High Gravimetric Capacity Research Articles

Rational design of MXene/activated carbon/polyoxometalate triple hybrid electrodes with enhanced capacitance for organic-electrolyte supercapacitors

We report a triple hybrid electrode (MXene/activated carbon (AC)/polyoxometalates (POMs)) combining the merits of three materials: MXene (high volumetric capacitance), AC (high gravimetric capacitance) and Phosphotungstate (fast redox). Phosphotungstic acid (HPW12) and tetraethylammonium phosphotungstate (TEAPW12) were the two POMs used to prepare MXene/AC/POMs triple hybrids. MXene/AC/TEAPW12 outperformed MXene/AC/HPW12 in 1 M tetraethylammonium tetrafluoroborate (TEABF4)/acetonitrile. Nano-dispersion of POMs facilitates charge storage through surface capacitive processes (91% at 2 mV s−1). MXene/AC/TEAPW12 delivered significantly higher gravimetric capacitance (87F g−1 at 1 mV s−1) than MXene (40F g−1 at 1 mV s−1) in the same organic electrolyte, without sacrificing much volumetric capacitance (less than 10%). The gravimetric capacitance of the triple hybrid was similar to that of MXene/AC, whereas its volumetric capacitance was 1.5 times higher. Replacing TEA cations with 1-ethyl-3-methylimidazolium cations (EMIM+), the capacitance improved by 21%. Coupled with AC positive electrodes in an asymmetric cell, MXene/AC/TEAPW12 delivered 4.6 times higher gravimetric energy density and 3.5 times higher volumetric energy density than a similar MXene asymmetric cell at relatively high-power densities. This study proves that MXene/AC/TEAPW12 combines the merits and compensates for the demerits of each component and is a promising electrode material for organic-electrolyte supercapacitors.

Two-dimensional GeC3: a reversible, high-capacity hydrogen molecule storage material predicted by first-principles calculations.

In order to improve the transport, electronics and storage of graphene properties layers, we have constructed compact structures with graphene sheets, adsorption of H2 molecules on GeC3 shows good results. A high binding energy up to 0.3628 eV with 3.3024 Å as equilibrium distance. A low activation energy allows the molecule to migrate on the surface so easily up to 0.0042 eV. The investigation revealed a high gravimetric (GC) and volumetric (Vc) capacities up to 7.25 wt% and 98.41 g/dm3 as a new 2D material for hydrogen storage. The hydrogenation/dehydrogenation (desorption) temperature is expected to be 224.25 K. The desorption temperatures of H2 molecules indicate that the monolayer GeC3 could function as a reversible hydrogen storage substrate. Therefore, the results reveal that the GeC3 monolayer is a prospective, efficient, reversible hydrogen storage substrate with high gravimetric capacity under feasible conditions.

Functional carbon dots from a mild oxidation of coal liquefaction residue

Effective utilization of the solid-waste coal liquefaction residue (CLR) is important for the development of direct coal liquefaction technology, but remains big challenge due to the high ash of about 30 wt% in CLR. Herein, we propose a mild oxidation method to prepare functional carbon dots (CDs) using CLR as the carbon precursor and piranha solution (H2O2/H2SO4) as the oxidant. Through catalytic hydrogenation, the highly conjugated structure of coal converts to weakly linked structure by aliphatic chains in CLR, leading to an improved oxidation reactivity. The highly reactive aliphatic chains are oxidized and cut during oxidation, leading to the formation of CDs with enriched oxygen-bearing functional groups at the edge sites and simultaneous removal of ash. To present the special properties of CDs, we prepare a microporous carbon with high-surface area and compaction density (1345 m2 g−1 and 0.86 g cm−3) through homogeneous activation of CDs, performing both high gravimetric and volumetric capacitance for supercapacitors. CDs are also used as the functional reinforcing phase for activated carbon nanofibers, enabling high surface area, improved mechanical property, good conductivity, and extremely high rate performance for supercapacitors. Our work provides a new avenue for high efficient and high value-added utilization of CLR.

