Redox Solute Doped Polypyrrole for High-Charge Capacity Polymer Electrodes

Growing demands for high energy/high power energy storage systems have driven research efforts toward devices such as supercapacitors that bridge the gap between high power capacitors and high energy batteries. Supercapacitors have experienced commercial success with high surface area activated carbon electrodes; however, these systems are limited by the surface area and physical charge storage through the electrical double layer mechanism. Redox materials, such as metal oxides and conductive polymers, have attracted interest because of the increase in energy density obtained through faradaic charge storage processes. One of the main drawbacks of conducting polymers, which are far more abundant and cost-effective relative to oxides, is their relatively low theoretical charge capacity. In this work, we report the use of a high-charge capacity redox molecule, 1,4-benzoquinone, to increase the energy density of polypyrrole electrodes. The electrode synthesis conditions are shown to have a significant influence on the composition and electrochemical properties of the mixed redox material films. Polypyrrole electrodes doped with 1,4-benzoquinone exhibit specific capacitances as high as 550 F g(-1) and charge capacities of 104 mA h g(-1) compared to 236 F g(-1) and 50 mA h g(-1) for reference polypyrrole electrodes. Importantly, these results demonstrate that materials with diverse redox behaviors and potentials can be combined in an electrochemical system to develop organic electrodes with high specific charge capacities.