This experimental work is performed in IIT Kharagpur.

1. Transition from solid to hollow nanostructures- a novel strategy for
improved electrochemical performance in supercapacitors
Presented
By
Sushanta Lenka
Roll No : 16PH62R23
Under the supervision of
Prof. Amreesh Chandra
Department of Physics
Indian Institute of Technology, Kharagpur
Kharagpur- 721302
West Bengal, India
May 2018

2. Outlines
• Introductions
• Classification of supercapacitor
• Internal configuration of supercapacitor
• Importance of Mn3O4 electrode materials
• Material Synthesis
• Structural and Morphological Analysis
• Electrochemical Analysis
• Conclusion and Suggestions for future works
• Reference

3. Introduction
Fig.1 (Ref.8)
 The utilization of fossil fuel are generating sever issues for
environmental polution and global warming.
 Until now, petroleum based fossil fuel has been largely used for
the power needs of the society.
 Scientist have turn their way from fossil fuel to intermittent
renewable sources (solar, wind).
 When the question of energy generation gets an answer, then the
other question starts evolving how we can store the generated
energy.
 Amongst the electrochemical energy storage devices,
Supercapacitors (SCs) are at the forefront with their distinctive
merits of rapid charging-discharging process, long lifespan,
superior durability, high specific power with low maintenance
 Gaps exist in both battery and supercapacitor technologies, with
neither one satisfying the need for both large power and energy
densities in a single device.

4. Classification of Supercapacitor
Electrolyte : Na2SO4, Li2SO4, NaOH, KOH,
NaCl etc.
Separator : Polymer polypyrolene,
polypropylene and other conducting
polymer etc
Electrode : Activated carbon, Metal
oxides, Conducting polymer etc.
Fig.2
Fig.3
Fig.4
Fig.2 shows classification of supercapacitor (Ref.4) , Fig.3 shows basic structure of
EDLC,Ref.5) , Fig.4 shows internal structure of supercapacitor (Ref.6).

5. Fig.6: Schematic diagram of the charged and discharged
electric double layer capacitor (Ref. J. Mater. Chem. A,
2014, 2, 4852).
Fig.5 Schematic internal configuration of
supercapacitor (Ref.2)
Ch=
Cd=
Where
= The Helmholtz layer capacitance
diffuse layer capacitance
δ = debye length
d = the thickness of the stern layer
€r = the dielectric constant of the solvent
€o = the permittivity of free space
K = Boltzmann constant
T = the temperature of the electrolyte solution,
Z = ionic charge
e = electronic charge
N = bulk concentration of ionic species.
Ch
Cd=
(1)
(2)
(3)
(4)
Internal configuration of Supercapacitor
δ= ∈𝒓∈𝒐 𝑲𝑻
𝟐 𝒁𝒆 𝟐𝑵

6. Importance of Mn3O4
Environmental compatibility.
Lot of progresses in the development of supercapacitor as reported many research papers
but low energy density and high production cost  major challenges.
Mn3O4 transition metal oxide abundant in nature.
Mainly to replace toxic and high cost RuO2 and IrO2.
 High theoretical capacity .
Good structural and chemical stability.
Mn3O4 is a unique mixed-valence oxide that adopts a tetragonal distorted spinel structure.
These materials have high scientific and technological interest due to their structural and
magnetic properties, which allow the development of theoretical and experimental
investigations.

7. Material Synthesis (Mn3O4)
Hexa-decyltrimethyl-ammonium
bromide +N-N-dimethyl formamide
Mixed with manganese acetate
solution and stir it 8 hrs at room
temperature
Centrifuge at 3000 RPM for 10
mints
Washed with distil water (3 times)
and ethanol (2 times)
Sample collected and calcined at
3000C
Dried at 800C for 8 hrs
Lubrizol (surfectant)+ Toloune (1 :
99 by wt )
Manganese acetate + above
solution (1:4 by molar)
Sonicate for 3 mints
Stir it over night at room
temperature
Centrifuge then dried it over night
Washed with distil water and
methanol (3 times)
Manganese chloride hexahydrate +
Sodium hydroxide solution
Mixed with CTAB and stir it 12 hrs
at room temperature
Centrifuge at 3000 RPM for 10
mints
Washed with distil water (3 times)
and ethanol (2 times)
Sample collected and calcined at
3000C
Dried at 800C for 12 hrs
Precipitate
method
(Solid Mn3O4)
Hydrothermal
method
(Porous Mn3O4)
Mini-emulsion
method
(Hollow Mn3O4)

8. Structure of Mn3O4
 General formulation AB2X4 (X anions Oxygen, A and B cations occupying some
of the octahedral and tetrahedral sites in the lattice)
Mn3O4 exist as Mn.Mn2O4, therefore Mn has two (+2 and +3) oxidation states.
A spinel unit-cell is made up of eight FCC cells made by oxygen ions in the configuration.
Fig.7
Fig.7 represents normal spinel structure of Mn3O4 transition metal oxide

