Cathodic Exfoliation Research Articles

The process of electrolyte-plasma cathode exfoliation of graphite

We discussed the development of cathodic electrochemical exfoliation of graphite, accompanied by a plasma discharge with a voltage of 200V DC, in an aqueous solution of various electrolytes. The method of cathodic electrochemical exfoliation of graphite has established itself as a promising eco-friendly industrial method for producing nanographite with subsequent grinding by ultrasound into low-layer graphene (FLG). Cathodic exfoliation allows selective doping of nanographite oxygen atoms.

Few-layered graphene from cathodic exfoliation in binary solvents and application as a protective layer for lithium metal anodes

Electrochemical exfoliation is a top-down method recognized for its environmentally friendly and scalable approach for producing solution-processable graphene. Among its variation, cathodic exfoliation stands out for its potential in generating few-layer graphene with minimal defects. In this study, we developed a cathodic exfoliation method for graphite foil using a binary solvent system to produce graphene with a reduced number of layers. By employing a 0.1 M LiClO4 solution in a dimethyl sulfoxide and dimethyl carbonate solvents mixture at a 1:2 vol ratio, we enhanced the intercalation of solvated lithium ions into graphite, successfully exfoliating graphene with 5–6 layers. The exfoliated graphene exhibited a low defect density (ID/IG ∼0.05) and a C/O ratio of 33.2. Furthermore, when used as a coating on a separator, the exfoliated few-layered graphene (FLG) sheets demonstrated notable performance as a protective layer for Li metal anode in Li metal battery technology.

Two-Dimensional MoS2 Nanosheets Derived from Cathodic Exfoliation for Lithium Storage Applications.

The preparation of 2H-phase MoS2 thin nanosheets by electrochemical delamination remains a challenge, despite numerous efforts in this direction. In this work, by choosing appropriate intercalating cations for cathodic delamination, the insertion process was facilitated, leading to a higher degree of exfoliation while maintaining the original 2H-phase of the starting bulk MoS2 material. Specifically, trimethylalkylammonium cations were tested as electrolytes, outperforming their bulkier tetraalkylammonium counterparts, which have been the focus of past studies. The performance of novel electrochemically derived 2H-phase MoS2 nanosheets as electrode material for electrochemical energy storage in lithium-ion batteries was investigated. The lower thickness and thus higher flexibility of cathodically exfoliated MoS2 promoted better electrochemical performance compared to liquid-phase and ultrasonically assisted exfoliated MoS2, both in terms of capacity (447 vs. 371 mA·h·g-1 at 0.2 A·g-1) and rate capability (30% vs. 8% capacity retained when the current density was increased from 0.2 A·g-1 to 5 A·g-1), as well as cycle life (44% vs. 17% capacity retention at 0.2 A·g-1 after 580 cycles). Overall, the present work provides a convenient route for obtaining MoS2 thin nanosheets for their advantageous use as anode material for lithium storage.

Electrolyte–Plasma Cathodic Exfoliation of Graphite

Electrolyte–Plasma Cathodic Exfoliation of Graphite

Interfacial carbon dots introduced distribution-structure modulation of Pt loading on graphene towards enhanced electrocatalytic hydrogen evolution reaction

To easily load Pt on smoothy graphene synthesized by cathodic exfoliation method and achieve adjacent plane distribution of Pt, carbon dots (CDs) are used to construct anchoring points to load highly dispersed Pt species due to strong interaction between CDs and Pt species. The composite of Pt-CDs/graphene is synthesized via a continuous process of cathodic exfoliation-hydrothermal-impregnation-reduction. Characterization results indicate the distribution configuration of Pt varies from coated structure of CDs@Pt to dispersed configuration of CDs&Pt or Pt&CDs, then to wrapping configuration of Pt@CDs with increased amount of CDs. It’s found that suitable introduction of CDs promotes the adjacent plane distribution of Pt species. The obtained best Pt-4CDs/G shows the low overpotential of 36 mV (10 mA⋅cm−2) and high mass activity of 3747.8 mA mg−1 at −40 mV towards electrocatalytic hydrogen evolution reaction (HER), 9.2 times more active than that of Pt/C (406.2 mA mg−1). The superior HER performance of Pt-4CDs/G is attributed to its relatively adjacent plane distribution of Pt, which supports high electrochemically active surface area and more adjacent Pt sites for H* adsorption. Benefitting from that, the HER process for Pt-4CDs/G favorably follows the Tafel pathway, resulting in low hydrogen adsorption free energy and excellent HER activity.

