Alkali Intercalation Research Articles

Novel alkali intercalated and acid-exfoliated biochars with enhanced surface areas for contaminant adsorption applications

Cost-effective and eco-friendly adsorbents are essential in environmental engineering and biochar is a promising material from the perspective. A novel and efficient surface modification approach involving alkali intercalation and acid exfoliation was designed in this study to enhance the physicochemical properties of biochar. The alkali intercalation process utilizes potassium hydroxide (KOH), while acid exfoliation involves varying HNO3, H2SO4, and H3PO4 concentrations. A simple two-stage pyrolysis process was employed to facilitate the intercalation-exfoliation modification. The modified biochars were characterized using BET, SEM, XRD, etc., to understand physicochemical properties. To quantify the effectiveness of the modifications, adsorption of malachite green dye as a model moiety was investigated. Dye removal sorption rates exceeding 99 % were recorded in the case of the biochars modified through a two-step process using KOH and 0.1MH3PO4. Specifically, the highest contaminant removal of 99.9 % was recorded when 60 mg of the KOH-0.1MH3PO4 biochar was employed, which is significantly higher than unmodified biochar’s 45.41 % removal at a higher dosage of 100 mg. Moreover, the adsorption kinetics revealed that all the modified biochars attained the maximum removal concentrations (∼99 % removal) in a mere 300 min, indicating a tenfold improvement in adsorption rate from unmodified biochar's requirement of over 5000 min. The results achieved through this study provide a cost-effective, fast, and environment-friendly technology for enhancing the adsorption characteristics and performance of biochars toward contaminant removal.

Topochemical intercalation reactions of ZrSe3

Intercalation of alkali and alkaline earth metals into ZrSe3 via soft chemical routes injects electrons and has a significant effect on the selenide-selenide bonding. K, Rb and Cs intercalates of ZrSe3 prepared at low temperatures (−78 ​°C) from metal ammonia solutions contrast with related polymorphs obtained at high temperature (850 ​°C). KxZrSe3 synthesised at low temperatures crystallises in orthorhombic Cmc21, while the polymorph obtained at high temperatures crystallises in Immm. The two structures prepared under drastically different conditions differ by relative shifting of ZrSe3 layers. In contrast, CsxZrSe3 shows the Immm polymorph at low temperature and the Cmc21 polymorph at high temperatures, while a single RbxZrSe3 polymorph in Immm is formed at both temperatures. Intercalation of Ca from liquid ammonia facilitates the co-intercalation of the solvent because of the strong solvation of Ca2+. This compound has severe faulting due to the flexibility in the relative shifts of adjacent ZrSe3 layers.

Controllable synthesis and tunable properties of topological material WTe<sub>2</sub>

<p indent=0mm>The two-dimensional topological insulator is expected to exhibit the quantum spin Hall effect because of the topologically protected helical edge state. The topological superconductor becomes one of the major material candidates for topological quantum computation due to the existence of Majorana zero-energy mode obeying non-Abelian statistics. Both two-dimensional topological insulator (2DTI) and topological superconductor (TS) can be realized in the monolayer (for 2DTI) or bulk (for TS) WTe₂. Using molecular beam epitaxy, we were able to grow a high-quality 1<italic>T</italic>′-WTe₂ monolayer. We revealed its semimetallic electron band structures using scanning tunneling microscopy/spectroscopy, an insulating phase with a fully opened energy gap is driven in the epitaxial 1<italic>T</italic>′-WTe₂ monolayer that is still topological nontrivial. Under ambient pressure, we performed alkali (K atoms) intercalation to dope electrons and achieved superconductivity transition in bulk Td-WTe₂ (type II Weyl semimetal). The intercalation of K atoms results in a negligible change in the crystal structure of Td-WTe₂, implying that superconductivity in intercalated Td-WTe₂ is still topologically nontrivial, according to X-ray diffraction characterizations.

