All these excellentperformances are attributed to extremely high conductivity of thedefect-free graphene flakes.Mass production ofdefect-free single-layer graphene flakes (SLGFs)by a cost-effective approach is still very challenging. Here, we reportsuch single-layer graphene flakes (SLGFs) (>90%) prepared by anondestructive,energy-efficient, and easy up-scalable physical approach. These high-qualitygraphene flakes are attributed to a novel 10 s microwave-modulatedsolid-state approach, which not only fast exfoliates graphite in airbut also self-heals the surface of graphite to remove the impurities.The fabricated high-quality graphene films (∼200 nm) exhibita sheet resistance of ∼280 Ω/sq without any chemicalor physical post-treatment. Furthermore, graphene-incorporated Ni–Feelectrodes represent a remarkable ∼140 mA/cm However, these processes tend tocreate defects on the graphene surface, which significantly disruptthe electronic properties of the material and increases the manufacturingcosts.13 In addition to the liquid-phase exfoliations, a gas-drivenexfoliation of graphite was also shown to be effective in preparingmonolayer flakes with a yield of 62%.14 Furthermore, conventional thermal expansion of intercalated graphitecompounds at high temperatures  under inert conditions was shown to be useful toprepare bi- and trilayer graphene solutions as the major productsafter sonication.15 However, short-termstability of these intercalated graphite materials required immediateprocessing just after preparation besides high-energy input required.Thus, chemical approaches are always believed to be a low-cost technologybut the resultant graphene products usually suffer from unavoidablesurface defects and low yields.18 A benchmark work using advancedchemical reduction of highly defective graphene oxide successfullyimproved the quality of graphene flakes with still ∼7 atom% total oxygen  and a few milligrams of yield.19 Similar phenomena were reported.21Thegraphene-based technologies heavily rely on the availabilityof mass production of high-quality and low-cost single-layer materialin a liquid-processable form,22 Furthermore, microwave radiation is known tobe an effective nondestructive technique to remove oxidative surfacemoieties on the graphitic framework.19 Asolution phase high-yielding exfoliation (yield of ∼93%) ofgraphite was achieved in an expensive solvent, a highly fluorinatedoligomeric ionic liquid,23 or similarlyby other methods, e.g., electrochemicalexfoliation24 or nondispersion exfoliation.25 The mechanism of the microwave process was attributedto the high-temperature decomposition of expensive solvent into highlytoxic hydrogen fluoride, which concurrently intercalated the graphitelayers. However, a nondestructive solvent-free physical approach tomanufacture high-quality single-layer graphene flakes (SLGFs) is highlysought for both academically and industrially as it does not havean impact on the environment and more importantly promises a high-qualityproduct. Herein, a microwave irradiation (MI) is strongly coupledwith graphite to efficiently weaken the strong π–πinteractions of graphitic layers in solid state in air within a veryshort time of ∼10 s. The MI-assisted nondestructive and irreversiblesolid-state expansion/exfoliation of graphite yields high-qualitygraphene with excellent physical and chemical properties. More importantly,such high-quality graphene flakes can improve the water splittingefficiency by a factor of 10 and also shows a cathodic shift of theonset potential by 120 mV. The fundamental studies prove the specialstrength of the special mode MI-promoted approach and the advantageof the produced graphene flakes.Microwaveirradiation (MI), in particular, operated in specialmode, provides rapid, noncontact, volumetric, and selective heatingby directly interacting with a material with high dielectric loss.The commercially available low-cost graphite is just such a candidatethat exhibits a large dielectric loss or is highly conductive.22/CHCl3) solution to produce the P-graphite, then exfoliationof the preactivated graphite (P-graphite) to yield the EGs by 10 sMI, and finally the liquid-dispersed graphene flakes (LDGFs). Allparameters affecting the final product quality were thoroughly investigatedand are summarized in the Supporting information (SI). First, different solvents and treatment periods usedin the pretreatment process were investigated and are presented inSI Figure S1. We found that the pretreatmentin Br2/CHCl3 solution for 2 h produced stableP-graphite. It is also worth noting that this P-graphite can be storedin a sealed glass container in air and can still yield high-qualityEGs by MI even after a year of storage. In parallel, a control experimentwas carried out, where the as-received graphite was irradiated underidentical experimental conditions using MI, which showed no volumeexpansion although the temperature of the as-received graphite wasincreased to ca. 360 °C. These findings clearly confirm the functionof Br2 in the special mode microwave-controlled solid-state(MCSS) approach. In a separate control experiment, the P-graphitewas subjected to a shock heating at 400 °C in a tube furnaceunder either nitrogen or airflow. Under both conditions, the volumeof the P-graphite initially expanded just after placing it in thehot zone; however, the starting small volume was retained after coolingdown to room temperature, suggesting that stable thermal expansionof the P-graphite cannot be achieved even till 400 °C using conventionalheating and an irreversible exfoliation process can only be achievedby MI. Therefore, these control experiments clearly confirm the synergybetween MI and Br2 treatments for efficient and stableexfoliation of graphite particles.ca. 26.50° in theXRD pattern of the P-graphite  for graphite-Br2 compounds.27 The XRD pattern of the EG exhibitsthree new peaks positioned at 38.97° (weak), 57.81° (weak),and 72.79° (strong) (2 molecules are likely tohave been completely removed by MI.The most intense peak at (strong) 1d. The sca. 84°for the graphite and P-graphite samples disappears and the strongestpeak (002) also becomes relatively weak (please see the insets) inthe XRD pattern of the EG, suggesting that the EG is probably composedof less than six graphitic layers in thickness, which is consistentwith previous reports.15 The change involume of graphite, P-graphite to EG, and the removal of Br2 molecules can be seen in the inset pictures , 322 cm–1 (2ω0), 472 cm–1 (3ω0), and706 cm–1 (4ω0) in comparison tothat of the graphite, indicating that Br2 molecules wereinserted into the graphite .29 Upon careful inspection of the P-graphiteRaman spectrum (ca. 1585 cm–1 (G1) and 1604 cm–1 (G2) are observed, compared to the G-band of thegraphite (ca. 1580 cm–1), whichcorresponds to the in-plane vibration of sp2-hybridizedcarbon atoms . The D-band at ca. 1350 cm–1 is widely used as a guide of surface defects and chemical functionalization,while the intensity ratio of D-band to G-band (ID/IG) is often used to indicatethe concentration of defects within a graphitic material.31 The EG exhibits an ID/IG ratio of 0.09, compared to 0.04 obtainedfor the graphite, indicating that the MI exfoliation step introducesrelatively few additional defects. After mild sonication in DMF, theobtained LDGF exhibits an ID/IG ratio of 0.07, almost identical to the ID/IG ratio of EG and graphite,confirming the presence of defect-free graphene flakes (32 The 2D-band of the P-graphite (I2D/I–1G at 1585 cm = 0.62) at ca. 2715 cm–1 compared to the graphite  of the EGs .34 These LDGFs exhibit an increased ID/IG ratio of 0.35, comparablewith the ID/IG ratio of edge-functionalized small graphene flakes (ID/IG ∼ 0.35), probablydue to the sonication process.35 It isworth mentioning that these bilayer flakes formed by dispersion ofthree- to four-layer EG in DMF are likely to be formed by the restackingof SLGFs during the sample preparation for Raman analysis as high-resolutiontransmission electron microscopy (HRTEM) results clearly show thepresence of SLGFs (see below) because the Raman spectra of many individualflakes of LDGFs clearly display the I2D/IG ratio of ∼2 . AFM analysis shows graphene flakes with lateral dimensionsof ∼0.5 to 5.0 μm .Larger bilayer graphene flakes (∼5 μm)are also observedin the analyzed dispersion 2c,d. HRTo 5.0 μm 2f and tho 5.0 μm 2g, compae.g., in electronics, sensors, and energystorage. Thus, the complete removal of any surface impurities is highlydesirable since they will potentially behave as impurity dopants,detrimental to the functional properties. Consistent with the Ramanspectra and XRD, X-ray photoelectron spectroscopy (XPS) analysis furthercorroborates that both the pretreatment and the MI exfoliation processesare almost nondestructive, which preserves the sp2 lattice. After 10 s of microwavetreatment, the EG exhibits an approximately 92% less intense Br 3dpeak (0.29 atom % Br compared to 3.30 atom % Br in P-graphite) togetherwith the other characteristic peaks of C 1s and O 1s  in just 10s, yielding almost contaminant- and defect-free EG without the needof a postpurification step, which is normally crucial when using othersynthetic methods with different intercalates . Consistent with the literatures,39 the deconvoluted C 1s XPS spectra of the graphite exhibit threepeaks at 289.0 (Cont. 18.1%), 285.2 (Cont. 26.9%), and 284.6 (Cont.54.6%) eV, attributed to O=C–O, sp3 C–H,and sp2 C=C, respectively  in the graphite,a decrease in the concentration of the O=C–O peak to11.4% after the MI exfoliation is noticed. Compositional analysisby XPS further confirms half of the total amount of oxygen in theEG (∼95.3 C% and 4.7 O%), compared to approximately 91.8 C%and 8.2 O% in the graphite. Furthermore, the deconvoluted O 1s XPSspectra of the graphite, P-graphite, and EG are found at the samebinding energies, all consisting of a major peak at ca. 532.4 eV.Similar to this, the P-graphite and EG also showC 1s peaks withthe same binding energies, suggesting that the chemical environmentof C atoms in all materials is identical.2, whichis present for both the original graphite and EG as commonly observedeven after annealing at 1100 °C;40 therefore, the similarity between the signals before and after treatmentsuggests that no additional functionalization occurs as also provedby HRTEM analysis and XPS. These findings also suggest that MI moreeffectively removes oxygen-containing surface species from the graphitic material surface than that