapacitors Based on Graphene/MnO2 and Activated Carbon Nanofiber Electrodes with High Power and Energy Density. Adv. Funct. Mater. 2011, 21 (12), 2366-2375. (38) Gund, G. S.; Dubal, D. P.; Chodankar, N. R.; Cho, J. Y.; Gomez-Romero, P.; Park, C.; Lokhande, C. D. Low-cost Flexible Supercapacitors with High-energy Density based on Nanostructured MnO2 and Fe2O3 Thin Films Directly Fabricated onto Stainless Steel. Sci. Rep. 2015, 5, 12454. (39) Wu, Z.-S.; Ren, W.; Wang, D.-W.; Li, F.; Liu, B.; Cheng, H.-M. High-Energy MnO2 Nanowire/Graphene and Graphene Asymmetric Electrochemical Capacitors. ACS Nano 2010, 4 (10), 5835-5842. (40) Gu, T.; Wei, B. High-performance All-solid-state Asymmetric Stretchable Supercapacitors based on Wrinkled MnO2/CNT and Fe2O3/CNT Macrofilms. J. Mater. Chem. A 2016, 4 (31), 12289-12295. (41) He, Y.; Chen, W.; Li, X.; Zhang, Z.; Fu, J.; Zhao, C.; Xie, E. Freestanding ThreeDimensional Graphene/MnO2 Composite Networks as Ultralight and Flexible Supercapacitor Electrodes. ACS Nano 2013, 7 (1), 174-182. (42) Zhang, J.; Jiang, J.; Li, H.; Zhao, X. S. A High-performance Asymmetric Supercapacitor Fabricated with Graphene-based Electrodes. Energy Environ. Sci. 2011, 4 (10), 4009-4015. (43) Jin, Y.; Chen, H.; Chen, M.; Liu, N.; Li, Q. Graphene-Patched CNT/MnO2 Nanocomposite Papers for the Electrode of High-Performance Flexible Asymmetric Supercapacitors. ACS Appl. Mater. Interfaces 2013, 5 (8), 3408-3416. (44) Chen, Z.; Qin, Y.; Weng, D.; Xiao, Q.; Peng, Y.; Wang, X.; Li, H.; Wei, F.; Lu, Y. Design and Synthesis of Hierarchical Nanowire Composites for Electrochemical Energy Storage. Adv. Funct. Mater. 2009, 19 (21), 3420-3426.



(45) Zhao, Y.; Ran, W.; He, J.; Huang, Y.; Liu, Z.; Liu, W.; Tang, Y.; Zhang, L.; Gao, D.; Gao, F. High-Performance Asymmetric Supercapacitors Based on Multilayer MnO2/Graphene Oxide Nanoflakes and Hierarchical Porous Carbon with Enhanced Cycling Stability. Small 2015, 11 (11), 1310-1319. (46) Khomenko, V.; Raymundo-Piñero, E.; Frackowiak, E.; Béguin, F. High-voltage Asymmetric Supercapacitors Operating in Aqueous Electrolyte. Appl. Phys. A 2006, 82 (4), 567-573.


Page 28 of 28

Realizing an Asymmetric Supercapacitor Employing Carbon

Recommend Documents