Beyond Batteries The Rise of Super Capacitors in Modern Energy Storage

ABSTRACT

The Ultimate source in the universe is the energy- which  can  neither be created nor destroyed. These energies can be stored in  several things of conventional capacitors, batteries, and supercapacitors. Due to the multiple drawbacks in capacitors and batteries, we are moving forward to the next category of supercapacitors.

In the last few decades, enormous electrode materials were synthesized and used to increase the energy storage in super capacitors such  as activated charcoal, which is amorphous in nature. CNT, which is 2D structured materials synthesized in 1991 by Iijima, is a difficult and several- step process to synthesize.

A revolution was created by a new carbon material of sp²  hybridized thin layer carbon atom called graphene. In recent years, symmetric and asymmetric solid-state super capacitor devices were investigated using newly synthesized electrode materials for practical application.

In our current scenario, we have investigated the electrochemical characteristic nature of one atom less boron and one atom more nitrogen- doped graphene nanosheet with the transition metal of copper oxide and tungsten gets anchored on the boron-doped graphene nanosheet.

Initially, the base materials of graphene oxide were synthesized by the oxidation of graphite powder using a strong oxidizing agent KMnO4 by  the modified hummer’s method. Using the synthesized GO as parent, precursors of copper sulphate pentahydrate (CuSO4. 5H2O) for copper and boron trioxide (B2O3) for boron. By simple hydrothermal method followed by pyrolysis at various temperatures from lower temperature 550 ˚C to a higher temperature of 950˚C with a certain increase in 100 ˚C temperature in

chemical vapour deposition (CVD) process by the flow of inert Argon gas in the flow rate of 100 sccm rates. The copper anchored boron-doped graphene nanosheet was synthesized and named as CuBG1 (550˚C), CuBG2 (650˚C), CuBG3 (750˚C), CuBG4 (850˚C), and CuBG5 (950˚C).

Using different weight ratios of graphene oxide and boron precursors of boric acid (H3BO3), boron trioxide (B2O3), and  amorphous  boron powder, the boron-doped graphene nanosheet was prepared initially by hydrothermal and followed by pyrolysis at high temperature 1000 ˚C for an hour. The as-prepared materials were named as HBG1 (1:2), HBG2 (1:1), HBG3 (2:1), HBG4 (3:1), BTG1 (1:2), BTG2 (1:1), BTG3 (2:1), BG1 (1:2),

BG2 (1:1), and BG3 (2:1).

Boron and nitrogen co-doped graphene nanosheet (BNUG) was synthesized by using the boric acid (H3BO3) and urea (Co(NH2)2) as a precursor by hydrothermal method at 180 ˚C followed by CVD method of pyrolysis at 1000 ˚C. The various samples were synthesized at different  weight ratios of urea by taking the graphene oxide and boric acid as  a  constant of 1:1. BNUG1 (1:1:0.25), BNUG2 (1:1:0.5), BNUG3 (1:1:0.75),

BNUG4 (1:1:1) and BNUG5 (1:1:1.25) were prepared.

A single heteropoly acid phosphor tungstenic acid was used as a precursor for both the phosphorous, tungsten, and boron trioxide (B2O3) for boron. Hierarchical tungsten oxide/carbide decorated boron and phosphorous doped graphene nanosheet (WBPG) was synthesized by hydrothermal method 150˚C followed by pyrolysis at various temperatures from 550˚C to 950˚C in an argon atmosphere. At different temperatures WBPG1 (550˚C), WBPG2 (650˚C), WBPG3 (750˚C), WBPG4 (850˚C) and WBPG5 (950˚C) were

synthesized.

The synthesized materials were initially characterized by an XRD pattern to know the crystalline nature of the materials, Raman spectra to calculate the ID/IG ratio which proceeds the level of order and disorder

patterns on the graphene sheet after the incorporation of the heteroatom on the sheet. Followed by above, the morphology of the materials was obtained by FESEM at lower magnification and HRTEM at higher magnification to  get  the fringes and the metal incorporation on the sheet. The chemical  composition and the bonding nature of the materials at various binding energies were picturized using XPS.

The energy storage potential of the synthesized materials was initially finding out at different potential voltages of positive or negative or both and the specific capacitance was calculated in the three-electrode system using the different aqueous electrolytes of H2SO4 and KOH. Among the synthesized electrode materials, the material which shows the higher capacitance was used for the solid-state supercapacitor device. The specific capacitance was calculated in the fabricated device and further used for practical applications.