reported recently.19 These results are also in good agreement withthe Raman spectra, which show similar D-bands in both the EG and thegraphite.Such 4.7% oxygen is believed to be adsorbed O2-free graphene flakes (EGs) as the residual Br2 was nearly completely removed by the fast microwave heating as indicatedby the XPS. The solvent-free MCSS system is thus able to produce EGs(3–4 layer graphene flakes) with a yield of 100% (based onthe amount of P-graphite loaded) in 10 s. In this respect, the efficiencyof the MCSS is higher than those of the others with similar several-layergraphenes produced such as by electrochemical exfoliation (yield of∼65%)24 or nondispersion exfoliation(yield of ∼82.5 wt %).25 Furthermore,the produced EGs are defect-free when compared to those produced bythe abovementioned methods. After the final step of sonication, 2%production of SLGFs can be obtained in one run, compared with theprevious method that produced ∼1 wt % of monolayer graphene.10 Although to some extent, this new method isnot superior to a few monolayer production methods such as by energy-intensivegas-driven exfoliation (62%)14 or solution-stateexfoliation by MI (∼93%),23 theobtained SLGFs herein are defect-free by a simple, energy-efficient,and green method that is much better than those prepared by the extremelystrong exfoliation. On the other hand, a strong sonication of theas-received natural graphite or P-graphite without microwave exfoliationonly produces a few layer graphene flakes with a low concentrationof 5.1 ± 0.86 and 3.8 ± 0.4 μg/mL, respectively.In summary, the prepared P-graphite was irradiatedby the MI forabout 10 s to obtain solid-state exfoliated and equally importantlyBr41 To evaluate the electrical properties of the high-qualitygraphene prepared here, we have studied the sheet resistance and thecorresponding conductivity of the graphene films produced using varyingvolumes of LDGF dispersion . Transferable graphene films were produced on PTFE membranes  by vacuum filtration of 6, 3, and1.5 mL stable dispersions of the LDGFs, washed with water, and driedat room temperature. The film was found to be composed of homogeneouslyoriented graphene sheets   1. Measure.g., 510 and35 S/m9 before annealing; 500010 and 1500 S/m9 afterannealing). It is noted that there is air embodied in the film preparedhere as no vacuuming was undertaken during film fabrication, whichto some extent reduces the electrical conductivity, even though themeasured conductivity is still comparable with the graphene filmsreported with a 50 times larger thickness.5 In addition, the prepared graphene films were easily transferrableonto various substrates such as glass  via an ethanol-facilitated hot-stampingtechnique. The UV–vis spectra of the typical graphene filmtransferred to the FTO glass and uncoated FTO glass as a referenceare shown in SI .The conductivity of the film was significantly higherthan thatprepared by strong physical exfoliation and post-treatment (as glass 4a and po44 Nickel iron layered double hydroxides(Ni–Fe LDH) and graphene–Ni–Fe LDH were depositedonto nickel foam substrates using a hydrothermal method (SI for details).45 Comparison of the OER properties of Ni–Fe LDH and graphene–Ni–FeLDH reveals that the OER onset potential shifts cathodically by roughly120 mV and the current density increases remarkably by more than anorder of magnitude (at ∼0.7 V vs Ag/Ag/Cl)upon the addition of graphene as a highly conductive support, as shownin vs Ag/AgCl and one can seethat an extremely stable current of 46 mA/cm2 is representedwithout noticeable change over 18 h  in water splitting, which is the rate-determiningstep.ver 18 h 4c. Such vs Ag/AgCl  measurements (Table S1. The charge-transfer resistance (Rct) of Ni–Fe LDH (8.4 Ω) is reduced by 50% due to grapheneincorporation. A smaller Rct indicatessuperior charge transport kinetics that benefits a fast OER reaction.The electrochemically active surface area (ECSA) of these two catalystswas estimated by comparing the electrochemical double-layer capacitance(Cdl), as Cdl is proportional to the ECSA of electrocatalysts. The Cdl of graphene–Ni–Fe LDH is confirmed tobe 1285 μF, which is more than two times higher than that ofNi–Fe LDH (536 μF).In addition, the reaction kinetics for oxygen evolution was investigatedby Tafel plots 5a. The Turements 5b. The i3ca. 280 Ω/sq , which can be readily obtained from theLDGFs without any chemical or physical post-treatment, indicatingthat they are ideal materials for diverse applications in electronics,sensors, and others. The graphene–Ni–Fe LDH film represents1 order of magnitude higher electrocatalytic activity (∼140mA/cm2 at 0.7 V) for water oxidation compared to pure Ni–FeLDH and ca 120 mV cathodic shift of onset potential,leading to a >90% faradic efficiency with an ideal ratio of H2 to O2 evolved due to the dramatically enhancedreaction kinetics and charge transfer by this high-quality graphene.All these advances are believed due to (i) a selective and nondestructiveMI source to rapidly and extensively exfoliate P-graphite into high-qualitygraphene flakes in air, (ii) a self-cleaning method that effectivelyremoves adsorbed reagents without a need of post-treatment, and (iii)a self-healing method for the defects  on the graphenesurface, likely due to selective heating by microwave. In total, thisproject potentially promises a wealth of single-layer and high-quality2D materials to be prepared by this green microwave exfoliation processand their applications in energy and environment.In summary,the MCSS method has been reported here for rapid andgram-scale manufacturing of defect-free and processable graphene flakesfrom commercial graphite. The majority of LDGFs are single layer (90%)with almost no detectable defects on the surface. A thin graphenefilm of ∼200 nm represents an extremely low sheet resistanceof 4n-decane , N,N-dimethylformamide (DMF) , and N-methyl-2-pyrrolidone(NMP)  were purchased from Sigma-Aldrich andused as received. High-purity distilled water was obtained from anElga PURELAB Prima deionized water machine (15 Ω). Graphenefilms were prepared on PTFE membranes by in-house-developed surfacetension-mediated self-assembly method .FTO-coated glass (TEC 15) was provided by Pilkington NSG.Graphite wasprovided by Graphexel Limited and used as received.Liquid bromine , chloroform , 4.12/solvent solution and thenleft for 2 h for intercalation at room temperature. Similarly, 1,3, and 7 day treatment terms were also used to optimize the pretreatmentprocess. Water, chloroform, and n-decane were selectedas solvents. P-graphite flakes were filtered through filter paperand washed with fresh chloroform to remove the remaining Br2 molecules and then was transferred into a clean vial and dried atroom temperature in a fume cupboard. Dried samples were labeled asthe P-graphite and stored at room temperature in a sealed glass vessel.In a typical procedure,commercial graphite flakes (2 g) were addedto a sealed vial containing Br4.2In a typical procedure,20–100 mg of the P-graphite was transferred into a sealed glasstube and irradiated by a microwave irradiation for about 10 s, usinga CEM microwave fitted with an Infrared (IR) temperature sensor. Thetemperature of the solid reaction material was recorded as 360 ±20 °C. The reaction medium was cooled to 50 °C, and theglass tube was opened in a fume cupboard. Highly exfoliated solidgraphitic material was obtained and labeled as EG. The EGs were furtherdispersed in organic solvents (DMF or NMP) or aqueous solution witha surfactant (sodium dodecylbenzenesulfonate (SDBS), cetyltrimethyl-ammoniumbromide (CTAB), or Triton X-100 (TX-100)) to produce a highly processableLDGFs, containing ∼90% SLGFs.4.347 Similarly, 0.3 g [Ni(NO3)2], 0.4 g [Fe(NO3)2], and 0.3 g urea were mixed in 80 mL of deionizedwater. Following dissolution, 20 mL of solution was transferred intoa 50 mL Teflon autoclave with a piece of Ni foam (washed in 5 M HClprior to use) rested against the wall. The growth of the Ni–FeLDH catalyst was carried out at 120 °C in an electric oven for12 h. After cooling to room temperature, the samples were removed,washed with deionized water, and dried under ambient conditions. Catalystloading mass was measured on average as 0.2 ± 0.02 mg/cm2. To synthesize graphene–Ni–Fe LDH electrodes,the EG (3 mg) in DMF (10 mL) was sonicated for 1 h. The supernatantwas added to a 1:1 water isopropanol mix (3 mL) containing 50 μLof 5% Nafion perfluorinated resin. The mixture was sonicated for afurther 30 min, then 1 mL of solution was drop-cast on the HCl-rinsedNi foam substrates, and then dried under a vacuum oven at 120 °C.These graphene–Ni foam substrates were then used for hydrothermaldeposition of Ni–Fe LDH.The Ni–Fe LDH was synthesized bya hydrothermal method according to a previous report.4.42 and O2 evolution, the cell was sealed and purged by argon gas  for 1 h prior to testing. Evolved gaseous H2 and O2 amounts were detected by an off-line gas chromatograph  equipped with a TCD detector usinga gas-tight syringe, e.g., manuallytaking 0.5 mL of gas samples from the reactor headspace using the1 mL syringe .Oxygen evolution reaction(OER) measurements were conducted usinga gas-tight single-compartment three-electrode electrochemical cell(Adams-Schittenden Co) linked to a potentiostat (Ivium Technology).The samples, deposited on Ni foam, were attached to a stainless steelalligator clip (RS components) with the nonexposed area coated withan ultraresistant ATACS epoxy resin and used as the working electrodes(the exposed area = 0.5 cm × 0.5 cm). Pt mesh and Ag/AgCl (3M KCl) were used as counter electrode and reference electrode, respectively.The scan speed was 20 mV/s, and the electrolyte was 1 M KOH (pH 14). For H4.5–1. Commercial graphite, the P-graphite, and EG weretested in powder form. A stable DMF dispersion of graphene flakes(LDGF) was deposited on the substrate surface and tested in powderform. Raman analysis was performed on a piece of clean Si-wafer substrateto prevent the interference of the substrate to the spectra and toobserve any peak shift relative to the Si reference material at 520cm–1. UV/vis spectra were obtained from stable dispersionsof the produced graphene in organic or aqueous solutions using a ShimadzuUV-2550 UV/vis spectrophotometer. High-resolution XPS was performedby a Thermo Scientific K-Alpha photoelectron spectrometer with monochromaticAl Kα radiation; peak positions were referenced to the C 1sline at 284.5 eV, and CasaXPS software was used