In the recent years, a significant progress has been achieved in the modeling of realistic porous carbon electrodes [J. C. Palmer and K. E. Gubbins, Micropor. Mesopor. Mat., 154, 24–37 (2012).], simulations under constant potential conditions [D. T. Limmer et al., Phys. Rev. Lett., 111, 106102 (2013).], description of the electrode material electronic structure [E. Paek, A. J. Pak, and G. S. Hwang, J. Electrochem. Soc., 160, A1–A10 (2013).], and ion packing relation to the capacitance [S. Kondrat, C. R. Pérez, V. Presser, Y. Gogotsi, and A. A. Kornyshev, Energy Environ. Sci., 5, 6474–6479 (2012).]. Let us turn the readers’ attention to two aspects of the theoretical predicted relation between the ion size and the pore size, suggesting higher capacitance values for certain pore sizes. First, the molecular dynamics and density functional theory simulations do confirm the theory in case of slit-pore models with rigorously defined width [D. Jiang and J. Wu, J. Phys. Chem. Lett., 4, 1260–1267 (2013).] & [G. Feng, S. Li, V. Presser, and P. T. Cummings, J. Phys. Chem. Lett., 4, 3367–3376 (2013).]. Therefore, the theory suggests that some electrode materials with a certain pore distribution the capacitance is higher due to specific ion packing. Yet, as has been elegantly pointed by Cummings and co-workers [G. Feng, S. Li, V. Presser, and P. T. Cummings, J. Phys. Chem. Lett., 4, 3367–3376 (2013).], due to a wide distribution of pore sizes in the real electrode material this effect might not at all affect the experimentally measured capacitance. Second, as noted above, the capacitance is greatly determined by the electronic structure of the electrode material. The state-of-the-art molecular dynamics studies do not yet include the electronic structure into account [M. V. Fedorov and A. A. Kornyshev, Chem. Rev., 114, 2978–3036 (2014).]. The situation is about to change in the future, for example with the help of ab initio molecular dynamics [M. Salanne, Phys. Chem. Chem. Phys., 17, 14270–14279 (2015).].
Note, the following text appeared in the artile: E. Tee, I. Tallo, T. Thomberg, A. Jänes, E. Lust, J. Electrochem. Soc. 163 (2016) A1317–A1325. See at http://jes.ecsdl.org/content/163/7/A1317.abstract (DOI: 10.1149/2.0931607jes)