Synthesis and Characterization of (Ru-Sn)O<sub>2</sub> Nanoparticles for Supercapacitors

doi:10.4236/msa.2011.29158

Paper Menu >>

Journal Menu >>

Materials Sciences and Applicatio ns, 2011, 2, 1175-1179

doi:10.4236/msa.2011.29158 Published Online September 2011 (http://www.SciRP.org/journal/msa)

1175

Synthesis and Characterization of (Ru-Sn)O2

Nanoparticles for Supercapacitors

Venkata Subba Reddy Channu1*, Rudolf Holze1, Scott Ambrose Wicker Sr.2, Edwin H. Walker Jr.2

Quinton L. Williams3, Rajamohan R. Kalluru3

1Institut für Chemie, AG Elektrochemie, Technische Universität Chemnitz, Chemnitz, Germany; 2Department of Chemistry, South-

ern University and A&M College, Baton Rouge, USA; 3Department of Physics, Atmospheric Sciences and Geoscience, Jackson State

University, Jackson, USA.

Email: [email protected]

Received February 17th, 2011; revised April 26th, 2011; accepted May 31st, 2011.

ABSTRACT

The electrode materials SnO2, RuO2 and (Sn-Ru)O2 were synthesized through precipitation method from SnCl22H2O

and RuCl22H2O solutions. The obtained nano-sized pristine products were characterized using X-ray diffractometry,

Scanning Electron Microscopy (SEM), differential scanning calorimetry (DSC)-thermogravimetric analysis (TGA) and

cyclic voltammetry (CV). The Debye–Scherrer formula was used to estimate the average size of the nanoparticles SnO2

(36 nm), RuO2(24 nm), and (Sn-Ru)O2 (19 nm). Electrochemical studies were carried out to examine the capacitance of

SnO2, RuO2, (Sn-Ru)O2 electrodes in 0.5 M H2SO4 at various scan rates. The estimated electrode capacitance was de-

termined to decrease with an increase of scan rate.

Keywords: Precipitation Synthesis, (Ru-Sn)O2 Nanocomposities, Supercapacitor

1. Introduction

Electrochemical capacitors (ECs) offer greater power

density than well-known batteries and can be quickly

discharged with no deleterious effect on lifetime. They

offer greater energy densities than electrostatic dielectric

capacitors, making them a better option for backup ap-

plications. ECs are becoming attractive energy storage

systems, particularly for applications involving high

power requirements. They are also being studied as a

means to improve battery performance when combined

as a hybrid power source. For instance, hybrid systems

consisting of batteries and electrochemical capacitors are

being pursued for electric vehicle momentum. In such

hybrid systems, ECs can provide the peak power during

acceleration and therefore, the batteries must be opti-

mized primarily for higher energy density and better cy-

cle life.

ECs are also attractive for other applications such as

power sources for lasers, pulsed light generators, digital

single lens reflex (SLR) camera and video flash equip-

ment, backup power sources for computer memory and

as appropriate sources to power quality applications like

Statcons and DVRs [1-3]. Power can be quickly injected

or absorbed to help minimize voltage fluctuations in dis-

tribution systems.

Energy storage mechanisms of electrochemical ca-

pacitors are of two types; first, double-layer capacitance

arising from the charge separation at the electrode/ elec-

trolyte interface and second, pseudocapacitance arising

from fast, reversible faradaic reactions occurring at or

near a solid electrode surface. Carbon materials which

offer high surface area are extensively used for dou-

ble-layer capacitors [4]. On the other hand, transition

metal oxides with relatively high surface area, such as

hydrous RuO2 [5], porous NiOx [6-8], CoOx. [9], and

MnO2 [10-12] have been acknowledged as possible elec-

trode materials for pseudocapacitors.

