Metal-organic Framework Electrode Research Articles

Revealing the effects of functional group in organic linkers on properties of metal organic frameworks electrode and their performance in supercapacitors

The history of developing supercapacitors with increased performance is inextricably linked to the exploration and design of suitable electrode materials. Metal-organic frameworks (MOFs) have attracted intensive attention for use in high-performance supercapacitors thanks to their large specific surface area, tuneable pore sizes and crystal structure. Understanding the influence of MOF structures and properties on the performance of supercapacitors is critical to enhancing their performance. However, so far researchers have been keen on exploring metal atoms in MOFs and have ignored the effects of organic ligands, especially the functional groups thereon, on supercapacitors. In this work, we have studied the impact of organic linkers’ functional groups on the properties of MOFs and how this influences their performance as supercapacitor electrode materials. We synthesized four MOFs with different functional groups, including hydroxyl, nitride and thiol groups and characterised their physicochemical properties and their performance as supercapacitor electrode materials. Characterisation of the specific surface area shows that the BET area decreases from 980.3 m2 g−1 for the original MOF to 12.2 m2 g−1 when the thiol group is incorporated. Furthermore the –OH, –NH, and −SH functionalities reduced the charge transfer resistance (< 1 Ω) and induced more pseudocapacitance, whereas the –OH group dramatically increased the hydrophilicity of the electrode and rate performance of supercapacitors. Although the MOFs without extra function group showed the highest specific capacitance of 1495F g−1, analysis of the normalized areal specific capacitance only shows 1.5 F m−2. The MOFs with the −SH group showed the highest normalized areal specific capacitance of 26F m−2 as well as stable cycling performance of 80 % retention after 10,000 cycles.

Electrodeposited nickel-manganese terephthalic acid metal organic framework for hybrid battery and water splitting

Metal-organic frameworks (MOFs) possessing great potential towards energy storage and conversion applications has led to the intensive investigation of these materials. MOFs are distinguished by their remarkable properties such as customizable pore topologies and abundant redox-active sites. The present investigation showcases the electro-synthesis of flake-like bimetallic nickel-manganese-Terephthalic acid (NiMn-T) MOF nanostructures on nickel foam, an inventive electrode material, in the absence of a binder. Emphasis has been made on the significance of controlling time of electrodeposition to achieve optimum electrochemical performance. The best performing NiMn-T MOF electrode exhibits notable electrochemical characteristics, and therefore integrated as a hybrid supercapacitor’s electrode. The fabricated hybrid device delivers decent energy and power density. From the perspective of water splitting characterizations, NiMn-T MOF showed good HER and excellent OER activities along with an exceptional OER stability of 103 % over 10 h demonstrating its capability for its incorporation into practical applications. Hence, this strategy offers a direct and innovative strategy for the advancement of binder-free electrodes in preparation for the energy storage and conversion systems of the next generation.

Alkali-Stable Metal-Organic Frameworks with Enhanced Electroconductivity for Black-Brown Electrochromic Energy Storage Smart Window.

Metal-organic frameworks (MOFs) deliver potential applications in electrochromism and energy storage. However, the poor intrinsic conductivity of MOFs in electrolytes seriously hampers the development of the above-mentioned electrochemical applications, especially in one MOF electrode. Herein, a new Ni-based MOF (denoted Ni-DPNDI) is proposed with enhanced conductivity by π-delocalized DPNDI connectors. Predictably, the obtained Ni-DPNDI MOF achieves a conductivity of up to 4.63 S∙m-1 at 300 K. Profiting from its unique electronic structure, the Ni-DPNDI MOF delivers excellent electrochromic and energy storage performance with a great optical modulation (60.8%), a fast switching speed (tc = 7.9 s and tb = 6.4 s), a moderate specific capacitance (25.3 mAh·g-1) and good cycle stability over 2000 times. Meanwhile, energy storage capacity is visual by the coloration states of Ni-DPNDI film. As a proof of the potential application, a large-area (100 cm2) electrochromic energy storage smart window is further designed and displayed. The strategy provides an interesting alternative to porous multifunctional materials for the new generation of electronic devices with diverse applications.

