Addition/Correction pubs.acs.org/JPCC
Correction to “Graphene-Based Supercapacitors: A Computer Simulation Study” Youngseon Shim,† YounJoon Jung,*,† and Hyung J. Kim*,‡,§,∥ †
Department of Chemistry, Seoul National University, Seoul 151-747, Korea Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States § School of Computational Sciences, Korea Institute for Advanced Study, Seoul 130-722, Korea ‡
J. Phys. Chem. C. 2011, 115 (47), 23574−23583. DOI: 10.1021/jp203458b
A
fter our work on single-sheet graphene supercapacitors was published,1 we found a numerical error in the
Figure 2. Average local charge density ρ̅α(z) (units: e/nm3) of (a) EMI+, (b) BF4−, and (c) CH3CN in the organic electrolyte supercapacitor at 350 K. The total charge density, ρ̅+(z) + ρ̅−(z) + ρ̅CH3CN(z), is displayed in panel d.
Figure 1. Average local charge density ρ̅α(z) (units: e/nm3) of (a) EMI+ and (b) BF4− in the RTIL supercapacitor at 350 K. In panel c, the total charge density, ρ̅+(z) + ρ̅−(z), is shown.
electrolyte charge densities. Whereas the qualitative aspects of our results there remain largely unaffected, some quantities, in particular, electric potential and specific capacitance of the supercapacitors, are influenced by this error. The correct results are presented in Table 1 and Figures 1−4 here. They supersede those in Table 1 and Figures 6−9 of ref 1. The corrected results for Q(z) (Figure 11 of ref 1) are not shown here because almost no changes occur. When EMI+BF4− is employed as an electrolyte, potential drops at the anode and cathode of the supercapacitor are calculated to be ΔΦ(+) = 1.55 V and ΔΦ(−) = −1.16 V for σS = ± 0.86 e/nm2, whereas PZC is ΔΦS = 0.20 V. The resulting values for anodic and cathodic capacitance, c(+) = 5.09 μF/cm2 and c(−) = 5.06 μF/cm2, are very close, that is, no cathode-anode asymmetry, because the difference in the magnitude of potential drop between the two electrodes is canceled by positive PZC. This aspect was not properly captured in ref 1 because of the error mentioned above. Our analysis indicates that not only the size of the ions but also their © 2012 American Chemical Society
Figure 3. ΦIL(z) (solid line) and −Φσ(z) (dotted line) in (a) pure EMI+BF4− and (b) the acetonitrile solution at 350 K. In panel b, the contribution to Φ from acetonitrile, ΦCH3CN(z) is shown in a dasheddotted line. For easy comparison of different components, the results for −Φσ(z) rather than Φσ(z) are exhibited, so that it has the same sign as ΦIL(z). Units for electric potential: V.
orientation plays an important role to govern their ability to screen charges. The anode is well-screened by small BF4− ions Published: August 22, 2012 18574
dx.doi.org/10.1021/jp307086f | J. Phys. Chem. C 2012, 116, 18574−18575
The Journal of Physical Chemistry C
Addition/Correction
Figure 4. Profile of total electric potential Φ(z) (in units of V) in the supercapacitor. Electrolytes employed are: (a) pure EMI+BF4− at 350 K, (b) pure EMI+BF4− at 450 K, and (c) 1.1 M acetonitrile solution of EMI+BF4− at 350 K. For clarity, Φ(z) at the electrode is set at 0 V for all cases. For comparison, MD results for Φ(z) for a conventional capacitor with pure acetonitrile used as a dielectric material at 350 K are displayed in panel d.
Table 1. Electrode Potential ΔΦS and Specific Capacitance cS solvent EMI
BF4−
+
at 350 K
EMI+BF4− at 450 K CH3CN/EMI+BF4− at 350 K
σS (e/nm2)
ΔΦS (V)a
cS (μF/cm2)
0.86 −0.86 0.86 −0.86 0.86 −0.86
1.55 −1.16 1.56 −1.23 1.60 −1.53
5.09 5.06 4.94 4.93 4.74 4.09
a
ΔΦS at PZC is 0.20 and 0.17 V at 350 and 450 K for the RTIL electrolyte supercapacitors, respectively. ΔΦS = 0.15 V (at PZC) at 350 K for the organic electrolyte supercapacitors.
in the first solvation layer. Despite their large size, EMI+ ions form π-stacking structure near the graphene surface. This property of EMI+ leads to efficient charge screening at the cathode and to positive PZC in the discharged case. The corresponding results for the organic electrolytes exhibit a considerable degree of cathode−anode asymmetry. The anodic capacitance c(+) = 4.74 μF/cm2 is higher than the cathodic value c(−) = 4.09 μF/cm2 by ∼15% for σS = ± 0.86 e/nm2. Positive PZC is mainly responsible for this disparity.
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AUTHOR INFORMATION
Present Address ∥
Carnegie Mellon University.
REFERENCES
(1) Shim, Y.; Jung, Y.; Kim, H. J. J. Phys. Chem. C 2011, 115, 23574.
18575
dx.doi.org/10.1021/jp307086f | J. Phys. Chem. C 2012, 116, 18574−18575
