Layered Transition Metal Carbides Research Articles

A comprehensive study on the surface property changes of antibodies on interacting with Ti3C2Tx, V2CTx, or Mo2TiC2Tx MXenes

MXenes are nanomaterials composed of layered transition metal carbides and nitridesand are considered to have considerable potential in the biomedical translation field. However, the biological and toxicological behaviours of nanomaterials (NMs) are regulated by protein-corona formation, which leads to conformational changes in proteins and impacts their biological functions. Thus, in this work, we synthesized four different MXenes (multi-layered titanium carbide (Ti3C2Tx-ML); single-layered titanium carbide (Ti3C2Tx-SL); single-layered molybdenum titanium carbide (Mo2TiC2Tx-SL); and multi-layered vanadium carbide (V2CTx-ML)) and studied their physicochemical interactions with a model protein immunoglobin G (IgG) from human serum. The conformational, thermal, and colloidal stabilities of IgG were investigated after exposing IgG to MXenes for 15 min at IgG/MXene ratios of 40:1 and 20:1. Circular dichroism (CD) spectroscopy revealed that the secondary structure of IgG underwent a concentration-dependent conformational change after exposure to all four MXenes. ζ-potential studies showed that Ti3C2Tx-ML MXene had the highest negative surface charge due to the presence of abundant fluorine (F) surface groups. However, this increased the hydrophilicity of IgG/MXene solution and eventually caused IgG aggregation and destabilization. Furthermore, Ti3C2Tx-ML MXene had a greater tendency to produce protein coronas than the other MXenes. This study describes a versatile means of examining the properties of MXenes responsible for protein coronas and lays a foundation for establishing the connection between protein corona formation and the biological functions of MXenes.

Dual-ultrasmall Sb and Sb6O13 nanodots co-anchored MXene with manipulable structural chemistry modulating bidirectional kinetics toward advanced lithium-sulfur batteries

Exfoliation and modulation of intercalated layered transition metal carbides and/or nitrides (MAX) into their derivatives (MXenes) featured with manipulable structural chemistry by remain enormous challenges toward practical applications. Herein, an extraordinary low-dimensional MXenes modulated by dual-ultrasmall Sb and Sb6O13 nanodots via in situ structural editing protocol using Lewis-basic fluorides in organic molten salts. Their original internal non-van der Waals bonds and physicochemical natures are simultaneously mediated by manipulating fluorine anions and antimony cations as chemical scissors generating into zero- and one-dimensional MXenes (MFNCTS-Z, MFNCTS-O) encapsulated by hierarchical porous N-doped carbon. Experimental and theoretical results manifest MFNCTSs as alternative dual-functional hosts toward both sulfur (S) cathode and lithium (Li) anode modulating bidirectional kinetics originated from their synergistic effect of physical confinement and chemical anchor effect accelerating polysulfides redox chemistry, and homogeneous lithium deposition. As a result, the assembled lithium-sulfur full batteries offer impressive electrochemical performances. This work paves a new avenue for developing low-dimensional MXenes by controllable structural editing strategy toward practical energy conversion and storage fields.

Enabling Stable and Low-Strain Lithium Plating/Stripping with 2D Layered Transition Metal Carbides by Forming Li-Zipped MXenes and a Li Halide-Rich Solid Electrolyte Interphase.

Two-dimensional (2D) layered materials demonstrate prominent advantage in regulating lithium plating/stripping behavior by confining lithium diffusion/plating within interlayer gaps. However, achieving effective interlayer confined lithium diffusion/plating without compromising the stability of bulk-structural and the solid electrolyte interphase (SEI) remains a considerable challenge. This paper presents an electrochemical scissor and lithium zipper-driven protocol for realizing interlayer confined lithium plating with pretty-low strain and volume change. In this protocol, lithium serves as a "zipper" to reunite the adjacent MXene back to MAX-like phase to markedly enhance the structural stability, and a lithium halide-rich SEI is formed by electrochemically removing the terminals of halogenated MXenes to maintain the stability and rapid lithium ions diffusion of SEI. When the Ti3 C2 I2 serves as the host for lithium plating, the average coulomb efficiency exceeds 97.0 % after 320 lithium plating/stripping cycles in conventional ester electrolyte. Furthermore, a full cell comprising of LiNi0.8 Mn0.1 Co0.1 O2 and Ti3 C2 I2 @Li exhibits a capacity retention rate of 73.4 % after 200 cycles even under high cathode mass-loading (20 mg cm-2 ) and a low negative/positive capacity ratio of 1.4. Our findings advance the understanding of interlayer confined lithium plating in 2D layered materials and provide a new direction in regulating lithium and other metal plating/stripping behaviors.