Modulated self-assembly of an interpenetrated MIL-53 Sc metal–organic framework with excellent volumetric H2 storage and working capacity

To achieve optimal performance in gas storage and delivery applications, metal–organic frameworks (MOFs) must combine high gravimetric and volumetric capacities. One potential route to balancing high pore volume with suitable crystal density is interpenetration, where identical nets sit within the void space of one another. Herein, we report an interpenetrated MIL-53 topology MOF, named GUF-1, where one-dimensional Sc(μ2-OH) chains are connected by 4,4′-(ethyne-1,2-diyl)dibenzoate linkers into a material that is an unusual example of an interpenetrated MOF with a rod-like secondary building unit. A combination of modulated self-assembly and grand canonical Monte Carlo simulations are used to optimise the porosity of GUF-1; H2 adsorption isotherms reveal a moderately high Qst for H2 of 7.6 kJ/mol and a working capacity of 41 g/L in a temperature–pressure swing system, which is comparable to benchmark MOFs. These results show that interpenetration is a potentially viable route to high-performance gas storage materials comprised of relatively simple building blocks.

Composition dependent electrochemical properties of earth-abundant ternary nitride anodes

Growing energy storage demands on lithium-ion batteries necessitate exploration of new electrochemical materials as next-generation battery electrode materials. In this work, we investigate the previously unexplored electrochemical properties of earth-abundant and tunable Zn1−xSn1+xN2 (x = −0.4 to x = 0.4) thin films, which show high electrical conductivity and high gravimetric capacity for Li insertion. Enhanced cycling performance is achieved compared to previously published end-members Zn3N2 and Sn3N4, showing decreased irreversible loss and increased total capacity and cycle stability. The average reversible capacity observed is >1050 mAh/g for all compositions and 1220 mAh/g for Zn-poor (x = 0.2) films. Extremely Zn-rich films (x = −0.4) show improved adhesion; however, Zn-rich films undergo a phase transformation on the first cycle. Zn-poor and stoichiometric films do not exhibit significant phase transformations which often plague nitride materials and show no required overpotential at the 0.5 V plateau. Cation composition x is explored as a mechanism for tuning relevant mechanical and electrochemical properties, such as capacity, overpotential, phase transformation, electrical conductivity, and adhesion. The lithiation/delithiation experiments confirm the reversible electrochemical reactions. Without any binding additives, the as-deposited electrodes delaminate resulting in fast capacity degradation. We demonstrate the mechanical nature of this degradation through decreased electrode thinning, resulting in cells with improved cycling stability due to increased mechanical stability. Combining composition and electrochemical analysis, this work demonstrates for the first time composition dependent electrochemical properties for the ternary Zn1−xSn1+xN2 and proposes earth-abundant ternary nitride anodes for increased reversible capacity and cycling stability.

Industrial molasses waste in the performant synthesis of few-layer graphene and its Au/Ag nanoparticles nanocomposites. Photocatalytic and supercapacitance applications

In view of clean environment, the industry needs to address multiple demands at different levels of production and processes via the sustainable approach including recycling or smart use of produced waste. On the other hand, a development and success of green energy requires the crucial materials synthesized via efficient, sustainable methodology. Herein, the green, simple, easily scalable, fast, and highly efficient synthesis of few-layer graphene (FLG) and its composites with Au and Ag nanoparticles using a waste is presented. The FLG synthesis based on the exfoliation of graphite runs in water in the presence of industrial co-product, molasses, which next also shows performant reductive properties during Ag and Au NPs formation. The decreased size of NPs deposited on FLG indicates the synergetic effect of molasses and FLG, exhibiting the add role of FLG/molasses as metal stabilizer species. The NPs/FLG composites are efficient photocatalysts of bisphenol (BisA) degradation in the presence of peroxy-monosulfate (PMS) activator. The Au/FLG (PVDF) and Ag/FLG (PVDF) based electrodes reveal as well relatively high gravimetric capacitance, 205 Fg-1 and 729 Fg-1. The presented approach is much worthy to be further applied in the synthesis of other layered materials as well as other non-noble supported metallic systems.