9. Structural and morphological Analysis
(a)
(c)
(b)
XRD analysis
Fig.8
 All the samples shown crystalline
peaks of Mn3O4 phases.
 The average mono-crystallite size
was calculated from the XRD line
width using the Scherer formula.
𝒅 =
𝟎.𝟗𝝀
𝜷𝒄𝒐𝒔𝜽
Where λ is the X ray wavelength,
β is the width at half-height of the
main diffraction peaks and θ is the
diffraction angle.
 The peaks were matched and
indexed using JCPDS card no. 18-
0803
(Fig.8 represents XRD pattern of Mn3O4 transition metal oxide, (a) for solid, (b) for porous and (c) for hollow structure)

10. Structural and morphological Analysis
(c)
(b)
(a)
FTIR analysis
Fig.9
For further confirmation of the materials’
phase FTIR spectra were recorded for the
synthesized materials.
To determine the information regarding
the chemical bonds in the synthesized
materials, the samples were characterized
by FTIR within the wavelength range
400-4000 cm-1 (see Fig. 5).
The adsorption at 3412 cm-1 indicates the
presence of hydroxide group.
 The absorption peak around at 1623 and
1400 cm-1 may be attributed to O-H
bending vibrations with Mn atoms. The
two broad absorption bands at 609 and
511 cm-1 are associated with coupling
mode between Mn-O stretching modes of
tetrahedral and octahedral sites.
(Fig.9 represents FTIR pattern of Mn3O4 transition metal oxide, (a) for
solid, (b) for porous and (c) for hollow structure)

11. Structural and morphological Analysis
BET surface area analysis
Fig.10
The specific surface area of the
synthesized Mn3O4 solid, porous and
hollow nanostructures were further
investigated by N2 adsorption-desorption
measurements.
The BET surface areas of the solid,
porous and hollow Mn3O4 samples are
measured to be 24.8 m2 g−1, 34 m2g-1 and
48 m2g-1 respectively.
The specific surface area can provide
more electroactive sites for faradic
reactions, which contributes to the
enhancement of specific capacitance.
We found the surface area is more in
porous structure, still it has low
capacitance value because the surface
sites of the porous metal oxide may not
be electrochemical active.
(a) (b)
(c)
(Fig.10 represents BET pattern of Mn3O4 transition metal oxide, (a) for solid,
(b) for porous and (c) for hollow structure)

12. Structural and morphological Analysis
(b)
(a)
(c)
(e)
(d)
(f)
SEM analysis
Fig.11
(Fig.11 represents SEM image of Mn3O4 transition metal oxide, (a) & (b) for solid
(c) & (d) for porous ,(e) & (f) for hollow structure at different magnifications)
 In general, the morphological features are very
important to renovate the electrochemical
performance of the material.
 It can be seen from Fig. 11(a-f) that most of the
Mn3O4 consist of spherical particles with nearly
uniform morphology, and roughly have a diameter
of 20-40 nm for solid, 50-100 nm for porous and
~100-200 nm for hollow structures.
 At higher magnifications, these microspheres with
hollow structures are composed of many petals
with an average thickness of less than 50 nm.
 it can be concluded that the micro/nano-structured
Mn3O4 microspheres are self-assembled by
nanoparticles. For better morphology, further
calcinations can be done.

13. Structural and morphological Analysis
(a) (b)
(d)
(c)
(e) (f)
TEM analysis
Fig.12
 It is visible from Fig. 12 (a-f) shows that the TEM
images are in accordance with the SEM images.
 Solid structures are distinctly visible with solid core
and no apparent variation in size of the particles was
observed.
 In fig. 12 (e,f), hollow nanostructures are clearly
visible and are composed of small nanoparticles
assembled around the soft template.
 When the template was removed, hollow cavity was
created, which is visible in the TEM images. All the
characterizations thus proved that the materials were
successfully synthesized in terms of structure, phase
morphology and surface area.
(Fig.12 represents SEM image of Mn3O4 transition metal oxide, (a) & (b) for solid (c) & (d) for porous ,(e) & (f) for hollow structure
at different magnifications)

14. 𝑪𝒔 =
𝟏
𝟐𝐦𝐕𝐒 −𝐯
𝐕
𝐈(𝐕)𝐝𝐕
m= mass of active material which
are interact with electrolyte
solution.
V =Applied potential window,
S=scan rate.
𝑪𝒔 =
𝐈
𝐦
𝐝𝐭
𝐕 − 𝐈𝐑
dt=discharge time
m = mass of electrode material
V = potential window.
R= internal resitance developed in
the supercapacitor
 Cyclic Voltamogram
 Charging and discharging
Electrochemical Analysis
Ref. bapatel@brighton.ac.uk

