Enhancing Cycling Stability of Aqueous Polyaniline Electrochemical Capacitors.

Electrochemical capacitors fabricated with polyaniline nanofibers are cycled 150 000 times with 98% capacitance retention. These devices maintain an energy density of 11.41 Wh/kg at a power density of 4000 W/kg, 64 times greater than that of an identically fabricated device based on activated carbon (0.177 Wh/kg at 4600 W/kg). For applications requiring a higher specific energy, 33.39 Wh/kg at a specific power of 600 W/kg is obtained by widening the voltage window; this device retains 93% capacitance after 10 000 cycles. We achieve a high cycling stability through careful device engineering paired with a renewed focus on the electrochemical processes occurring at the positive and negative electrodes during cycling.