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Title: Theory of charge storage in nanostructured electrodes
Author: Rochester, Christopher
ISNI:       0000 0004 5920 792X
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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The use of nanostructured electrodes in supercapacitor design have the potential to in- crease both the specific capacitance, via the superionic effect, and the surface electrode interfacial area optimising the energy stored in such a device. When this increase in specific capacitance was first rationalised the electrodes that formed the supercapacitor were assumed to be ideally metallic. Accordingly, interionic interactions between coun- terions are exponentially screened by metallic electrons. This allows a denser packing of counter charge than what one would usually assume possible, which in turn leads to an increased specific capacitance. This was named the superionic effect. Modern nanoporous electrodes are predominantly made of carbon materials and are not ideally metallic. To test the applicability of the superionic state to an electrode constructed of non-ideal ma- terials we study Coulomb interaction of charges in cylindrical and slit pores that allow finite electric field penetration into the pore walls. In both geometries the screening is found to be subtly different than in metallic nanopores, but still strong enough to sup- port realization of the superionic state in such pores. Furthermore, the screening is found to be strong enough to neglect long range interactions between ions packed into these pores. Motivated by this we develop several nearest neighbour lattice models of charge storage for electrodes consisting of many similar cylindrical pores wetted with an ionic liquid. Finally, we present a theoretical study of structural deformation that has been seen to occur in carbon electrodes containing pores that are comparable in size to the size of a charging ion. Our model shows qualitative agreement with the features of the experimentally observed expansion caused by variation of electrode potential.
Supervisor: Kornyshev, Alexei ; Pruessner, Gunnar ; Haynes, Peter Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral