Zheng Shasha, Sun Yan, Xue Huaiguo, Braunstein Pierre, Huang Wei, Pang Huan
School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225009, China.
Institut de Chimie UMR 7177, Universite´ de Strasbourg, CNRS, Strasbourg 67081, France.
Natl Sci Rev. 2021 Nov 1;9(7):nwab197. doi: 10.1093/nsr/nwab197. eCollection 2022 Jul.
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)] 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) 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.
大多数金属有机框架材料（MOF）在暴露于酸性、中性或碱性水溶液后几乎无法保持其物理和化学性质，导致稳定性不足，因此限制了它们的应用。因此，设计和合成稳定的尺寸/形态可控的MOF纳米晶体至关重要但具有挑战性。在本研究中，采用双配体和软硬酸碱策略，通过改变4,4-联吡啶的浓度从而控制晶体生长方向，制备了多种具有可控形态的三维柱状层状[Ni(噻吩-2,5-二羧酸)(4,4-联吡啶)]MOF纳米晶体（一维纳米纤维、二维纳米片和三维聚集体）。由于离子扩散长度较短、电子/离子转移增强以及噻吩-2,5-二羧酸与4,4-联吡啶之间的强相互作用，二维纳米片表现出比一维纳米纤维和三维聚集体大得多的比电容。通过串联配置两个水系不对称超级电容器器件，实现了单个器件高达3.0 V的输出电压和优异的循环性能（在3 mA cm下5000次循环后保持率为95%）。优异的循环性能和充放电机制与软硬酸碱理论一致。
