Hierarchical architecture of PANI@TiO2/Ti3C2Tx ternary composite electrode for enhanced electrochemical performance

MXenes as emerging materials to repair electroactive tissues and organs

Nanomaterials with electroactive properties have taken a big leap for tissue repair and regeneration due to their unique physiochemical properties and biocompatibility. MXenes, an emerging class of electroactive materials have generated considerable interest for their biomedical applications from bench to bedside. Recently, the application of these two-dimensional wonder materials have been extensively investigated in the areas of biosensors, bioimaging and repair of electroactive organs, owing to their outstanding electromechanical properties, photothermal capabilities, hydrophilicity, and flexibility. The currently available data reports that there is significant potential to employ MXene nanomaterials for repair, regeneration and functioning of electroactive tissues and organs such as brain, spinal cord, heart, bone, skeletal muscle and skin. The current review is the first report that compiles the most recent advances in the application of MXenes in bioelectronics and the development of biomimetic scaffolds for repair, regeneration and functioning of electroactive tissues and organs including heart, nervous system, skin, bone and skeletal muscle. The content in this article focuses on unique features of MXenes, synthesis process, with emphasis on MXene-based electroactive tissue engineering constructs, biosensors and wearable biointerfaces. Additionally, a section on the future of MXenes is presented with a focus on the clinical applications of MXenes.

MXenes from MAX phases: synthesis, hybridization, and advances in supercapacitor applications

MXenes, which are essentially 2D layered structures composed of transition metal carbides and nitrides obtained from MAX phases, have gained substantial interest in the field of energy storage, especially for their potential as electrodes in supercapacitors due to their unique properties such as high electrical conductivity, large surface area, and tunable surface chemistry that enable efficient charge storage. However, their practical implementation is hindered by challenges like self-restacking, oxidation, and restricted ion transport within the layered structure. This review focuses on the synthesis process of MXenes from MAX phases, highlighting the different etching techniques employed and how they significantly influence the resulting MXene structure and subsequent electrochemical performance. It further highlights the hybridization of MXenes with carbon-based materials, conducting polymers, and metal oxides to enhance charge storage capacity, cyclic stability, and ion diffusion. The influence of dimensional structuring (1D, 2D, and 3D architectures) on electrochemical performance is critically analyzed, showcasing their role in optimizing electrolyte accessibility and energy density. Additionally, the review highlights that while MXene-based supercapacitors have seen significant advancements in terms of energy storage efficiency through various material combinations and fabrication techniques, key challenges like large-scale production, long-term stability, and compatibility with electrolytes still need to be addressed. Future research should prioritize developing scalable synthesis methods, optimizing hybrid material interactions, and investigating new electrolyte systems to fully realize the potential of MXene-based supercapacitors for commercial applications. This comprehensive review provides a roadmap for researchers aiming to bridge the gap between laboratory research and commercial supercapacitor applications.

In situ developed NiCo2O4-Ti3C2Tx nanohybrid towards non-enzymatic electrochemical detection of glucose and hydrogen peroxide

Owing to the adverse consequences of excess glucose (Glu) and hydrogen peroxide (H2O2) on humans, it is imperative to develop an electrochemical sensor for detection of these analytes with good selectivity and sensitivity. Herein, a nanohybrid comprising nickel cobaltite nanoparticles (NiCo2O4 NPs) embedded on conductive Ti3C2Tx nanosheets (NSs) has been prudently designed and employed for the electrochemical detection of Glu and H2O2. The developed nanohybrid has been systematically characterized using morphological and spectral techniques, and then immobilized on a glassy carbon electrode (GCE). Under optimized conditions, the developed NiCo2O4-Ti3C2Tx/GCE based electrochemical sensor has demonstrated an impressive analytical response towards Glu and H2O2 with good sensitivity and selectivity. The non-enzymatic sensor has demonstrated a broad linear range from 30 μM to 1.83 mM for Glu, and two linear ranges of 20-100 μM and 100 μM-2.01 mM for H2O2. The sensor has exhibited limits of detection (LOD) of 9 μM and 6 μM with sensitivities of 101.2 μA μM-1 cm-2 and 107.03 μA μM-1 cm-2, respectively, for Glu and H2O2 detection. The impressive analytical performance of the fabricated sensor in terms of linear range, LOD and sensitivity are ascribed to the (i) enhanced conductivity of Ti3C2Tx NSs, (ii) mediated electrocatalytic activity of NiCo2O4 NPs and (iii) large number of catalytically active sites on the NiCo2O4-Ti3C2Tx heterostructure. Notably, the NiCo2O4-Ti3C2Tx/GCE has demonstrated impressive stability and reproducibility, which is mainly due to the in situ uniform growth of NiCo2O4 NPs over Ti3C2Tx NSs.

