Cathodic Exfoliation Research Articles

Current-perpendicular-to-plane giant magnetoresistance in Co/Cu multilayered nanocylinders electrodeposited into anodized aluminum oxide nanochannels with ultra-large aspect ratio

An anodized aluminum oxide (AAO) thick film with numerous nanochannels was synthesized by a cathodic exfoliation technique from a metallic aluminum rod. The nanochannel diameter D and length L were about 60 nm and 60 µm, respectively. The aspect ratio L/D reached ~ 1000. A rectangular pulsed potential deposition technique was applied to electrochemically grow the multilayered nanocylinders with alternating Cu and Co thin layers in the AAO nanochannels. The Co/Cu bilayer thickness was decreased to around 7 nm at the minimum by controlling the pulsed potential and duty cycle during the electrodeposition process. An electrochemical in situ single contact process was demonstrated by monitoring the observed current until a Co/Cu multilayered nanocylinder reached the nanoporous Au film on the AAO thick film. The resistance of the Co/Cu multilayered nanocylinder was determined to range from 1 to 2 kΩ, which corresponded well with a theoretical estimation. Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) of a Co/Cu multilayered nanocylinder with ~ 6000 bilayers (Cu = 2.4 nm, Co = 7.1 nm) reached up to 31.5% at room temperature. Valet–Fert model agreed well with the present study concerning the effect of Cu-layer thickness on CPP-GMR.

Electrochemically Exfoliated Platinum Dichalcogenide Atomic Layers for High-Performance Air-Stable Infrared Photodetectors.

Platinum dichalcogenide (PtX2), an emergent group-10 transition metal dichalcogenide (TMD) has shown great potential in infrared photonic and optoelectronic applications due to its layer-dependent electronic structure with potentially suitable bandgap. However, a scalable synthesis of PtSe2 and PtTe2 atomic layers with controlled thickness still represents a major challenge in this field because of the strong interlayer interactions. Herein, we develop a facile cathodic exfoliation approach for the synthesis of solution-processable high-quality PtSe2 and PtTe2 atomic layers for high-performance infrared (IR) photodetection. As-exfoliated PtSe2 and PtTe2 bilayer exhibit an excellent photoresponsivity of 72 and 1620 mA W-1 at zero gate voltage under a 1540 nm laser illumination, respectively, approximately several orders of magnitude higher than that of the majority of IR photodetectors based on graphene, TMDs, and black phosphorus. In addition, our PtSe2 and PtTe2 bilayer device also shows a decent specific detectivity of beyond 109 Jones with remarkable air-stability (>several months), outperforming the mechanically exfoliated counterparts under the laser illumination with a similar wavelength. Moreover, a high yield of PtSe2 and PtTe2 atomic layers dispersed in solution also allows for a facile fabrication of air-stable wafer-scale IR photodetector. This work demonstrates a new route for the synthesis of solution-processable layered materials with the narrow bandgap for the infrared optoelectronic applications.

Regulating cations and solvents of the electrolyte for ultra-efficient electrochemical production of high-quality graphene

Electrochemical exfoliation of graphite has been regarded as a potential approach to produce graphene on a large scale. Despite recent progress in the production of graphene with few defects by cathodic exfoliation, current methods suffer from uncontrolled thicknesses and limited yield. Here we devise a novel cathodic exfoliation method using diverse tetraalkylammonium cations in various non-aqueous solvents toward efficient preparation of high-quality graphene. Sandwich-structured graphite electrode enables sufficient ion intercalation and uniform exfoliation into few-layer graphene (>80%, 1–3 layers), along with remarkable yield (91.5%) and ultralow defect density (ID/IG = 0.05). The interplay of electrolyte cation and solvent on its intercalation efficiency and electrochemical stability was also studied, which are in direct correlation with the exfoliation ability. Further mechanism investigation demonstrates that tetrabutylammonium cations in propylene carbonate can intercalate into graphite efficiently under reducing condition. Adjacent layers were then taken apart rapidly due to gas formation reactions, resulting in non-destructive exfoliation. The preparation process can be easily scaled up and yield a high production rate (exceeding 50 g h−1), demonstrating its potential to facilitate the mass production of high-quality graphene for extensive applications.

