Feeling Your Neighbors across the Walls: How Interpore Ionic Interactions Affect Capacitive Energy Storage

Progress in low-dimensional carbon materials has intensified research on supercapacitors with nanostructured/nanoporous electrodes. The theoretical and simulation work so far has focused on charging single nanopores or nanoporous networks and the effects due to ionic interactions inside the pores, while the effect of interpore ion-ion correlations has received less attention. Herein, we study how the interactions between the ions in the neighboring pores across the pore walls affect capacitive energy storage. We develop a simple lattice model for the ions in a stack of parallel-aligned nanotubes, solve it by using the perturbation and "semi-mean-field" theories, and test the results by Monte Carlo simulations. We demonstrate that the interpore ionic interactions can have a profound effect on charge storage; in particular, such interactions can enhance or diminish the stored energy density, depending on the sign of like-charge interactions. We also find that charging can proceed either continuously or via a phase transition. Our results call for more detailed investigations of the properties of carbon pore walls and suggest that tuning their electrostatic response may be promising for the rational design of an optimal supercapacitor.