Catalytic effect of Al2TiO5 on the dehydrogenation properties of LiAlH4

Lithium alanate (LiAlH4) is considered as a promising material for storing hydrogen (H2) in solid-state form for onboard applications due to its advantage of high gravimetric H2 capacity. LiAlH4 could release H2 ∼7.9 wt.% when heated up to ∼250 °C. Nevertheless, the high desorption temperature, sluggish desorption kinetics, and irreversibility hamper the application of LiAlH4 for solid-state H2 storage materials. Therefore, in this study, we have used aluminum titanate (Al2TiO5) as an additive to diminish the desorption temperature and enhance the desorption kinetics of LiAlH4. The addition of a small amount of Al2TiO5 (5 wt.%) into LiAlH4 significantly decreased the decomposition temperature and enhanced the desorption kinetics, in which Al2TiO5-doped LiAlH4 started to release H2 at ∼90 °C and was able to desorb H2 as much as ∼3.5 wt.% at 90 °C within 1 h. Without the catalyst, pure LiAlH4 starts to release H2 at ∼145 °C and only desorbs H2 as low as 0.3 wt.% at 90 °C within 1 h. The activation energies for H2 release in the two-step desorption process of LiAlH4 were reduced after catalysis with Al2TiO5. The activation energies of as-milled LiAlH4 were 80 kJ/mol and 91 kJ/mol, respectively, as calculated by the Arrhenius plot. The activation energies were lowered to 68 kJ/mol and 79 kJ/mol after milling with Al2TiO5. The scanning electron microscopy images revealed that the LiAlH4 particles became smaller and less agglomerated when Al2TiO5 was added. It is believed that the in-situ formation of active species during the desorption process and reduction in particles size play a vital role in improving the dehydrogenation properties of the Al2TiO5-doped LiAlH4 system.

Hydrogen Storage in Complex Metal Hydrides NaBH4: Hydrolysis Reaction and Experimental Strategies

Worldwide, hydrogen is gaining ground since it is a promising alternative energy source to conventional fuels, which include fossil fuel. Thus, numerous techniques to generate hydrogen have been suggested. This literature review describes the challenges and obstacles identified through a series of the publications that target the hydrolysis of sodium borohydride. This review present several catalysts and reactor systems for the generation of hydrogen gas using the hydrolysis of sodium borohydride, selecting articles in the literature that show a promising future for this technology, although some challenges lie ahead. Sodium borohydride has been widely considered as a low-cost hydrogen storage material with high gravimetric hydrogen capacity of about 10 wt.%. However, its thermodynamic stability seriously hinders the application of sodium borohydride to obtain hydrogen. The performances of the reviewed systems of sodium borohydride hydrolysis include analysis from both the thermodynamic and kinetic points of view. The feasibility of an efficient hydrogen generation system, where a mixture of sodium borohydride and catalysts is hydrolyzed, is considered. This review aims to provide a useful resource to aid researchers starting work on the generation of hydrogen gas using the hydrolysis of sodium borohydride, so they can select the catalysts and reactor systems that best suit them. Thus far, no single catalyst and reactor system can simultaneously meet all of the required standards for efficient practical applications.

Enhancing the Areal Capacity and Stability of Cu2ZnSnS4 Anode Materials by Carbon Coating: Mechanistic and Structural Studies During Lithiation and Delithiation.