Tin oxide has been considered as one of the potential

electrode materials for pseudocapacitors. The sol–gel

process, hydrothermal synthesis and sonication methods

have been reported as methods for fabricating porous

SnO2 as an electrode material of ECs [13-16]. These

process methods are highly sophisticated and difficult to

employ in a controlled manner. For instance, the sol–gel

technique is a complicated multi-step process and it is

not easy to precisely control film thickness. The chemical

co-precipitation method is a simple and easy way to pre-

Synthesis and Characterization of (Ru-Sn)O Nanoparticles for Supercapacitors

1176 2

pare electroactive materials. Electrode materials for elec-

trochemical capacitors should exhibit high surface area

along with electrochemical activity in the given potential

range and high electric conductivity. The power loss of

ECs is essentially determined by the ohmic IR drop at

high power rate. The conductivity of stoichiometric tin

oxide is very low and pseudo capacitors fabricated by

SnO2 electrodes have low power and energy density.

However, materials mixed with conductive oxides of

transition metals (e.g., RuO2) and characterized by a high

surface area, have a high pseudocapacitive behavior and

a wider potential window of 1V between the anodic and

cathodic solvent discharge [14].

In this work, (Sn-Ru)O2 oxide nanocomposite elec-

trodes were prepared as a candidate for capacitors. A

mixed oxide composition containing 30 wt.% RuO2 was

chosen as it is adequate to modulate the conductive

properties of the system. The effect of the introduction of

RuO2 on the main physiochemical properties was ana-

lyzed.

2. Experimental

The SnCl22H2O powder (28 mM) was dissolved in 100

mL distilled water at room temperature. The pH of the

solution was adjusted to 9 by adding a 3 M NH4OH solu-

tion and stirred for 24 h. The pH-adjusted solution was

placed in an oven at 90˚C for 2 days to obtain dense col-

loid suspension. The obtained colloid suspension was

dried at 60˚C under static-air conditions, for 6 h. The

product was filtered, washed with distilled water, and

dried in air. Calcination was performed at 400˚C for 24 h.

A similar procedure was applied to prepare both RuO2

and (Sn-Ru)O2 nanomaterials.

Crystallographic information of the samples was ob-

tained using an X-ray powder diffractometer (D8 Ad-

vanced Brucker) equipped with graphite monochroma-

tized Cu Kα radiation (λ = 1.54187 Å). Diffraction data

was collected over the 2θ range of 20˚ to 80˚. Micro-

graphs of the nanoproducts were obtained by using a

JEOL Scanning Electron microscope (JSM6390F). For

the TGA measurements, a TA 600 operating in dynamic

mode (heating rate = 10˚C/min), was used. Samples of

5mg weight were placed in an alumina crucible. The

electrochemical properties of the SnO2, (Sn-Ru)O2 and

RuO2 nanoparticles were analyzed by using a

three-electrode cell with a platinum counter electrode and

a silver wire in the 0.1 mol/L AgCl solution as the refer-

ence electrode. The working electrode, prepared by mix-

ing 80 wt% of active material, 15 wt% of acetylene black

and 5 wt% of polytetrafluoroethylene (PTFE), was then

coated on a 1.0 cm2 ITO glass. A 0.5 mol/L solution of

H2SO4 was used as the electrolyte. Cyclic voltammetric

(CV) measurements were carried out between the poten-

tial limits of –0.2 and 1.0 V against Ag/AgCl using a

potentiostat/galvanostat (PRA 273). The CV curves were

recorded at scan rates of 10, 50 and 100 mVs–1

3. Results and Discussion

The phase purity and crystal structure of the samples

have been examined by powder XRD (Figure 1). Sam-

ples are identified as SnO2 and RuO2. The sample pre-

pared from the solution SnCl22H2O was SnO2 and all of

the reflection peaks are indexed to tetragonal SnO2

(JCPDS No: 01-088-0287) with lattice parameters a =

4.73735 Å and c = 3.18640 Å. The diffraction peaks of

the sample prepared from RuCl2.2H2O solution are in-

dexed to the tetragonal RuO2 (JCPDS No: 00-43-1027)

with lattice parameters of a = 4.49940 Å and c = 3.10710

Å. However, in the (Sn-Ru)O2 nanocomposite, peak in-

tensities are decreased and FWHM (broadness) of the

peaks is increased. The broadness of the peaks indicates

either particles of very small crystalline size or particles

which are semicrystalline in nature [15]. Sizes of the

SnO2, RuO2, (Sn-Ru)O2 crystallites were estimated using

the Debye-Scherrer formula to the first peak in the XRD

patterns. The size of SnO2, RuO2 and (Sn-Ru)O2 nano-

particles is 36 nm, 24 nm and 19 nm, respectively.

