Ni/Co bimetallic organic framework nanosheet assemblies for high-performance electrochemical energy storage

Layered double hydroxide-derived bimetallic-MOF as a promising platform: Urea-coupled water oxidation and supercapattery-driven water electrolyzer

Developing a two-dimensional (2D) ultrathin metal-organic framework plays a significant role in energy conversion and storage systems. This work introduced a facile strategy for engineering ultrathin NiMn-MOF nanosheets on Ni foam (NF) via in situ conversion from NiMn-layered double hydroxide (LDH). The as-synthesized LDH-derived NiMn-MOF (LDH-D NiMn-MOF) nanosheet exhibited an overpotential of 350 mV to drive a current density of 100 mA cm-2 during oxygen evolution reaction (OER) owing to its better redox activity, hierarchical architecture, and intercalating ability. The similar effective catalytic trend was noticed during the urea-assisted water oxidation process. The developed catalyst required only a potential of 1.39 V vs. RHE at 100 mA cm-2 towards urea oxidation reaction (UOR). Moreover, the urea-assisted overall water-splitting voltage was found to be 1.5 V at the current density of 10 mA cm-2. Furthermore, the same catalyst was explored as an energy-storage material for supercapattery application with an aerial specific capacity value of 2613.9 mC cm-2 at 1 mA cm-2 which was found to be 1.5 times higher than NiMn-LDH (1724.3 mC cm-2). Additionally, an aqueous asymmetric supercapattery device was fabricated which demonstrated the best electrochemical performance and provided a maximum energy density of 64.1 Wh kg-1 at a power density of 493 W kg-1 with 77.8 percent capacity retention after a continuous run of 8000 cycles at 10 mA cm-2 current density. Hence, the multifaceted properties of energy conversion and storage of LDH-D NiMn-MOF outline its performance in real-world applications.

Biosensor Based on ZIF-67-HRP and MWCNTs Nanocomposite Modified Glass Carbon Electrode for the Detection of Luteolin in Vegetables

Luteolin has various pharmacological properties, including anti-inflammatory, antioxidant, and antitumor characteristics. Due to its potential value in drugs and functional foods, it is important to develop an efficient method for detecting luteolin. In this work, the poor selectivity of existing luteolin nonenzymatic sensors was solved by translating the enzyme-catalyzed reaction from bulk solution to the surface of a horseradish peroxidase (HRP) modified electrode through an electrocatalytic oxidation process. Here, we modified the surface of a glassy carbon electrode (GCE) with metal-organic frameworks (MOFs; ZIF-67 here, abbreviated as ZIF), functional nanomaterials, and HRP and finally covered it with Nafion (NF). In this case, luteolin acts as a hydrogen donor, and the electrode acts as a hydrogen acceptor; the oxidation reaction occurs on the electrode surface. The use of ZIF-67 ensured the conformational stability of HRP to ensure the selectivity and anti-interference property, and SDS-dispersed multiwalled carbon nanotubes (MWCNTs) enhanced the electrode conductivity. The use of NF avoids shedding of the electrode material during the testing process. A UV-vis spectrophotometer was used to study the selectivity of luteolin by HRP and the compatibility between HRP and ZIF. The materials were characterized and analyzed by scanning electron microscopy and transmission electron microscopy. Due to the synergistic effect of these nanomaterials, the linear range of NF/ZIF-HRP/MWCNTs-SDS/GCE was 1.0 × 10-2 to 6.0 μM, with detection limits of 25.3 nM (S/N = 3). The biosensor showed long-term stability and reproducibility, with a relative standard deviation of 4.2% for the peak current (n = 5). Finally, the biosensor was successfully used to detect luteolin in carrots, celery, and cauliflower.

Crystal engineering of bimetallic cobalt-based metal-organic framework nanosheets for high-performance aqueous rechargeable cobalt-zinc batteries

Aqueous rechargeable Zn-based batteries (ARZBs) have attracted increasing attention as favorable candidates for energy storage systems due to their high security, environmental friendliness, and abundance of electrode materials. At present, the most widely reported materials used in cobalt-zinc (Co-Zn) batteries are cobalt-based oxides and their derivatives, however, they still exhibit low actual capacities and unsatisfactory cycle lives. Metal-organic frameworks (MOFs), as a new class of porous materials with high specific surface area and adjustable pore size, have attracted considerable attention in the field of energy storage. Currently, pristine MOFs have currently few applications in Co-Zn batteries, and their performance is not ideal. Herein, we report a series of two-dimensional (2D) bimetallic CoM-MOF (M = Ni, Mn, Mg and Cu) nanosheets based on trimesic acid (H3BTC) ligand as cathodes for alkaline Co-Zn batteries via a simple one-pot hydrothermal synthesis. Among the synthesized MOFs, the CoNi-MOF nanosheets have the best performance, exhibiting a high reversible capacity of 344 mA h g-1 and demonstrating a good cycling life with 90 % capacity retention at 20 A g-1 after 1500 cycles. The energy storage mechanism is studied through a series of ex-situ characterizations. This study is of great importance in advancing the application of 2D pristine MOFs for high-performance Co-Zn batteries.

