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        reported on the electrochemical stratification of non-conducting boron into thin-layer borons. This unique effect is achieved by incorporating bulk boron into a metal mesh that induces electrical conduction and opens up space for boron fabrication with this viable strategy. Experiments performed in various electrolytes provide a powerful tool for obtaining borene flakes of various phases with a thickness of ~3–6 nm. The mechanism of electrochemical elimination of boron is also revealed and discussed. Thus, the proposed method can serve as a new tool for large-scale production of thin-layer burs and accelerate the development of research related to burs and their potential applications.
        Two-dimensional (2D) materials have received a lot of interest in recent years due to their unique properties such as electrical conductivity or prominent active surfaces. The development of graphene materials has drawn attention to other 2D materials, so new 2D materials are being extensively researched. In addition to the well-known graphene, transition metal dichalcogenides (TMD) such as WS21, MoS22, MoSe3, and WSe4 have also been intensively studied recently. Despite the aforementioned materials, hexagonal boron nitride (hBN), black phosphorus and the recently successfully produced boronene. Among them, boron attracted much attention as one of the youngest two-dimensional systems. It is layered like graphene but exhibits interesting properties due to its anisotropy, polymorphism and crystal structure. Bulk boron appears as the basic building block in the B12 icosahedron, but different types of boron crystals are formed through different joining and bonding methods in B12. As a result, boron blocks are usually not layered like graphene or graphite, which complicates the process of obtaining boron. In addition, many polymorphic forms of borophene (eg, α, β, α1, pmmm) make it even more complex5. The various stages achieved during the synthesis directly affect the properties of harrows. Therefore, the development of synthetic methods that make it possible to obtain phase-specific borocenes with large lateral dimensions and small thickness of flakes currently requires deep study.
        Many methods for synthesizing 2D materials are based on sonochemical processes in which bulk materials are placed in a solvent, usually an organic solvent, and sonicated for several hours. Ranjan et al. 6 successfully exfoliated bulk boron into borophene using the method described above. They studied a range of organic solvents (methanol, ethanol, isopropanol, acetone, DMF, DMSO) and showed that sonication exfoliation is a simple method for obtaining large and thin boron flakes. In addition, they demonstrated that the modified Hummers method can also be used to exfoliate boron. Liquid stratification has been demonstrated by others: Lin et al. 7 used crystalline boron as a source to synthesize low-layer β12-borene sheets and further used them in borene-based lithium-sulfur batteries, and Li et al. 8 demonstrated low-layer boronene sheets. . It can be obtained by sonochemical synthesis and used as a supercapacitor electrode. However, atomic layer deposition (ALD) is also one of the bottom-up synthesis methods for boron. Mannix et al.9 deposited boron atoms on an atomically pure silver support. This approach makes it possible to obtain sheets of ultra-pure boronene, however laboratory-scale production of boronene is severely limited due to the harsh process conditions (ultra-high vacuum). Therefore, it is critical to develop new efficient strategies for the manufacture of boronene, explain the growth/stratification mechanism, and then conduct an accurate theoretical analysis of its properties, such as polymorphism, electrical and thermal transfer. H. Liu et al. 10 discussed and explained the mechanism of boron growth on Cu(111) substrates. It turned out that boron atoms tend to form 2D dense clusters based on triangular units, and the formation energy steadily decreases with increasing cluster size, suggesting that 2D boron clusters on copper substrates can grow indefinitely. A more detailed analysis of two-dimensional boron sheets is presented by D. Li et al. 11, where various substrates are described and possible applications are discussed. It is clearly indicated that there are some discrepancies between theoretical calculations and experimental results. Therefore, theoretical calculations are needed to fully understand the properties and mechanisms of boron growth. One way to achieve this goal is to use a simple adhesive tape to remove boron, but this is still too small to investigate the basic properties and modify its practical application12.