Contribution of Different Exfoliation Mechanisms in the Bipolar Electrochemical Fabrication of Graphene

Since the discovery of graphene, two-dimensional (2D) materials have attracted increasing interest due to their extraordinary properties such as high thermal conductivity, high specific surface area, and broad electrochemical window. In general, different techniques have been employed to fabricate these materials, including chemical vapor deposition, mechanical, chemical, and electrochemical exfoliation. Bipolar electrochemistry (BPE) is one of the newest methods which has been used for the fabrication of 2D materials. In our previous study, a modified BPE concept was developed for simultaneous exfoliating and deposition of both reduced graphene oxide (rGO) and graphene oxide (GO) layers on conductive objects. Although the characteristics of the produced materials have been studied and reported, there are still remaining questions that need more investigations to be answered. The main focus of this study is investigating the active exfoliation mechanisms in the BPE process and finding out the dominant exfoliation reactions (either cathodic or anodic exfoliation).For this purpose, a novel and unique modified bipolar system has been developed, which could retard either anodic or cathodic exfoliation of graphite by replacing the relevant sites of the bipolar electrode with a platinum wire. This helped to have a better understanding of the source of produced rGO and GO. The morphology and functional groups of deposited materials on both negative and positive feeding electrodes were investigated when the graphite was polarized to either positive or negative potentials. The results proved that both anodic and cathodic exfoliation mechanisms are active at the same time when using graphite as the bipolar electrode. However, the morphology, functional groups, level of oxidation, the bipolar current, and deposition rate vary according to the exfoliation mechanism. The developed modified BPE technique and materials characterizations will be discussed in detail at the conference.Keywords: Electrochemical exfoliation, bipolar electrochemistry, 2D materials, graphene fabrication

Cathodic exfoliation of graphite into graphene nanoplatelets in aqueous solution of alkali metal salts

Electrochemical exfoliation has emerged as a green, effective and scalable route for mass production of graphene. Cathodic exfoliation of graphite, offers a direct production of high quality and low defect graphene. However, the protocols for cathodic exfoliation reported to date, use mostly non-aqueous electrolytes which require extended period of intercalation, and post-treatment to further exfoliate the intercalated graphene layers. In contrast, the employment of environment friendly aqueous-based electrolytes, coupling with a shorter exfoliation period would be attractive features of any new protocol. Here, we demonstrate efficient cathodic electrochemical exfoliation of graphite to graphene nanoplatelets in aqueous electrolytes using common and inexpensive alkali-metal salts such as KCl. The key driving force to exfoliate graphite successfully in aqueous electrolyte is applying a sufficiently high voltage, and a high salt concentration which facilitate cation intercalation, and promotes hydrogen evolution to exfoliate the graphene. The cathodic exfoliated graphene nanoplatelets using KCl aqueous electrolyte exhibits a low defect density (ID/IG of 0.06, a C/O ratio of 57.8), high graphite exfoliation yields (> 80%) in short times (< 10 min for a graphite foil of 1 cm × 1 cm × 0.0254 cm, 30.0 mg). The highly conductive structure consists mainly of 10–13 layers graphene sheets that serve as an excellent support material for electrocatalytic reactions. This environment-benign aqueous-based cathodic electrochemical exfoliation of graphite opens a new opportunity in large-scale and low-cost production of high-quality graphene nanoplatelets.

Electrochemical exfoliation and functionalization of black phosphorene to enhance mechanical properties and flame retardancy of waterborne polyurethane

Similar to graphene, few-layer black phosphorus possesses many excellent properties such as good thermal stability, mechanical properties and unique characteristic dimension effects, which is considered as promising nanoadditives. But the low yield and inferior interfacial adhesion with polymer matrix are unavoidable obstruction to fabricate high performance nanocomposites. Herein, we report a facile and environmentally friendly approach to simultaneously exfoliate and modify black phosphorus (BP) by electrochemical cathodic exfoliation, where BP crystal acted as the cathode and ethylene imine polymer (PEI) acted as electrolyte and modifier. The positively charged PEI would uniformly anchor on the surface of the newly peeled-off BP nanosheets through electrostatic attraction effect, resulting in preventing the agglomeration of BP nanosheets and improve the compatibility between BP and waterborne polyurethane (WPU) matrix. Significantly, with the addition of 2.0 wt% PEI modified BP in WPU matrix, the fire safety of WPU composites was enhanced. The peak heat-release rate, total heat release, total smoke production and total CO yield are decreased by 34.3%, 21.2%, 22.3% and 50.2% compared to pure WPU, respectively. Also, the tensile strength of WPU composites was increased by 71% (from 21.9 to 31.0 MPa) at the cost of the breaking elongation slightly decreased by 5.6%. This work provides the possibility for the scalable preparation and a real application of BP in polymer nanocomposites.

