Water Intercalation Research Articles

Preparation of Montmorillonite–Melamine Cyanurate and Inhibition of the Emission of Phosphine from PA6/Aluminum Hypophosphate

In order to mitigate the release of toxic phosphine from aluminum hypophosphite in twin-screw processing, montmorillonite–melamine cyanurate was prepared by three methods: (1) mechanical intercalation, (2) water intercalation and (3) in situ intercalation. The sheet spacing of montmorillonite was increased from 1.140 nm to 1.141 nm, 1.208 nm and 1.217 nm for these three methods, respectively, and scanning electron microscope (SEM) and transmission electron microscopy (TEM) proved that melamine cyanurate was successfully inserted into the montmorillonite sheets. The montmorillonite–melamine cyanurate from in situ intercalation can best inhibit the release of PH3 from aluminum hypophosphite, and the peaks of phosphine, mean values of phosphine and integral of phosphine were reduced by 81.9%, 72.1% and 72.2%, respectively. The mode of action of montmorillonite–melamine cyanuric inhibition of the emission of phosphine from aluminum hypophosphite can be attributed to the physical absorption of montmorillonite and the chemical bonding of melamine cyanurate. In addition, in situ intercalation can slightly improve flame retardancy, attributed to incomplete exfoliation of montmorillonite sheets.

Revisiting oxidation and reduction reactions for synthesizing a three-dimensional hydrogel of reduced graphene oxide.

An improvement to Hummers' method involving a cascade-design graphite oxidation reaction is reported to optimize safety and efficiency in the production of graphite oxide (GrO) and graphene oxide (GO). Chemical reduction using highly alkaline ammonia solution is a novel approach to synthesizing reduced graphene oxide (RGO). In this original research, we revisit the oxidation and reduction reactions, providing significant findings regarding the synthetic pathway to obtain a bioinspired water-intercalated hydrogel of RGO nanosheets. Influential factors in the graphite oxidation reaction, typically the exothermic reaction temperature and hydrogen peroxide effect, are described. Furthermore, the chemical reaction of GO reduction using highly alkaline ammonia solution (pH 14) was investigated to produce hydrated RGO nanosheets assembled in a hydrogel structure (97% water). Three-dimensional assembly and water intercalation are key to preserve the non-stacking state of RGO nanosheets. Therefore, ultrasound transmission to aqueous channels in the macroscopic RGO hydrogel vibrated and dispersed the RGO nanosheets in water. Analytical results revealed the single-layer nanostructures, functional groups, optical band gaps, optimized C/O ratios, particle sizes and zeta potentials of GO and RGO nanosheets. The reversible self-assembly of RGO hydrogels is essential for many applications, such as RGO coatings and polymer/RGO nanocomposites. In a water purification application, the RGO hydrogel was dispersed in aqueous solution by simple agitation and showed a high capacity for organic dye adsorption. After the adsorption, the RGO/dye particles were easily removed by filtration through ordinary cellulose paper. The process of adsorption and filtration is effective and inexpensive for practical environmental remediation. In summary, a bioinspired structure of RGO hydrogel is conceptualized for prospective nanotechnology.

(Invited) OER Active Phases, Catalytic Mechanism and Reaction Centers of Ni (oxy)Hydroxide with and without Fe Impurities

Identifying atomic-scale structures of catalytically active phases, catalytic mechanism and reaction centers are crucial for establishing rigorous structure-activity relationship of highly active catalysts and for designing new catalysts with further improved performance. Due to the lack of theoretical guidance and challenges in experimental structural characterization during OER conditions, in-situ structures and stabilities of two (a-Ni(OH)2 and g-NiOOH with water and ion intercalation) out of four (oxy)hydroxide phases (another two are b-Ni(OH)2 and b-NiOOH without water and ion intercalations) remain elusive after at least half a century study, which has hindered the establishment of rigorous structure-activity relationship of Ni (oxy)hydroxides and their derivatives for the OER. As a consequence, it is still unclear regarding which phases should be the hosts and the precursors of choice for highly active catalysts. Here, by combining ab initio molecular dynamics simulation, in-situ wide-angle X-ray scattering, and electrochemical measurements, we provide direct atomic-scale and self-consistent insights into the crystal structure, water and ion intercalation, and stable potential windows of complex a-Ni(OH)2 and g-NiOOH with respect to b-phases. DFT calculations indicate that b-NiOOH and g-NiOOH with Fe impurities have similar OER activity to or even higher OER activity than that of g-NiFe LDH, with a dependence on the Fe coverage on the edges. Current work suggests that both b-NiOOH and g-NiOOH are potential hosts of highly active OER catalysts, which enlarges the phase space for the design of OER catalysts with further improved performance.We will discuss the implications of the above insights toward understanding of the active phases, reaction centers and catalytic mechanism of NiM and CoM layered double hydroxides. If time permits, we will further review our work our work regarding the promotion effects of non-covalent ligand-oxide interaction in OER and mitigation of RuO6 octahedron distortion by enhanced A-site electronegativity in pyrochlore for acidic water oxidation.