Copper-Based Para-Phthalic Acid Metal-Organic Framework: An Efficient Anodic material for Super-capattery Hybrid Systems

The battery-supercapacitor hybrid, an asymmetric energy storage system, has garnered considerable attention due to its outstanding energy storage capabilities. Anodic materials have become a central focus, driven by the quest for enhanced energy density, power density, cycle life, and overall performance. In this study, we have synthesized copper-based para-phthalic acid (PTA) metal-organic frameworks (MOFs) via a facile hydrothermal method to be employed as the positive electrode material in a battery-supercapacitor hybrid matrix. The initial testing indicates the battery-type nature of the prepared electrode along with maximum specific capacity of 260.5 C g-1 at 0.7 A g-1. Subjection of Cu-PTA MOF electrode to real device configuration (Super-capattery device) results in considerable specific capacity of 152.2 C g-1 along with specific energy and power of 35.9 Wh kg-1 and 5950 W kg-1, respectively at 0.3 A g-1. The device also demonstrated a stability potential of 92.15% when tested for 5000 continuous charge-discharge cycles. The present study presents Cu-PTA MOF an exciting addition for advancing current state of research in the field of energy storage technology.

All roads lead to Rome: Trace water-dominated the formation of nanosheet-assembled hollow metal-organic frameworks for high performance supercapacitors

Controlling the structure of metal-organic frameworks (MOFs) is a crucial strategy to enhance electrochemical performance. In this work, nanosheet-assembled hollow Ni-MOF spheres are synthesized by controlling the transition states through a facile trace water-assisted solvothermal method. During the research, it is found that water in the system, whether from the precursor Ni(NO3)2·6H2O or from an additional source, is a key influencing factor that can regulate the reaction process to control structural changes. Theoretical calculations prove that the water present in the reaction system can affect the distribution of terephthalic acid (TPA) and Ni2+, indicating that trace water can provide an accelerating effect. The nanosheet-assembled sphere shells can expose more active surface area, and the hollow structure can prevent the restacking of nanosheets and shorten the charge transport path. Based on these structural advantages, the prepared Ni-TPA MOF electrode achieves a high specific capacitance of 1010 F g−1 at 1 A g−1 and a 61 % rate capability at 20 A g−1. This work offers a feasible and highly effective strategy to design nanosheet-assembled hollow MOF spheres for high-performance supercapacitors and helps to understand the key factors influencing the formation of hollow MOF spheres.

Copper-doped strontium metal-organic framework: Dual-function active material for supercapacitor and oxygen evolution reaction

Bimetallic metal-organic frameworks (MOFs) have recently been a research hotspot for numerous energy applications because of the heightened synergistic impact between their elements. Nevertheless, MOFs' relatively low electrical conductivity and ability to mask active sites severely restrict their use. Herein, we synthesize a novel copper-doped strontium metal-organic framework (Cu-doped Sr MOF) material via a facile hydrothermal method. Interestingly, it demonstrates a notable energy storage performance with a specific capacity of 243.6 C g−1 (443 F g−1) compared to the undoped Sr MOF (81.3 C g−1 and 147.8 F g−1) at 1 A g−1. It also reveals long-term cycling stability (98.7 % over 10,000 GCD cycles) and fast ion diffusion. Moreover, an asymmetrical supercapacitor device assembled using Cu-doped Sr MOF as the positive electrode and AC as the negative electrode can provide an energy density of 19 Wh kg−1 and a power density of 801 W kg−1. The Cu-doped Sr MOF electrode exhibits a distinct overpotential of 398 mV compared to undoped Sr MOF (600 mV) at 10 mA cm−2, with a Tafel slope of 58 mV dec−1. The outstanding electrochemical performance and OER activity can be attributed to the synergistic effects between Cu and Sr in the MOF cluster. This study provides valuable insight into the doping strategy in the MOF cluster. Also, it opens new possibilities for designing alternative MOF electrodes and catalysts for commercial applications in supercapacitors and oxygen evolution reactions.

