Intercalation Of Layers Research Articles

Layered Intercalation Materials.

2D layered materials typically feature strong in-plane covalent chemical bonding within each atomic layer and weak out-of-plane van der Waals (vdW) interactions between adjacent layers. The non-bonding nature between neighboring layers naturally results in a vdW gap, in which various foreign species may be inserted without breaking the in-plane covalent bonds. By tailoring the composition, size, structure, and electronic properties of the intercalated guest species and the hosting layered materials, an expansive family of layered intercalation materials may be produced with highly variable compositional and structural features as well as widely tunable physical/chemical properties, invoking unprecedented opportunities in fundamental studies of property modulation and potential applications in diverse technologies, including electronics, optics, superconductors, thermoelectrics, catalysis, and energy storage. Here, the principles and protocols for various intercalation methods, including wet chemical intercalation, gas-phase intercalation, electrochemical intercalation, and ion-exchange intercalation, are comprehensively reviewed and how the intercalated species alter the crystal structure and the interlayer coupling of the host 2D layered materials, introducing unusual physical and chemical properties and enabling devices with superior performance or unique functions, is discussed. To conclude, a brief summary on future research opportunities and emerging challenges in the layered intercalation materials is given.

Bulk O2 formation and Mg displacement explain O-redox in Na0.67Mn0.72Mg0.28O2

Summary O-redox in compounds with Li on the transition-metal layers (TML) has recently been attributed to the formation of molecular O2 on charge, trapped in the lattice. Here, we show that a similar process occurs for P2-Na0.67[Mn0.72Mg0.28]O2, which contains Mg2+ on the TML. The molecular O2 is identified by high-resolution RIXS and quantified by magnetometry, showing that it equates to the charge passed. This O2 is trapped in voids that are formed by Mg2+ out-of-plane displacement and Mn4+ in-plane disordering and is then reduced on discharge associated with a large voltage hysteresis. In contrast to compounds containing Li+ in the TML, in which the honeycomb ordering and the high-voltage plateau are irreversibly lost after the first cycle, in P2-Na0.67[Mn0.72Mg0.28]O2, the plateau reappears partially on the second charge due to the partial reversibility of Mn in-plane and Mg out-of-plane migration and the local reformation of the honeycomb ordering.

Flourishing an Electrochemical Synthetic Route toward Carbon Black-Intercalated Graphene As a Neoteric Hybrid Nanofiller for Multifunctional Polymer Nanocomposites

This research work presents a creative and facile process for intercalation of graphite layers with the use of carbon black (CB) spacers, opening up the graphite layers to the nanolevel and producing a hybrid nanostructure. This unique tri-component three-dimensional hybrid structure, which consisted of graphene sheets exfoliated with graphene platelets and CB nanoparticle spacers, was extensively characterized by various sophisticated techniques. This surfactant-assisted electrolysis produced graphene with three layers on average. Disaggregated CB particles keep the graphene layers separated, and the material was structurally stable in water dispersion for more than a week. Such a water-dispersible filler was particularly suitable for a latex-based nanocomposite and typically advantageous concerning the dispersion of graphene-type fillers in polymers. This specifically tailored nanomaterial acted as a proficient functional filler for polymer nanocomposites, and upon incorporation in the styrene-butadiene rubber latex, the filler was brilliantly reinforcing, resulting in a 34% enhancement in the ultimate tensile strength and a 72% increase in the modulus of the rubber. The resultant polymer nanocomposite also unveiled multifunctional properties including a high specific capacitance, such as 244 F/g, and room-temperature magnetic hysteresis with fairly low remnant magnetization. This approach toward the fabrication of metal-free soft magnets comprising a carbon-based nanostructure in a polymeric matrix is scarce, and the study introduces the scope for utilization of similar composite materials in electronic as well as spintronic applications such as flexible supercapacitors even in clinically designed rubber shoes and smart tires.

