Bimetallic-Tetrathiafulvalene Metal-Organic Frameworks: Finely Tailoring Crystal Morphologies and Enhancing Positrode Performance of Supercapatteries

Integrating mixed-metal ions and redox-active ligands into bimetal-organic frameworks (BMOFs) represents a promising yet relatively underexplored strategy for enhancing positrode performance in emerging supercapatteries. This work presents a series of isostructural monometal-organic frameworks (MMOFs, 1 and 5) and BMOFs (2, 3, and 4) with varying Co(II)/Ni(II) ratios and a redox-active tetrathiafulvalene (TTF) ligand. MOFs 1-5 exhibit a high-density three-dimensional 8-fold interpenetrating diamond-like topology. Competitive coordination from secondary metal ions enables unprecedented systematic control over the crystal morphology. Combined experimental and theoretical analyses reveal enhanced conductivity resulting from synergistic interactions between mixed-metal ions and the TTF ligand, with the Co/Ni 1:1 ratio (MOF 3) exhibiting optimal electron transport. Notably, iodine-treated BMOF 3 (3-ox) achieves a specific capacity of 884.3 C g^-1 at 1 A g^-1. The AC||3-ox supercapattery delivers a specific energy of 91.8 Wh kg^-1 at 0.97 kW kg^-1, surpassing that of other CoNi-MOF-based electrodes. The device retains 87.5% of its capacity after 10,000 cycles. This work proposes a novel strategy for designing MOF-based supercapattery electrodes using BMOFs with redox-active ligands, which diverges from conventional metal-centric approaches to achieve targeted electrochemical performance.