EP3482404A1

EP3482404A1 - Nanolaminated material, two-dimensional material and process for manufacturing a two-dimensional material

Info

Publication number: EP3482404A1
Application number: EP17727747.2A
Authority: EP
Inventors: Quanzheng TAO; Jun Lu; Per Persson; Johanna ROSÉN
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-07-07
Filing date: 2017-05-23
Publication date: 2019-05-15
Also published as: WO2018009115A1

Abstract

The disclosure relates to a nanolaminated material of the formula (Mx ± β, M2y ± ɛ)2-δAl1 -αC1 ± ρ wherein M1 is Mo and M2 is selected from the group consisting of Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu. The M1 and M2 atoms are chemically ordered in relation to each other within the M-plane of the nanolaminated material. The disclosure also relates to a process for producing a substantially two-dimensional material from said nanolaminated material, as well as a substantially two-dimensional material.

Description

NANOLAMINATED MATERIAL, TWO-DIMENSIONAL MATERIAL AND PROCESS FOR

MANUFACTURING A TWO-DIMENSIONAL MATERIAL

TECHNICAL FIELD

The present disclosure relates in general to a nanolaminated material with the formula (Ml_{x ± p},M2_{y ±} e -eAli-c +p, wherein M l and M2 constitutes two different transition metals. The present disclosure further relates to a substantially two-dimensional material comprising a layer having an empirical formula (Μ1_{χ ±} β,Μ2_{γ ± ε})₂-δ^_±ρ, and process for manufacturing such a material. The present disclosure further relates to a process for manufacturing a substantially two-dimensional material comprising a layer having an empirical formula (Ml_x±p wherein re constitutes a vacancy.

BACKGROUND

So called MAX phases, or MAX phase alloys, constitute a class of materials with the formula M_n+iAX_n where n = 1 to 3, M constitutes at least one transition metal, A constitutes at least one A-group element, and X is at least one of C, N and O. MAX phases with compositions diverging from n being an integer are also known, and MAX phases with n above 3 have been reported in the literature.

Thus, MAX phases may be more appropriately described with the formula Μ_η+ι__δΑι__αΧ_η±ρ, wherein n= 1, 2, 3 or higher, δ <0.2, a <0.2 and p <0.2, M is at least one transition metal, A is at least one A-group element, and X is at least one of C, N and O. MAX phases are in the literature often divided into different classes of MAX phases depending on the relative amounts of the M, A and X elements and the most common classes constitute 211 MAX phases, 312 MAX phases and 413 MAX phases.

MAX phases have a layered hexagonal crystal structure with P6₃/mmc symmetry. Each unit cell comprises two formula units. Near-closed packed layers of the M-element(s) are interleaved with pure A-group element(s) layers, with the X-atoms filling the octahedral sites between the former. Therefore, MAX phases form laminated structures. These laminated structures have anisotropic properties as a result of the structure. MAX phases possess unique properties combining ceramic and metallic properties. They are for example electrically and thermally conductive, resistant to thermal shock, plastic at high

temperatures and readily machinable. Many MAX phases also have comparatively low weight, are corrosion resistant, and also have excellent creep and fatigue resistance. For said reason, MAX phases have previously been suggested for applications such as heating elements, gas burner nozzles in corrosive environments, high-temperature bearings as well in composites for dry drilling of concrete. MAX phases have also been proposed as coatings for electrical components, for example for fuel cell bipolar plates and electrical contacts. MAX phases may also have other properties. For example, WO 2012/070991 Al and WO

2015/065252 Al discloses MAX phases having magnetic properties. The MAX phases comprise two transition metals, wherein one of the transition metals contributes to the magnetic properties and the other contributes to the ability to synthesize the MAX phase. MAX phases may be synthesised by bulk synthesis wherein the constituent elements of the intended MAX phase are mixed in the intended amounts of the MAX phase and subjected to high temperature so as to form the MAX phase. Examples of such bulk synthesis methods include hot isostatic pressing (HIP), reactive sintering, self-propagating high temperature synthesis (SHS), and combustion synthesis. MAX phases may also be synthesised using thin film synthesis methods, such as by physical vapour deposition (PVD) or chemical vapour deposition (CVD).

It is previously known to synthesise two-dimensional materials, also known as MXenes, from MAX phases. MXenes are a class of two-dimensional inorganic compounds which consist of a few atoms thick layers of transition metal carbides or carbonitrides. MXenes are often described with the formula M_n+iX_n. However, since the surfaces of MXene generally are terminated by functional groups, a more correct description is the formula M_n+iX_nT_s, where T_s is a functional group such as O, F or OH.

The synthesis of MXenes comprises etching of various MAX phases to thereby remove the A-atoms of the MAX phase. For example, the MAX phase M₂AIC (M denominating a transition metal) may be etched in hydrofluoric acid (HF), resulting in removal of the Al-layer and formation of two dimensional M₂C sheets. Specific examples of MXenes that have been previously synthesized include Ti₂C, V₂C, Nb₂C, Ti₃C₂, Ti₃CN, Nb₄C₃ and Ta₄C₃. For example, Naguib et al., "Two-Dimensional Nanocrystals Produced by Exfoliation of Ti^lC , Advanced Materials, 2011, 23, 4248-4253, reported synthesis of a two dimensional material starting from the MAX phase Ti₃AIC₂. They extracted the Al from Ti₃AIC₂ by use of hydrofluoric solution and thereby arrived at isolated layers of Ti₃C₂.

Furthermore, WO 2014/088995 Al discloses compositions comprising free standing and stacked assemblies of two-dimensional crystalline solids. The compositions comprise at least one layer having first and second surfaces, each layer comprising a substantially two-dimensional array of crystal cells, each crystal cell having an empirical formula of M_n+iX_n, such that X is positioned within an octahedral array of M. M is at least one Group 1MB, IVB, VB or VIB metal, X is C and/or N and n= 1, 2 or 3. The compositions may be produced by removing substantially all of the A atoms from a MAX-phase composition having an empirical formula of M_n+iAX_n, wherein M is at least one Group 1MB, IVB, VB or VIB metal, A is an A-group element, X is C and/or N, and n=l, 2 or 3. SUMMARY

The object of the present invention is to provide new tailored nanolaminated materials of the MAX phase type which may enable new possibilities for said type of materials. The object is achieved by a nanolaminated material which has the formula (Μ1_{χ ± β},Μ2_{γ ± ε})₂__δΑΙι__α(Ιι _{± ρ} , wherein

is 0 to < 0.1,

ε is O to < 0.1,

6 is 0 to < 0.2,

a is 0 to < 0.2,

p is 0 to < 0.2,

x + y = 1,

x is between 0.60 and 0.75, preferably wherein x is between 0.65 and 0.69,

wherein

Ml is Mo, and

M2 is a transition metal selected from the group consisting of Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu.

