Dual-ligand and hard-soft-acid-base strategies to optimize metal-organic framework nanocrystals for stable electrochemical cycling performance

Shasha Zheng; Yan Sun; Huaiguo Xue; Pierre Braunstein; Wei Huang; Huan Pang

doi:10.1093/nsr/nwab197

Dual-ligand and hard-soft-acid-base strategies to optimize metal-organic framework nanocrystals for stable electrochemical cycling performance

Natl Sci Rev. 2021 Nov 1;9(7):nwab197. doi: 10.1093/nsr/nwab197. eCollection 2022 Jul.

Authors

Shasha Zheng¹, Yan Sun¹, Huaiguo Xue¹, Pierre Braunstein², Wei Huang³, Huan Pang¹

Affiliations

¹ School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225009, China.
² Institut de Chimie UMR 7177, Universite´ de Strasbourg, CNRS, Strasbourg 67081, France.
³ State Key Laboratory of Organic Electronics and Information Displays, and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications, Nanjing 210023, China.

Abstract

Most metal-organic frameworks (MOFs) hardly maintain their physical and chemical properties after exposure to acidic, neutral, or alkaline aqueous solutions, resulting in insufficient stability, therefore limiting their applications. Thus, the design and synthesis of stable size/morphology-controlled MOF nanocrystals is critical but challenging. In this study, dual-ligand and hard-soft-acid-base strategies were used to fabricate a variety of 3D pillared-layer [Ni(thiophene-2,5-dicarboxylate)(4,4^'-bipyridine)]_n MOF nanocrystals (1D nanofibers, 2D nanosheets and 3D aggregates) with controllable morphology by varying the concentration of 4,4^'-bipyridine and thus controlling the crystal growth direction. Owing to the shorter ion diffusion length, enhanced electron/ion transfer and strong interactions between thiophene-2,5-dicarboxylate and 4,4^'-bipyridine, the 2D nanosheets showed much larger specific capacitance than 1D nanofibers and 3D aggregates. A single device with an output voltage as high as 3.0 V and exceptional cycling performance (95% of retention after 5000 cycles at 3 mA cm^-2) was realized by configuring two aqueous asymmetric supercapacitive devices in series. The excellent cycling property and charge-discharge mechanism are consistent with the hard-soft-acid-base theory.

Keywords: dual ligand; electrochemical energy storage; hard-soft-acid-base; metal-organic framework; supercapacitor.