Small polaron transport in cathode materials of rechargeable ion batteries

Small polarons are quasi-particles in materials formed by a charge carrier and its self-induced distortion. In cathode materials containing transition metal elements, small polarons play an important role in the diffusion of charge carriers. In order to grasp the fundamentals of small polarons inside cathodes, we highlight the recent progress from both experiments and simulations focusing on the formation of small polarons and their migration. Because of their strong binding to small polarons, alkali ions accompany polarons during diffusion and thus the polaron – ion couple can be considered a complex quasi-particle. The diffusion mechanism of alkali ions inside cathodic materials can be explored by a simultaneous diffusion simulation approach, which naturally and accurately depicts the diffusion of alkali ions (and alkali vacancies) and their accompanying small polarons as complex diffusion particles during alkali intercalation and de-intercalation. The successful employment of this approach paves a new direction toward elucidating the diffusion mechanism in several promising cathode materials containing transition metals. This model and its application to the investigation of the electrochemical properties of several typical cathodic materials such as NASICON, P O 4 4 − –, S O 4 4 − –, and S i O 4 4 − – anion– based compounds are comprehensively demonstrated. • Traditional polarons and small polarons are introduced and clarified. • Evidence of polaron formation is demonstrated in both experimental and theoretical aspects. • Role of small polarons in electrochemical properties is explained. • An advanced simulation approach by which ion diffusion can be precisely explored is introduced.

(Invited) Emission Origin of Lowly-Oxidized Graphene Quantum Dot Toward Light Emitting Devices

Graphene quantum dots (GQDs), simply making graphene typically under 10 nm, and the change of emission behavior from known fluorescence on graphene draws huge interest for potential applications to display, lighting, and optoelectronic devices. GQD could be a new class of optical material with useful properties of tunable luminescence, low cost, and superior photo and chemical stability. Our group has developed unique exfoliation and dispersion methods of 2D materials by the intercalation of alkali metal/organics. With the advantage of the methods generally excluding, or controlling, the oxidation of 2D materials, we have studied the origin of intrinsic emission (~ 400 nm) of graphene in depth. With those samples, I will introduce the role of oxidation in GQDs which forms isolated small sp2 carbon hexagons within a GQD, known as subdomains. Experimental evidences supported with calculation of the formation energy of subdomains and bandgap will give a guideline to improve emission properties. With those understanding the first demonstration of GQD light-emitting diodes (GQD-LEDs) with 1,000 cd/m2, alternating current powder elctroluminescence (ACPEL) device, and GQD phosphorescence for security application promise the optical applications of 2D materials with further improvement.

Improved Alkali Intercalation of Carbonaceous Materials in Ammonia Solution

Alkali‐intercalated graphite compounds represent a compelling modification of carbon with significant application potential and various fundamentally important phases. The intercalation of graphite with alkali atoms (Li and K) using liquid ammonia solution as a mediating agent is reported. Alkali atoms dissolve well in liquid ammonia, which simplifies and speeds up the intercalation process, and it also avoids the high temperature formation of alkali carbides. Optical microscopy, Raman, and electron spin‐resonance spectroscopy attest that the prepared samples are highly and homogeneously intercalated to a level approaching stage‐I intercalation compounds. The method and the synthesis route may serve as a starting point for the various forms of alkali‐atom‐intercalated carbon compounds (including carbon nanotubes and graphene), which can be exploited in energy storage and further chemical modifications.

Siloxene: A Potential Layered Silicon Intercalation Anode for Na, Li and K Ion Batteries