Ambipolar Behavior of Ge-Intercalated Graphene: Interfacial Dynamics and Possible Applications

For the realization of graphene-based electronic and optic devices, the functionalization of this material becomes essential. Graphene doping through intercalation and tuning the chemical potential is one among other promising concepts. Intercalation of germanium is particularly interesting in view of its ambipolar doping behavior. Both p- and n-type doped graphene and their doping levels were identified by x-ray photoelectron emission microscopy (XPEEM), low-energy electron microscopy (LEEM), and angle-resolved photoemission microspectroscopy (μ-ARPES). The absolute amount of intercalated Ge was determined to be roughly 1 ML and 2 MLs for n- and p-phases, respectively. For the samples in the present study, we utilized the transition from 2 ML to 1 ML Ge via a mix phase after a high temperature annealing. Concrete implementation of mutual distribution of p- and n-phases depends on the temperature, mobility of Ge atoms in the second intercalated layer, and cooling/heating protocol, and can be nicely followed live in low-energy electron microscope (LEEM) during heating/cooling below 500°C. The process has a significant temperature hysteresis, which is an indication of the first-order phase transition. The enhanced Ge diffusion in the second layer can be suitable for tailoring ultrashort junction lengths so that pseudo-spin mismatch can be used in future electronic concepts. Another application can utilize the negative relative refractive index at the p–n boundary and can find possible applications in focusing electron optics.

Study on thermal and mechanical behaviors of polypropylene grade 552R/Cloisite 15A nanocomposites suitable for yarn applications

The investigation of polypropylene (PP)/clay nanocomposites has received considerable scientific and technological attention during the last decades due to their good mechanical and barrier properties. In the present article, the effects of adding Cloisite15A (C15A) nanoclay in polypropylene (PP) were investigated. PP nanocomposites were prepared by a direct melt mixing method. For better dispersion of C15A, 30 wt% of nanoclay masterbatch was first prepared by melt mixing of PP matrix and acrylic acid grafted PP oligomer (PP- g-AA) in a compounder, before being used to produce nanocomposites with 2 and 5 wt% of C15A. The aim of this work was to used nanoclay filled nanocomposites with suitable properties for cable application like good flame-retardant property; improve dye-ability and resilience of polypropylene. The XRD results indicated an intercalated layer structure for nanocomposites, The SEM examination showed satisfactory dispersion of nanoclay in 2 wt% of C15A and some degree of agglomeration in 5 wt% of C15A. DSC analysis indicated that C15A acts as a nucleating agent and increases crystallinity in the nanocomposite. TGA showed with increasing nanoclay, heat resistance was improved and degradation temperatures increased. Limiting oxygen index (LOI) tests showed increased flame retardancy from 25% for neat polypropylene t0 32.2% for nanocomposites of 5 wt% of C15A. The tensile modulus was improved from 423 MPa for neat polypropylene to 474 MPa for nanocomposites with 5 wt% of C15A.This result indicates that increasing C15A content had a suitable effect on the tensile properties. Melt spinning investigation on low oriented yarn (LOY), draw textured yarn (DTY), and fully drawn yarn (FDY) of 2 wt% C15A nanocomposite showed a reduction of linear density for FDY and an increase of the shrinkage. Furthermore, the obtained results for the improvement of dye-ability and compression resilience showed that PP/C15A is appropriate for textile products.

Narrowing of d bands of FeCo layers intercalated under graphene

We report on the electronic properties of an artificial system obtained by the intercalation of equiatomic FeCo layers under graphene grown on Ir(111). Upon intercalation, the FeCo film grows epitaxially on Ir(111), resulting in a lattice-mismatched system. By performing density functional theory calculations, we show that the intercalated FeCo layer leads to a pronounced corrugation of the graphene film. At the same time, the FeCo intercalated layers induce a clear transition from a nearly undisturbed to a strongly hybridized graphene π-band, as measured by angle-resolved photoemission spectroscopy. A comparison of experimental results with the computed band structure and the projected density of states unveils a spin-selective hybridization between the π band of graphene and FeCo-3d states. Our results demonstrate that the reduced dimensionality, as well as the hybridization within the FeCo layers, induces a narrowing and a clear splitting of Fe 3d-up and Fe 3d-down-spin bands of the confined FeCo layers with respect to bulk Fe and Co.