The nanolaminated material according to the present disclosure is thus a quaternary MAX phase alloy of the 211 type, wherein A is Al and X is C. The nanolaminated material exhibits in-plane chemical ordering of the transition metals Ml and M2. That is, in the M-plane of the MAX phase alloy, the Ml and M2 atoms are ordered in relation to each other in contrast to randomly distributed within the M-plane. The nanolaminated material according to the present invention may for example be used in synthesis of MXenes.

In the nanolaminated material according to the present disclosure, x is most preferably 2/3.

According to one exemplifying embodiment, M2 in the nanolaminated material may be selected from the group consisting of Ce, Ho and Er. According to another exemplifying embodiment, M2 in the nanolaminated material may be selected from the group consisting of Pr, Nd, Sm, Gd, Tb, Dy, Tm and Lu.

The present invention also relates to a substantially two-dimensional material comprising a layer having an empirical formula (Ml_x±p ,M2_y±£)₂-6Ci_±p, wherein

is 0 to < 0.1,

ε is O to < 0.1,

6 is 0 to < 0.2,

p is 0 to < 0.2,

x + y = 1,

x is between 0.60 and 0.75, preferably wherein x is between 0.65 and 0.69,

Ml is Mo, and

M2 is a transition metal selected from the group consisting of Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu. In the substantially two-dimensional material according to the present disclosure, x is most preferably 2/3.

According to an exemplifying embodiment of the substantially two-dimensional material according to the present disclosure, M2 is selected from the group consisting of Ce, Ho and Er. According to another exemplifying embodiment of the substantially two-dimensional material according to the present disclosure, M2 is selected from the group consisting of Pr, Nd, Sm, Gd, Tb, Dy, Tm and Lu.

The layer of the substantially two-dimensional material has a first surface and a second surface, and may comprise a surface termination T_s. The surface termination may result from the etching process or be a surface termination T'_s achieved in a processing step subsequent to the etching step. The substantially two-dimensional material may according to one aspect consist solely of the layer with the surface termination T_s or T'_s.

The substantially two-dimensional material as described above may be produced by a method comprising the steps of

a) providing a nanolaminated material with the formula (Μ1_χ±β ,Μ2_γ±ε)₂__δΑΙι__α(Ιι_±ρ as disclosed above

b) selectively etching the nanolaminated material so as to remove substantially all of the Al atoms, thereby obtaining a plurality of substantially two-dimensional layers each having a formula (Μ1_χ±β ,Μ2_γ±ε)₂__δ(Ιι_±ρ, and wherein each substantially two-dimensional layer comprises a surface termination T_s resulting from the etching, and

c) thereafter isolating at least one first layer of the plurality of substantially two-dimensional layers.

The above described nanolaminated material may also be used for manufacturing a substantially two-dimensional material comprising a controlled amount of vacancies. Such a substantially two- dimensional material can be expressed as a substantially two-dimensional material comprising a layer having an empirical formula (Ml_x±p wherein

is 0 to < 0.1,

ε is O to < 0.1,

6 is 0 to < 0.2,

p is 0 to < 0.2,

x + y = 1,

x is between 0.60 and 0.75,

Ml is Mo, and

re constitutes a vacancy.

The process for manufacturing such a substantially two-dimensional material comprising r comprises the following steps:

a) preparing a nanolaminated material with the formula (Μ1_χ±β ,Μ2_γ±ε)₂__δΑΙι__α(Ιι_±ρ as disclosed above,

b) selectively etching the nanolaminated material so as to remove substantially all of the Al atoms and substantially all of the M2 atoms, thereby obtaining a plurality of substantially two-dimensional layers each having a formula (Μ 1_χ±β ,Γ _γ±ε)₂._δ0ι_±ρ, and wherein each substantially two-dimensional layer comprises a surface termination T_s resulting from the etching, and

c) thereafter isolating at least one first layer of the plurality of substantially two- dimensional layers.

The present disclosure further relates to a method for manufacturing a material comprising a stacked assembly of a plurality of substantially two-dimensional layers, the method comprising the following steps:

a) preparing a nanolaminated material with the formula (Ml_x±p ,M2_y±£)₂-6Ali._aCi_±p as disclosed above,

b) selectively etching the nanolaminated material so as to remove substantially all of the Al atoms and optionally substantially all of the M2 atoms, thereby obtaining a plurality of substantially two-dimensional layers each having a formula (Ml_x±p ,r _y±£)₂- sCi_+p wherein r is either M2 or a vacancy, and wherein each substantially two- dimensional layer comprises a surface termination T_s resulting from the etching.

The method may optionally comprise a step of exchanging the surface termination T_s of each of the substantially two-dimensional layers resulting from the etching to another surface termination T'_s. The purpose of such a step would be to achieve a surface termination of the layers of the stacked assembly which is suitable for the intended use of the stacked assembly.

The present invention further relates to a stacked assembly comprising a plurality of layers wherein at least one of the layers constitutes a substantially two-dimensional material as described above. The stacked assembly may preferably comprise more than one layer of the substantially two- dimensional material. The stacked assembly may further comprise layers of other compositions or materials. Alternatively, the stacked assembly may be a stacked assembly as produced by the method for manufacturing a material comprising a stacked assembly as disclosed above.

The present invention further relates to a composite comprising a substantially two-dimensional material as disclosed above.

The present invention further relates to an energy storage device comprising a substantially two- dimensional material as disclosed above. BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 schematically illustrates a side view of the atomic structure of a conventional 211

MAX phase

Fig. 2a schematically illustrates a side view of the atomic structure of a nanolaminated material according to one exemplifying embodiment of the present invention

Fig. 2b schematically illustrates a perspective view of the atomic structure of a

nanolaminated material shown in Fig. 2a

Fig. 3 schematically illustrate a process for manufacturing a substantially two-dimensional material according to the present disclosure Fig. 4a schematically illustrates a side view of the atomic structure of a nanolaminated material of Fig. 2a

Fig. 4b schematically illustrates a side view of the atomic structure of a stacked assembly obtained through etching of the nanolaminated material as illustrated in Figure 4a according to one embodiment

Fig. 4c schematically illustrates a top view of an isolated substantially two-dimensional layer obtained from the stacked assembly as illustrated in Fig. 4b Fig. 4d schematically illustrates a side view of the atomic structure of a stacked assembly obtained through etching of the nanolaminated material as illustrated in Figure 4a according to another embodiment

Fig. 4e schematically illustrates a top view of an isolated substantially two-dimensional layer obtained from the stacked assembly as illustrated in Fig. 4d

