An Overview of Metal‐Organic Framework Based Electrocatalysts: Design and Synthesis for Electrochemical Hydrogen Evolution, Oxygen Evolution, and Carbon Dioxide Reduction Reactions

Due to the increasing global energy demands, scarce fossil fuel supplies, and environmental issues, the pursued goals of energy technologies are being sustainable, more efficient, accessible, and produce near zero greenhouse gas emissions. Electrochemical water splitting is considered as a highly viable and eco‐friendly energy technology. Further, electrochemical carbon dioxide (CO2) reduction reaction (CO2RR) is a cleaner strategy for CO2 utilization and conversion to stable energy (fuels). One of the critical issues in these cleaner technologies is the development of efficient and economical electrocatalyst. Among various materials, metal‐organic frameworks (MOFs) are becoming increasingly popular because of their structural tunability, such as pre‐ and post‐ synthetic modifications, flexibility in ligand design and its functional groups, and incorporation of different metal nodes, that allows for the design of suitable MOFs with desired quality required for each process. In this review, the design of MOF was discussed for specific process together with different synthetic methods and their effects on the MOF properties. The MOFs as electrocatalysts were highlighted with their performances from the aspects of hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and electrochemical CO2RR. Finally, the challenges and opportunities in this field are discussed.


Introduction
[11] Water splitting, [12][13][14][15] rechargeable batteries, and fuel cells are just a few of the technologies that have been thoroughly researched and analysed for better energy generation. [16,17]These technologies encompass essential electrocatalytic processes such as the oxygen evolution reaction (OER), [18][19][20] hydrogen evolution reaction (HER), [21][22][23][24][25] oxygen reduction reaction (ORR), [26][27][28][29] nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CO 2 RR). [1,4,30]s a result, they hold great promises in effectively tackling energy and environmental challenges.One of the most pressing difficulties in these cleaner technologies is the development of effective electrocatalysts.Although platinum (Pt) is the standard material for the majority of these electrocatalytic processes, its use is limited due to scarcity and high cost.To address this, Pt-based carbon catalysts with drastically lower Pt content were created. [12]urrent research has shown tremendous success in substituting Pt with transition metal compounds (TMCs) such as chalcogenides, phosphides, nitrides, metal organic frameworks (MOFs), covalent organic frameworks (COFs) and so on. [31,32]s a result, there has been a considerable emphasis on developing efficient non-precious metal electrocatalysts with increased activity and lifespan. [33,34]In this aspect, designing materials with tailored structures is critical for producing efficient electrocatalytic materials. [35]The adsorption energy on the catalysts were boosted by modifying the shape, composition, and surface properties, which leads to materials with optimal catalytic performance.MOFs, in particular, are being studied extensively in a wide range of applications, including electrocatalysis and electrochemical energy storage devices. [36,37]OFs are a particular type of coordination polymers with voids and persistent porosity. [38]In this specific context, MOF is described in line with the guidelines established by IUPAC in 2013 as follows: "MOFs are subsets of coordination polymers extending in at least one dimension in which inorganic nodes (such as metal clusters or ions) are connected by organic ligands".
Along with crystalline MOFs, non-crystalline MOFs (amorphous MOF, MOF glasses and MOF liquids) are gaining interests because of the remarkable active sites, customizable pore distribution [39,40] and programmable morphologies.MOFs have a well-ordered arrangement of metal ions and organic linkers. [40,41]The MOFs possess the combined properties of both homogeneous and heterogeneous catalysts and have garnered interest as potential electrocatalysts due to their extensive specific surface areas, distinctive composition, clearly defined metal centres, and rich pore structures. [42,43]OFs have been deployed for many other applications. [44]In this review, we focus on the recent progress and new directions in HER, OER and electrochemical CO 2 RR (ECR) using metal organic frameworks.
,46] Because no harmful emissions are created during the electrochemical water splitting procedures, it provides highly pure hydrogen (H 2 ) or/and oxygen (O 2 ), these processes are called clean energy technologies.The two primary half-cell processes involved in electrochemical water splitting are the cathodic HER and the anodic OER.Both the OER at the anode and the HER at the cathode are concurrently driven in an electrocatalytic cell.The primary operating concept for industrial water electrolyzers or proton exchange membrane (PEM) water electrolysis systems is the electric-driven water splitting.Therefore, developing effective and inexpensive electrocatalysts would have a significant impact on enhancing the overall water-splitting process. [47,48]or example, Duan et al. designed a MOF based on nickel and iron that exhibited increased electrocatalytic capabilities throughout the oxygen evolution process.The minimal overpotential observed during testing was 240 mV at 10 mA cm À 2 , and the system was able to perform robustly for 20,000 seconds without showing any decline in OER activity. [49]Liao and co-workers reported a semiconductive amine functionalized noble metal-free cobalt MOF (Co(II)-MOF) for HER and CO 2 reduction and stated photocatalytic hydrogen evolution and CO 2 reduction using trinuclear Co-MOFs with cobalt oxygen clusters as catalytic nodes.Experiments have shown that the activity in hydrogen evolution is influenced by factors such as the type of photosensitizer used, triethanolamine (TEOA), the solvent employed, and the size of the catalyst.The highest activity for hydrogen production was achieved through optimization, resulting in a rate of 1102 mol g À 1 h À 1 by grinding the catalyst and immersing it in a solution containing the photosensitizer prior to the photoreaction. [50]OFs are suitable for electrocatalytic applications because to their large surface area (more active sites are exposed), welldefined metal centres, and porous structure.These features make MOFs suitable as templates or precursors for the production of carbon-based nano-electrocatalysts in an inert environment via a process known as pyrolysis.This technique permits the original porosity structure of the MOF to be retained, allowing simple access to active sites, and the electrical conductivity of the final material can be increased by the nano-carbonaceous matrix generated from the organic ligands. [33,51]In recent studies, various materials other than carbon-based nano-electrocatalysts, such as nitrides, phos-

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phides, sulphides, and selenide derivatives of MOFs, have demonstrated promising activities for the OER as illustrated in (Figure 1). [9,52]The efficiency such as faradaic efficiency of electrocatalysts can vary significantly when used for the HER, OER, CO 2 RR, and it is heavily influenced by the electrolyte used. [53]The overall selectivity of an electrochemical process is described by faradaic efficiency (FE), which is defined as the amount (moles) of collected product relative to the amount that might be created from the total charge transferred, represented as a fraction or a percentage. ::::::::: z-number of electrons required to produce a given product n-number of moles of the product