The thermal data of the SnO2, RuO2 and (Sn-Ru)O2

were measured using the thermogravimetric/differential

scanning calorimeters (TGA/DSC). Typical TGA curves

of the SnO2, RuO2 and (Sn-Ru)O2 measured from room

temperature to 700˚C with heating rate of 10˚C/min are

shown in Figure 2. The total weight loss of SnO2, RuO2

and (Sn-Ru)O2 is 2.7, 3.5 and 4.6 wt%, respectively. The

weight loss of water at temperatures above 300˚C was

due to dehydration of hydroxide groups on the surface of

the oxides. Compared to SnO2 and RuO2, the (Sn-Ru)O2

has more weight loss due to having more water involved

during the formation of composite Sn-Ru oxides.

The SEM observations of the SnO2, RuO2 and

20 30 40 50 60 70 80

(211)

(200)

(101) SnO2 ( JCP DS # 01-088-0287)

(110)

SnO2

2 (degree)

(211)

(200)

(101)

(110)

Intensity (CPS)

RuO2 ( JCPDS # 00-043-1027)

RuO2

70 % SnO 2 + 30 % RuO2

Figure 1. XRD patterns of nanoparticles: SnO2, RuO2 and

(Sn-Ru)O2.

Synthesis and Characterization of (Ru-Sn)O Nanoparticles for Supercapacitors1177

0100 200 300 400 500 600 700

95.0

95.5

96.0

96.5

97.0

97.5

98.0

98.5

99.0

99.5

100.0

100.5

SnO2

RuO2

70% S nO 2 + 30% RuO 2

Weight loss (%)

Tem perature( OC)

Figure 2. TGA curves of nanoparticles: SnO2, RuO2 and

(Sn-Ru)O2.

(Sn-Ru)O2 nanomaterials are shown in Figure 3. It is

apparent that the SnO2, RuO2 and (Sn-Ru)O2 nanoparti-

cles are conical and the particles are grown together.

There are several studies available in the literature on

RuO2 complexed as a second component with other ox-

ides [17-22]. The second component RuO2 includes SnO2,

CaO, Carbon, VOx, TiO2, MoO3 [23]. Over the other

complexed oxides, SnO2-RuO2 complex shows higher

electrochemical performance because of higher conduc-

tivity of SnO2.

The capacitance behavior of SnO2, RuO2, (Sn-Ru)O2

nanoparticles in a 0.5M H2SO4 electrolyte with a poten-

tial range of –0.2 V to 1.0 V vs. Ag/AgCl at a scan rate

of 10 mVs–1 is shown in Figure 4. Specific capacitance

of the nanoparticles was calculated from cyclic voltam-

metric (CV) curves using the following equation: C =

i/sm, where i is the average cathodic current, s is the scan

(a) (b)

(c)

Figure 3. SEM photographs of the nanoparticles (a) SnO2,

(b) RuO2 and (c) (Sn-Ru)O2.

-0.20.00.20.40.60.81.0

-4.0x10-3

-3.5x10-3

-3.0x10-3

-2.5x10-3

-2.0x10-3

-1.5x10-3

-1.0x10-3

-5.0x10-4

0.0

5.0x10-4

1.0x10-3

1.5x10-3

2.0x10-3

SnO2

(Sn-Ru )O 2

RuO2

Current[A]

Pot e n tial[ V vs.Ag/ AgCl]

Scanrate:10mV/s

Figure 4. Cyclic voltammograms(CV) of nanoparticles ob-

tained with scan rate 10 mV/s in a 0.5 M H2SO4 as an elec-

trolyte.

rate, and m is the mass of the electrode. The shapes of the

CV curves looks more or less rectangular, and no redox

peaks are observed for SnO2 electrode. From the CV

curve of the (Sn-Ru)O2 composite electrode, a large cur-

rent and symmetrical type of voltammogram with a rec-

tangular shape is found in both anodic and cathodic di-

rections compared to the SnO2 voltammogram. The en-

hancement in electrochemical performance of the com-

posite electrode can be attributed to surface faradic reac-

tions of the doped Ruthenium oxide phase in addition to

the original electrical capacitance of SnO2 electrode.

