  Carbon-carbon supercapacitors are high power electrochemical energy storage
systems which store energy through reversible ion adsorption at the
electrode-electrolyte interface. Due to the complex structure of the porous
carbons used as electrodes, extracting structure-property relationships in
these systems remains a challenge. In this work, we conduct molecular
simulations of two model supercapacitors based on nanoporous electrodes with
the same average pore size, a property often used when comparing porous
materials, but different morphologies. We show that the carbon with the more
ordered structure, and a well defined pore size, has a much higher capacitance
than the carbon with the more disordered structure, and a broader pore size
distribution. We analyze the structure of the confined electrolyte and show
that the ions adsorbed in the ordered carbon are present in larger quantities
and are also more confined than for the disordered carbon. Both aspects favor a
better charge separation and thus a larger capacitance. In addition, the
disordered electrodes contain a significant amount of carbon atoms which are
never in contact with the electrolyte, carry a close to zero charge and are
thus not involved in the charge storage. The total quantities of adsorbed ions
and degrees of confinement do not change much with the applied potential and as
such, this work opens the door to computationally tractable screening
strategies.
