Insights into the effect of hydroxyl-, epoxy-, and carboxyl-pores on the desolvation of K+ with water as a solvent: a first-principles study

Abstract

The oxygen-containing functional group is particularly effective at the capacity and cycle performance of porous carbon, but there are few reports on the influence of ionic desolvation. The desolvated behavior in porous carbon could be availably simulated through the bilayer graphene with the interlayer spacings of 4–10 Å as the flat pore model by a first-principles calculation. The desolvated behavior of hydrated potassium ion ([K(H2O)]+) is calculated in AA- and AB-stacking hydroxyl-, epoxy-, carboxyl-flat pores. The results show that the fully desolvated sizes of [K(H2O)]+ in hydroxyl-, epoxy-, carboxyl-pores are 4.6 Å, 4.7 Å, and 4.2 Å, respectively. The fully desolvated pore size increases under the modification of hydroxyl- and epoxy-groups in pores and the size slightly reduces in carboxyl-pores compared with the fully desolvated size of (4.4 Å) [K(H2O)]+ in flat pores without oxygen-containing functional group. Electron density difference and Hirshfeld charge analysis show that K+ primarily interacts with the oxygen-containing functional groups of pores. Our present results are helpful to improve the capacity of supercapacitors by adjusting the types of oxygen-containing functional groups on the pore walls of porous carbon materials.