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. 2024 Oct 31;146(45):31159–31168. doi: 10.1021/jacs.4c11111

Synthesis of Three Isoelemental MXenes and Their Structure–Property Relationships

Marley Downes 1, Christopher E Shuck 1,2, Ruocun John Wang 1, Paweł Piotr Michałowski 3, Jonathan Shochat 1, Danzhen Zhang 1, Mikhail Shekhirev 1, Yizhou Yang 1, Nestor J Zaluzec 4, Raul Arenal 5,6,7, Steven J May 1, Yury Gogotsi 1,*
PMCID: PMC11565644  PMID: 39479877

Abstract

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The MXene family has rapidly expanded since its discovery in 2011 to include nearly 50 unique MXenes, not accounting for solid solutions and diverse surface terminations. However, a question raised since their discovery has been: What is the effect of n? In other words, how does the number of layers affect the MXene properties? To date, no direct study of the impact of n has been conducted due to the lack of isoelemental MXene compositions spanning more than two n values. Herein, we report on a system of three MXenes with identical M-site chemistries, (Mo2/3V1/3)n+1CnTx (n = 1, 2, and 3), allowing for the study of MXene structure–property relationships across n, for the first time. Chemical analysis of the samples shows complete and partial ordering of the M-elements in the n = 2 and 3 samples, respectively. We show that sample stability gradually evolves as n is increased from 1 to 3, while electronic and electrochemical properties exhibit more significant changes in going from n = 1 to 2 than from n = 2 to 3.

Introduction

MXenes are a large class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides with the general formula of Mn+1XnTx, where M is an early transition metal (Ti, V, Mo, Nb, etc.), X is C and/or N, Tx represents the surface groups (typically −O, −OH, −F, and −Cl, but will not be continually expressed for clarity), and n is an integer 1–4 that represents the number of X-site atomic layers.1,2 Because MXenes are readily scalable,3,4 easily processable,5−7 and have highly desirable optical,8−13 electrical,9,12,14−16 and mechanical properties,16−19 they have been widely explored in fields such as electrochemical energy storage,8,20−23 electromagnetic interference (EMI) shielding,24−26 and biomedicine.27−29 Nearly 50 stoichiometric MXenes have been synthesized to date, including multiple structures, such as ordered double transition metal MXenes,30,31 in-plane ordered MXenes,32−34 high-entropy MXenes,35,36 and solid-solution MXenes,2,12,37−39 illustrating the variety of MXene structures that already exist. There are also numerous solid solutions on M and X sites, as well as MXenes with diverse surface terminations reported. However, considering how diverse the MXene family is, a question that has been posed since MXenes were first discovered remains unanswered: how does n affect MXene properties?

Experimentally, this poses a challenge: Ti2C and Ti3C2 exist, but not Ti4C3; Nb2C and Nb4C3, but not Nb3C2; Mo2TiC2 and Mo2Ti2C3, but not (MoTi)2C. This trend has been repeated across all MXene chemistries discovered thus far, where no series of MXene compositions with the same transition metals currently exist. Despite the lack of a directly comparable sample set, there have been numerous attempts to study the impact of n on different functional properties. For instance, increasing n increases the thermal stability of the MXene. This trend has been observed across M—with Ti3C2 having higher thermal stability than Nb2C and Mo2C.40 Thicker MXenes have also shown increased colloidal stability over their thinner counterparts, as shown by the higher oxidative stability of Ti3C2 over Ti2C, and Nb4C3 over Nb2C.41,42 However, many of the approaches used to improve the stability of Ti3C2, including cooling, bubbling with inert gas, minimizing the volume of headspace in the bottle, and others, can also be applied to improve the stability of Ti2C.41 It is not easy to extrapolate and make predictions based on 2 data points. Thus, further studies are needed to understand the direct influence of n on the atomic structure of MXenes (e.g., Ti and C vacancy formation energies) as well as the physicochemical behavior of MXene nanosheets (e.g., surface acidity, charge, and zeta potential).

Once again, when the application-driven properties, are examined, a strong dependence on n is observed. In terms of the mechanical properties, increasing n will result in increased rigidity and mechanical strength.17,18,43 Higher n MXenes have been shown to exhibit higher electronic conductivity and, thus, higher electromagnetic interference (EMI) shielding in a broad frequency range, making them more promising for EMI shielding when normalized by the film thickness.25 The optical properties of MXenes have shown a dependency on both M and n, with blue shifts of the wavelength of the absorption peak thought to occur with increasing free carrier concentration of the MXene.11 Even considering these studies, experimental determination of the effect of n is severely limited, and with only two points, it is difficult to determine any trends. Additionally, many studies focus only on Ti3C2 and its derivatives, largely due to its greatly improved synthesis and popularity across research fields. Computationally, there have been several studies focused on this issue; it is much easier to vary n in theoretical models than in experimentally. Many of these studies have shown that the MXene thickness significantly affects their electronic properties.44,45 There have also been theoretical studies on the mechanical properties,43,46 thermal stability,47 oxidative stability,48 and others.49 However, experimental validation of these results has been limited due to MXene availability and the differing synthesis methods utilized across research groups, preventing true comparisons of results.

Herein, we use the (Mo2/3V1/3)n+1Cn (n = 1, 2, 3) system as a model to study the effect of n on MXene properties. The syntheses of each MAX phase, (Mo2/3V1/3)2AlC, (Mo2/3V1/3)3AlC2, and (Mo2/3V1/3)4AlC3 were synthesized with no other MAX impurities, followed by topochemical MXene synthesis and delamination to produce the corresponding (Mo2/3V1/3)2C, (Mo2/3V1/3)3C2, and (Mo2/3V1/3)4C3. We provide structural and chemical characterizations of these materials using high-resolution scanning transmission electron microscopy (HRSTEM) imaging, STEM energy-dispersive X-ray spectroscopy (STEM-EDS), X-ray diffraction (XRD), and secondary ion mass spectrometry (SIMS) and explore their colloidal, optical, and electronic properties. Finally, the electrochemical behavior of these MXenes is studied to gain insights into their accessible voltage windows, cycling stability, and capacitance.

Experimental Section

Synthesis of (Mo2/3V1/3)n+1AlCn MAX Phases

Molybdenum (Thermo Fisher Scientific, ∼250 mesh, 99.9% metals basis), vanadium (Thermo Fisher Scientific, ∼325 mesh, 99.5%), vanadium(III) oxide (Alfa Aesar, 99.2%), aluminum (Thermo Fisher Scientific, ∼325 mesh, 99.5% (metals basis)), and graphite (Alfa Aesar, ∼325 mesh, 99%) powders were combined in the appropriate atomic ratios. For all powders, the Mo:V ratio was held constant at 2/3:1/3. For (Mo2/3V1/3)2AlC the powders were mixed in a MoV:Al:C = 2:1.1:0.9 molar ratio; for (Mo2/3V1/3)3AlC2 the ratio was MoV:Al:C = 2:1:1.1:1.8 + 5% V2O3; and for (Mo2/3V1/3)4AlC3 the ratio was MoV:Al:C = 4:1.1:2.7. After mixing the powders were ball-milled at 70 rpm for 12 h at a ratio of 1:2 = powder:yttria-stabilized zirconia (YSZ) balls by mass. The mixtures were then heated in alumina crucibles at a 3 °C min–1 ramp (the same rate was used for cooling) under 350 cm3 min–1 flowing argon in a tube furnace (Carbolite Gero). To synthesize (Mo2/3V1/3)2AlC and (Mo2/3V1/3)3AlC2, the powders were held at 1550 °C for 2 h. To synthesize (Mo2/3V1/3)4AlC3, the powders were held at 1600 °C for 4 h.

