THESIS
2015
xvii, 107 pages : illustrations ; 30 cm
Abstract
Carbon-based materials are currently considered as promising candidates for electrode
material of supercapacitors due to its excellent electric conductivity and desirable specific
surface area. The capacitance performance of carbon-based material can be improved from
two aspects: firstly, one can enlarge the specific surface area (SSA) to improve the electric
double layer capacitance (EDLC); secondly, the pseudo-capacitance behavior of
carbon-based materials can be enhanced by doping with other elements like N or
compositing with transitional metal oxides.
In the present study, dopamine (DPA) and urea were employed to derive porous carbon
spheres by solution route. For the DPA-derived carbon spheres, the nitrogen-doped porous
spheres (NPCS) with different activation conditions...[
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Carbon-based materials are currently considered as promising candidates for electrode
material of supercapacitors due to its excellent electric conductivity and desirable specific
surface area. The capacitance performance of carbon-based material can be improved from
two aspects: firstly, one can enlarge the specific surface area (SSA) to improve the electric
double layer capacitance (EDLC); secondly, the pseudo-capacitance behavior of
carbon-based materials can be enhanced by doping with other elements like N or
compositing with transitional metal oxides.
In the present study, dopamine (DPA) and urea were employed to derive porous carbon
spheres by solution route. For the DPA-derived carbon spheres, the nitrogen-doped porous
spheres (NPCS) with different activation conditions were synthesized to compare their
electrochemical performances. The results indicate that NPCS-3, obtained with the
calcination of nitrogen-doped carbon spheres (NCS) in KOH in the mass ratio of
NCS:KOH=3, exhibits the best performance, delivering 38 mAh g
-1 specific discharge
capacity after 1000 cycles. XPS analysis demonstrates that the NPCS-3 sample contains
more N element, and the doped N may contribute to the enhanced pseudo-capacitance.
When the obtained NPCS-3 sample was further activated with CaCl
2, the obtained
Ca-NPCS exhibits even higher capacity, with 73 mAh g
-1 at initial cycle and maintaining
53.5 mAh g
-1 after 1000 cycles. BET and XPS were measured to explain the enhanced
electrochemical performance.
Concerning the high cost of DPA, urea was used to replace DPA to derive carbon spheres
denoted as UPCS. The synthesized carbon spheres are desirable, with perfect sphere-like
shape and consistent size. When treated with calcination and activation like NPCS-3, the
obtained UPCS delivered comparable electrochemical performance with NPCS-3.
Moreover, CaCl2 activation poses no obvious influence on the performance of urea-derived
carbon spheres, unlike that of DPA derived spheres.
The electrochemical performance of the prepared samples (NPCS-3, Ca-NPCS, UPCS and
Ca-UPCS) was also tested in KOH aqueous electrolyte. The obtained results are consistent
with that in organic electrolyte. Furthermore, symmetric and asymmetric supercapacitors
were assembled to explore the performance of Ca-NPCS sample. The assembled
supercapacitors delivers desirable capacity but unpromising cycling ability.
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