Silicon is one of the most promising anodes for lithium-ion (LIB) and sodium-ion (NIB) batteries due to its high theoretical capacity, 3590 mAh/g for Li15Si4 [1] and 954 mAh/g for NaSi.[2] Nevertheless, its practical application is hindered by a series of obstacles. For lithium (Li), the access to such high lithiated phases causes extreme volume expansion (310%), resulting in a rapid capacity fade. For sodium (Na), the slow kinetics and the ionic radius restrict the sodiation of c-Si. In an attempt to address these problems, recent attention has been given to the two-dimensional 2D silicon structures, comprising calcium silicide (CaSi2), polysilane (Si6H6) and siloxene (Si6O3H6), due to their potential structural stability during cycling and their facile synthesis through soft-chemical methods. In this work, the lamellar siloxene was obtained via topotactic deintercalation of Ca from CaSi2 and its electrochemical performance was evaluated with Li, Na and K. The results show the versatility of siloxene as anode for LIB, NIB and KIB, with delivered reversible capacities of 2300, 311 and 203 mAh/g for Li, Na and K, respectively. The material exhibits a noticeable structural stability after several cycles, leading to a good capacity retention and coulombic efficiency. The electrochemical mechanism taking place upon cycling is highlighted on the basis of a combination of ex situ characterization techniques; Raman, Infrared, Nuclear Magnetic Resonance and X-Ray photoelectron spectroscopy combined with Scanning and Transmission Electron Microscopy. The observed phenomena cannot be explained merely by a silicon alloying mechanism, therefore a possible alkali intercalation alternative has been proposed. Preliminary evidence of this electrochemical mechanism can be found in the siloxene structural integrity after several cycles followed by SEM and TEM, the absence of the diffraction peaks from NaSi/Li15Si4 (both crystalline and proper from the alloying mechanism) by XRD, and the lack of their respective Raman vibration bands, [3,4] at the end of the discharge. By Raman spectroscopy it was possible to observe a reversible shift of the main Si-plane vibration band for the discharged and charged siloxene, accompanied by a loss of the –OH and Si-H vibrations observed in the pristine siloxene. Undoubtedly, this last one is likely related to a change in the bond nature of the Si-planes, probably an exchange between –OH and –H with Li/Na/K is favored. In fact, the intercalation of Na/Li/K into a layered Si-based materials has been theoretically predicted for a single layer of siloxene (silicene), with no experimental record. The calculations foresee a high coverage of the silicene with alkali ions like Na, Li and K due to the nature of their interactions. The full sodiated/lithiated state of silicene corresponds to X1Si1 (X=Li/Na), the predicted binding energies and diffusion barriers indicate that their intercalation is achievable without the kinetic limitations (higher diffusion coefficient for silicene), structure degradation and volume expansion of bulk Si. [5–9] Complimentary information obtained by XPS and NMR is under analysis. The feasibility for alkali intercalation with a high structural stability presents siloxene as a potential anode for LIB, NIB and KIB batteries. Nevertheless, an understanding of the nature of the electrochemical mechanism is vital to develop its maximum performance. To the best of our knowledge, it is the first time that a lamellar Silicon based material shows such high stable capacity likely due to a very limited volume expansion, representing a real breakthrough for the batteries field and particularly for NIB.

Experimental study on gasification mechanism of unburned pulverized coal catalyzed by alkali metal vapor

The catalytic behavior of alkali vapor on unburned pulverized coal (UPC) prepared from bituminous coal, anthracite, semi coke and coke have been investigated. Experiment results show that the alkali metal vapor has catalytic effect on the gasification reaction of UPC. The catalytic effect of coke UPC is the most obvious, followed by anthracite UPC and bituminous coal UPC. Semi coke UPC is the least catalyzed by alkali metals but its gasification reactivity is the best. As the concentration of alkali metal vapor increases, the alkali metal content adsorbed by UPC increases, and there may be a phenomenon of saturated adsorption. The amount of alkali metal adsorbed is between 2% and 6%. AUPC has the highest ability to adsorb alkali metals, and SUPC is the weakest, which may be related to the minerals (CaO, Al2O3) in the coal ash. Changes in stomatal parameters are not the main factors affecting the catalytic effect. The results of X-ray diffraction experiments show that alkali metal aluminosilicate exists in the ash of coal after adsorption of alkali metal, and the average stack height of carbon atoms decreases significantly. The alkali metal catalytic gasification reaction is mainly achieved by destroying the carbon basic structural unit. The alkali metal nepheline and the interlayer compound may be the main catalytic substances, and the destructive ability of alkali intercalation is obviously stronger than that of alkali nepheline. The catalytic mechanism of alkali metals on unburned coal and the destruction mechanism of alkali metals on carbon crystals were discussed. It can provide reference for reducing alkali metal corrosion on coke and improving pulverized coal utilization rate.