Layer spacing gradient (NaLi)1−xCoO2 for electrochemical Li extraction

Layer spacing gradient (NaLi)1−xCoO2 for electrochemical Li extraction

Rechargeable quasi-solid-state aqueous hybrid Al3+/H+ battery with 10,000 ultralong cycle stability and smart switching capability

Safe and long lifespan batteries facilitate the development of portable electronics and electric vehicles. Owing to the low-cost, naturally abundance, and trivalent charge carrier of aluminum with the highest theoretical volumetric capacity, rechargeable aqueous aluminum-ion-based batteries are considered as promising next-generation secondary batteries. However, traditional electrolytes and frequent collapse of the host structure of electrode materials greatly jeopardize the cycle stability of the batteries. Here, we develop a novel hydrogel-based electrolyte coupled with stable layered intercalation electrodes for the first time to fabricate a highly safe and flexible rechargeable hybrid Al3+/H+ battery. The as-fabricated hybrid-ion battery (HIB) delivers a high specific capacity of 125 mAh·g−1 at 0.1 A·g−1 and exhibits an unprecedented super long-term cycling stability with no capacity fading over 10,000 cycles at 2 A·g−1. In addition, the hydrogel-based electrolyte possesses smart function of thermoresponsive switching, which can effectively prevent thermal runaway for the batteries. The unprecedented long cycle stability, highly intrinsic safety as well as low-cost indicate that the flexible aqueous HIBs are promising for applications.

Three-dimensional hierarchical porous hard carbon for excellent sodium/potassium storage and mechanism investigation

Hard carbons are one of the most promising anode materials for sodium/potassium-ion batteries (SIBs/PIBs), which demonstrate favorable long charge/discharge plateaus, but suffer from low rate performance. Herein, we report a new design of N–P codoped hard carbon (NPHC) with three-dimensional (3D) hierarchical porous frameworks. Such unique structure provides bicontinuous ion/electron transportation paths, regulated electronic structure, enlarged interlayer spacing, and moderate surface area. The as prepared NPHC demonstrates a high reversible specific capacity (336 mAh g−1 for SIBs, 339 mAh g−1 for PIBs), along with a good rate performance of ~5.3 C. Particularly, an in-depth study on the charge storage mechanism for both SIBs and PIBs is conducted by combining in-situ Raman spectra and quasi in-situ synchrotron X-ray diffraction analysis, whereby the coexistence of physical adsorption/graphitic layer intercalation, or intercalation/pore filling within certain potential ranges is detected, and the ion storage behavior at different charge/discharge stages is precisely identified.

Understanding the Effect of Interplanar Space and Preintercalated Cations of Vanadate Cathode Materials on Potassium-Ion Battery Performance.

Nonaqueous potassium-ion batteries (KIBs) have been regarded as a promising alternative energy system to lithium-ion batteries, due to the abundance of the K resource and unique electrochemical properties. However, exploring suitable KIB cathode materials remains a great challenge, owing to the much larger size of the K ion than that of the Li ion. Here, a series of layered vanadates have been developed as cathodes for KIBs to elucidate the key factors that determine the electrochemical performance of KIBs, including the interlayer distance between adjacent (100) planes (d100) and preintercalated cations. Compared to NH4V3O8 nanowires with a d100 of 7.80 Å, (NH4)0.5V2O5 nanowires with a wider d100 of 9.52 Å show a faster K+ diffusion and much higher reversible capacity. The preintercalation of potassium ions into V-O slabs is also crucial to the stability of the structure of vanadates, which leads to better electrochemical cycling stability in K0.5V2O5 than that in (NH4)0.5V2O5 and NH4V3O8 nanowires. These findings reveal the great potential of the vanadate cathode in future KIBs and provide a new direction to rationally design a stable layered intercalation compound for practical KIBs.