The sintered materials were then ground to powder using a combination of CNC mill and mortar and pestle. The resulting MAX-phases were stirred in 9 M HCl for 24 h to dissolve intermetallic impurities, then washed to neutral pH by vacuum filtration with water. The powders were collected and dried overnight at room temperature under vacuum. The powders were then sieved using stainless-steel meshes to obtain a particle size of <45 μm for uniform etching.

Synthesis of (Mo2/3V1/3)n+1Cn MXenes

For uniformity in the synthesis method, all of the studied MAX phases were etched via the same method. For the synthesis of multilayer MXenes, 5 g of HCl-washed MAX phase powders were slowly added to a solution of 60 mL of HF (48–51%, Arcos Organics), 60 mL of HCl (12 M, Fisher Chemical), and 30 mL of deionized water while being stirred with a polytetrafluoroethylene (PTFE)-coated stir bar at 300 rpm. The reaction proceeded for 5 days at 35 °C. After the etching reaction completion, the samples were washed via a series of cycles involving centrifugation at 3500 rpm (2550 rcf) for 10 min, decanting the acidic supernatant, and redispersion of the sediment using deionized (DI) water until the supernatant reached a neutral pH.

The multilayer MXene powder was then collected and used to make a 5 wt % tetramethylammonium hydroxide solution (TMAOH, 25 wt % Sigma-Aldrich). The delamination intercalation reaction proceeded for 24 h at room temperature (25 °C). TMAOH was then washed out through a series of cycles involving centrifugation at 10,000 rpm (12,850 rcf) for 10 min, discarding the supernatant, and redispersing the sediment with DI water. This process was repeated until the supernatant had a pH < 8. From here, the sediment was redispersed in DI water, shaken for 30 min, and then centrifuged at 3500 rpm (2550 rcf) for 30 min. The resulting black supernatant was carefully decanted to collect the delaminated MXene.

To obtain free-standing films, the delaminated MXene flake colloid was filtered via vacuum-assisted filtration through a porous membrane (Celgard 3501, 64 nm pore size, polypropylene). The resulting films were separated from Celgard and stored in a vacuum desiccator at room temperature.

Structural Characterization

Rigaku SmartLab (40 kV/30 mA) and MiniFlex (40 kV/15 mA) X-ray diffractometers were used with Ni-filtered Cu Kα radiation. The step size of the scan was 0.01°, with a step duration of 4 s for MAX-phase powders and 2 s for films. Rietveld refinement of the MAX phases was done with the GSAS II Python code.

Scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS) measurements were conducted using two aberration-corrected microscopes from Thermo Fisher Scientific (USA), the Argonne PicoProbe Analytical Electron Microscope (AEM)50 [A] and the Titan Low-Base microscope. All these works have been performed at 300 kV employing high-angle annular dark field (HAADF)-STEM imaging. EDS was developed using the ANL XPAD system, having access to its ultrasensitivity 4.5 sR detector. During STEM-EDS acquisitions, the electron beam current on the samples was <110 pA.

All SIMS experiments were performed on the CAMECA IMS SC Ultra instrument with cesium ions as primary ions. To reach the atomic depth resolution, a series of modifications of the measurement procedure was applied, which included high incident angle bombardment (75°), ultralow impact energy (100 eV), in situ ion polishing, optimization of extraction parameters, super cycle, and advanced beam positioning. The details of each concept were presented in the previous article.51 Deconvolution and calibration protocols were applied to quantify the results and determine the exact composition of each atomic layer with ±1% precision.52

Electrochemistry

For electrochemical characterization, PFA Swagelok cells were used to construct three-electrode cells. The current collector was a glassy carbon electrode, while the free-standing MXene films were used as the working electrodes (electrode surface area 7.060 mm2). 95 wt % Activated carbon (YP-50) and 5 wt % polytetrafluoroethylene (PTFE) were used to construct the counter electrode. The separator was a Celgard 3501. The reference electrode used was Hg/Hg2SO4 in saturated K2SO4. Three M H2SO4 (degassed with Argon, 1 h) was used as the electrolyte for all electrochemical measurements. All electrochemical cells were precycled at 20 mV s–1 for 100 cycles before testing. Specific capacitance was calculated from the anodic CV scans according to

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where C is the specific capacitance, i is the measured current as a function of time (t), m is the mass of the working electrode, and ΔV is the potential window.

Optical Properties and Stability

UV–vis–NIR spectra were collected using a Thermo Scientific Evolution 201 spectrometer in transmission mode from 200 to 1000 nm using a blank cuvette with DI water as the background. UV–vis–NIR was conducted from 200 to 1000 nm with an integration time of 1 s (Evolution 201, Thermo Fisher Scientific, USA). When the change in absorbance over time was quantified, the absorbance values were extracted from the wavelengths marked in Figure S9.

Magnetotransport Measurements

The resistivity and MR behavior of the films were measured with a Quantum Design EverCool II physical property measurement system (PPMS). For all measurements, sections of the freestanding MXene films were wired into a four-point probe geometry with silver paint, and the data was recorded from 10 to 300 K at <5 Torr helium pressure. Resistivity (ρ) was calculated via the following equation:

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where R is the resistance (in Ohms), d is the sample thickness (in cm), and α is a geometric correction factor (where a and b are the length and width of the rectangular film, respectively, and s is the distance between the probes). The electrical conductivity of the films was measured both with a four-point probe (ResTest, Jandel Engineering Ltd., Bedfordshire, U.K., probe distance 1 mm, average of 5 points across the film) and with the PPMS system. Magnetoresistance (MR) measurements were performed with the magnetic field applied out-of-plane to the MXene films. MR is defined as

graphic file with name ja4c11111_m003.jpg

where ρH and ρH=0 are the resistivities in the presence and absence of the applied magnetic field (H), respectively.

Results and Discussion

Synthesis of the (Mo2/3V1/3)n+1Cn System

To synthesize a family of MAX phases with the composition (Mo2/3V1/3)n+1AlCn, the Mo:V ratio was held constant at Mo:V = 2/3:1/3 based on the previously reported (Mo2/3V1/3)4AlC3 MAX phase.38 While (Mo2/3V1/3)3AlC2 has been previously reported, it has yet to be synthesized as a pure MAX phase.37,53 Herein, the addition of a small amount of V2O3 promotes the synthesis of (Mo2/3V1/3)3AlC2 free of other MAX phase impurities. All synthesized MAX phases were HCl-washed in 9 M HCl (Figure S1) and analyzed via XRD as a confirmation of synthesis (Figure 1). Through Rietveld refinement (Figure S2), the lattice parameters of each MAX phase were determined. For (Mo2/3V1/3)2AlC, the a-lattice parameter was 2.97 Å with a c-lattice of 13.34 Å. For (Mo2/3V1/3)3AlC2, the a-lattice parameter was also 2.97 Å with a c-lattice of 18.40 Å. For (Mo2/3V1/3)4AlC3, the a-lattice parameter was 2.99 Å with a c-lattice of 23.21 Å. There is a clear dependency of the c-lattice on n, as increasing n results in an increase in the c-lattice parameter by ∼5 Å per integer value of n. This trend is observed in other MAX phases as well; for example, Ti2AlC (13.4 Å) and Ti3AlC2 (18.4 Å); Nb2AlC (13.9 Å) and Nb4AlC3 (24.0 Å).25 However, the a-lattice parameter does not exhibit this dependence on n. Apart from the MAX phases, intermetallic and carbide impurities were present in (Mo2/3V1/3)2AlC and (Mo2/3V1/3)3AlC2, and to a lesser extent (Mo2/3V1/3)4AlC3 (Figure S2). Notably, the relative intensity of the (002) peak in the n = 1 sample is much greater than that of the n = 2 and 3 samples. This is common in Mo-based MXenes, where the low atomic scattering factor of Mo, in combination with the ordered structure, results in a lower intensity of the characteristic (002) peak.30,38

Figure 1.