Utilizing Topological Insulator Two-Dimensional Bismuth for Ultrasensitive Acoustic Detection.

Topological insulators (TIs) are characterized by a full insulating gap in the bulk and gapless edge or surface states, which have attracted tremendous attention. 2D Bi (110), as a typical TI, is of particular interest due to its low symmetry structure and topologically protected and spin-momentum-locked Dirac surface states. However, the material's potential applications are hindered by difficulties in fabrication, due to its strong semi-metallic bonding and poor stability. In this study, a novel electrochemical intercalation method for the fabrication of ultrathin Bi (110) nanosheets with the highest yield ever reported is presented. These nanosheets are stabilized through cathodic exfoliation in a reductive environment and further modification with polymer ionic liquids. The versatility of these nanosheets is demonstrated by fabricating flexible acoustic sensors with ultrahigh sensitivity. These sensors can even detect sounds as quiet as 45dB. Furthermore, these sensors are utilized for acoustic-to-electric energy conversion and information transfer. This work offers a promising approach for scalable fabrication and preservation of ultrathin 2D TI Bi (110) nanosheets and paves the way for their integration into smart devices.

Enhanced Electrochemical Performance of Metallic CoS-Based Supercapacitor by Cathodic Exfoliation.

Two-dimensional nanomaterials hold great promise as electrode materials for the construction of excellent electrochemical energy storage and transformation apparatuses. In the study, metallic layered cobalt sulfide was, firstly, applied to the area of energy storage as a supercapacitor electrode. By a facile and scalable method for cathodic electrochemical exfoliation, metallic layered cobalt sulfide bulk can be exfoliated into high-quality and few-layered nanosheets with size distributions in the micrometer scale range and thickness in the order of several nanometers. With a two-dimensional thin sheet structure of metallic cobalt sulfide nanosheets, not only was a larger active surface area created, but also, the insertion/extraction of ions in the procedure of charge and discharge were enhanced. The exfoliated cobalt sulfide was applied as a supercapacitor electrode with obvious improvement compared with the original sample, and the specific capacitance increased from 307 F∙g-1 to 450 F∙g-1 at the current density of 1 A∙g-1. The capacitance retention rate of exfoliated cobalt sulfide enlarged to 84.7% from the original 81.9% of unexfoliated samples while the current density multiplied by 5 times. Moreover, a button-type asymmetric supercapacitor assembled using exfoliated cobalt sulfide as the positive electrode exhibits a maximum specific energy of 9.4 Wh∙kg-1 at the specific power of 1520 W∙kg-1.

In-Situ Electrochemical Exfoliation and Methylation of Black Phosphorus into Functionalized Phosphorene Nanosheets.

Two-dimensional black phosphorus (BP) has attracted great attention as a perspective material for various applications. The chemical functionalization of BP is an important pathway for the preparation of materials with improved stability and enhanced intrinsic electronic properties. Currently, most of the methods for BP functionalization with organic substrates require either the use of low-stable precursors of highly reactive intermediates or the use of difficult-to-manufacture and flammable BP intercalates. Herein we report a facile route for simultaneous electrochemical exfoliation and methylation of BP. Conducting the cathodic exfoliation of BP in the presence of iodomethane makes it possible to generate highly active methyl radicals, which readily react with the electrode's surface yielding the functionalized material. The covalent functionalization of BP nanosheets with the P-C bond formation has been proven by various microscopic and spectroscopic methods. The functionalization degree estimated by solid-state 31P NMR spectroscopy analysis reached 9.7%.

(Digital Presentation) Cathodic Exfoliation of Few-Layer Tellurium As Electrocatalyst Support for Hydrogen Evolution