Carbon Isotope Chemostratigraphy Across the Permian-Triassic Boundary at Chaotian, China: Implications for the Global Methane Cycle in the Aftermath of the Extinction

During the end-Permian extinction, a substantial amount of methane (CH4) was likely released into the ocean-atmosphere system associated with the Siberian Traps volcanism, although fluctuations in the global CH4cycle in the aftermath of the extinction remain poorly understood. The carbon (C) isotopic composition of carbonate (δ13Ccarb) across the Permian-Triassic boundary (P-TB) was analyzed at Chaotian, South China. The δ13Ccarbvalues decrease from ca. +1 to –2‰ across the P-TB, possibly caused by a collapse of primary productivity associated with the shallow-marine extinction. The frequent intercalation of felsic tuff layers around the P-TB suggests that a volcanogenic carbon dioxide (CO2) input to the surface oceans may also have contributed to the δ13Ccarbdecline. The magnitude of the δ13Ccarbdecrease (∼3‰) is substantially smaller than the magnitude of a decrease in C isotopic composition of organic matter (δ13Corg) in the same P-TB interval (∼7‰). This apparent δ13Ccarb-δ13Corgdecoupling could be explained by proliferation of methanogen (“methanogenic burst”) in the sediments. A global δ13C compilation shows a large variation in marine δ13Corgrecords, implying that the “methanogenic burst” according to the Siberian Traps volcanism may have contributed, at least in part, to the δ13Corgvariability and to the elevated CH4levels in the atmosphere. The present and previous observations allow us to infer that the global CH4cycle may have fluctuated substantially in the aftermath of the extinction.

Selective electrosorption of Ca2+ by MXene cathodes coupled with NiAl-LMO anodes through ion intercalation

Capacitive deionization (CDI), or electrosorption, is a desalination technology that exhibits significant potential; however, its major technical requirement of selective ion separation poses a challenge for its further practical application. Herein, a titanium carbide (MXene)–layered electrosorption electrode with high selectivity for Ca2+ was fabricated. The prepared MXene electrode had many surface hydroxyl functional groups that serve as adsorption sites for Ca2+. Ca2+ was successfully inserted into the interlayers of the MXene cathode and formed a strong interaction with [Ti-O] bonds during the capacitive deionization process. When a Ni-Al layered metal oxide anion intercalation electrode was employed as the counter electrode, Ca2+ adsorption by the MXene electrode was significantly enhanced due to the valence compensation balance effect. The maximum Ca2+ electrosorption capacity of the MXene electrode reached 1011.82 mg per gram effective MXene material, which is 6.3 times higher than that of Na+ based on the Langmuir adsorption isotherm model. The MXene electrode exhibited prominent selectivity for Ca2+ ions in the presence of Na+ and Mg2+. The Ca2+/Mg2+ selectivity factor for electrosorption reached 2.63, and Ca2+/Na+ selectivity factor could achieve 9.84, respectively. After five electrosorption/desorption cycles, the Ca2+ removal rate only decreased from 46.96% to 45.34%, suggesting that the MXene electrode has excellent stability. Our study demonstrated a novel CDI electrode and technical approach for softening water.

Electronic band structure of Bi-intercalate layers in graphene and SiC(0001)

A potential way to tune the electronic band structure of graphene is to intercalate foreign atoms in the interface between graphene and substrate. However, such an intercalate layer covered by graphene is difficult to directly study with microscopic probes, and relatively little is known about its crystal and electronic structures. In this work, we study epitaxial graphene on SiC(0001) intercalated by bismuth atoms by means of angle-resolved photoemission spectroscopy. We reveal the electronic band structure of Bi-intercalate layers, from which we could identify two distinct phases, one is metallic and the other is insulating. The metallic phase composed of closely packed Bi atoms shows nearly free electron bands that are repeated to follow the period of SiC(0001)-(1 $$\times $$ 1). The lower coverage insulating phase shows characteristic flat bands in the period of SiC(0001)-( $$\sqrt{3} {\times } \sqrt{3}$$ )R30 $$^\circ $$ with respect to the surface lattice constant of SiC(0001). Even though there exists such two distinct phases in the Bi intercalate layer, the doping level of graphene is found to vary rather continuously with the coverage of Bi. Based on the observed band structures and Bi 5d core-level spectra, we suggest a structural model for the metallic and insulating phases of Bi-terminated SiC(0001).