Enabling Stable and Low‐Strain Lithium Plating/Stripping with 2D Layered Transition Metal Carbides by Forming Li‐Zipped MXenes and a Li Halide‐Rich Solid Electrolyte Interphase

AbstractTwo‐dimensional (2D) layered materials demonstrate prominent advantage in regulating lithium plating/stripping behavior by confining lithium diffusion/plating within interlayer gaps. However, achieving effective interlayer confined lithium diffusion/plating without compromising the stability of bulk‐structural and the solid electrolyte interphase (SEI) remains a considerable challenge. This paper presents an electrochemical scissor and lithium zipper‐driven protocol for realizing interlayer confined lithium plating with pretty‐low strain and volume change. In this protocol, lithium serves as a “zipper” to reunite the adjacent MXene back to MAX‐like phase to markedly enhance the structural stability, and a lithium halide‐rich SEI is formed by electrochemically removing the terminals of halogenated MXenes to maintain the stability and rapid lithium ions diffusion of SEI. When the Ti3C2I2 serves as the host for lithium plating, the average coulomb efficiency exceeds 97.0 % after 320 lithium plating/stripping cycles in conventional ester electrolyte. Furthermore, a full cell comprising of LiNi0.8Mn0.1Co0.1O2 and Ti3C2I2@Li exhibits a capacity retention rate of 73.4 % after 200 cycles even under high cathode mass‐loading (20 mg cm−2) and a low negative/positive capacity ratio of 1.4. Our findings advance the understanding of interlayer confined lithium plating in 2D layered materials and provide a new direction in regulating lithium and other metal plating/stripping behaviors.

Broadband optical properties of Ti3C2 MXene revisited.

The exceptional optical, electrical, and mechanical capabilities of layered transition metal carbides, nitrides, and carbonitrides, called MXenes, revolutionized materials science. Among them, Ti3C2 received the most attention owing to the developed synthesis and processing methods, high conductivity, and pronounced plasmonic response. The latter, however, remains controversial with the open question of whether the peak around 800 nm has plasmonic or interband transition origin. To address this issue, we combine spectroscopic ellipsometry and transmittance results with first-principle computations. Their combination reveals that although Ti3C2 is a metal, its optical response becomes plasmonic (Re ε < 0) above 1415 nm, in contrast to the previous understanding. In addition to fundamental significance, this dual dielectric/plasmonic optical response opens a path for theranostic applications, as we demonstrated on the example of Ti3C2 nanospheres. Thus, our study revisits broadband (300-3300 nm) optical constants of Ti3C2 and broadens its application scope in photonics.

Functional MXenes: Progress and Perspectives on Synthetic Strategies and Structure-Property Interplay for Next-Generation Technologies.

MXenes are a class of 2D materials that include layered transition metal carbides, nitrides, and carbonitrides. Since their inception in 2011, they have garnered significant attention due to their diverse compositions, unique structures, and extraordinary properties, such as high specific surface areas and excellent electrical conductivity. This versatility has opened up immense potential in various fields, catalyzing a surge in MXene research and leading to note worthy advancements. This review offers an in-depth overview of the evolution of MXenes over the past 5 years, with an emphasis on synthetic strategies, structure-property relationships, and technological prospects. A classification scheme for MXene structures based on entropy is presented and an updated summary of the elemental constituents of the MXene family is provided, as documented in recent literature. Delving into the microscopic structure and synthesis routes, the intricate structure-property relationships are explored at the nano/micro level that dictate the macroscopic applications of MXenes. Through an extensive review of the latest representative works, the utilization of MXenes in energy, environmental, electronic, and biomedical fields is showcased, offering a glimpse into the current technological bottlenecks, such asstability, scalability, and device integration. Moreover, potential pathways for advancing MXenes toward next-generation technologies are highlighted.