Siloxene: A potential layered silicon intercalation anode for Na, Li and K ion batteries

The alloying reaction between 14th group elements and alkali can be detrimental for Li, Na or K-ion batteries due to the large associated volume expansion that leads to a rapid capacity fading. In order to overcome this issue, their associated 2D phases are promising anodes that enable alkali intercalation without alloying reaction and volume expansion. In this study, the lamellar siloxene obtained from topotactic deintercalation of Ca from CaSi2 delivered reversible capacities of 2300, 311 and 203 mAh/g for Li, Na and K, respectively, with good capacity retention and coulombic efficiency for Li and Na. The intercalation mechanism taking place upon cycling is highlighted on the basis of ex situ Raman characterization combined with IR spectroscopy, SEM and TEM. To the best of our knowledge, it is the first time that a lamellar Silicon based material shows such high stable capacity without volume expansion, representing a real breakthrough for the batteries field and particularly for NIB.

Siloxene: A Potential Layered Silicon Intercalation Anode for Na, Li and K Ion Batteries

Silicon is one of the most promising anodes for lithium-ion (LIB) and sodium-ion (NIB) batteries due to its high theoretical capacity, 3590 mAh/g for Li15Si4 [1] and 954 mAh/g for NaSi.[2] Nevertheless, its practical application is hindered by a series of obstacles. For lithium (Li), the access to such high lithiated phases causes extreme volume expansion (310%), resulting in a rapid capacity fade. For sodium (Na), the slow kinetics and the ionic radius restrict the sodiation of c-Si. In an attempt to address these problems, recent attention has been given to the two-dimensional 2D silicon structures, comprising calcium silicide (CaSi2), polysilane (Si6H6) and siloxene (Si6O3H6), due to their potential ability to buffer the electrode volume changes during cycling and their facile synthesis through soft-chemical methods. In this work, the lamellar siloxene was obtained via topotactic deintercalation of Ca from CaSi2 and its electrochemical performance was evaluated with Li, Na and K. The results show the versatility of siloxene as anode for LIB, NIB and KIB, with delivered reversible capacities of 2300, 311 and 203 mAh/g for Li, Na and K, respectively. The material exhibits a noticeable structural stability after several cycles, deriving in a good capacity retention and coulombic efficiency. The electrochemical mechanism taking place upon cycling is highlighted on the basis of ex situ Raman characterization combined with IR spectroscopy, SEM and TEM. The results are unsuccessful in explaining all the observed phenomena by means of a merely silicon alloying mechanism, therefore a possible alkali intercalation alternative has been proposed. Preliminary evidence of this approach can be found in the siloxene structural integrity after several cycles, the presence of Na in the discharged compound as observed by EDX, the absence of any of the diffraction peaks from NaSi/Li15Si4 (both crystalline and proper from the alloying mechanism) by XRD, and the lack of their respective Raman vibration bands [3- 4], at the end of the discharge. Indeed, by Raman spectroscopy it was possible to observe a reversible shift of the main Si-plane vibration band for the discharged and charged siloxene, accompanied by a loss of the –OH and Si-H vibrations observed in the pristine siloxene. Undoubtedly, these two last ones are likely related to a change in the bond nature of the Si-planes with the substituent group producing a different interlayer separation, probably the electrochemical cycling induces an exchange between –OH and –H with Li/Na. In fact, the intercalation of Na/Li into a layered Si-based materials has been theoretically predicted for a single layer of siloxene (silicene), with no experimental record. The calculations foresee a high coverage of the silicene with alkali ions like Na, Li and K due to the nature of their interactions. The full sodiated/lithiated state of silicene corresponds to X1Si1 (X=Li/Na), the predicted binding energies and diffusion barriers indicate that their intercalation is achievable without the kinetic limitations (higher diffusion coefficient for silicene), structure degradation and volume expansion of bulk Si. [5–9] This feasibility for alkali intercalation with such high structural stability introduces siloxene as a potential anode for LIB, NIB and KIB batteries. Nevertheless, a better understanding of its electrochemical mechanism is necessary to develop its maximum performance. To the best of our knowledge, it is the first time that a lamellar Silicon based material shows such high stable capacity without volume expansion, representing a real breakthrough for the batteries field and particularly for NIB.

Thermodynamics of Phase Selection in MnO2 Framework Structures through Alkali Intercalation and Hydration.