Fabrication of NiCo Bimetallic MOF Films on 3D Foam with Assistance of Atomic Layer Deposition for Non-Invasive Lactic Acid Sensing

Lactic acid (LA) is an important downstream product of glycolysis in living cells and is abundant in our body fluids, which are strongly associated with diseases. The development of enzyme-free LA sensors with high sensitivity and low consumption remains a challenge. 2D metal-organic frameworks (MOFs) are considered to be promising electrochemical sensing materials and have attracted much attention in recent years. Compared to monometallic MOFs, the construction of bimetallic MOFs (BMOFs) can obtain a larger specific surface area, thereby increasing the exposed active site. 3D petal-like NixCoy MOF films on nickel foams (NixCoy BMOF@Ni foams) are successfully prepared by combining atomic layer deposition-assisted technology and hydrothermal strategy. The established NixCoy BMOF@Ni foams demonstrate noticeable LA sensing activity, and the study is carried out on behalf of the Ni1Co5 BMOF@Ni foam, which has a sensitivity of up to 9030 μA mM-1 cm-2 with a linear range of 0.01-2.2 mM and the detection limit is as low as 0.16 μM. Additionally, the composite has excellent stability and repeatability for the detection of LA under a natural air environment with high accuracy and reliability. Density functional theory calculation is applied to study the reaction process between composites and LA, and the result suggests that the active site in the NiCo BMOF film favors the adsorption of LA relative to the active site of monometallic MOF film, resulting in improved performance. The developed composite has a great potential for the application of noninvasive LA biosensors.

Synthesis of Graphene Oxide-Coupled CoNi Bimetallic MOF Nanocomposites for the Simultaneous Analysis of Catechol and Hydroquinone

Herein, a three-dimensional flower-like cobalt-nickel bimetallic metal-organic framework (CoNi-MOF) coupled with two-dimensional graphene oxide (GO) nanocomposites was successfully synthesized for the selective and simultaneous electrochemical determination of catechol (CC) and hydroquinone (HQ). The three-dimensional flower-like structure of the CoNi-MOF/GO nanocomposite has a multilayer structure and a large surface area, which greatly improves its electrocatalytic activity towards CC and HQ. Differential pulse voltammetry (DPV) results showed that the peak-to-peak separation of CC (0.223 V) and HQ (0.120 V) was 103 mV at a CoNi-MOF/GO modified glassy carbon electrode (CoNi-MOF/GO/GCE), suggesting that the proposed modified electrode can selectively and simultaneously determine them. Under optimal conditions, the CoNi-MOF/GO/GCE showed an excellent analytical performance for the simultaneous determination of CC and HQ, including a wide linear range (0.1-100 μM), low detection limit (0.04 μM for HQ and 0.03 μM for CC) and high anti-interference ability. As expected, the developed modified electrode has been used to analyze CC and HQ in river water, with acceptable results.

Ligand-Controlled Growth of Different Morphological Bimetallic Metal-Organic Frameworks for Enhanced Charge-Storage Performance and Quasi-Solid-State Hybrid Supercapacitors

The present research work facilitates a ligand-mediated effective strategy to achieve different morphological surface structures of bimetallic (Ni and Co) metal-organic frameworks (MOFs) by utilizing different types of organic ligands like terephthalic acid (BDC), 2-methylimidazole (2-Melm), and trimesic acid (BTC). Different morphological structures, rectangular-like nanosheets, petal-like nanosheets, and nanosheet-assembled flower-like spheres (NSFS) of NiCo MOFs, are confirmed from the structural characterization for ligands BDC, 2-Melm, and BTC, respectively. The basic characterization studies like scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and Brunauer-Emmett-Teller revealed that the NiCo MOF prepared by using trimesic acid as the ligand (NiCo MOF_BTC) with a long organic linker exhibits a three-dimensional architecture of NSFS that possesses higher surface area and pore dimensions, which enables better ion kinetics. Also, the NiCo MOF_BTC delivered the highest capacity of 1471.4 C g^-1 (and 408 mA h g^-1) at 1 A g^-1 current density, compared to the other prepared NiCo MOFs and already reported different NiCo MOF structures. High interaction of trimesic acid with the metal ions confirmed from ultraviolet-visible spectroscopy and X-ray photoelectron spectroscopy leads to a NSFS structure of NiCo MOF_BTC. For practical application, an asymmetric supercapacitor device (NiCo MOF_BTC//AC) is fabricated by taking NiCo MOF_BTC and activated carbon as the positive and negative electrode, respectively, where the PVA + KOH gel electrolyte serves as a separator as well as an electrolyte. The device delivered an outstanding energy density of 78.1 Wh kg^-1 at a power density of 750 W kg^-1 in an operating potential window of 1.5 V. In addition, it displays a long cycle life of 5000 cycles with only 12% decay of the initial specific capacitance. Therefore, these findings manifest the morphology control of MOFs by using different ligands and the mechanism behind the different morphologies that will provide an effective way to synthesize differently structured MOF materials for future energy-storage applications.