for data processing.Samples for AFM analysis were produced by drop deposition (4 μL)onto the Si-wafer of the corresponding solution of graphene flakes(ca. 0.005 mg/mL) in DMF. Samples were dried in airbefore imaging in tapping mode using a Digital Instruments MultimodeAFM instrument with a Nanoscope IV controller. X-ray diffraction (XRD)was performed using a Stoe STADI-P diffractometer using Cu Kα1 (using 40 kV and 30 mA) radiation (λ = 1.54 Å).Diffraction patterns were collected from 5 to 90°, and a stepsize of 0.09° s–1 was used. Scanning electronmicroscopy (SEM) of graphene films was carried out using a JEOL-6700Mfield-emission scanning electron microscope, operated in gentle beammode  to minimize surface charging effects. Transmissionelectron microscopy (TEM) and high-resolution transmission electronmicroscopy (HRTEM) were performed using Jeol JEM-1010 and JEOL-2010Fcoupled with an EDS detector (Oxford Instruments) instruments, respectively.For hexagonal lattice analysis of graphene flakes dispersed in DMFand deposited on TEM grid, high-resolution transmission electron microscopywas performed on an aberration-corrected FEI Titan operated at 80kV. To achieve low-noise images, each area was captured approximately15 times with 1 s exposures and subsequently aligned and then summed.An average background subtraction filter was then applied to removethe smoothly varying background due to uneven illumination acrossthe full image. TEM samples were prepared from stable dispersionsof graphene flakes prepared in DMF by dropping on carbon-coated coppergrids, which were dried in air before imaging. A four-probe electricalconductivity of graphene films on PTFE membrane was measured usinga Keithley 2450 SourceMeter at six different locations on the sample.All graphs and statistical analysis were obtained using OriginLabsoftware (Origin 9.1).Raman spectrawere obtained from a Renishaw InVia Raman Microscope, using a 514.5nm excitation laser and wavenumber ranging between 100 and 3000 cm


Graphene or chemically modified graphene, because of its high specific surface area and abundant functional groups, provides an ideal template for the controllable growth of metal–organic framework (MOF) particles. The nanocomposite assembled from graphene and MOFs can effectively overcome the limitations of low stability and poor conductivity of MOFs, greatly widening their application in the field of electrochemistry. Furthermore, it can also be utilized as a versatile precursor due to the tunable structure and composition for various derivatives with sophisticated structures, showing their unique advantages and great potential in many applications, especially energy storage and conversion. Therefore, the related studies have been becoming a hot research topic and have achieved great progress. This review summarizes comprehensively the latest methods of synthesizing MOFs/graphene and their derivatives, and their application in energy storage and conversion with a detailed analysis of the structure–property relationship. Additionally, the current challenges and opportunities in this field will be discussed with an outlook also provided. This review summarizes comprehensively the latest methods of synthesizing MOFs/graphene and their derivatives, and their application in energy storage and conversion with a detailed analysis of the structure–property relationship. Nevertheless, it should be noted that most pristine MOFs still suffer from the intrinsic drawbacks of low structural stability and poor electrical conductivity, which hinder their practical applications, especially in the field of electrochemical energy storage and conversion.22,23 Encouragingly, many efforts have been made to address these issues. Typically, three strategies have been developed, including designing conductive MOFs by using metal ions and organic ligands with loosely bound electrons,24 post-synthetic modification of MOFs by modifying the linker and/or metal node, and adsorption/exchange of guest species,25,26 and constructing composites with MOFs and other materials,17,27 such as MOF/carbon hybrid materials, including MOF/carbon paper,28 and MOF/carbon nanotubes.29 Among them, the resultant MOF composites have become more prominent due to the synergic effects between the two components.Metal–organic frameworks (MOFs), also known as porous coordination polymers with tunable pore sizes and structures, as well as high specific surface area and pore volume, have been extensively investigated as a new class of inorganic–organic hybrid materials and grown to be an ideal platform for various advanced functional materials and applications. Owing to the easily tunable chemical compositions of the organic linkers and metal nodes , more than 20 000 different MOFs have been designed and synthesized in the past two decades. Their unique structures and properties make them potential candidates in many applications, such as environmental protection,30–34 However, the aggregation and restacking phenomena caused by the strong π–π interaction between graphene layers lead to a great loss of both accessible specific surface area and outstanding single-layer electric properties of graphene, presenting a relatively low electrochemical performance.35–37 Assembling graphene and other electrochemical materials to generate a composite has so far been well-accepted to be an effective approach to solve the problem since the introduced component between individual graphene layers can separate them. This composite material is likely to inherit the advantages of the two parent components, but at the same time eliminate their respective shortcomings, which is conducive to the improvement of overall electrochemical performance.Graphene, a fascinating two-dimensional (2D) carbon nanosheet with a conjugated hexagonal lattice, has drawn great interest in energy storage and conversion fields due to its huge theoretical surface area, superior electrical conductivity, excellent electrochemical stability, and other unique physical and chemical properties.38 (iv) The hierarchical pore structures generated in the composite offer a perfect space for accessing the electrolyte and reducing the mass transfer resistance, thus boosting the reaction kinetics.36,38 In particular, some unexpected effects take place during the preparation and application process of MOF/graphene-based composites. Ultra-small MOFs with an average size below 10 nm grown on graphene oxide (GO) have been achieved as the excess metal ions facilitate the effective deposition of MOFs by electrostatic and coordination interactions and inhibit their overgrowth.39 Moreover, the strong chemical interface between MOF nanocrystals and reduced graphene oxide (rGO) can substantially enhance the adsorption energy and ion transport kinetics for outstanding energy storage performance.40 What's more, construction of MOF/graphene nanocomposites with their tunable composition and structures can be easily transformed into single atoms, carbonaceous nanomaterials, metal oxides, sulfides, phosphides, carbides, and nitrides with sophisticated structures,39,41–47 showing their unique advantages and great potential in energy storage and conversion, such as supercapacitors,48 lithium-ion batteries (LIBs),49 lithium–sulfur batteries,50–53 sodium-ion batteries, potassium-ion batteries, lithium–oxygen batteries,54 CO2 reduction,17,55 oxygen evolution and reduction reactions,46,56,57etc.58,59Based on the above analysis, it is desirable to design MOF/graphene-based composites for enhanced electrochemical application. Graphene or chemically modified graphene, because of its high specific surface area and abundant functional groups, provides an ideal template for the controllable growth of MOF particles. With the assembly of MOFs and graphene, the disadvantages of each component can be circumvented and the advantages imparted. (i) The ultrathin graphene nanosheets are stabilized in the presence of MOFs, which ensures that a large accessible surface and many active sites are exposed. (ii) The limitation of poor conductivity of MOFs is alleviated when coupled with graphene, hence promoting electron transport in the whole electrode. (iii) Wrapping MOFs within graphene endows them with much better structural stability during the rapid electrochemical process, resulting in longer cycle life of electrodes.38–42,44,45,60–64 Although there are a few reviews about MOF/graphene-based materials and their applications, they do not include the most recent/latest developments of MOF/graphene-based materials in energy-focused applications, or only focus on limited or other aspects .2,23,43,65 Different from previous reviews, we will comprehensively summarize the recent advances of MOFs/graphene and their derivatives, and focus on their application in energy storage and conversion  is initially used and then reduced to obtain MOF/graphene nanocomposites. It should be pointed out that “graphene” in this review may also refer to GO, and rGO.In recent years, significant efforts have been made on developing different synthetic strategies for preparing MOF/graphene nanocomposites with various functional components, structures, morphologies, and applications . The syn66 rGO/HKUST-1,67 Cu-MOF/rGO,68 ZIF/GO,69 PB/GO,70etc.,71–74 were prepared in the early days by stirring, ultrasonication, or grinding the mixtures of MOFs and graphene, as shown in 75,76 and polydopamine (PDA).77 With the decoration of modifiers, the surface of MOFs will be charged. On the other hand, GO is intrinsically negatively charged because of the abundant oxygen-containing groups on the surface. So it is easy for GO to assemble with positively charged MOFs via electrostatic interactions. For example, a MIL-88-Fe/GO nanocomposite was fabricated by mixing GO and PDDA modified MIL-88-Fe crystals, which showed tightly interlocked interaction  MOF/graphene nanocomposites has drawn a lot of attention due to their continuous porous network structures, which can provide large accessible surface area, efficient charge and mass transport pathways, and robust mechanical strength. The 3D MOF/graphene aerogel was mainly prepared through a two-step method, involving the self-assembly of MOFs/GO hydrogel and the subsequent reduction process by a reducing agent, hydrothermal reaction, or annealing.citances .79In situ growth is one of the most extensively used strategies for MOF/graphene nanocomposites owing to its facile and fast preparation. Through this way, MOFs grown on