Selective Center Charge Density Enables Conductive 2D Metal−Organic Frameworks with Exceptionally High Pseudocapacitance and Energy Density for Energy Storage Devices

Abstract

Conductive 2D conjugated metal−organic frameworks (c-MOFs) are attractive electrode materials due to their high intrinsic electrical conductivities, large specific surface area, and abundant unsaturated bonds/functional groups. However, the 2D c-MOFs reported so far have limited charge storage capacity during electrochemical charging and discharging, and the energy density is still unsatisfactory. In this work, a strategy of selective center charge density to expand the traditional electrode materials to the electrode−electrolyte coupled system with the prototypical of 2D Co-catecholate (Co-CAT) is proposed. Electrochemical mechanism studies and density functional theory calculations reveal that dual redox sites are achieved with the quinone groups (CAT) and metal-ion linkages (Co−O) serving as the active sites of pseudocapacitive cation (Na+) and redox electrolyte species (SO32−). The resultant electrode delivers an exceptionally high capacity of 1160 F g−1 at 1 A g−1 and a special self-discharge rate (86.8% after 48 h). Moreover, the packaged asymmetric device exhibits a state-of-the-art energy density of 158 W h kg−1 at the power density of 2000 W kg−1 and an excellent self-discharge rate of 80.6% after 48 h. This success will provide a new perspective for the performance enhancement for the 2D-MOF-based energy storage devices.