Accordion-like bimetal-organic framework anchoring on the partially-exfoliated graphite paper for high-performance supercapacitors

Metal-organic frameworks (MOFs) are considered as a promising energy storage material owing to their inherent advantages of large surface area, regulatable pore size and functional groups. However, the relative poor electronic conductivity is an obstacle to their wide practical application. Herein, the partially-exfoliated graphite paper (EGP) composed of graphene nanosheets is prepared by a controlled cathodic exfoliation. EGP exhibits 3D hierarchical porous structure and good electronic conductivity, which acts as an ideal substrate for growing accordion-like structure NiCo-based bimetal-organic framework (NCMOF). The as-synthesized NCMOF/EGP shows high areal specific capacitance of 2.41 F cm−2 at 0.5 mA cm−2, and good rate performance of 72.6% at the current densities from 0.5 to 20 mA cm−2. Furthermore, the constructed NCMOF/EGP//active carbon delivers an energy density of 0.11 mW h cm−2 at a power density of 0.75 mW cm−2, and long cycle life. The outstanding electrochemical energy storage performance of NCMOF/EGP are assigned to 3D hierarchical porous structure and good electronic conductivity of EGP combined with layered structure of NCMOF.

Scalable Fabrication of Carbon Nanomaterials by Electrochemical Dual-Electrode Exfoliation of Graphite in Hydroxide Molten Salt

Simultaneous electroexfoliation of graphite on both cathode and anode in molten NaOH–KOH was proposed and found to be a feasible method for the mass production of carbon nanomaterials. During this electrolysis process, alkaline cations and hydroxide ions were intercalated into the bulk graphite and then discharged to generate alkaline metals and hydrogen at the cathode, and oxygen at the anode. The simultaneous intercalation on both electrodes and the escape of gas enhanced the exfoliation efficiency, leading to a high production rate of nanostructured carbon exceeding 26.9 g h–1. The four to seven layers of graphene nanosheets with negligible defect (ID/IG = 0.079) and low oxidation degree (C/O ratio = 20.32) were obtained through cathodic exfoliation, while the corresponding anodic exfoliation products featured more oxygen-containing functional groups (7.59%). This introduced method was beneficial for the mass production of carbon materials in a highly efficient way.

The Influence of the Ionic Form of Input Diatomite on the Cathodic Disbondment of Bitumen–Polymer Coatings

The effect of diatomite introduced as an active filler in nickel 2(+) and sodium (+) ionic forms on the adhesion resistance of bitumen–diatomite protective systems during their cathodic polarization is studied. A significant effect of the introduced diatomite clay, the method of its activation, its ionic form on the cathodic exfoliation, and, as a result, the adhesive durability of bitumen–polymer protective coatings during their cathodic polarization are shown. This effect can be used to create protective anticorrosion coatings with increased durability.

Design and construction of few-layer graphene cathode for ultrafast and high-capacity aluminum-ion batteries

Graphite is a key cathode material for aluminum-ion batteries (AIBs), but appears poor structural stability and cyclability due to the slow kinetics of intercalation and usage of conductive additives. So far, reasonable design and construction of high-conductive, flexible, binder-free graphitic film cathodes with fast kinetics of anion intercalation mechanism still remains challenging for high-power and high-energy AIBs. Herein, we report the reasonable design for facile construction of high-conductive and mechanically flexible film cathode of high-quality few-layer graphene (FLG) nanosheets for high capacity and fast AIBs, thanks to the strong synergy of ionic surface adsorption/desorption of graphene and ionic intercalation/deintercalation of graphite. The FLG nanosheets prepared by electrochemical cathodic exfoliation from graphite, exhibit predominantly 3–5 layers, extremely low ID/IG ratio of <0.05, ultrahigh C/O atom ratio of 43, and excellent solution-processability, which allow for large-area production of highly conducting (1300 ​S ​cm−1), binder-free and densely stacked FLG films as extremely stable cathodes for ultrafast AIBs. It’s worth mentioning that the resulting AIBs exhibit high capacity of 173 mAh g−1 at 1 ​A ​g−1, outstanding rate capability with exceptionally large capacity of 101 mAh g−1 at 10 ​A ​g−1 that outperforms the most reported graphitic materials, long-term cyclability without noticeable capacity loss after 10000 cycles, and good performance at wide range of temperatures. The multiple characterizations and theoretical simulation further confirm that the unique performance is attributed to the synergistic mechanisms of diffusion-controlled intercalation and surface adsorption of FLG film. Therefore, this work will open intriguing opportunities for the development of advanced AIBs.