Effect of LiCl Electrolyte Concentration on Energy Storage of Supercapacitor with Multilayered Ti3C2Tx MXene Electrodes Synthesized by Hydrothermal Etching

The development of new electrode materials for electrochemical systems for various purposes is a significant and in-demand task of scientific research. Layered transition metal carbides and nitrides, known as MXenes, show great potential for use as electrodes in electrochemical energy storage devices operating in aqueous electrolytes. In this work, a multilayer Ti3C2Tx MXene was obtained from a Ti3AlC2 precursor and studied as the electrode material of a symmetrical supercapacitor with an aqueous LiCl electrolyte. The formation of the MXene structure was confirmed by the data from X-ray phase analysis and scanning electron microscopy. The X-ray diffraction pattern showed the disappearance of the main reflections related to the Ti3AlC2 phase and the shift of the reflection peak (002) from 9.4° to 6.7°, which indicated successful etching of the Al layers from the Ti3AlC2 precursor. At electrolyte concentrations of 1, 5, 10, and 20 M, the supercapacitors demonstrated high specific capacitances of 105, 120, 126, and 151 F·g−1 at a scan rate of 5 mV·s−1. In addition, an increase in the LiCl concentration contributed to the expansion of the potential window from 0.7 to 1 V. It was shown that the contribution of the surface capacitance to the total capacitance of the electrode is about 40% and depends little on the scan rate. In addition, the symmetrical supercapacitor with 5 M electrolyte showed good cyclic stability with capacitance retention of 88% over 10,000 cycles. The parameters of the main components of the physical processes of supercapacitors based on Ti3C2Tx were determined by the method of impedance spectroscopy.

Heterostructure engineering of MoS2/Mo2CTx nanoarray via molten salt synthesis for enhanced hydrogen evolution reaction

Two-dimensional layered transition metal carbides (MXenes), have huge potential advantage for applications in hydrogen evolution reaction (HER). However, the hindered hydrogen evolution at large current densities and the instability of MXenes during HER remains major challenges. Herein, we report the MoS2/Mo2CTx nanoarray with aerophobic structure via molten salt synthesis. In situ vertical distribution of MoS2 nanoarray on the surface of Mo2CTx accelerates hydrogen gas release from the electrode, exhibiting significantly enhanced catalytic activity and stability to bare MoS2 and Mo2CTx. The MoS2/Mo2CTx nanoarray possesses excellent stability at −100 mA/cm2 for 100 h with only 3% overpotential increase. Our work provides guidance for developing high-stability MXene-based catalysts by virtue of in situ bonding between nanoarray and MXene.

Flexible and mechanically strong MXene/cellulose-lamellae sheets for electromagnetic interference shielding

MXene, two-dimensional layered transition metal carbides, nitride, or carbonitrides, have shown promise for ultrahigh electromagnetic interference (EMI) shielding in flexible electronics and aerospace due to their intrinsic metallic conductivity and mechanical strength. However, weak interfacial interactions, void microstructure defects, and oxidative degradation can leave MXene sheets in a thermodynamically metastable state, resulting in poor EMI shielding and mechanical strength. Herein, we utilized abundant hydrogen-bonded ultrafine cellulose lamella (UCL) to sequentially bridging induced densification of MXene nanosheets. This resulted in improved the tensile strength, toughness, oxidative stability, resistance to ultrasonic decomposition, and super-foldable conductivity of MXene sheets. The resulting MXene@UCL sheets (MXCS) exhibited high electrical conductivity of up to 7649 S cm−1 and ultrahigh weight-normalized shielding efficiency (SSE/t, 53003.45 dB∙cm2 g−1), making them mechanically strong and highly conductive. The MXCS material has a tensile modulus of up to 10.9 ± 0.7 GPa and provides excellent weight-normalized shielding efficiency. Simultaneously, it is capable of enduring 100,000 repetitions of folding without experiencing any damage to its construction or fluctuations in conductivity. Furthermore, high-strength scalable MXCS sheets can be produced using doctor blade casting, commercial resin bonding, and aerogel calendering methods, without compromising their performance. This has significant scientific and practical application potential.