Q-Charge Released
Combining two separate types of electrocatalysts in the same medium commonly results in a performance loss due to a mismatch between the ideal pH domains at which these electrocatalysts maintain their stability and activity.Currently, many electrocatalysts have strong OER activity in alkaline solutions but low HER activity.However, because of its lower overpotential, the HER is preferable in acidic solutions.In acidic circumstances, however, OER activity is considerably diminished.As a result, high-performance bifunctional electrocatalysts that can catalyse both the HER and OER at the same time are very important.Their present level of resolution is inadequate. [41]Catalyst surface changes such as coating, alloying, and doping can be used to functionalize simultaneous catalysis for HER and OER.Furthermore, a binary catalyst may increase the catalytic behaviour of both processes.Rapid use of non-renewable fossil fuels for industrial evolution and providing energy for human life has resulted in an increase in CO 2 in the atmosphere, which is one of the principal components of greenhouse gas.Excess CO 2 emissions cause major environmental issues.The significant increase in CO 2 levels is the primary driver of global warming and climate change.As a result, good efforts are done to minimise CO 2 emissions from the environment.To reduce CO 2 emissions

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from the combustion of fossil fuels, CO 2 must be converted into value-added goods such as chemicals and used to solve the energy issue.In recent years, electrocatalytic CO 2 reduction reaction (CO 2 RR) has attracted more attention due to advantages related to industrial-level processing. [54]The increased industrialization led to an enhancement in the amount of CO 2 emission to the atmosphere. [55]This results in global warming, a crucial concern for climate change. [56]Therefore, converting CO 2 into valuable chemicals and fuels has become a challenging task for the chemist. [50,57]umerous approaches, including electrochemical, photochemical, thermochemical, and biological, have been widely tested to lower CO 2 levels.The high temperature, high pressure, and clean H 2 input as a reductant necessary for thermochemical CO 2 reduction, on the other hand, render the operation cost inapplicable.CO 2 photochemical reduction has limited activity due to a high energy barrier.Electrochemical CO 2 RR, on the other hand, is a more promising technology since it can be utilised in ambient conditions and has a potential action.One of the most spectacular and beneficial technologies is electrocatalytic CO 2 conversion.The reaction temperature and electrode potential help in process control.The use of chemicals is relatively low, allowing for the recycling of supporting electrolytes.Modifying the electrochemical cells is simple.The energy needed to transform CO 2 is given in the form of electricity.Electrochemical CO 2 reduction could be achieved by utilizing renewable energy sources.
In recent times, electrochemical reduction of CO 2 (ECR) effectively transforms CO 2 into valuable products like carbon monoxide, hydrocarbons, acids, alcohols, and syngas, etc. Electrocatalysis of CO 2 (e. g., CO 2 RR) has been widely proposed as a strategy to generate carbon-based chemicals and fuels, aiming to achieve the storage and use of energy.Due to its simple operation and ability to control the yield and selectivity of the produced chemicals, the electrochemical method is the most favorable and secure technology.Since electrochemical CO 2 conversion can operate with high reaction rates and stable performance at ambient conditions, it is a suitable option for large-scale carbon management applications.
For instance, CO 2 can be converted into ethylene, carbon monoxide (CO), oxalic acid, methanol, methane, formaldehyde, and ethanol at normal temperatures and pressure. [58]Various electrocatalysts have been fabricated and validated for CO 2 reduction applications.Applications involving the adsorption, storage, and separation of CO 2 have made extensive use of MOFs and their derivatives.As the globe faces environmental issues with CO 2 emissions, converting CO 2 into valuable products and fuels has become challenging.In recent years, catalytic CO 2 reduction reaction (CO 2 RR) has consumed more attention due to rewards related to industriallevel processing. [54]MOFs are the potential materials for heterogeneous catalysis due to tuneable characteristics and various species of metals and organic linking.
The present study discusses the MOFs and their derivatives as highly efficient catalysts for diverse applications such as OER, HER, and CO 2 RR.To best of our knowledge, a review that explains the influence of MOF design on their performance towards different electrochemical process is very limited.Further, as the research interest towards MOF has been increasing exponentially (Figure 2), this review summarizes the recent results on MOF as electrocatalyst is very crucial.In this review, synthetic parameters associated with different synthetic methods and their effects on the properties of MOFs are comprehensively analysed.The overview of basic reaction

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mechanism of HER, OER and CO 2 RR and the prerequisite materials properties required for these reactions are discussed.Several CO 2 reduction reactions for various stable products are discussed.The electrochemical performance of the MOF towards HER, OER and CO 2 RR are highlighted based on the recent studies.Finally, the summary and future perspective are presented.

Synthesis of MOFs
The formation of MOFs involves the combination of metal ions/clusters (inorganic nodes) and functional organic ligands (linkers) using coordination bonds.Several techniques are available for synthesizing MOFs, such as solvothermal and hydrothermal, electrochemical, sonochemical, microwave-assisted synthesis, liquid-phase epitaxial layer-by-layer (LPE-LbL) method, and chemical vapour deposition (Figure 3), which are briefly discussed below.MOFs and their derivatives suffer from low mass permeability and conductivity, which can be overcome by functionalizing the surface of the MOFs with different types of chemical groups to enhance their mass permeability and conductivity by assisting synthesis methods.

Solvothermal and Hydrothermal Synthesis
Solvothermal synthesis is a popular approach for producing MOFs, which are noted for their large surface area and adjustable characteristics.These properties make MOFs an appealing alternative for a variety of applications, including drug delivery, catalytic processes, gas storage, and separation.The selection of an adequate solvent is a critical aspect in this approach.In the solvothermal process, the organic ligand and metal react in a solvent such as acetonitrile, acetone, ethanol, methanol, dimethylformamide [59] or diethyl formamide. [60]roper solvent selection can significantly affect the efficiency and outcome of the reaction.Dimethyl formamide (DMF) and diethyl formamide (DEF) are commonly utilized solvents in the synthesis of MOFs and their composites due to their high boiling points and high solubility for organic ligands and metal precursors.If water is used as the solvent to synthesize materials, then the process is known as the hydrothermal method.The temperature of the process should be above the solvent's boiling point [61] and typically between 353 and 523 K.The synthesis process can take 3 to 96 hours [62] and generates fine powders that cannot be created through traditional methods. [63]A systematic high throughput investigation on the reaction between FeCl 3 and 2-aminoterephthalic acid in

