XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O A 07
The Capacitive Behavior of Self-assembled
Manganese Dioxide Thin Films
Suh Cem Pang, Boon Hong Wee
Department of Chemistry, Faculty of Resource Science & Technology,
Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia.
scpang@frst.unimas.my or suhcem@gmail.com
Self-assembled manganese dioxide thin films were deposited directly on
metalized plastic supporting substrates by a horizontal submersion process which
entailed the spontaneous assembly of preformed manganese dioxide nanoparticles in the
form of stable colloidal suspension under controlled conditions. Films with desired
thicknesses were deposited simply by repeating the submersion process a desirable
number of times. The surface morphological characteristics of deposited films were
observed to be substantially affected by the deposition conditions such as duration of
submersion, temperature, suspension concentration, pH and ionic strength of the
suspension, as well as the post-deposition calcination temperature. Self-assembled films
of tailored microstructure were prepared by optimizing deposition conditions and
elucidation of the underlying deposition mechanisms. The electrochemical properties of
self-assembled manganese dioxide films were characterized by cyclic voltammetry (CV)
and electrochemical impedance spectroscopy (EIS) based on a standard 3-electrode
configuration. These films were observed to exhibit excellent capacitive behavior as
evidenced by the almost perfectly rectangular shape of cyclic voltamograms within the
potential range of 0.0 to 1.0 V (versus SCE) in mild aqueous Na 2 SO 4 electrolyte as well
as in polymeric gel electrolyte (Fig. 1). Nyquist plots generated from EIS data showed a
linear vertical spike within the frequency range of 1 MHz and 10 mHz, had further
confirmed the excellent capacitive behavior of self-assembled manganese dioxide thin
films. The good capacitive behavior of self-assembled manganese dioxide thin films
could be attributed to redox reactions involving homogeneous intercalation and
deintercalation of protons and Na + ions during charging and discharging cycles.
-film electrochemical capacitors were fabricated from
such self-assembled manganese dioxide thin films and polymer gel electrolyte. Such
prototypes of optimized dual-planar electrode configuration exhibited high cycling
stability and reversibility upon prolonged cycling of more than 1,000 cycles (Fig. 2).
The potential utility of self-assembled manganese dioxide thin films as electrode
material for the fabrication of electrochemical capacitors or related charge-storage
devices is therefore highly envisaged.
Current density (A/g)
12
10
8
6
4
2
0
-2
-4
-6
-8
-10
-12
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
Potential (V)
Cycle50
Cycle1000
Liquid Electrolyte
Figure 1. CV curves of thin-film electrochemical
capacitor prototype with liquid or gel electrolytes.
Specific capacitance (F/g)
160
140
120
100
80
60
40
20
0
Configuration 3
Configuration 1
Configuration 2
Capacitance (F/g)
Configuration 1, 2, and 3
(Overlapping lines)
Qa/Qc ratio
0 100 200 300 400 500 600 700 800 900 1000
Fig. 2. Cycling behaviors of electrochemical
capacitor prototypes with different device
configurations.
5
4
3
2
1
0
September, 811, 2010. ISEL - Lisbon 32