Covalent Organic Frameworks (COFs)/MXenes Heterostructures for Electrochemical Energy Storage

Covalent organic frameworks (COFs), a distinguished class of porous materials exhibiting precise modularity and crystallinity, and two-dimensional (2D) MXenes, a highly conductive, atomic layered transition metal carbides or nitrides or carbonitrides, are the two fascinating classes of advanced materials that have been intensively researched for energy storage recently. Thanks to the high surface area and porosity of COFs and high electrical conductivity coupled with highly redox active surfaces of MXenes, they have shown great potential in the energy storage applications such as batteries and supercapacitors. However, their electrochemical performance is limited by several inherent issues such as the restacking tendency of MXene sheets and low conductivity of COFs, when applied individually. Combining MXenes and COFs into heterostructures and their use as a single electrode helps in overcoming challenges for improving the energy storage capability. The current perspective intends to provide an overview of designing such COF/MXene heterostructures in the context of the energy storage applications. The research gaps that exist in designing COF/MXene heterostructures and the governing factors for improving the energy storage capability have also been highlighted as opportunities.

Chemical scissor-mediated structural editing of layered transition metal carbides.

Intercalated layered materials offer distinctive properties and serve as precursors for important two-dimensional (2D) materials. However, intercalation of non-van der Waals structures, which can expand the family of 2D materials, is difficult. We report a structural editing protocol for layered carbides (MAX phases) and their 2D derivatives (MXenes). Gap-opening and species-intercalating stages were respectively mediated by chemical scissors and intercalants, which created a large family of MAX phases with unconventional elements and structures, as well as MXenes with versatile terminals. The removal of terminals in MXenes with metal scissors and then the stitching of 2D carbide nanosheets with atom intercalation leads to the reconstruction of MAX phases and a family of metal-intercalated 2D carbides, both of which may drive advances in fields ranging from energy to printed electronics.

Additive-free Electrophoretic-deposited Ti3AlC2 MAX phase Li-ion battery anode

• We demonstrated its excellent cycling stability and reversible recovery for MAX anode. • Delamination process activates both faradic and non-faradaic processes. • Pseudocapacitive redox reactions led to reversible battery charging/discharging cycles. M n+1 AX n (MAX, n=1, 2, 3…) is the precursor of Mxene, which is two-dimensional layered transition metal carbides and nitrides. The two-dimensional Mxene layers are fabricated through selective etching of element “A”. To probe the intrinsic electrochemical properties of Ti 3 AlC 2 MAX phase as Li-ion battery anode, we fabricated an additive-free electrophoretically-deposited MAX phase anode electrode. As demonstrated in this report, the MAX phase is highly reversible during charging and discharging cycles, as a result of pseudocapacitive redox reactions caused by delamination of Ti 3 AlC 2 nanolayer aggregates into nanosheets during delithiation. In the present study, we demonstrate excellent cycling reversibility for a Ti 3 AlC 2 MAX phase electrode electrophoretically deposited without additives with a specific capacity of ∼120 mAh/g after cycles up to 10 C-rate.

Zr2SeB and Hf2SeB: Two new MAB phase compounds with the Cr2AlC-type MAX phase (211 phase) crystal structures

The ternary or quaternary layered compounds called MAB phases are frequently mentioned recently together with the well-known MAX phases. However, MAB phases are generally referred to layered transition metal borides, while MAX phases are layered transition metal carbides and nitrides with different types of crystal structure although they share the common nano-laminated structure characteristics. In order to prove that MAB phases can share the same type of crystal structure with MAX phases and extend the composition window of MAX phases from carbides and nitrides to borides, two new MAB phase compounds Zr2SeB and Hf2SeB with the Cr2AlC-type MAX phase (211 phase) crystal structure were discovered by a combination of first-principles calculations and experimental verification in this work. First-principles calculations predicted the stability and lattice parameters of the two new MAB phase compounds Zr2SeB and Hf2SeB. Then they were successfully synthesized by using a thermal explosion method in a spark plasma sintering (SPS) furnace. The crystal structures of Zr2SeB and Hf2SeB were determined by a combination of the X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The lattice parameters of Zr2SeB and Hf2SeB are a = 3.64398 Å, c = 12.63223 Å and a = 3.52280 Å, c = 12.47804 Å, respectively. And the atomic positions are M at 4f (1/3, 2/3, 0.60288 [Zr] or 0.59889 [Hf]), Se at 2c (1/3, 2/3, 1/4), and B at 2a (0, 0, 0). And the atomic stacking sequences follow those of the Cr2AlC-type MAX phases. This work opens up the composition window for the MAB phases and MAX phases and will trigger the interests of material scientists and physicists to explore new compounds and properties in this new family of materials.