Synthesis and applications of MXene-based composites: a review

Recently, there has been considerable interest in a new family of transition metal carbides, carbonitrides, and nitrides referred to as MXenes (Ti₃C₂T_x) due to the variety of their elemental compositions and surface terminations that exhibit many fascinating physical and chemical properties. As a result of their easy formability, MXenes may be combined with other materials, such as polymers, oxides, and carbon nanotubes, which can be used to tune their properties for various applications. As is widely known, MXenes and MXene-based composites have gained considerable prominence as electrode materials in the energy storage field. In addition to their high conductivity, reducibility, and biocompatibility, they have also demonstrated outstanding potential for applications related to the environment, including electro/photocatalytic water splitting, photocatalytic carbon dioxide reduction, water purification, and sensors. This review discusses MXene-based composite used in anode materials, while the electrochemical performance of MXene-based anodes for Li-based batteries (LiBs) is discussed in addition to key findings, operating processes, and factors influencing electrochemical performance.

Recent Advances in Two-Dimensional MXene for Supercapacitor Applications: Progress, Challenges, and Perspectives

MXene is a type of two-dimensional (2D) transition metal carbide and nitride, and its promising energy storage materials highlight its characteristics of high density, high metal-like conductivity, tunable terminals, and charge storage mechanisms known as pseudo-alternative capacitance. MXenes are a class of 2D materials synthesized by chemical etching of the A element in MAX phases. Since they were first discovered more than 10 years ago, the number of distinct MXenes has grown substantially to include numerous M_nX_n-1 (n = 1, 2, 3, 4, or 5), solid solutions (ordered and disordered), and vacancy solids. To date, MXenes used in energy storage system applications have been broadly synthesized, and this paper summarizes the current developments, successes, and challenges of using MXenes in supercapacitors. This paper also reports the synthesis approaches, various compositional issues, material and electrode topology, chemistry, and hybridization of MXene with other active materials. The present study also summarizes MXene's electrochemical properties, applicability in pliant-structured electrodes, and energy storage capabilities when using aqueous/non-aqueous electrolytes. Finally, we conclude by discussing how to reshape the face of the latest MXene and what to consider when designing the next generation of MXene-based capacitors and supercapacitors.

In-situ fabrication of manganese ferrite grafted polyaniline nanocomposite: A magnetically reusable visible light photocatalyst and a robust electrode material for supercapacitor

Herein, we reported the in-situ preparation of manganese ferrite (MnFe₂O₄) grafted polyaniline (Pani), a magnetic nanocomposite for the potential visible light photocatalytic material as well as electrode material for supercapacitor. The physical characterization of the prepared nanoparticle and nanocomposite was examined with various spectroscopic and microscopic analyses. The peaks observed in the X-ray diffraction study confirm the face-centered cubic phase of MnFe₂O₄ nanoparticles with a grain size of ∼17.6 nm. The surface morphology analysis revealed the uniform distribution of spherical-like MnFe₂O₄ nanoparticles on the surface of Pani. The degradation of malachite green (MG) dye under exposure to visible light was investigated using MnFe₂O₄/Pani nanocomposite as a photocatalyst. The results exposed the faster degradation of MG dye was accomplished by MnFe₂O₄/Pani nanocomposite than MnFe₂O₄ nanoparticles. The energy storage performance of the MnFe₂O₄/Pani nanocomposite was analyzed through cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy analyses. The results exposed that the MnFe₂O₄/Pani electrode achieved a capacitance of 287.1 F/g than the MnFe₂O₄ electrode (94.55 F/g). Further, the respectable capacitance of 96.92% was achieved even after 3000 repetitive cycles stability . Based on the outcomes, the MnFe₂O₄/Pani nanocomposite can be suggested as a promising material for both photocatalytic and supercapacitor applications.