Few-layer tellurium represents the two-dimensional (2D) form of tellurium crystal with the majority of the Te atoms exposed on its surface. Recent studies demonstrated that 2D Te has good environmental stability and high charge carrier mobility, making it suitable electrocatalyst support to host active sites and assist electron transfer between the electrode and the sites [1]. Yet, its mass production for electrocatalysis application remains challenging.In this study, we present a simple cathodic exfoliation method to exfoliate commercially available Te crystal directly into few-layer tellurium with exceptionally high yield [2] (see Figure 1A). Using alkaline aqueous electrolyte (1.0 M KOH), Te nanosheets with the thickness of 7~10 nm and lateral size of 1~4 µm were produced at an applied potential of −0.42 V (vs. RHE). Combining in situ Raman spectroscopy and ex situcharacterization results, we were able to reveal the exfoliation mechanism, where the in situ generated ditelluride (Te2 2−) anions on the nanosheets played the critical role of separating nanosheets from the bulk crystal (see Figure 1B).At the presence of transition metal ions in the electrolyte, such as Pt2+ and Ni2+, simultaneous surface doping of Te nanosheets was enabled by the interaction between Te2 2− anions and metal ions, producing Pt/Ni-doped Te with tunable doping level. Such doped nanosheets exhibited high stability and hydrogen evolution reaction (HER) activity. Particularly at high potential, Pt-doped Te nanosheets outperformed both polycrystalline Pt and commercial Pt/C catalysts (see Figure 1C). We suggested a collaborative hydrogen production mechanism via Volmer–Heyrovsky pathway to justify such unusual activity. In short, at HER conditions, the surface Te atoms of Pt-doped Te nanosheets are reduced to Te2 2− anions. Such species can help attract protons and assist their transfer to adjacent Pt atoms, where the protons are reduced to form hydrogen (see Figure 1D). Figure 1 (A) Experimental setup and photos of the electrochemical exfoliation of Te crystal; (B) Exfoliation mechanism; (C) HER performance and relative energy of Pt-doped Te with various doping levels; (D) Collaborative HER mechanism. Reference: Shi, Z.; Cao, R.; Khan, K.; Tareen, A. K.; Liu, X.; Liang, W.; Zhang, Y.; Ma, C.; Guo, Z.; Luo, X.; Zhang, H., Nano-Micro Lett. 2020, 12 (1), 99. Zheng, W.; Li, Y.; Liu, M.; Lee, L. Y. S., Small 2021, 17 (18), e2007768. Figure 1

High-Quality Electrochemically Exfoliated Graphene Protective Layer for Metal Batteries

Graphene has attracted substantial attention due to its exceptional mechanical, thermal, electrical, and chemical properties. There has been active research for the scalable production of high-quality graphene. Among various techniques, electrochemical exfoliation is facile, fast, and cost-effective for graphene production. Our previous finding on anodic exfoliation suggested that the binding energy between the intercalator and graphene sheet plays an important role in exfoliation efficiency.1 We further extended the hypothesis to the cathodic exfoliation process to produce high-quality graphene. The characteristics and morphologies of electrochemically exfoliated graphene using alkali metals (e.g. Na, K, and Cs) are compared. Then, we will employ the exfoliated graphene on lithium metal anodes as carbon support for efficient lithium deposition in lithium metal batteries.References Lee, H.; Choi, J. I.; Park, J.; Jang, S. S.; Lee, S. W. Role of anions on electrochemical exfoliation of graphite into graphene in aqueous acids. Carbon 2020, 167, 816-825.

Electrochemical Exfoliation of Naturally Occurring Layered Mineral Stibnite (Sb2S3) for Highly Sensitive and Fast Room‐Temperature Acetone Sensing

AbstractThe analysis of exhaled acetone is used as a noninvasive diagnosis for diabetes. Compared with traditional breath analysis tools, chemiresistive gas sensors have attracted more attention for real‐time monitoring, owing to the possibility of integration and facile operation. However, most reported room‐temperature acetone gas sensors suffer from complicated preparation, costly raw materials, or relatively long response and recovery time. In this work, naturally occurring layered mineral stibnite is used to prepare Sb2S3 by a one‐step method of electrochemical cathodic exfoliation. As‐prepared Sb2S3 displays an amorphous feature with porous, hierarchical nanostructure, and its formation mechanism is rationally proposed. The porous, hierarchical and amorphous Sb2S3‐based gas sensors show excellent gas sensing performance toward acetone at room temperature, with the high response up to 1.46 toward 100 ppm acetone, and fast gas response and recovery toward acetone at room temperature (7 s for response and 30 s for one response–recovery cycle), which is one of the top three shortest response times among the reported room‐temperature acetone gas sensors. The electrochemical cathodic exfoliation may offer a new strategy for facile preparation of mineral materials, and the discussed devices may hold great promise for developing cost‐effective and high‐performance acetone sensors at room temperature.

