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by Hansung Kim and Branko N. Popov Department of Chemical Engineering

Optimization of Nanostructured hydrous RuO 2 /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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by Hansung Kim and Branko N. Popov Department of Chemical Engineering

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  1. 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

  2. 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 (50~64 F/g), MnO2 (140~160 F/g), Co3O4 ( ~290 F/g).. • RuO2 (~700 F/g)

  3. 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

  4. 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

  5. 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

  6. 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 mm filtering membrane Annealing in air Mixing with 5wt% PTFE Grounding to a pellet type electrode Cold pressing with two tantalum grids

  7. 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

  8. XRD patterns of pure RuO2·nH2O powder with annealing temperature

  9. FTRaman spectra of pure RuO2·nH2O powder annealed at 100 oC and 25 oC 100 oC 25 oC

  10. 25 nm TEM image of RuO2·nH2O/carbon composite electrode (40 wt% Ru)

  11. Cyclic voltammograms of RuO2.nH2O/carbon electrode at different annealing temperatures (40 wt% Ru)

  12. 2cycle 4cycle 6cycle Cyclic voltammogram of RuO2/carbon composite electrode without heat treatment

  13. Cyclic voltammograms of RuO2.nH2O/carbon composite electrode with different Ru loading

  14. Specific capacitance of RuO2·nH2O /carbon composite electrode as a function of Ru loading

  15. 3 m 3 m SEM images of RuO2.nH2O/carbon composite electrode (80 wt% Ru) (60 wt% Ru )

  16. Specific capacitance of RuO2·nH2O as a function of Ru loading

  17. 0.9 0.8 0.7 0.6 0.5 Potential (V vs. SCE) 0.4 2 200 mA/cm 322 F/g 0.3 2 100 mA/cm 0.2 344 F/g 2 300 mA/cm 300 F/g 0.1 2 400 mA/cm 277 F/g 0.0 0 10 20 30 40 50 60 70 Electrochemical performance of the 40wt% Ru on Vulcan XC-72 at various current densities Time (s)

  18. Discharged energy density curves at the constant power discharge of 4000W/kg based on the single electrode.

  19. Ragone plot for RuO2/carbon composite electrode containing different Ru loading

  20. Cycling behavior of RuO2·nH2O /carbon composite electrode (40 wt% Ru)

  21. 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 • 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.

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