Flexible MXene-Based Composite Films: Synthesis, Modification, and Applications as Electrodes of Supercapacitors

MXenes, as a 2D planar structure nanomaterial, were first reported in 2011. Due to their large specific surface area, high ductility, high electrical conductivity, strong hydrophilic surface, and high mechanical flexibility, MXenes have been extensively explored in the development of various functional materials with desired performances. This review is aimed to summarize the current progress in synthesis, modification, and applications of MXene-based composite films as electrode materials of flexible energy storage devices. In the synthesis of MXenes, the evolution and exploration of etchants are emphasized. Furthermore, in order to develop MXene-based composite films, the components used to modify the MXene nanoflakes, including 0D, 1D, and 2D nanomaterials, are summarized, and the perspectives and research direction of such materials are also discussed.

Intercalation of Nanoscale Multiferroic Spacers between the Two-Dimensional Interlayers of MXene

We report a facile synthesis of MXene/bismuth ferrite (Ti₃C₂T _x @ BiFeO₃) nanocomposites using hydrazine hydrate induced with the hydrothermal method. Preparation of the composite with hydrazine hydrate prevents the formation of Bi₂₅FeO₃₉ inside the matrix. The 25 wt % loading of BiFeO₃ acts as spacers for the multilayer restacking of MXene flakes by retaining the (002) plane. This promotes large dc conductivity with interfacial and defect dipole polarization mechanisms inside the composite material. The thinner M-H loop also indicates the minimal magnetic loss inside the composites. The facile synthesis strategy provides outstanding properties in Ti₃C₂T _x @ BiFeO₃ composites as two-dimensional multiferroic materials.

Two-dimensional Ti3C2 MXene-based nanostructures for emerging optoelectronic applications

Since the first discovery of Ti₃C₂ in 2011, two-dimensional (2D) transition-metal carbides, carbonitrides and nitrides, known as MXenes, have attracted significant attention. Due to their outstanding electronic, optical, mechanical, and thermal properties, versatile structures and surface chemistries, Ti₃C₂ MXenes have emerged as new candidates with great potential for applications in optoelectronic devices, such as photovoltaics, photodetectors and photoelectrochemical devices. The excellent metallic conductivity, high anisotropic carrier mobility, good structural and chemical stabilities, high optical transmittance, excellent mechanical strength, tunable work functions, and wide range of optical absorption properties of Ti₃C₂ MXene nanostructures are the key to their success in a number of electronic and photonic device applications. Herein, we summarize the fundamental properties and preparation of pure Ti₃C₂ MXenes, functionalized Ti₃C₂ MXenes and their hybrid nanocomposites, as well as their optoelectronic applications. In the end, the perspective and current challenges of Ti₃C₂ MXenes toward the development of advanced MXene-based nanostructures are briefly discussed for future optoelectronic applications.

Recent Advances in MXene/Polyaniline-Based Composites for Electrochemical Devices and Electromagnetic Interference Shielding Applications

Due to serious global warming and environmental issues, the demand for clean and sustainable energy storage devices is significantly increased. Often accompanied by rapid growth of portable electronic vehicles and devices, massive electromagnetic wave pollution becomes unavoidable. To mitigate the above two issues, this mini-review summaries preparation methods and recent developments of MXene/polyaniline-based composites for their applications in electrochemical devices and electromagnetic interference shielding. Based on excellent synergistic effects between single compounds and designed hierarchical structures, MXene/polyaniline-based composites usually exhibit enhanced physical and chemical properties, showing great potentials in sustainable electrochemical properties and electromagnetic wave protections for human health as well as normal operation of precise electronic devices.

