Robust Redox-Active Tetrathiafulvalene–Cobalt Metal–Organic Frameworks for Supercapatteries with Promoting Electrochemical Performances

Integrating abundant electroactive sites and redox reactions into stable metal-organic framework (MOF) electrodes is an effective and relatively unexplored approach to improve the performance of emerging supercapatteries. In this study, electroactive Co(II) was chosen to coordinate with a redox-active tetrathiafulvalene (TTF) ligand to construct a new MOF, formulated as [Co(TTF(py)₄)(BDC)] (1) (TTF(py)₄ is tetra(4-pyridyl)-TTF and H₂BDC is terephthalic acid). Crystallographic characterization indicated that 1 possesses a three-dimensional 6-fold interpenetrating diamond-like topology with high crystal density. Isostructural [Zn(TTF(py)₄)(BDC)] (2) was also synthesized to explore the effect of metal ions on the performance of supercapatteries. When directly used as an electrode material in a 3-electrode system, the iodine-treated MOFs 1 and 2 (namely 1-ox and 2-ox, respectively) electrodes exhibit battery-type performance and high capacities. The specific capacities are 1072.2 and 857.8 C g^-1 at 1 A g^-1 for 1-ox and 2-ox, respectively. The AC||1-ox supercapattery device presents a specific energy of 100.8 Wh kg^-1 at a specific power of 0.975 kW kg^-1. Ex situ characterizations and theoretical calculations revealed that the excellent performance of 1-ox originates from the synergistic effect of the robust topology, Co(II) metal centers, and ligand dominant mechanism.