The electric double layer (EDL) supercapacitors are very promising energy storage technologies particularly useful these days for applications requiring short-time high-power burst of energy. As the energy storage in EDL capacitors involves only electrolyte rearrangement near surface (i.e. no chemical reactions) these devices can outperform the power densities and the life-time of electrochemical batteries. However a major disadvantage of supercapacitors is their low integral capacity and extensive experimental research is investigating and searching porous structures having high specific surface area that allows high energy densities.Utilizing a constant potential atomistic simulations methodology that accounts for the electrode polarization, this work explores possible routes to improve the non-Faradic energy densities in electric double layer supercapacitors. The systematic study presented here identifies relationships between the electrode capacity and the geometry of the pores for several more common room temperature ionic liquids. For example, comparing the differential capacitance and confined electrolyte composition as a function of voltage for RTILs we identified that electrolyte ions with large partial charge or dipole moment exposed on the edge groups could promote ion separation inside pore at lower voltages generating higher capacities. In contrast, ions with more distributed charge (or 'buried' heteroatoms) generate smaller capacities.We showed that the capacitance enhancement and the mechanism of pore charging could be asymmetric with respect to the electrode polarity. We will prove here how such asymmetry can be useful to optimize the individual pores for optimal energy density. Comparing the capacitance generated by various types of pores such as slit, nanotube, nanoforests of C-chains, as well as pores with various degrees of roughness, we will identify which pore geometries are better candidates for increasing the non-Faradic capacitance.

How to improve the non-Faradic energy densities in C-based conductive nanopores? Insights form atomistic simulations

248th National Meeting (2014)

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