Preparation Strategies and Applications of MXene-Polymer Composites: A Review

As a new member of the 2D material family, MXene integrates high metallic conductivity and hydrophilic property simultaneously. It shows tremendous potential in fields of energy storage, sensing, electromagnetic shielding, and so forth. Due to the abundant surface functional groups, the physical and chemical properties of MXene can be tuned by the formation of MXene-polymer composites. The introduction of polymers can expand the interlayer spacing, reduce the distance of ion/electron transport, improve the surface hydrophilicity, and thus guide the assembly of MXene-polymer structures. Herein, the preparation strategies of MXene-polymer composites including physical mixing, surface modification, such as anchoring through TiN and Ti-O-C bonds, bonding through esterification, grafting functional groups through TiOSi/TiOP bonds, photograft reaction, as well as in situ polymerization are highlighted. In addition, the possible mechanisms for each strategy are explained. Furthermore, the applications of MXene-polymer composites obtained by different preparation strategies are summarized. Finally, perspectives and challenges are presented for the designs of MXene-polymer composites.

Opening MXene Ion Transport Channels by Intercalating PANI Nanoparticles from the Self-Assembly Approach for High Volumetric and Areal Energy Density Supercapacitors

Two-dimensional (2D) MXene materials have attracted great attention as advanced energy storage devices. A Ti₃C₂ MXene film can be used as a high-performance electrode material for flexible supercapacitors owing to its high specific capacitance, excellent conductivity, and remarkable flexibility. Unfortunately, self-stacking of MXene nanosheets makes them hard to balance the volumetric and areal capacitance performance. Herein, high conductive polyaniline nanoparticles (PANI NPs, ∼10 nm) are proposed as intercalators to regulate the MXene nanosheet interlayer by the self-assembly method. Interlayered PANI NPs not only restrain MXene self-stacking but also enable more ion transport routes, and conductive PANI NPs filled in MXene interlayer are in the form of nanoparticles that can build interconnected conductive channels. Meanwhile, PANI NPs slightly changes the thickness of the MX/PANI NPs hybrid film, thus bringing a high volumetric capacitance. As a result, the freestanding MX/PANI NPs-10% electrode displays an excellent areal capacitance of 1885 mF cm^-2 (377 F g^-1), meanwhile maintains a high volumetric capacitance of 873 F cm^-3 even when the load of MXene reaches 5 mg cm^-2. Moreover, the symmetric supercapacitor assembled by MX/PANI NPs hybrid film demonstrates high areal energy density (90.3 μWh cm^-2) and volumetric energy density (20.9 Wh L^-1) compared to MXene-based symmetric supercapacitors reported in the literature. This rational design balancing areal and volumetric energy densities provides another approach for solving the inherent problems of MXene and further exploiting MXene materials toward application in advanced energy storage devices.

Fabrication of Cobaltous Sulfide Nanoparticle-Modified 3D MXene/Carbon Foam Hybrid Aerogels for All-Solid-State Supercapacitors

MXene is a neoteric type of bidimensional (2D) transition metal carbide/nitride with broad application prospects, in particular with electrochemical energy storage. The electrochemical performance of MXene is unsatisfactory because it is easy to stack resulting in the difficulty of electrolyte penetration and ion transport. In this study, the cobaltous sulfide-modified 3D MXene/N-doped carbon foam (CoS@MXene/CF) hybrid aerogel is projected and manufactured via simple in situ growth and thermal annealing strategies. The capacitance of the as-fabricated 300-CMC-31:1 electrode material reaches 250 F g^-1 (1 A g^-1), which is obviously higher than those of MXene, CoS@CF, 400-CMC-31:1, 300-CMC-10:1, 300-CMC-50:1, CF, and MXene/CF electrode materials. Moreover, it can hold 97.5% of the original capacitance after 10,000 cycles and the internal resistance (R_s) is only 0.50 Ω. A green bulb can be lit by two all-solid asymmetric supercapacitors installed in series. The prepared CoS@MXene/CF hybrid aerogel exhibits promising potential for practical application in energy storage areas.

Composite Fe3O4-MXene-Carbon Nanotube Electrodes for Supercapacitors Prepared Using the New Colloidal Method

MXenes, such as Ti3C2Tx, are promising materials for electrodes of supercapacitors (SCs). Colloidal techniques have potential for the fabrication of advanced Ti3C2Tx composites with high areal capacitance (CS). This paper reports the fabrication of Ti3C2TX-Fe3O4-multiwalled carbon nanotube (CNT) electrodes, which show CS of 5.52 F cm-2 in the negative potential range in 0.5 M Na2SO4 electrolyte. Good capacitive performance is achieved at a mass loading of 35 mg cm-2 due to the use of Celestine blue (CB) as a co-dispersant for individual materials. The mechanisms of CB adsorption on Ti3C2TX, Fe3O4, and CNTs and their electrostatic co-dispersion are discussed. The comparison of the capacitive behavior of Ti3C2TX-Fe3O4-CNT electrodes with Ti3C2TX-CNT and Fe3O4-CNT electrodes for the same active mass, electrode thickness and CNT content reveals a synergistic effect of the individual capacitive materials, which is observed due to the use of CB. The high CS of Ti3C2TX-Fe3O4-CNT composites makes them promising materials for application in negative electrodes of asymmetric SC devices.

