Capacitance Enhancement of Metal–Organic Framework (MOF) Materials by Their Morphology and Structural Formation

Abstract

Three types of metal–organic framework (MOF) materials were designed, synthesized, characterized, and thoroughly evaluated for their specific capacitance. Imidazole, adenine, and a mixture of both compounds along with nickel were used to synthesize the three MOFs (Imz-MOF, Imz + Adn-MOF, and Adn-MOF). The synthesized materials were subjected to standard characterization techniques. The surface morphology of the materials was studied using field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and atomic force microscopy (AFM) analyses. The Imz-MOF possesses a cubic structure, while Imz + Adn-MOF and Adn-MOF show a flake and mixed flake-like structures. The effect of the morphology and molecular structural formation was studied and explained systematically. The Brunauer–Emmett–Teller (BET) analysis was used to study the surface area and porous nature of the materials. The capacitance of the materials was evaluated using an electrochemical workstation with 3 M KOH as an electrolyte at various sweep rates and a galvanostatic charge–discharge (GCD) test at different current densities. The results show that the maximum efficiencies of Imz-MOF, Imz + Adn-MOF, and Adn-MOF were obtained at 407.42, 80, and 60 F g–1 values, respectively. The materials demonstrated good recycling properties even after 5000 cycles. The higher capacitance of Imz-MOF could be attributed to the structural formation and the ligand-to-metal electron donation, which enhances the conductivity of the material. The imidazole group contributes to the material’s conductivity and charge-transfer (CT) nature. Based on the capacitance performance results of the materials, it is confirmed that Imz-MOF possesses a superior efficiency over Imz + Adn-MOF and Adn-MOF.