Figure 1

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X-ray diffraction (XRD) patterns of the phase pure (Mo2/3V1/3)n+1AlCn MAX phases and the single-layer (Mo2/3V1/3)n+1Cn MXene family. For the MAX phase patterns, the dashed line aligns with the (002) peak of the MAX phase for n = 1, 2, and 3, showing that the (002) of each MAX phase does not overlap with the other patterns. Inset pictures show the delaminated films corresponding to each MXene (Ø = 47 mm).

As a result of the removal of the A-layer during etching and subsequent delamination of the flakes, the (002) peak of the MAX phases shifts to lower 2θ to indicate the expansion of the c-lattice parameter. As with the MAX phases, the c-lattice parameter increases by approximately 5 Å as n increases. The broadening of the peaks is the result of the semirandom alignment of the flakes in the free-standing film. The lack of MAX phase peaks in the film XRD patterns indicates successful conversion to the MXene phase from the MAX phase precursors during synthesis. As typical with MXene XRD patterns, only the (00l) peaks are present. While MAX phases show an increased number of (002) reflections as n increases, this trend does not necessarily apply to the delaminated MXene films due to the in-plane alignment of the flakes.16

Structural Analysis of the (Mo2/3V1/3)n+1Cn System

Microscopic analysis of the (Mo2/3V1/3)n+1Cn system was conducted via HRSTEM imaging to confirm the number of layers associated with each MAX phase and corresponding MXene. As can be seen in Figure 2, the MAX phases exhibit uniform layering of the MXene unit cell sandwiched by the A-layer, confirming the Mn+1AXn structure characteristic of MAX phases. After etching, the A-layer is removed, resulting in separated MXene layers, some of which exhibit slight buckling. Interestingly, (Mo2/3V1/3)3C2 exhibits evidence of out-of-plane ordering of Mo and V observable as a difference in brightness between the outside and inside layers on the MXene unit cell. STEM energy-dispersive X-ray Spectroscopy (EDS) was utilized to investigate the ordering within the lattices, but electron beam damage limitations prevented accurate determination of ordering (Figures S3–S8 and Table S1).

Figure 2.

Figure 2

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High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images of the (Mo2/3V1/3)n+1Cn system showing cross-sectional images of the MAX phases and Multilayer (ML) MXenes. (A) (Mo2/3V1/3)2AlC MAX phase and (B) ML (Mo2/3V1/3)2C MXene showing two layers of transition metals and the disappearance of the A-layer after etching. (C) (Mo2/3V1/3)3AlC2 MAX phase and (D) ML (Mo2/3V1/3)3C2 MXene show evidence of atomic ordering due to the brighter outer layers of the MXene unit. (E) (Mo2/3V1/3)4AlC3 MAX phase and (F) ML (Mo2/3V1/3)4C3 MXene.

To confirm the possibility of Mo and V ordering within the surface and subsurface metal layers, secondary ion mass spectrometry (SIMS) was performed on (Mo2/3V1/3)3AlC2 and (Mo2/3V1/3)4AlC3 but not (Mo2/3V1/3)2AlC since the latter does not have subsurface metal layers. Confirming the results in Figure 2, (Mo2/3V1/3)3AlC2 displays ordering on the M-site, with Mo occupying the outer layers and V in the inner layer (Figure 3A). Interestingly, (Mo2/3V1/3)4AlC3 exhibits preferential site occupancy also, with Mo residing primarily in the outer layers and V in the inner layers (Figure 3B). The presence of order in this system is likely due to the large size difference between Mo and V, which results in the favorable separation of the atoms.54 The SIMS analysis also reveals that (Mo2/3V1/3)3AlC2 and (Mo2/3V1/3)4AlC3 are both oxycarbides with ∼20% of the X-site occupied by oxygen (Table S2). While many MAX phases (and MXenes) are oxycarbides due to unoptimized synthesis, the oxycarbide nature of these MAX phases may be attributed to the use of vanadium powders during synthesis, which has the propensity to oxidize.51 While this SIMS analysis focuses on the MAX phase, further studies of this system should extend the analysis to the MXene composition including identification of the surface terminations.

Figure 3.

Figure 3

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Depth profiles of atomic concentrations obtained by secondary ion mass spectrometry (SIMS) measurements of (A) (Mo2/3V1/3)3AlC2 and (B) (Mo2/3V1/3)4AlC3 with accompanying crystal structures. The atoms in the structures are colored according to the concentration of each element measured via SIMS.

Optical Properties and Stability

The stability of MXenes is a highly researched topic, with studies attempting to understand the mechanisms behind MXene hydrolysis and oxidation,55 or to improve MXene’s colloidal stability through improvements in synthesis techniques.56 While many techniques, such as chromatography, can be used to track the decomposition process, UV–vis spectroscopy is most commonly used, providing an ability to compare between MXenes of different compositions.57 To monitor the decomposition behavior of the (Mo2/3V1/3)n+1Cn MXenes over time, dilute single-layer solutions in water were stored at ambient temperature in air, and their absorbance was measured over time in accelerated decomposition studies (Figure 4). Consistently, the (Mo2/3V1/3)n+1Cn system exhibits one broad extinction peak in the UV–vis–NIR spectrum that appears to shift to lower wavelengths with increasing n, though further studies are required to properly interpret the spectrum (Figure S9). The stability was quantified by fitting the change in absorbance with an exponential decay function; from these fittings, the time constant (τ) of decay can be extracted, which for (Mo2/3V1/3)2C is 3.0 days, for (Mo2/3V1/3)3C2 is 3.3 days, and for (Mo2/3V1/3)4C3 is 5.6 days. This data establishes a trend of higher n MXenes being more stable than their counterparts.2,58 This trend is seen in other MXenes, as Ti3C2 is more stable than Ti2C, and Nb4C3 is more stable than Nb2C.41,42,55 Therefore, it is likely that increasing n results in increased colloidal stability of the MXene.

Figure 4.

Figure 4

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Accelerated stability measurements of the (Mo2/3V1/3)n+1Cn system. (A) Single-layer MXene suspended in water for stability measurements. (B) Solution stability of the MXene-in-water solutions. The dashed lines represent the fitted exponential decay function f(x) = y0 + Ae–x/τ where y0 is the offset value, A is the amplitude, and τ is the time constant. The samples were stored in air at ambient temperature in the dark.