The electrode materials CuBG which are prepared at five different temperatures CuBG4 (850˚C) exhibits the higher capacitance in the potential range of -0.4 V to 0.2 V in H2SO4. By using the CuBG4 as negative electrode materials and reduced graphene oxide as positive electrode materials the asymmetric supercapacitor device was fabricated using the H2SO4/PVA as a solid-gel electrolyte. Using the fabricated device rGO//CuBG4 the specific capacitance was calculated from charge-discharge at different potential ranges from 0.8 V to 2.0 V. Using the CuBG4 as positive and activated charcoal as negative a device was fabricated in KOH/PVA gel electrolyte. Using the device CuBG4//AC the specific capacitance was calculated at the different operating potential ranges of 0.8 V to 1.6 V.

The positive electrode materials of the synthesized HBG, BTG, and BG operated at a differential voltage of 0.9 V in H2SO4 electrolyte the capacitance was calculated at various stages.  Using the synthesized  material as an anode (+ve electrode) and reduced graphene oxide as a cathode (-ve

electrode) with H2SO4/PVA as a solid-gel electrolyte to calculate the capacitance of  the various two-electrode asymmetric supercapacitor devices  of HB1G//rGO, BTG2//rGO and BG3//rGO were investigated at the different potential range of 0.8 V to 2.0 V.

On the synthesize of electrode BNUG using a different weight ratio of urea, BNUG4 shows the higher capacitance in the higher operating  potential window of 0.0 V to 0.9 V in H2SO4 electrolyte. By using BNUG4 as

+ve electrode active material and activated charcoal as –ve  electrode  materials an asymmetric solid-state supercapacitor (BNUG4//AC) was fabricated and by using BNUG4 as active material a symmetric solid-state supercapacitor was fabricated with H2SO4/PVA as solid-gel electrolyte. Both the device was investigated for specific capacitance at a different electrode potential of 0.8 V to 1.8 V.

The well-structured WBPG material was used as the electrode material in the positive operating potential of 0.0 V to 1.0 V in an aqueous H2SO4 electrolyte, by using the discharge time the specific capacitance was calculated. WBPG3 which shows the higher capacitance in the 3 electrode system was used as the anode electrode material and rGO as  cathode  electrode material an asymmetric solid-state supercapacitor device was fabricated using the H2SO4/PVA as solid-gel electrolyte. By using  the  WBPG3 as active electrode material a symmetric solid-state device was fabricated and specific capacitance was calculated at different potentials 0.8 V to 1.8 V.

All the devices were investigated for the long-life cycle stability from the charge-discharge process, which is the most important for practical applications. The resistance of the electrode materials was calculated by using the Nyquist plot at various frequencies before and after the cycle stability. Ragone plot gives the energy and power density of all the electrode materials which is essential for energy storage.

TABLE NO. TITLE PAGE NO.

––––––––

3.4  Summary  of  boron  doped  graphene  in supercapacitor of the earlier and present  work  with the different sources, method and electrode for specific capacitance at different current

density/scan rate 146

Specific capacitance, electron density and power

density of all samples at different current density 184

Electrochemical parameters of EIS-Nyquist plot

in 1M H2SO4 187

Nyquist  plot  electrochemical  characterization parameters for BNUG4//AC ASSC device  193

Nyquist  plot  electrochemical  characterization parameters for BNUG4//BNUG4 SSC device  198

Specific capacitance (Csp) at different current densities 1 Ag-1 to 5 Ag-1, energy density (E.D) and power density (P.D) calculated from specific

capacitance 222

Nyquist plot - electrochemical impedance spectra

of resistance parameters in H2SO4 electrolyte 225

Nyquist  plot  electrochemical  characterization parameters for WBPG3//.rGO ASSC device  232

Nyquist  plot  electrochemical  characterization parameters for WBPG3//WBPG3 SSC device  238

6.1 A comparative study of the results obtained in

our work 245

LIST OF FIGURES

FIGURE NO. TITLE PAGE NO.