graphene will be more uniform, as well as having strong interaction with graphene. In a typical synthesis, GO can coordinate with metal ions first due to its abundant oxygenated functional groups followed by the in situ nucleation and growth of MOF nanocrystals when adding the ligands. For instance, wrinkled 3D microspherical ZIF-8@rGO composites were prepared by embedding in situ grown ZIF-8 nanoparticles between GO nanosheets, followed by high-temperature reduction self-assembly  promoted the motion of negative anions (BTC3−) toward the reaction with the cation (Cu2+) and helped the nucleation of CuBTC. Otherwise, CuBTC could not be formed at the relatively low temperature without adding DMF.96The selection of solvents is an important factor in controlling the et al. fabricated a layered rGO/UiO-66-NH2 sandwich hybrid using a noncovalent methodology for graphene modification combined with an in situ self-assembly technique.97 As shown in +) via π–π interaction. Then the attached pyrene+ served as an effective mediator to anchor 2-aminoterephthalate acid by electrostatic interaction. Finally, rGO/UiO-66-NH2 was obtained after adding Zr4+ and a subsequent solvothermal reaction , followed by metal ions coordinating with the 2,5-dioxido-1,4-benzene dicarboxylate (DOBDC) linker to form MOFs  and 3D graphene networks (3DGNs)) with various sites for coupling with MOFs were first synthesized by hydrothermal assembly reaction,104 chemical vapor deposition (CVD),105–109etc.110,111 Subsequently, the obtained graphene matrix was immersed into the mixed precursor solutions of MOFs for further in situ growth as shown in Recently, more and more efforts have been devoted to synthesizing 3D MOF/graphene nanocomposites through an in situ growth strategy employed to fabricate MOF/graphene nanocomposites usually yields relatively large MOF nanoparticles due to the rapid coordination reaction between metal ions and ligands, which suffer from insufficient available surface area and active sites. To address this issue, our group recently developed a versatile strategy of excess metal-ion induced in situ growth to fabricate MOF/graphene nanocomposites with small MOF nanocrystals, through which the obtained MOFs possess an average size below 10 nm.39 As show in The traditional via strong chemical coupling interaction  and modified MOFs  with graphene may present amazing properties and needs to be further investigated.43To date, although a large number of MOF/graphene composites have been synthesized and applied in many fields, the MOF types in these materials are very limited, as a lot of work has focused on some common and pristine MOFs, such as Zn-MOF, Fe-MOF, Co-MOF, Ni-MOF, Cu-MOF, and Zr-MOF. The exploration of other pristine MOFs /graphene-derived carbonaceous materials are intensively investigated, mainly due to the large surface area and effective nitrogen doping caused by the methylimidazole (MeIM) ligand, which are beneficial for the improved electrical conductivity, catalytic activity, capacitive performance, etc.61MOFs have been considered to be a class of ideal precursors to synthesize nanoporous carbon materials 113 To ensure homogeneous and complete growth of ZIF-8 on GO, poly(vinylpyrrolidone) (PVP) was added to modify GO with the amide carbonyl groups, which would coordinate with Zn ions and facilitate the uniform nucleation of ZIF-8. The obtained GNPCSs showed a sheet-like morphology and porous structure  upon direct pyrolysis of the 2D sandwich-like GO/ZIF-8 composite and subsequent etching of the possible residual Zn species with acid .113 To etructure . The synrecursor .123 The e sheets , facilitet al. developed a facile method to fabricate a 3D porous carbon framework (PCF) constructed from 2D heterostructured carbon nanosheets.121 As shown in 2) atmosphere  with controllable morphology (124 The formation mechanism was that the K2CO3 impurities that were generated during the carbonization of a rod-shaped potassium-based MOF (K-MOF) on GO intercalated into the layers of partially decomposed hollow rods, which facilitated the formation of porous nanoribbons. As shown in Although 2D carbon materials derived from MOF/graphene composites have shown unique advantages in many applications and made great progress, currently all of them are difficult to scale due to the time-consuming and careful assembly of MOFs on the surface of graphene. Compared with 2D carbon materials, 3D carbon architectures present faster electron/ion transport and higher ion-accessible surface area. Ding mosphere . The sizrphology .124 The 125–127 However, during the synthesis and application of single atoms, they tend to agglomerate to form clusters due to their high surface energy, leading to a decrease in catalytic performance. Using MOF/graphene materials as precursors to prepare single atom nanocomposites is an effective way to overcome the challenge. On the one hand, MOFs with a regular arrangement of metal-based nodes and organic linkers are perfect templates to achieve uniformly dispersed metal single atoms. On the other hand, graphene enables a good conductivity of the derived composites. What's more, graphene is an ideal support for fabricating 2D MOF/graphene derivatives, which is beneficial for more exposed single atoms anchored on the surface, ameliorating the troubling issue that abundant single atoms are buried in MOF-derived solid carbon. To this end, several MOF/graphene precursors have been employed to prepare such satisfactory single atom nanocomposites.Single atom materials with isolated metal atoms anchored on supports are emerging as a new frontier in energy conversion applications. The extraordinary characteristics, such as maximum atom-utilization efficiency, special quantum size effect, unsaturated coordination configuration, unique electronic structure, and strong interaction with support materials, endow them with remarkable catalytic activity, selectivity and stability.et al. prepared 2D porous Fe–N-doped graphene nanosheets (Fe–N/GNs) via a novel ZIF-8 “thermal melting” strategy by direct high-temperature pyrolysis of the Fe modified ZIF-8 “seeds”/graphene oxide (s-Fe/ZIF-8/GO) precursors at 900 °C  were immobilized on the surface. It is worth mentioning that the Zn signal disappeared in the Fe–N/GNs, mainly because the ultrathin porous carbon reduced the diffusion distance of zinc atoms, making their evaporation easier at high temperatures. As a result, the Fe–N/GN electrocatalyst displayed efficient and stable ORR performances due to the following reasons: (i) single atom Fe active sites anchored on the surface of porous carbon were exposed completely to electrolytes, realizing their fullest utilization; (ii) the high specific surface area of the well-designed structure provided sufficient space to host a high concentration of atomic Fe–Nx sites; and (iii) the porous graphene ensured high electrical conductivity for fast electron transfer.Liu t 900 °C .128 The nosheets . Fig. 6eet al. also synthesized a highly dispersed Fe–Nx catalyst derived from a graphene supported Fe–Zn-ZIF nanocomposite.129 The authors emphasized that the introduction of graphene and PVP was helpful for regulating the size and morphology of ZIFs intercalated into the graphene sheets and avoiding iron particle agglomeration during pyrolysis. They obtained a high Fe–Nx active site content of 4.29%, surpassing that of most monodisperse non-precious metal catalysts reported. The as-prepared catalyst exhibited a respectable ORR performance with comparable onset and half-wave potentials in acidic medium. Up to now, significant progress has been made toward the fabrication of MOF/graphene-derived single atom nanocomposites with fascinating structures. However, the related research is still in its infancy, and needs to be further conducted.Yang 17,23 In recent years, metal compounds  have attracted extensive interest due to their potential applications as electrode materials for supercapacitors, lithium-ion batteries, sodium/potassium-ion batteries, lithium–sulfur batteries, oxygen evolution and reduction reactions, CO2 reduction, and so on.18,43 Encouragingly, these materials can be easily prepared by utilizing a MOF/graphene composite as a precursor. Since the spatially controlled metal node is embedded in the organic ligand environment of MOFs, the prepared metal compounds are usually encapsulated in carbon materials derived from organic ligands, which can result in superior performance. To date, significant progress has been made in the synthesis of lots of MOF/graphene-derived metal compounds with sophisticated structures.Although MOF/graphene composites have achieved great success in the field of energy storage and conversion, they still suffer from some drawbacks, such as low conductivity (MOFs/GO), single pore structure, limited active sites and activity, and absence of multifunctionality, which prevents them from achieving high electrochemical performance and restricts widespread applications.66,79,105,130–133 For instance, an rGO/Fe2O3 composite aerogel was fabricated by annealing a GO/Fe-MOF aerogel under a N2 atmosphere at 450 °C, followed by another thermal treatment in air at 380 °C.79 Men et al. reported that an rGO-wrapped Co@CoO composite with a yolk–shell structure (Co@CoO@rGO) could be achieved by pyrolysis of GO-wrapped ZIF-67 (ZIF-67@GO) in N2 with 5 vol% H2 at 750 °C. Then, by subsequent pyrolysis of Co@CoO@rGO in air at 350 °C, they obtained the rGO encapsulated hollow Co3O4 composite (h-Co3O4@rGO).133 Hollow structures can afford large surface areas and shorter diffusion pathways, making it easier to access the electrolyte and reduce the mass transfer resistance, thus boosting the kinetics of electrochemical reactions. Zou's group developed a N-doped graphene aerogel (NG-A) assisted method to prepare monodisperse CoOx hollow nanoparticles with highly defective surfaces by a simple thermal activation of bulk Co-MOF crystals  hybrid by pyrolyzing MIL-88B-NH2@NGA at 900 °C under Ar.137 Besides, multi-component bimetal oxides  tightly and conformably grown on holey reduced graphene oxide (H-RGO) via a facile calcination route by utilizing PB/GO composite aerogels as the precursor  using thioacetamide,107,151–153 thiourea,154 or Na2S92,155 as a sulfur source, and gas–solid reaction methods using H2S/argon as a reducing gas156 or direct carbonization of a S-containing precursor in inert gas.157 Thus, many kinds of metal sulfide have been obtained, such as FeS,60 FeS2,63,145,146 Fe7S8,76 