Boosting capacitive performance of electrode material by facile incorporation of phthalic acid ligand-based bimetallic MOF for supercapacitors

The bimetallic approach can offer a synergistic effect and energy-efficient metal-organic frameworks (MOFs) based electrode materials for electrochemical applications. The interconnected frameworks convert themselves into a two-dimensional conducting stacked structure with the favorable entity of metal ions bonded to metal-ligand covalence. This network prioritizes charge transport within the plane, minimizing the importance of out-plane transport. To achieve this, we propose a straightforward and efficient method for integrating Ni2+ and Co2+ metal ions with 1, 2-benzene dicarboxylic acid (phthalic acid) ligands. By employing this strategy, we can fabricate a bimetallic metal-organic framework electrode using a simple aromatic ligand, thus avoiding the complex synthesis typically associated with MOFs. This specially designed MOF electrode material enhances the electrochemical activities of the selected ligands. The presence of redox-active centers and conductive structure provides excellent behavior of the material with a high performance of 1755 Fg−1 (754.82 Cg−1) at 2 Ag−1. Also, the fabricated asymmetric device delivers (58.25 Whkg−1 energy density and 1299.90 Wkg−1 power density) with only a 9 % reduction in capacitance over 22 K cycles. The strategic design of a bimetallic Ni-Co-based metal-organic framework with bidentate ligand offers the potential to increase the electrochemical activities relative to single metallic MOFs.

By Introducing Multiple Hydrogen Bonds Endows MOF Electrodes with an Enhanced Structural Stability.

Recently, metal-organic frameworks (MOFs) have attracted great interest in energy storage areas. However, the poor structural stability of MOFs derived from weak coordination bonds limits their applications. Here, quadruple hydrogen bonds (H-bonds) were introduced onto the MOFs to enhance their structural stability. Cross-linked networks could be formed between molecules owing to multiple H-bonds, strengthening the framework stability. Moreover, the dynamic reversibility of H-bonds could endow MOFs with self-healing ability. Furthermore, due to lower binding energy compared to coordination bonds, H-bonds break preferentially when subjected to internal stress, thus protecting the MOFs. Consequently, the as-prepared self-healing hybrid (SHH-Cu-MOF@Ti3C2TX) exhibited high capacitance retention (89.4%) after 5000 cycles at 1 A g-1, while that hybrid without dynamic H-bonds (H-Cu-MOF@Ti3C2TX) presented a 79.9% retention, delivering an enhancement in cycling stability. Moreover, an asymmetric supercapacitor (ASC) was fabricated by employing SHH-Cu-MOF@Ti3C2TX and activated carbon (AC) as the electrodes. The ASC delivered a specific capacitance (47.4 F g-1 at 1 A g-1), an energy density (16.9 Wh kg-1), and a power density (800 W kg-1) as well as good rate ability (retains 81% of its initial capacitance from 0.2 A g-1 to 5 A g-1).

Improved rate capability and energy density of high-mass hybrid supercapacitor realized through long-term cycling stability testing and selective electrode design

