Faraday Discuss., 2011, 154

Additions and corrections

Graphene-based supercapacitors in the parallel-plate electrode configuration: Ionic liquids versus organic electrolytes

Youngseon Shim, Hyung J. Kim and YounJoon Jung

Faraday Discuss., 2012, 154, 249–263 (DOI: 10.1039/c1fd00086a). Amendment published 27th July 2012

After publication of our work on parallel plate supercapacitors, we found an error in charge density of the electrolytes. To be specific, the local charge density and its integrated charge Q(z) were shifted erroneously in the negative z direction by 1 Å in Fig. 4 and 8 of the paper. While the qualitative aspects of our results remain largely unaffected, some quantities, in particular, the electric potential and specific capacitance of the supercapacitors, are influenced by this error. The correct results are presented in Table C1 and Fig. C1–C3 here, which replace Table 1 and Fig. 5, 6 and 9 of our original paper.

Fig. C1. Profile of total electric potential Φ(z) (in units of V) in (a) RTIL and (b) organic electrolyte supercapacitors. MD results for a conventional capacitor with pure acetonitrile used as a dielectric material are displayed in (c). For clear comparison, the results for d = 2 nm are shifted upwards with respect to the d = 6.4 nm case. The positions of the anode and cathode are denoted as dashed vertical lines.

Fig. C2. Components of the Poisson potential Φ(z) between the charged electrodes (units: V): ΦIL(z) (red solid line) and –Φσ(z) (black dotted line). The electrode/electrolyte configurations are the same as in Fig. C1. In (b) and (d), ΦCH3CN is plotted in green.

Fig. C3. Comparison of Φ(z) in the parallel plate H6.4 configuration (red lines) and in the two-sided electrode configuration (green lines, labeled as ref. 23 in the original paper) around the anode (solid lines) and cathode (dotted lines) of (a) RTIL and (b) organic electrolyte supercapacitors at 350 K. For clear exposition, Φ(z) at each electrode surface is set to 0. The surface charge density of the single-electrode supercapacitor is σS = ±0.86 e nm–2.

Table C1. Results of electric potential drop and specific capacitanceab

For the electrode separation of d = 6.4 nm, the anodic and cathodic potential drops with respect to PZC, ΔΔΦ(+) and ΔΔΦ(–), are calculated to be 2.8 V and –3.6 V for σS = ±0.86 e nm–2, respectively. The smaller BF4 is more efficient in screening the charged electrode at short distances than bulkier EMI+, especially in the case of high surface charge density. This results in anodic capacitance higher than the cathodic value, viz., c(+) = 4.9 μF cm–2 and c(–) = 3.8 μF cm–2. As we reduce the surface charge density to σS = ±0.43 e nm–2, the cathode–anode disparity almost disappears as c(±) = 5.3 μF cm–2. The latter feature is consistent with very recent simulation results of Merlet et al. obtained using a coarse-grained model for EMI+BF4 (C. Merlet, M. Salanne and B. Rotenberg, J. Phys. Chem. C, 2012, 116, 7687). By contrast, the cathode–anode disparity occurs even at σS = ±0.43 e nm–2 in the organic electrolyte.

Electric potentials in the double-sided (this work) and single-sided electrode configurations (Y. Shim, Y. Jung and H. J. Kim, J. Phys. Chem. C, 2011, 115, 23574) are compared in Fig. C3. For both the EMI+BF4 and organic electrolyte cases, the potential near a charged electrode exhibits a similar behavior regardless of the electrode configuration. Analogously, the average charge density (not presented here) shows little dependence on the electrode configuration. The spurious dependence of the potential on the electrode configuration in this work was due to the aforementioned error in the position of charge density there.

The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

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