A 3D flower-like Co/Ni bimetallic organic framework as an excellent material for electrochemical determination of quercetin

A scheme of the fabrication of 3D flower-like CoNi-MOF nanosheets and their application in electrocatalytic oxidation of quercetin.

Ultrathin trimetallic metal-organic framework nanosheets for accelerating bacteria-infected wound healing

Bacteria-infected wounds are commonly regarded as a hidden threat to human health that can create persistent infection and even bring about amputation or death. Two-dimensional metal-organic frameworks (2D MOFs) with biomimetic enzyme activity have been used to reduce the huge harm caused by antibiotic resistance due to their massive active sites and ultralarge specific surface area. However, their therapeutic efficiency is unsatisfactory because of their relatively low catalytic activity and poor productivity. In this paper, we presented a simple and mild one-pot solution phase method for the large-scale synthesis of NiCoCu-based MOF nanosheets. The NiCoCu nanosheets (denoted as (Ni₂Co₁)_1-xCu_x) with controlled molar ratios have different morphologies and sizes. Specifically, the (Ni₂Co₁)_0.5Cu_0.5 nanosheets showed the best catalytic performance toward the reduction of H₂O₂ and H₂O₂ was efficiently catalyzed to generate toxic •OH in the presence of MOF nanosheets with peroxidase-like activity. (Ni₂Co₁)_0.5Cu_0.5 exhibited the best antibacterial activity against gram-positive Escherichia coli and methicillin-resistant Staphylococcus aureus bacteria. Animal wound healing experiments demonstrate that ultrathin trimetallic nanosheets can effectively contribute to wound healing with excellent biocompatibility. This study reveals the immense potential of ultrathin trimetallic MOF nanosheets for clinical antibacterial therapy for future pragmatic clinical applications.

Controllable In Situ Transformation of Layered Double Hydroxides into Ultrathin Metal-Organic Framework Nanosheet Arrays for Energy Storage

Ultrathin two-dimensional metal-organic frameworks (MOFs) have convincing performances in energy storage, which can be put down to their accessible active sites with rapid charge transfer. Herein, NiCo-layered double hydroxide (LDH) nanosheet arrays are used as self-sacrificial templates to in situ fabricate ultrathin NiCo-MOF nanosheet arrays on Ni foam (NS/NF) by using organic ligands without adding metal sources. Two ultrathin MOF nanosheets with different ligands, terephthalate (BDC) and 2-aminoterephthalate (NH₂-BDC), are synthesized, characterized, and discussed in detail. Specifically, NiCo-NH₂-BDC-MOF NS/NF exhibits the best electrochemical performance as a battery-type electrode for supercapacitors, achieves an areal capacitance of 12.13 F cm^-2 at a current density of 2 mA cm^-2, and retains the original capacitance of 73.08 % after 5000 cycles at a current density of 50 mA cm^-2. Furthermore, when NiCo-NH₂-BDC-MOF NS/NF is assembled with activated carbon (AC) to form an asymmetric supercapacitor (ASC), an energy density of 0.81 mWh cm^-2 can be provided at a power density of 1.60 mW cm^-2. These results offer an effective and controllable synthetic strategy to in situ prepare ultrathin MOF nanosheet arrays with different ligands and metal ions from LDH precursors.

Oriented Assembly of Anisotropic Nanosheets into Ultrathin Flowerlike Superstructures for Energy Storage

The hierarchical ultrathin nanostructures are excellent electrode materials for supercapacitors because of their large surface area and their ability to promote ion and electron transport. Herein, we investigated nine l-amino acids (LAs) as inductive agents to synthesize a series of CoNi-OH/LAs materials for energy storage. With the different amino acids, the assembled CoNi-OH/LAs form a lamellar, flower-shaped, and bulk structure. Among all materials, the ultrathin flowerlike CoNi₂-OH/l-asparagine (CoNi₂-OH/l-Asn) exhibits an excellent specific capacity of 405.4 mAh g^-1 (2608 F g^-1) and a 100% retention rate after 3000 cycles. We also assembled asymmetrical supercapacitor CoNi₂-OH/l-Asn//N-rGO devices, which demonstrated an energy density of 64.9 Wh kg^-1 at 799.9 W kg^-1 and superlong cycling stability (82.4% at 10 A g^-1) over 5000 cycles.