Vanadium‐Based Cathodes Modification via Defect Engineering: Strategies to Support the Leap from Lab to Commercialization of Aqueous Zinc‐Ion Batteries

AbstractIn advancing aqueous zinc‐ion batteries (AZIBs) toward commercial viability, vanadium (V)‐based cathodes are pivotal, offering broad redox ranges, and compatibility with water's electrochemical limits. Despite their great potentials, V‐based cathodes face challenges in transitioning from lab to commercialization. Defect engineering is exploited as a pivotal technique that endows the cathodes with unexpected physical and chemical properties to break the intrinsic bottleneck and, in turn, enhance their electrochemical performances. This review delves into the role of defect engineering on V‐based materials, underscoring its potential in mitigating the critical challenges. It starts by encapsulating the current characteristics of V‐based cathodes in AZIBs. Research efforts related to various defects, such as oxygen vacancies, cation vacancies, cationic doping, anionic doping, water intercalation, and lattice disorders/amorphization, are then rationalized and discussed. The fabrication and characterization techniques of defect engineering are also summarized. By integrating the conclusions from existing works and tailoring defect engineering strategies, a few perspectives are provided for systematically employing defect engineering to pave the way for a more efficient transition of these promising materials from laboratory breakthroughs to commercially viable energy storage solutions.

The fate of graphene on copper: Intercalation / de-intercalation processes and the role of silicon

Intercalation and de-intercalation processes below graphene (g) grown by chemical vapor deposition (CVD) on Cu foils (g/Cu) were investigated in a combined low-energy electron microscopy and X-ray photoemission electron microscopy study. Exposure of g/Cu to air induces oxygen and water intercalation which can be removed by annealing in vacuum leading to clean and well-ordered graphene on Cu. However, prolonged air exposure leads to intercalation of large amounts of oxygen, most likely inducing the formation of copper oxides. If sufficient intercalated oxygen remains at the interface when exceeding 320 °C, graphene is oxidized and burned off. Cu foils can be loaded with silicon on purpose during foil pre-treatment or accidently during long growth time when applying high temperatures at elevated H2 pressure inducing the reactive removal of Si species from the quartz reactor wall. Due to the dissolution of Si in the Cu bulk, the Si surface concentration remains below detection limit and graphene of equal crystalline quality is grown as if the Cu foil was silicon-free. However, oxygen intercalation underneath graphene on Si-containing Cu foils can induce Si segregation towards the surface and formation of intercalated silica without attacking the covering graphene. Even at high temperatures, segregating Si acts as oxygen scavenger so that graphene resists oxidation. The observed effect explains the usefulness of certain synthesis protocols and paves the way towards large-scale fabrication of electronically decoupled graphene. The effect can be used to immobilize adsorbing oxygen at the interface and image the initial steps of intercalation below graphene in-situ.

Activation and degradation mechanisms of α-V2O5 cathode materials in Zn-ion battery

Vanadium oxides with high specific capacity have been widely used as cathode materials for aqueous Zn-ion batteries. However, the interactions between the aqueous electrolytes and Vanadium oxides are still unclear. In particular, the intercalation of proton and water which can play a critical role in the degradation process is less well understood. Moreover, the mechanism for the capacity increase during the electrochemical cycling, known as the activation process, is still under debate. In this study, we systematically investigated the α-V2O5||Zn battery system with state-of-the-art characterization tools and electrochemical testing techniques to reveal the activation and degradation processes. It is discovered that the activation can be mainly attributed to the intercalation of protons and water in the first 100 cycles, which destabilizes the overall structural integrity, leading to capacity degradation afterward. It is also revealed that two main cathode electrolyte interface (CEI) components can be formed on the cathode surface, namely Zn3(V2O7)(OH)2·2H2O and Znm(CF3SO3)n(OH)2m-n·nH2O. The formation of Zn3(V2O7)(OH)2·2H2O-based CEI component is irreversible, while Znm(CF3SO3)n(OH)2m-n·nH2O-based CEI component can be reversibly cycled. Different structure-stabilizing charge/discharge protocols are proposed accordingly, which could leverage the structural integrity with thorough phase transition in the activation stage to enhance the cycling performance of the V-based cathodes. We hope to spur further interest in the fundamental understanding of the cathode materials in Zn-ion batteries.

