Hansung Kim and Branko N' Popov

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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
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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
• 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 (5064 F/g), MnO2 (140160 F/g), Co3O4 ( 290
  F/g)..
• RuO2 (700 F/g)

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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

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Comparison of Preparation Techniques for RuO2
/carbon composite electrode

• Heat decomposition
• 300 oC annealing temperature
• 2nm particle size of RuO2
• Crystalline structure
• 330 F/g of RuO2
• Sol-gel method
• 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

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Objectives

• By using the new colloidal method,
• To increase the specific capacitance of RuO2nH2O
  
• decreasing particle size of RuO2nH2O to nano
  scale
• synthesizing amorphous RuO2nH2O
• optimizing the annealing temperature
• To optimize the RuO2nH2O and carbon ratio in
  composite electrode
• To improve the power rate at high current
  discharge

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Electrode Preparation using the Colloidal Method
Preparation of the colloidal solution using
RuCl3xH2O (39.99 wt Ru) and NaHCO3
Adsorption of the colloidal particles using
carbon black
Filtration using a 0.45 mm filtering membrane
Annealing in air
Mixing with 5wt PTFE
Grounding to a pellet type electrode
Cold pressing with two tantalum grids
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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 RuO2nH2O
• 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
  RuO2nH2O adsorbed on the carbon
• BET was done to measure the specific surface area

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XRD patterns of pure RuO2nH2O powder with
annealing temperature
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FTRaman spectra of pure RuO2nH2O powder
annealed at 100 oC and 25 oC
100 oC
25 oC
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TEM image of RuO2nH2O/carbon composite
electrode (40 wt Ru)
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Cyclic voltammograms of RuO2.nH2O/carbon
electrode at different annealing temperatures
(40 wt Ru)
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Cyclic voltammogram of RuO2/carbon composite
electrode without heat treatment
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Cyclic voltammograms of RuO2.nH2O/carbon
composite electrode with different Ru loading
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Specific capacitance of RuO2nH2O /carbon
composite electrode as a function of Ru loading
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SEM images of RuO2.nH2O/carbon composite electrode
(80 wt Ru)
(60 wt Ru )
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Specific capacitance of RuO2nH2O as a function
of Ru loading
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Electrochemical performance of the 40wt Ru on
Vulcan XC-72 at various current densities
Time (s)
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Discharged energy density curves at the constant
power discharge of 4000W/kg based on the single
electrode.
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Ragone plot for RuO2/carbon composite electrode
containing different Ru loading
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Cycling behavior of RuO2nH2O /carbon composite
electrode (40 wt Ru)
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Conclusions

• Various contents of RuO2nH2O /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 RuO2nH2O with 35nm 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
• 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.
• 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.