Fig. 5a illustrates XRD spectra for (Mo₂/3Cei/₃)₂AIC synthesised according to Experimental result 1 Fig. 5b constitutes images from STEM, taken from various zone axes, of (Mo₂/3Cei/₃)₂AIC synthesised according to Experimental result 1

Fig. 6a illustrates XRD spectra for (Mo₂/₃Tbi/₃)₂AIC synthesised according to Experimental result 1

Fig. 6b constitutes images from STEM, taken from various zone axes, of (Mo₂/₃Tbi/₃)₂AIC synthesised according to Experimental result 1 Fig. 7a illustrates XRD spectra for (Mo₂/₃Pri/₃)₂AIC synthesised according to Experimental result 2

Fig. 7b constitutes an image from STEM of (Mo₂/₃Pri/₃)₂AIC synthesised according to

Experimental result 2

Fig. 8a illustrates XRD spectra for (Mo₂/₃Ndi/₃)₂AIC synthesised according to Experimental result 2

Fig. 8b constitutes an image from STEM of (Mo₂/₃Ndi/₃)₂AIC synthesised according to

Experimental result 2

Fig. 9a illustrates XRD spectra for (Mo₂/₃Smi/₃)₂AIC synthesised according to Experimental result 2 Fig. 9b constitutes an image from STEM of (Mo₂/₃Smi/₃)₂AIC synthesised according to

Experimental result 2

Fig. 10a illustrates XRD spectra for (Mo₂/₃Gdi/₃)₂AIC synthesised according to Experimental result 2

Fig. 10b constitutes an image from STEM of (Mo₂/₃Gdi/₃)₂AIC synthesised according to

Experimental result 2

Fig. 11a illustrates XRD spectra for (Mo₂/₃Dyi/₃)₂AIC synthesised according to Experimental result 2 Fig. lib constitutes an image from STEM of (Mo₂/₃Dy_1/3)₂AIC synthesised according to

Experimental result 2 Fig. 12a illustrates XRD spectra for (Mo₂/3Hoi/3)₂AIC synthesised according to Experimental result 2

Fig. 12b constitutes an image from STEM of (Mo₂/₃Ho_1/3)₂AIC synthesised according to

Experimental result 2

Fig. 13a illustrates XRD spectra for (Mo₂/₃Eri/3)₂AIC synthesised according to Experimental result 2

Fig. 13b constitutes an image from STEM of (Mo₂/₃Er_1/3)₂AlC synthesised according to

Experimental result 2

Fig. 14a illustrates XRD spectra for (Mo₂/₃Tmi/3)₂AIC synthesised according to Experimental result 2 Fig. 14b constitutes an image from STEM of (Mo₂/₃Tm_1/3)₂AIC synthesised according to

Experimental result 2

Fig. 15a illustrates XRD spectra for (Mo₂/3Lui/3)₂AIC synthesised according to Experimental result 2

Fig. 15b constitutes an image from STEM of (Mo₂/3Lui/3)₂AlC synthesised according to

Experimental result 2

Fig. 16a illustrates XRD spectra for (Mo₂/3Hoi/3)₂AIC synthesised according to Experimental result 3

Fig. 16b constitutes an image from STEM of (Mo₂/3Hoi_/3)₂AIC synthesised according to

Experimental result 3 Fig. 17a illustrates X D spectra for (Mo₂/3Eri/₃)₂AIC synthesised according to Experimental result 3

Fig. 17b constitutes an image from STEM of (Mo₂/3Eri/₃)₂AIC synthesised according to

Experimental result 3

Fig. 18a illustrates XRD spectra for (Mo₂/₃Cei/₃)₂AIC synthesised according to Experimental result 3 Fig. 18b constitutes an image from STEM of (Mo₂/₃Cei/₃)₂AIC synthesised according to

Experimental result 3

DEFINITIONS

A two-dimensional material constitutes a material consisting of a single layer of atoms or crystal cells, and is sometimes referred to as a "single layer material". Thus, in a two dimensional material, the atoms or, where applicable, crystal cells are repeated in two dimensions (x and y direction) but not in the third dimension (z direction), in contrast to a three-dimensional material where the atoms/crystal cells are repeated in all directions. However, as well known to the skilled person, no material constitutes a perfectly two-dimensional material since there will always be normally occurring defects present. Therefore, in the present disclosure, the term "substantially two- dimensional material" is used, which shall be considered to encompass both a perfect two- dimensional material as well as a two-dimensional material comprising normally occurring defects. Furthermore, a two-dimensional material or a substantially two-dimensional material shall not be considered to necessarily be flat but may for example also have a single-curved, double-curved, undulating, rolled-up, or tube shape without departing from the scope of the present invention.

Moreover, in view of the fact that the M atoms in a MAX phase will most likely not be arranged in a perfectly octahedral array in view of the different atomic radii and possible normally occurring defects, the term "essentially octahedral array" is used herein. "Essentially octahedral array" shall thus be considered to encompass a perfect octahedral array as well as a slightly distorted octahedral array as will occur as a result of normally occurring defects and/or different atomic radii of the atoms. DETAILED DESCRI PTION

The invention will be described in more detail below with reference to the accompanying drawings, and certain embodiments. The invention is however not limited to the embodiments discussed but may be varied within the scope of the appended claims. Furthermore, the drawings shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate the invention.

The present inventors have discovered new three-dimensional nanolaminated materials, more specifically new quaternary MAX phase alloys from the 211 class of MAX phases, which provide chemical in-plane order. The quaternary MAX phase alloys comprise two transition metals, hereinafter denominated M l and M2, in specific amounts. The MAX phase alloys provide chemical in-plane order since the M l and M2 atoms of the newly identified MAX phase alloys are not randomly distributed within the M-layers of the MAX phase, but are arranged in a particular order. The fact that the M l and M 2 atoms are ordered provides new possibilities for application of MAX phases, for example when synthesizing MXenes from such a MAX phases.

Tailoring MAX phase properties and realizing novel MXenes requires novel MAX phases. A density Functional Theory (DFT) formulation for predicting new stable phases within higher order materials systems has been developed, see M . Dahlqvist et al., Phys. Rev. B 81, 024111 (2010), Phys. Rev. B 81, 220102(R) (2010). Using DFT calculations and the simplex-optimization scheme, the relative stability of any hypothetical compound may be calculated relative to an identified set of stable competing phases. By this approach, numerous new MAX phases have been realized; see P. Eklund et al, Phys. Rev. Lett. 109, 035502 (2012) and A.S. Ingason et al, Phys. Rev. Lett. 110, 195502 (2013). The results reported indicate that MAX phase formation is mainly governed by the enthalpy term in the Gibbs free energy. However, for borderline cases, entropy and vibrational effects may come into play at higher temperatures. Thus, new nanolaminated materials can be identified through theoretical simulations as discussed above to primarily determine if the nanolaminated materials can be expected to be stable. Prediction of chemically ordered MAX phase alloys can be based on evaluation of formation enthalpy of chemically ordered as well as disordered alloy configurations. If the ordered configuration is found to be more stable than the disordered one, then the chemically ordered material is suggested to be possible to synthesize. For borderline cases, the temperature at which entropy favours chemical disorder can be estimated along the lines as disclosed in Dahlqvist et al, Phys. Chem. Chem. Phys., 2015, 17, 31810-31821.

