Transcript Optimization of Nanostructured hydrous RuO /carbon composite supercapacitor using colloidal method

Optimization of Nanostructured hydrous RuO2/carbon
composite supercapacitor using colloidal method
by
Hansung Kim and Branko N. Popov
Department of Chemical Engineering
Center for Electrochemical Engineering
University of South Carolina
Department of Chemical Engineering
University of South Carolina
Supercapacitors for a high power density application
• High energy density compared to conventional dielectric capacitors
• High power density compared to secondary rechargeable batteries
• Combining with batteries and supercapacitor provides high efficiency
in the management of power system
• Electric double layer capacitance
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Charge separation between electrode surface and electrolyte
High surface area of carbon
~200 F/g of specific capacitance
Inaccessibility of electrolyte smaller than10Å micropore size
• Pseudocapacitance
– Fast reversible redox reaction occurring on the transition metal oxide
– NiO (50~64 F/g), MnO2 (140~160 F/g), Co3O4 ( ~290 F/g)..
– RuO2 (~700 F/g)
RuO (OH )  H  e  RuO  (OH ) 

x
y

x
y
Department of Chemical Engineering
University of South Carolina
Carbon composite material
• Problems of RuO2 supercapacitors
– High cost
– Low porosity
– Low rate capability due to the depletion of the electrolyte
• Advantages of carbon composite material
– Reducing cost material
– Utilizing both the pseudocapacitance and double layer capacitance
– Increasing porosity
– Increasing high rate discharge
Department of Chemical Engineering
University of South Carolina
Comparison of Preparation Techniques
for RuO2 /carbon composite electrode
• Heat decomposition
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–
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300 oC annealing temperature
2nm particle size of RuO2
Crystalline structure
330 F/g of RuO2
• Sol-gel method
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150 oC annealing temperature
amorphous structure
720 F/g of RuO2
Limitation on increasing RuO2 ratio ( ~10wt%)
Several m bulk size of RuO2 due to the formation of networked structure
by a series of hydrolysis and condensation reaction of metal alkoxide
precursors
Department of Chemical Engineering
University of South Carolina
Objectives
• By using the new colloidal method,
• To increase the specific capacitance of RuO2·nH2O
– decreasing particle size of RuO2·nH2O to nano scale
– synthesizing amorphous RuO2·nH2O
– optimizing the annealing temperature
• To optimize the RuO2·nH2O and carbon ratio in composite electrode
• To improve the power rate at high current discharge
Department of Chemical Engineering
University of South Carolina
Electrode Preparation using the Colloidal Method
Preparation of the colloidal solution using RuCl3·xH2O (39.99 wt% Ru) and NaHCO3
Adsorption of the colloidal particles using carbon black
Filtration using a 0.45 m filtering membrane
Annealing in air
Mixing with 5wt% PTFE
Grounding to a pellet type electrode
Cold pressing with two tantalum grids
Department of Chemical Engineering
University of South Carolina
Materials Characterization
• Cyclic voltammogram was used to measure the capacitance of the
electrode
• Constant current and constant power discharge test
• XRD was used to check the structure of RuO2·nH2O
• FTRaman spectroscopy was carried out to identify the change of the
material after the annealing process
• TEM and SEM was used to view the particle size of RuO2·nH2O
adsorbed on the carbon
• BET was done to measure the specific surface area
Department of Chemical Engineering
University of South Carolina
XRD patterns of pure RuO2·nH2O powder
with annealing temperature
Department of Chemical Engineering
University of South Carolina
