Metal-organic frameworks (MOFs) are attractive active materials for pseudocapacitor electrodes owing to their high porosities, large specific surface areas, and unique morphologies. MOFs comprising various metal ions have been studied to improve the electrochemical performance of pseudocapacitor electrodes. Bimetallic MOFs form more abundant redox sites owing to the synergetic effect of metal ions. In this work, we fabricated a NiCo-BDC ligand based bimetallic MOF (NiCo-BDC) directly on a Ni-foam substrate via a facile hydrothermal process. After the in-situ growth of NiCo-BDC, some of the 1,4-benzenedicarboxylic acid (BDC) ligands combined with metal ions on the surface and were exchanged to form a new ligand, 2-methylimidazole (MIM), through a solvent-assisted ligand exchange (SALE) reaction. Although the chemical composition of the MOF changed during the SALE reaction, the original nanosheet morphology and high specific surface area were maintained. The chemical state of the metal ions as well as the elemental composition were changed during the SALE reaction, resulting in an increase in the number of electrochemically active sites. Furthermore, this unique binary ligand system decreased the charge transfer resistance and facilitated redox reactions. The NiCo-BDC@MIM binary ligand based bimetallic MOF with a Ni/Co molar ratio of 2:3 (NiCo-23-BDC@MIM) exhibited a specific capacitance of 2252 F g⁻¹ at 1 A g⁻¹, which was considerably improved compared to that before the SALE reaction (1047 F g⁻¹). Moreover, it not only showed a high energy density of 40.2 Wh kg⁻¹ at a power density of 972 W kg⁻¹, but maintained 73.2% of its initial capacitance and 100% Coulombic efficiency after 2000 cycles. These results demonstrate the potential of MOFs with binary ligand systems as well as bimetallic structures for application as energy storage materials.

金属有机骨架 (MOF) 具有高孔隙率、大比表面积和独特的形貌，是赝电容器电极的有吸引力的活性材料。已经研究了包含各种金属离子的 MOF，以提高赝电容器电极的电化学性能。由于金属离子的协同作用，双金属 MOFs 形成更丰富的氧化还原位点。在这项工作中，我们通过简便的水热工艺直接在镍泡沫基板上制造了基于 NiCo-BDC 配体的双金属 MOF (NiCo-BDC)。NiCo-BDC原位生长后，部分1,4-苯二甲酸（BDC）配体与表面金属离子结合并通过溶剂交换形成新的配体2-甲基咪唑（MIM） -辅助配体交换 (SALE) 反应。尽管 MOF 的化学成分在 SALE 反应过程中发生了变化，但仍保持了原始的纳米片形态和高比表面积。在 SALE 反应过程中，金属离子的化学状态以及元素组成发生了变化，导致电化学活性位点数量增加。此外，这种独特的二元配体系统降低了电荷转移电阻并促进了氧化还原反应。基于NiCo-BDC@MIM二元配体的Ni/Co摩尔比为2:3的双金属MOF（NiCo-23-BDC@MIM）表现出2252 F g的比电容 导致电化学活性位点数量的增加。此外，这种独特的二元配体系统降低了电荷转移电阻并促进了氧化还原反应。基于NiCo-BDC@MIM二元配体的Ni/Co摩尔比为2:3的双金属MOF（NiCo-23-BDC@MIM）表现出2252 F g的比电容 导致电化学活性位点数量的增加。此外，这种独特的二元配体系统降低了电荷转移电阻并促进了氧化还原反应。基于NiCo-BDC@MIM二元配体的Ni/Co摩尔比为2:3的双金属MOF（NiCo-23-BDC@MIM）表现出2252 F g的比电容^-1 at 1 A g ^-1，与SALE反应之前（1047 F g ^-1）相比有相当大的改善。此外，它不仅在 972 W kg ^-1的功率密度下显示出 40.2 Wh kg ^-1的高能量密度，而且在 2000 次循环后仍保持其初始电容的 73.2% 和 100% 的库仑效率。这些结果证明了具有二元配体系统和双金属结构的 MOF 在用作储能材料方面的潜力。