MOF-based Electrode Research Articles

Accelerating glucose electrolysis on Cu-doped MIL-88B for an energy efficient anodic reaction in water splitting.

This work reports a promising and sustainable method for valorization of abundantly available biomass feedstocks to overcome the thermodynamic high energy barrier of the OER via glucose electrolysis as a proxy anodic reaction, thereby driving the energy-efficient water splitting for green hydrogen generation. For this, a robust and efficient MIL-88B(Fe) based electrocatalyst is engineered via Cu doping. The ultrasonically prepared Cu-doped@ MIL-88B ink when drop-cast on nickel foam (NF) produces thin nano-porous 2D-sheet like films having a thickness of ca. 300 nm and demonstrates an excellent glucose oxidation reaction (GOR) with a lower potential of 1.35 V versus RHE at 10 mA cm-2. In addition, this electrode shows outstanding long-term electrochemical durability for 50 h and exhibits the maximum GOR current load of 350 mA cm-2 at 1.48 V vs. RHE, while the pristine MIL-88B based electrode exhibits a current load of only 180 mA cm-2 at the same potential bias. The remarkably higher current density after doping indicates an accelerated GOR, which is ascribed to the electronic structure modulation of the Fe nodes by Cu, thereby enhancing the active sites and charge transport characteristics of the frameworks. Most importantly, the MOF-based electrodes demonstrate the occurrence of the GOR prior to the OER at a large potential difference, hence assisting the energy-efficient water splitting for green hydrogen production.

Solvent-regulated synthesis and phosphating of nickel-cobalt bimetal organic framework microflowers with hierarchical structure for high-performance supercapacitors

Bimetallic metal-organic frameworks (MOFs) with a controlled morphology are potential materials for boosting the electrochemical performance of supercapacitors owing to their unique structural merits. Herein, a solvent-regulated strategy was proposed to synthesize bimetallic MOFs with various morphologies, such as microflowers, microspheres, and nanosheets, and the possible mechanisms of morphology control during nucleation and crystal growth were analyzed. When employed as electrode materials for supercapacitors, the NiCo-MOF microflowers possessed the biggest specific capacitance, which could achieve 1086 F g−1 at a current density of 1 A g−1. To further improve the electrochemical performance of materials, NiCo-P was prepared via a low-temperature phosphating method using NiCo-MOF microflowers as the precursor. Electrochemical studies displayed that the NiCo-P(6) microflowers exhibited good capacitance and superior rate capability with specific capacitances of 1592 and 1384 F g−1 at 1 and 20 A g−1, respectively. Furthermore, an asymmetric supercapacitor assembled by NiCo-P(6) and active carbon exhibited a high energy density of 51.2 Wh kg−1 at a power density of 749.8 W kg−1 and outstanding cycling stability. This work is easy to operate and can be extended to the preparation of other MOF-based electrode materials. The delivered excellent electrochemical performance suggests the resulted flower-like NiCo-P is a promising electrode material for advanced energy storage devices.

Regulating Exposed Facets of Metal-Organic Frameworks for High-rate Alkaline Aqueous Zinc Batteries.

Metal-organic frameworks (MOFs) have drawn growing attention as promising electrode candidates for rechargeable batteries. However, most studies focus on the direct use of MOF electrodes without any modification. Post-synthetic modification, a judicious tool to modify targeted properties of MOFs, has been long-neglected in the field of batteries. Herein, crystal-facet engineering is proposed to design MOF-based electrodes with high capacity and fast electrochemical kinetics. We found that a thermally-modified strategy can regulate the dominant exposed facet of Ni-based MOF (PFC-8). With the optimally exposed facets, the battery exhibited admirable rate capability (139.4 mAh g-1 at 2.5 A g-1 and 110.0 mAh g-1 at 30 A g-1 ) and long-term stability. Furthermore, density functional theory calculations demonstrate that stronger OH- adsorption behaviors and optimized electronic structures induced by the regulated exposed facets boost the electrochemical performance.

Pseudocapacitive Features of Freestanding Nickel-Zinc Organometallic Nanostructure for High-energy Density Coin-cell Asymmetric Supercapacitors.