The widespread use of energy storage technologies has created a high demand for the development of novel anode materials in Li-ion batteries (LIBs) with high areal capacity and faster electron-transfer kinetics. In this work, carbon-coated Cu2ZnSnS4 with a hierarchical 3D structure (CZTS@C) is used as an anode material for LIBs. The CZTS@C microstructures with enhanced electrical conductivity and improved Li-ion diffusivity exhibit high areal and gravimetric capacities of 2.45 mA h/cm2 and 1366 mA h/g, respectively. The areal capacity achieved in the present study is higher than that of previously reported CZTS-based materials. Moreover, in situ X-ray diffraction results show that lithium ions are stored in CZTS through the insertion reaction, followed by the alloying and conversion reactions at ∼1 V. The structural evolution of Li2S and Cu–Sn/Cu–Zn alloy phases occurs during the conversion and alloying reactions. The present work provides a cost-effective and simple method to prepare bulk CZTS and highlights the conformal carbon coating over CZTS, which can enhance the electrical and ionic conductivities of CZTS materials and increase the mass loading (1–2.3 mg/cm2). The improved stability and rate capability of CZTS@C anode materials can therefore be achieved.

Clean production of N, O-doped activated carbon by water vapor carbonization/activation of expired coffee for high-volumetric supercapacitor

Clean production of activated carbon from household expired food provide an alternative way to get value-added product thus benefits waste reutilization and environmental protection. Herein, we fabricated N, O co-doped activated carbons (HCDC) from expired coffee to by a green route of direct water vapor carbonization/activation approach. In our approach, the expired coffee was firstly grinded and then carbonized under water vapor atmosphere. The derived HCDC owns low surface area (172–184 m2/g), large packing density (1.81–1.83 cm3/g), rich redox-active nitrogen (4.5 atom%) and oxygenic (12.0 atom%) functionalities. As electrode for supercapacitor, the HCDC achieves a high gravimetric capacitance of 312F/g at 1.0 A/g (vs 258F/g of commercial AC) and the value can be maintained 223F/g at 20 A/g, showing a high rate capability of 71.5%. Particularly, because of the large packing density, the HCDC exhibits an excellent volumetric supercapacitor performances: ultrahigh volumetric capacitance of 567F/cm3 (vs 165F/cm3 of commercial AC) and large energy density of 27.8 Wh/L@1820 W/L (vs 7.5 Wh/L@576 W/L for commercial AC) and superlong cycling stability with near 100 capacitance retention after continual 30 000 cycles at large current density of 9.0 A/g, suggesting a promising application for practical energy storage devices.

A General Multi-Interface Strategy toward Densified Carbon Materials with Enhanced Comprehensive Electrochemical Performance for Li/Na-Ion Batteries.

Fast charging rate and large energy storage are key requirements for lithium-ion batteries (LIBs) in electric vehicles. Developing electrode materials with high volumetric and gravimetric capacity that could be operated at a high rate is the most challenging problem. In this work, a general multi-interface strategy toward densified carbon materials with enhanced comprehensive electrochemical performance for Li/Na-ion batteries is proposed. The mixture of graphene oxide and sucrose solution is sprayed into a water/oil system and furtherly carbonized to get graphene/hard carbon spheres (GHSs). In this material, abundant ingenious internal interfaces between the crystalline graphene and the carbon matrix are created inside the hard carbon spheres. The constructed interfaces can not only work as a pathway for the escape of volatile gas generated during sucrose pyrolysis to prevent the formation of abundant pores, which leads high packing density of 0.910gcm-3 and low surface area of 13.3m2 g-1 , but can also provide a conductive "highway" for ions and electrons. When used as the anode material for both LIBs and sodium-ion batteries (SIBs), the GHS shows the high gravimetric/volumetric reversible capacities, high-rate performance, and low temperature properties simultaneously, implying the great potential application in practical LIBs and SIBs.