        A promising way of engineering peeling of 2D materials from bulk materials is electrochemical peeling. Here one of the electrodes consists of bulk material. In general, compounds that are typically exfoliated by electrochemical methods are highly conductive. They are available as compressed sticks or tablets. Graphite can be successfully exfoliated in this way due to its high electrical conductivity. Achi and his team14 have successfully exfoliated graphite by converting graphite rods into pressed graphite in the presence of a membrane used to prevent decomposition of the bulk material. Other bulky laminates are successfully exfoliated in a similar manner, for example, using Janus15 electrochemical delamination. Similarly, layered black phosphorus is electrochemically stratified, with acidic electrolyte ions diffusing into the space between the layers due to the applied voltage. Unfortunately, the same approach cannot simply be applied to the stratification of boron into borophene due to the low electrical conductivity of the bulk material. But what happens if loose boron powder is included in a metal mesh (nickel-nickel or copper-copper) to be used as an electrode? Is it possible to induce the conductivity of boron, which can be further electrochemically split as a layered system of electrical conductors? What is the phase of the developed low-layer boronene?
       In this study, we answer these questions and demonstrate that this simple strategy provides a new general approach to fabricating thin burs, as shown in Figure 1.
        Lithium chloride (LiCl, 99.0%, CAS: 7447-41-8) and boron powder (B, CAS: 7440-42-8) were purchased from Sigma Aldrich (USA). Sodium sulfate (Na2SO4, ≥ 99.0%, CAS: 7757-82-6) supplied from Chempur (Poland). Dimethyl sulfoxide (DMSO, CAS: 67-68-5) from Karpinex (Poland) was used.
        Atomic force microscopy (AFM MultiMode 8 (Bruker)) provides information on the thickness and lattice size of the layered material. High resolution transmission electron microscopy (HR-TEM) was performed using an FEI Tecnai F20 microscope at an accelerating voltage of 200 kV. Atomic absorption spectroscopy (AAS) analysis was performed using a Hitachi Zeeman polarized atomic absorption spectrophotometer and a flame nebulizer to determine the migration of metal ions into solution during electrochemical exfoliation. The zeta potential of the bulk boron was measured and carried out on a Zeta Sizer (ZS Nano ZEN 3600, Malvern) to determine the surface potential of the bulk boron. The chemical composition and relative atomic percentages of the surface of the samples were studied by X-ray photoelectron spectroscopy (XPS). The measurements were carried out using Mg Ka radiation (hν = 1253.6 eV) in the PREVAC system (Poland) equipped with a Scienta SES 2002 electron energy analyzer (Sweden) operating at a constant transmitted energy (Ep = 50 eV). The analysis chamber is evacuated to a pressure below 5×10-9 mbar.
        Typically, 0.1 g of free-flowing boron powder is first pressed into a metal mesh disk (nickel or copper) using a hydraulic press. The disk has a diameter of 15 mm. Prepared disks are used as electrodes. Two types of electrolytes were used: (i) 1 M LiCl in DMSO and (ii) 1 M Na2SO4 in deionized water. A platinum wire was used as an auxiliary electrode. The schematic diagram of the workstation is shown in Figure 1. In electrochemical stripping, a given current (1 A, 0.5 A, or 0.1 A) is applied between the cathode and anode. The duration of each experiment is 1 hour. After that, the supernatant was collected, centrifuged at 5000 rpm and washed several times (3-5 times) with deionized water.
        Various parameters, such as time and distance between electrodes, affect the morphology of the final product of electrochemical separation. Here we examine the influence of the electrolyte, the applied current (1 A, 0.5 A and 0.1 A; voltage 30 V) and the type of metal grid (Ni depending on the impact size). Two different electrolytes were tested: (i) 1 M lithium chloride (LiCl) in dimethyl sulfoxide (DMSO) and (ii) 1 M sodium sulfate (Na2SO4) in deionized (DI) water. In the first, lithium cations (Li+) will intercalate into boron, which is associated with a negative charge in the process. In the latter case, the sulfate anion (SO42-) will intercalate into a positively charged boron.
        Initially, the action of the above electrolytes was shown at a current of 1 A. The process took 1 hour with two types of metal grids (Ni and Cu), respectively. Figure 2 shows an atomic force microscopy (AFM) image of the resulting material, and the corresponding height profile is shown in Figure S1. In addition, the height and dimensions of the flakes made in each experiment are shown in Table 1. Apparently, when using Na2SO4 as an electrolyte, the thickness of the flakes is much less when using a copper grid. Compared to flakes peeled off in the presence of a nickel carrier, the thickness decreases by about 5 times. Interestingly, the size distribution of scales was similar. However, LiCl/DMSO was effective in the exfoliation process using both metal meshes, resulting in 5–15 layers of borocene, similar to other exfoliating fluids, resulting in multiple layers of borocene7,8. Therefore, further studies will reveal the detailed structure of samples stratified in this electrolyte.
