Optimization of Nanostructured hydrous RuO 2. /carbon composite supercapacitor using colloidal method

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1 Optimization of Nanostructured hydrous RuO 2 /carbon composite supercapacitor using colloidal method by Hansung Kim and Branko N. Popov Center for Electrochemical Engineering

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), MnO 2 (140~160 F/g), Co 3 O4 ( ~290 F/g).. RuO 2 (~700 F/g) RuO ( OH ) + H + δe RuO ( OH ) x + δ y x δ y+ δ

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 RuO 2 /carbon composite electrode Heat decomposition 300 o C annealing temperature 2nm particle size of RuO 2 Crystalline structure 330 F/g of RuO 2 Sol-gel method 150 o C annealing temperature amorphous structure 720 F/g of RuO 2 Limitation on increasing RuO 2 ratio ( ~10wt%) Several µm bulk size of RuO 2 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 RuO 2 nh 2 O decreasing particle size of RuO 2 nh 2 O to nano scale synthesizing amorphous RuO 2 nh 2 O optimizing the annealing temperature To optimize the RuO 2 nh 2 O 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 RuCl 3 xh 2 O (39.99 wt% Ru) and NaHCO 3 Adsorption of the colloidal particles using carbon black Filtration using a 0.45 µm 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 RuO 2 nh 2 O 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 RuO 2 nh 2 O adsorbed on the carbon BET was done to measure the specific surface area

8 XRD patterns of pure RuO 2 nh 2 O powder with annealing temperature

9 FTRaman spectra of pure RuO 2 nh 2 O powder annealed at 100 o C and 25 o C Raman Intensity o C o C Wavenumber (cm -1 )

10 TEM image of RuO 2 nh 2 O/carbon composite electrode (40 wt% Ru) 25 nm

11 Cyclic voltammograms of RuO 2. nh 2 O/carbon electrode at different annealing temperatures (40 wt% Ru)

12 Cyclic voltammogram of RuO2/carbon composite electrode without heat treatment cycle Specific current (A/g) cycle 6cycle Potential (V vs. SCE)

13 Cyclic voltammograms of RuO 2.nH 2 O/carbon composite electrode with different Ru loading Bare Vulcan XC wt% Ru 40 wt% Ru 60 wt% Ru 80 wt% Ru Specific Current (A/g) Potential (V vs. SCE)

14 Specific capacitance of RuO 2 nh 2 O /carbon composite electrode as a function of Ru loading Specific Capacitance (F/g) Weight Percent of Ru (%)

15 SEM images of RuO 2.nH 2 O/carbon composite electrode 3 µm 3 µm (60 wt% Ru ) (80 wt% Ru)

16 Specific capacitance of RuO 2 nh 2 O as a function of Ru loading 900 Specific Capacitance (F/g of RuO 2 ) Weight Percent of Ru (%)

17 Electrochemical performance of the 40wt% Ru on Vulcan XC-72 at various current densities Potential (V vs. SCE) ma/cm F/g 300 ma/cm ma/cm F/g 277 F/g 100 ma/cm F/g Time (s)

18 Discharged energy density curves at the constant power discharge of 4000W/kg based on the single electrode wt% Ru 60 wt% Ru 80 wt% Ru 20 wt% Ru Potential (V) Energy density (Wh/kg)

19 Ragone plot for RuO 2 /carbon composite electrode containing different Ru loading wt% Ru 40wt% Ru 60wt% Ru 80wt% Ru Energy density (Wh/Kg) Power density (W/Kg)

20 Cycling behavior of RuO 2 nh 2 O /carbon composite electrode (40 wt% Ru) 400 Specific capacitance (F/g) Cycle Number

21 Conclusions Various contents of RuO 2 nh 2 O /carbon composite electrodes were synthesized successfully by colloidal method. The annealing temperature was optimized to 100 o C Optimum ratio of Ru on carbon was 40wt% and it showed amorphous RuO 2 nh 2 O 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 µm, 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.