Electronic Transport

The (Mo2/3V1/3)n+1Cn family provides a unique opportunity to directly investigate the role of n in macroscopic electronic transport. As seen in Figure 5A, the transport behavior of the n = 1 sample differs significantly from that of the n = 2 and 3 materials. (Mo2/3V1/3)3C2 and (Mo2/3V1/3)4C3 exhibit resistivity that is orders of magnitude less than (Mo2/3V1/3)2C (Figure S10). This results in (Mo2/3V1/3)2C having the lowest conductivity of the three measured MXenes (3.5 S cm–1, compared to 490 S cm–1 for (Mo2/3V1/3)3C2, and 300 S cm–1 for (Mo2/3V1/3)4C3, measured at 300 K; see Table S3). Strikingly, the resistivity of (Mo2/3V1/3)3C2 and (Mo2/3V1/3)4C3 displays a minimal temperature dependence behavior, which is typical for disordered metals. In contrast, the resistivity of (Mo2/3V1/3)2C increases by over a factor of 104 on cooling from 300 to 50 K. This behavior is consistent with previous reports of Mo-based MXenes. In Mo1.33C, a dρ/dT < 0 spanning orders of magnitude of resistivity was observed, while in Mo2TiC2 and Mo2Ti2C3, behavior similar to our n = 2 and 3 samples was reported.59,60 The general consistency of the transport trends as a function of n highlights the importance of having a subsurface M-site layer for maintaining low resistivity (<0.01 Ω cm) down to low temperatures. It is likely that the structure of M2X MXenes results in lower conductivity because all metal layers are bound to strongly electronegative surface functional groups (−O and −F) that decrease the contribution from metal orbitals to the density of states near the Fermi edge.44 This trend is also observed in Ti2C (∼1600 S cm–1) vs Ti3C2 (>20,000 S cm–1), Nb2C (∼5 S cm–1) vs Nb4C3 (∼75 S cm–1), and V2C (∼1250 S cm–1) vs V4C3 (1350 S cm–1).25,61,62

Figure 5.

Figure 5

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Electronic properties of the (Mo2/3V1/3)n+1Cn system. Resistivity (ρ) versus Temperature behavior of (A) all (Mo2/3V1/3)n+1Cn MXenes plotted on the log scale. The thermal hysteresis loop present after 250 K can be attributed to intercalated water. (B) Magnetoresistance at 10 K of (Mo2/3V1/3)3C2 and (Mo2/3V1/3)4C3. Although measurements were attempted, no data at 10 K could be obtained from (Mo2/3V1/3)2C as it was too insulating.

To further investigate the transport mechanisms, the magnetoresistance (MR) of the samples was measured at 10 K. As seen from Figure 5B, the measured MXenes have positive MR dependence, common to Mo-MXenes but in contrast to Ti3C2 and Cr2TiC2, which exhibit a negative dependence.37,63,64 However, the positive MR measured in (Mo2/3V1/3)3C2 and (Mo2/3V1/3)4C3 does not follow a simple H2 dependence as expected for nonmagnetic metals. Given that metallic MXenes derived largely from 3d transition metals exhibit negative MR while 4d-derived MXenes exhibit positive MR, we speculate that spin–orbit coupling may play a central role in the low-temperature magnetotransport behavior, as has previously been established in ultrathin metals that exhibit weak localization.65 For example, low-temperature positive MR in thin Mo–C films was observed and displayed excellent agreement with models based on spin–orbit scattering with an antilocalization mechanism.66 While further work is needed to clarify the mechanisms giving rise to the diverse magnetoresistive properties of MXenes, this study confirms that positive MR is a robust feature of Mo-based MXenes.

Electrochemical Energy Storage

The electrochemical behavior of the (Mo2/3V1/3)n+1Cn system was studied in 3 M H2SO4. As seen in Figure 6A,C,E, the CV profiles for the (Mo2/3V1/3)n+1Cn system all display small anodic and cathodic peaks with a quasi-rectangular shape. This redox couple agrees with what we observed from Mo4VC4 in 3 M H2SO4, which was attributed to pseudocapacitive redox of proton adsorption on oxygen terminations with a charge transfer at the transition metal sites.67 The redox peaks that are present in all the CVs shift toward negative potential as n decreases. Additionally, as n decreases, there is a shift of the electrochemical window toward negative potentials (Figure S11). (Mo2/3V1/3)2C shows a stable electrochemical window from −0.90 to −0.10 V vs Hg/Hg2SO4; (Mo2/3V1/3)3C2 from −0.80 to −0.10 V vs Hg/Hg2SO4; (Mo2/3V1/3)4C3 from −0.75 to −0.05 V vs Hg/Hg2SO4. (Mo2/3V1/3)2C has the largest and most negative behavior, likely due to a combination of M and n influencing factors: the M2X structure is essentially entirely surface, giving it the highest concentration of active surface sites. Additionally, (Mo2/3V1/3)2C has the most exposed vanadium of all the structures, which likely influences its behavior to act more like V2C with its lower and larger electrochemical window.62 As for (Mo2/3V1/3)3C2 and (Mo2/3V1/3)4C3, the increased hydrogen evolution catalytic behavior, as indicated by the smaller windows, may be attributed to Mo, which dominated the surface sites (Figure 3).68

Figure 6.

Figure 6

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Cyclic voltammograms of (A) (Mo2/3V1/3)2C, (C) (Mo2/3V1/3)3C2, and (E) (Mo2/3V1/3)4C3. Specific capacitances of (B) (Mo2/3V1/3)2C, (D) (Mo2/3V1/3)3C2, and (F) (Mo2/3V1/3)4C3 as a function of sweep rate. For all measurements, the electrolyte was 3 M H2SO4.

Of the tested MXenes, (Mo2/3V1/3)2C has the highest specific capacitance, whereas (Mo2/3V1/3)3C2, and (Mo2/3V1/3)4C3 show similar performance (Figure 6B,D,F). This superior gravimetric performance of (Mo2/3V1/3)2C can likely be attributed to the higher concentration of active transition metal surface sites in the M2X structure compared to the larger M3X2 or M4X3 structures. However, (Mo2/3V1/3)2C shows the lowest rate capability of the (Mo2/3V1/3)n+1Cn system, likely due to its lower conductivity. Optimization of the synthesis procedure for (Mo2/3V1/3)2C may increase its overall quality, stability, and conductivity and result in a higher rate capability for this system. Overall, the performance of the (Mo2/3V1/3)n+1Cn system indicates that M2X MXenes are likely superior for electrochemical applications due to their increased concentrations of active sites.

Conclusions and Outlook

Herein, we have synthesized (Mo2/3V1/3)n+1AlCn MAX phases and successfully etched and delaminated them to (Mo2/3V1/3)n+1Cn MXenes with n = 1, 2, and 3. This allowed, for the first time, the study of MXene properties as a function of transition metal layers from n = 1 to 3. Structural analysis revealed full and partial ordering of the M-elements in (Mo2/3V1/3)3C2 and (Mo2/3V1/3)4C3, respectively, which can be attributed to the differences in the size of Mo and V. By studying their colloidal and electronic properties alongside their electrochemical behavior, trends with respect to n were established. The colloidal stability was found to directly increase with increasing n, with (Mo2/3V1/3)4C3 having much-improved stability over its lower n counterparts. With regard to the electronic transport behavior and electrochemical properties, it was found that the transport and electrochemical behavior of (Mo2/3V1/3)2C differ significantly from its higher-order counterparts. This is likely due to the lack of core layers resulting in all metal layers being bound to surface functional groups. While this supplies gravimetrically a greater concentration of active surface sites for improved electrochemical behavior, the lack of conducting core results in significantly increased resistivity. While this is only the first examination into the effects of n, this system of MXenes will allow for more concrete studies into the effects of n to allow for better tailoring of the MXene properties across Mn+1Xn.