       AFM images of borocene sheets after electrochemical delamination into A Cu_Li+_1 A, B Cu_SO42−_1 A, C Ni_Li+_1 A, and D Ni_SO42−_1 A.
        Analysis was carried out using transmission electron microscopy (TEM). As shown in Figure 3, the bulk structure of boron is crystalline, as evidenced by the TEM images of both boron and layered boron, as well as the corresponding Fast Fourier Transform (FFT) and subsequent Selected Area Electron Diffraction (SAED) patterns. The main differences between the samples after the delamination process are easily seen in the TEM images, where the d-spacings are sharper and the distances are much shorter (0.35–0.9 nm; Table S2). While the samples fabricated on the copper mesh matched the β-rhombohedral structure of boron8, the samples fabricated using the nickel mesh matched the theoretical predictions of the lattice parameters: β12 and χ317. This proved that the structure of the borocene was crystalline, but the thickness and crystal structure changed upon exfoliation. However, it clearly shows the dependence of the grid used (Cu or Ni) on the crystallinity of the resulting borene. For Cu or Ni, it can be single-crystal or polycrystalline, respectively. Crystal modifications have also been found in other exfoliation techniques18,19. In our case, the step d and the final structure strongly depend on the type of grid used (Ni, Cu). Significant variations can be found in the SAED patterns, suggesting that our method leads to the formation of more uniform crystal structures. In addition, elemental mapping (EDX) and STEM imaging proved that the fabricated 2D material consisted of the element boron (Fig. S5). However, for a deeper understanding of the structure, further studies of the properties of artificial borophenes are required. In particular, the analysis of borene edges should be continued, as they play a crucial role in the stability of the material and its catalytic performance20,21,22.
        TEM images of bulk boron A, B Cu_Li+_1 A and C Ni_Li+_1 A and corresponding SAED patterns (A’, B’, C’); fast Fourier transform (FFT) insertion to the TEM image.
        X-ray photoelectron spectroscopy (XPS) was performed to determine the degree of oxidation of borene samples. During heating of the borophene samples, the boron-boron ratio increased from 6.97% to 28.13% (Table S3). Meanwhile, the reduction of boron suboxide (BO) bonds occurs mainly due to the separation of surface oxides and the conversion of boron suboxide to B2O3, as indicated by an increased amount of B2O3 in the samples. On fig. S8 shows changes in the bonding ratio of boron and oxide elements upon heating. The overall spectrum is shown in fig. S7. Tests showed that boronene oxidized on the surface at a boron:oxide ratio of 1:1 before heating and 1.5:1 after heating. For a more detailed description of XPS, see Supplementary Information.
        Subsequent experiments were carried out to test the effect of the current applied between the electrodes during electrochemical separation. The tests were carried out at currents of 0.5 A and 0.1 A in LiCl/DMSO, respectively. The results of AFM studies are shown in Fig. 4, and the corresponding height profiles are shown in Figs. S2 and S3. Considering that the thickness of a borophene monolayer is about 0.4 nm,12,23 in experiments at 0.5 A and the presence of a copper grid, the thinnest flakes correspond to 5–11 borophene layers with lateral dimensions of about 0.6–2.5 μm. In addition, in experiments with nickel grids, flakes with an extremely small thickness distribution (4.82–5.27 nm) were obtained. Interestingly, boron flakes obtained by sonochemical methods have similar flake sizes in the range of 1.32–2.32 nm7 or 1.8–4.7 nm8. In addition, the electrochemical exfoliation of graphene proposed by Achi et al. 14 resulted in larger flakes (>30 µm), which may be related to the size of the starting material. However, graphene flakes are 2–7 nm thick. Flakes of a more uniform size and height can be obtained by reducing the applied current from 1 A to 0.1 A. Thus, controlling this key texture parameter of 2D materials is a simple strategy. It should be noted that the experiments carried out on a nickel grid with a current of 0.1 A were not successful. This is due to the low electrical conductivity of nickel compared to copper and the insufficient energy required to form borophene24. TEM analysis of Cu_Li+_0.5 A, Cu_Li+_0.1 A, Cu_SO42-_1 A, Ni_Li-_0.5 A and Ni_SO42-_1 A is shown in Figure S3 and Figure S4, respectively.