While theoretical simulation as disclosed above is a useful tool to seek to identify possible new MAX phase materials, it should be experimentally verified in order to determine if the theoretical simulation is sufficiently accurate. For the materials according to the present invention, it is difficult to theoretically simulate the MAX phases for example because of the need to also consider magnetism etc. However, experimental results (for example as presented below) have shown that it is possible to obtain stable nanolaminated materials of the 211 MAX phase group comprising two transition metals, Ml and M2, wherein Ml is Molybdenum (Mo) and M2 is a lanthanide. More specifically, M2 is selected from the group consisting of Cerium (Ce), Praseodym (Pr), Neodym (Nd), Samarium (Sm), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Tulium (Tu) and Lutentium (Lu). Furthermore, in said 211 MAX phases, the A element constitutes Aluminium (Al) and the X element constitutes Carbon (C). Thereby, MAX phases with the formula (Μ1_χ±β ,Μ2_γ±ε)₂-_δΑΙι. c ip, wherein M l and M2 are selected as given above and wherein the sum of x and y is 1, have been realised. These new MAX phases obtained through alloying with a second transition metal selected from the group of lanthanides may in many cases be used for synthesis of substantially two-dimensional materials, i.e. MXenes, which specific properties mainly depending on the M2 selected.

The present inventors have previously found that the relative amounts of two different transition metals in a nanolaminated material cannot be arbitrarily selected, but must be selected

appropriately in order to enable formation of a stable MAX phase as well as obtaining a chemical ordering within the M-plane of the MAX phases. A chemical ordering of M atoms is not automatically achieved for any arbitrary relative amount of Ml and M2. Furthermore, any arbitrary selection of the relative amount of Ml and M2 will not lead to formation of a MAX phase during synthesis, and in particular will not necessarily lead to a MAX phase which is stable. It is therefore important to properly adjust the relative amounts of M l and M2 atoms during synthesis of the MAX phase.

Thus, the relative amount of the two different transition metals, Ml and M2, in the nanolaminated material is purposively selected such as to obtain a chemical in-plane ordering of the M atoms as well as to ensure that the nanolaminated materials are stable such that they can readily be synthesised. In generally, the amount of M l (which in this case is Mo) should be about twice the amount of M2. Thus, in the nanolaminated material according to the present invention, x is between 0.60 and 0.75 and the sum of x and y is 1.00. Preferably, x is between 0.65 and 0.69. More preferably, x is 0.67, or more accurately x is preferably 2/3. The accuracy in the chemical ordering increases with reduced deviation from the preferred value of x = 2/3. In other words, the number of defects (albeit already very low) decreases with reduced deviation from the preferred value of x = 2/3.

It has further been found that in the resulting crystal cells of the nanolaminated material, i.e. the MAX phase, the M2 atoms in most cases extend somewhat out of the M-plane towards the A-plane of the MAX phase alloy. Consequently, new symmetries can be identified, and three additional space groups have been found which describe the crystal structure; C2/m (#12), C2/c (#15), and Cmcm (#63). Furthermore in the resulting crystal cells of the nanolaminated material, the M l and M2 atoms are ordered, in contrast to randomly distributed, in relation to each other within the M-plane of the MAX phase. The reason is currently not fully understood since even though it is easy to understand that some modification of a the conventional crystal cell of a MAX phase can be expected due to the difference in atomic radius between different M elements, an arbitrary selection of M l and M2 may not necessarily have the same result and the chemical in-plane order may not always be achieved as also disclosed above.

Conventional MAX phases typically comprise three elements, M, A and X, forming for example M₂AX in the case of 211 MAX phase. Figure 1 illustrates a side view of the atomic structure of a

conventional 211 MAX phase. As can be seen from Figure 1, near-closed packed payers of the M- element are interleaved with pure A-group element layers, with the X atoms filling the octahedral sites between the former.

In contrast to the conventional MAX phase described above and shown in Figure 1, the new MAX phases found by the present inventors originate from alloying with a second M element, to realise quaternary alloys where there is chemical ordering in the M-plane as disclosed above. The resulting nanolaminated material has thus the general formula (Ml_x,M2_y)₂AIC, wherein the sum of x and y is 1, and x is from 0.60 to 0.75 (including the end values). However, in reality the (Ml_x,M2_y)₂AIC formula may invite to a too strict interpretation inter alia since there are always normally occurring defects in a material, such as unintended and randomly distributed vacancies. Furthermore, the composition of the nanolaminated material may diverge from the exact (Ml_x,M2_y)₂AIC formula for example due to partial sublimation of Al, and/or possible uptake of carbon from a graphite crucible and/or die, if such are used, during synthesis. There is also a risk for loss of carbon during synthesis in many cases. Therefore, a more accurate formula for the nanolaminated material is (Μ1χ _{± β},Μ2_{γ ± ε})₂__δΑΙι__α(Ιι _{± ρ}, wherein β, ε, δ, a and p takes into account expected possible divergence from a true (Ml_x,M2_y)₂AIC composition. Each of β and ε may be from 0 to < 0.10, preferably from 0 to <0.05, most preferably from 0 to <0.02. Each of δ, a and p may be from 0 to < 0.20, preferably from 0 to < 0.10, most preferably from 0 to <0.05.

An alternative way of expressing the present nanolaminated material is a nanolaminated material having the composition (Ml_x,M2_y)₂AIC but comprising normally occurring defects, and wherein x is 0.60-0.75, the sum of x and y is 1, and Ml and M2 each are selected as disclosed above.

However, for the purpose of facilitating the reading of the present disclosure, the actual formula (Μ1_{χ ± β},Μ2_{γ ± ε})₂-_δΑΙι__α ⁽Ιι _{± ρ} of the nanolaminated material according to the present invention will be simplified in the following by using the general formula (M l_x,M2_y)₂AIC. Thus, whenever the general formula (Ml_x,M2_y)₂AIC is used in the following disclosure, it shall be considered to in fact constitute the formula (Μ1_{χ ± β},Μ2_{γ ± ε})₂__δΑΙι__α(Ιι _{± ρ}. This is also the case when specific elements of M l and M2 are given in the formula and/or where specific figures are given for x and/or y in the formula, unless explicitly disclosed otherwise. By way of example, "(Mo_x,M2_y)₂AIC" shall in fact be interpreted as "(Mo_{x± p}M2_v±£)₂_₆Al₁__aC_{1 ± p}", and "(Mo₀.₆7,M2o.3₃)₂AIC" shall in fact be interpreted as "(Mo₀._67± _βΜ2₀.33±_ε)₂-_δΑΙι__α ⁽Ιι ± _p", unless explicitly disclosed otherwise.

