Multifunctional Carbon for Electrochemical Double‐Layer Capacitors

Abstract

Multifunctional carbon materials are prepared for application as an active electrode material in an electrochemical capacitor displaying both charge storage and binder properties. The synthesis of the materials involves the functionalization of high surface area Black Pearls 2000 carbon black by a covalent attachment of polyacrylic acid. The polyacrylic acid polymer is formed by atom transfer radical polymerization using 1‐(bromoethyl)benzene groups initially bonded to the carbon by spontaneous grafting from the corresponding diazonium ions. The grafting of 1‐(bromoethyl)benzene and polyacrylic acid is confirmed by thermogravimetric analysis, Fourier transform infrared spectroscopy, energy‐dispersive X‐ray spectroscopy, and nitrogen gas adsorption isotherm. The composite electrode films prepared from the modified carbon are more hydrophilic and have better wettability in an aqueous electrolyte than the one prepared with the unmodified carbon. The modified electrodes also show a higher specific capacitance (≈140 F g−1), a wider working potential window (1.5 V) and excellent specific capacitance retention upon cycling (99.9% after 5000 cycles) in an aqueous 0.65 m K2SO4 electrolyte. Moreover, a relatively high specific capacitance (≈90 F g−1) is maintained at a scan rate of 1000 mV s−1 with the polyacrylic‐acid‐modified carbon electrode.