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different solvents revealed that the product formation depends on the nature of the solvent (protic /aprotic) with temperature as an important parameter as it determines the equilibrium of dissociated product. [64]Recently, the microstructures and coreshell thickness of the MOFs are adjusted by varying the solvents used in the post-synthetic linker exchange. [65]This tuning process relies on the diffusion rate of the linker through the MOF, which is influenced by the alkyl chain length of the solvents.Thus, the synthesis parameters, such as solvent composition, pressure, reagent concentration, and temperature, can be adjusted to create specific structures.Also, this method offers a high yield and allows control over the geometry of the synthesized product. [66]hile the solvothermal approach, which employs organic solvents, has been widely used in the creation of MOFs, the solvents' toxicity and environmental effect limit its widespread usage.Another disadvantage of this technology is the difficulty in eliminating the solvents employed in the synthesis process.Another disadvantage of the solvothermal method is that it can be difficult to scale up the synthesis process for industrial production due to the high temperatures and pressures used in the solvothermal method, and the use of organic solvents may also be impractical due to their cost and potential safety hazards.To address these issues, scientists are investigating the utilisation of microreactors and continuous flow synthesis methods for the solvothermal synthesis of MOFs.These techniques have the potential to minimise the synthesis process's energy and solvent usage, making it more appropriate for large-scale manufacturing.Efforts are also being undertaken to produce more environmentally friendly solvents for use in the solvothermal process, such as ionic liquids, which may be less hazardous and simpler to remove after synthesis.Overall, the solvothermal approach is still a popular and adaptable method for synthesising MOFs, although researchers are always looking for methods to increase its efficiency, scalability, and sustainability.

Electrochemical Synthesis
[69][70] Metal ions generated by anode dissolution are used as the metal ion source in this procedure.These ions are continually supplied by anodic dissolution for 5 to 30 minutes, and in the reaction media, they interact with the distributed linker molecules and a conducting salt to synthesise MOFs. [71]The use of protic solvents can inhibit the cathodic dissolution of the metal, but this method also generates hydrogen gas as a byproduct. [72,73]The electrochemical synthesis technique has several merits over other techniques for MOF production as it is highly efficient, rapid, scalable, and environmentally friendly and does not require high pressures or temperatures for MOF production.
Additionally, as no metal salts are used, this method does not produce counter ions, resulting in a pure production process.It can be conducted at room temperature by manipulating solvent pH, and a simple experimental apparatus is required. [74,75]This technique is favourable for producing HKUST-1 MOFs and is classified into three subtypes such as anodic electrodeposition, cathodic electrodeposition, and electrophoretic deposition.All three subtypes of the electrochemical synthesis process may synthesise diverse MOFs with different metal ions and linker molecules in aqueous or nonaqueous solvents.During the anodic electrodeposition process, the metal source is anodically dissolved in the reaction media, and the dissolved metal ions are subsequently reduced on the cathode. [76]he cathodic electrodeposition method involves the reduction of the metal ions on the cathode and their subsequent transport through the reaction medium to the anode. [77]By varying the potential during cathodic deposition, selective specific phases of MOF can be produced.By this way, both biphasic bulk as well as biphasic layered MOF can be prepared.The variation in potential during the cathodic deposition modulates the local pH to produce selective phase, thus resulting in these heterogeneous structures.In the electrophoretic deposition method, charged particles move in an electric field, accumulating the particles at a specific location. [78]ne limitation of the electrochemical synthesis method is that it is not suitable for synthesizing MOFs with highly reactive metal ions because the high reactivity of these metal ions can result in the formation of additional unwanted side products.In addition, the efficiency of the synthesis process can be affected by the electrochemical properties of the metal ions, the nature of the linker molecules, and the composition of the reaction medium.Despite these limitations, the electrochemical synthesis method remains a widely utilized and effective technique for producing MOFs.

Microwave-Assisted Synthesis
Microwave-assisted synthesis is an effective and widely used method for rapidly synthesizing MOFs. [79,80][83][84][85][86][87] It is simple, efficient, environmentally friendly, and effective for producing MOFs. [88,89]Microwave-assisted synthesis is frequently applied in organic synthesis and for synthesizing nanoporous materials.During the reaction process, electromagnetic radiation with a frequency ranging from 0.2 to 200 GHz and a wavelength of 1 mm to 1 m is utilized.This energy is efficiently transferred to the reaction precursor. [90,91]n order to synthesize MOFs, the required heat for the feasibility of the process is generated by microwave through a process called dielectric heating. [92]When microwaves flow through certain materials, they cause dielectric heating.When exposed to an alternating electric field, these materials, known as dielectric materials, may store electrical energy.Microwaves passing through these materials cause the molecules within to vibrate quickly.This motion creates the heat necessary for MOF synthesis.
Unlike traditional approaches such as solvothermal synthesis, [93,94] microwave synthesis heats the reaction medium directly rather than indirectly heating the vessel.Traditionally, reactions are heated by heating the vessel, whereas microwave synthesis directly heats the reaction medium through the conversion of electromagnetic waves, removing the need for an intermediate.This direct heating enables more efficient MOF production. [95]The whole heating procedure is usually quick, lasting anything from 3 minutes to 3 hours.This significantly reduces the necessary temperature and synthesis time, making it a viable and successful technique.The synthesis process may be precisely regulated to provide MOFs with specified features such as size, shape, and so on. [96]This is accomplished by regulating the intensity of the microwave and the duration of the microwave process.The effectiveness of the MOF synthesis depends on the solvent's ability to absorb electromagnetic wave energy and convert it to heat.Therefore, the type of solvent used is an essential factor in this method. [92]he rapid heating during microwave-assisted synthesis can considerably speed up the nucleation and development of MOF particles, resulting in smaller and more evenly dispersed MOFs.These materials have potential applications in catalysis. [97,98]Research groups have widely adopted the microwave method for synthesizing MOFs due to its safety and efficiency compared to the conventional solvothermal method. [99,100]Controlling the morphology and size of materials fabricated by the microwave method can be challenging.Although the use of microwave radiation has been successful in creating MOFs, there are still difficulties in controlling the structure and size of the developed materials; this can be attributed to various factors, including the properties of the reactants and conditions used, as well as the characteristics of the microwave radiation itself.Researchers are actively working on more effective strategies for controlling the shape and size of materials produced through microwave synthesis.