The nanolaminated material according to the present disclosure is thus a nanolaminated material selected from the group consisting of:

(Mo_{x + p},Ce_{y + £})₂-6Ali__aCi _{+ p},

(Mo_{x + p},Gd_{y + £})₂-6Ali__aCi _{+ p},

(Mo_{x + p},Tb_{y + £})₂-6Ali__aCi _{+ p},

( o_x ± _p, H Oy + _ε)₂._δΑΙ i__aCi + _p, Figure 2a schematically illustrates a side view and Figure 2b schematically illustrates a perspective view of a nanolaminated material according to one exemplifying embodiment of the present disclosure. The nanolaminated material comprises a first transition metal Ml and a second transition metal M2, as well as aluminium (Al) and carbon (C). In the exemplifying embodiment shown in Figures 2a and 2b, x would be 2/3 and y would be 1/3. In other words, the amount of Ml atoms is twice the amount of M2 atoms. The nanolaminated material according to this exemplifying embodiment thus has the general formula (Ml₂/₃,M2i/₃)₂AIC. Furthermore, in the nanolaminated material, Ml is Mo and M2 is selected from the group consisting of Ce, Pr, Nb, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu. Thereby, the atomic radius of the M2 atoms is greater than the atomic radius of the Ml atoms. As can be seen from the figures 2a and 2b, the Ml and M2 atoms are chemically ordered in relation to each other and the M2 atoms extend out of the Ml-plane towards the A-plane formed by the Al atoms. The C atoms are positioned within essentially octahedral arrays formed by the M l and M2 atoms. The present disclosure further relates to a substantially two-dimensional material which may be synthesized from the nanolaminated material as disclosed above.

According to one exemplifying embodiment, the substantially two-dimensional material comprises a layer having an empirical formula (Ml_x±p ,M2_y±£)₂-6Ci_±p, wherein

is 0 to < 0.1,

ε is O to < 0.1,

6 is 0 to < 0.2,

p is 0 to < 0.2,

x + y = 1,

x is between 0.60 and 0.75, preferably wherein x is between 0.65 and 0.69,

Ml is Mo, and

M2 is a transition metal selected from the group consisting of Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu. It is also possible to synthesize a substantially two-dimensional material comprising a controlled high amount of vacancies from the nanolaminated material as disclosed above. Such a material would have the formula (Ml_x±p wherein

is 0 to < 0.1,

ε is O to < 0.1,

δ is 0 to < 0.2, p is 0 to < 0.2,

x + y = 1,

x is between 0.60 and 0.75,

Ml is Mo, and

r constitutes a vacancy.

The present disclosure further relates to a process for manufacturing a substantially two-dimensional material as well as a process for manufacturing a material comprising a stacked assembly of a plurality of substantially two-dimensional layers. In other words, the present invention further provides a process for synthesis of new MXenes as well as stacked assemblies thereof.

Figure 3 schematically illustrates a process according to the present disclosure. The process comprises a first step, SI, comprising preparing a nanolaminated material having the formula (M l_x±p ,Μ2_γ±ε)₂-_δΑΙι__α(Ιι_±ρ. Ml is Mo and M2 is selected from the group consisting of Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu. The sum of x and y in the formula is 1, and x is between 0.60 and 0.75.

Preferably, x is between 0.65 and 0.69. More preferably, x is 0.67, or more accurately x is preferably 2/3.

The nanolaminated material may be prepared according to conventional methods for producing MAX materials as known in the art. Preferably, the nanolaminated material is produced by a bulk method for sake of simplicity. However, other processes, such as chemical vapour deposition (CVD) or physical vapour deposition (PVD), are also possible. The nanolaminated material may according to a preferred embodiment for example be produced by mixing powders of the elements in the stoichiometric amounts of the intended nanolaminated material and heating the mixture to an appropriate temperature under argon atmosphere.

The nanolaminated material is in a second step, S2, selectively etched so as to remove substantially all of the Al atoms thereby obtaining a plurality of substantially two-dimensional layers. According to one embodiment, only the Al atoms are removed from the nanolaminated material by the etching step. According to an alternative embodiment, the etching may be performed such as to remove substantially all of the Al atoms as well as substantially all of the M2 atoms. Etching of the M2 atoms may be conducted either simultaneously with the Al atoms or in a separate etching step. In the separate etching step, the same or another etching solution as in the etching step where Al atoms are removed may be used. The resulting substantially two-dimensional layers thus each have an empirical formula (Ml_x±p is either M2 or a vacancy. Etching may suitably be made using an etching solution comprising hydrogen fluoride (HF), hydrogen fluoride (HF) and hydrochloric acid (HCI), ammonium bifluoride (NH₄HF₂), lithium fluoride (LiF), or lithium fluoride (LiF) and hydrochloric acid (HCI). The presence of HCI in the etching solution may in some cases facilitate the delamination of the individual substantially two-dimensional layers of the nanolaminated material.

It will be readily understood by the skilled person that each substantially two-dimensional layer further comprises a surface termination T_s resulting from the etching. The surface termination constitutes a functional group and depends on the etching solution used. The surface termination may for example be -O, -H, -OH or -F, or any combination thereof. Other surface terminations are however also plausible depending on the etching solution used. It should furthermore be noted that the surface termination may be altered after etching, in accordance with any previously known method, without departing from the scope of the present invention. For example, the surface termination may be altered during an optional intercalation step and/or an optional subsequent washing step used for isolating the individual substantially two-dimensional layers.

The method may optionally also comprise an intercalation step subsequent to the etching step, but before the optional step of isolating one or more of the substantially two-dimensional layers as disclosed below. An intercalation step may for example be beneficial in case of using an etching solution comprising HF.

The method may further comprise one or more washing steps as known in the art. Such washing steps depend for example on the etching solution used and/or the desired surface termination of the individual two-dimensional layers. For example, in case the etching solution comprises LiF and HCI, washing may suitably be made in three steps wherein in the first washing step HCI may be used, in the second washing step LiCI solution may be used and in the third washing step water may be used used. The resulting plurality of substantially two-dimensional layers each having an empirical formula (Ml_x±p is either M2 or a vacancy, may be used as a stacked assembly (in the as-etched form) for the intended application. Alternatively, the process may further comprise a third step, S3, comprising isolating a first layer of said plurality of substantially two- dimensional layers. In the step of isolating the first layer out of said plurality of substantially two- dimensional layers, the as-etched stacked assembly is delaminated. The process as disclosed above results either in a plurality of substantially two-dimensional layers in an as-obtained stacked assembly (as-etched stacked assembly) or as one or more isolated layer(s) of said plurality of substantially two-dimensional layers. In the case of the M2 atoms being etched out of the nanolaminated material, the resulting two-dimensional layers (or the isolated layers) will comprise vacancies.