MXene-based flexible sensors: A review

MXenes are an emerging family of two-dimensional (2D) materials which exhibits unique characteristics such as metal-like thermal and electrical conductivity, huge surface area, biocompatibility, low toxicity, excellent electrochemical performance, remarkable chemical stability, antibacterial activity, and hydrophilicity. Initially, MXene materials were synthesized by selectively etching metal layers from MAX phases, layered transition metal carbides, and carbonitrides with hydrofluoric acid. Multiple novel synthesis methods have since been developed for the creation of MXenes with improved surface chemistries using non-aqueous etchants, molten salts, fluoride salts, and various acid halogens. Due to the promising potential of MXenes, they have emerged as attractive 2D materials with applications in various fields such as energy storage, sensing, and biomedical. This review provides a comprehensive overview of MXenes and discusses the synthesis and properties of MXenes, including the methods of etching, delamination, and modification/functionalization, as well as the electrical properties of MXenes. Following this, the recent advances in the development of various MXene-based sensors are presented. Finally, the challenges and opportunities for future research on the development of MXenes-based sensors are discussed.

Thermal Properties of MXenes and Relevant Applications.

The properties and applications of MXenes (a family of layered transition metal carbides, nitrides, and carbonitrides) have aroused enormous research interests for a decade since the successful synthesis of few-layer transition metal carbides in 2011. Though MXenes, as the building blocks, have already been applied in various fields (such as wearable electronics) owing to the distinctive optical, mechanical and electrical properties, their thermal stability and intrinsic thermal properties were less thoroughly investigated compared to other characteristics in early reports. The pioneering theoretical prediction of the thermoelectric nature of MXenes was performed in 2013 while the first experiment-based report concerning the degradation behavior of the 2D structure at elevated temperatures in a controlled atmosphere was published in 2015, followed by numerous discoveries regarding the thermal properties of MXenes. Herein, after a brief description of the synthesis, this Review summarized the latest insights into the thermal stability and thermophysical properties of MXenes, and further associated these unique properties with relevant applications by multiple examples. Finally, current hurdles and challenges in this field were provided along with some advices on potential research directions in the future.

Applications of 2D MXenes for Electrochemical Energy Conversion and Storage

As newly emerged 2D layered transition metal carbides or carbonitrides, MXenes have attracted growing attention in energy conversion and storage applications due to their exceptional high electronic conductivity, ample functional groups (e.g., -OH, -F, -O), desirable hydrophilicity, and superior dispersibility in aqueous solutions. The significant advantages of MXenes enable them to be intriguing structural units to engineer advanced MXene-based nanocomposites for electrochemical storage devices with remarkable performances. Herein, this review summarizes the current advances of MXene-based materials for energy storage (e.g., supercapacitors, lithium ion batteries, and zinc ion storage devices), in which the fabrication routes and the special functions of MXenes for electrode materials, conductive matrix, surface modification, heteroatom doping, crumpling, and protective layer to prevent dendrite growth are highlighted. Additionally, given that MXene are versatile for self-assembling into specific configuration with geometric flexibility, great efforts about methodologies (e.g., vacuum filtration, mask-assisted filtration, screen printing, extrusion printing technique, and directly writing) of patterned MXene-based composite film or MXene-based conductive ink for fabricating more types of energy storage device were also discussed. Finally, the existing challenges and prospects of MXene-based materials and growing trend for further energy storage devices are also presented.

MXene/Carbon Nanotube Hybrids: Synthesis, Structures, Properties, and Applications.

Since the successful preparation of few-layer transition metal carbides from three-dimensional MAX phases in 2011, MXenes (known as a family of layered transition metal carbides, nitrides, and carbonitrides) have been intensively studied. Though MXenes have been adopted as active materials in many applications, issues including aggregation and restacking are likely to hamper their potential applications. In order to address these prevailing challenges, the concept of MXene/carbon nanotube (CNT) hybrids was proposed initially in 2015, where CNTs were incorporated as the spacers and conductive additives. Ever since, MXene/CNT hybrids with different architectures have been synthesized by a number of methods and applied in numerous fields. Herein, after the discussion about general synthesis approaches, architectures, and properties of the hybrids, this Review summarized the recent advances in the application of MXene/CNT hybrids in energy storage devices, sensors, electrocatalysis, electromagnetic interference shielding, and water treatment, in which the function of individual components was clarified. In the end, the current research trend in this field were discussed and several technical issues were highlighted along with some suggestions on future research directions.