Assessing cathode property prediction via exchange-correlation functionals with and without long-range dispersion corrections.

We benchmark calculated interlayer spacings, average topotactic voltages, thermodynamic stabilities, and band gaps in layered lithium transition-metal oxides (TMOs) and their de-lithiated counterparts, which are used in lithium-ion batteries as positive electrode materials, against available experimental data. Specifically, we examine the accuracy of properties calculated within density functional theory (DFT) using eight different treatments of electron exchange-correlation: the strongly constrained and appropriately normed (SCAN) and Perdew-Burke-Ernzerhof (PBE) density functionals, Hubbard-U-corrected SCAN and PBE (i.e., SCAN+U and PBE+U), and SCAN(+U) and PBE(+U) with added long-range dispersion (D) interactions (i.e., DFT(+U)+D). van der Waals interactions are included respectively via the revised Vydrov-Van Voorhis (rVV10) for SCAN(+U) and the DFT-D3 for PBE(+U). We find that SCAN-based functionals predict larger voltages due to an underestimation of stability of the MO2 systems, while also predicting smaller interlayer spacings compared to their PBE-based counterparts. Furthermore, adding dispersion corrections to PBE has a greater effect on voltage predictions and interlayer spacings than with SCAN, indicating that DFT-SCAN - despite being a ground-state theory - fortuitously captures some short and medium-range dispersion interactions better than PBE. While SCAN-based and PBE-based functionals yield qualitatively similar band gap predictions, there is no significant quantitative improvement of SCAN-based functionals over the corresponding PBE-based versions. Finally, we expect SCAN-based functionals to yield more accurate property predictions than the respective PBE-based functionals for most TMOs, given SCAN's stronger theoretical underpinning and better predictions of systematic trends in interlayer spacings, intercalation voltages, and band gaps obtained in this work.

Capacitive Performance of Reduced Graphene Oxide Modified Sodium Ion-Intercalated Manganese Oxide Composite Electrode

Abstract The reduced graphene oxide modified sodium ion-intercalated manganese oxide (RGO-NaxMnO2) is designed as a supercapacitor electrode material. The layered intercalation compound NaxMnO2 is prepared through a solid-state reaction process. RGO-NaxMnO2 is then formed by the chemical reduction of graphene oxide coated NaxMnO2 through a hydrothermal process. RGO-NaxMnO2 is supported on the substrate of nickel form (NF) and titanium nitride (TiN) to form RGO-NaxMnO2/NF and RGO-NaxMnO2/TiN composite electrodes. NaxMnO2 has a particle aggregate structure with the individual particle size of 1–2 µm. RGO-NaxMnO2 composite shows the densely packed arrangement of particles with the particle aggregate size of 8 µm. RGO modification can well improve the electrical conductivity of RGO-NaxMnO2. The current response is highly enhanced from 0.127 A g−1 for NaxMnO2/NF to 0.372 A g−1 for RGO-NaxMnO2/NF at 2 mV s−1. Furthermore, the TiN substrate with superior electrical conductivity and electrochemical anti-corrosion contributes to improving the electrochemical capacitance and cycle stability of RGO-NaxMnO2. RGO-NaxMnO2/TiN reveals higher specific capacitance (244.2 F g−1 at 2.0 A g−1) and higher cycling capacitance retention (99.7%) after 500 cycles at 2.0 A g−1 than RGO-NaxMnO2/NF (177.1 F g−1, 43.6%). So, RGO-NaxMnO2/TiN exhibits much higher capacitive performance than RGO-NaxMnO2/NF, which presents a potential application for electrochemical energy storage.

