Largely Pseudocapacitive Two-Dimensional Conjugated Metal–Organic Framework Anodes with Lowest Unoccupied Molecular Orbital Localized in Nickel-bis(dithiolene) Linkages

Although two-dimensional conjugated metal-organic frameworks (2D c-MOFs) provide an ideal platform for precise tailoring of capacitive electrode materials, high-capacitance 2D c-MOFs for non-aqueous supercapacitors remain to be further explored. Herein, we report a novel phthalocyanine-based nickel-bis(dithiolene) (NiS4)-linked 2D c-MOF (denoted as Ni2CuPcS8) with outstanding pseudocapacitive properties in 1 M TEABF4/acetonitrile. Each NiS4 linkage is disclosed to reversibly accommodate two electrons, conferring the Ni2CuPcS8 electrode a two-step Faradic reaction with a record-high specific capacitance among the reported 2D c-MOFs in non-aqueous electrolytes (312 F g-1) and remarkable cycling stability (93.5% after 10,000 cycles). Multiple analyses unveil that the unique electron-storage capability of Ni2CuPcS8 originates from its localized lowest unoccupied molecular orbital (LUMO) over the nickel-bis(dithiolene) linkage, which allows the efficient delocalization of the injected electrons throughout the conjugated linkage units without inducing apparent bonding stress. The Ni2CuPcS8 anode is used to demonstrate an asymmetric supercapacitor device that delivers a high operating voltage of 2.3 V, a maximum energy density of 57.4 Wh kg-1, and ultralong stability over 5000 cycles.