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Dual-Redox-Sites Enable Two-Dimensional Conjugated Metal–Organic Frameworks with Large Pseudocapacitance and Wide Potential Window

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journal contribution
posted on 29.06.2021, 19:37 authored by Panpan Zhang, Mingchao Wang, Yannan Liu, Sheng Yang, Faxing Wang, Yang Li, Guangbo Chen, Zichao Li, Gang Wang, Minshen Zhu, Renhao Dong, Minghao Yu, Oliver G. Schmidt, Xinliang Feng
Advanced supercapacitor electrodes require the development of materials with dense redox sites embedded into conductive and porous skeletons. Two-dimensional (2D) conjugated metal–organic frameworks (c-MOFs) are attractive supercapacitor electrode materials due to their high intrinsic electrical conductivities, large specific surface areas, and quasi-one-dimensional aligned pore arrays. However, the reported 2D c-MOFs still suffer from unsatisfying specific capacitances and narrow potential windows because large and redox-inactive building blocks lead to low redox-site densities of 2D c-MOFs. Herein, we demonstrate the dual-redox-site 2D c-MOFs with copper phthalocyanine building blocks linked by metal-bis­(iminobenzo­semiquinoid) (M2[CuPc­(NH)8], M = Ni or Cu), which depict both large specific capacitances and wide potential windows. Experimental results accompanied by theoretical calculations verify that phthalocyanine monomers and metal-bis­(iminobenzo­semiquinoid) linkages serve as respective redox sites for pseudocapacitive cation (Na+) and anion (SO42–) storage, enabling the continuous Faradaic reactions of M2[CuPc­(NH)8] occurring in a large potential window of −0.8 to 0.8 V vs Ag/AgCl (3 M KCl). The decent conductivity (0.8 S m–1) and high active-site density further endow the Ni2[CuPc­(NH)8] with a remarkable specific capacitance (400 F g–1 at 0.5 A g–1) and excellent rate capability (183 F g–1 at 20 A g–1). Quasi-solid-state symmetric supercapacitors are further assembled to demonstrate the practical application of Ni2[CuPc­(NH)8] electrode, which deliver a state-of-the-art energy density of 51.6 Wh kg–1 and a peak power density of 32.1 kW kg–1.