High Pressure Effect on Structural and Electrochemical Properties of Anionic Redox-Based Lithium Transition Metal Oxides

Summary The richness of anionic redox chemistry in the solid state offers new opportunities and a possible paradigm shift in energy storage. The excess capacity that goes beyond conventional theoretical values is attributed to the anionic redox in Li-rich transition metal oxide cathodes for Li-ion batteries. Their electrochemical behavior is thermodynamically determined by structural evolution. To better understand the electrochemical dependence on structural factors, we have induced structural modifications in pristine and electrochemically activated Li1.144Ni0.136Co0.136Mn0.544O2 through high-pressure treatment. A unique cyclical change of structural reordering is observed in the anionic redox-activated material during operando pressure sweep, characterized by a periodic evolution of superlattice peak intensity in synchrotron X-ray diffraction patterns. During the structural reordering period, the bulk compressibility of the material decreases, even becoming negative. These insights elucidate the structural flexibility and metastability of anionic redox-based materials, which can undergo large compressions and structural modifications while delivering good electrochemical properties.

Numerical analysis of loess and weak intercalated layer failure behavior under direct shearing and cyclic loading

The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China. The shear behavior of the joints in the loess stratum during direct shear and cyclic loadings was investigated using the PFC2D discrete element software. Loess mudstone and mudstone with weak intercalated layer materials were subjected to direct testing, and cyclic shear tests were conducted with consideration to the influence of normal stress and shear velocity. The macroscopic properties and damage patterns were obtained for six numerical configurations; namely, loess-weathered mudstone with 0°, 10°, and −10° joints and weathered mudstone with 0°, 10°, and −10° weak intercalated layers. The numerical test results revealed that, in the direct shear tests, the shear stress and shear displacement of the samples increased with the normal stress. In the cyclic shear tests with a total cycle number N=20, the shear stress-shear strain curve of the six different configurations exhibited a hysteresis loop. The numerical tests also revealed that, under cyclic shear, the normal stress and shear velocity affected the shear strength. The degree of damage increased as the shear velocity decreased from 0.1 mm/s to 0.005 mm/s for all six numerical configurations. Compared with the damage pattern of the direct shear tests, the damage of the cyclic shear tests mainly comprised shear cracks and fractures, some shaking consolidation settlement and fewer shear strain occurred around the joints. In the direct shear tests, more compression cracks and fractures occurred in the samples. The damage mainly developed along the joints, and shearing-off damage occurred. The results obtained by this study further elucidate the failure mechanism and microscopic damage response of the joints in the loess stratum in Northwest China.

Lower Kimmeridgian facies and sedimentary succession of a shallow-water coated-grain-dominated carbonate ramp of the northern peri-Tethyan shelf: an example from the Radomsko Folds (central Poland)