A Robust 2D Photo‐Electrochemical Detector Based on NiPS3 Flakes

AbstractPhotodetectors fabricated from very thin two‐dimensional (2D) materials with high photoelectric conversion efficiency have unprecedented potential to overcome the limitations of conventional photodetectors. In particular, recent interest in 2D metal phosphorus trichalcogenides (MPTs) has derived from their strong light absorption, tunable bandgap, and robust stability. Here, large and atomically thin NiPS3 flakes, prepared by electrochemical cathodic exfoliation, are used as electrodes for a self‐powered photo‐electrochemical (PEC) detector. It exhibits high photocurrent density, sensitive responsivity, cycling stability, and excellent on/off behavior under sunlight in a 0.1 m KOH solution. The KOH concentration and the external potential affect the performance, indicating that it can be an excellent PEC‐type detector. This work provides fundamental knowledge about PEC‐type MPT photodetectors and reveals the great potential of NiPS3 as an optoelectronic device.

Aqueous Cathodic Exfoliation Strategy toward Solution-Processable and Phase-Preserved MoS2 Nanosheets for Energy Storage and Catalytic Applications.

The production of MoS2 nanosheets by electrochemical exfoliation routes holds great promise as a means to access this two-dimensional material in large quantities for different practical applications. However, the use of electrolytes based on synthetic organic salts and solvents, as well as issues related to the unwanted oxidation and/or phase transformation of the exfoliated nanosheets, constitute significant obstacles that hinder the industrial adoption of the electrochemical approach. Here, we introduce a safe and sustainable method for the cathodic delamination of MoS2 that makes use of aqueous solutions of very simple and widely available salts, mainly KCl, as the electrolyte. Combined with an appropriate biomolecule-based solvent transfer protocol, such an electrolytic exfoliation route is shown to afford colloidally dispersed, oxide-free, and phase-preserved MoS2 nanosheets of high structural quality in considerable yields. The mechanisms behind the efficient aqueous delamination of the bulk MoS2 cathode are also discussed and rationalized on the basis of the penetration of hydrated cations from the electrolyte between its layers and the immediate reduction of the accompanying water molecules. An asymmetric supercapacitor assembled with a cathodic MoS2 nanosheet-single walled carbon nanotube hybrid as the positive electrode and activated carbon as the negative electrode delivered energy densities (e.g., 26 W h kg-1 at 750 W kg-1 in 6 M KOH) that were competitive with those of other MoS2-based asymmetric devices. When used as a catalyst for the reduction of nitroarenes, the present cathodically exfoliated nanosheets exhibited one of the highest activities reported so far with MoS2 nanostructures, the origin of which is accounted for as well. Overall, by facilitating access to this two-dimensional material through a particularly simple, efficient, and cost-effective technique, these results should expedite the practical implementation of MoS2 nanosheets in energy storage, catalysis, and beyond.

Simultaneous Electrochemical Dual‐Electrode Exfoliation of Graphite toward Scalable Production of High‐Quality Graphene

AbstractDeveloping scalable methods to produce large quantities of high‐quality and solution‐processable graphene is essential to bridge the gap between laboratory study and commercial applications. Here an efficient electrochemical dual‐electrode exfoliation approach is developed, which combines simultaneous anodic and cathodic exfoliation of graphite. Newly designed sandwich‐structured graphite electrodes which are wrapped in a confined space with porous metal mesh serve as both electrodes, enabling a sufficient ionic intercalation. Mechanism studies reveal that the combination of electrochemical intercalation with subsequent thermal decomposition results in drastic expansion of graphite toward high‐efficiency production of graphene with high quality. By precisely controlling the intercalation chemistry, the two‐step approach leads to graphene with outstanding yields (85% and 48% for cathode and anode, respectively) comprising few‐layer graphene (1–3 layers, &gt;70%), ultralow defects (ID/IG &lt; 0.08), and high production rate (exceeding 25 g h−1). Moreover, its excellent electrical conductivity (&gt;3 × 104 S m−1) and great solution dispersibility in N‐methyl pyrrolidone (10 mg mL−1) enable the fabrication of highly conductive (11 Ω sq−1) and flexible graphene films by inkjet printing. This simple and efficient exfoliation approach will facilitate the development of large‐scale production of high‐quality graphene and holds great promise for its wide application.

Electro-Exfoliation of Graphite to Graphene in an Aqueous Solution of Inorganic Salt and the Stabilization of Its Sponge Structure with Poly(Furfuryl Alcohol).