        Electrochemical ablation followed by AFM imaging. (A) Cu_Li+_1A, (B) Cu_Li+_0.5A, (C) Cu_Li+_0.1A, (D) Ni_Li+_1A, (E) Ni_Li+_0.5A.
        Here we also propose a possible mechanism for the stratification of a bulk drill into thin-layer drills (Fig. 5). Initially, the bulk bur was pressed into the Cu/Ni grid to induce conduction in the electrode, which successfully applied a voltage between the auxiliary electrode (Pt wire) and the working electrode. This allows the ions to migrate through the electrolyte and become embedded in the cathode/anode material, depending on the electrolyte used. AAS analysis demonstrated that no ions were released from the metal mesh during this process (see Supplementary Information). showed that only ions from the electrolyte can penetrate into the boron structure. The bulk commercial boron used in this process is often referred to as “amorphous boron” because of its random distribution of primary cell units, icosahedral B12, which is heated to 1000°C to form an ordered β-rhombohedral structure (Fig. S6) 25 . According to the data, lithium cations are easily introduced into the boron structure at the first stage and tear off fragments of the B12 battery, eventually forming a two-dimensional boronene structure with a highly ordered structure, such as β-rhombohedra, β12 or χ3, depending on the applied current and the mesh material. To reveal the affinity Li+ to bulk boron and its key role in the delamination process, its zeta potential (ZP) was measured to be -38 ± 3.5 mV (see Supplementary Information) . The negative ZP value for bulk boron indicates that intercalation of positive lithium cations is more efficient than other ions used in this study (such as SO42-). This also explains the more efficient penetration of Li+ into the boron structure, resulting in more efficient electrochemical removal.
        Thus, we have developed a new method for obtaining low-layer borons by electrochemical stratification of boron using Cu/Ni grids in Li+/DMSO and SO42-/H2O solutions. It also seems to give output at different stages depending on the current applied and the grid used. The mechanism of the exfoliation process is also proposed and discussed. It can be concluded that quality-controlled low-layer boronene can be easily produced by choosing a suitable metal mesh as a boron carrier and optimizing the applied current, which can be further used in basic research or practical applications. More importantly, this is the first successful attempt at electrochemical stratification of boron. It is believed that this path can usually be used to exfoliate non-conductive materials into two-dimensional forms. However, a better understanding of the structure and properties of the synthesized low-layer burs is needed, as well as additional research.
       Datasets created and/or analyzed during the current study are available from the RepOD repository, https://doi.org/10.18150/X5LWAN.
        Desai, J. A., Adhikari, N. and Kaul, A. B. Semiconductor WS2 peel chemical efficiency and its application in additively fabricated graphene-WS2-graphene heterostructured photodiodes. RSC Advances 9, 25805–25816. https://doi.org/10.1039/C9RA03644J (2019).
        Li, L. et al. MoS2 delamination under the action of an electric field. J. Alloys. Compare. 862, 158551. https://doi.org/10.1016/J.JALLCOM.2020.158551 (2021).
        Chen, X. et al. Liquid-phase layered 2D MoSe2 nanosheets for high-performance NO2 gas sensor at room temperature. Nanotechnology 30, 445503. https://doi.org/10.1088/1361-6528/AB35EC (2019).
        Yuan, L. et al. A reliable method for qualitative mechanical delamination of large-scale 2D materials. AIP Advances 6, 125201. https://doi.org/10.1063/1.4967967 (2016).
        Ou, M. et al. The emergence and evolution of boron. Advanced science. 8, 2001 801. https://doi.org/10.1002/ADVS.202001801 (2021).
        Ranjan, P. et al. Individual harrows and their hybrids. Advanced alma mater. 31:1-8. https://doi.org/10.1002/adma.201900353 (2019).
        Lin, H. et al. Large-scale production of off-grid low-layer single wafers of β12-borene as efficient electrocatalysts for lithium-sulfur batteries. SAU Nano 15, 17327–17336. https://doi.org/10.1021/acsnano.1c04961 (2021).
        Lee, H. et al. Large-scale production of low-layer boron sheets and their excellent supercapacitance performance by liquid phase separation. SAU Nano 12, 1262–1272. https://doi.org/10.1021/acsnano.7b07444 (2018).
        Mannix, A.J. Boron Synthesis: Anisotropic Two-Dimensional Boron Polymorphs. Science 350 (2015), 1513-1516. https://doi.org/10.1126/science.aad1080 (1979).
