Ligand ratio engineering in manganese-based metal–organic frameworks for high-performance supercapacitors

In this research, a series of manganese-based metal–organic frameworks (Mn-MOFs) were prepared through a mixed-ligand coordination approach, employing different molar proportions of 1,3,5-benzenetricarboxylic acid (BTC) and 1,4-benzenedicarboxylic acid (BDC) as organic linkers. Three individual Mn-MOF materials designated as MOF-1 (75% BTC), MOF-2 (50% BTC), and MOF-3 (25% BTC) were synthesized and subjected to comprehensive physicochemical characterization. MOF-1 exhibited superior structural properties, including a highest moderate surface area (21.573 m²/g) and a mesopore size distribution (12.859 nm), which are favorable for ion transport and electrolyte diffusion. Electrochemical measurements conducted in 6 M KOH aqueous electrolyte revealed that MOF-1 delivered an outstanding specific capacitance of 1015 F/g at 0.5 A/g, surpassing MOF-2 (818 F/g) and MOF-3 (420 F/g). Moreover, MOF-1 demonstrated remarkable cycling stability, retaining 111% of its initial capacitance after 1000 charge–discharge cycles, indicating progressive activation and excellent structural robustness. Electrochemical impedance spectroscopy (EIS) confirmed a low series resistance (7.46 Ω) and minimal charge transfer resistance (3.97 Ω), ensuring efficient electron and ion transport. The superior capacitive performance and durability of MOF-1 are attributed to the synergistic effects of BTC-rich ligand coordination, enhanced redox-active site density, and improved framework stability.