Three-dimensional, free-standing polyaniline/carbon nanotube composite-based electrode for high-performance supercapacitors

Vertically aligned Carbon Nanotube (CNT) arrays are synthesized directly on CNT sheets used as substrates by plasma enhanced chemical vapor deposition (PECVD) in NH3 plasma environment. The resulting 3-D nanostructured, N-doped CNT (NCNT) architecture combines high conductivity and superior mechanical properties of CNT sheets with porous structure and high electrochemical activity of CNT arrays. NCNT sheets are then used as scaffolds for polyaniline (PANI) deposited by electrodeposition. PANI coating thickness is optimized to create a core-shell morphology with PANI shell supported by CNT core. Freestanding and flexible PANI/NCNT electrodes are fabricated without using any metal supports/foil or binders with the CNT sheets serving as current collectors. PANI/NCNT electrodes with 56 wt% polymer content demonstrate a gravimetric capacitance of 359 F/g at a current density of 1.56 mA/cm2. The electrode also shows high rate capabilities and retains 82% of original capacitance after current density is increased 30-fold to 46.87 mA/cm2. PANI/NCNT electrodes are used to assemble a symmetric supercapacitor device with PVA/H2SO4 hydrogel as separator and electrolyte. The flexible PANI/NCNT supercapacitor showed a specific capacitance of 128 F/g at 2.47 A/g current density and retained over 92% of initial capacitance after 10000 cycles of charge-discharge at 24.7 A/g current density.