Binder-free two-dimensional mesh-like structure of nickel-zinc metal-organic framework on in-situ-coated carbon cloth (Ni-Zn MOF/CC) and Ni-Zn MOF powder were developed via a solvo-hydrothermal reaction for electrochemical storage application. The electrochemical properties of these electrodes show that the electrodes self-assembled on carbon cloth substrates exhibit remarkably excellent performance. The Ni-Zn MOF/CC electrode exhibited a capacitance of 653.54 F/g at 1 A/g through a capacity retaining of 87.65% after 10000 cycles. Furthermore, the Ni-Zn MOF//AC coin-cell asymmetric supercapacitor device (CASD) exhibited remarkable energy and power densities of 54.31 Wh/kg and 825 W/kg, respectively, with adequate capacitance retention up to 94.63% over 5000 cycles at 1.5 V. The CASD also exhibited a significant power density of 4950 W/kg at 19.67 W h/kg, which suggests that these in-situ developed MOF-based electrodes may discover application in energy storage devices.

Advanced MOF-based electrode materials for supercapacitors and electrocatalytic oxygen reduction

Advanced MOF-based electrode materials for supercapacitors and electrocatalytic oxygen reduction

A dual-control strategy based on electrode material and electrolyte optimization to construct an asymmetric supercapacitor with high energy density

Metal-organic frames (MOFs) are regarded as excellent candidates for supercapacitors that have attracted much attention because of their diversity, adjustability and porosity. However, both poor structural stability in aqueous alkaline electrolytes and the low electrical conductivity of MOF materials constrain their practical implementation in supercapacitors. In this study, bimetallic CoNi-MOF were synthesized to enhance the electrical conductivity and electrochemical activity of nickel-based MOF, as well as the electrochemical performance of the CoNi-MOF in multiple alkaline electrolytes was investigated. The CoNi-MOF/active carbon device, as-fabricated with a 1 M KOH electrolyte, possesses a high energy density of 35 W h kg−1 with a power density of 1450 W kg−1, exhibiting outstanding cycling stability of 95% over 10,000 cycles. The design of MOF-based electrode materials and the optimization selection of electrolytes pave the way for constructing high-performance supercapacitors.

In situ growth of hierarchical bimetal-organic frameworks on nickel-iron foam as robust electrodes for the electrocatalytic oxygen evolution reaction

Evidence shows that self-supported electrocatalysts are crucial role to solving environmental and energy issues. In this study, self-supported 2D metal–organic framework (MOF) nanosheets grown in situ on nickel–iron foam (NFF) were prepared by a one-step solvothermal process. The hierarchical nanostructure possesses a high specific surface area and abundant metal sites, which are beneficial for electrocatalytic reactions. In the electrocatalytic oxygen evolution reaction (OER), the optimal NiFe(20Ni)-MOF/NFF can drive current densities of 10, 50 and 100 mA cm−2 at small overpotentials of 226, 277 and 294 mV, respectively. According to the characterization results, the OER performance is improved by the synergistic action of bimetals and the generation of hydroxides/oxyhydroxides. This work provides new insights into fabricating self-supported MOF-based electrodes for water splitting that are simple and highly efficient.

Double linker MOF-derived NiO and NiO/Ni supercapacitor electrodes for enhanced energy storage

Metal-organic frameworks (MOFs)-derived nanomaterials have emerged as novel electrodes for electrochemical energy storage application. Herein, MOF-derived NiO and NiO/Ni composite electrodes have been successfully synthesized by a unique double-linker MOF-strategy involving a series of calcination procedures (400 °C, 500 °C and 600 °C). The introduction of calcination temperature influenced both the textural and electrochemical properties of the MOF-derived NiO/Ni-400 and NiO/Ni-500 composite electrodes obtained at 400 °C and 500 °C respectively, as well as the NiO-600 electrode produced at 600 °C. With the combined benefits of improved uniform pore-size distribution and electrical conductivity, the composite electrodes delivered an enhanced supercapacitor performance with specific capacitances of 104.6 mAg−1 (NiO/Ni-400) and 37.4 mAg−1 (NiO/Ni-500) compared with 28.5 mAg−1 for the NiO-600 electrode at the same current density. Interestingly, NiO/Ni retained about 90% of its original capacitance after 1000 cycles when measured in 3 M KOH electrolyte solution. Furthermore, the electrochemical kinetic analysis used to probe the energy storage mechanism revealed pseudocapacitive behaviors at all tested scan rates; with NiO/Ni contributing 67% of the total capacitance at a scan rate of 5 mV/s which increased to 87% at 100 mV/s. The results obtained confirm that the approach described in this study is promising for the design of MOF-based electrodes for energy storage applications.