Different forms of energy for  the  production  of electricity 1

Ragone plot  for  different  electrochemical  energy storage device 2

Three different energy storage technology with

their mechanism of storage and applications 3

Historical development of conventional capacitor

from old technology to new technology 4

Lifeline of  battery  at  various  periods  and  its application in various electronics  5

Chronicles of supercapacitor at the versatile period

of over 300 years 8

Evolution, development and progress of supercapacitor        10

Divisions of supercapacitor via the charge storage mechanism 14

Mechanism  of  electro  chemical  double  layer capacitance 15

Mechanism of electrochemical pseudocapacitor 17

Mechanism of hybrid supercapacitor 18

Factors affecting the performance of supercapacitor        21

Development of supercapacitor for various electronic applications      26

Applications of supercapacitor in various product

which is environment friendly 27

Eight different allotropes of carbon 29

Basic features of graphene  in  various  synthesized material 31

Historical survey of graphene in various years 33

Properties  of  graphene  and  their  characteristics features 35

Various  application  of  graphene  at  different structures 37

Various types of electrolytes with an example 39

Ionic  liquid  used  in  various  fields  of  energy storage devices  40

Various organic electrolytes and  its  properties  in different functions  42

Various modes of aqueous electrolytes  and  its construction for high-voltage supercapacitors  43

Electron dot structure of boron, carbon, nitrogen,

and phosphorous 46

Unit  cell  structure  of  cupric  oxide  (CuO)  and cuprous oxide (Cu2O)  50

Hexagonal grid structure of tungsten carbide (WC) 51

Schematic representation of the synthesis of  copper nano particles anchored boron doped

reduced graphene nanosheet 71

Wide  angle  X-ray  diffraction  pattern  of  GO, CuBG1, CuBG2, CuBG3, CuBG4 and CuBG5  76

Raman spectra of  GO,  CuBG1,  CuBG2,  CuBG3, CuBG4 and CuBG5  79

FESEM images of CuBG1, CuBG2, CuBG3, CuBG4 and CuBG5 with an insertion images of different shapes of particles at high magnification

range 80

HRTEM images of CuBG1, CuBG2, CuBG3,

CuBG4 and CuBG5 at high magnification range

of 5 nm 81

HRTEM  images  of  all  samples  at  various magnification ranges  82

Particle size distribution histogram of prepared

CuBG samples 83

SAED  pattern  of  CuBG1,  CuBG2,  CuBG3, CuBG4 and CuBG5  84

X-ray  photo  electron  spectrum  of  Cu2p,  (a) CuBG3  and (b) CuBG4  85

X-ray photo electron spectrum of C1s, (a) CuBG3

and (b) CuBG4 86

X-ray photo electron spectrum of B1s, (a) CuBG3

and (b) CuBG4 87

(a) Cyclic voltammogram of  all  samples  at  5  mV s-1 and (b) Specific capacitance of all samples

at different scan rate from 10 to 100 mV s-1 90

(a) Cyclic voltammetery of CuBG4 from higher to lower scan rate and (b) Charge discharge of

CuBG4 at different current density 90

(a) Charge discharge curve of all sample at 1 Ag-1 and (b) Specific capacitance of all samples at

different current density from 1 Ag-1 to 20 Ag-1 91

(a) EIS-Nyquist plot of all samples at a frequency range of 1 MHz to 0.1 Hz, (b) Ragone plot of energy and power density of all sample calculated from specific capacitance obtained in charge

discharge 93

(a) Cyclic voltammogram of rGO at different scan rate, (b) the specific capacitance obtained at different scan rate from 100 to 10 mV s-1, (c) Charge/discharge curve of rGO at different current densities from 1 to 10 Ag-1 and (d) the specific

capacitance at different current densities. 95

(a) Specific capacitance and capacitance retention for a long cyclic stability of 5000 cycles at 5 Ag-1, and (b) Specific capacitance and capacitance retention calculated using the CV curve, cyclic

stability for 2000 cycles. 96

(a) Schematic representation of ASSC device rGO//CuBG4, (b) 2.0 V of red LED being illuminated with an ASSC device, (c) Cyclic voltammogram of rGO//CuBG3 device at 50 mV s-1,

(d) Cyclic voltammogram of rGO//CuBG4 device at  50  mV  s-1,  and  (e)  Cyclic  voltammogram of

rGO//CuBG5 device at 50 mV s-1 98

(a) CV curve of ASSC device at different potential from 0.8 V to 2.0 V, (b) Charge-discharge  curve  of ASSC device at different potential from 0.8 V  to 2.0 V in a current density of 0.5 Ag-1, (c) CV curve of rGO//CuBG4 at high potential with different scan rate and (d) Charge-discharge curve of device at different current density from 1 to 20

