Figure 4 . (a) Normalized density distribution of MeCN near a
full-atomic graphene wall, and (b) the corresponding
layer-by-layer
two-dimensional density
map.
(c) The solvation number and (d) solvation diameter of
Cl- versus the pore width of nanoslit.
The
grey dash lines represent the corresponding bulk values. The red and
black dotted lines are drawn to guide the eye.
3.2.Microstructure
of Liquid Electrolytes in Nanoslit
The
electrochemical properties of supercapacitors are determined by the
microstructure of
electrolytes
in each nanopore.
The
electrolytes are usually modeled with RPM model with the ion size
identical with its solvation diameter.20, 32To explore the ion size effect, the density distributions of cation and
anion are investigated in the same nanopore with identical ion
concentration.
Three
typical
sizes
of cation and anion () are chosen, i.e .,
=
0.33 nm, 0.57 nm, and 0.73 nm, which corresponds to, respectively, the
bare ion size, the solvation diameter in confined MeCN with pore
size
= 0.92 nm, and the solvation diameter in bulk MeCN.
The
other system parameters are given as follows: the relative dielectric
constant = 1.0, the system temperature = 298 K, the surface voltage =
1.15 V, and the bulk ion concentration = 1.50 M.
The
predicted ion density profiles by the CDFT are shown in Figure
5 .
As
expected, anions accumulate near the positively charged surfaces while
cations are repelled to the center of nanoslit.
In
addition, we note that the ion distribution is sensitive to the
solvation diameter. Specifically, when increasing the solvation diameter
of ion, the contact value of anion increases, and the accumulation of
both cations and anions are enhanced.