NiS,156 NiS2,147 Ni7S6,154 Co9S8,150 Cox9−FexS8,92 CoFeS2,148 ZnSnS3,151 CuCoS,152 CoZnNiS,155 and so on.Metal sulfides, which show more enhanced conductivity than their corresponding oxide counterparts, are recognized as an important class of materials with potential applications in energy storage and conversion. The sulfur atoms with high electronegativity can extract electrons from metal atoms for facilitated electron transport.et al. synthesized a fancy composite assembled from a macroporous rGO-wrapped mesoporous hollow carbon polyhedral matrix with Co9S8 quantum dots embedded in it (denoted as (Co9S8 QD@HCP)@rGO) using S powder to vulcanize a ZIF-67@GO composite.150 The authors found that the presence of coupled rGO not only benefited the growth of small nanoparticles, but also expanded the lattice parameters of Co9S8 QDs, facilitating sodium storage. Inspired by this work, our group designed a multi-scale nanostructure through one-step sulfidation of PB/GO aerogel in the same way  and then encapsulated into 3DG, effectively overcame some key issues of FeS2, such as poor electrical conductivity, large volume expansion and agglomeration during electrochemical reactions, and sluggish charge diffusion, showing excellent sodium storage performance. Furthermore, Xie et al. prepared an RGO wrapped yolk–shell FeS2/C composite via facile sulfidation of Fe@RGO, which was evolved by PB@GO in N2 at high temperature.146 In another study, Xu et al. fabricated bimetal ZnSnS3 nanodots encapsulated into the interconnected three-dimensional N-doped graphene framework (denoted as ZnSnS3@NG) by a hydrothermal vulcanization reaction between a Sn/Zn-bimetal–organic framework and thioacetamide  anchored on rGO via one-step low temperature (275 °C) phosphorization of MOF-74-Ni/GO hybrids, which served as a bifunctional catalyst and showed high performance for overall water splitting.168 Zhang et al. designed hierarchically porous structures composed of FeP hollow nanospheres embedded in a 3DG skeleton (3DG/FeP) through the spatially confined one-step thermal conversion of the 3DG/PB precursor with NaH2PO2 P nanoframes into a N,P-codoped graphene aerogel for highly efficient water splitting.172 In addition, other bimetal phosphide composites  have also been developed to achieve better performance. Different from the traditional method above, our group developed a novel ultrafast microwave-assisted thermal conversion route to synthesize bimetal phosphide/graphene composites. As shown in 2PO2 sponge as the precursor.45 However, traditional programmed heat treatment only led to FeNiP/non-doped graphene (FeNiP/RGO). A high content of NaH2PO2 was essential for obtaining FeNiP/PG in this rapid conversion reaction because the decomposition of more NaH2PO2 absorbed more heat, leading to insufficient temperature for the formation of GC. Furthermore, Na4P2O7 derived from NaH2PO2 was harmful for the microwave-based thermal transformation reaction.To further improve the activity, introduction of another metallic element into the crystal structures of a monometallic phosphide is an effective method to manipulate the electronic state, thereby enhancing the electrochemical properties.173,174 Unfortunately, the unmodified pure materials make it difficult to meet the actual needs due to their unfavorable reaction activity. MOF/graphene-derived metal carbides and nitrides can significantly facilitate the reaction kinetics, mainly because the small particles encapsulated in the MOF derived carbon matrix will expose more active sites. What's more, graphene acting as an interconnected matrix offers a highway to promote the electron transfer. In addition, the hierarchical architecture of the composite provides shortened pathways for mass transportation. As mentioned above, the microwave-assisted strategy developed by our group is an effective method to synthesize core–shell metal carbides@C structures.39 Besides, most metal carbide derivatives are prepared through one-step carbonization of MOF/graphene precursors in inert gas.70,175–178 For instance, Tan et al. fabricated an rGO@C/Fe3C composite with porous carbon coated Fe3C nanoparticles loaded onto rGO nanosheets by in situ carbonization of rGO/Fe-MOFs at 700 °C 6]2 MOFs at 800 °C  by annealing ZIF-67/GA at 500 °C under an ammonia atmosphere.179 The CoNx/NGA hybrid presented exceptional catalytic performance comparable to that of precious metals due to the plentiful dual active sites of CoNx and NxC and hierarchically porous structure. Kwag et al. synthesized 2D bimetal Fe2Ni2N/rGO nanohybrid sheets by nitridation of Ni2.25Fe0.75[Fe(CN)6]2/rGO nanosheets in a N2/NH3 co-atmosphere at 450 °C, which showed outstanding OER performance.180 Furthermore, Liang et al. constructed core–shell Co3Fe7@Fe2N nanoparticles supported on rGO by direct pyrolysis of FeCo-BTC@GO at 600 °C in NH3  and pseudocapacitors. In EDLCs, electrical energy storage is based on the formation of a double layer of electrolyte ions on the surface of the electrode via electrostatic charge adsorption. Carbon materials, such as activated carbon (AC), graphene, and other porous carbons, are typical EDLC electrode materials. They possess a fast charge–discharge rate and long lifetime but low capacitance and energy density. In pseudocapacitors, the energy is stored through rapid and reversible redox reaction with electron transfer on the interface of the electrode and electrolyte. Conducting polymers and metal compounds are commonly used as pseudocapacitive electrode materials, showing large capacitance and delivering high energy density. However, they suffer from relatively poor cycling stability and low power density.188 Thus, both EDLCs and pseudocapacitors have their inherent drawbacks, which limits their widespread applications that require high energy density and power density at the same time. It is well known that electrode materials dominate the performance of SCs. Ideal electrode materials for high-performance SCs need to have some vital characteristics, such as large specific surface area, hierarchically porous structure, superior conductivity, and more active sites,19,189 which are highly consistent with the properties of materials derived from MOF/graphene nanocomposites. In this regard, developing MOF/graphene-derived nanocomposites with sophisticated structures is an effective strategy for advanced SC applications.Supercapacitors (SCs), also known as electrochemical capacitors, are considered to be one of the most efficient and favored electrochemical energy storage devices, due to their various merits including fast charge–discharge rate, high specific density, long cycle life, and low cost.et al. prepared a nitrogen-rich porous carbon–graphene aerogel electrode (C/NG-A) through carbonization of Co-MOF/NG-A followed by etching in concentrated hydrochloric acid.132 As shown in −1 at 1 A g−1, outperforming most reported nitrogen-doped graphene materials. Furthermore, even at a high current density of 50 A g−1, 72.5% of its initial value was still retained, suggesting fast ion and electron transport within C/NG-A at high current density (−1) at an energy density of 33.89 W h kg−1. To achieve higher capacitance and energy density, various metal compound/graphene composites were designed, such as rGO/Fe2O3,79 rGO/MoO3,66 rGO/Co3O4,95 3DGN/Mn2O3,108 R–NiS/rGO,156 rGO@C/Fe3C,176 CoZnNiS@CNTs/rGO,155 and so on.148,190–193 In particular, Xin et al. fabricated a 3D Co/Zn–S@rGO film through a mild in situ synthesis method and vulcanization of Co/Zn-MOF@GO film.1910.76Co0.24S nanoparticles were homogeneously embedded between rGO sheets, and also acted as spacers to prevent the rGO sheets from agglomerating. The resultant 3D sandwich film with porous and continuous networks was employed as a binder-free electrode for SCs and exhibited a high capacitance of 1640 F g−1 at a current density of 1 A g−1. The assembled symmetric SCs (Co/Zn–S@rGO-7//AC) showed an ultra-high energy density (91.8 W h kg−1) at a power density of 800 W kg−1 and excellent cycle stability (90.3% capacity retention after 8000 cycles at 10 A g−1).Xia  density . When us density . Besides density . Finallyet al. synthesized a hierarchical hollow Se2 nanocubes@rGO hybrid, in which the porous rGO not only acted as the conductive network to increase conductivity, but also served as a protector and space separator to maintain structural integrity.193 Besides, the hollow Se2 nanocubes could offer abundant electrochemically active sites, as well as enhancing the diffusion of ions in electrolyte  calculation revealed that CoFe2O4(100) exhibited a higher potential than CoS(110), and the electrons could transfer from the conductivity-poor CoFe2O4 to conductive CoS through the heterointerfaces and then to rGO, thus realizing rapid Faraday reactions  as the positive electrode materials.198,199 Although great progress has been achieved, they are still insufficient for the above applications due to the relatively low capacity, as well as low energy and power density.16 Recently, tremendous efforts have been devoted to fabricating MOF/graphene-derived nanocomposites with sophisticated structures, which are considered to be one of the most promising candidates to improve the LIB performance.In today's society, lithium-ion batteries (LIBs) are indispensable in people's daily lives. Since the commercialization of LIBs in 1991, they quickly governed the battery market owing to their large voltage, high energy density, and long cycle life,200,201 To address these issues, researchers have paid attention to construct a porous structure or introduction of heteroatoms  to the graphene frameworks. The porous structure can provide a larger surface area and more active sites for interfacial electron transfer reaction. Moreover, the pores can play a role in alleviating the volume change during the charging and discharging process to reduce capacity fading. Meanwhile, the doping of heteroatoms can improve the conductivity and reduce the diffusion resistance of Li ions within graphene frameworks.202 For example, nitrogen-doped porous graphene hybrid nanosheets derived from a ZIF-8/GO composite were reported to be a superior anode material for LIBs with a high reversible specific capacity of more than 700 mA h g−1.118,120 Furthermore, reasonable control of the pore size distribution to the mesoporous range can accelerate the migration of ions, since the micropores will restrict the ion/electrolyte transport at high discharge rates.203 Therefore, Gayathri et al. prepared mesoporous-rich nitrogen-doped carbon@graphene nanosheets derived from a ZIF-8 precursor using melamine as a pore expanding agent and surface modifier, which exhibited high specific capacity and excellent long cycle life compared to the melamine-unmodified anode.123As an attractive anode material in LIBs, graphene shows a favourable low operating potential and long cycle life. However, it still suffers from unsatisfactory electrochemical activity, sluggish Li ion transport rate and insufficient accessible active sites, which leads to low energy and power density.