To render supercapacitors (SCs) more practical, they must exhibit high cycling stability of at least ten thousand cycles with commercial-level mass loadings, which differentiates them from batteries. Metal-organic framework (MOF)-based electrode materials are promising for use in energy storage systems owing to their excellent electrochemical performance. In this study, we report the electroactivities of bimetallic MOFs (Co, Ni, and Co–Ni) using a single-step, facile, and cost-effective hydro/solvothermal method. To optimize their performances, we develop a general strategy for analyzing various binder-free MOFs. Additionally, the effects of the reaction time, reaction temperature, solvents, and elements (Ni, Co, and H2BDC) on the surface morphology and electrochemical performance are investigated. Based on an analysis of the electrochemical properties of all the synthesized electrode materials, the optimal electrode delivers an ultrahigh areal capacity of 2621 µAh cm−2 (297.1 mAh g−1) at 7 mA cm−2, with a high-rate capability of 82.5 % even at 40 mA cm−2. The optimized Co–Ni MOF electrode is employed as a positive electrode to fabricate an aqueous hybrid SC (HSC) with an activated carbon-coated nickel foam electrode as a negative electrode. The as-fabricated HSC exhibits excellent electrochemical properties with exceptional cycling stability (120k cycles) and improved rate capability (60 %). Additionally, we identify factors that contribute to improved redox reactions in the Co–Ni MOF-based HSC, such as the role of Co–Ni MOFs in the redox reaction and the influences of other structural parameters on charge storage and transfer processes. Our aim is to further understand the underlying mechanisms of the improved redox reactions and thus obtain new insights into the design and optimization of Co–Ni MOF-based HSCs. Finally, the energy storage properties of the HSC are validated by using it to power different electronic devices. The promising outcomes obtained in this work can serve as a basis for the future practical implementation of high-energy-density HSCs with high mass loadings and charging rates. SynopsisTo render the practicability of hybrid supercapacitor (HSC) with enhanced energy storage properties, we investigate the electroactivities of bimetallic metal-organic frameworks (MOFs) (Co, Ni, and Co–Ni) using a single-step, facile, and cost-effective hydro/solvothermal method. To optimize their performances, a general strategy is developed for analyzing various binder-free MOFs. Additionally, the effects of the reaction time, reaction temperature, solvents, and elements (Ni, Co, and H2BDC) on the surface morphology and electrochemical performance are studied. In addition, we validate the energy storage properties of the HSC by using it to power different electronic devices. The promising outcomes obtained in this study can serve as a basis for the future practical implementation of high-energy-density HSCs with high mass loadings and charging rates.

Metal-organic frameworks and composites on their basis: structure, synthesis methods, electrochemical properties and application prospects (a review)

Various types of metal-organic frameworks (MOF) and their structural parameters have been reviewed and their classification has been presented. Most widely used synthesis methods and approaches for MOF and composites on their basis have been discussed. MOF structure is a regular 3D lattice formed by organic linkers and metallic clusters. It has been shown for an example of literary data on MOF synthesis and structural studies that the types of bonds and metals can strongly affect the spatial structure and dimensions of MOF crystals: they can have nano-, micro- and meso-dimensions, be dense or porous, bulk or layered. This variety of structural parameters determines the wide range of their properties and potential applications. Prospects and methods of controlling the shapes of the crystals, their size and spatial bonds between organic components and metal ions have been reviewed. Major attention has been paid to zeolite-like frameworks (ZIF) as the most promising ones from the viewpoint of structure, synthesis and electrochemical current source applications. Discussion has touched on possible modifications and methods of controlling the properties of those MOFs and composites on their basis and introduction of impurities, including those having magnetic properties. Possible synthesis options of complex composites through controlled MOF pyrolysis have been presented, for either small-batch or scalable processes. The effect of heat treatment conditions on the final properties and electrochemical applications of those materials has been demonstrated. ZIF-67 structured MOF doping with one more metal has been presented as variant of modifying the properties of MOF and composites on their basis. For example, the Authors have implemented cobalt MOF synthesis wherein cobalt is partially substituted for manganese at the synthesis stage. Furthermore, a simple water solution co-deposition synthesis technique has been modified with ultrasonication thus reducing the time consumption of the process. Electrochemical studies have shown that the unit electrochemical capacity of pyrolyzed MOF electrodes with partial cobalt substitution for manganese is appreciably higher as compared to the manganese-free materials. The unit capacity and energy density increase with manganese content in the MOF. MOF manganese doping delivers a considerable improvement in the electrochemical parameters of the electrode materials for hybrid supercapacitors on their basis (from 100 to 298 F/g at 0.25 A/g current density). The results suggest that cobalt substitution for manganese is an effective method of improving the electrochemical parameters of MOFs. It has been demonstrated that the development of new approaches to the design of MOF based composite materials and the study of the physicochemical regularities of their interaction with various carriers is an important task.

Enhanced Electrochemical Performance in Supercapacitors through KCu-Cy Based Metal-Organic Framework Electrodes.

