Binder-free supercapacitors based on nanosheets of Bi-ligand Co metal-organic frameworks: Density functional theory validation

Abstract

Metal-organic frameworks (MOFs) are one of the most promising energy storage materials in supercapacitors (SCs). In this work, the Co MOF with mixed ligands (1,4-benzendicarboxylic acid, BDC and hexamethylenetetramine, HMTA) have been grown on Ni foam (NF) via an in situ solvothermal method. The Co-BCD-HMTA MOF/NF binder-free electrode has been shown to have a remarkable specific capacity of 14.4 mF cm−2 at 2.5 mA cm−2 and excellent rate performance. Specifically, the assembled symmetrical device Co-BCD-HMTA MOF/NF: Co-BCD-HMTA MOF/NF deliverd a high energy density of 3.27 mW h cm−2 at a power density of 9.9 mW cm−2 and a satisfactory capacity retention of 96 % after 6000 continuous cycles at 50 mA cm−2. In addition, a symmetric solid-state supercapacitor successfully lit a light-emitting diode (LED) for 1 min, indicating significant potential for practical applications in energy storage devices. The result of EIS indicated that HMTA presence as a second ligand accelerates electron transfer kinetics compared to Co-BDC MOF/NF. Moreover, the results of frontier molecular orbitals theory showed that the Co-BDC-HMTA MOF have a larger energy gap than the Co-BDC MOF, which allow to justify its better chemical reactivity and kinetic stability.