        Liu H., Gao J., and Zhao J. From boron clusters to 2D boron sheets on Cu(111) surfaces: growth mechanism and pore formation. the science. Report 3, 1–9. https://doi.org/10.1038/srep03238 (2013).
        Lee, D. et al. Two-dimensional boron sheets: structure, growth, electronic and thermal transport properties. Extended capabilities. alma mater. 30, 1904349. https://doi.org/10.1002/adfm.201904349 (2020).
        Chahal, S. et al. Boren exfoliates by micromechanics. Advanced alma mater. 2102039(33), 1-13. https://doi.org/10.1002/adma.202102039 (2021).
        Liu, F. et al. Synthesis of graphene materials by electrochemical exfoliation: recent progress and future potential. Carbon Energy 1, 173–199. https://doi.org/10.1002/CEY2.14 (2019).
        Achi, T.S. et al. Scalable, high yield graphene nanosheets produced from compressed graphite using electrochemical stratification. the science. Report 8(1), 8. https://doi.org/10.1038/s41598-018-32741-3 (2018).
        Fang, Y. et al. Janus electrochemical delamination of two-dimensional materials. J. Alma mater. Chemical. A. 7, 25691–25711. https://doi.org/10.1039/c9ta10487a (2019).
        Ambrosi A., Sofer Z. and Pumera M. Electrochemical delamination of layered black phosphorus to phosphorene. Angie. Chemical. 129, 10579–10581. https://doi.org/10.1002/ange.201705071 (2017).
        Feng, B. et al. Experimental implementation of a two-dimensional boron sheet. National Chemical. 8, 563–568. https://doi.org/10.1038/nchem.2491 (2016).
        Xie Z. et al. Two-dimensional boronene: properties, preparation and promising applications. Research 2020, 1-23. https://doi.org/10.34133/2020/2624617 (2020).
        Gee, X. et al. Novel top-down synthesis of ultra-thin two-dimensional boron nanosheets for image-guided multimodal cancer therapy. Advanced alma mater. 30, 1803031. https://doi.org/10.1002/ADMA.201803031 (2018).
        Chang, Y., Zhai, P., Hou, J., Zhao, J., and Gao, J. Superior HER and OER catalytic performance of selenium vacancies in defect-engineered PtSe 2: from simulation to experiment. Alma mater of advanced energy. 12, 2102359. https://doi.org/10.1002/aenm.202102359 (2022).
        Li, S. et al. Elimination of edge electronic and phonon states of phosphorene nanoribbons by unique edge reconstruction. 18 years younger, 2105130. https://doi.org/10.1002/smll.202105130 (2022).
        Zhang, Yu, et al. Universal zigzag reconstruction of wrinkled α-phase monolayers and their resulting robust space charge separation. Nanolet. 21, 8095–8102. https://doi.org/10.1021/acs.nanolett.1c02461 (2021).
        Lee, W. et al. Experimental implementation of honeycomb boronene. the science. bull. 63, 282-286. https://doi.org/10.1016/J.SCIB.2018.02.006 (2018).
        Taherian, R. Conductivity Theory, Conductivity. In Polymer-Based Composites: Experiments, Modeling, and Applications (Kausar, A. ed.) 1–18 (Elsevier, Amsterdam, 2019). https://doi.org/10.1016/B978-0-12-812541-0.00001-X.
        Gillespie, J.S., Talley, P., Line, L.E., Overman, K.D., Synthesis, B., Kohn, JAWF, Nye, G.K., Gole, E., Laubengayer, V ., Hurd, D.T., Newkirk, A.E., Hoard, J.L., Johnston, HLN, Hersh, EC Kerr, J., Rossini, FD, Wagman, DD, Evans, WH, Levine, S ., Jaffee, I. Newkirk and boranes. Add. chem. ser. 65, 1112. https://pubs.acs.org/sharingguidelines (January 21, 2022).
       This study was supported by the National Science Center (Poland) under grant no. OPUS21 (2021/41/B/ST5/03279).
       Nickel wire mesh is a type of industrial wire cloth made from nickel wire. It is characterized by its durability, electrical conductivity, and resistance to corrosion and rust. Due to its unique properties, nickel wire mesh is commonly used in applications such as filtration, sieving, and separation in industries such as aerospace, chemical, and food processing. It is available in a range of mesh sizes and wire diameters to suit various requirements.