+ intercalation storage mechanism of carbon materials, metal compounds based on reversible conversion reactions can provide higher capacity, energy density and power density.17 However, metal compounds often exhibit poor conductivity and large volume expansion during the charging and discharging process, which leads to sluggish electron transport and structure pulverization in the lithiation reaction, resulting in rapid deterioration of battery performance. Combining metal compounds with graphene to form a hybrid material can effectively solve these problems because of the excellent conductivity and confinement effect of graphene. Based on these understandings, various metal compounds/graphene have been synthesized, including Fe2O3/RGO,39,41,62,75,105 Fe–Co oxide@GA,80 ZnO/C/rGO,86 rGO/Co3O4,95,130,133 3DGN/CuO,109 MnO/C@rGO,134 3DG@Co0.85Se@C,204 N–ZnSe@rGO,87 FeP@C/rGO,98 ZnSnS3@NG,151etc.140,143 Among them, our group deliberately synthesized a 3D graphene/Fe2O3 aerogel (3DG/Fe2O3) with porous Fe2O3 nanoframeworks well encapsulated within a graphene skeleton by employing a 3DG/MOF aerogel as a template  delivered high capacities and superior rate capability, much better than those of a large hollow Fe2O3 nanoparticle/RGO composite (L-H-Fe2O3/RGO) and a solid Fe2O3 nanoparticle/RGO composite (Fe2O3/RGO)  . Further cycling .+/Na+ diffusion and insertion.17,205 For example, Awaga and co-workers reported Cu-AQDC with redox activity on both the metal ions and organic linkers for cathode materials of LIBs. The charge–discharge curves involved two distinct electrochemical processes, that is, two-electron redox reaction from anthraquinone groups in the ligands and one-electron reaction from the CuII/CuI redox couple. As a result, Cu-AQDC exhibited a high specific capacity of 147 mA h g−1.206 However, Cu-AQDC showed large capacity fading in 50 cycles, which was mainly caused by the poor electrical conductivity and highly localized electron density. The conductive MOFs may open up a new path for better electrochemical performance because their electrical conductivities and porous structures are favourable for electron and ion transport in the framework.207 The potential applications of conductive MOFs in lithium/sodium-ion batteries have been confirmed by Dincă and co-workers who showed that the prepared Ni3(HITP)2 MOF with high bulk electrical conductivity delivered high performance in electrochemical supercapacitors,208 as well as some other researchers using conductive MOFs in various battery systems, such as Na+/Zn2+ batteries,209,210 Li–S batteries,211 and so on. Moreover, the emerging new MOFs based on new ligands (e.g. organic Li-ion compounds) are promising cathode materials for lithium/sodium-ion batteries.212 What's more, we believe that the composites composed of traditional or conductive MOFs with graphene could show surprising performance due to their synergistic effect, which has been demonstrated by our group.38In addition to the MOF/graphene-derived nanocomposites discussed above as anode materials for lithium-ion batteries, MOFs have also been explored as cathode materials due to their redox active sites from both transition metal cations and/or organic linkers with redox active functional groups. Besides, the regular channels of MOFs can facilitate Li213 Compared to lithium, sodium and potassium are much more abundant in the crust, and thus cheaper. Besides, sodium and potassium exhibit similar physical and chemical properties to lithium due to the same alkali metal group. Moreover, sodium/potassium-ion batteries have similar electrical storage mechanisms to that of LIBs. Therefore, sodium/potassium-ion batteries have garnered extensive attention and are expected to be potential alternatives to LIBs.34,214,215In recent years, LIBs have expanded their application in the field of electric vehicles and large-scale electrical energy storage systems, and achieved considerable progress. Nevertheless, the relatively scarce lithium resources and high cost greatly hinder the development.216,217 In addition, many electrode materials suffer from sluggish reaction kinetics and inferior electrochemical activity because of the large ionic radius and heavier atomic mass of Na+, which leads to low specific capacity and poor cycling stability.218 Therefore, it is urgent to develop desirable electrode materials for high performance SIBs. Meanwhile, thanks to the unique advantages mentioned earlier, MOF/graphene-based materials seem to be one of the ideal choices. For instance, our group synthesized a 3DG wrapped PB aerogel, and used it as a free-standing cathode material for SIBs. Excitingly, it delivered an extraordinary rate performance (84 mA h g−1 at 25C) and long-term cycling stability (90% capacity retention after 1000 cycles at 10C), which was attributed to the highly efficient electron and ion transport in the whole electrode.38 Furthermore, MOF/graphene-derived nanocomposites, especially sulfides,60,63,70,72,76,145,150 selenides,84,87 and phosphides,91,111,170 are widely studied for SIBs, due to their environmental benignity and higher theoretical specific capacities based on conversion reactions.It has been proven that the commonly used graphite in LIBs is almost electrochemically inactive in sodium-ion batteries (SIBs) due to the energy instability of Na–graphite intercalation compounds.111,145 Our group fabricated an exquisite 3DG composite with a core–shell FeS@C encapsulated in 3DG by one-step thermal transformation of a 3DG/MOF composite, which exhibited excellent rate capacities of 363.3 and 152.5 mA h g−1 at 1 and 6 A g−1, and outstanding cycling stability with a capacity retention of 97.9% after 300 cycles at 1 A g−1, when directly used as a flexible anode for SIBs 2@PB nanocomposite.170 The well-designed structure showed high reversible capacity, and excellent rate capability and cycle life. A hierarchical hybrid structure with multicompositional features will bring about an unexpected synergistic effect for enhanced SIB performance. For example, Shi et al. synthesized a sandwich hierarchical architecture with ZnSe nanoparticles fastened in N-doped carbon polyhedra anchored onto graphene with the modification of MoSe2 nanosheets outside  via a self-template of MOFs and subsequent selenization strategy ), which allows potassium-ion batteries (PIBs) to have higher energy densities than SIBs. Besides, K+ exhibits a weaker solvation effect due to weaker Lewis acidity, ensuring its quicker kinetics in PIBs.214,219 However, the larger ionic radius (K: 1.38 Å and Na: 1.02 Å) will cause greater difficulty for K+ intercalation and a dramatic volume change during the discharge–charge process. Therefore, the electrode materials should be designed with large channels to promote the efficient insertion or extraction of K+. Due to the adjustable pore structure and relatively open channels as well as high specific surface area, MOFs are considered to be suitable for reversible K+ storage and transmission. Our group constructed a Co-MOF–rGO hybrid with Co-MOFs tightly encapsulated into rGO by growing Co-MOF nanocrystals on GO via synergistic coordination and electrostatic interactions and a subsequent annealing strategy.40 We found that there existed a chemical-bonded interface between Co-MOF nanocrystals and rGO  were explored as anode materials for PIBs. In particular, the flexible 3DG/FeP anode with hollow FeP nanospheres encapsulated within a 3D graphene skeleton delivered a high reversible capacity of 323 mA h g−1 at 0.1 A g−1 and ultrastable cycle life with a capacity retention of 97.6% at 2 A g−1 after 2000 cycles  and theoretical energy density (2600 W h kg−1), and environmental benignity as well as the natural abundance of the sulfur cathodes.34 Unfortunately, LSBs are facing some severe challenges, which hinder their commercialization. For example, the insulating nature of sulfur  leads to inferior electron transfer ability and poor coulombic efficiency. Besides, the large volume change of sulfur (∼80%) during cycling damages the integrity of the cathode structure. What's worse, the dissolution of intermediate polysulfides  and their “shuttle effect” result in the loss of active materials. These drawbacks give rise to low capacity and poor cycling stability.115,221 To date, several approaches have been developed to address these issues, including the structural design of host materials, development of functional separators and new electrolytes, and modification of the lithium anode.222 In this context, MOF/graphene composites and their derivatives play an important role in improving the performance of LSBs.223,224Lithium–sulfur batteries (LSBs) are appealing as next-generation electrochemical energy storage devices because of their ultrahigh capacity  hybrid by thermal treatment of a ZIF/GO composite  presented a high specific capacity of 1372 mA h g−1 and good cycling stability over 300 cycles  derived from GO/ZIF-8 with poly (PEDOT) outside. The resultant composite cathode exhibited higher capacity and longer cycle life than that without PEDOT coating.225 Furthermore, Co,N-co-doped porous carbon hosts showed enhanced LSB performance.226–229 For example, Wang et al. fabricated a free-standing sulfur host consisting of Co,N-co-doped porous carbon nanocages on 3D rGO (Co/N–PCN@rGO) through pyrolyzation of ZIF-67@rGO followed by acid leaching.226 After being penetrated by sulfur, the obtained cathode manifested a high discharge capability and an extremely low capacity decay rate, which was better than that of most reported carbon–sulfur-based cathodes.Heteroatom doped carbon has been demonstrated to be a favorable host material due to its large surface area, abundant pore structure, and high electrical conductivity, as well as physical confinement and chemical adsorption of polysulfides. Chen omposite .115 In t0 cycles . In a see.g., oxide, sulfide, and phosphide) based