Voltage dependent charge storage modes and capacity in sub-nanometre pores

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. SECTION: Energy Conversion and Storage; Energy and Charge Transport Supercapacitors continue to gain increasing attention aspromising electrical energy storage systems with superior power density and excellent durability.1,2 The principal limitation of supercapacitors, which store charge physically using the electrical double layers (EDLs) at electrode