Rapid fabrication of high-quality few-layer graphene through gel-phase electrochemical exfoliation of graphite for high-energy-density ionogel-based micro-supercapacitors

Electrochemical exfoliation has been identified as a promising top-down method for obtaining high-quality graphene from graphite. However, conventional anodic exfoliation introduces undesirable oxidation and defects in resultant graphene while cathodic exfoliation eliminates that issue but is time and energy intensive. Herein we report a versatile and rapid fabrication approach for gentle (<1 h ultrasonication) cathodic exfoliation of graphite using only 0.05 M K2SO4 in a polyvinyl alcohol (PVA)-based aqueous gel medium as electrolyte. The few-layer graphene obtained via this route demonstrates high quality (ID/IG ratio of 0.07) and minimal oxidation (3.02 at% oxygen). This gel-exfoliated graphene is found to be particularly suitable for micro-supercapacitors (MSCs) achieving a stable working voltage of 1.2 V in aqueous gel electrolyte, good rate capability, high capacitance of 13.7 F cm−3 at 10 mV s−1 and energy density of 2.74 mW h cm−3. Importantly, gel-exfoliated graphene is also compatible with ionogel electrolyte, achieving a high voltage of 3.4 V and resulting in competitive energy density of 14.5 mW h cm−3, outperforming most reported graphene-based MSCs. The MSCs show excellent long cycling performance retaining nearly 100% capacitance over 10,000 cycles. We also demonstrate the mechanical flexibility and integration of the MSCs connected in series and parallel for powering future microscale flexible electronics.

Electrocleavage Synthesis of Solution-Processed, Imine-Linked, and Crystalline Covalent Organic Framework Thin Films

Developing a general, facile, and direct strategy for synthesizing thin films of covalent organic frameworks (COFs) is a major challenge in this field. Herein, we report an unprecedented electrocleavage synthesis strategy to produce imine-linked COF films directly on electrodes from electrolyte solutions at room temperature. This strategy enables the cathodic exfoliation of the COF powders to nanosheets by electrochemical reduction and protonation, followed by nanosheets migrating to the anode and reproducing the COF structures by anodic oxidation. Our method is adaptable with most imine-linked COFs by virtue of the low redox potential of the imine bonds, whereas the COF films possess high crystallinity and hierarchical porosity. We highlight these COF films as a superb platform for promoting mass transfer by demonstrating their extraordinarily rapid iodine adsorption with record-high rate constants.

Electro-exfoliated PdTe2 nanosheets for enhanced methanol electrooxidation performance in alkaline media

Electrochemical cathodic exfoliation method to obtain PdTe2 nanosheets with [001] preferential orientation and superior alkaline methanol oxidation performance.

Simultaneous Anodic and Cathodic Exfoliation of Graphite Electrodes in an Aqueous Solution of Inorganic Salt

AbstractElectrochemical exfoliation of graphite offers a scalable and efficient approach to synthesise graphene nanomaterials. This process is commonly performed either anodically or cathodically, whereas simultaneous dual processes offer an attractive energy efficient means to produce graphene materials with tuneable properties. Here, we demonstrate a simple electro synthetic approach to produce graphene simultaneously from both a graphite anode and a graphite cathode in K2SO4 aqueous solution. Graphite exfoliation was facilitated by employing 0.5 M K2SO4 as an electrolyte at 10 V, where efficient exfoliation simultaneously occurs at graphite foils serving as both anode and cathode. The anodically exfoliated graphene has a high defect density (ID/IG=0.58) and higher degree of oxidation (C/O=11.36), in comparison to graphene produced at cathode having a lower defect density (ID/IG=0.06) and a low oxidation degree (C/O=31.68). The usage of aqueous solution for scalable and efficient concurrent‐dual electrochemical exfoliation of graphite electrodes will facilitate the development of large‐scale production of graphene.

CO2 Electroreduction to Formate at a Partial Current Density up to 590mA mg-1 via Micrometer-Scale Lateral Structuring of Bismuth Nanosheets.