Acknowledgments

The authors would like to acknowledge the U.S. National Science Foundation (Grant DMR-2041050) for funding this work. M.D. thanks the Drexel UREP Undergraduate Research Grant and Murata Manufacturing, Japan, for their funding of her undergraduate research. P.P.M. was supported by the National Centre for Research and Development (NCBR) within LIDER XII LIDER/8/0055/L-12/20/NCBR/2021 project. Support for the electronic characterization (Y.Y. and S.J.M.) was provided by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, grant No. DE-SC0018618. R.A. acknowledges funding from the Spanish MICIU (PID2019-104739GB-100/AEI/10.13039/501100011033), CEX2023-001286-S MICIU/AEI/10.13039/501100011033) and by the MICIU with funding from European Union Next Generation EU (PRTR-C17.I1) promoted by the Government of Aragon (DGA) as well from the DGA project E13-23R. Part of the STEM imaging studies have been conducted in the Laboratorio de Microscopias Avanzadas (LMA) at Universidad de Zaragoza. The STEM work at Argonne National Laboratory (NJZ/RA) was supported by the Advanced Materials for Energy-Water Systems (AMEWS) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences at Argonne National Laboratory under contract DE-AC02-06CH11357 and at the University of Chicago the National Science Foundation MRI Award # 2117896. The Argonne Picoprobe AEM was developed under CRADA 1300701 between Argonne National Laboratory and Thermo Fisher Scientific Instruments. The authors would like to acknowledge Dr. Ray Unocic for his contribution to TEM characterization. M.D. would like to thank Aidan Cotton for his assistance in documentation. Finally, the authors would like to acknowledge the usage of the XRD instrumentation provided by the Drexel University Materials Characterization Core (MCC). This work has been adapted from the M.S. thesis titled “The Effect of n: A Delve into MXene Structure–Property Relations” by M.D. (Drexel University, 2024).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.4c11111.

  • Rietveld refinement of the MAX phase XRD patterns; local chemical composition via STEM-EDS analysis and SIMS analysis quantification; UV–vis–NIR spectrum; conductivities of the (Mo2/3V1/3)n+1Cn system measured by both the 4-point probe and the physical properties measurement (PPMS) system; and electrochemical figure replotted with identical axis (PDF)

Author Contributions

All authors contributed to the writing of the manuscript and have given approval to the final version of the manuscript.

The authors declare no competing financial interest.

Supplementary Material

ja4c11111_si_001.pdf (2.2MB, pdf)