Coordinately Unsaturated Manganese-Based Metal-Organic Frameworks as a High-Performance Cathode for Aqueous Zinc-Ion Batteries.

The slow Zn2+ intercalation/deintercalation kinetics in cathodes severely limits the electrochemical performance of aqueous zinc-ion batteries (ZIBs). Herein, we demonstrate a new kind of coordinately unsaturated manganese-based metal-organic framework (MOF) as an advanced cathode for ZIBs. Coordination unsaturation of Mn is performed with oxygen atoms of two adjacent -COO-. Its proper unsaturated coordination degree guarantees the high-efficiency Zn2+ transport and electron exchange, thereby ensuring high intrinsic activity and fast electrochemical reaction kinetics during repeated charging/discharging processes. Consequently, this MOF-based electrode possesses a high capacity of 138 mAh g-1 at 100 mA g-1 and a long life span (93.5% capacity retention after 1000 cycles at 3000 mA g-1) due to the above advantages. Such distinct Zn2+ ion storage performance surpasses those of most of the recently reported MOF cathodes. This concept of adjusting the coordination degree to tune the energy storage capability provides new avenues for exploring high-performance MOF cathodes in aqueous ZIBs.

A new straightforward uncalcined approach for morphology modulating to enhance the electrical capacity performance of Co-MOF

Development of low-energy-consumption and low-cost process to prepare high-performance uncalcined MOF-based electrode materials is in line with the concept of green synthesis. We present here an uncalcined strategy of reorganizing the nano-sized MOF into a stable structure by anion intervention and doping with conductive substances to improve the conductivity. Three MOF electrode materials of Co-BTC nanoparticles (CBN), Co-BTC microspheres (CBM) and CNTs@Co-BTC microspheres (CCBM) have been prepared by a one-step approach of solvothermal. Results reveal that the introduction of phosphomolybdic acid (POM) can induce Co-BTC nanoparticles self-assemble into microspheres, which can provide CBM a superior specific capacitance compared to CBN. And doping with CNTs can further improve the electrochemical performance in term of the capacitance. Consequently, CCBM holds the highest specific capacitance as 553.3 F g−1 at 1 A g−1, and keeps an outstanding cyclic stability that retention of capacitance after 5000 cycles is around 90%.

Wire spherical-shaped Co-MOF electrode materials for high-performance all-solid-state flexible asymmetric supercapacitor device

The exploration of an inexpensive, low-energy consumption and environmentally friendly preparation process to synthesize high capacitance performance MOF-based electrode materials is an important prerequisite for their commercialization. We propose a non-calcined strategy to synthesize nanowire microsphere shaped Co-BTC (CBNWM). Making MOF into one-dimensional nanowire structure can effectively increase its active sites and the ion transfer rate. After the MOF nanowires are entangle and reunite into microspheres, their mechanical property and chemical stability are improved. Therefore, compared with Co-BTC crystal (CBC), the electrochemical properties of CBNWM have been significantly improved. The specific capacity of CBNWM reaches 1020 F g−1 at 5 mV s−1 or 657 F g−1 at 0.5 A g−1 with the capacity remains 81.4% after 3000 cycles. Subsequently, a flexible asymmetric device of CBNWM//AC was fabricated, whose maximum energy density can achieve 34.4 W h kg−1 with the related power density of 375.3 W kg−1.

Influence of hydrothermal reaction time on the supercapacitor performance of Ni-MOF nanostructures

Metal–organic frameworks (MOFs)-based electrode materials have drawn wide interest in energy storage applications. Herein, a nickel-based metal–organic framework (Ni-MOF) has been synthesized by simple hydrothermal reaction with different reaction times. The hydrothermal reaction time has an impact on the energy storage performance of the synthesized material. Structural characterization confirms the layered structure and purity of the synthesized Ni-MOF. Significantly, improved energy storage performance was found for the Ni-MOF prepared under reaction time 30 h as compared to other reaction times. It exhibits the highest specific capacity of 1498.6 F/g at a current density of 1 A/g along with good rate of capability. This investigation provides useful approach to improve the capacitive performance of MOF-based electrode materials.