Calcination activation of three-dimensional cobalt organic phosphate nanoflake assemblies for supercapacitors

Three-dimensional organic phosphate nanoflake assemblies were obtained by calcination activation. In the two-electrode system, 3D COP assemblies showed excellent cycle stability, and the capacity retention was 99.61% after 3000 long cycles.

FeCo nanoalloys embedded in nitrogen-doped carbon nanosheets/bamboo-like carbon nanotubes for the oxygen reduction reaction

Herein, FeCo bimetallic organic frameworks (MOFs) with different compositions were fabricated by controlling the initial molar ratio of Fe³⁺/Co²⁺ ions.

2D framework materials for energy applications

In recent years a massive increase in publications on conventional 2D materials (graphene, h-BN, MoS2) is documented, accompanied by the transfer of the 2D concept to porous (crystalline) materials, such as ordered 2D layered polymers, covalent-organic frameworks, and metal-organic frameworks. Over the years, the 3D frameworks have gained a lot of attention for use in applications, ranging from electronic devices to catalysis, and from information to separation technologies, mostly due to the modular construction concept and exceptionally high porosity. A key challenge lies in the implementation of these materials into devices arising from the deliberate manipulation of properties upon delamination of their layered counterparts, including an increase in surface area, higher diffusivity, better access to surface sites and a change in the band structure. Within this minireview, we would like to highlight recent achievements in the synthesis of 2D framework materials and their advantages for certain applications, and give some future perspectives.

Ternary MOF-Based Redox Active Sites Enabled 3D-on-2D Nanoarchitectured Battery-Type Electrodes for High-Energy-Density Supercapatteries

Designing rationally combined metal-organic frameworks (MOFs) with multifunctional nanogeometries is of significant research interest to enable the electrochemical properties in advanced energy storage devices. Herein, we explored a new class of binder-free dual-layered Ni-Co-Mn-based MOFs (NCM-based MOFs) with three-dimensional (3D)-on-2D nanoarchitectures through a polarity-induced solution-phase method for high-performance supercapatteries. The hierarchical NCM-based MOFs having grown on nickel foam exhibit a battery-type charge storage mechanism with superior areal capacity (1311.4 μAh cm^-2 at 5 mA cm^-2), good rate capability (61.8%; 811.67 μAh cm^-2 at 50 mA cm^-2), and an excellent cycling durability. The superior charge storage properties are ascribed to the synergistic features, higher accessible active sites of dual-layered nanogeometries, and exalted redox chemistry of multi metallic guest species, respectively. The bilayered NCM-based MOFs are further employed as a battery-type electrode for the fabrication of supercapattery paradigm with biomass-derived nitrogen/oxygen doped porous carbon as a negative electrode, which demonstrates excellent capacity of 1.6 mAh cm^-2 along with high energy and power densities of 1.21 mWh cm^-2 and 32.49 mW cm^-2, respectively. Following, the MOF-based supercapattery was further assembled with a renewable solar power harvester to use as a self-charging station for various portable electronic applications.

Controlled preparation of interconnected 3D hierarchical porous carbons from bacterial cellulose-based composite monoliths for supercapacitors

The controlled design and synthesis of porous carbons with anticipated microstructures and morphologies, and a high specific surface area (SSA) have been focused on for supercapacitor development. Here, hierarchical porous carbons (HPCs) with an interconnected three-dimensional morphology derived from a natural-based bacterial cellulose (BC) composite have been successfully prepared by thermally induced phase separation of poly(ethylene-co-vinyl alcohol) (EVOH) and subsequent carbonization/activation. The SSA and porous architectures can be controlled by fine-tuning the preparation conditions such as the precursor morphology and structure, activator dosage and activation temperature, and the relationships between the super-capacitive properties and the SSA and pore size distribution have been further investigated. The obtained porous carbon material possesses a hierarchical porous structure with moderate micropores, favorable mesopores, interconnected macropores, a high SSA of 2161 m² g^-1 and a maximum oxygen-dopant content of 9.99%, enabling an increase in the active materials utilization efficiency and wettability. Due to the synergistic effects of these features, the obtained porous carbon electrode used in a supercapacitor shows a high specific capacitance of 420 F g^-1 at 0.5 A g^-1, excellent rate performance with 75% capacitance retention at 20 A g^-1, and good cycling stability with ∼96.1% retention even after 10 000 continuous charge-discharge cycles at 5 A g^-1. Additionally, the assembled supercapacitor based on porous carbon displays a moderate energy density of 20 W h kg^-1. The good electrochemical performance and facile effective synthesis of bio-derived carbon materials with tunable porous structures indicate promising applications in supercapacitors.