Largely Pseudocapacitive Two-Dimensional Conjugated Metal–Organic Framework Anodes with Lowest Unoccupied Molecular Orbital Localized in Nickel-bis(dithiolene) Linkages
Panpan Zhang, Mingchao Wang, Yannan Liu, Yubin Fu, Mingming Gao, Gang Wang, Faxing Wang, Zhiyong Wang, Guangbo Chen, Sheng Yang, Youwen Liu, Renhao Dong⧫, Minghao Yu, Xing Lü, Xinliang Feng
Abstract
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) (NiS 4 )-linked 2D c -MOF (denoted as Ni 2 [CuPcS 8 ]) with outstanding pseudocapacitive properties in 1 M TEABF 4 /acetonitrile. Each NiS 4 linkage is disclosed to reversibly accommodate two electrons, conferring the Ni 2 [CuPcS 8 ] 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 Ni 2 [CuPcS 8 ] 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 Ni 2 [CuPcS 8 ] 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.