MXene derivatives: synthesis and applications in energy convention and storage

Transition metal carbides or nitrides (MXene) have shown promising applications in energy convention and storage (ECS), owing to their high conductivity and adjustable surface functional groups. In the past several years, many MXene derivatives with different structures have been successfully prepared and their impressive performance demonstrated in ECS. This review summarizes the progress in the synthesis of MXene and typical Ti3C2T x MXene derivatives with different morphologies, including 0D quantum dots, 1D nanoribbons, 2D nanosheets and 3D nanoflowers. The mechanisms involved and their performance in photocatalysis, electrocatalysis and rechargeable batteries are also discussed. Furthermore, the challenges of MXene derivatives in ECS are also proposed.

The Electrode Materials of Supercapacitor Based on TiO2 Nanorod/MnO2 Ultrathin Nanosheet Core/Shell Arrays

A hierarchical structure of TiO2 nanorod/MnO2 ultrathin nanosheet core/shell nanocomposite arrays on a conductive substrate has been prepared by two facile steps of hydrothermal reaction and annealing progress, which serving as electrodes present great potential application for high-performance supercapacitors. By adjusting the concentration of precursor aqueous solution, it can be found that the thickness of the MnO2 shell in the as-designed hierarchical electrode material can be facilely controlled. By comparison, the obtained TiO2 nanorod/MnO2 ultrathin nanosheet as an electrode material can achieve the best electrochemical performance in terms of the area-specific capacitance up to 34.79 mF/cm2 from the cyclic voltammetry (CV) test at the scan rate of 5 mV/s. Furthermore, the composited electrode has also demonstrated good stability, with the capacitance retention rate of about 91% through the cycle experiment test after 1000 cycles.

Interlayer Space Engineering of MXenes for Electrochemical Energy Storage Applications

The increasing demand for high-performance rechargeable energy storage systems has stimulated the exploration of advanced electrode materials. MXenes are a class of two-dimensional (2D) inorganic transition metal carbides/nitrides, which are promising candidates in electrodes. The layered structure facilitates ion insertion/extraction, which offers promising electrochemical characteristics for electrochemical energy storage. However, the low capacity accompanied by sluggish electrochemical kinetics of electrodes as well as interlayer restacking and collapse significantly impede their practical applications. Recently, interlayer space engineering of MXenes by different chemical strategies have been widely investigated in designing functional materials for various applications. In this review, an overview of the most recent progress of 2D MXenes engineering by intercalation, surface modification as well as heterostructures design is provided. Moreover, some critical challenges in future research on MXene-based electrodes have been also proposed.

Progress of Two-Dimensional Ti3 C2 Tx in Supercapacitors

Exploring stable cycling electrode materials with high energy and power density is the key to accelerating the development and application of supercapacitors. Ti₃ C₂ T_x , which is the most investigated member of the family of two-dimensional layered transition-metal carbides, has attracted considerable attention, owing to its unique two-dimensional morphology, large interlayer spacing, outstanding metallic conductivity, abundant chemical surface, and ultrahigh volumetric capacitance. However, the inherent restacking tendency of ultrathin Ti₃ C₂ T_x sheets hinder its practical application. In this review, the synthetic methods and charge-storage mechanisms of Ti₃ C₂ T_x are stressed to provide clues for improving its electrochemical performance. Functionalization, including architectural construction, hybridization, and surface modification of the Ti₃ C₂ T_x sheets, to circumvent difficulties and application in supercapacitors is then summarized. Accordingly, the aim is to highlight the opportunities and challenges for Ti₃ C₂ T_x -based materials in practical applications in supercapacitors.

