Modelling the influence of nonelectrostatic properties of electrolytes on the capacitance and energy storage capacity of supercapacitors and pseudocapacitors
||Prof. Drew F. Parsons|
School of Engineering & IT Murdoch University, West Australia
||ROOM 9004, Hefei National Laboratory Building|
We present a theoretical model that describes how nonelectrostatic (van der Waals) interactions of electrolyte ions influence adsorption of the ions at electrode surfaces. The model enables the dependence of the capacitance on the specific electrolyte to be described using a modified Poisson-Boltzmann formalism employing quantum chemical calculations for van der Waals interactions. We compare lithium electrolytes with PF6−, BF4− and ClO4− and Cl− anions in water and in propylene carbonate, with graphite electrodes. Van der Waals interactions affect the physisorption of ions and thereby control electrolyte specificity in the capacitance of supercapacitors.
We build a theory of pseudocapacitors by adding chemisorption to the same model, chemically binding ions to the electrode surface. This introduces an additional degree of dependence of the capacitance on the specific electrolyte. Capacitance varies with the strength of the chemisorption binding energy. Significantly, even though physisorption and chemisorption refer to two distinct ion-surface interaction mechanisms, the chemisorption contribution to the total free energy is partially determined by the nonelectrostatic (van der Waals) physisorption energy of the binding ion. In this way nonelectrostatic properties of ions influence the overall energy storage capacity of a pseudocapacitor.
||Hefei National Laboratory for Physical Sciences at the Microscale|
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