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.