While control over crystal structure is one of the primary objectives in crystal growth, the present lack of predictive understanding of the mechanisms driving structure selection precludes the predictive synthesis of polymorphic materials. We address the formation of off-stoichiometric intermediates as one such handle driving polymorph selection in the diverse class of MnO2-framework structures. Specifically, we build on the recent benchmark of the SCAN functional for the ab initio modeling of MnO2 to examine the effect of alkali-insertion, protonation, and hydration to derive the thermodynamic conditions favoring the formation of the most common MnO2 phases-β, γ, R, α, δ, and λ-from aqueous solution. We explain the phase selection trends through the geometric and chemical compatibility of the alkali cations and the available phases, the interaction of water with the system, and the critical role of protons. Our results offer both a quantitative synthesis roadmap for this important class of functional oxides, and a description of the various structural phase transformations that may occur in this system.

Comparison of the polymorphs of VOPO4 as multi-electron cathodes for rechargeable alkali-ion batteries

VO6/VO5–PO4 frameworks govern electrochemical performance in VOPO4 polymorphs.

Review—Manganese-Based P2-Type Transition Metal Oxides as Sodium-Ion Battery Cathode Materials

Sodium transition metal oxides (NaMO2) with a P2 structure exhibit good Na+ ion conductivity and are promising sodium-ion battery cathode materials. Manganese-based compounds have a high working potential vs. Na+/Na, and high capacity. Yet, the layered nature of these materials means that they are prone to structural rearrangements at high voltage/low Na contents, the phase transformations and Na+ ion/vacancy ordering transitions resulting in capacity fade and poor reversibility. This review discusses the latest advances in the field and focuses mainly on recent work on NayMn1-xMxO2 (x, y ≤ 1, M = Ni, Mg, Li) compounds. We compare the different lithium and sodium transition metal layered oxides (P2, O3, etc.) and describe the structures and mechanisms observed on alkali (de)intercalation. The strategies used to enhance the electrochemical properties and stabilize the structural framework of sodium transition metal oxides are reviewed. We show how X-ray diffraction and 7Li/23Na solid-state Nuclear Magnetic Resonance can be combined to provide a detailed insight into the structural and electronic processes occurring upon electrochemical cycling of these materials.

Sequential oxygen and alkali intercalation of epitaxial graphene on Ir(111): enhanced many-body effects and formation of pn-interfaces

High quality epitaxial graphene films can be applied as templates for tailoring graphene–substrate interfaces that allow for precise control of the charge carrier behavior in graphene through doping and many-body effects. By combining scanning tunneling microscopy, angle-resolved photoemission spectroscopy and density functional theory we demonstrate that oxygen intercalated epitaxial graphene on Ir(111) has high structural quality, is quasi free-standing, and shows signatures of many-body interactions. Using this system as a template, we show that pn-interfaces can be patterned by adsorption and intercalation of rubidium, and that the n-doped graphene regions exhibit a reduced Coulomb screening via enhanced electron–plasmon coupling. These findings are central for understanding and tailoring the properties of graphene-metal contacts e.g. for realizing quantum tunneling devices.

First-Principles Study of Alkali and Alkaline Earth Ion Intercalation in Iron Hexacyanoferrate: The Important Role of Ionic Radius

Hexacyanoferrate compounds recently have attracted much interest because of their potential as aqueous and nonaqueous battery cathodes in the application of large-scale energy storage. Here, the feasibility to use iron hexacyanoferrate, Fe[Fe(CN)6], as a cathode candidate for nonaqueous rechargeable batteries is assessed with first-principle calculations. The structural deformation induced by the intercalation of alkali (Li+, Na+, K+, Rb+, Cs+) and alkaline earth (Mg2+, Ca2+, Sr2+, Ba2+) ions into Fe[Fe(CN)6] induces is negligible as compared to other Li-ion battery cathodes. The intercalation is strongly affected by the ionic radius of inserted species. With increasing ionic size, the most stable interstitial site changes from face-centered site to body-centered site. More importantly, the voltages for the intercalation are highly correlated to the ionic radius of the inserted species. The insertion of cations with larger ionic radius happens at higher voltages, and thus provides higher energy density. However, the intercalation of larger cations may also suffer from slower migration kinetics. Thus, it is important to choose inserted cation with appropriate ionic size to achieve the optimized performance. Overall, our results suggest hexacyanoferrate compounds are promising cathode materials for various types of nonaqueous rechargeable batteries.

