Double-layer capacitance from the charged surface
Date
2016
Authors
Malaza, Nkosinathi
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Abstract
Energy storage has become an important issue for society, there is a need
for affordable and efficient devices that can store energy optimally. Supercapacitors
are energy storage devices that can solve society’s energy storage
problem. They can store the energy generated by renewable energy systems.
In this work approaches will be studied that may be used to estimate capacitance
of materials that can be used as the electrode of these devices. These
materials must have high energy density, which will address one of the limitations
of supercapacitors. To estimate the capacitance of the double layer, the
double layer theory and ab initio numerical tools based on density functional
theory (DFT) are used. The ab initio tools work with periodic systems, when
charging the system one violates the periodicity of the system. This is overcome
by using the effective screening medium method, which prevents energy
divergent of the system. In this work different configurations of the water
molecules are used to average the different orientations of water molecules
in the electrolyte. The Pt(111) electrode is used, and electrolyte of sodium
ion and water. In different configurations the sodium ion in the electrolyte is
located at different positions. The capacitances calculated using two different
approaches that we developed in this work are comparable to previously
estimated capacitance. This is achieved by using minimal computational efforts.
We obtained capacitance within that range. Double layer capacitance can be estimated to a good accuracy
with the methods developed in this work. Though there are improvements
that can be made on the methods that have been developed in this work to
better estimate the double layer capacitance. And also more research has to
be done in this field to come up with a theory that will accurately estimate
capacitance. At the moment calculating the double layer capacitance is not
trivial due to the lack of theory that describe the processes taking place at
the surface of the electrode where the capacitance is calculated.
Description
A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science.
28 October 2016.
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Citation
Malaza, Nkosinathi (2016) Double-layer capacitance from the charged surface, University of Witwatersrand, Johannesburg, <http://wiredspace.wits.ac.za/handle/10539/21665>