Voltage Dependent Charge
Storage Modes and Capacity
in Subnanometer Pores
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Abstract
Using molecular dynamics simulations, we show that charge
storage
in subnanometer pores follows a distinct voltage-dependent behavior.
Specifically, at lower voltages, charge storage is achieved by swapping
co-ions in the pore with counterions in the bulk electrolyte. As voltage
increases, further charge storage is due mainly to the removal of
co-ions from the pore, leading to a capacitance increase. The capacitance
eventually reaches a maximum when all co-ions are expelled from the
pore. At even higher electrode voltages, additional charge storage
is realized by counterion insertion into the pore, accompanied by
a reduction of capacitance. The molecular mechanisms of these observations
are elucidated and provide useful insight for optimizing energy storage
based on supercapacitors