An equimolar mixture of 1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)-imide ([C3mpy][Tf2N]) and 1-methyl-1-butylpiperidinium bis(trifluoromethylsulfonyl)imide ([C4mpip][Tf2N]) was investigated by classical molecular dynamics (MD) simulation. Differential scanning calorimetry (DSC) measurements verified that the binary mixture exhibited lower glass transition temperature than either of the pure RTILs. Moreover, the binary mixture gave rise to higher conductivity than the neat RTILs at lower temperature range.  In order to study its capacitive performance in supercapacitors, simulations were performed of the mixture and the neat RTILs used as electrolytes near an onion-like carbon (OLC), single-walled (SWCNT) and multi-walled carbon nanotube (MWCNT) electrodes at varying temperatures. The differential capacitance (C) exhibited independence of the electrical potential (V) applied for three different electrodes, corresponding to a near-flat C-V curve. Positive temperature dependence of the capacitance was observed in OLC-based capacitors and it was dominated by the electrical double layer (EDL) thickness, which is substantiated for the first time in MD simulation. In comparison, the temperature-independent differential capacitance was demonstrated in SWCNT-based as well as MWCNT-based supercapacitors; additionally SWCNT-based capacitors were shown to exhibit higher capacitance than MWCNT-based one.

Molecular dynamics simulation of binary mixture of ionic liquids near carbon electrode: The capacitive performance and temperature effects

245th National Meeting (2013)

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