2D bismuth nanosheets are a promising layered material for formate-producing via electrocatalytic CO2 conversion. However, the commercial interest of bismuth nanosheets in CO2 electroreduction is still rare due to the undesirable current density for formate at moderate operation potentials (about 200 mA mg-1 ) and harsh synthesis conditions (high temperature and/or high pressure). This work reports the preparation of Bi nanosheets with a lateral size in micrometer-scale via electrochemical cathodic exfoliation in aqueous solution at normal pressure and temperature. As-prepared Bi LNSs (L indicates large lateral size) possess high Faradaic efficiencies over 90% within a broad potential window from -0.44 to -1.10 V versus RHE and a superior partial current density about 590 mA mg-1 for formate in comparison with state-of-the-art results. Structure analysis, electrochemical results, and density functional theory calculations demonstrate that the increasing tensile lattice strain observed in Bi LNSs leads to less overlap of d orbitals and a narrower d-band width, which tuning the intermediate binding energies, and therefore promotes the intrinsic activity.

Facile and environmentally friendly fabrication of few-layer bismuthene by electrochemical exfoliation method for ultrafast photonic applications

Bismuthene, an unique kind of two-dimensional material beyond graphene, has attracted considerable attention recently for its unique electronic and photonic properties. These unique properties render of Bismuthene as an excellent candidate for various applications, e.g., nonlinear optical limiters, optical switchers, and optical photonic devices. Toward this goal, we report herein an easy and quick alternative method to exfoliate a semi-metal Bi crystal to obtain few layer nanosheets in two different sizes based on electrochemical exfoliation approaches. At the different wavelengths and intensity, the resulting nonlinear optical activity is studied. The nonlinear absorption coefficient was calculated using Z-scan measurements. The exfoliated materials have been well characterized using various techniques, e.g., UV-Vis-NIR absorption, photoluminescence (PL), X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman spectroscopy, transmission electron microscopy (TEM), and, XPS. The influence of different experimental conditions, such as the voltage on linear/nonlinear optical properties has been well examined. In addition, the mechanism of electrochemical cathodic exfoliation under different applied voltage in aqueous solution is described. This finding suggests that the bismuthene-based reverse saturable absorber RSA is a promising new material for broadband ultrafast optical limiters that protect against Vis-IR ultrashort pulse laser damage.

On the mechanistic pathways of exfoliation-and-deposition of graphene by bipolar electrochemistry

Amongst the different graphene fabrication techniques, bipolar electrochemistry (BPE) has been recently reported as a simple, controllable, low cost, eco-friendly, and scalable method. It consists of a wirelessly placed carbon source between two feeding electrodes subjected to direct current (DC) voltage in a deionized water bath. Although the physicochemical characteristics of produced graphene have been evaluated, the exfoliation and deposition mechanisms are still unclear. In this study, a novel modified BPE system with an electrically-connected graphite-platinum couple acting as the bipolar electrode has been designed in order to decouple and investigate the contribution of anodic/cathodic exfoliation and deposition of graphene in the BPE process. Electron microscopy and Fourier transform infrared spectroscopy results indicate that both anodic and cathodic exfoliation of graphene could take place regardless of the type of polarization; however, the morphology and deposition rate highly depend on the polarization. Furthermore, the graphene fabricated by anodic exfoliation was found to show higher levels of oxidation compared to the graphene produced by cathodic exfoliation.

Cathodic Exfoliation: Few‐Layer Tellurium: Cathodic Exfoliation and Doping for Collaborative Hydrogen Evolution (Small 18/2021)

Cathodic Exfoliation: Few‐Layer Tellurium: Cathodic Exfoliation and Doping for Collaborative Hydrogen Evolution (Small 18/2021)

Few-Layer Tellurium: Cathodic Exfoliation and Doping for Collaborative Hydrogen Evolution.

2D tellurium is a suitable electrocatalyst support that can assist electron transport while hosting active sites, yet its production remains challenging. Herein, a cathodic exfoliation method that can exfoliate Te crystal directly to Te nanosheets at low potential, also enabling simultaneous transition metal doping on Te nanosheet surface is presented. In situ Raman spectra and ex situ characterizations reveal that the cathodic exfoliation relies on the electrostatic repulsion between Te flakes covered with in situ generated ditelluride (Te2 2- ) anions. The Te2 2- anions can anchor metal ions to the surface, and the doping concentration can be tuned by adjusting the concentration of metal ion in the electrolyte. The metal-doped Te nanosheets exhibit highly improved hydrogen evolution activities. In particular, Pt-doped Te outperforms polycrystalline Pt at high overpotential. A collaborative hydrogen production mechanism via Volmer-Heyrovsky pathway is suggested: Te2 2- adsorbs protons and assists the mass transfer to adjacent Pt atoms where the protons are reduced and released as hydrogen.