Increasing Energy Storage in Activated Carbon Based Ultra-Capacitors through Plasma Treatment

The relatively low cost, high surface area/mass ratio (>1000 m²/g), and ease of manufacture, of activated carbon (AC) makes it the prototypical material for electrochemical capacitor (EC) electrodes. However, the net obtainable capacitance is hampered by a space charge capacitance (C_sc), which adds in series with the expected double-layer capacitance (C_dl).  We present a method to enhance the capacitance of AC electrodes based on plasma processing techniques previously used on few-layer graphene (FLG) and carbon nanotubes¹, where a three-fold enhancement in the measured capacitance was obtained. We will indicate the development of a novel AC electrode that is of low pore size², and which has been purposefully introduced with charged defects via Argon ion irradiation. Extensive characterization using electrochemical techniques such as cyclic voltammetry, impedance spectroscopy, as well as structural characterization through the use of Raman spectroscopy will be reported. Our work will show that the ion-irradiation would lead to a change (i) of the C_dl through modulating the effective charge storage surface area, as well as through (ii) a decrease of the C_sc through the addition of charged states³. Additionally, we will probe the possible contribution to the net measured capacitance, due to the introduced charges, from a parallel pseudocapacitance, (C_p), composed of Faradaic charge-transfer or redox reactions⁴.

References:

[1] Narayanan, R., Yamada, H., Karakaya, M., Podila, R., Rao, A.M., and Bandaru, P.R. 2014

[2] Chmiola, J., Yushin, G., Gogotsi, Y., Portet, C., Simon, P.,  and Taberna, P.L. Science 313, 1760 (2006).

[3] Hoefer, M.A., and Bandaru, P.R.  Journal of Applied Physics 108, 034308 (2010).

[4] Conway, B.E. J. Electrochem. Soc. 1991, 1539-1548.