Hierarchical self-supporting sugar gourd-shape MOF-derived NiCo2O4 hollow nanocages@SiC nanowires for high-performance flexible hybrid supercapacitors

Rational construction of hierarchical electrode materials has been a research hotspot in the field of energy storage. In this work, metal–organic framework (MOF) derived hollow NiCo2O4 nanocages (NCs) were strung by interwoven SiC nanowires (NWs) network on carbon cloth (CC), forming a unique sugar gourd-like core–shell architecture, which were fabricated via a multi-step process containing of chemical vapor deposition, solution reaction of MOF templates, ion exchanging/etching and subsequent heat treatment. Benefiting from the unique structural advantages, such as hierarchical porous structure with abundant active sites for electrochemical reactions and interwoven conductive networks for electron transport, the formed core-shelled CC/SiCNWs@NiCo2O4NCs as a binder supercapacitor electrode exhibits excellent electrochemical performance with a large specific capacitance (1377.6F g−1 at a current density of 1 A g−1), good rate capability (68.8% capacitance retention at 20 A g−1) and excellent cycling stability (88.3% capacitance retention after 6000 cycles). Furthermore, the hybrid supercapacitor based on CC/SiCNWs@NiCo2O4NCs and activated carbon, not only delivers a high energy density of 46.58 Wh kg−1 at the power density of 800 W kg−1, but also possesses good flexibility with high capacitance retention, exhibiting the application potential in the field of flexible energy storage. More importantly, our work gives a new thinking for structural design of SiCNWs-based and MOF-based electrode materials for high-performance flexible energy storage.

Quantitative Electro-Reduction of CO2 to Liquid Fuel over Electro-Synthesized Metal-Organic Frameworks.

Efficient electro-reduction of CO2 over metal–organic framework (MOF) materials is hindered by the poor contact between thermally synthesized MOF particles and the electrode surface, which leads to low Faradaic efficiency for a given product and poor electrochemical stability of the catalyst. We report a MOF-based electrode prepared via electro-synthesis of MFM-300(In) on an indium foil, and its activity for the electrochemical reduction of CO2 is assessed. The resultant MFM-300(In)-e/In electrode shows a 1 order of magnitude improvement in conductivity compared with that for MFM-300(In)/carbon-paper electrodes. MFM-300(In)-e/In exhibits a current density of 46.1 mA cm–2 at an applied potential of −2.15 V vs Ag/Ag+ for the electro-reduction of CO2 in organic electrolyte, achieving an exceptional Faradaic efficiency of 99.1% for the formation of formic acid. The facile preparation of the MFM-300(In)-e/In electrode, coupled with its excellent electrochemical stability, provides a new pathway to develop efficient electro-catalysts for CO2 reduction.

3D-printed lab-in-a-syringe voltammetric cell based on a working electrode modified with a highly efficient Ca-MOF sorbent for the determination of Hg(II)

This work combines, for the first time, 3D-printing technology and a highly efficient metal organic framework (Ca-MOF) as an electrode modifier to produce a novel fully integrated lab-in-a-syringe device for the sensitive determination of Hg(II) by anodic stripping voltammetry. The specific Ca-MOF ([Ca(H4L)(DMA)2]·2DMA where H6L is the N,N’-bis(2,4-dicarboxyphenyl)-oxalamide and DMA is the N,N-dimethylacetamide) shows an exceptional Hg(II) sorption capability over a wide pH range and its mechanism is elucidated via spectroscopic and X-ray diffraction studies. The voltammetric lab-in-a-syringe device is fabricated through a single-step process using a dual extruder 3D printer and is composed of a vessel integrating two thermoplastic conductive electrodes (serving as the counter and pseudo-reference electrodes) and of a small detachable 3D-printed syringe loaded with a graphite paste/Ca-MOF mixture (which serves as the working electrode). After optimization of the fabrication and operational variables, a limit of detection of 0.6 μg L−1 Hg(II) was achieved, which is comparable or lower than that of existing sensors (plastic 3D-printed, gold and MOF-based electrodes). The adoption of 3D printing technology in combination with the highly efficient Ca-MOF enables the fabrication of a simple, low-cost and sensitive electrochemical sensor for Hg(II), which is suitable for on-site applications.

Flexible supercapacitor electrodes using metal-organic frameworks.