In the realm of electronics and electric energy storage, the convergence of organic and metallic materials has yielded promising outcomes. In this study, we introduce a novel metal-organic polymer synthesized from Cyamelurate and copper (KCu-Cy) and explore its application as an electrode for a supercapacitor. This material was pressed onto a stainless-steel grid as a thin film and synthesized on nickel foam. Comprehensive characterization was carried out to confirm the synthesis, ensure phase purity, and investigate atomic interactions. Single Crystal X-ray Diffraction (SCXRD) and Powder X-ray Diffraction (PXRD) analyses verified the synthesis and phase purity, shedding light on atomic arrangements. Fourier Transform Infrared Spectroscopy (FTIR) analyses provided insights into characteristic peaks within the material. Thermal Gravimetric Analysis (TGA) gauged stability and durability. Electrochemical performance was assessed through cyclic voltammetry. Notably, the nickel-supported electrodes, devoid of binders, exhibited exceptional specific capacity, reaching 1210.89 F/g at a scan rate of 5 mV/s, in contrast to 363.73 F/g for the pressed thin film on the stainless-steel grid, which incorporated a conductive agent and binder. Cu-Cy displayed impressive cyclization resistance, with a capacity retention of 90 % even after 11000 cycles. These findings underline the promise of Cu-Cy as a high-performance electrode material for supercapacitors, particularly in binder-free configurations, and suggest its potential in advanced energy storage applications.

S-doped g-C3N4 on Co/Ni metal-organic framework as efficient bifunctional electrocatalyst for in-situ hydrogen production from high-salt wastewater

An efficient and stable catalyst is the key to electrocatalytic hydrogen production. Herein, a bifunctional electrocatalyst is developed for electrocatalytic hydrogen production by depositing S-doped g-C3N4 on Co/Ni metal-organic framework electrode (namely CoNi-MOFs/S-g-C3N4). Compared with the original Co/Ni metal-organic framework (CoNi-MOFs), the overpotential of hydrogen production on CoNi-MOFs/S-g-C3N4 is reduced by 49.5 %, the charge transfer resistance is reduced by 74.5 %, and the electrochemically active area is expanded by 60.1 times. Moreover, CoNi-MOFs/S-g-C3N4 can be used as an efficient bifunctional electrocatalyst for overall water splitting. Impressively, using CoNi-MOFs/S-g-C3N4 as the anode and cathode, the hydrogen yield can reach 5.513 mmol h−1 and the energy consumption is 5.822 kWh Nm−3 at a current density of 250 mA cm−2. In addition, an in-situ overall water splitting system was designed for hydrogen production using high-salt wastewater as water source without additional pre-desalination process, which realizes green hydrogen production and reduces the cost. The hydrogen yield was hold in the range of 5.2–5.3 mmol h−1 for a week, showing excellent performance of hydrogen production and strong stability. More importantly, the system can be applied to various high-salt wastewater with wider pH and salinity, and shows promising application potential for hydrogen production in actual wastewater.

Pristine Metal‐Organic Frameworks for Sodium‐Ion Batteries: Past, Present, and Future

AbstractOwing to their adjustable redox‐active sites, designable structures high porosity, and fully activated organic ligands, pristine metal‐organic frameworks (MOFs) have been widely utilized as advanced electrode materials (i. e., both anodes and cathodes) for sodium‐ion batteries (SIBs) to satisfied the insertion/extraction larger size and mass of Na+ cations, achieving significant progresses with excellent electrochemical performance in electrochemical energy storage devices. Here, the recent advances on pristine MOFs as anodes and cathodes for SIBs are summarized. A thorough investigation delves into the detailed characteristics, energy storage mechanisms, and electrochemical performance of diverse pristine MOFs for SIBs are also clarified. Furthermore, the outlooks on pristine MOF electrodes in SIBs are also provided.