We demonstrate an accessible and effective technique for exfoliating graphite foil and graphite powder into graphene in a water solution of inorganic salt. In our research, we report an electrochemical cathodic exfoliation in an aqueous solution of Na2SO4. After electro-exfoliation, the resulting graphene was premixed with furfuryl alcohol (FA) and an inorganic template (CaCO3 and Na2CO3). Once FA was polymerized to poly(furfuryl alcohol) (PFA), the mixture was carbonized. Carbon bridges originating in thermally-decomposed PFA joined exfoliated graphene flakes and stabilized the whole sponge-type structure after the nano-template was removed. Gases evolved at the graphite electrode (cathode) played an important role in the process of graphene-flake splitting and accelerated the change of graphite into graphene flakes. Starting graphite materials and graphene sponges were characterized using Raman spectroscopy, SEM, high-resolution transmission electron microscopy (HRTEM), elemental analysis, and low-temperature adsorption of nitrogen to determine their structure, morphology, and chemical composition. The discovered manufacturing protocol had a positive influence on the specific surface area and porosity of the sponges. The SEM and HRTEM studies confirmed a high separation degree of graphite and different agglomeration pathways. Raman spectra were analyzed with particular focus on the intensities of ID and IG peaks; the graphene-type nature of the sponges was confirmed.

High‐Yield Electrochemical Production of Large‐Sized and Thinly Layered NiPS3 Flakes for Overall Water Splitting

Achieving large-sized and thinly layered 2D metal phosphorus trichalcogenides with high quality and yield has been an urgent quest due to extraordinary physical/chemical characteristics for multiple applications. Nevertheless, current preparation methodologies suffer from uncontrolled thicknesses, uneven morphologies and area distributions, long processing times, and inferior quality. Here, a sonication-free and fast (in minutes) electrochemical cathodic exfoliation approach is reported that can prepare large-sized (typically ≈150 µm2 ) and thinly layered (≈70% monolayer) NiPS3 flakes with high crystallinity and pure phase structure with a yield ≈80%. During the electrochemical exfoliation process, the tetra-n-butylammonium salt with a large ionic diameter is decomposed into gaseous species after the intercalation and efficiently expands the tightly stratified bulk NiPS3 crystals, as revealed by in situ and ex situ characterizations. Atomically thin NiPS3 flakes can be obtained by slight manual shaking rather than sonication, which largely preserves in-plane structural integrity with large size and minimum damage. The obtained high quality NiPS3 offers a new and ideal model for overall water splitting due to its inherent fully exposed S and P atoms that are often the active sites for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Consequently, the bifunctional NiPS3 exhibits outstanding performance for overall water splitting.

Ultrafast Cathodic Exfoliation of Few-Layer Black Phosphorus in Aqueous Solution

Preparing few-layer black phosphorus flakes, in a scalable, fast, and benign way, is a key step to promote both the fundamental research and practical applications of black phosphorus. Although the electrochemically assisted liquid exfoliation of bulk black phosphorus is a promising strategy, it is still challenging to obtain few-layer black phosphorus flakes in polar protic solvent through cathodic exfoliation. In this work, we demonstrate an ultrafast approach to exfoliate bulk black phosphorus, under a cathodic potential, in an aqueous solution of hexadecyltrimethylammonium chloride. Particularly, the exfoliation can be trigged within ∼20 s, and the obtained flakes exhibit satisfactory quality. Further detailed mechanical explorations reveal that the cathodic intercalation of hexadecyltrimethylammonium cations and their subsequent decomposition contribute to the ultrafast expansion and exfoliation of bulk black phosphorus crystals. In addition, the as-exfoliated flakes show improved stability due to the protection of hexadecyltrimethylammonium chloride. This exfoliation method, together with the findings, should shed light on the development of new exfoliation methods for preparing few-layer black phosphorus flakes in various liquid systems, thus facilitating the future applications of black phosphorus.

Regulation of the degree of hydrogenation and electrochemical properties of graphene generated by electrochemical cathodic exfoliation by using different solvents

Hydrogenated graphene has attracted much attention because its properties can be tuned by varying the degree of hydrogenation. In this work we adjusted the degree of hydrogenation of hydrogenated graphene by using different solvents in the electrochemical cathodic exfoliation process. Interestingly, the graphene obtained by exfoliation in different solvents showed a range of electrochemical performances. The characterization data indicated that the highest level of hydrogenation was observed with the sample produced in N,N-dimethylformamide (G-DMF). Moreover, the G-DMF also showed superior electrochemical performance in terms of electron-transfer rate and sensitivity towards ascorbic acid, which is attributed to the fact that it has most catalytic active defect sites, induced by the high degree of hydrogenation. In addition, the sample produced in propylene carbonate (G-PC) showed the lowest density of defects, while the sample produced in dimethyl sulfoxide (G-DMSO) did not appear to have any electrochemical benefits. Overall, the results suggest a route to the scalable production of graphene with a tunable degree of hydrogenation using a facile and simple strategy.

