Structural and electrochemical properties of nickel-cobalt oxide/activated carbon for supercapacitor application
Co-precipitation method was adopted in the preparation of nickel-cobalt oxides for potential application in supercapacitors. The formation of spinel nickel-cobalt oxide, NiCo2O4 prepared by oxalate co-precipitation started below 400 °C as confirmed by Xray diffraction (XRD) analysis. Single ph...
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| Format: | Thesis |
| Language: | English |
| Published: |
2012
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/67004/1/FS%202012%2091%20IR.pdf |
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| Summary: | Co-precipitation method was adopted in the preparation of nickel-cobalt oxides for
potential application in supercapacitors. The formation of spinel nickel-cobalt oxide,
NiCo2O4 prepared by oxalate co-precipitation started below 400 °C as confirmed by Xray
diffraction (XRD) analysis. Single phase nickel-cobalt oxide with cation ratio of 1:2
(Ni:Co) was obtained at calcination temperature of 400 °C. The spinel phase
decomposed gradually until 700 °C. The calcination time for the formation of NiCo2O4
was found to be between 2 to 4 hours. The particle size of the prepared sample studied
by transmission electron microscopy (TEM) showed a value of 9.5 nm. Investigation on
the compositional effect of NiCo2O4 revealed that the crystallinity of the synthesized
oxides improved with the increment of Ni content. The entire range of Ni:Co
compositions at 400 C and 700 C were investigated with respect to the formation of
phases, lattice parameter and crystallite size. Nickel-cobalt oxide series was prepared
through solid-state route as well. However, NiCo2O4 co-existed with NiO in this method
preparation. Moreover, solid-state route produced metal oxides with larger crystallite size than co-precipitation method. Therefore, co-precipitation served as a better method
in synthesizing pure phase nanostructured NiCo2O4 compared to solid-state technique.
The electrochemical properties of NiCo2O4 were measured in various acidic, neutral and
alkaline electrolyte systems (1.0 M HCl, 1.0 M KCl and 1.0 M KOH) by employment
of cyclic voltammetry (CV), galvanostatic charge-discharge test and electrochemical
impedance spectroscopy (EIS). Ideal capacitor behaviour with the largest operating
voltage of 1.0 V and good electrochemical stability were observed in NiCo2O4 using
neutral KCl aqueous electrolyte. Meanwhile, the prepared sample displayed the highest
surface redox activity in 1.0 M KOH alkaline electrolyte but showed the lowest
electrochemical performance in acidic electrolyte.
Single phase NiCo2O4 and NiMn0.5Co1.5O4 spinel powders have been synthesized by
hydroxide co-precipitation method, and the effects of Mn substitution for Co have been
studied. Electrodes of both materials exhibit nearly ideal electrochemical capacitor
behaviour in neutral electrolyte solution (1.0 M KCl). Mn substitution greatly enhanced
the specific capacitance of the spinel, giving a value of approximate 110 F g-1 due to the
facile charge-transfer characteristic of the Mn ions, as revealed by in-situ X-ray
absorption near-edge structure analysis.
Nickel-cobalt oxide/activated carbon composite was synthesised by adapting oxalate
co-precipitation synthesis protocol followed by heat treatment under an open air
atmosphere. X-ray diffraction analysis confirmed that nickel-cobalt oxide spinel phase
was maintained in the pure and composite phases while transmission electron microscopy revealed the nanostructured synthesis of nickel-cobalt oxide/activated
carbon composite. The specific capacitance which was the sum of double-layer
capacitance of the activated carbon and pseudocapacitance of the metal oxide increased
with the composition of nickel-cobalt oxide before showing a decrement for heavily
loaded electrodes. Utilisation of nickel-cobalt oxide component in the composite with
50 wt. % loading displayed a capacitance value of ~59 F g-1 in 1.0 M KCl. The prepared
composite electrodes had good electrochemical stability upon cycling with tolerable
variation in specific capacitance with increasing charge-discharge cycles. |
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