The fact that the M2 atoms of the nanolaminated material extend somewhat out of the M-plane towards the A-plane facilitates the selective etching of the M2 atoms while maintaining the Mo atoms in the material.

The process is further illustrated with reference to Figures 4a to 4e. Figure 4a schematically illustrates a side view of a nanolaminated material in accordance with the exemplifying embodiment discussed with reference to Figures 2a and 2b, Figure 4a thus corresponds to Figure 2a.

Figure 4b schematically illustrates one example of a stacked assembly obtained through etching of the nanolaminated material as illustrated in Figure 4a so as to remove essentially all of the Al atoms, i.e. the A-layer of the nanolaminated material. In the stacked assembly as illustrated in Figure 4b, the M2 atoms have not been etched away. The stacked assembly thus comprises a plurality of substantially two-dimensional layers 10 (only one completely shown in the figure) each having an empirical formula (Ml_x±p ,M2_y±£)₂-6Ci_±p and comprising a surface termination T_s (not illustrated) as disclosed above. Depending on the etching solution used, the individual two-dimensional layers 10 can be separated and isolated from one another in the etching solution or in a separate delamination step.

Figure 4c schematically illustrates a top view of an isolated substantially two-dimensional layer 10. As can be seen from Figures 4b and 4c, the Ml and M2 atoms are chemically ordered in relation to each other, i.e. not randomly distributed in the M sites of the crystal cells. Figure 4d schematically illustrates a stacked assembly obtained through etching of the

nanolaminated material as illustrated in Figure 4a so as to remove essentially all of the Al atoms as well as essentially all of the M2 atoms. In the resulting substantially two-dimensional layers, the sites where M2 were present in the crystal cells of the nanolaminated material will thus result in a vacancy 11. The stacked assembly thus comprises a plurality of substantially two-dimensional layers 12 (only one completely shown in the figure) each having an empirical formula (M l_x±p ,r _y±£)₂-6Ci_±p wherein r is a vacancy. Each substantially two-dimensional layer also comprises a surface termination T_s (not illustrated) as disclosed above. The individual two-dimensional layers 12 can be separated and isolated from each other as previously disclosed. Figure 4e schematically illustrates a top view of an isolated substantially two-dimensional layer 12. As can be seen from Figure 4e, the two-dimensional layer comprises ordered vacancies 11.

For sake of simplicity, the Figures 4b-4e show a case wherein the chemical ordering of the Ml atoms and the M2 atoms, or the vacancies resulting from the removal of the M2 atoms, is maintained after etching. However, the present disclosure is not limited to such a case. In some instances, the selective etching may cause some reordering of the Ml atoms and M2 atoms in relation to each other, or some transfer of M l atoms to vacancies. Therefore, the present disclosure is not limited to a two-dimensional material exhibiting chemical ordering or comprising ordered vacancies, or stacked assemblies thereof, but also encompasses unordered structures.

The present disclosure also relates to a substantially two-dimensional material which may be obtained through the process as disclosed above.

The resulting two-dimensional material according to the present invention comprises a layer having the general formula (Ml_x ,r _y)₂C, wherein Ml is Mo and r is either M2 or a vacancy. The sum of x and y is 1.00, and x is between 0.60 and 0.75. Preferably, x is between 0.65 and 0.69. More preferably, x is 0.67, or more accurately x is preferably 2/3. Furthermore, when r is M2, M2 is a transition metal selected from the group consisting of Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu. However, in reality the (Ml_x ,r _y)₂C formula may invite to a too strict interpretation inter alia since there are always normally occurring defects in a material. Furthermore, in view of the fact that the composition of the nanolaminated material from which the two-dimensional material is synthesized may diverge from the exact (Ml_x,M2_y)₂AIC formula as discussed above, the corresponding difference will also be present in the substantially two-dimensional material. Therefore, a more accurate formula for the layer of the substantially two-dimensional material is (Ml_x±p _p wherein β, ε, δ, and p takes into account expected possible divergence from a true (Ml_x ,r _y)₂C formula. Each of β and ε may be from 0 to < 0.10, preferably from 0 to <0.05. Each of δ and p may be from 0 to < 0.20, preferably from 0 to < 0.10. However, for the purpose of facilitating the reading of the present disclosure, the actual formula (Ml_x±p of the layer of the substantially two-dimensional material according to the present invention will be simplified in the following by using the general formula (M l_x ,r _y)₂C. Thus, whenever the general formula (Ml_x ,r _y)₂C is used in the following disclosure, it shall be considered to in fact constitute the formula (Μ1_χ±β ,Γ _γ±ε)₂__δ(Ιι_±ρ. This is also the case when specific elements of Ml and possibly M2 are given in the formula and/or where specific figures are given for x and/or y in the formula. By way of example, "(Mo₂/₃Eri/₃)₂C" shall in fact be interpreted as (Μο₂/_{3± β} ΕΓ ι/_3±ε)₂._δ0ι_±ρ..

According to one exemplifying embodiment, the substantially two-dimensional material comprises a layer having an empirical formula (Ml_x±p ,M2_y±i;)₂_₆Ci_±p, wherein

is 0 to < 0.1,

ε is O to < 0.1,

6 is 0 to < 0.2,

p is 0 to < 0.2,

x + y = 1,

x is between 0.60 and 0.75, preferably wherein x is between 0.65 and 0.69,

Ml is Mo, and

Preferably, in the layer having an empirical formula (Μ1_χ±β ,Μ2_γ±ε)₂._δΟι_±ρ, x is 2/3.

The layer may have a first and a second surface and comprise a surface termination as disclosed above with regard to the process for the manufacture of the substantially two-dimensional material.

The present disclosure also relates to a stacked assembly comprising a plurality of layers wherein at least one of the layers constitutes a substantially two-dimensional material as disclosed above.

The present disclosure also relates to a composite comprising a substantially two-dimensional material as disclosed above, or a stacked assembly as disclosed above.