Structural energy storage composites based on etching engineering Fe-doped Co MOF electrode toward high energy density supercapacitors

Metal organic frameworks (MOFs) have been used widely as cathode materials for supercapacitors because of their adjustable chemical composition, variable topological structures, and relatively simple synthesis methods. However, most MOFs are insulated and their metal organic ligand coordination bonds are not stable enough in electrolytes, which greatly limits the application of MOFs in supercapacitors. The synergistic effect between transition metal doped and chemical etching is of great significance for the preparation of high-performance MOF electrodes. This study introduces Fe into Co MOF prepared by co precipitation to optimize the electronic structure of Co, and then constructed e-Fe-doped Co MOF hierarchical structure through ammonia etching. The Co MOF achieves rapid electron exchange at the electrode electrolyte interface through this synergistic effect, improving conductivity, and increasing specific surface area, exposing more active sites, effectively enhancing the electrochemical activity of the electrode. Therefore, the e-Fe-doped Co MOF-4 h has a high specific capacity of 700 C g−1 at 1 A g−1 with a 90.08 % high-rate performance. The assembled e-Fe-doped Co MOF-4 h//N-doped WC ASC provides the energy density of 80 Wh kg−1 at a power density of 800 W kg−1 with a ∼88 % capacitance retention after 10000 cycles. These results provide ideas for utilizing synergistic effects to prepare high-energy density supercapacitors using MOF materials.

Improvement in the Electrochemical Properties of Intercalated Metal–Organic Framework Electrode Materials by Controlling Crystal Growth (Vol. 83, No. 10, 861–863)

Improvement in the Electrochemical Properties of Intercalated Metal–Organic Framework Electrode Materials by Controlling Crystal Growth (Vol. 83, No. 10, 861–863)

Comparative study of different metal-organic framework electrodes synthesized using waste PET bottles for supercapacitor applications

The conversion of plastic waste into high-value metal-organic framework (MOF) materials has currently grabbed the attention as an important research area for mitigating environmental and economic issues. Due to their large surface area and high porosity, MOFs have a significant advantage as supercapacitor electrode material. In this study, MOFs (Cu-MOF, Zr-MOF, and Ti-MOF) were produced from plastic wastes (PET bottles) using hydrothermal approach. These MOFs were tested electrochemically in 1 M H2SO4 electrolyte using three-electrode setup. Among them, Cu-MOF (104.8 F/g at 0.5 A/g) showed higher capacitance and increased diffusion contribution (78.4 %) than its counterparts Zr-MOF (70.5 F/g at 0.5 A/g; 70.4 %) and Ti-MOF (55.5 F/g at 0.5 A/g; 67.5 %). Further, solid-state symmetrical supercapacitor devices have been assembled using all the plastic wastes derived MOFs viz. Cu-MOF//Cu-MOF, Zr-MOF//Zr-MOF, and Ti-MOF//Ti-MOF. Among them, Cu-MOF//Cu-MOF symmetric supercapacitor device performed better than the others by rendering energy density of 18.2 Wh/kg at 825 W/kg power density along with a cyclic stability of 87 % after 10,000 charge-discharge cycles. These studies open new avenues to utilize waste PET bottles to synthesize high functional MOFs for next generation supercapacitors.

Mono-coordinated defect toward metal-organic framework anode with remarkable electrochemical performance

The ultrahigh porosity and ligand tunability features of Metal organic frameworks (MOFs) make them excellent platforms for energy conversion and storage. Nevertheless, the practical applications of these materials are restricted due to their low conductivity and insufficient redox sites. Herein, a mono-coordinated ferrocenecarboxylic acid (Fc) was incorporated into MIL-53(Al) via a straightforward hydrothermal process to regulate the local coordination structure. In comparison to the MIL-53(Al) with a capacity of only 113 mAh/g, the MIL-53(Al)-Fc anode delivered an ultrahigh reversible capacity of 823 mAh/g over 700 cycles at 1 A·g−1. Furthermore, the developed MIL-53(Al)-Fc anode can exhibit a super high rate capacity of 489 mAh/g at 2 A/g. Importantly, it is discovered that the incorporation of Fc-doped MIL-53(Al) leads to a sustained increase in capacity throughout the process of charge/discharge cycling. Through a combination of experimental analysis and theoretical calculations, it has been demonstrated that the presence of unsaturated coordination metal sites into Fc-doped MIL-53(Al) not only improve its conductivity and the kinetics of Li+ storage, but also expose more reaction sites for Li+ facile desorption. This, in turn, facilitate the order–disorder transition during cycles. Meanwhile, the 1D nanorods morphologies can provide superior interaction between the active sites and electrolyte. Thus, this work will pave a new way to engineer advanced MOFs electrode materials for practical utilization of ultrahigh performance LIBs.