From the CV curve of the RuO2 electrode, a pair of oxi-

dation and reduction peaks is clearly found on the posi-

tive and negative sweeps at +0.05 V, +0.47 V, +0.41 V

and +0.1 V with high current density compare to the

SnO2, (Sn-Ru)O2 electrodes.

Figures 5-7 shows the cyclic voltammetric(CV) re-

sponses of the SnO2, (Sn-Ru)O2, RuO2 electrodes with

scan rates of 10, 50 and 100 mVs–1. The current under

the curve increased with the increasing scan rate due to

the reaction time is shorter and voltammetric current is

increased if the reversibility is excellent [16]. The meas-

ured specific capacitances were 1.84, 1.63 and 1.46 Fg–1

for SnO2 electrode, 6.08, 4.56 and 3.86 Fg–1 for

(Sn-Ru)O2 electrode, 10.19, 5.79 and 4.65 Fg–1 for RuO2

electrode at scan rates 10, 50, 100 mVs–1, respectively.

The capacitance values decreased with the increase in

scan rate. The observed specific capacitance values are

comparable with reported values of SnO2, (Sn-Ru)O2,

and RuO2 synthesized by other wet chemical methods

[14,24]. Literature reports indicate that the factors af-

fecting the capacitance are particle sizes and electro-

chemical conditions, namely type of electrolyte, concen-

tration of electrolyte, scan rate etc. [14,24]. Some other

factors affecting the capacitance are surface activation

Synthesis and Characterization of (Ru-Sn)O Nanoparticles for Supercapacitors

1178 2

-0.20.0 0.2 0.4 0.6 0.8 1.0

-2.5x10-3

-2.0x10-3

-1.5x10-3

-1.0x10-3

-5.0x10-4

0.0

5.0x10-4

1.0x10-3

1.5x10-3

10mV/s

50mV/s

100mV/s

Current[A]

P ote n tia l[V v s . Ag/AgCl]

SnO2

Figure 5. CV of SnO2 nanoparticles obtained at different

scan rates in a 0.5 M H2SO4 as an electrolyte.

-0.20.00.20.40.60.81.0

-6.0x10-3

-4.0x10-3

-2.0x10-3

0.0

2.0x10-3

4.0x10-3

6.0x10-3

10mV/s

50mV/s

100m V/ s

Current[A]

Potentia l[V vs. Ag/Ag Cl]

(Sn-R u)O2

Figure 6. CV of (Sn-Ru)O2 nanoparticles obtained at dif-

ferent scan rates in a 0.5 M H2SO4 as an electrolyte.

-0.20.0 0.20.40.60.81.0

-8.0x10-3

-6.0x10-3

-4.0x10-3

-2.0x10-3

0.0

2.0x10-3

4.0x10-3

6.0x10-3

8.0x10-3

1.0x10-2

10mV/s

50mV/s

100mV/s

Current[A]

Potential[V vs.Ag/AgCl]

RuO2

Figure 7. CV of RuO2 nanoparticles obtained at different

scan rates in a 0.5 M H2SO4 as an electrolyte.

under the electrochemical conditions, oxygen content on

the surface, surface oxides and lattice defects resulting

from the method of preparation.

4. Conclusions

The SnO2, RuO2 and (Sn-Ru)O2 nanoparticles were syn-

thesized using a precipitation method. Pristine nanoparti-

cles were characterized using XRD, SEM and TGA

techniques. The average size of the (Sn-Ru)O2 nanopar-

ticles is smaller than that of SnO2 and RuO2 nanoparti-

cles. Compared to SnO2 and RuO2 nanoparticles, the

(Sn-Ru)O2 nanoparticles have more weight loss. An

electrochemical study shows that the RuO2 electrode

exhibits higher capacity than SnO2 and (Sn-Ru)O2 elec-

trodes. The capacitances of the electrodes were found to

decrease with an increase of the scan rate.