Nitrogen Doped Intercalation TiO2/TiN/Ti3C2Tx Nanocomposite Electrodes with Enhanced Pseudocapacitance

Layered two-dimensional titanium carbide (Ti₃C₂T_x), as an outstanding MXene member, has captured increasing attention in supercapacitor applications due to its excellent chemical and physical properties. However, the low gravimetric capacitance of Ti₃C₂T_x restricts its rapid development in such applications. Herein, this work demonstrates an effective and facile hydrothermal approach to synthesize nitrogen doped intercalation TiO₂/TiN/Ti₃C₂T_x with greatly improved gravimetric capacitance and excellent cycling stability. The hexamethylenetetramine (C₆H₁₂N₄) in hydrothermal environment acted as the nitrogen source and intercalants, while the Ti₃C₂T_x itself was the titanium source of TiO₂ and TiN. We tested the optimized nitrogen doped intercalation TiO₂/TiN/Ti₃C₂T_x electrodes in H₂SO₄, Li₂SO₄, Na₂SO₄, LiOH and KOH electrolytes, respectively. The electrode in H₂SO₄ electrolyte delivered the best electrochemical performance with high gravimetric capacitance of 361 F g⁻¹ at 1 A g⁻¹ and excellent cycling stability of 85.8% after 10,000 charge/discharge cycles. A systematic study of material characterization combined with the electrochemical performances disclosed that TiO₂/TiN nanoparticles, the introduction of nitrogen and the NH₄⁺ intercalation efficaciously increased the specific surface areas, which is beneficial for facilitating electrolyte ions transportation. Given the excellent performance, nitrogen doped intercalation TiO₂/TiN/Ti₃C₂T_x bodes well as a promising pseudocapacitor electrode for energy storage applications.

Research Progress on Applications of Polyaniline (PANI) for Electrochemical Energy Storage and Conversion

Conducting polyaniline (PANI) with high conductivity, ease of synthesis, high flexibility, low cost, environmental friendliness and unique redox properties has been extensively applied in electrochemical energy storage and conversion technologies including supercapacitors, rechargeable batteries and fuel cells. Pure PANI exhibits inferior stability as supercapacitive electrode, and can not meet the ever-increasing demand for more stable molecular structure, higher power/energy density and more N-active sites. The combination of PANI and other active materials like carbon materials, metal compounds and other conducting polymers (CPs) can make up for these disadvantages as supercapacitive electrode. As for rechargeable batteries and fuel cells, recent research related to PANI mainly focus on PANI modified composite electrodes and supported composite electrocatalysts respectively. In various PANI based composite structures, PANI usually acts as a conductive layer and network, and the resultant PANI based composites with various unique structures have demonstrated superior electrochemical performance in supercapacitors, rechargeable batteries and fuel cells due to the synergistic effect. Additionally, PANI derived N-doped carbon materials also have been widely used as metal-free electrocatalysts for fuel cells, which is also involved in this review. In the end, we give a brief outline of future advances and research directions on PANI.

Emerging 2D MXenes for supercapacitors: status, challenges and prospects

This review provides a comprehensive understanding of the emerging 2D MXene electrode materials for supercapacitor application.

Rational Construction of Ti3C2T x/Co-MOF-Derived Laminated Co/TiO2-C Hybrids for Enhanced Electromagnetic Wave Absorption

Lightweight and compatible metal-organic framework (MOF)-derived carbon-based composites are widely used in electromagnetic (EM) absorption. Their combination with laminated TiO₂-C (derived from Ti₃C₂T _x) is expected to further strengthen the EM attenuation ability. Herein, novel laminated Co/TiO₂-C hybrids were derived from Ti₃C₂T _x/Co-MOF using heat treatment. Compared with pristine MOF-derived carbon-based composites, the EM absorption ability of Co/TiO₂-C was improved by multiple reflections between multilayered microstructures and the improved polarization loss (due to the heterogeneous interfaces, residual defects, and dipole polarization) and the strengthened conductivity loss caused by the carbon layers. Specifically, for the Co/TiO₂-C hybrids at thicknesses of 3.0 and 2.0 mm, the optimal reflection loss (RL) was -41.1 dB at 9.0 GHz and -31.0 dB at 13.9 GHz, with effective bandwidths (RL ≤ -10 dB) of 3.04 and 4.04 GHz, respectively. This study will underline the preparation of carbon-based absorbing materials starting from MXene/MOF hybrids.

