Self-Assembled Cobalt–Nickel Bimetallic-Organic Framework Materials with High Supercapacitor Performance

Abstract

Two new metal–organic frameworks (MOFs), [Co(bcpp)(bbip)]·H2O (Co-MOF) and [Ni(bcpp)(bbip)]·H2O (Ni-MOF), have been generated based on a V-type flexible carboxylic ligand 3,5-bis(4-carboxyl phenoxy) pyridine (H2bcpp) and a rigid N-donor ligand 1,1′-(1,4-phenylene)bis(1H-benzimidazole) (bbip) by a solvothermal method. Co-MOF and Ni-MOF are isostructural with a 2-fold interpenetrated layered structure. Moreover, a series of bimetallic Co x Ni y -MOFs (x/y = 1:1, 2.5:1, 2.75:1, 3:1, 3.25:1, and 3.5:1) were obtained by using one-pot synthesis. Owing to their mixed metallic components and internal layered structure, the bimetallic Co x Ni y -MOFs possess a remarkable electrochemical storage property. Significantly, the Co2.75Ni1-MOF has high specific capacitance (699 F g–1) at 0.5 A g–1 and good cycling durability (retained 72.7% over 3100 turns). Additionally, an asymmetrical ultra-capacitor based on Co2.75Ni1-MOF and activated carbon (AC) delivers a maximum energy density of 20.44 Wh kg–1 at 387.49 W kg–1 and a high cycle-to-cycle stability with 85.4% of the primary capacitance over 15,000 turns.

Assembly of Functional Co(II) Metal–Organic Frameworks through a Mixed Ligand Strategy: Structure and Photocatalytic Degradation Properties

“…Metal–organic frameworks (MOFs) are crystalline structural materials with periodic infinitely extended networks formed by metal ions or metal clusters connected to organic ligands through coordination bonds. − Compared to traditional inorganic and organic materials, MOFs are characterized by controllable structure, large porosity, ultrahigh specific surface area, etc. − Thus, MOFs have been widely applied in various fields such as adsorption and separation of gases, sensing, and proton conduction. − Cobalt MOFs were widely used in the field of catalysis due to their excellent chemical stability, eminent catalytic activity, rich geometries (octahedral, tetrahedral, or square planar), and variable oxidation states (Co­(II) and Co­(III)). − In addition, many Co-MOFs have small band gaps and high-density catalytic centers, exhibit semiconducting properties under irradiation, and can be used as novel heterogeneous photocatalysts. − For example, Fan and co-workers reported four Co-MOFs, which showed good photocatalytic activity in the degradation of methyl violet (MV), methylene blue (MB), and rhodamine B (RhB) under a Hg lamp source . A cobalt-based MOF with two-fold interpenetrating structures used in the detection, discrimination, and degradation of phenolic pollutants was reported .…”