5. Acknowledgments

One of the authors (VS Reddy Channu) thank the Alex-

ander von Humboldt Foundation for a fellowship.

REFERENCES

[1] B. E. Conway, “Transition from ‘Supercapacitor’ to

‘Battery’ Behavior in Electrochemical Energy Storage,”

Journal of the Electrochemical Society, Vol. 138, No. 6,

1991, pp. 1539-1548. doi:10.1149/1.2085829

[2] S. Trasatti and P. Kurzweil, “Electrochemical Superca-

pacitors as Versatile Energy Stores,” Platinum Metals

Review, Vol. 38, 1994, pp. 46-56.

[3] S. Sarangapani, B. V. Tilak and C. P. Chen, “Materials

for Electrochemical Capacitors,” Journal of the Electro-

chemical Society, Vol. 143, 1996, pp. 3791-3799.

doi:10.1149/1.1837291

[4] J. M. Miller, B. Dunn, T. D. Tran and R. W. Pekala,

“Deposition of Ruthenium Nanoparticles on Carbon

Aerogels for High Energy Density Supercapacitor Elec-

trodes,” Journal of the Electrochemical Society, Vol. 144,

No. 12, 1997, pp. L309-L311. doi:10.1149/1.1838142

[5] J. P. Zheng, P. J. Cygan and T. R. Zow, “Hydrous Ruthe-

nium Oxide as an Electrode Material for Electrochemical

Capacitors,” Journal of the Electrochemical Society, Vol.

142, 1995, pp. 2699- 2703. doi:10.1149/1.2050077

[6] K. C. Liu and M. A. Anderson, “Porous Nickel Oxide/

Nickel Films for Electrochemical Capacitors,” Journal of

the Electrochemical Society, Vol. 143, No. 1, 1996, pp.

124-130. doi:10.1149/1.1836396

[7] V. Srinivasan and J. W. Weinder, “An Electrochemical

Route for Making Porous Nickel Oxide Electrochemical

Capacitors,” Journal of the Electrochemical Society, Vol.

144, No. 8, 1997, pp. L210-L213. doi:10.1149/1.1837859

[8] V. Srinivasan and J. W. Weinder, “Studies on the Ca-

pacitance of Nickel Oxide Films: Effect of Heating Tem-

perature and Electrolyte Concentration,” Journal of the

Electrochemical Society, Vol. 147, No. 3, 2000, pp. 880-

885. doi:10.1149/1.1393286

Synthesis and Characterization of (Ru-Sn)O2 Nanoparticles for Supercapacitors

1179

[9] C. Lin, J. A. Ritter and B. N. Popov, “Characterization of

Sol-Gel-Derived Cobalt Oxide Xerogels as Electro-

chemical Capacitors,” Journal of the Electrochemical So-

ciety, Vol. 145, No. 12, 1998, pp. 4097-4103.

doi:10.1149/1.1838920

[10] S. C. Pang, M. A. Anderson and T. W. Chapman, “Novel

Electrode Materials for Thin-Film Ultracapacitors: Com-

parison of Electrochemical Properties of Sol-Gel-Derived

and Electrodeposited Manganese Dioxide,” Journal of the

Electrochemical Society, Vol.147, No. 2, 2000, pp. 444-

450. doi:10.1149/1.1393216

[11] S. C. Pang and M. A. Anderson, “Novel Electrode mate-

rials for Electrochemical Capacitors: Part II. Material

Characterization of Sol-Gel-Derived and Electrodeposited

Manganese Dioxide Thin Films,” Journal of Materials

Research, Vol. 15, No. 10, 2000, pp. 2096-2106.

doi:10.1557/JMR.2000.0302

[12] X. U. Jeong and A. Manthiram, “Nanocrystalline Man-

ganese Oxides for Electrochemical Capacitors with Neu-

tral Electrolytes,” Journal of the Electrochemical Society,

Vol. 149, No. 11, 2002, pp. A1419-A1422.