Sonochemical Synthesis
The sonochemical synthesis is a technique that uses ultrasonic radiation in the 20 kHz to 10 MHz frequency range for creating MOFs.This method has several benefits, such as costeffectiveness, safety, rapidness, and environmental friendliness. [101,102]In this method, applying intensive ultra-sonic radiation causes chemical changes in the molecules.The formation of the desired MOF is accelerated by the energy provided by ultrasonic radiation, which activates the interaction between the metal ions and the organic ligands.This method utilizes the energy from ultrasonic radiation to facilitate chemical reactions rather than relying on traditional methods such as heat or pressure.To synthesize a desired MOF, a solution mixture containing the necessary metal ions and organic ligands is placed in a conical Pyrex reactor outfitted with a sonicator bar.This bar generates ultrasonic radiation with adjustable power output, which is then applied to the solution for a time period of 30 to 180 minutes (Figure 4), facilitating chemical reactions between the metal ions and organic ligands, leading to the formation of the desired MOF.It is important to note that the chemical reactions that result in the formation of the MOF do not occur through direct interaction between the ultrasonic radiation and the molecules.
Since water was present throughout the synthesis, the alternating pressure patterns created by ultrasonic irradiation can produce bubbles known as acoustic cavitation.The development and burst of bubbles in cavities create tiny, extremely hot, pressurised zones with temperatures up to 5000 °C and pressures up to 500 atmospheres.According to the literature, using ultrasonic radiation may generate a considerable amount of energy and pressure, which can activate novel chemical reactions and the formation of unique structures. [103]Because of the rapid heating, this method can also generate a stable, finely crystalline structure.In a short amount of time, this approach creates tiny particles with homogeneous nucleation. [104,105]This method can potentially be a more efficient and cost-effective way to synthesize MOFs on a large scale, as it can be done at room temperature.In addition, the MOFs synthesized using the sonication method are more durable and contain a larger surface area than those produced using other methods.However, while the sonication method shows great promise in synthesizing MOFs, many studies have not been conducted on this method and additional research is required to comprehend its capabilities and possible constraints.

Liquid-Phase Epitaxial Layer-by-Layer (LPE-LbL) Method
Compared to other methods, LPE-LbL offers tuneable oriented growth of surface anchored MOFs (SURMOFs).The basic procedure of this method involves sequentially immersing a substrate that has modified with a self-assembled monolayer (SAM) into solutions containing the metal precursor and organic linker, respectively. [106]At first, Bein et al. demonstrated the growth of HKUST-1 on the differently functionalized SAM and observed that highly oriented SURMOF along

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the [100] and [111] direction for À COOH functionalized SAM and À OH functionalized SAM, respectively, while À CH 3 terminated Sam yield less oriented SURMOFs.The SUR-MOFs films are homogenous irrespective of functional groups. [107]By employing this technique, it is possible to produce uniform and homogenous thin films of MOFs.The orientation of the resulting SURMOF is determined by the SAM, while the desired layer thickness and porosity can be regulated by adjusting the number of dipping cycles and organic linkers, respectively. [108,109]The exceptional homogeneity and tailorable properties of SURMOFs make them potential candidate for HER, OER, and CO 2 RR.The 3D Co/ Ni(BDC) 2 TED SURMOF grew on Cu foam by a LPE-LBL method with [001]-orientation.The superior OER activity was observed for MOF nanosheet arrays having Co: Ni ratio of 1 : 1, grown with 40 cycles.The overpotential of only 260 and 287 mV are observed at geometric current density of 10 and 50 mA cm À 2 in 1.0 M KOH aqueous solution, respectively.The SURFMOF, ReL(CO) 3 Cl ["L = 2,2'-bipyridine-5,5'-dicarboxylic acid)"] grown on fluorine doped tin oxide (FTO) in [001] direction exhibited an excellent faradaic efficiency of 93 � 5% for the conversion CO 2 to CO. [110] Although there are few studies on examining the electrocatalytic performance of SURMOFs, a comprehensive investigation into the influence of functionalized SAMs on morphology and electrical conductivity is necessary for a thorough understanding of their electrocatalytic capabilities and widespread applicability. [111]

Chemical Vapour Deposition (CVD) Method
In 2016, Staseen et al. [112] demonstrated the preparation of ZIF-8, zinc-(2-methylimidazolate) 2 by chemical vapour deposition, which has been used for preparing other materials. [113]he formation of MOF was achieved by reaction exposing the zinc oxide (ZnO) layers deposited by atomic layer deposition to the 2-methylimidazole (HmIM) vapours.In addition, the possibility towards the preparation of related MOFs, such as ZIF-61, ZIF-67 and ZIF-72 were explored.The average thickness of ZIF-8 films obtained from 3 and 6 nm thick ZnO oxide films were 52 and 104 nm, respectively.This increase in thickness is explained by the volume expansion for Zn ion occupied in ZIF-8 compared to Zn ions occupied in ZnO.However, this increase in thickness is not proportional to thickness of oxide layer, because formed MOF film itself act as diffusion layer for the vapour phase reactants.The same selflimiting of growth was observed for the thin films of copper dicarboxylate metal-organic framework. [114]Miao et al. [115] developed e-beam assisted patterns of ZIF-8 and ZIF-67 by chemical vapour deposition.The localization of ions during the CVD process attributes to the formation of smooth and pin-hole free MOF films.The chemical vapour deposition of MOF could facilitate the easy integration of MOF in microand nano-electronic devices, by alleviating the concerns such as corrosion, contamination, contact corrosion, and other incompatibilities associated to solution-based approaches. [116]

