Ultrahigh stability of high-power nanofibrillar PEDOT supercapacitors

Keeping pace with the increasing energy demand, the scientific community continues to develop superior energy storage technologies by expanding the field of nanostructured organic electronics and by engineering advanced electrochemical capacitors. Here, we demonstrate enhanced performance of a nanofibrillar electrochemical capacitor from a conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), conformally deposited on a substrate via evaporative vapour phase polymerization (EVPP). The synthesis grafts polymer nanofibers to aromatic groups on a carbon paper current collector via Friedel–Crafts alkylation utilizing iron chloride oxidant facilitated by nitromethane as a catalyst activator. By grafting EVPP-PEDOT, our devices attain remarkable stability, retaining 90% of their initial capacitance over 350 000 cycles in 1 M H2SO4 at 5 A g−1 current density in a 1 V window; at 10 A g−1, 90% of the capacitance is retained over 200 000 cycles. Besides showing ultra-high stability, these devices possess high power density (25 kW kg−1 at 1 V and 30 kW kg−1 at 1.2 V) with a respective energy density of 4.3 W h kg−1 and 4.9 W h kg−1, as well as a 0.8 Ω minimal electrochemical series resistance that enables fast charge–discharge rates. For applications requiring high energy densities, 5.8 W h kg−1 at 1 V and 7.6 W h kg−1 at 1.2 V are obtained at power densities of 500 W kg−1, 1 V and 550 W kg−1, 1.2 V respectively. This work proposes a synthetic mechanism for the deposition of nanofibrillar PEDOT that controls device performance and demonstrates stable energy storage technology with high power density.