sulfur hosts derived from MOF/graphene nanocomposites were extensively studied due to their strong adsorption of polysulfides on polar surfaces.107,162,230–232 For example, rGO wrapped mesoporous MoO2 microrods derived from Mo-MOFs were synthesized and used as the sulfur host in LSBs. The metallic MoO2/rGO composite not only enhanced the transport of electrons and Li+ diffusion, but also restricted the dissolution and shuttling of polysulfides. Moreover, the catalytic effects of MoO2 facilitate polysulfide conversion kinetics. Therefore, the S–MoO2/rGO cathode exhibited a high discharge capacity of 1145 mA h g−1 at 0.5C and ultralong cycle life over 3200 cycles at 3C.230 Particularly, Xu and co-workers confirmed that the doping of nitrogen into cobalt oxides could provide additional affinity sites and strengthen the binding energy for polysulfide absorption.232 As a result, the well-defined porous N–Co3O4@N–C/rGO synthesized by pyrolysis of ZIF-67 and subsequent rGO wrapping delivered a high reversible capacity of 1223 mA h g−1 at 0.2C and excellent cycling stability of 611 mA h g−1 retained at 2C after 1000 cycles  as a free-standing sulfur host for long-life LSBs. The Co9S8-3DGF/S cathode containing an ultrahigh sulfur loading of 10.4 mg cm−2 realized an incredibly high areal capacity of 10.9 mA h cm−2 at a rate of C/10 and still good cycling stability for 200 cycles.107Polar metal compound  of the used HKUST-1 than the diameters of lithium polysulfides, the soluble polysulfides were efficiently blocked at the anode side while Li+ ions were selectively sieved. In this case, LSBs with the MOF-based separator achieved a low capacity decay rate of 0.019% per cycle over 1500 cycles. Besides, Yu and co-authors fabricated a modified separator with electrocatalytic activity by dispersing Ni-MOF-74/GO derived graphene-supported Ni nanoparticles with a carbon coating (Ni@C/graphene) on a commercial glass fiber membrane  and oxygen reduction reaction (ORR) are two important parts of electrochemical energy conversion systems. The OER is a key electrochemical reaction involved in rechargeable metal–air batteries, fuel cells, and water electrolysis for oxygen and hydrogen generation with the mechanism of oxidation of water/hydroxyl ions on the surface of electrocatalysts and simultaneous evolution of oxygen gas. Meanwhile, the ORR is the reverse reaction of the OER, and is a critical process in metal–air batteries and fuel cells.et al. developed a lamellar bimetallic MIL-53(FeNi) encapsulated in graphene aerogel-grafted Ni foam by an in situ solvothermal approach.110 The metal centers located in the edge-sharing octahedral MO6 layers in MIL-53 helped to optimize the absorption energies of the oxygen-containing intermediates. And the porous graphene aerogel could act as a conductive bridge to connect MIL-53 crystals with Ni foam. As a result, the catalyst showed excellent OER performances in alkaline media. In another study, a highly active CoxNix1− MOF/3DG electrocatalyst was prepared by a similar method for the OER, which exhibited a high catalytic activity attributed to the synergistic effect of Co and Ni in MOFs and the 3D structure of graphene.238 Besides, various MOF/graphene-derived composites  have been demonstrated as active OER electrocatalysts. For instance, our group developed an ultrafast microwave-assisted CVD-like method to convert a MOF/GO precursor into well-dispersed core@shell metal@NC nanocrystals with few-layer NC on RGO (M@NC/RGO) composite  near the Fermi level and few-layer NC could facilitate electron transfer from the metal core to the graphene shell. Benefiting from these structural advantages, the obtained FeNi@NC/RGO displayed a low overpotential of 261 mV at 10 mA cm−2 in 1 M KOH and a small Tafel slope of 40 mV dec−1, which was superior to that of a commercial IrO2 catalyst  is a good choice.116,128,129,241–244 On the one hand, the NC structure could play its original role to facilitate fast mass transport and electron transfer. On the other hand, the additional M–Nx active sites could promote oxygen adsorption and accelerate the ORR kinetics, thus leading to better ORR performance. For example, Wei et al. fabricated Co nanoparticles/N-doped porous carbon nanosheets through the pyrolysis of a sandwich-like GO/ZIF-8@ZIF-67 precursor at 900 °C, which was synthesized via a ZIF-8 seed-mediated deposition route , which was a slightly higher than that of Pt/C but better than that of porous NC nanosheets prepared under the same conditions  was reported by Zou and co-authors  is considered to be a promising way to alleviate global warming and energy issues.247 Photocatalytic CO2 reduction is an attractive approach owing to its direct use of visible light or sunlight as the energy source. A strong capability for CO2 capture, abundant reaction active sites, high electron–hole separation properties, and wide optical absorption spectrum are imperative for high-efficiency photocatalysts. In this regard, MOF/graphene-based composites were reported to be efficient for photocatalytic CO2 reduction.248–251 Wang et al. constructed a small-sized UIO-66-NH2 nanocrystals/graphene (UIO-66-NH2/GR) structure with a high dispersion and strong junctions of UIO-66-NH2 on the surface of graphene via a microwave-assisted in situ growth and assembly route  irradiation  Z-scheme heterojunction via a solvothermal method  for electroreduction of CO2 to ethanol.253 The obtained Cu GNC-VL catalyst presented a 3D structure with high electronic conductivity and uniformly dispersed Cu/Cu2O active sites (−2 at −0.87 V versus RHE and excellent faradaic efficiency of 70.52% for ethanol production in 0.5 M KHCO3 solution (2 on Cu(111) and favorable thermodynamics and kinetics of C–C coupling on Cu2O(111).The electrochemical COve sites . Catalytsolution , which win situ growth, and excess metal-ion induced in situ growth, and the respective synthesis mechanism of each strategy involving the unique role of graphene was carefully discussed. Then we systematically discussed the formation mechanisms/methods of MOF/graphene-derived nanocomposites, including carbonaceous materials, single atom nanocomposites, and metal oxides, sulfides, phosphides, carbides, and nitrides with sophisticated structures, and their promising applications with a detailed analysis of the structure–property relationship in energy storage and conversion, such as SCs, LIBs, SIBs, PIBs, LSBs, OER, ORR, and CO2 reduction. The current issues of various energy storage and conversion devices and how to improve the performance by employing MOF/graphene-based materials were also presented. We hope that this review will help researchers in related fields to have a comprehensive understanding of the recent progress in MOF/graphene-based materials, and stimulate further development of new high-performance materials for energy storage and conversion in the future.MOFs have been extensively investigated as a new class of inorganic–organic hybrid materials in various applications due to their high specific surface area, tunable pore structures, adjustable composition and morphological features. Nevertheless, the intrinsically poor electrical conductivity and low stability restrict their practical applications, especially in the field of energy storage and conversion. Constructing MOF/graphene composites is an effective approach to alleviate these issues due to the synergic effects between MOFs and highly conductive graphene. More importantly, MOF/graphene-derived materials open up new paths toward their widespread applications. In this review, we first summarized comprehensively the latest methods of synthesizing MOF/graphene hybrids, including physical mixing, in situ techniques will play important roles in future studies. (v) The coulombic efficiency and volumetric performance should be further increased without sacrificing the capacity and rate through an elaborate balance of porosity, micro/nano-structures, etc. to meet the practical application. As a result, MOF/graphene-derived materials will definitely show a bright future toward energy storage and conversion.Though great advances have been achieved in this field so far, several key challenges as well as opportunities regarding high-performance MOF/graphene-based materials and future practical application should be considered. (i) The strength of interface interaction between MOFs and graphene can not only significantly affect the charge transfer but also has an important impact on the ion adsorption energy and diffusion kinetics, thus impacting the electrochemical performance. Therefore, exploring MOF/graphene-based materials with strong interface interaction is very necessary for enhanced electrochemical performance. Meanwhile, constructing MOF/graphene-derived materials with heterostructures or heteroatom doped active components can precisely regulate the local electronic configuration for better properties. (ii) Reducing the size of MOF nanocrystals and their derivatives on graphene to expose more active sites for efficient electrochemical reactions without aggregation is of profound importance for high-performance applications. It is essential to develop a new and controllable strategy to synthesize such ultrasmall nanomaterials. (iii) Although MOF/graphene-derived materials exhibit a porous structure, the arrangement of these pores is usually disordered, which will lead to relatively limited mass transport kinetics compared to the ordered pore structure. Therefore, a material morphology with a hierarchically ordered porous structure needs to be pursued. (iv) A profound understanding of the formation processes of MOF/graphene-derived nanocomposites and the structure evolution as well as the structure–property relationships is in high demand, where theoretical calculations and K. Wang and K. N. Hui contributed equally.There are no conflicts to declare.


