الفهرس 
Title : A DFT Study of Graphene Based Electrodes in Supercapacitors and Their Defects
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Abstract
Graphene-based supercapacitors have high energy density potential which is beneficial for renewable energy related applications or electrical vehicles. However, further improvement
to its energy density is possible by improving the electrode’s intrinsic capacitance.
By using density functional theory (DFT), many models based on fixed-band approximation
(FBA) were developed to estimate the quantum capacitance of free-standing
graphene with different type of point defects. Nonetheless, these models had numerous
major shortcomings that affect the accuracy of the results, making the results incomparable
with experimental measurements. Therefore, another methodology based on DFT
was recently developed called the interfacial capacitance model (ICM). This methodology,
however, was only tested and used on pristine graphene mono/bi-layer adsorbed on
copper or nickel substrates. The models didn’t include any defects which would be commonly
found in graphene. Therefore, in this work we have developed 6 various models
(including pristine model) of mono-layer graphene with various point-like defects such as
single-vacancy, double-vacancy, and stone-wales. ICM was implemented to estimate the
interfacial capacitance of each model. The results ranged from 1.692 to 1.872 F cm2
for all models with respect to the pristine model with a capacitance of 1.733 F cm2.
The general trend was found that the capacitance is enhanced by 1 to 8% as long as no
chemical bonds exist between the defect and the underlying copper substrate. In other
words, the presence of chemical bonds was found to transform graphene’s adsorption
from physisorption to chemisorption. Our results were found to be in the same order of
magnitude of experimental results which ranged from 1 to 10 F cm2, depending on
the tested graphene sample and type of electrolyte. The interplays between the defects and the underlying copper substrate were also discussed and investigated with the help of
DOS/PDOS analysis.