References

  1. Naguib M.; Kurtoglu M.; Presser V.; Lu J.; Niu J.; Heon M.; Hultman L.; Gogotsi Y.; Barsoum M. W. Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Adv. Mater. 2011, 23 (37), 4248–4253. 10.1002/adma.201102306. [DOI] [PubMed] [Google Scholar]
  2. Downes M.; Shuck C. E.; Lord R. W.; Anayee M.; Shekhirev M.; Wang R. J.; Hryhorchuk T.; Dahlqvist M.; Rosen J.; Gogotsi Y. M5X4: A Family of MXenes. ACS Nano 2023, 17 (17), 17158–17168. 10.1021/acsnano.3c04967. [DOI] [PubMed] [Google Scholar]
  3. Shuck C. E.; Sarycheva A.; Anayee M.; Levitt A.; Zhu Y.; Uzun S.; Balitskiy V.; Zahorodna V.; Gogotsi O.; Gogotsi Y. Scalable Synthesis of Ti3C2Tx MXene. Adv. Eng. Mater. 2020, 22 (3), 1901241 10.1002/adem.201901241. [DOI] [Google Scholar]
  4. Shuck C. E.; Gogotsi Y. Taking MXenes from the Lab to Commercial Products. Chem. Eng. J. 2020, 401, 125786 10.1016/j.cej.2020.125786. [DOI] [Google Scholar]
  5. Maleski K.; Mochalin V. N.; Gogotsi Y. Dispersions of Two-Dimensional Titanium Carbide MXene in Organic Solvents. Chem. Mater. 2017, 29 (4), 1632–1640. 10.1021/acs.chemmater.6b04830. [DOI] [Google Scholar]
  6. Akuzum B.; Maleski K.; Anasori B.; Lelyukh P.; Alvarez N. J.; Kumbur E. C.; Gogotsi Y. Rheological Characteristics of 2D Titanium Carbide (MXene) Dispersions: A Guide for Processing MXenes. ACS Nano 2018, 12 (3), 2685–2694. 10.1021/acsnano.7b08889. [DOI] [PubMed] [Google Scholar]
  7. Zhang Y.-Z.; Wang Y.; Jiang Q.; El-Demellawi J. K.; Kim H.; Alshareef H. N. MXene Printing and Patterned Coating for Device Applications. Adv. Mater. 2020, 32 (21), 1908486 10.1002/adma.201908486. [DOI] [PubMed] [Google Scholar]
  8. Dillon A. D.; Ghidiu M. J.; Krick A. L.; Griggs J.; May S. J.; Gogotsi Y.; Barsoum M. W.; Fafarman A. T. Highly Conductive Optical Quality Solution-Processed Films of 2D Titanium Carbide. Adv. Funct. Mater. 2016, 26 (23), 4162–4168. 10.1002/adfm.201600357. [DOI] [Google Scholar]
  9. Hantanasirisakul K.; Gogotsi Y. Electronic and Optical Properties of 2D Transition Metal Carbides and Nitrides (MXenes). Adv. Mater. 2018, 30 (52), 1804779 10.1002/adma.201804779. [DOI] [PubMed] [Google Scholar]
  10. Salles P.; Pinto D.; Hantanasirisakul K.; Maleski K.; Shuck C. E.; Gogotsi Y. Electrochromic Effect in Titanium Carbide MXene Thin Films Produced by Dip-Coating. Adv. Funct. Mater. 2019, 29 (17), 1809223 10.1002/adfm.201809223. [DOI] [Google Scholar]
  11. Maleski K.; Shuck C. E.; Fafarman A. T.; Gogotsi Y. The Broad Chromatic Range of Two-Dimensional Transition Metal Carbides. Adv. Opt. Mater. 2021, 9 (4), 2001563 10.1002/adom.202001563. [DOI] [Google Scholar]
  12. Han M.; Maleski K.; Shuck C. E.; Yang Y.; Glazar J. T.; Foucher A. C.; Hantanasirisakul K.; Sarycheva A.; Frey N. C.; May S. J.; Shenoy V. B.; Stach E. A.; Gogotsi Y. Tailoring Electronic and Optical Properties of MXenes through Forming Solid Solutions. J. Am. Chem. Soc. 2020, 142 (45), 19110–19118. 10.1021/jacs.0c07395. [DOI] [PubMed] [Google Scholar]
  13. Li J.; Wang X.; Sun W.; Maleski K.; Shuck C. E.; Li K.; Urbankowski P.; Hantanasirisakul K.; Wang X.; Kent P.; Wang H.; Gogotsi Y. Intercalation-Induced Reversible Electrochromic Behavior of Two-Dimensional Ti3C2Tx MXene in Organic Electrolytes. ChemElectroChem. 2021, 8 (1), 151–156. 10.1002/celc.202001449. [DOI] [Google Scholar]
  14. Alhabeb M.; Maleski K.; Anasori B.; Lelyukh P.; Clark L.; Sin S.; Gogotsi Y. Guidelines for Synthesis and Processing of Two-Dimensional Titanium Carbide (Ti3C2Tx MXene). Chem. Mater. 2017, 29 (18), 7633–7644. 10.1021/acs.chemmater.7b02847. [DOI] [Google Scholar]
  15. Zhang J.; Kong N.; Uzun S.; Levitt A.; Seyedin S.; Lynch P. A.; Qin S.; Han M.; Yang W.; Liu J.; Wang X.; Gogotsi Y.; Razal J. M. Scalable Manufacturing of Free-Standing, Strong Ti3C2Tx MXene Films with Outstanding Conductivity. Adv. Mater. 2020, 32 (23), 2001093 10.1002/adma.202001093. [DOI] [PubMed] [Google Scholar]
  16. Shekhirev M.; Shuck C. E.; Sarycheva A.; Gogotsi Y. Characterization of MXenes at Every Step, from Their Precursors to Single Flakes and Assembled Films. Prog. Mater. Sci. 2021, 120, 100757 10.1016/j.pmatsci.2020.100757. [DOI] [Google Scholar]
  17. Lipatov A.; Lu H.; Alhabeb M.; Anasori B.; Gruverman A.; Gogotsi Y.; Sinitskii A. Elastic Properties of 2D Ti3C2Tx MXene Monolayers and Bilayers. Sci. Adv. 2018, 4 (6), eaat0491 10.1126/sciadv.aat0491. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Lipatov A.; Alhabeb M.; Lu H.; Zhao S.; Loes M. J.; Vorobeva N. S.; Dall’Agnese Y.; Gao Y.; Gruverman A.; Gogotsi Y.; Sinitskii A. Electrical and Elastic Properties of Individual Single-Layer Nb4C3Tx MXene Flakes. Adv. Electron. Mater. 2020, 6 (4), 1901382 10.1002/aelm.201901382. [DOI] [Google Scholar]
  19. Wan S.; Li X.; Chen Y.; Liu N.; Du Y.; Dou S.; Jiang L.; Cheng Q. High-Strength Scalable MXene Films Through Bridging-Induced Densification. Science 2021, 374 (6563), 96–99. 10.1126/science.abg2026. [DOI] [PubMed] [Google Scholar]
  20. Lukatskaya M. R.; Mashtalir O.; Ren C. E.; Dall’Agnese Y.; Rozier P.; Taberna P. L.; Naguib M.; Simon P.; Barsoum M. W.; Gogotsi Y. Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide. Science 2013, 341 (6153), 1502–1505. 10.1126/science.1241488. [DOI] [PubMed] [Google Scholar]
  21. Zhang J.; Seyedin S.; Qin S.; Wang Z.; Moradi S.; Yang F.; Lynch P. A.; Yang W.; Liu J.; Wang X.; Razal J. M. Highly Conductive Ti3C2Tx MXene Hybrid Fibers for Flexible and Elastic Fiber-Shaped Supercapacitors. Small 2019, 15 (8), 1804732 10.1002/smll.201804732. [DOI] [PubMed] [Google Scholar]
  22. Li Y.; Shao H.; Lin Z.; Lu J.; Liu L.; Duployer B.; Persson P. O. Å.; Eklund P.; Hultman L.; Li M.; Chen K.; Zha X.-H.; Du S.; Rozier P.; Chai Z.; Raymundo-Piñero E.; Taberna P.-L.; Simon P.; Huang Q. A General Lewis Acidic Etching Route for Preparing MXenes with Enhanced Electrochemical Performance in Non-Aqueous Electrolyte. Nat. Mater. 2020, 19 (8), 894–899. 10.1038/s41563-020-0657-0. [DOI] [PubMed] [Google Scholar]
  23. Bao W.; Shuck C. E.; Zhang W.; Guo X.; Gogotsi Y.; Wang G. Boosting Performance of Na–S Batteries Using Sulfur-Doped Ti3C2Tx MXene Nanosheets with a Strong Affinity to Sodium Polysulfides. ACS Nano 2019, 13 (10), 11500–11509. 10.1021/acsnano.9b04977. [DOI] [PubMed] [Google Scholar]