MOFs as Electrocatalysts
Metal-organic frameworks (MOFs)' structural variety has led to a wide range of applications in catalysis, gas separation, drug storage, medical imaging, sensing, and energy storage. [117]he electrochemist is responsible for creating and advancing the above-mentioned application for an industrialist in a feasible and economically viable manner.According to a recent analysis on global energy usage per capita, adequate alternate renewable energy sources should provide long-term energy sustainability.The hydrogen fuel cell is an appealing, clean (no greenhouse gas emissions), and the sole renewable energy source that employs pure H 2 created by electrolysis to divide the more plentiful water molecules in the Earth's crust for energy conversion and storage applications. [42,118]The thermodynamic potential required for driving the electrolysis is only about 1.23 V (vs.RHE), [119] whereas, in practice, it was applied more than 1.23 V to drive the reaction forward due to the Ohmic drop and overpotential associated with reactions on the anode and cathode.The catalytic activity of conventional Pt, Ru, or Ir metal-based electrocatalysts, particularly in water splitting reactions, is restricted by high cost, low abundance of electrode material, and solid corrosive nature towards electrolytes. [35,42]OFs are complex inorganic materials framed by the secondary building units of (SBU) inorganic moieties linked with polydentate organic ligands (organic linkers with O, N, or S donors) as a linking unit. [118]The SBU is inorganic materials such as oxide, hydroxide, halides, and nitrates of corresponding metal ions.Generally, MOFs are crystalline materials with the highest porosity (> 80 %) of their volume with good electrical conductivity.Moreover, the MOF's active surface and electrical conductivity could be tailored by optimizing the SBUs and organic linkers for electrochemical applications.These salient features make such MOFs effec-tively utilized for various electrochemical conversions by industrialists and electrochemists.Particularly, surface and conductivity-based catalytic behaviour increase the interest in fabricating novel MOFs with the electrochemical behaviour for catalytic applications.
Various MOFs have been thoroughly developed and validated by electrochemists to generate electricity via fuel cell applications because to their zero-greenhouse gas, reduced operating cost, and moderate energy density as opposed to oilgas and nuclear resources.There is a particular opportunity to investigate the many types of MOF derivatives, such as 1D, 2D, and 3D, for specific electrochemical applications.For example, Xue et al. reported a dithiolene -diamine (MS 2 N 2 , M = Co and Ni) based 2D conductive carbon-rich MOF incorporated material with enhanced active metallic sites along conjugated structure for HER in acidic and alkaline medium.In addition, Ni 0.3 Co 0.7 MOF nanosheets for similar HER applications. [120]Similarly, 2D Ni-BDC/Ni(OH) 2 hybrid nanosheets were designed and demonstrated for OER, and the results revealed that the investigated MOF displayed higher activity, faster kinetics, and extended durability.On the other hand, 2D porous Bi-MOF was extensively studied and reported for CO 2 RR, which converts CO 2 to HCOOH with 92.2 % Faradaic efficiency at an overpotential of 0.65 V and a remarkable stability of 30 h.The recent advancements of MOF-derived electrocatalysts for OER, HER, and CO 2 RR applications are summarized in this section.

Hydrogen Evolution Reaction (HER)
Several MOF-derived electrocatalysts validated for HER application are compared and summarised in Table 1

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hydrogen evolution reactions.Significantly, the work was demonstrated with CoP-based nanoparticles (CoP 3 NPs) with an extensive pH range.CoP 3 NPs were investigated in a 1.0 M KOH medium, and it showed a Tafel slope of 88 mV dec À 1 and required an overpotential of À 124 mV to obtain a current density of 10 mA cm À 2 after 3000 CV cycles.These values were commensurable, with the majority of the reported HER electrocatalysts in an alkaline medium.The Faradaic efficiency of the above-demonstrated electrocatalyst was calculated by quantifying liberated H 2 and found to be almost comparable with its theoretical values. [34]hi et al. worked on Co-Mo 2 N MOF, which has a tubelike structure and tested its efficacy in HER, using 1.0 M KOH electrolyte without iR corrections.The results were compared with Mo-MOFsÀ T5, ZIF-67-T5, and commercial Pt/C as control, and it was found that a combination of Co with Mo 2 N promoted the HER.Furthermore, to confirm the better catalytic activity of hybrid Co-Mo 2 N MOF, overpotentials were measured at different current densities (10, 20, 50, and 100 mA cm À 2 ) and compared to the S-2-T5 (overpotentials of 76, 106, 167 and 240 mV at 10, 20, 50 and 100 mA cm À 2) , Mo-MOFsÀ T5 derived from Mo-MOFs (296, 344, 427 and 517 mV), and ZIF-67-T5 derived from ZIF-(67 180, 221, 295 and 377 mV). [35]hai et al. studied the HER activity of MIL-(IrNiFe)@NF with a tiny amount of Ir, exhibiting improved HER activity.For instance, It required an overpotential of 69 mV to drive a current density of 100 mA cm À 2 , which falls well below those of reported MIL-(NiFe)@NF (230 mV), MIL-(Fe)@NF (340 mV), and Pt/C (280 mV).The HER performance of MIL-(IrNiFe)@NF was superior to previously reported MOF and noble metal-based HER electrocatalysts. [121]Mogwasna et al. reported the use of Graphene oxide (GO) incorporated Cu-MOF as electrocatalyst for HER, and the results revealed that enhanced HER activity is observed by incorporation of GO into Cu-MOF.For example, GO has a Tafel slope of 144 mV dec À 1 in 0.30 mol L À 1 H 2 SO 4 , whereas, in the same conditions, it is found to be 125 mV dec À 1 for GO/MOF, which is low as compared to the pristine GO. [122] Wang et al. developed MOF-derived MoCoP nanosheets to achieve enhanced HER activities over conventional MOF.The HER performance was evaluated using 1.0 M KOH electrolyte in a conventional three-electrode system and compared with Mo-CoP, CoP, and commercial Pt/C catalysts. [123]The results revealed that relatively lower HER overpotential of 89 mV at a current density of 10 mA cm À 2 was achieved for MOF-derived MoCoP nanosheets, which is slightly above that of Pt/C (42 mV) and well below that of Mo-CoP (154 mV), CoP (165 mV).In addition, the estimated Tafel slope of MOFderived MoCoP nanosheets (69.7 mV dec À 1 ) was also much lower than those of Mo-CoP (83.7 mV dec À 1 ), CoP (113.4 mV dec À 1 ) and close to that of Pt/C (56.1 mV dec À 1 ), which specify faster HER reaction kinetics by following Volmer-Heyrovsky mechanism (Figure 5a).Gan et al. developed ternary CuNiFeN-based MOF for bi-functional HER and OER activities.The overpotential of 33 mV is observed for the HER test, which is lower than that of the abovediscussed MOFs derivatives. [124]Similarly transition metalbased hybrid MOF with the composition of Co x P-FeP@C (239 mV) and Zn-NiCoP (150 mV) were also reported as a potential catalyst for HER. [125,126]

Oxygen Evolution Reaction (OER)
Various MOF derivatives validated for OER electrocatalysis are summarised in Table 2. Jingjing et al. developed NiFe-MOF for HER applications.In addition to HER, NiFe-MOF also showed enhanced OER activity than the benchmark catalyst IrO 2. It displayed an over potential of 240 mV at 10 mA cm À 2 current density which is substantially lower than the 320 mV at 10 mA cm À 2 displayed by the benchmark catalyst IrO 2 and a current density of 300 mA at 1.7 V versus RHE, which is 2.7 times higher current density than IrO 2 which displays 80 mA cm À 2 at 1.7 V versus RHE .The superior electrocatalytic activity of NiFe-MOF is confirmed by its smaller Tafel slope values derived from LSVs (34 mV dec À 1 ) than other reference samples such as Ni-MOF (45 mV dec À 1 ), bulk NiFe-MOF (56 mV dec À 1 ) and IrO 2 (43 mV dec À 1 ). [18]he equation given below discusses the OER mechanism in alkaline and acidic conditions,

