Design of bimetallic NiCo-MOFs via dual-ligand strategy for enhanced supercapacitor performance

Abstract

In electrochemical capacitors, metal-organic frameworks (MOFs) have attracted increasing attention due to their fascinating organic-inorganic structures and remarkable properties, including high specific surface area, tunable porosity, and variable chemical functionality. In this study, two bimetallic nickel-cobalt metal-organic frameworks (NiCo-MOFs) were synthesized via a one-step precipitation method using different ligand strategies: A single-ligand approach employing only 2-methylimidazole (1L-NiCo-MOF), and a dual-ligand approach combining 2-methylimidazole with 1,3,5-benzene tricarboxylic acid (2L-NiCo-MOF). The incorporation of both ligands provides abundant active redox nickel and cobalt metal centers that are accessible for an efficient supercapacitor. Moreover, Raman, XRD, FTIR, BET, AFM and SEM were used to study the functional groups, crystallinity, porosity, and morphology present in the single and double-ligand NiCo-MOF. Electrochemically, the 2L-NiCo-MOF delivered along with fast kinetics, high reversibility, and excellent specific capacity of 137 mAh g⁻¹ at 1 A g⁻¹ and exhibited a good capacity retention of 86.8 % over 5,000 cycles. An asymmetric supercapacitor device (2L-NiCo-MOF//AC) fabricated using dual-ligand NiCo-MOF as the positive electrode and peanut shell activated carbon (AC) as the negative electrode achieved a specific capacity of 61.3 mAh g⁻¹ at 0.5 A g⁻¹, corresponding to a specific energy and specific power of 38.1 Wh kg⁻¹ and 612 W kg⁻¹, respectively, and a maximum power density of 401 kW kg⁻¹. These results demonstrate that the dual-ligand strategy effectively engineers pore architecture and surface morphology compared to the one ligand, yielding promising electrode materials for high-performance asymmetric supercapacitors.

HIGHLIGHTS • Mixed metal ions revealed synergistic enhancement effects. • NiCo-MOFs single and dual-ligands were synthesis at room temperature via precipitation methods. • Bimetallic rhombohedral change to polyhedral-like structures. • Dual-ligand NiCo metal-organic framework exhibited a high specific capacity and high stability for better energy storage.