An aqueous cathodic delamination route towards high quality graphene flakes for oil sorption and electrochemical charge storage applications

The electrochemical exfoliation of graphite in aqueous medium stands out as an attractive, scalable approach for the production of graphenes for different applications, due to its simplicity, cost-effectiveness and environmental friendliness. In particular, cathodic exfoliation in water should allow access to high quality, non-oxidized graphene flakes, as it avoids the intrinsic oxidizing conditions that typically plague the anodic route, but this possibility has been limited by a poor intercalation ability of aqueous cations. Here, we demonstrate that with a proper choice of starting graphite and electrolyte, high quality graphene flakes can be obtained in substantial yields via cathodic delamination in water. Graphites having some pre-expanded edges and interlayer voids (e.g., graphite foil) were found to be critical for a successful exfoliation. Large differences in the efficiency of a range of aqueous quaternary ammonium-based electrolytes were observed, quantitatively compared and rationalized on the basis of their chemical structure. Graphene yields up to 40–50 wt% were attained with the most efficient cations (tetrapropylammonium and hexyltrimethylammonium). Hydrophobic sponges made up of cathodic graphene-coated melamine foam exhibited a notable capacity towards the sorption of oils and organic solvents from water with good re-usability. Hybrids comprised of cathodically exfoliated graphite and a small amount of vertically oriented cobalt oxide nanosheets displayed good electrochemical charge storage behavior. Overall, the ability to access graphene flakes in considerable yields by the aqueous cathodic route disclosed here should raise the prospects of cathodic exfoliation as a competitive method for the industrial manufacturing of high quality graphene for practical applications.

Electrochemically Exfoliated High-Quality 2H-MoS2 for Multiflake Thin Film Flexible Biosensors.

2D molybdenum disulfide (MoS2 ) gives a new inspiration for the field of nanoelectronics, photovoltaics, and sensorics. However, the most common processing technology, e.g., liquid-phase based scalable exfoliation used for device fabrication, leads to the number of shortcomings that impede their large area production and integration. Major challenges are associated with the small size and low concentration of MoS2 flakes, as well as insufficient control over their physical properties, e.g., internal heterogeneity of the metallic and semiconducting phases. Here it is demonstrated that large semiconducting MoS2 sheets (with dimensions up to 50 µm) can be obtained by a facile cathodic exfoliation approach in nonaqueous electrolyte. The synthetic process avoids surface oxidation thus preserving the MoS2 sheets with intact crystalline structure. It is further demonstrated at the proof-of-concept level, a solution-processed large area (60 × 60 µm) flexible Ebola biosensor, based on a MoS2 thin film (6 µm thickness) fabricated via restacking of the multiple flakes on the polyimide substrate. The experimental results reveal a low detection limit (in femtomolar-picomolar range) of the fabricated sensor devices. The presented exfoliation method opens up new opportunities for fabrication of large arrays of multifunctional biomedical devices based on novel 2D materials.

Electrochemical exfoliation from an industrial ingot: ultrathin metallic bismuth nanosheets for excellent CO2 capture and electrocatalytic conversion.

Formic acid (or formate) is a liquid fuel and chemical feedstock, and it is considered as one of the most useful value-added reductive products from electrochemical CO2 conversion. Green metallic Bi nanosheets are believed be a promising candidate for formic acid production in CO2 electroreduction. However, the complexity of their preparation with a low yield hinders their practical application on a large scale. Herein, we report that by using a cheap and commonly used industrial ingot, phase-pure two-dimensional bismuth nanosheets are fabricated on a large scale by a rapid electrochemical cathodic exfoliation method. In addition to featuring abundant active sites, the obtained Bi nanosheets possess exceptionally high adsorption capacity to CO2 compared to its bulk counterpart, resulting in remarkable enhancement in CO2 electroreduction with high selectivity toward formic acid over a wide range of negative potentials, high current density and satisfactory durability. This facile strategy opens a promising avenue for massive fabrication of metallic Bi nanosheets with excellent electrocatalytic performance for large-scale commercial utilization of CO2.