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OER mechanism in the alkaline electrolyte (Figure 5b) black line: Step Step Step Step 4 : OER mechanism in the acidic electrolyte (Figure 5b) red line: Step Step Step Step Wu et al. reported MOF-derived porous cobalt polyphosphide (CoP3) concave polyhedrons (CP) based composite particles for HER and OER activities (Figure 6).OER current density for CoP3 CPs is reported to surpass RuO 2 after an overpotential of 421 mV. [6]Furthermore, the calculated Tafel slope values were found to be 76 mV dec À 1 , which is comparable with the performance of the majority of the previously reported OER electrocatalysts.As discussed earlier, Shi et al. developed S-2-T5 (Co-Mo 2 N hybrid MOF) as a potential catalyst for the OER.In this connection, the demonstrated catalytic activity of S-2-T5 (overpotentials of 302, 334, 400, and 485 mV at 10, 20, 50, and 100 mA cm À 2 ), which are much lower than Mo-MOFsÀ T5 (407, 442, 509 and 604 mV), ZIF-67-T5 (387, 422, 488 and 581 mV), and with benchmark OER catalyst RuO 2 (355, 389, 456 and 546 mV) respectively (Figure 7).In addition, the Tafel slope of S-2-T5 is also found to be 90 mV dec À 1 , which is also lower compared to Mo-MOFs-T5 (93 mV dec À 1 ), ZIF-67-T5 (92 mV dec À 1 ) and RuO 2 (104 mV dec À 1 ). [35]IL-(IrNiFe)@NF, developed by Zhai et al., was tested for OER activities.It is essential to highlight that the highest electrocatalytic activity observed towards the OER with an overpotential of only 300 mV to attain a large current density of 500 mA cm À 2 (η 500 values for MIL-(NiFe)@NF, MIL-(Fe)@NF, NF, and RuO 2 are 320, 340, 590, and 480 mV, respectively). [121]MOF-derived MoCoP, developed for HER by Wang et al., was also tested for its OER activities in 1.0 M KOH solutions. [123]In the OER test, an overpotential of only 273 mV at a current density 10 mA cm À 2 is observed and found to be relatively lower than that of Mo-CoP, CoP, and the benchmark OER catalyst RuO 2 .Apart from over potential, the estimated Tafel slope of 54.9 mV dec À 1 is found to be below that of Mo-CoP (60.4 mV dec À 1 ), CoP (71.5 dec À 1 ) and RuO 2 (86.4   (44.32 mV dec À 1 ) based MOF also investigated and reported as potential catalyst for OER reactions. [127,128].

MOFs derivatives in CO 2 Reduction Reaction (CO 2 RR)
CO 2 is one of the most stable molecules because it has strong C=O double bonds.As a result of its chemical stability, high energy is required to activate the CO 2 molecule for CO 2 conversion to occur.The crucial step in CO 2 reduction is the generation of CO 2

À
and the coordination of mode this intermediate on the catalyst surface determines the product selectivity.Achieving a high rate and energy-efficient CO 2 reduction process thus depends on stabilizing this high-energy intermediate.Compared to the first step, the following reduction steps occur almost directly.However, its multistep reduction through an electrochemical approach is much more complicated than the water-splitting reaction and has many technical difficulties.
The electrocatalytic reduction of CO 2 consists of two half reactions that can occur via a two to fourteen-electron exchange process.CO 2 electro-reduction can occur through a two-, four-, six-, or eight-electron pathway, etc., depending on the selectivity of the electrocatalysts.Two electrically biased electrodes make up a typical electrochemical system.The negatively charged cathode converts protons and CO 2 into products, while the positively charged anode oxidizes H 2 O to produce protons and O 2 .Several products can be made from CO 2 .The chemical conversion of CO 2 into reduced carbon species is the initial step in the reduction of CO 2 , but this is a challenging process because of the slow kinetics of CO 2 electro-reduction.The overall design process for the CO 2 reduction reaction depends on the target product needed.
Additionally, the CO 2 RR's multi-electron transfer mechanism allowed for a variety of reduction products, which decreases selectivity.Even on the surface of highly selective catalysts, poor kinetics complicate the electrochemical CO 2 reduction mechanism.Consequently, many researchers focus on the preparation of catalysts to boost the activity and selectivity of electrocatalytic CO 2 RR.The design of catalyst systems for selective CO 2 reduction with minimal H 2 generation, long-term stability, catalytic efficiency at low electrochemical overpotential, and compositions of earthabundant materials continue to require these major challenges.
The first MOF to be discussed as a catalyst for electrochemical CO 2 reduction was a Cu-rubeanic acid MOF. [129]oble metals with good catalytic activity in the CO 2 RR include Au, Ag, and Pd.Its practical applications are restricted by their expensive cost.It is still challenging to find electrochemical catalysts with excellent selectivity, low cost, good stability, and minimum operation over-potentials.A few transition metals (Fe, Co, Ni) and N-doped carbon materials (MÀ N-C) have recently been discovered to exhibit remarkable selectivity, strong chemical stability, and attractive conductivity in the CO 2 RR.Fe, Co, or Ni atoms can drastically alter their electronic structures and create an unsaturated coordination environment in N-doped carbon materials, which improves catalytic activity. [130]t has been shown that post-transition metals, such as In, Sn, Hg, and Pb, favor the production of HCOOH/HCOO À due to their poor CO 2 adsorption capabilities.Because of its affordability, earthiness, nontoxicity, and low activity for the competing HER during ECR at cathodic potentials, bismuth (Bi) is regarded as a desirable metal for ECR. [131]Typically, Cu-based catalysts lead to a multistep CO 2 electro-reduction process that produces mixed gas and liquid products with a C 2 H 4 , in CO 2 -saturated aqueous solutions under certain conditions.These catalysts focus on a high reaction rate. [132]For the CO 2 RR durability test, polyoxometalate-based MOFs (PMOF) consistently exhibit strong structural robustness and chemical stability.These PMOFs' synergistic combination of Zn-Keggin and M-ligand from the MOF can act as the