Potential areas of application of MAX phases in general are given in the background portion of the present disclosure. The potential areas of the MAX phase alloys according to the present disclosure, i.e. the nanolaminated material according to the present disclosure, include, but are not limited to, all these applications. The MAX phase alloys according to the present disclosure increase the family of to date known MAX phase elements with lanthanides, and therefore novel properties are expected. The rich chemistries of the enlarged family of MAX phases also suggest routes for property tuning by varying the composition. Furthermore, additional applications of the MAX phases of the present application are plausible. In case M2 is Gd, the MAX phase may for example be suitable as neutron absorber. In case M2 is Ce, the MAX phase may for example be suitable for catalysis. In case M2 is Tb, the MAX phase may for example be suitable for use in optical components. In case M2 is Nd, the MAX phase may for example be suitable for use in permanent magnets. Moreover, in case M2 is Sm, the MAX phase may for example be suitable for use in permanent magnets, as neutron absorber, or for catalysis. The above given possible applications of the MAX phases for various M2 elements shall not be construed as a limiting list of applications, but only serve as examples of possible applications.

Potential applications for MXenes in general include sensors, electronic device materials, catalysts for example in the chemical industry, conductive reinforcement additives to polymers,

electrochemical energy storage materials, etc. The potential areas of the herein presented MXenes, i.e. the substantially two dimensional material, include, but are not limited to, all these applications. Furthermore, one can envisage that the possible vacancy formation in the MXenes strongly influence the range of attainable properties, where the vacancy can serve as a site with increased reactivity, and as a site for dopants, allowing atoms/ions/molecules to be inserted as well as extracted, which in turn may be of importance for general property tuning, for filtering applications, biomedical applications, etc. The substantially two-dimensional material according to the present invention is believed to be especially suitable for use in energy storage devices, for example supercapacitors, lithium-ion batteries, or in catalytic applications. Some of the MXenes presented herein wherein the M2 atoms have not been etched away may also be suitable in nuclear applications.

Experimental results Experimen tal result 1 - MAX phases

MAX phases with the compositions as given in Table 1 were synthesised. Commercially available powders were used for synthesis. The powders used for obtaining the C, Mo and Al atoms were graphite (99.999%, -200 mesh, Alfar Asar), Mo (99.99%, 10 μη% Sigma-Aldrich), and Al (99.8%, -200 mesh, Sigma-Aldrich), wherein the figures in parentheses are representing the minimum purity of the powders and the particle size of the powders. Furthermore, Ce and Tb powders (99.9%, -200 mesh, Stanford Advanced Materials) were used.

Table 1.

To obtain the powder samples, stoichiometric amounts were mixed in an agate mortar, heated to 1500 °C at 5 °C/min in an alumina crucible under flowing argon and held at their respective temperature for about 300 minutes. After being cooled down to room temperature in the furnace, loosely packed powders were obtained. Each loosely packed powder was crushed in the agate mortar into powder. The crushed powder was used for X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) analysis.

Each powder sample was characterized by XRD (theta-2theta scan) at a continuous scanning mode. XRD patterns were recorded with a powder diffractometer (PANalytical X'Pert powder

diffractometer) using CuK_aradiation (λ=1.54 A) with 0.0084° steps of 2Θ and with a dwelling time of 20s.

Powder (from the same batch as the powder sample used for XRD) was used directly for STEM analysis and prepared in accordance with conventional processes. STEM analysis of the

nanolaminated material was performed in a double-corrected FEI Titan³ 60-300, operated at 300 kV. Powder was dispersed onto a standard holey amorphous carbon support films suspended by a Cu grid.

The result of the XRD analysis and STEM analysis, respectively, are shown in the figures as given in Table 1. The results show that that MAX phases with chemical in-plane ordering was obtained in both cases.

The XRD pattern was defined by the Rietveld method. Tickers from top to bottom corresponds to the expected peak positions of different phases (MoCeAI₂C, CeAI₂, (Mo₂/₃Cei/₃)₂AIC and Mo₂C, respectively, in the case of M2 = Ce; (Mo₂/₃Tbi/₃)₂AIC, Mo₂C and Mo₃AI₂C, Tb₂0₃ and TbAI₂, respectively, in case of M2 = Tb). The observed pattern (dots), refined ( ietveld) pattern (line) and difference between observed/refined (line at the bottom) are shown in the Figures 5a and 6a.

STEM images were taken from various zone axes as shown in the Figures 5b and 6b. Figure 5b illustrates images at two different magnifications for each respective zone axis [010], [100], [110]. In Figure 6b, boxes have been included in each image illustrating the atomic structures seen. It should be noted that the images from STEM may be taken at different magnitudes and the scale has not been given in the figures, except in the upper left image of Fig. 5b. The images should therefore in the present disclosure only be considered as far as to illustrate the observed ordering of the transition metals of the nanolaminated materials and how the atoms are arranged in relation to each other.

Experimental result 2 - MAX phases MAX phases with the compositions as given in Table 2 were synthesised according to the same procedure as disclosed above with regard to Experimental result 1. The Mo, Al and C powders used were in accordance with disclosure as given in Experimental result 1. For Pr, Nd, Sm, Gd, Dy and Er, respectively, powders (99.9%, -200 mesh, Stanford Advanced Materials) were used. For Ho, Tm and Lu 2-10 mm pieces (99.9%, Stanford Advanced Materials) were used.

The result of the XRD analysis and STEM analysis, respectively are shown in the figures as given in Table 2. It should be noted that the images from STEM may be taken at different magnitudes and the scale has not been given in the figures. The images should therefore in the present disclosure only be considered as far as to illustrate the observed ordering of the transition metals of the nanolaminated materials and how the atoms are arranged in relation to each other. Furthermore, the obtained

STEM images for the different materials may be obtained along different zone axes, which explains why stacking sequences of different materials may look different. The mass contrast between M l and M2, and the choice of zone axis, decides how clearly the elements as well as their positions are visible.

The results show that MAX phases with in-plane chemical ordering was obtained for all of the materials given in Table 2. Table 2.

Experimen tal result 3 - MAX phases

MAX-phases were synthesised according to essentially the same procedure as disclosed above with regard to Experimental result 1, with the differences being the starting materials for the M2 atoms, the temperature during synthesis, and holding time. Furthermore, the heating rate up to the holding temperature was 10 °C/min. The materials and process details are given in Table 3 below.

The powder samples were characterized by XRD (theta-2theta scan) at a continuous scanning mode. XRD patterns were recorded with a powder diffractometer (PANalytical X'Pert powder

nanolaminated material was performed in a double-corrected FEI Titan3 60-300, operated at 200 kV. Powder was dispersed onto a standard holey amorphous carbon support films suspended by a Cu grid. Table 3.