doi:10.1149/1.1511188

[13] N.-L. Wu and S.-Y. Wang, “Preparation of Tin Oxide

Gels with Versatile Pore Structures,” Journal of Materi-

als Science, Vol. 34, No. 12, 1999, pp. 2807-2812.

doi:10.1023/A:1004618915020

[14] C.-C. Hu, K.-H. Chang and C.-C. Wang, “Two-Step

Hydrothermal Synthesis of Ru-Sn Oxide Composites for

Electrochemical Supercapacitors,” Electrochimica Acta,

Vol. 52, No. 3, 2007, pp. 4411-4418.

doi:10.1016/j.electacta.2006.12.022

[15] J. Zhu, Z. Lu, S. T. Aruna, D. Aurbach and A. Gedanken,

“Sonochemical Synthesis of SnO2 Nanoparticles and

Their Preliminary Study as Li Insertion Electrodes,”

Chemistry of Materials, Vol. 12, No. 9, 2000, pp. 2557-

2566. doi:10.1021/cm990683l

[16] R. K. Selvan, I. Perelshtein, N. Perkas and A. Gedanken,

“Synthesis of Hexagonal-Shaped SnO2 Nanocrystals and

SnO2@C Nanocomposites for Electrochemical Redox

Supercapacitors,” The Journal of Physical Chemistry C,

Vol. 112, No. 6, 2008, pp. 1825-1830.

doi:10.1021/jp076995q

[17] C.-C. Hu and K.-H. Chang, “Cyclic Voltammetric Depo-

sition of Hydrous Ruthenium Oxide for Electrochemical

Capacitors: Effects of Codepositing Iridium Oxide,”

Electrochimica Acta, Vol. 45, No. 17, 2000, pp. 2685-

2696. doi:10.1016/S0013-4686(00)00386-8

[18] K.-H. Chang and C.-C. Hu, “Hydrothermal Synthesis of

Binary Ru-Ti Oxides with Excellent Performances for

Supercapacitors,” Electrochimica Acta, Vol. 52, No. 4,

2006, pp. 1749-1757. doi:10.1016/j.electacta.2006.01.076

[19] C.-C. Hu and K.-H. Chang, “Cyclic Voltammetric Depo-

sition of Hydrous Ruthenium Oxide for Electrochemical

Supercapacitors: Effects of the Chloride Precursor Trans-

formation,” Journal of Power Sources, Vol. 112, No. 2,

2002, pp. 401-409. doi:10.1016/S0378-7753(02)00397-X

[20] C.-C. Hu, H.-Yi. Guo, K-H. Chang and C.-C. Huang,

“Anodic Composite Deposition of RuO2·xH2O-TiO2 for

Electrochemical Supercapacitors,” Electrochemistry Com-

munica tions, Vol. 11, No. 8, 2009, pp. 1631-1634.

doi:10.1016/j.elecom.2009.06.014

[21] J. Ribeiro and A. R. De Andrade, “Characterization of

RuO2-Ta2O5 Coated Titanium Electrode,” Journal of the

Electrochemical Society, Vol. 151, No. 10, 2004, pp.

D106-D112. doi:10.1149/1.1787174

[22] C.-C. Hu, Yi-L. Yang and T.-C. Lee, “Microwave-As-

sisted Hydrothermal Synthesis of RuO2·xH2O-TiO2

Nanocomposites for High Power Supercapacitors,” Elec-

trochemical and Solid-State Letters, Vol. 13, No. 12,

2010, pp. A173-A176. doi:10.1149/1.3486437

[23] N.-L. Wu, “Nanocrystalline Oxide Supercapacitors,”

Materials Chemistry and Physics, Vol. 75, No. 1, 2002,

pp. 6-11.

[24] C. C. Hu, C. C. Wang and K. H. Chang, “A Comparison

Study of the Capacitive Behavior for Sol-Gel-Derived

and Co-Annealed Ruthenium-Tin Oxide Composites,”

Electrochimica Acta, Vol. 52, No. 7, 2007, pp. 2691-2700.

doi:10.1016/j.electacta.2006.09.026