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CO 2 RR's active component for electron donation, migration, and electrocatalysis.Tests are conducted on the electroreduction capabilities of various PMOFs based on transition metals (Co, Fe, Ni, and Zn).PMOFs have remarkable electrocatalytic CO 2 RR characteristics, particularly Co-PMOF, which has a high faradaic efficiency of 99 % (the highest in known MOFs) and excellent stability.It is important to note that this is the first instance of polyoxometalate-based MOF being investigated as a catalyst in electrochemical CO 2 RR. [133]n Zn-based complexes or metal-organic frameworks (MOFs), the major electrocatalytic active sites are typically not the metal centers due to Zn II 's fully occupied 3d orbital for CO 2 RR reaction, but rather the ligands coordinating with the Zn centers.This opens new possibilities for adjusting the ligand itself.By the ligand doping approach, a particular ligand with a potent capacity to donate electrons could operate on MOFs to increase the charge density on the nearby original ligand sites, boosting their electrocatalytic activity for CO 2 RR.Overall, ligand doping is a novel way to achieve increased electrocatalytic activity of MOFs for CO 2 RR. [134]The mechanism for reducing CO 2 into valuable products such as methanol, formic acid, and CO is described below.CO 2 RR mechanism in aqueous electrolyte:

Reduction potentials (vs. RHE) of various products in CO 2 reduction reactions
The selectivity of the process is one of the main obstacles to ensure an effective CO 2 RR.The hydrogen evolution reaction (HER), which takes place at low overpotential on several catalysts, competes with the CO 2 RR in aqueous electrolytes (eq.20), where the generation of H 2 suppresses the electrochemical CO 2 reduction at low overpotentials.Therefore, the pH value should be considered because it lowers the undesirable HER.
During the electrocatalytic CO 2 reduction reaction, the morphology, roughness, and size of the catalyst used immensely influence the activity and product selectivity.This makes it necessary to consider the MOF's stability in aqueous electrolytes and the presence of bicarbonate ions, the preferred medium for CO 2 electrolysis.The electrolysis potential that is employed may also have an impact on the MOF's chemical stability.Metal impregnation or deposition increases the electrocatalysis of MOFs for CO 2 reduction.The existence of stable MOFs under these circumstances will thus be necessary for any future applications of MOFs for CO 2 RR electrocatalysis.

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The presence of specific ions in solution can be harmful to MOFs because they can interact with the carboxylic ligands and coordinate with the metal centers.Examples of these anions include phosphate, carbonate, and fluoride.Therefore, the neutral aqueous electrolytes used during this process, typically bicarbonate or phosphate buffers that are CO 2 saturated, can make MOFs unstable and thus increase the difficulty in CO 2 RR.As a result, non-aqueous electrolytes such as tetrabutylammonium hexafluorophosphate (TBAPF 6 ) in acetonitrile or DMF have been used to study the catalytic activity of MOFs that are unstable in aqueous electrolytes. [135]he importance of using these organic solvents is their high CO 2 solubility, which can lessen mass transport restrictions.Moreover, their proton concentration is low, which hinders the hydrogen evolution reaction, a rival process.However, then again, aqueous electrolytes are still highly desired because water is a reliable and readily available solvent that can be applied to large-scale processes.
In this context, the electrocatalytic activity of various MOF derivatives is summarized (Table 3).Tareq et al. framed CALF-20 (Zn-triazole MOF developed by the university of Calgary) to produce CO from CO 2 .In their investigations, the highest CO partial current density of À 53.2 mA/cm 2 was observed for CALF 20 with faradaic efficiency of about 94 % at À 0.97 V versus a reversible hydrogen electrode.Similarly, InCuO and NiPc-NiO 4 NS MOF are also used for converting CO 2 to CO using 0.5 M KOH as an electrolyte.As mentioned above, the faradaic efficiency of the MOF catalysts was found to be 91.8 % and 98.4 %, respectively (Figure 8). [136]Jian-Xiang et al. demonstrated Sn(101)-MOF for producing formate from CO 2 .Indium (In) foil-based MOF was tested for producing formic acid by reducing CO 2 through an electrochemical process. [137]In these reactions, a current density of 46.1 mA cm À 2 was applied at a potential of À 2.15 V vs. Ag/ Ag + for the electro-reduction of CO 2 in organic electrolyte with a Faradaic efficiency of 99.1 %.In addition, 2D Bi-MOF was developed and studied for a similar formic acid preparation with a faradaic efficiency of 92.1 %.Senthil et al. demonstrated Cu-BTC-MOF for synthesizing oxalic acid from CO 2 through electrochemical reduction with a Faradaic efficiency of 99.1 %. [98]

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MOF [Cu 3 (HHTQ) 2 ] and oxide-derived Cu-MOF (OD CuÀ C) for efficient conversion of CO 2 into methanol with the Faradaic efficiency of greater than 50 % using 0.1 M KHCO 3 as electrolyte. [138,139]inchen et al. conducted electrochemical reduction of CO 2 with the combination of Zn-BTC MOFs deposited on carbon paper as the electrode and ionic liquid (IL) as electrolyte.It showed higher selectivity for CH 4 than 80 % at a current density higher than 3 mA cm À 2 .The morphology of this MOF exhibits a large electroactive surface area, and ILs with fluorine are effective electrolytes that are more active for the conversion of CO 2 to CH 4 .
Qiu et al. designed Copper phthalocyanine-based MOF and carried out the electrocatalytic conversion of CO 2 to C 2 H 4. High crystalline ordered framework structure, enhanced CuÀ N interaction, and strong designability of active sites of CuÀ Pc served as the single active site to achieve high selectivity and durability for CO 2 RR to ethylene conversion.The electrocatalytic behavior of PcCu-CuÀ O was measured.The working electrode for measuring the electrochemical CO 2 RR activity in an H-type cell with two compartments, the microcrystalline PcCu-CuÀ O powder was coated on a glassy carbon electrode (GCE) with Nafion binder.A 0.1 M KHCO 3 aqueous solution saturated with CO 2 /Ar was used for the cyclic voltammetry (CV) observations.Cu(II) to Cu(I) ion reduction can be attributed to the compound's reduction in the Ar environment, which was seen at potentials of À 1.0 to À 1.3 V vs. RHE.In the CO 2 -saturated solution, the current density increased, which is an indication of the CO 2 RR process.At various potentials, the FEs of various reduced compounds were examined.In contrast to the exfoliated sample, the assynthesized bulk sample performed poorly (FE-(C 2 H 4 ) = 43 %, current density = 4.2 mA cm À 2 ) under the same conditions, suggesting that particle size may have an impact on electrochemical activity.
PcCu-CuÀ O demonstrated high selectivity towards C 2 H 4 (FE(C 2 H 4 ) = 50 %) and a current density of 7.3 mA cm À 2 at À 1.2 V vs. RHE.Remarkably, PcCu-CuÀ O exhibited significantly better performance than discrete molecule PcCu, which has a FE(C 2 H 4 ) of 25 %, as well as all known MOFs and MOF derivatives, as well as the majority of copper salts, copper nanoparticles, and copper alloys, including CuOHFCl (FE(C 2 H 4 ) of 36.3 %), CuPd (FE(C 2 H 4 ) of 48 %), and Cu nanocube-O (FE(C 2 H 4 ) of 45 %).However, the high selectivity was achieved at a higher potential of about À 2.0 V vs. RHE, indicating a higher energy consumption.In fact, only a reconstructed nano copper electrocatalyst showed a higher FE(C 2 H 4 ) than that of PcCu-CuÀ O in a neutral electrolyte.PcCu-CuÀ O was subjected to constant electro-reduction of CO 2 at À 1.2 V to assess the durability.The i-t curve showed that PcCu-CuÀ O maintained its capability for at least 4 hours [143] (Figure 9).