In the figures 16a, 17a and 18a, respectively, the actually obtained spectrum in the XRD analysis is shown. Major peaks marked with * correspond to the MAX phase. Corresponding peaks can also seen in a simulated spectra (simulated with Crystalmaker software, based on structure obtained from theoretical simulations), albeit not illustrated in these figures. The chemically ordered MAX phase alloys have to a large extent the same XRD spectra as traditional MAX phases (which can be found in reference databases of the diffractometer). Still, the chemical in-plane ordering gives for most phases rise to an additional peak around 19 degrees, which can be used to identify new phases for further analysis with STEM.

The above given results shown in the Figures 16a-18b again (compare with Experimental results 1 and 2) demonstrate that MAX phases with in-plane chemical ordering of the transition metals were obtained for all of the synthesised nanolaminated materials as given in Table 3.

Experimental result 4 - MXene

To obtain a MXene, the MAX phase (Mo₂/₃Eri/₃)₂AIC obtained from experimental results above was etched in LiF and HCI.

2g LiF was dissolved in 30 ml 12M HCI. lg of sieved powder of the MAX phase was added to the LiF/HCI solution and stirred for 5h at 35 °C. After etching, the suspension was filtered. The obtained powder was added to a centrifuge tube and washed three times with 1M HCI to remove excess LiF, and the three times in water. The HCI washed slurry was thereafter washed three times with 1M LiCI, and the three times with water. The supernatant was removed by centrifuging at 3000 rpm for 5 minutes in the above HCI and LiCI washing procedure. Finally, water was added to the washed slurry, and shaken for 5 minutes for delamination into single, or few, layered MXene. Delamination flakes were dispersed onto standard holey amorphous carbon support films suspended by Cu grids. STEM combined with high angle annular dark field imaging (STEM-HAADF) and EDX analysis with a super-X EDX detector was performed in a double-corrected FEI Titan³ 60-300, operated at 300 kV and 60 kV, respectively. Atomic resolution STEM-HAADF images were recorded using an optimized 30 mrad convergence angle, which provided A-resolution probes at 60kV, and 50 pA probe current. The HAADF detector's inner acceptance angle was wet to 25 mrad. The images and spectroscopy showed a two-dimensional material containing Mo as well as Er. The experiment was repeated with the exception of increasing the time for etching to the double. The result showed that in the resulting MXene, substantially all of the Er had also been removed as a result of the etching thus resulting in a MXene with the general formula (Mo₂/₃, nJ₂C wherein r constitutes a vacancy.

Claims

1. Nanolaminated material with the formula (Ml_x±p,M2_y±£)₂-6Ali._aCi_±p, wherein

is0to<0.1,

ε is Oto < 0.1,

6is0to<0.2,

a is 0 to < 0.2,

pis0to<0.2,

x + y = 1,

x is between 0.60 and 0.75, preferably wherein x is between 0.65 and 0.69;

wherein

Ml is Mo, and

2. Nanolaminated material according to claim 1, wherein x is 2/3.

3. Nanolaminated material according to any one of claims 1 and 2, wherein M2 is selected from the group consisting of Ce, Ho and Er.

4. Nanolaminated material according to any of claim 1 and 2, wherein M2 is selected from the group consisting of Pr, Nd, Sm, Gd, Tb, Dy, Tm and Lu.

5. A substantially two-dimensional material comprising a layer having an empirical formula (Ml_x±p,M2_v±£)₂-6C_1±p, wherein

is0to<0.1,

ε is Oto < 0.1,

6is0to<0.2,

pis0to<0.2,

x + y = 1,

x is between 0.60 and 0.75, preferably wherein x is between 0.65 and 0.69,

Ml is Mo, and

6. A substantially two-dimensional material according to claim 5, wherein x is 2/3.

7. A substantially two-dimensional material according to any one of claims 5 and 6, wherein M2 is selected from the group consisting of Ce, Ho and Er.

8. A substantially two-dimensional material according to any one of claims 5 and 6, wherein M2 is selected from the group consisting of Pr, Nd, Sm, Gd, Tb, Dy, Tm and Lu.

9. A substantially two-dimensional material according to any one of claims 5 to 8, wherein the layer has a first surface and a second surface, and wherein the layer comprises a surface termination T_s.

10. Process for manufacturing a substantially two-dimensional material according to any one of claims 5 to 9, the process comprising the following steps:

a) preparing a nanolaminated material with the formula (Ml_x±p ,M2_y±£)₂-6Ali._aCi_±p

according to any one of claims 1 to 4,

b) selectively etching the nanolaminated material so as to remove substantially all of the Al atoms, thereby obtaining a plurality of substantially two-dimensional layers each having a formula (Ml_x±p ,M2_y±£)₂-6Ci_±p, and wherein each substantially two- dimensional layer comprises a surface termination T_s resulting from the etching, and c) thereafter isolating at least one first layer of the plurality of substantially two- dimensional layers.

11. Process for manufacturing a substantially two-dimensional material comprising a layer having an empirical formula (Ml_x±p wherein

is 0 to < 0.1,

ε is O to < 0.1,

6 is 0 to < 0.2,

p is 0 to < 0.2,

x + y = 1,

x is between 0.60 and 0.75,

wherein Ml is Mo and re constitutes a vacancy,

the process comprising d) preparing a nanolaminated material with the formula (Ml_x±p ,M2_y±£)₂_₆Ali__aCi_±p according to any one of claims 1 to 4,

e) selectively etching the nanolaminated material so as to remove substantially all of the Al atoms and substantially all of the M2 atoms, thereby obtaining a plurality of substantially two-dimensional layers each having a formula (M l_x±p and wherein each substantially two-dimensional layer comprises a surface termination T_s resulting from the etching, and

f) thereafter isolating at least one first layer of the plurality of substantially two- dimensional layers.

12. Method for manufacturing a material comprising a stacked assembly of a plurality of

substantially two-dimensional layers, the method comprising the following steps:

c) preparing a nanolaminated material with the formula (Μ1_χ±β ,Μ2_γ±£)₂__δΑΙι__α(Ιι_±ρ

according to any one of claims 1 to 4,

d) selectively etching the nanolaminated material so as to remove substantially all of the Al atoms and optionally substantially all of the M2 atoms, thereby obtaining a plurality of substantially two-dimensional layers each having a formula (M l_x±p ,r _y±£)₂- sCi_+p wherein r is either M2 or a vacancy, and wherein each substantially two- dimensional layer comprises a surface termination T_s resulting from the etching.

13. Method according claim 12, further comprising a step of exchanging the surface termination T_s of each of the substantially two-dimensional layers resulting from the etching to another surface termination T_s.

14. A stacked assembly comprising a plurality of layers wherein at least one of the layers

constitutes a substantially two-dimensional material according to any one of claims 5 to 9.

15. A composite comprising a substantially two-dimensional material according to any one of claims 5 to 9.

16. Energy storage device comprising a substantially two-dimensional material according to any one of claims 5 to 9.