Background: electroconvulsive therapy (ECT) is the most effective treatment in treatment-resistant depression (TRD), but its response remains partial. Identifying useful indicators to guide decision making for treatment and improve clinical response remains a major issue. The objective of the present retrospective study was to determine if clinical response—early (after 5 ECT sessions) or longer-term (after 12 ECT sessions)—was associated with postictal suppression during the first ECT course and/or with postictal suppression frequency during the whole ECT course. Methods: in a retrospective study, the data of 42 patients suffering from treatment-resistant depression and receiving at least 5 ECT sessions were collected. Two sessions per week of bitemporal brief-pulse ECT sessions were administered to patients. Each of the electroencephalography (EEG) recordings were assessed to determine the presence of postictal suppression. Results: the postictal suppression from the first ECT session predicted a better long-term clinical response (after 12 ECT sessions), but not early clinical response (after only 5 ECT sessions). The postictal suppression frequency was associated with neither the short- nor the long-term clinical response. In addition, postictal suppression and short-term cognitive performances were not associated. Conclusions: this EEG indicator is clinically useful if it appears in the first ECT sessions, but it is no longer relevant in the following sessions. It is widely accepted that electroconvulsive therapy (ECT) is the most effective treatment in treatment-resistant depression (TRD). However, its response may vary from patient to patient, with response rates ranging from 39% to 85% in patients with previous pharmacotherapy failure . IdentifThis inhibition is due to the release of inhibitory neurotransmitters, with the greatest evidence indicating a role for gamma aminobutyric acid (GABA) . FrancisUntil now, few studies have focused on relationships between ictal EEG measures and the side-effects of ECT. To our knowledge, only Perera et al. (2004) included cognitive outcome measures to assess whether peri-ictal EEG features were associated with the cognitive effects of ECT . No signWith these issues in mind, the aim of the present retrospective study is to determine if clinical response—early (after 5 ECT) or longer-term (after 12 ECT)—is associated with postictal suppression during the first ECT, or with postictal suppression frequency during the whole ECT course. In the second aim, the evolution of postictal suppression over the ECT sessions is studied. In the third and final aim, the relationship between cognition side effects and postictal suppression is explored. We hypothesize that postictal suppression during the first ECT predicts an early and longer-term clinical response, and that postictal suppression frequency during the whole ECT course is significantly associated with early and longer-term clinical response.In this retrospective study, information was extracted from clinical files of Rouvray Hospital in Sotteville-Lès-Rouen (France). Participants were inpatients referred for ECT by their psychiatrist for treatment-resistant depression. These patients typically failed to achieve a clinical response to three separate trials of antidepressants from different classes (at least one of which was a tricyclic) at sufficient dose for at least six weeks, according to stage III of Thase and Rush criteria . The numInclusion criteria for the present study were patients who: (i) were aged 18 to 70 years; (ii) had a current DSM-IV diagnosis of major depressive episode, with a 21-item Hamilton Depression Rating Scale (HDRS) score of at least 15 ; (iii) hInformed consent was obtained from all patients involved in the study. Under French ethical law , retrospective studies based on the exploitation of routine care data do not have to be submitted to an ethics committee. This study was conducted in accordance with the declaration of Helsinki.ECT treatment was delivered using a MECTA Spectrum 5000 Q  or a Thymatron System IV device  and used bitemporal brief-pulse ECT sessions with two sessions per week. The seizure threshold was determined by an individual titration method during the first ECT session . A maximEach EEG was assessed by two psychiatrists and one senior psychiatrist with over 10 years of experience in the field of ECT. In case of disagreements between the two psychiatrists, the senior psychiatrist made the decision. Postictal suppression was defined as a flat line (at least 5 s) in the period immediately following the electrically-induced seizure. The postictal suppression frequency was calculated by dividing the number of sessions where the patient had postictal suppression by the total number of sessions administered to the patient.HDRS was used to assess depressive symptoms before ECT, and after 5 and 12 ECT sessions . AssessiA Squire Subjective Memory Questionnaire (SSMQ) and Cognitive Failures Questionnaire (CFQ) were self-administered to assess subjective cognitive functioning ,26.2) [The relative improvement in HDRS scores—between Pre-treatment and after 5 ECT sessions, and between Pre-treatment and after 12 ECT sessions—were compared between patients who underwent postictal suppression during the first ECT and those who did not, using Mann–Whitney’s nonparametric test; this was because of the small sample size. Size effects were estimated with eta squared (ɳ2) . Linear n = 29) did not statistically differ from other patients (n = 13) for all characteristics, except for the total number of ECT sessions (mean (SD) = 18.8 (3.7) in the group receiving at least 12 ECT sessions versus 13.5 (5.5) in the other patients; p = 0.004). The determination of postictal suppression during the first ECT session was not possible in two patients due to the too-early interruption of the EEG, and the HDRS score after 5 ECT sessions was missing for one patient.The data of 42 patients receiving at least 5 ECT sessions were collected. Additional information for up to 12 ECT sessions could be collected among 29 patients. The demographic and clinical characteristics are reported in n = 42), 263.60 (177.57) during the 5th ECT session (n = 42) and 404.34 (331.01) during the 12th ECT session (n = 25). According to ECT devices, pulse width varied between 0.3 and 0.5 ms (mean (SD) = 0.38 (0.10)) during the first ECT session and between 0.3 and 1 ms (mean (SD) = 0.44 (0.20)) during the 12th ECT session. The seizure durations in seconds were: 31.62 (26.25) during the first ECT session (n = 37), 27.83 (14.43) during the 5th ECT session (n = 40) and 29.73 (12.71) during the 12th ECT session (n = 30). During the first five ECT sessions (n = 42), the mean (SD) percentage of sessions requiring restimulation was 20.95 (22.50).The mean (SD) electrical charges in milliCoulombs were: 80.19 (35.32) during the first ECT session (n = 6) after 12 ECT sessions than patients without postictal suppression during the first ECT session (mean (SD) = 55.37% (19.19), n = 22; p = 0.02, ɳ2 = 0.188). For verification purposes, the clinical response after 12 ECT sessions was not different between patients who had seizures during the first ECT session and patients who did not . The clinical response after only 5 ECT sessions was not significantly different between patients experiencing postictal suppression during the first ECT session (mean (SD) = 33.94% (17.11), n = 10) and those who did not (mean (SD) = 31.45 (23.31), n = 29; p = 0.76, ɳ2 = 0.0024). Patients with and without postictal suppression during the first ECT session did not significantly differ in their demographic and clinical characteristics  = 74.25% (08.18), eristics .p = 0.458). Postictal suppression frequency during the 12 sessions was not associated with the clinical response after 12 sessions ECT either .The mean (SD) postictal suppression frequency during treatment was 49.29% (29.44) during the first five sessions and 50.86% (21.29) during the 12 sessions. In the linear regression model, postictal suppression frequency during the first five sessions was not significantly associated with the clinical response after 5 ECT sessions . Only 13.8% of the patients had postictal suppression from the first ECT session, while there were 79.3% in the 12th session (p = 0.042).The percentage of patients experiencing postictal suppression significantly increased over the ECT sessions , nor the CFQ score .The postictal suppression frequency during the first five sessions was not correlated with the evolution of scores of any cognitive tests assessing attention, memory and visuospatial abilities between baseline and after 5 ECT sessions . The posAccording to our retrospective study, experiencing postictal suppression from the first ECT session might predict a better long-term clinical response (after 12 ECT sessions). This outcome is consistent with previous studies, which showed that postictal suppression from the first ECT sessions  was associated with a better clinical response at the end of treatment ,9. It isRegarding postictal suppression frequency , the absence of a correlation between this index and cognition, especially cognitive impairment, confirms the study of Perera et al. (2004), which found no significant association between peri-ictal EEG features and the acute or short-term cognitive effects of ECT . In addiIn view of our results, postictal suppression may be considered an indicator of good clinical response, if it appears immediately during the first ECT sessions. However, as the proportion of patients experiencing postictal suppression increased over the course of the sessions, reaching 79.3% of the patients at the 12th ECT session, postictal suppression no longer makes it possible to discriminate between the good (or bad) responders during the following sessions. Postictal suppression accumulation does not seem to be associated with clinical response. As suggested by Perera et al. (2004), the presence of postictal suppression in the first ECT sessions may reflect individual differences in the strength of inhibitory processes that terminate the seizure . PatientIn summary, this retrospective study showed that postictal suppression from the first ECT session might predict a better long-term clinical response (after 12 ECT sessions), but that postictal suppression frequency was neither associated with the short- or long-term clinical response. In addition, postictal suppression and short-term cognitive performance were not associated. This indicator is clinically useful if it appears in the first ECT sessions, but is no longer relevant in the following sessions. However, we currently do not know how to favor the presence of postictal suppression during the first sessions. One possibility would be to administer another neuromodulation technique before ECT sessions, for example, rTMS or transcranial direct current stimulation (tDCS), which might strengthen the GABA system, possibly facilitating the presence of postictal suppression, thus increasing the clinical response. This hypothesis should be investigated in a future study.