Ag-1 in H2SO4/PVA gel electrolyte. 99

(a) Specific capacitance at different potentials and at different current densities from 1 to 20

Ag-1 calculated from the discharge curve, (b) Energy and power density calculated from the specific capacitance at different potentials and at different current densities, (c) Percentage of capacitance retention and percentage of coulombic efficiency of rGO//CuBG4 for 5000 cycles, (d) Nyquist plot before and after the cyclic stability test of 5000 cycles, the inset shows the  circuit  used for the calculation and the table showing the

electrochemical studies is shown. 100

(a) CV of all CuBG samples at a scan rate of 10 mV s-1, (b) Variation of the specific capacitance of CuBG samples at different scan rates, (c) CV of CuBG4 at different scan rate  from  100  to  10  mV s-1 and (d) Charge-discharge of CuBG4 at

various current densities from 1 to 20 Ag-1. 104

(a) Charge/discharge curve of CuBG samples at 1 Ag-1, and (b) Specific capacitance of samples at

different current densities from 1 to 20 Ag-1. 105

(a) EIS-Nyquist plot for all of the CuBG samples.

(b) Energy and power density of all samples calculated from the discharge time at different

current densities in the KOH electrolyte. 106

(a) CV curve of activated charcoal at different  scan rate (b) CD curve of activated charcoal at different current densities from 1 to 5 Ag-1 and (c)

Specific capacitance of activated charcoal calculated at different current densities    107

(a) Schematic diagram of ASSC device CuBG4//AC with KOH/PVA electrolyte, and (b)

CV of CuBG4 and Activated carbon at 50 mV s-1. 108

(a) CV curve of ASSC device at different potentials from 0.8 to 1.6 V, (b) Charge/discharge curve of ASSC device at different potentials,  (c and d) CV and charge-discharge curve of ASSC at

different scan rates in a high potential of 1.6 V. 110

(a) Specific capacitance at different potentials and at different current densities from 1 to 20 Ag-1 calculated from the discharge curve, (b) Energy and power density calculated from the specific capacitance at different potentials and different 1current densities, (c) Percentage of capacitance retention and percentage of coulombic efficiency for CuBG4//AC for 5000 cycles in a KOH/PVA electrolyte and (d) Nyquist plot before and after

the cyclic stability test of 5000 cycles. 111

Schematic representation of boron  doped  reduced graphene nanosheet  119

X-ray diffraction spectra of GO, HBG1, HBG2, HBG3, HBG4, BG1, BG2, BG3, Graphite, BTG1,

BTG2 and BTG3 122

Raman spectra of GO, HBG1, HBG2, HBG3,

HBG4, BG1, BG2, BG3, Graphite, BTG1, BTG2

and BTG3 123

FESEM images of (a) HBG1, (b) HBG2, (c) HBG3, (d) BG1, (e) BG2, (f) BG3, (g) BTG1, (h)

BTG2, and (i) BTG3 124

HRTEM images of (a) HBG1, (b) HBG2, (c) HBG3, (d) BG1, (e) BG2, (f) BG3, (g) BTG1, (h) BTG2, and (i) BTG3 at higher magnification of

5nm 126

HRTEM images of HBG1, HBG2, and HBG3, at

various magnification 127

HRTEM images of BG1, BG2, and BG3 at

various magnification 128

HRTEM images of BTG1, BTG2, and BTG3 at

various magnification 129

SAED pattern of (a) HBG1, (b) HBG2, (c) HBG3,

(d) BG1, (e) BG2, (f) BG3, (g) BTG1, (h) BTG2,

and (i) BTG3 at 5 1/nm. 130

X-ray photo electron spectra of Carbon1s,

(a)  HBG1, (b) BG3, and (c) BTG2 132

X-ray   photo electron spectra of Boron1s,

(a)  HBG1, (b) BG3, and (c) BTG2 133

X-ray photo electron spectra of Oxygen1s,

(a)  HBG1, (b) BG3, and (c) BTG2 134

(a) Cyclic voltammetry curve of samples at a

scan rate of 10 mV s-1. 137

CV and CD curve of HBG1, HBG2  and  HBG3  at different  scan  rate  and  at  different  current densities  138

CV  and  CD  curve  of  BG1,