Nonporous, conducting bimetallic coordination polymers with an advantageous electronic structure for boosted faradaic capacitance

Conductive coordination polymers (c-CPs) are promising electrode materials for supercapacitors (SCs) owing to their excellent conductivity, designable structures and dense redox sites. However, despite their high intrinsic density and outstanding electrical properties, nonporous c-CPs have largely been overlooked in SCs because of their low specific surface areas and deficient ion-diffusion channels. Herein, we demonstrate that the nonporous c-CPs Ag₅BHT (BHT = benzenehexathiolate) and CuAg₄BHT are both battery-type capacitor materials with high specific capacitances and a large potential window. Notably, nonporous CuAg₄BHT with bimetallic bis(dithiolene) units exhibits superior specific capacitance (372 F g^-1 at 0.5 A g^-1) and better rate capability than isostructural Ag₅BHT. Structural and electrochemical studies showed that the enhanced charge transfer between different metal sites is responsible for its outstanding capacitive performance. Additionally, the assembled CuAg₄BHT//AC SC device displays a favorable energy density of 17.1 W h kg^-1 at a power density of 446.1 W kg^-1 and an excellent cycling stability (90% capacitance retention after 5000 cycles). This work demonstrates the potential applications of such nonporous redox-active c-CPs in SCs and highlights the roles of bimetallic redox sites in capacitive performance, which hold promise for the future development of c-CP-based energy storage technologies.