FTRaman spectra of pure RuO2·nH2O powder
annealed at 100 oC and 25 oC
1000
Raman Intensity
800
600
400
100 oC
200
25 oC
0
400
600
800
1000
1200
Wavenumber (cm-1)
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University of South Carolina
TEM image of RuO2·nH2O/carbon composite electrode
(40 wt% Ru)
25 nm
Department of Chemical Engineering
University of South Carolina
Cyclic voltammograms of RuO2.nH2O/carbon electrode
at different annealing temperatures (40 wt% Ru)
Department of Chemical Engineering
University of South Carolina
Cyclic voltammogram of RuO2/carbon composite
electrode without heat treatment
Specific current (A/g)
0.6
0.4
2cycle
0.2
4cycle
6cycle
0.0
-0.2
-0.4
-0.6
0.0
0.2
0.4
0.6
0.8
1.0
Potential (V vs. SCE)
Department of Chemical Engineering
University of South Carolina
Cyclic voltammograms of RuO2.nH2O/carbon
composite electrode with different Ru loading
1.2
Bare Vulcan XC-72
20 wt% Ru
40 wt% Ru
60 wt% Ru
80 wt% Ru
Specific Current (A/g)
0.9
0.6
0.3
0.0
-0.3
-0.6
-0.9
0.0
0.2
0.4
0.6
0.8
1.0
Potential (V vs. SCE)
Department of Chemical Engineering
University of South Carolina
Specific capacitance of RuO2·nH2O /carbon
composite electrode as a function of Ru loading
700
Specific Capacitance (F/g)
600
500
400
300
200
100
0
0
10
20
30
40
50
60
70
80
90
Weight Percent of Ru (%)
Department of Chemical Engineering
University of South Carolina
SEM images of RuO2.nH2O/carbon composite electrode
3 m
3 m
(60 wt% Ru )
(80 wt% Ru)
Department of Chemical Engineering
University of South Carolina
Specific capacitance of RuO2·nH2O
as a function of Ru loading
Specific Capacitance (F/g of RuO 2)
900
850
800
750
700
650
600
10
20
30
40
50
60
70
80
90
Weight Percent of Ru (%)
Department of Chemical Engineering
University of South Carolina
Electrochemical performance of the 40wt% Ru on
Vulcan XC-72 at various current densities
0.9
0.8
0.7
0.6
0.5
0.4
200 mA/cm2
322 F/g
0.3
100 mA/cm2
0.2
344 F/g
300 mA/cm2
0.1
400 mA/cm2
277 F/g
300 F/g
0.0
0
10
20
30
40
50
60
70
Time (s)
Department of Chemical Engineering
University of South Carolina
Discharged energy density curves at the constant power
discharge of 4000W/kg based on the single electrode.
0.8
40wt% Ru
60 wt% Ru
80 wt% Ru
20 wt% Ru
Potential (V)
0.6
0.4
0.2
0.0
0
2
4
6
8
10
12
14
16
18
Energy density (Wh/kg)
Department of Chemical Engineering
University of South Carolina
Ragone plot for RuO2/carbon composite electrode containing
different Ru loading
60
20wt%
40wt%
60wt%
80wt%
Energy density (Wh/Kg)
50
Ru
Ru
Ru
Ru
40
30
20
10
0
70
200
500
1000
2000 30004000
Power density (W/Kg)
Department of Chemical Engineering
University of South Carolina
Cycling behavior of RuO2·nH2O /carbon composite electrode
(40 wt% Ru)
Specific capacitance (F/g)
400
380
360
340
320
300
0
200
400
600
800
1000
Cycle Number
Department of Chemical Engineering
University of South Carolina
Conclusions
•
Various contents of RuO2·nH2O /carbon composite electrodes were
synthesized successfully by colloidal method.
•
The annealing temperature was optimized to 100 oC
•
Optimum ratio of Ru on carbon was 40wt% and it showed amorphous
RuO2·nH2O with 3~5nm particle size and has specific capacitance of 863 F/g
•
It showed energy density of 17.6 Wh/kg (single electrode) at constant power
discharge of 4000 W/kg
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With increasing Ru content over 40 wt%, the particle size of Ru increased to
several m, which caused capacitance,BET and power rate to decrease sharply.
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From this fact, it can be concluded that nano size of hydrated ruthenium oxide
particle can attribute to increase specific capacitance and power rate.
•
Approximately 10% of capacitance was lost during 1000 cycles.
Department of Chemical Engineering
University of South Carolina