In Situ Fabrication of NiMn‐LDH@MWCNT Composites with Hierarchical Structure for Superior Electrochemical Energy Storage

Interfacial Engineering of Pillared Co(II) Metal-Organic Framework@NiMn-Layered Double Hydroxide Nanocomposite for Oxygen Evolution Reaction Electrocatalysis

Clean energy conversion and storage require simple, economical, and effective electrode materials to achieve promising results. The development of high-performance electrocatalysts with adequate stability and cost-effectiveness is essential to ensure low overpotentials toward the oxygen evolution reaction (OER). Herein, a cobalt-based metal-organic framework with 4,4,4-6T14 topology in combination with various ratios of NiMn-layered double hydroxide (Co-MOF@X%NiMn-LDH, X = 5, 10, 20, and 40%) is applied as an effective electrocatalyst for the oxidation of water. The optimum sample, Co-MOF@20%NiMn-LDH nanocomposite, showed an overpotential of 174 mV at a current density of 10 mA cm-2 and a reduced Tafel slope of 64 mV dec-1 in 1 M KOH, which makes it an excellent candidate, significantly superior to commercial IrO2 and most MOF- and LDH-based electrocatalysts. Chronopotentiometry tests for the OER over several hours confirmed that these electrocatalysts have been sufficiently stable. Pillared MOFs can obstruct active entities from NiMn-LDH cubic agglomeration, thus facilitating mass transportation and ensuring the continuous exposure of active sites. Accordingly, the synthesized Co-MOF@20%NiMn-LDH composite demonstrates considerable electrocatalytic efficiency and stability toward the OER, as a consequence of the porous structure, external surface area, and synergistic effects among Co-MOF and NiMn-LDH samples.

Enhanced Electrochemical Performance of NiMn Layered Double Hydroxides/Graphene Oxide Composites Synthesized by One-Step Hydrothermal Method for Supercapacitors

This study aims to enhance the performance of supercapacitors, focusing particularly on optimizing electrode materials. While pure NiMn layered double hydroxides (LDHs) exhibit excellent electrochemical properties, they have limitations in achieving high specific capacitance. Therefore, this paper successfully synthesized composite materials of NiMn LDHs with varying loadings of graphene oxide (GO) using a hydrothermal method. Systematic physicochemical characterization of the synthesized materials, such as powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), and Raman spectroscopy, revealed the influence of GO doping on the microstructure and electrochemical performance of NiMn LDHs. Electrochemical tests demonstrated that the NiMn LDHs/GO electrode material exhibited optimal electrochemical performance with a specific capacitance of 2096 F g-1 at 1 A g-1 current density and 1471 F g-1 at 10 A g-1, when GO doping level was 0.45 wt %. Furthermore, after 1000 cycles of stability testing, the material retained 53.3 % capacitance at 5 A g-1, indicating good cyclic stability. This study not only provides new directions for research on supercapacitor electrode materials but also offers new strategies for developing low-cost and efficient electrode materials.

Copper-Based Bio-MOF/GO with Lewis Basic Sites for CO2 Fixation into Cyclic Carbonates and C-C Bond-Forming Reactions

Several measures, including crude oil recovery improvement and carbon dioxide (CO2) conversion into valuable chemicals, have been considered to decrease the greenhouse effect and ensure a sustainable low-carbon future. The Knoevenagel condensation and CO2 fixation have been introduced as two principal solutions to these challenges. In the present study for the first time, bio-metal-organic frameworks (MOF)(Cu)/graphene oxide (GO) nanocomposites have been used as catalytic agents for these two reactions. In view of the attendance of amine groups, biological MOFs with NH2 functional groups as Lewis base sites protruding on the channels' internal surface were used. The bio-MOF(Cu)/20%GO performs efficaciously in CO2 fixation, leading to more than 99.9% conversion with TON = 525 via a solvent-free reaction under a 1 bar CO2 atmosphere. It has been shown that these frameworks are highly catalytic due to the Lewis basic sites, i.e., NH2, pyrimidine, and C═O groups. Besides, the Lewis base active sites exert synergistic effects and render bio-MOF(Cu)/10%GO nanostructures as highly efficient catalysts, significantly accelerating Knoevenagel condensation reactions of aldehydes and malononitrile as substrates, thanks to the high TOF (1327 h-1) and acceptable reusability. Bio-MOFs can be stabilized in reactions using GO with oxygen-containing functional groups that contribute as efficient substitutes, leading to an expeditious reaction speed and facilitating substrate absorption.