An Upper Jurassic succession is exposed in the active Rogaszyn Quarry (Kodrąb area) located in the Radomsko Folds structure (central Poland). Six facies types were distinguished, comprising oolitic, oncolitic, biodetrital and pelitic limestones as well as marls and marly clays. Typical lithologies are limestones with coated grains deposited in shallow-water, fore-shoal, shoal and lagoonal parts of a carbonate ramp. Three types of ooid and three types of oncoid were identified, which display several shapes and sizes, and a complex structure of cortices. The ooid types show micritic, radial-fibrous and mixed, micritic/radial-fibrous cortices. Type 1 oncoids comprise micritic or bioclastic nuclei enveloped by non-laminated or laminated micritic cortices. Type 2 oncoids are composed of micritic or bioclastic nuclei and laminated, fossil-bearing cortices covered by microbial envelopes. Type 3 oncoids are the largest of the oncoids observed, attaining cm-scale dimensions. These oncoids are formed of a Bacinella-dominated meshwork incorporating smaller ooids and oncoids, or they have bioclastic or micritic nuclei covered by complex cortices with micritic, laminated, fossil-bearing, Bacinella-dominated fabric and microbial envelopes. Boundaries between the specific types of cortical envelopes are usually sharp and accentuated by organic encrustations, elongated bioclasts or borings. Commonly found are chambers of the ichnogenus Entobia representing the boring traces of carbonate-excavating sponges and the cryptoendolithic foraminifer Troglotella incrustants . The complex cortices indicate different growth stages of oncoids at different conditions of currents and microbial activity. Carbonate deposition was accompanied by mixed siliciclastic-carbonate sedimentation resulting in multiple intercalated layers of marls and pelitic limestones as well as marly clays. The deposits exposed in the Rogaszyn Quarry as well as in the Kodrąb area are compared with the neighbouring Upper Jurassic deposits of the Szczerców area and the SW margin of the Holy Cross Mts. (both central Poland). The successions from the Kodrąb area are generally similar to the Lower Kimmeridgian sequences known from adjacent areas, but with locally observed facies variability.

Anomalous Hall effect in a magnetically extended topological insulator heterostructure

Constructing heterostructures of a topological insulator (TI) with an undoped magnetic insulator (MI) is a clean and versatile approach to break the time-reversible symmetry in the TI surface states. Despite a lot of efforts, the strength of interfacial magnetic proximity effect (MPE) is still too weak to achieve the quantum anomalous Hall effect and many other topological quantum phenomena. Recently, a new approach based on intercalation of atomic layers of MI, referred to as magnetic extension, was proposed to realize strong MPE [2D Mater. 4, 025082(2017)]. Motivated by this proposal, here, we study a magnetic extension system prepared by molecular beam epitaxy growth of MnSe thin films on topological insulator (Bi,Sb)2Te3. Direct evidence is obtained for intercalation of MnSe atomic layer into a few quintuple layers of (Bi,Sb)2Te3, forming either a double magnetic septuple layer (SL) or an isolated single SL at the interface, where one SL denotes a van der Waals building block consisting of B-A-B-Mn-B-A-B (A=Bi1-xSbx, B= Te1-ySey). The two types of interfaces (namely TI/mono-SL and TI/bi-SL) have different MPE, which is manifested as distinctively different transport behaviors. Specifically, the mono-SL induces a spinflip transition with a sharp change at small magnetic field in the anomalous Hall effect of TI layers, while the bi-SL induces a spin-flop transition with a slow change at large field. Our work demonstrates a useful platform to realize the full potential of the magnetic extension approach for pursuing novel topological physics and related device applications.

Recent progress in graphene-based and ion-intercalation electrode materials for capacitive deionization

Capacitive deionization (CDI) has attracted considerable interest as an energy-efficient and cost-effective approach for water desalination. The fundamental working principle of CDI relies on ion electrosorption on the surface of a pair of electrically charged electrodes. Therefore, the development of more efficient electrode materials with high salt adsorption capacity is at the heart of CDI technology, and has motivated considerable efforts over the past decade. In particular, various carbon materials, including conventional activated carbon and various forms of porous carbon and graphene, have been intensively investigated as the CDI electrode materials for their electrochemical stability and large surface area, which typically relies solely on ion absorption and the formation of Helmholtz electrical double layer. It has more recently been shown that significant improvements in salt adsorption capacity can be further achieved either by functionalization of carbon surface with redox-active groups, or by introducing electrochemically active transition metal oxides or conductive polymers into the carbon matrix. Herein, we briefly summarize the fundamental principle of CDI technology, and review the recent progress in the design and development of high performance CDI electrode materials. We will conclude with a brief perspective on the current challenges and future opportunities in CDI technology. • The ion storage mechanisms of electric double layer (EDL) materials and intercalation materials. • Summary of the recent progress in the design and development of high performance CDI electrode materials. • Summary of the fundamental principle of CDI technology. • We outlined some important issues/challenges for the development of CDI electrode materials.