Iron salicylaldehydate conjugated metal–organic framework for quasi solid-state supercapacitor

Conjugated metal–organic frameworks (c-MOFs) are potential candidates for excellent electro and photochemical activities such as energy storage and catalysis. However, the poor chemical stability of c-MOFs obstructs them from the practical utilities in acid or base-functioned energy storage devices. Herein, we have introduced a novel iron-based salicylaldehydate 3D-c-MOF (Fe-Tp) with high chemical stability in strong acid environments. The robust coordination bond between iron and C₃ symmetric salicylaldehyde organic pockets results in a doubly interpenetrated 3D framework with ultra-high chemical stability. The biphasic doubly interpenetrated structure of Fe-Tp was elucidated using theoretical modeling with the assistance of single-crystal electron diffraction analysis. The Fe-Tp showed chemical stability even in 10 M H₂SO₄ for 24 h. Moreover, we have investigated the dynamic charge storages in Fe-Tp in varying concentrations of acid electrolyte (122 F g⁻¹ at 0.1 M H₂SO₄ to 400 F g⁻¹ at 5 M H₂SO₄ at 0.1 A/g). The Fe-Tp-based flexible quasi-solid-state supercapacitor was fabricated using proton-loaded PVA electrolyte gel. It showed an excellent electrode capacitance of 106.25 mF cm⁻² (at 0.25 mA cm⁻²) with remarkable cyclic stability (36,000 cycles with 80 % capacitance retention at 5 mA cm⁻²).