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 Lu, and Xinliang Feng*
J. Am. Chem. Soc. 2023
https://doi.org/10.1021/jacs.2c12684
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) (NiS4)-linked 2D c-MOF (denoted as Ni2[CuPcS8]) with outstanding pseudocapacitive properties in 1 M TEABF4/acetonitrile. Each NiS4 linkage is disclosed to reversibly accommodate two electrons, conferring the Ni2[CuPcS8] 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 Ni2[CuPcS8] 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 Ni2[CuPcS8] 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.