Architecturally Robust Graphene-Encapsulated MXene Ti2CT x@Polyaniline Composite for High-Performance Pouch-Type Asymmetric Supercapacitor

A harmonized three-component composite system which preserves the characteristics of individual components is of interest in the field of energy storage. Here, we present a graphene-encapsulated MXene Ti₂CT _x@polyaniline composite (GMP) material realized in a systematically stable configuration with different ternary nanomaterials for supercapacitor electrodes. Due to the different ζ-potentials in a high-pH solution, chemically converted graphene (negatively charged) is thoroughly unfolded to allow full encapsulation, but the MXene Ti₂CT _x@polyaniline composite with a low positive ζ-potential is easily attracted toward a counter-charged substance. The obtained GMP electrode exhibits improved cycling stability and better electrochemical performance owing to the use of mechanically robust and chemically inert graphene and the densely intercalated conductive polyaniline between the multilayer MXenes. The GMP electrode has a high gravimetric capacitance of 635 F g^-1 (volumetric capacitance of 1143 F cm^-3) at a current density of 1 A g^-1 with excellent cycling stability of 97.54% after 10 000 cycles. Furthermore, the asymmetric pouch-type supercapacitor assembled using the GMP as a positive electrode and graphene as a negative electrode yields a high energy density of 42.3 Wh kg^-1 at a power density of 950 W kg^-1 and remarkable cycling stability (94.25% after 10 000 cycles at 10 A g^-1).

Recent Advances in Layered Ti3 C2 Tx MXene for Electrochemical Energy Storage

Ti₃ C₂ T_x , a typical representative among the emerging family of 2D layered transition metal carbides and/or nitrides referred to as MXenes, has exhibited multiple advantages including metallic conductivity, a plastic layer structure, small band gaps, and the hydrophilic nature of its functionalized surface. As a result, this 2D material is intensively investigated for application in the energy storage field. The composition, morphology and texture, surface chemistry, and structural configuration of Ti₃ C₂ T_x directly influence its electrochemical performance, e.g., the use of a well-designed 2D Ti₃ C₂ T_x as a rechargeable battery anode has significantly enhanced battery performance by providing more chemically active interfaces, shortened ion-diffusion lengths, and improved in-plane carrier/charge-transport kinetics. Some recent progresses of Ti₃ C₂ T_x MXene are achieved in energy storage. This Review summarizes recent advances in the synthesis and electrochemical energy storage applications of Ti₃ C₂ T_x MXene including supercapacitors, lithium-ion batteries, sodium-ion batteries, and lithium-sulfur batteries. The current opportunities and future challenges of Ti₃ C₂ T_x MXene are addressed for energy-storage devices. This Review seeks to provide a rational and in-depth understanding of the relation between the electrochemical performance and the nanostructural/chemical composition of Ti₃ C₂ T_x , which will promote the further development of 2D MXenes in energy-storage applications.

Clay-Inspired MXene-Based Electrochemical Devices and Photo-Electrocatalyst: State-of-the-Art Progresses and Challenges

MXene, an important and increasingly popular category of postgraphene 2D nanomaterials, has been rigorously investigated since early 2011 because of advantages including flexible tunability in element composition, hydrophobicity, metallic nature, unique in-plane anisotropic structure, high charge-carrier mobility, tunable band gap, and favorable optical and mechanical properties. To fully exploit these potentials and further expand beyond the existing boundaries, novel functional nanostructures spanning monolayer, multilayer, nanoparticles, and composites have been developed by means of intercalation, delamination, functionalization, hybridization, among others. Undeniably, the cutting-edge developments and applications of clay-inspired 2D MXene platform as electrochemical electrode or photo-electrocatalyst have conferred superior performance and have made significant impact in the field of energy and advanced catalysis. This review provides an overview of the fundamental properties and synthesis routes of pure MXene, functionalized MXene and their hybrids, highlights the state-of-the-art progresses of MXene-based applications with respect to supercapacitors, batteries, electrocatalysis and photocatalysis, and presents the challenges and prospects in the burgeoning field.