Advancements in the field of flexible and wearable devices require flexible energy storage devices to cater their power demands. Metal-ion batteries (such as lithium-ion batteries, sodium-ion batteries, etc.) and electrochemical capacitors (also called supercapacitors or ultracapacitors) have achieved great interest in the recent past due to their superior energy storage characteristics like high power density and long cycle life. A major bottleneck of using metal-ion batteries in wearable devices is their lack of flexibility. Low power density, toxicity and flammability due to organic electrolytes inhibit them from safe on-body device applications. On the other hand, supercapacitors can be made with aqueous electrolytes, making them a safer alternative for wearable applications. Metal-organic frameworks (MOFs) are novel candidates as electrode materials due to their salient features such as large surface area, three-dimensional porous architecture, permeability to foreign entities, structural tailorability, etc. Though pristine MOFs suffer from poor intrinsic conductivity, this can be rectified by preparing composites with other electronically conducting materials. MOF-based electrodes are highly promising for flexible and wearable supercapacitors since they exhibit good energy and power densities. This review focuses on the new developments in the field of MOF-based composite electrodes for developing flexible supercapacitors.

Bimetallic MOF Nanosheets Decorated on Electrospun Nanofibers for High-Performance Asymmetric Supercapacitors.

The rational design of metal-organic framework (MOF)-based materials with a huge specific surface area, high redox activity, and favorable conductivity is currently a hot subject for their potential usage in supercapacitor electrodes. Herein, novel bimetallic MOFs with a flowerlike nanosheet structure grown on the electrospun nanofibers (PPNF@M-Ni MOF, M = Co, Zn, Cu, Fe) have been prepared by controlling the incorporation of various types of metal ions, which display superior electrochemical performance. For example, PPNF@Co-Ni MOF possesses a large specific capacitance of 1096.2 F g-1 (specific capacity of 548.1 C g-1) at 1 A g-1 and excellent rate performance. In addition, an asymmetric solid-state device composed of PPNF@Co-Ni MOF (positive materials) and KOH-activated carbon nanofibers embedded with reduced graphene oxide (negative materials) reaches a maximum energy density of 93.6 Wh kg-1 at the power density of 1600.0 W kg-1 and long cycling life. This work may greatly advance the research toward the design of supported MOF-based electrode materials for a promising prospect in energy conversion and storage.

Nanopatterned metal–organic framework electrodes with improved capacitive deionization properties for highly efficient water desalination

Metal–organic frameworks (MOFs) are a family of highly porous materials with great potential to replace the dominance of porous carbon materials for capacitive deionization (CDI) application. However, MOF particles cannot be directly applied to fabricate CDI electrodes without the support of polymeric binders, which would consequently lead to the formation of a pyknotic electrode structure with poorer electrical conductivity, and lower accessible surface area, limiting their further CDI application. Herein we report the preparation of free-standing MOF electrodes by patterning MOFs nanocrystals directly on carbon cloth scaffold. Through such binder-free preparation procedure, the nanopatterned MOF electrode showcases an improved electrical conductivity and accessible surface area, giving rise to a maximum desalination capacity of 21.3 mg g−1, which is higher than those of the reported MOF electrodes and many carbon-based electrodes. This work highlights the significance of binder-dree preparation procedure on the CDI performance of MOF-based electrodes, and holds great potential for practical CDI application.

A metal–organic framework film with a switchable anodic and cathodic behaviour in a photo-electrochemical cell

We show that a single MOF-based electrode can act as both a photo-anode and photo-cathode in a photo-electrochemical cell.

Pillared sulfonate-based metal-organic framework as negative electrode for Li-ion batteries

The syntheses of sulfonate-based metal-organic frameworks (MOFs) following or not a pillared strategy using a linear N-donor ligand have been successfully developed. These MOFs based on Co, Ni or Mn present a layered structure separated by a solvent molecule of DMF or by a bridging ligand (4,4′-BiPyridine – bpy). Due to the presence of transition metals on the coordination nodes bridged by ligands (bpy), these materials have been tested as negative electrodes materials in a coin cell. It reveals that materials have capacities up to 350 mAh·g−1 and good electrochemical stability over 50 charge/discharge cycles. This strategy may shed light on designing new MOF-based electrode materials with the use of organic ligands structured in a hybrid material.