Horizontally aligned lamellar porous graphene/nickel composite for high volumetric capacity lithium-sulfur batteries

Although lithium-sulfur batteries have the advantages of gravimetric energy density, it remains a challenge to achieve high volumetric energy density in lithium-sulfur batteries due to the employment of conductive porous carbon with low tap density and high porosity. To this context, we synthesized a horizontally aligned lamellar porous graphene/nickel composite (LPG-Ni) as a dense sulfur host material to increase the volumetric capacity of lithium-sulfur batteries while retaining high gravimetric capacity. The nickel decorated on the surface of the porous graphene serves as active sites, effectively adsorbing and catalytically converting polysulfides, thus improving the redox kinetics and reducing shuttle effect. More importantly, the abundant pores on the graphene sheet are considered as a shortcut for lithium-ion diffusion, which accelerates the ion transport through the whole electrode. Owing to the synergistic effect, the as-prepared sulfur cathode exhibits both excellent ionic and electronic conductivity, and has a dense-stacked structure. Thus, the LPG-Ni/S cathode provides high gravimetric and volumetric capacity (718.7 mA h g-1cathode and 884.0 mA h cm-3cathode at 0.1C). Meanwhile, the battery exhibits superior rate capability (369.7 mA h cm-3cathode at 5C) and cycling performance (1000 cycles, 0.037% decay per cycle at 1C).

Electrochemically Surface‐modified Aluminum Electrode Enabling High Performance and Ultra‐long Cycling Life Al‐ion Batteries

AbstractInnovation in electronic devices has created a demand for energy storage systems. Recently, rechargeable Al‐ion batteries (AIBs) have received significant attention owing to their high gravimetric capacity and low cost. In this study, the electrochemical performances of pristine, etched, and electropolished Al negative electrodes via surface modification were investigated to determine their efficiency in AIBs. Herein, pristine, etched, and electropolished Al acted as the negative electrodes (anodes), and pure graphite and aluminum chloride (AlCl3)/1‐ethyl‐3‐methylimidazolium chloride ([EMIm]Cl) were used as the positive electrode (cathode) and ionic liquid electrolyte, respectively. This new type of electropolished Al‐based battery cell shows good cyclability and high performance compared to pristine and etched Al electrodes. The electropolished Al electrode stabilized at an average capacity of 50 mAh g−1 over 10,000 cycles at an ultrafast current rate of 5,000 mA g−1.

Influence of charging protocols on the charging capability and aging of lithium-ion cells with silicon-containing anodes

Silicon with a high gravimetric capacity of 3579 mAh g−1 of the pure material becomes increasingly common in the anode of lithium-ion batteries to increase energy density on the full cell level. However, silicon changes its volume excessively during (de-)lithiation making it prone to aging. In commercial cells, it is typically applied either as SiOx or nano-Si in small quantities in a composite anode together with graphite. A different operation voltage window of silicon, varying quantities of silicon in the anode but also different technologies of the applied silicon materials, however, result in different aging behavior of the full cell—even if silicon content and capacities are similar on the data sheet. In this study, two commercial cylindrical cells in the 18650 format with differing silicon technologies are thus compared with a focus on their charging behavior and degradation mechanisms. One way to increase cycling stability with respect to the different silicon cell chemistries is the adaption of the charging protocols. Voltage limits as well as current have therefore been varied in this study using five different charging protocols. Their influence on the charging times and aging behavior is analyzed in great depth: dilatometer investigations of the anodes and their lithiation behavior, differential voltage investigations as well as a detailed post-mortem analysis including ICP-OES, SEM and EDX have identified silicon expansion at low full cell voltages as root aging mechanism in both cells.

Ni-CNTs as an efficient confining framework and catalyst for improving dehydriding/rehydriding properties of MgH2

