Electroactive Ionic Polymer of Intrinsic Microporosity for High-Performance Capacitive Energy Storage

Here, an ionic polymer of intrinsic microporosity (PIM) as a high-functioning supercapacitor electrode without the need for conductive additives or binders is reported. The performance of this material is directly related to its large accessible surface area. By comparing electrochemical performance between a porous viologen PIM and a nonporous viologen polymer, it is revealed that the high energy and power density are both due to the ability of ions to rapidly access the ionic PIM. In 0.1 m H₂SO₄ electrolyte, a pseudocapacitve energy of 315 F g^-1 is observed, whereas in 0.1 m Na₂SO4, a capacitive energy density of 250 F g^-1 is obtained. In both cases, this capacity is retained over 10 000 charge-discharge cycles, without the need for stabilizing binders or conductive additives even at moderate loadings (5 mg cm^-2). This desirable performance is maintained in a prototype symmetric two-electrode capacitor device, which has >99% Coloumbic efficiency and a <10 mF capacity drop over 2000 cycles. These results demonstrate that ionic PIMs function well as standalone supercapacitor electrodes and suggest ionic PIMs may perform well in other electrochemical devices such as sensors, ion-separation membranes, or displays.