Freestanding Graphene/Carbide Derived Carbon Films As High-Performance Electrodes for Electrochemical Capacitors

Freestanding films of reduced graphene oxide (rGO) have attracted much attention as electrodes for electrochemical capacitor, especially for flexible device applications. However, graphene paper electrodes are usually limited in thicknesses to less than 10 μm, as increasing the electrode thickness hinders its performance due to restacking of rGO sheets and slow diffusion of ions  [1]. To prevent this problem, carbon nanoparticels such as carbon nanotubes (CNTs) are frequently used as nanospacers between the rGO sheets to increase the electrolyte accessibility and electronic conductivity of the films [2]. However, CNTs have a much lower capacitance compared to rGO and their addition limits the overall capacitance of the freestanding electrodes.

In this study, for the first time, we have used highly porous carbide derived carbon (CDC) nanoparticles as spacer between graphene sheets and fabricated thick rGO/CDC hybrid electrodes. The electrodes were made by thermal reduction of GO/CDC papers fabricated by vacuum-assisted filtration of aqueous solutions of GO and CDC containing 10, 20, and 30 wt. % of CDC. Utilizing the high surface area and conductivity of rGO and the accessible pores of the CDC [3], the hybrid electrodes showed specific capacitances as high as 200-210 F/g at a high scan rate of 100 mV/s in an aqueous electrolyte. The addition of CDC between the rGO layers increases the accessibility of active material to the electrolyte ions and we observed good performance of the electrodes with the thickness of 40-50 μm.

References:

1.  Oh, Y.J., et al., Oxygen functional groups and electrochemical capacitive behavior of incompletely reduced graphene oxides as a thin-film electrode of supercapacitor. Electrochimica Acta, 2014. 116: p. 118-128.

2.  Wang, Y., et al., Preventing Graphene Sheets from Restacking for High-Capacitance Performance. Journal of Physical Chemistry C, 2011. 115 (46): p. 23192-23197.

3.  Chmiola, J., et al., Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer. Science, 2006. 313 (5794): p. 1760-3.