MgH2 is one of the most potential hydrogen storage material with a high gravimetric hydrogen storage capacity. however, its applications have been plagued by its high operating temperature and the relatively poor kinetics for releasing and absorbing hydrogen. In the present study, nanoconfinement or catalytic doping were introduced to improve de/rehydrogenation kinetic properties of MgH2. The MgH2@Ni-CNTs was fabricated by holding the MgH2 particles on the surface of the CNT-Ni. MgH2 supported by carbon nanotubes loaded with Ni nanoparticles (MgH2@Ni-CNTs) shows a superior H2 de/ab-sorption kinetics than that of MgH2. This nano-composite releases H2 at 250 °C with the dehydrogenation capacity of 7.29 wt% within 60 min. The dehydrogenation Ea of MgH2 in MgH2@Ni-CNTs is reduced to 74.8 kJ/mol by the confining and catalytic impact of Ni-CNTs. It also has a significant improvement on rehydriding kinetics, with a 7.20 wt% H2 absorption in 30 min even at a temperature as low as 200 °C. Moreover, the MgH2@Ni-CNTs also shows good cycling stability without distinct capacity decay after cycling ten times. Studies show that during dehydrogenation and hydrogenation processes, the CNTs-Ni act as confining framework and catalyst, can accelerate diffusion of hydrogen and prevent the Mg/MgH2 agglomeration. The application of this novel MgH2@Ni-CNTs extends the horizon of transition metallic catalyst and nanoconfinement, and offers a novel way to enhance the hydrogen storage property of the nanoconfined MgH2.

An Overview of the Recent Advances of Additive-Improved Mg(BH4)2 for Solid-State Hydrogen Storage Material

Recently, hydrogen (H2) has emerged as a superior energy carrier that has the potential to replace fossil fuel. However, storing H2 under safe and operable conditions is still a challenging process due to the current commercial method, i.e., H2 storage in a pressurised and liquified state, which requires extremely high pressure and extremely low temperature. To solve this problem, research on solid-state H2 storage materials is being actively conducted. Among the solid-state H2 storage materials, borohydride is a potential candidate for H2 storage owing to its high gravimetric capacity (majority borohydride materials release >10 wt% of H2). Mg(BH4)2, which is included in the borohydride family, shows promise as a good H2 storage material owing to its high gravimetric capacity (14.9 wt%). However, its practical application is hindered by high thermal decomposition temperature (above 300 °C), slow sorption kinetics and poor reversibility. Currently, the general research on the use of additives to enhance the H2 storage performance of Mg(BH4)2 is still under investigation. This article reviews the latest research on additive-enhanced Mg(BH4)2 and its impact on the H2 storage performance. The future prospect and challenges in the development of additive-enhanced Mg(BH4)2 are also discussed in this review paper. To the best of our knowledge, this is the first systematic review paper that focuses on the additive-enhanced Mg(BH4)2 for solid-state H2 storage.

Ultrafast pore-tailoring of dense microporous carbon for high volumetric performance supercapacitors in organic electrolyte

Preparing activated carbon with high volumetric performance in organic electrolyte is crucial for developing high-energy and miniaturized supercapacitors, but still challenging because high surface area and large pore size are required to effectively store large-sized organic electrolyte ions, which usually result in the low density. Herein, an ultrafast strategy is proposed to tailor the interconnected porous structure of activated carbon through introducing CO2 at the end of homogeneous activation. The uniformly distributed potassium components in carbon matrix promote a robust catalytic etching by CO2, leading to precise tailoring of the ultramicropores (0.50–0.72 nm) to large micropores (0.81–1.14 nm) within only 2 min. The optimized sample with both high surface area and compaction density (2147 m2 g−1, 0.68 g cm−3) shows high gravimetric and volumetric capacitances (155 F g−1 and 106 F cm−3 at 1 A g−1) as well as good rate performance (102 F g−1 and 70 F cm−3 at 20 A g−1) in organic electrolyte. The symmetric supercapacitor achieves high energy densities of 35 Wh kg−1 and 24 Wh L−1 at 573 W kg−1 and 395 W L−1, respectively, indicating great potential of the ultrafast tailoring strategy for practical application.

