Molecular dynamics simulation of electrodes for capacitors made with nano-onions

Jordan Alexis Caraballo Vega, Frances Martínez Miranda

Abstract


Supercapacitors are electrical devices composed by two electrodes and a dielectric material. They have the high storage capacity of batteries and the fast charging characteristic of capacitors.  An approach to make such devices smaller while preserving the capacity to hold significant amounts of charge depends on the use of materials for electrodes that provide a large surface area for the adsorption of electrolytes.  This work develops a model for molecular dynamics simulations of carbon nano-onions and tests how well electrodes made by agglomerating such structures increase the effective surface area on which electrolytes adsorb.  Nano-onions are modeled using a few layers of fullerenes.  The internal layers serve to give the molecule more realistic mechanical and geometrical properties. Molecular dynamics simulations with controlled pressure at one atmosphere and room temperature were performed with different combinations of nano-onions with outer shells made of:  C720, C500, C320, C240, C180, C80, and C20 fullerenes in water in order to observe the adsorption of electrolytes onto the nano-onions. Electrolytes were added and positive or negative charges were assigned to the carbon atoms in the nano-onions.  The amount of ions adsorbed onto the onions was counted as a measure of effective area. It was found that nano-onions had enough binding energy to stay bundled in plain water as well as in the presence of electrolytes.  The effective adsorption area is greater than in a plane electrode.  Ions easily penetrate crevices and holes.


Keywords


Molecular dynamics, Electrodes, Nano-onions

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