  24. Shahzad F.; Alhabeb M.; Hatter C. B.; Anasori B.; Man Hong S.; Koo C. M.; Gogotsi Y. Electromagnetic Interference Shielding with 2D Transition Metal Carbides (MXenes). Science 2016, 353 (6304), 1137–1140. 10.1126/science.aag2421. [DOI] [PubMed] [Google Scholar]
  25. Han M.; Shuck C. E.; Rakhmanov R.; Parchment D.; Anasori B.; Koo C. M.; Friedman G.; Gogotsi Y. Beyond Ti3C2Tx: MXenes for Electromagnetic Interference Shielding. ACS Nano 2020, 14 (4), 5008–5016. 10.1021/acsnano.0c01312. [DOI] [PubMed] [Google Scholar]
  26. Yun T.; Kim H.; Iqbal A.; Cho Y. S.; Lee G. S.; Kim M.-K.; Kim S. J.; Kim D.; Gogotsi Y.; Kim S. O.; Koo C. M. Electromagnetic Shielding of Monolayer MXene Assemblies. Adv. Mater. 2020, 32 (9), 1906769 10.1002/adma.201906769. [DOI] [PubMed] [Google Scholar]
  27. Huang K.; Li Z.; Lin J.; Han G.; Huang P. Two-Dimensional Transition Metal Carbides and Nitrides (MXenes) for Biomedical Applications. Chem. Soc. Rev. 2018, 47 (14), 5109–5124. 10.1039/C7CS00838D. [DOI] [PubMed] [Google Scholar]
  28. Dai C.; Chen Y.; Jing X.; Xiang L.; Yang D.; Lin H.; Liu Z.; Han X.; Wu R. Two-Dimensional Tantalum Carbide (MXenes) Composite Nanosheets for Multiple Imaging-Guided Photothermal Tumor Ablation. ACS Nano 2017, 11 (12), 12696–12712. 10.1021/acsnano.7b07241. [DOI] [PubMed] [Google Scholar]
  29. Unal M. A.; Bayrakdar F.; Fusco L.; Besbinar O.; Shuck C. E.; Yalcin S.; Erken M. T.; Ozkul A.; Gurcan C.; Panatli O.; Summak G. Y.; Gokce C.; Orecchioni M.; Gazzi A.; Vitale F.; Somers J.; Demir E.; Yildiz S. S.; Nazir H.; Grivel J.-C.; Bedognetti D.; Crisanti A.; Akcali K. C.; Gogotsi Y.; Delogu L. G.; Yilmazer A. 2D MXenes with Antiviral and Immunomodulatory Properties: A Pilot Study Against SARS-CoV-2. Nano Today 2021, 38, 101136 10.1016/j.nantod.2021.101136. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Anasori B.; Xie Y.; Beidaghi M.; Lu J.; Hosler B. C.; Hultman L.; Kent P. R. C.; Gogotsi Y.; Barsoum M. W. Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes). ACS Nano 2015, 9 (10), 9507–9516. 10.1021/acsnano.5b03591. [DOI] [PubMed] [Google Scholar]
  31. Meshkian R.; Tao Q.; Dahlqvist M.; Lu J.; Hultman L.; Rosen J. Theoretical Stability and Materials Synthesis of a Chemically Ordered MAX Phase, Mo2ScAlC2, and Its Two-Dimensional Derivate Mo2ScC2 MXene. Acta Mater. 2017, 125, 476–480. 10.1016/j.actamat.2016.12.008. [DOI] [Google Scholar]
  32. Tao Q.; Dahlqvist M.; Lu J.; Kota S.; Meshkian R.; Halim J.; Palisaitis J.; Hultman L.; Barsoum M. W.; Persson P. O. Å.; Rosen J. Two-Dimensional Mo1.33C MXene With Divacancy Ordering Prepared from Parent 3D Laminate With In-Plane Chemical Ordering. Nat. Commun. 2017, 8 (1), 14949. 10.1038/ncomms14949. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Meshkian R.; Dahlqvist M.; Lu J.; Wickman B.; Halim J.; Thörnberg J.; Tao Q.; Li S.; Intikhab S.; Snyder J.; Barsoum M. W.; Yildizhan M.; Palisaitis J.; Hultman L.; Persson P. O. Å.; Rosen J. W-Based Atomic Laminates and Their 2D Derivative W1.33C MXene with Vacancy Ordering. Adv. Mater. 2018, 30 (21), 1706409 10.1002/adma.201706409. [DOI] [PubMed] [Google Scholar]
  34. Thörnberg J.; Halim J.; Lu J.; Meshkian R.; Palisaitis J.; Hultman L.; Persson P. O.Å.; Rosen J. Synthesis of (V2/3Sc1/3)2AlC i-MAX Phase and V2–xC MXene Scrolls. Nanoscale 2019, 11 (31), 14720–14726. 10.1039/C9NR02354B. [DOI] [PubMed] [Google Scholar]
  35. Du Z.; Wu C.; Chen Y.; Cao Z.; Hu R.; Zhang Y.; Gu J.; Cui Y.; Chen H.; Shi Y.; Shang J.; Li B.; Yang S. High-Entropy Atomic Layers of Transition-Metal Carbides (MXenes). Adv. Mater. 2021, 33 (39), 2101473 10.1002/adma.202101473. [DOI] [PubMed] [Google Scholar]
  36. Nemani S. K.; Zhang B.; Wyatt B. C.; Hood Z. D.; Manna S.; Khaledialidusti R.; Hong W.; Sternberg M. G.; Sankaranarayanan S. K. R. S.; Anasori B. High-Entropy 2D Carbide MXenes: TiVNbMoC3 and TiVCrMoC3. ACS Nano 2021, 15 (8), 12815–12825. 10.1021/acsnano.1c02775. [DOI] [PubMed] [Google Scholar]
  37. Deysher G.; Shuck C. E.; Hantanasirisakul K.; Frey N. C.; Foucher A. C.; Maleski K.; Sarycheva A.; Shenoy V. B.; Stach E. A.; Anasori B.; Gogotsi Y. Synthesis of Mo4VAlC4 MAX Phase and Two-Dimensional Mo4VC4 MXene with Five Atomic Layers of Transition Metals. ACS Nano 2020, 14 (1), 204–217. 10.1021/acsnano.9b07708. [DOI] [PubMed] [Google Scholar]
  38. Pinto D.; Anasori B.; Avireddy H.; Shuck C. E.; Hantanasirisakul K.; Deysher G.; Morante J. R.; Porzio W.; Alshareef H. N.; Gogotsi Y. Synthesis and Electrochemical Properties of 2D Molybdenum Vanadium Carbides–Solid Solution MXenes. J. Mater. Chem. A 2020, 8 (18), 8957–8968. 10.1039/D0TA01798A. [DOI] [Google Scholar]
  39. Wang L.; Han M.; Shuck C. E.; Wang X.; Gogotsi Y. Adjustable Electrochemical Properties of Solid-Solution MXenes. Nano Energy 2021, 88, 106308 10.1016/j.nanoen.2021.106308. [DOI] [Google Scholar]
  40. Seredych M.; Shuck C. E.; Pinto D.; Alhabeb M.; Precetti E.; Deysher G.; Anasori B.; Kurra N.; Gogotsi Y. High-Temperature Behavior and Surface Chemistry of Carbide MXenes Studied by Thermal Analysis. Chem. Mater. 2019, 31 (9), 3324–3332. 10.1021/acs.chemmater.9b00397. [DOI] [Google Scholar]
  41. Zhang C. J.; Pinilla S.; McEvoy N.; Cullen C. P.; Anasori B.; Long E.; Park S.-H.; Seral-Ascaso A.; Shmeliov A.; Krishnan D.; Morant C.; Liu X.; Duesberg G. S.; Gogotsi Y.; Nicolosi V. Oxidation Stability of Colloidal Two-Dimensional Titanium Carbides (MXenes). Chem. Mater. 2017, 29 (11), 4848–4856. 10.1021/acs.chemmater.7b00745. [DOI] [Google Scholar]
  42. Echols I. J.; Holta D. E.; Kotasthane V. S.; Tan Z.; Radovic M.; Lutkenhaus J. L.; Green M. J. Oxidative Stability of Nbn+1CnTz MXenes. J. Phys. Chem. C 2021, 125 (25), 13990–13996. 10.1021/acs.jpcc.1c01064. [DOI] [Google Scholar]
  43. Borysiuk V. N.; Mochalin V. N.; Gogotsi Y. Molecular Dynamic Study of the Mechanical Properties of Two-Dimensional Titanium Carbides Tin+1Cn (MXenes). Nanotechnology 2015, 26 (26), 265705 10.1088/0957-4484/26/26/265705. [DOI] [PubMed] [Google Scholar]
  44. Khazaei M.; Ranjbar A.; Arai M.; Sasaki T.; Yunoki S. Electronic Properties and Applications of MXenes: A Theoretical Review. J. Mater. Chem. C 2017, 5 (10), 2488–2503. 10.1039/C7TC00140A. [DOI] [Google Scholar]