Study of the intercalation of graphene on Ni(111) with Cs atoms: Towards the quasi-free graphene

In this work we present an experimental study of the intercalation of the graphene/Ni(111) system by cesium atoms. The evidence of a complete alkali intercalation has been obtained by Auger and angle-resolved electron-energy-loss measurements. The changes in the electronic and vibrational properties demonstrate that a weakly bonded graphene layer can be synthesized on Ni(111) by means of Cs intercalation.

Reversible superconductivity in electrochromic indium-tin oxide films

Transparent conductive indium tin oxide (ITO) thin films, electrochemically intercalated with sodium or other cations, show tunable superconducting transitions with a maximum Tc at 5 K. The transition temperature and the density of states, D(EF) (extracted from the measured Pauli susceptibility χp) exhibit the same dome shaped behavior as a function of electron density. Optimally intercalated samples have an upper critical field ≈ 4 T and Δ/kBTc ≈ 2.0. Accompanying the development of superconductivity, the films show a reversible electrochromic change from transparent to colored and are partially transparent (orange) at the peak of the superconducting dome. This reversible intercalation of alkali and alkali earth ions into thin ITO films opens diverse opportunities for tunable, optically transparent superconductors.

Transport Properties of Alkali-Doped Multi Walled Carbon Nanotubes

In this work we propose a study on electrical properties of multiwalled carbon nanotubes (MWCNT) doped with the most commonly used alkali metals. We report resistivity measurements of MWCNT exposed to doping with Li, Na, K and Cs. Our results show that, increasing the alkali exposure, the resistance of the doped sample decreases denoting a progressive sample metallization. The changes in resistivity, contrary to that observed for single walled carbon nanotubes (SWCNT) in our previous work, are independent upon the alkali properties but appear related to alkali intercalation effects in the MWCNT random network. The doping effects have been also controlled by X-ray photo electron spectroscopy (XPS). The spectra confirm the absence of chemical bonds between carbon nanotubes and alkali, validating the hypothesis of intercalation of alkali in the interstitial channels between the tubes. Our results are also confirmed by comparison between SEM images of single walled and multiwalled carbon nanotubes.

A New Purification Technique for Single-Walled Carbon Nanotubes by Interaction with Alkali and Oxygen

In this work we present a purification technique for oxygen removal from carbon nanotubes (CNTs) at relatively low temperature monitored by X-ray Photoelectron Spectroscopy and electrical characterization (change in resistance). We dope the sample with alkali metal (Na, K and Cs), which successively bind with the residual impurities of oxygen. The removal of the so formed oxides occur by heating the sample at relatively low temperatures (500-600 degrees C) without collateral damage to CNTs mat. In particular we investigate the in situ intercalation of alkali in SWNT followed by oxygen adsorption monitored by DC resistance measurements and X-ray photo-spectroscopy (XPS), demonstrating that the alkali intercalation in the samples trigger the oxygen adsorption. A subsequent sample heating at 500 degrees C removes both oxygen and alkali. Furthermore, the amount of the oxygen removal depends upon the deposited alkali species: in effect only with Na and K we obtain a complete oxygen removal, while other alkalis probably do not intercalate properly inside the nanotube walls. We hypothesize that the atomic radius of alkali can affect the intercalation properties of them inside the CNT structure.

Review and Prospect of Surface Modification of Kaolin

Surface modification of kaolin, which included coupling agent, calcination, acid modification and alkali activation, mechanochemical activation and intercalation etc, is reviewed. The modification mechanisms and modification methods of kaolinite are discussed. The application of kaolin in ceramics, paints, plastics and rubber etc are also analyzed. Afterwards, the prospect of future researches on modification of kaolin is taken. Surface modification of kaolin denotes use physical, chemical methods and mechanical method, which changes surface properties of kaolinite (surface functional groups, crystal structure and surface adsorption and surface electrical) to satisfy the requirements of the industrial application. Surface properties of kaolinite are controlled by the position of Si-O bonding and Al-(O, OH) groups. Any physical or chemical processing methods which may change Si-O and Al-(O, OH) bonding forms of kaolinite surface could complete the surface modification of kaolin. The surface modification of includes coupling agent, calcination, acid modification and alkali activation, mechanochemical activation, intercalation and so on.