Recent Progress on Functional Metal–Organic Frameworks for Supercapacitive Energy Storage Systems

As porous coordination organic polymers, both metal–organic frameworks (MOFs) and their derived materials and MOF‐based composites offer unique organic or inorganic chemistries that display superior features of high specific surface area, accessible active sites, robust structural and chemical diversity, tailorable pore size, exceptional porosity, and pre‐ and postsynthesis structural tunability. Therefore, MOF‐based materials are attractive for energy storage applications, specifically for supercapacitor devices. This review presents recent progress in designing and utilizing pristine MOFs, MOF‐derived nanomaterials, and MOF‐based composite materials for supercapacitors. Most importantly, herein, recent highlights and classifications of electrolytes and their vital role in the structure–property correlation between the structures of MOF‐based materials and suitable electrolyte choices for ideal supercapacitor devices are discussed. Finally, together with a discussion of the progress and outcomes of MOF electrodes, the obstacles and prospects for future MOF‐related research and applications are discussed. To help this intriguing topic continue to advance, this review offers useful insights into the logical design of MOF‐based electrode materials.

Synthesis of 2D Co-MOF Nanosheets and Low-Temperature Calcination Activation for Lithium-Ion Batteries

Metal-organic frameworks (MOFs), a novel type of porous crystalline material, have aroused widespread interest in lithium-ion batteries (LIBs). The design and preparation of MOF electrodes with a stable structure and excellent electrochemical performance are primary concerns for improving the capacity of LIBs. Among them, two-dimensional (2D) materials with larger specific surface areas, richer active sites, and higher aspect ratios have great potential. We adopted a facile approach to synthesize unique Co-MOF nanosheets with a 2D flaky morphology and a mesoporous structure. In addition, low-temperature calcination increases the specific surface area and improves the porosity to achieve mass transfer. Sample M2 delivers high specific capacities and long lives (1402.0 mA h g-1 after 100 cycles at 500 mA g-1 and 462.4 mA h g-1 after 300 cycles at 1.0 A g-1) when the calcination temperature is 200 °C. Significant improvements in the cycle life and stability are attributed to the 2D flaky structure of the M2 sample and the available low-temperature calcination activation, which provide a simple strategy for the fabrication of inexpensive and excellent anodes for LIBs.

Spike Current Induction by Photogenerated Charge Accumulation at the Surface Sites of Porous Porphyrinic Zirconium Metal-Organic Framework Electrodes in Photoelectrochemical Cells

Abstract Photoelectrochemical (PEC) capacitors have recently garnered increasing interest based on their charge accumulation and dissipation mechanisms, particularly with respect to spike and overshoot currents, and have therefore been investigated for biomedical applications, including nerve photostimulation and biomolecular sensing. Porous metal-organic frameworks (MOFs) are capable of accumulating large amounts of photogenerated charge at their surface sites, owing to their large surface areas, and therefore may have potential as a new material for use in PEC capacitors. To explore the PEC capacitor properties of MOFs, we performed transient photocurrent measurements using PEC cells comprising porphyrinic zirconium MOF (PZ-MOF) electrodes in a phosphate-buffered saline solution. We observed a clear growth and decay of the cathodic current during light irradiation and the generation of an anodic reverse current when the light was turned off, thus inducing spike and overshoot currents. However, no spike or overshoot currents were observed when excess oxygen was introduced into the electrolyte. These results indicate that PZ-MOFs have the ability for photogenerated charge accumulation at the surface pores near the interface between the PZ-MOF electrode and the electrolyte. Thus, we have confirmed that PZ-MOFs are a promising PEC capacitor material that may be used in future biomedical applications.