15. CyclicVoltameter
Scan rate
(mV/s)
Specific Capacitance (F/g)
Solid
Mn3O4
Porous
Mn3O4
Hollow Mn3O4
10 98.075 107.47 165.68
20 81.5 96.5 140.93
30 69.33 87.66 133.03
50 54.14 75.8 117.06
80 42.37 63.25 97.18
100 37.78 57.63 87.39
(a)
(c)
(b)
 Cyclic Voltamogram𝑪𝒔 =
𝟏
2𝐦𝐕𝐒 −𝐯
𝐕
𝐈(𝐕)𝐝𝐕
Electrochemical Analysis
Fig.13
 In order to understand the
working potential window,
redox potential of the active
species and charge storage
kinetics of the electrode, the
cyclic voltammetry was
carried out in 2 M KOH
electrolyte solution.
 The specific capacitance
was decreased with increase
in scan rate, which is due to
the decrease in charge
diffusion of the electrolyte
ions into the inner active
sites at higher scan rates.
(Fig.13 represents CV profile of Mn3O4 transition metal oxide, (a) for solid, (b) for porous
and (c) for hollow structure)

16. Current
Density(
A/g)
Specific Capacitance (F/g)
Solid Mn3O4 Porous
Mn3O4
Hollow Mn3O4
1 66.3 119.08 174
2 64.21 100.4 135.22
3 51.69 81.24 116.52
4 52.48 79.08 109.36
5 40.6 81.85 104.23
8 29.68 72.96 88.8
10 20.44 60.37 87.6
 Charging and Discharging method𝑪𝒔 =
𝐈
𝐦
𝐝𝐭
𝐕−𝐈𝐑
Electrochemical Analysis
Fig.14
 The linear region implies that the
electrode stores the charge based on
adsorption-desorption reaction at the
electrode surface. While, the non-
linear region indicates towards the
charge storage based on redox or
intercalation mechanism. It
demonstrates the pseudocapacitive
nature of the materials.
 We have performed CD
measurements at current densities 1-
5 A/g. The specific capacitance was
decreased with increase in current
density, which is normal behaviour
as discussed in the CV section.
(a) (b)
(c)
(Fig.14 represents CD profile of Mn3O4 transition metal oxide, (a) for solid, (b) for
porous and (c) for hollow structure)

17. Electrochemical Analysis
(a) (b)
(c) (d)
Fig.15
 The cycle stability test was carried
out by the GCD technique at a
current density of 8 A/g. The
specific capacitance as a function of
the cycle number is presented in
Fig. 11 (d). It can be seen from Fig.
11 (d) that the capacitance retention
is 95%, 89% and 87% after 3000
cycles for hollow, porous and solid
structures respectively.
 Capacitance retention decreases
with increase in cycle numbers. It is
clear that the hollow Mn3O4
electrode material obtained in the
present work has a better-activated
property than the solid and porous
Mn3O4 structures.
(Fig.15 represents comparative studies of Mn3O4 transition metal oxide, (a) for CD profile
(b) for CV profile (c) for current densities vs specific capacitance and (d) for cycle
retention)

18. Where we stand !
Materials
Current
Density
Specific
Capacitance (F/g) References
Graphene/Mn3O4 1 A/g 121 10
Mn3O4/CB-0.05 1 A/g 134 11
Mn3O4 Solid 1 A/g 113 12
Mn3O4 micro Hollow
cubic structure
1A/g 124 12
Mn3O4/G/CB-
0.02/0.01
1A/g 274 13
Mn3O4/CB-0.05 1 A/g 134 14
Mn3O4-Carbon
Composite
1A/g 150 15
Mn3O4 /Ni foam 1A/g 165 16
Mn3O4 Hollow Nano-
sphere
1A/g 174 Present Work
 hollow morphologies can enhance the electrochemical properties without the need of any extra additive efforts.
 These material on one side increases the specific capacitance values but on the other side increases cost of the overall
device.
 Therefore, development of hollow morphologies has great significance in terms of cost and economic feasibility.

19. Conclusion and Suggestions for future works
 Solid, Porous and Hollow nanostructures of Mn3O4, synthesized successfully and used as electrode materials in
supercapacitor applications.
 This proves the present study important in the field of energy storage, which opens a new dimension for the
researchers and supports the claim: “Hollowing the cavity of conventional solid nanoparticles can lead to next
generation materials for supercapacitors”.
 Cyclic stability was tested and capacitive retention was found for solid, porous and hollow structures are 89%, 88%
and 92% respectively.
 The specific capacitance is found more in Hollow structure as compared to its solid and Porous structures because
of more availability of surface sites.
 Future work in this field should be directed to focus on the synthesis of hollow structures with complex composition
of metal ions and the clear understanding of the synergetic effect should be focused on Mn3O4 spinel structure.
 For optimizing specific capacitance, different electrolyte solutions with different concentrations will be tested.
 Effect of organic electrolytes will be tested for better capacitive performance.
 Excellent electronic conductivity, high stability and mechanical flexibility of Mn3O4 based composite polymer
electrodes material will be studied for better capacitive performance.
 Temperature effect will be studied for better devices and for its industrial applications.

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22. Thank you