Assemble 2D redox-active covalent organic framework/graphene hybrids as high-performance capacitive materials

Graphene and two-dimension covalent organic frameworks (2D COFs) with a redox-active skeleton are promising potential capacitive materials for energy storage applications. However, their tendency to form thick laminates severely limits electron transfer and ion diffusion. Herein, we demonstrate graphene hybrids assembled by mixing 2D COFs and reduced graphene oxide (rGO) nanosheets to address their problems effectively. Electrochemical analysis shows that the two different 2D nanosheets prevent their restacking into thick laminates. Electrically conductive rGO nanosheets provide fast electron paths, while 2D COFs with abundant mesopores make graphene surface and redox-active sites in COFs accessible to electrolyte ions. The optimized hybrid containing 30 wt% COFs delivers a high gravimetric capacitance of 599 F g−1, much higher than the pristine rGO (203 F g−1) and COFs (110 F g−1). It also exhibits excellent rate capability with over 80% capacity retention when the charging/discharging current density increases by 40 times. This mixing strategy of different types of 2D nanosheets by hydrothermal assembly can be further extended to various graphene hybrids containing COFs and other 2D materials, creating a wide range of novel carbon composite materials for fundamental research and applications.

Vanadium carbide and nitrogen-doped graphene nanosheets based layered architecture for electrochemical evaluation of clioquinol detection and energy storage application

Herein, we report the oxidized-vanadium carbide (V8C7Tx) hybridized with nitrogen-doped graphene nanosheets (VC/NG NSs) nanocomposite using hydrothermal followed by sonochemical approach. The oxidized V8C7Tx is shown to be enriched with O-terminated functional groups, which also improves the electrochemical performance of the nanocomposite. Then for the first time, VC/NG NSs nanocomposite is reported as an efficient electrocatalyst for the detection of CQL. The cyclic voltammetry (CV) experiments were performed at the working potential from 0 to 0.7 V (vs. Ag/AgCl). Surprisingly, the nanocomposite's multilayer structure offers a large number of active sites with a high electron transfer rate for CQL detection. The fabricated drug sensor exhibits a lower oxidation potential (0.46 V) and a greater peak current response (12.05 µA) than previously reported sensors. Under optimum circumstances, the fabricated sensors analytically well performed by means of low detection limit (9 nM), wide linear range (0.5–585 µM), and appreciable recovery results (∼98%, (n = 3)) in human urine samples. Furthermore, the nanocomposite shows a high gravimetric capacitance of 235 F g−1 at 1 A g−1 in 1 M KOH, which is the highest value among alkali-based electrolytes for VC based electrodes. Moreover, the nanocomposite demonstrated robust cycling performance even after 8000 cycles with ∼95% capacitance retention. The presence of O-terminated functional groups, various oxidation states of vanadium (+2, +3, and +4), good conducting and catalytic characteristics of N-graphene are worked together to improve electrochemical performance in sensor and energy storage. Thus, the current study offers a promising MXene based nanocomposite material for high-performance electrochemical applications.

3D MXene-holey graphene hydrogel for supercapacitor with superior energy storage

MXene, a new two-dimensional material, has attracted much attention in the field of energy storage. Assembling it into a three-dimensional structure is an effective way to solve the self-stacking problem. However, the assembly of MXene into a three-dimensional structure inevitably reduces the density of the electrode, resulting in a low volumetric capacitance. Here, three-dimensional MXene-holey reduced graphene oxide hydrogel with hierarchical porous structure was obtained by low-temperature hydrothermal treatment, which was used as superior performance binder-free supercapacitor electrode. In the MXene-holey reduced graphene oxide hydrogel electrode, holey reduced graphene oxide can accelerate ion transport, shorten ion and electron transport pathways, and improve the gravimetric capacitance as well as the volumetric capacitance of the electrode. When MX-HGH is applied to the electrode of supercapacitor, it can release gravimetric capacitance up to 415 F g−1 and volumetric capacitance of 597 F cm−3. This work demonstrates a practical method to construct three-dimensional MXene structures with high gravimetric capacitance and relatively high volumetric capacitance, opening up a fresh idea for the application of MXene three-dimensional structures in supercapacitors.