(783a) Simulation of Propylene Carbonate As Solvent for Electrochemical Double-Layer Capacitors

Simulation of Propylene Carbonate as
Solvent for

Electrochemical Double-layer Capacitors

X. You, L. R. Pratt, and N. Pesika

Abstract    Propylene carbonate (PC) is a
popular choice of solvent for electric double-layer capacitors (EDLCs).^1,2
Despite recent encouraging simulations of EDLCs³ based on carbon
nanotube forests, thorough testing of the required force-field features has not
been available. Recent work^3,4 shows that the modeled liquid PC completely wets a planar graphite
surface (contact angle,
 =0), in disagreement with experimental
droplet formation (
=37°). Empirical
adjustment of PC:graphite attractive interactions
brings those results into agreement. Molecular dynamics simulations of PC
droplets, bulk PC liquid, and a saturated solution of tetraethylammonium
tetrafluoroborate in PC, using the GROMACS package,
further characterize the assumed force-field. We present and discuss a range of
interfacial properties including surface tensions, and their temperature and
concentration dependences. We consider the applicability of the Kelvin
equation, describing the vapor pressure of small droplets, for evaluating the
curvature dependence of surface tension. ⁵

FIG: (left)
Interfacial density profiles and simulation geometry for slab calculation of
1000 PC with 85 tetraethylammonium and 85 tetrafluoroborate at 300K. Compared
with pure PC (surface tension = 40.8erg/cm2), the ionic material increases the
surface tension to 41.5erg/cm².  (right) Simulation configuration of a droplet with 600 PC molecules.

1.     
Yang, L., Fishbine,
B. H., Migliori, A., and Pratt, L. R. J.
Am. Chem. Soc, 131, 12373
(2009).

2.     
Yang, L., Fishbine,
B. H., Migliori, A., and Pratt, L. R. J.
Chem. Phys. 132, 044701 (2010).

3.      W. Zhang, G. G. Hoffman¹, L. R. Pratt¹,
N. Pesika¹, K. M.  Aritakula² and S. W. Rick²(¹Tulane
University, ²University
of New Orleans 2012)

4.     
"Simulation of
Propylene Carbonate as Solvent for Electrochemical Double-layer Capacitors",
Hoffman, G. G., Mariano, R., Pesika, N., Pratt, L. R., Rick, S. W., and X. You
(Proc. LA EPSCoR RII LA-SiGMA 2011 Symp.), p 101-104.

5.     
Powles, J. G.,
Fowler, R. F., and Evans, W. A. B. Chem.
Phys. Letts. 76, 289 (1983).