Prediction of high spin polarization and perpendicular magnetic anisotropy in two dimensional ferromagnetic Mn2CXX’ (X, X′=F, Cl, Br, I) Janus monolayers

Two dimensional layered transition metal carbides and nitrides, owing to their unique electronic properties, have potential applications in novel low-dimensional spintronic devices. However, only a few materials with half metallic and easy axis in perpendicular direction make possible for practical applications in spintronics. Here, the electronic structure and magnetic anisotropy of Mn2CXX’ (X, X' = F, Cl, Br, I) Janus monolayers are investigated by first-principles calculations. It is found that the Mn2CXX′ Janus monolayers are half metallic, showing a high spin polarization at Fermi level. The magnetic anisotropy of Mn2CXX′ monolayers can be modulated by replacing the adsorbed atoms. Mn2CFCl, Mn2CClI and Mn2CClBr show easy axis in perpendicular direction, while the easy axis of Mn2CFBr is in-plane direction. When biaxial strains are −2%, ±4 % and −6%, the easy axis direction of Mn2CClI changes from out-of-plane to in-plane, where the total magnetic anisotropy of I atom can be regulated. The easy axis in in-plane direction comes from the hybridization between I-pz and I-px orbital. However, the easy axis of Mn2CClI maintains perpendicular direction at biaxial strains of 2 % and 6 %. The Mn2CXX′ monolayers with half metallicity and easy axis in perpendicular direction have the potential applications in spintronic devices.

Ten Years of Progress in the Synthesis and Development of MXenes.

Since their discovery in 2011, the number of 2D transition metal carbides and nitrides (MXenes) has steadily increased. Currently more than 40 MXene compositions exist. The ultimate number is far greater and in time they may develop into the largest family of 2D materials known. MXenes' unique properties, such as their metal-like electrical conductivity reaching ≈20000 S cm-1 , render them quite useful in a large number of applications, including energy storage, optoelectronic, biomedical, communications, and environmental. The number of MXene papers and patents published has been growing quickly. The first MXene generation is synthesized using selective etching of metal layers from the MAX phases, layered transition metal carbides and carbonitrides using hydrofluoric acid. Since then, multiple synthesis approaches have been developed, including selective etching in a mixture of fluoride salts and various acids, non-aqueous etchants, halogens, and molten salts, allowing for the synthesis of new MXenes with better control over their surface chemistries. Herein, a brief historical overview of the first 10 years of MXene research and a perspective on their synthesis and future development are provided. The fact that their production is readily scalable in aqueous environments, with high yields bodes well for their commercialization.

Acoustomicrofluidic Synthesis of Pristine Ultrathin Ti3C2Tz MXene Nanosheets and Quantum Dots.

The conversion of layered transition metal carbides and/or nitrides (MXenes) into zero-dimensional structures with thicknesses and lateral dimensions of a few nanometers allows these recently discovered materials with exceptional electronic properties to exploit the additional benefits of quantum confinement, edge effects, and large surface area. Conventional methods for the conversion of MXene nanosheets and quantum dots, however, involve extreme conditions such as high temperatures and/or harsh chemicals that, among other disadvantages, lead to significant degradation of the material as a consequence of their oxidation. Herein, we show that the large surface acceleration-on the order of 10 million g's-produced by high-frequency (10 MHz) nanometer-order electromechanical vibrations on a chip-scale piezoelectric substrate is capable of efficiently nebulizing, and consequently dimensionally reducing, a suspension of multilayer Ti3C2Tz (MXene) into predominantly monolayer nanosheets and quantum dots while, importantly, preserving the material from any appreciable oxidation. As an example application, we show that the high-purity MXene quantum dots produced using this room-temperature chemical-free synthesis method exhibit superior performance as electrode materials for electrochemical sensing of hydrogen peroxide compared to the highly oxidized samples obtained through conventional hydrothermal synthesis. The ability to detect concentrations as low as 5 nM is a 10-fold improvement to the best reported performance of Ti3C2Tz MXene electrochemical sensors to date.