Ultrahigh-Power Flexible Electrochemical Capacitors Using Binder-Free Single-Walled Carbon Nanotube Electrodes and Hydrogel Membranes

Binder-free single-walled carbon nanotubes were self-assembled to form a highly dense 20 μm thick carbon nanotube electrode to be used in electrochemical capacitors. Fabrication of symmetric nanotube capacitors using these electrodes and highly ionically conducting poly(vinyl alcohol)-based hydrogel membranes soaked in aqueous sulfuric acid resulted in a capacitor with power density as high as 1040 kW/kg based on the mass of both electrodes. The time constant of the assembled capacitor was ∼15 ms. The capacitors showed no degradation in performance even after 10 000 cycles. Pseudocapacitance was further induced by modifying the surface of nanotube electrodes to almost double the specific capacitance while retaining the high power and cycling performance.