  45. Zhang N.; Hong Y.; Yazdanparast S.; Zaeem M. A. Superior Structural, Elastic and Electronic Properties of 2D Titanium Nitride MXenes over Carbide MXenes: A Comprehensive First Principles Study. 2D Mater. 2018, 5 (4), 045004 10.1088/2053-1583/aacfb3. [DOI] [Google Scholar]
  46. Tian S.; Zhou K.; Huang C.-Q.; Qian C.; Gao Z.; Liu Y. Investigation and Understanding of the Mechanical Properties of MXene by High-Throughput Computations and Interpretable Machine Learning. Extreme Mech. Lett. 2022, 57, 101921 10.1016/j.eml.2022.101921. [DOI] [Google Scholar]
  47. Borysiuk V.; Mochalin V. N. Thermal Stability of Two-Dimensional Titanium Carbides Tin+1Cn (MXenes) from Classical Molecular Dynamics Simulations. MRS Commun. 2019, 9 (1), 203–208. 10.1557/mrc.2019.2. [DOI] [Google Scholar]
  48. Zheng P.; Zhang X.; Yan M.; Ma Y.; Jiang Y.; Li H. The Eruption of Carbon Chains in the Oxidation of 2D Tin+1Cn (n = 1, 2, 3) MXenes. Appl. Surf. Sci. 2021, 550, 149310 10.1016/j.apsusc.2021.149310. [DOI] [Google Scholar]
  49. Zhou J.; Dahlqvist M.; Björk J.; Rosen J. Atomic Scale Design of MXenes and Their Parent Materials—From Theoretical and Experimental Perspectives. Chem. Rev. 2023, 123 (23), 13291–13322. 10.1021/acs.chemrev.3c00241. [DOI] [PMC free article] [PubMed] [Google Scholar]
  50. Zaluzec N. First Light on the Argonne PicoProbe and The X-Ray Perimeter Array Detector (XPAD). Microsc. Microanal. 2021, 27 (S1), 2070–2074. 10.1017/S1431927621007492. [DOI] [Google Scholar]
  51. Michałowski P. P.; Anayee M.; Mathis T. S.; Kozdra S.; Wójcik A.; Hantanasirisakul K.; Jóźwik I.; Piątkowska A.; Możdżonek M.; Malinowska A.; Diduszko R.; Wierzbicka E.; Gogotsi Y. Oxycarbide MXenes and MAX Phases Identification Using Monoatomic Layer-By-Layer Analysis with Ultralow-Energy Secondary-Ion Mass Spectrometry. Nat. Nanotechnol. 2022, 17 (11), 1192–1197. 10.1038/s41565-022-01214-0. [DOI] [PubMed] [Google Scholar]
  52. Michałowski P. P. Unraveling the Composition of Each Atomic Layer in the MXene/MAX Phase Structure–Identification of Oxycarbides, Oxynitrides, and Oxycarbonitrides Subfamilies of MXenes. Nanoscale Horiz. 2024, 9, 1493–1497. 10.1039/D4NH00151F. [DOI] [PubMed] [Google Scholar]
  53. Feng X.; Zeng C.; Sui F.; Liu J.; Wu K.; Cheng Y.; Xiao B. Synthesis and Characterization of a New Out-of-Plane Ordered Double-Transition-Metal MAX Phase, Mo2VAlC2, and Its Two-Dimensional Derivate Mo2VC2Tx MXene. Mater. Sci. Eng., B 2024, 305, 117403 10.1016/j.mseb.2024.117403. [DOI] [Google Scholar]
  54. Dahlqvist M.; Rosen J. The Rise of MAX Phase Alloys–Large-Scale Theoretical Screening for the Prediction of Chemical Order and Disorder. Nanoscale 2022, 14 (30), 10958–10971. 10.1039/D2NR02414D. [DOI] [PubMed] [Google Scholar]
  55. Huang S.; Mochalin V. N. Hydrolysis of 2D Transition-Metal Carbides (MXenes) in Colloidal Solutions. Inorg. Chem. 2019, 58 (3), 1958–1966. 10.1021/acs.inorgchem.8b02890. [DOI] [PubMed] [Google Scholar]
  56. Shuck C. E.; Han M.; Maleski K.; Hantanasirisakul K.; Kim S. J.; Choi J.; Reil W. E. B.; Gogotsi Y. Effect of Ti3AlC2 MAX Phase on Structure and Properties of Resultant Ti3C2Tx MXene. ACS Appl. Nano Mater. 2019, 2 (6), 3368–3376. 10.1021/acsanm.9b00286. [DOI] [Google Scholar]
  57. Soomro R. A.; Zhang P.; Fan B.; Wei Y.; Xu B. Progression in the Oxidation Stability of MXenes. Nano-Micro Lett. 2023, 15 (1), 108. 10.1007/s40820-023-01069-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  58. Lim K. R. G.; Shekhirev M.; Wyatt B. C.; Anasori B.; Gogotsi Y.; Seh Z. W. Fundamentals of MXene Synthesis. Nat. Synth. 2022, 1 (8), 601–614. 10.1038/s44160-022-00104-6. [DOI] [Google Scholar]
  59. Anasori B.; Shi C.; Moon E. J.; Xie Y.; Voigt C. A.; Kent P. R. C.; May S. J.; Billinge S. J. L.; Barsoum M. W.; Gogotsi Y. Control of Electronic Properties of 2D Carbides (MXenes) by Manipulating Their Transition Metal Layers. Nanoscale Horiz. 2016, 1 (3), 227–234. 10.1039/C5NH00125K. [DOI] [PubMed] [Google Scholar]
  60. Halim J.; Moon E. J.; Eklund P.; Rosen J.; Barsoum M. W.; Ouisse T. Variable Range Hopping and Thermally Activated Transport in Molybdenum-Based MXenes. Phys. Rev. B 2018, 98 (10), 104202 10.1103/PhysRevB.98.104202. [DOI] [Google Scholar]
  61. Downes M.; Shuck C. E.; McBride B.; Busa J.; Gogotsi Y. Comprehensive Synthesis of Ti3C2Tx from MAX Phase to MXene. Nat. Protoc. 2024, 19 (6), 1807–1834. 10.1038/s41596-024-00969-1. [DOI] [PubMed] [Google Scholar]
  62. Zhang T.; Matthews K.; VahidMohammadi A.; Han M.; Gogotsi Y. Pseudocapacitance of Vanadium Carbide MXenes in Basic and Acidic Aqueous Electrolytes. ACS Energy Lett. 2022, 7 (11), 3864–3870. 10.1021/acsenergylett.2c01508. [DOI] [Google Scholar]
  63. Halim J.; Kota S.; Lukatskaya M. R.; Naguib M.; Zhao M.-Q.; Moon E. J.; Pitock J.; Nanda J.; May S. J.; Gogotsi Y.; Barsoum M. W. Synthesis and Characterization of 2D Molybdenum Carbide (MXene). Adv. Funct. Mater. 2016, 26 (18), 3118–3127. 10.1002/adfm.201505328. [DOI] [Google Scholar]
  64. Hantanasirisakul K.; Anasori B.; Nemsak S.; Hart J. L.; Wu J.; Yang Y.; Chopdekar R. V.; Shafer P.; May A. F.; Moon E. J.; Zhou J.; Zhang Q.; Taheri M. L.; May S. J.; Gogotsi Y. Evidence of a Magnetic Transition in Atomically Thin Cr2TiC2Tx MXene. Nanoscale Horiz. 2020, 5 (12), 1557–1565. 10.1039/D0NH00343C. [DOI] [PubMed] [Google Scholar]
  65. Bergman G. Influence of Spin-Orbit Coupling on Weak Localization. Phys. Rev. Lett. 1982, 48 (15), 1046–1049. 10.1103/PhysRevLett.48.1046. [DOI] [Google Scholar]
  66. Lee S. J.; Ketterson J. B. Electron Localization in Mo-C Films. Phys. Rev. B 1994, 49 (19), 13882–13885. 10.1103/PhysRevB.49.13882. [DOI] [PubMed] [Google Scholar]
  67. Hussain I.; Rehman F.; Saraf M.; Zhang T.; Wang R.; Das T.; Luo Z.; Gogotsi Y.; Zhang K. Electrochemical Properties of Mo4VC4Tx MXene in Aqueous Electrolytes. ACS Appl. Mater. Interfaces 2024, 16 (29), 38053–38060. 10.1021/acsami.4c06519. [DOI] [PMC free article] [PubMed] [Google Scholar]
  68. Seh Z. W.; Fredrickson K. D.; Anasori B.; Kibsgaard J.; Strickler A. L.; Lukatskaya M. R.; Gogotsi Y.; Jaramillo T. F.; Vojvodic A. Two-Dimensional Molybdenum Carbide (MXene) as an Efficient Electrocatalyst for Hydrogen Evolution. ACS Energy Lett. 2016, 1 (3), 589–594. 10.1021/acsenergylett.6b00247. [DOI] [Google Scholar]

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