Summary and Future Perspectives
In conclusion, the development of efficient and cost-effective electrocatalysts is critical in driving the advancements in clean energy technologies such as water splitting and CO 2 RR.MOFs have gained significant attention as potential heterogeneous electrocatalysts because of their single-metal catalyst site.The potential benefits of MOFs as heterogeneous catalysts include high transition metal densities, size selectivity, coordinatively unsaturated sites, adjustable pore size and surface area, enhanced stability, and oxidant activation through Lewis acid.This review has explored various MOF synthesis methods, and evaluates their efficiency, environmental challenges, and alternative solutions to mitigate them.Due to their synthetic adaptability, long-range order, and diverse host-guest chemistry, they are excellent candidates for easy synthesis, as well as pre-and post-synthetic modifications to achieve desired functions.Due to their inclusion of organic and inorganic components, MOFs have been shown to exhibit outstanding mechanical resilience, chemical stability, and structural variety.Further, this review highlighted the recent advancements in MOFs as electrocatalyst towards HER, OER and CO 2 RR.When the active species for HER or OER are uniformly dispersed on the surface of the MOF or integrated into the matrix of the MOF, they are more effective as catalysts.High electrical conductivity, extensive porosity, and extremely active reaction centers are properties possessed by MOF-derived carbon compounds that make them suitable catalysts for efficient CO 2 reduction.The combined data on recently reported MOF based HER, OER, and CO 2 RR in this review will be helpful to electrochemists to synthesize and validate the novel MOFs for further development.
However, MOF as electrocatalysts still have several drawbacks, such as limited mass permeability, poor stability, low conductivity, and blockage of the active and obstructive metal centers by organic linkers.To overcome these limitations, the MOF derivatives should be structurally modified to achieve better/improved electrocatalytic activity.Such structural alterations should benefit from enhanced electron transfer, rapid mass transport, better availability of active catalytic sites, and readily recognizable and easily tuneable surface structures.The in-depth studies on structure-performance relationship to expand the functions of MOFs remains to be explored, such as how to expose more active sites in the film, which units to connect and how to connect to facilitate the reaction.Furthermore, the exploration of scalable and sustainable synthesis process for MOFs will be crucial for their practical implementation.

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communication equipment, the electromagnetic environment has deteriorated.The redundant electromagnetic waves released by numerous electronic facilities might endanger one's health and disrupt regular equipment operation. [44]Electromagnetic wave (EMW) absorption materials are extensively sought after to tackle these issues.To satisfy the needs of various applications, ideal EMW absorption materials should be light in weight, absorb well, have a wide bandwidth, and have a thin matching thickness.As a result, several EMW absorption materials are now being investigated.MOFs, a type of unique multi-functional material, were created by covalently bonding a metallic ion with an organic ligand.Isoreticular metal-organic framework (IRMOF), zeolitic imidazolate framework (ZIF), Coordination Pillared-Layer (CPL), Materials of Institute Lavoisier (MIL), Porous Coordination Network (PCN), University of Oslo (UiO), and others are examples of common MOFs. [149]MOFs have recently risen to prominence as a result of their large specific surface area, high porosity, and unique periodic structure, and have been widely used in gas separation, medicine, catalysis, and other fields.Furthermore, using MOFs as building blocks to create porous carbon-based MOF derivatives with diverse properties such as controlled defects, adjustable architectures, and alterable compositions has piqued the interest of EMW absorption researchers.Wang et al. developed Magnetic CoFe alloy@C nanocomposites derived from ZnCo-MOF and stated that pyrolysis temperatures had a significant impact on the microstructures and characteristics of the nanocomposites.In addition, the integration of highly conductive 2D rGO and 1D CNT into the CoFe@C to establish conductive networks can increase dielectric loss and impedance matching, resulting in improved EMW absorption capabilities.Meanwhile, as compared to the majority of magnetic-dielectric composite absorbers, the rGOor CNT-supported CoFe@C and QD-like CoFe@C nanocomposites demonstrated comparatively good SRL values and effective bandwidth.

Figure 1 .
Figure 1.Overview of synthesis of MOF and their derivatives for enhanced electrocatalytic OER applications.Reproduced with permission from RSC from Ref. [9] (2023).

Figure 2 .
Figure 2. Number of the publications containing the string "Metal Organic Framework" and (b) Number of the publications containing the strings "Metal Organic Framework" and "HER or OER or CO 2 " in article title

Figure 4 .
Figure 4. Frequently employed solution-based synthesis conditions in MOF.

Figure 5 .
Figure 5. (a) HER mechanism at low and high H * coverage (left semicircle at low and right semicircle at high) and (b) OER mechanism black arrow in alkaline and red arrows in acidic medium.Reproduced with permission from RSC from Ref. [42] (2023).
. 2023, 23, e202300317 (11 of 21) © 2023 The Authors.The Chemical Record published by The Chemical Society of Japan and Wiley-VCH GmbH

Figure 6 .
Figure 6.Operating principle of HER and OER of based CoP 3 CP.Reproduced with the permission of RSC from Ref. [34] (2023).

Figure 8 .
Figure 8.(a) CO Faradaic efficiencies and (b) CO partial current densities and TOF at different applied potentials for CALF20 and ZIF-8 in 1.0 M KOH.Reproduced with the permission of RSC from Ref. [136] (2023).

Table 1 .
Comparison of different MOF derivatives reported as a catalyst for HER reaction.

Table 2 .
Comparison of different MOF derivatives reported as a catalyst for OER reaction.
Jingjuan et al. and Kun Zho et al. independently developed and validated 2D conductive Cu-

Table 3 .
Comparison of different MOF derivatives reported as a catalyst for CO 2 RR reaction.