Li+ Cations Activate NiFeOOH for Oxygen Evolution in Sodium and Potassium Hydroxide.

The efficiency of electrolysis is reduced due to the sluggish oxygen evolution reaction (OER). Besides catalyst properties, electrocatalytic activity also depends on the interaction of the electrocatalyst with the electrolyte. Here, we show that the addition of small amounts of Li+ to Fe-free NaOH or KOH electrolytes activates NiFeOOH for the OER compared to single-cation electrolytes. Moreover, the activation was maintained when the solution was returned to pure NaOH. Importantly, we show that the origin of activation by Li+ cations is primarily non-kinetic in nature, as the OER onset for the mixed electrolyte does not change and the Tafel slope at low current density is ~30 mV/dec in both electrolytes. However, the increase of the apparent Tafel slope remains lower at increasing current densities in the presence of Li+. Based on electrochemical quartz crystal microbalance and in situ X-ray absorption spectroscopy measurements, we show that this reduction of non-kinetic effects is due to enhanced intercalation of sodium, water and hydroxide. This enhanced electrolyte penetration facilitates the OER, especially at higher current densities and for increased catalyst loading. Our work shows that mixed electrolytes where distinct cations can have different roles provide a simple and promising strategy towards improved OER rates.

Li+ Kationen aktivieren NiFeOOH für die Sauerstoffentwicklung in Natrium‐ und Kaliumhydroxid

AbstractDie Effizienz der Elektrolyse wird durch die träge Sauerstoffentwicklung (OER) verringert. Neben den Katalysatoreigenschaften hängt die elektrokatalytische Aktivität auch von der Interaktion des Elektrokatalysators mit dem Elektrolyten ab. Hier zeigen wir, dass die Zugabe kleiner Mengen Li+ zu eisenfreien NaOH‐ oder KOH‐Elektrolyten NiFeOOH für die OER aktiviert, verglichen mit monokationischen Elektrolyten. Außerdem blieb der aktivierte Zustand erhalten, wenn zu reiner NaOH zurück gewechselt wurde. Wichtig ist, dass wir zeigen, dass der Ursprung der Aktivierung durch Li+‐Kationen in erster Linie nicht‐kinetischer Natur ist, da sich der Beginn der OER für den gemischten Elektrolyten nicht ändert und die Tafelsteigung bei niedriger Stromdichte in beiden Elektrolyten ~30 mV/dec beträgt. Der Anstieg der Tafelsteigung bleibt jedoch bei steigenden Stromdichten in Gegenwart von Li+ geringer. Basierend auf elektrochemischen Quarzkristall‐Mikrowaagen‐ und In situ‐Röntgenabsorptionsspektroskopie‐Messungen zeigen wir, dass diese Verringerung der nichtkinetischen Effekte auf eine verstärkte Interkalation von Natrium, Wasser und Hydroxid zurückzuführen ist. Diese verstärkte Elektrolytpenetration erleichtert die OER, insbesondere bei höheren Stromdichten und bei erhöhter Katalysatorbeladung. Unsere Arbeit zeigt, dass gemischte Elektrolyte, in denen verschiedene Kationen unterschiedliche Rollen einnehmen können, eine einfache und vielversprechende Strategie zur Verbesserung der OER‐Raten darstellen.

Electronic and thermal properties of Nb2CCl2 MXenes

The molten salt synthesis has recently opened up new opportunities to functionalize two-dimensional MXenes with uniform halogen terminations. In this work, we synthesize Nb2CCl2 MXenes by etching the Al layer from the Nb2AlC precursor in the melt of CuCl2 Lewis acid. In Cl-terminated MXenes, intercalation of water is negligible, so that MXenes get closer to ideal, ordered van der Waals solids. We identify the preferential atomic stacking arrangement, which is of the AB type, as opposed to the AA stack assumed in previous works. We combine X-ray absorption near edge spectroscopy with density functional theory to clarify the local chemical environment of Cl atoms. Using vibrating sample magnetometry and specific heat measurements, we confirm that Nb2CCl2 MXenes are superconducting with a transition temperature of 6.0 K and find a Debye temperature of 320 K. We further show that the transition temperature slightly decreases with applied isostatic pressure.

Nucleate boiling enhancement on hybrid graphene-nanoplatelets/carbon nanotubes coatings for light-emitting diode cooling

This study explores the remarkable enhancement of light-emitting diode (LED) cooling through nucleate boiling using hybrid coatings of graphene-nanoplatelets (GNP) and carbon nanotubes (CNT). The introduction of oxygenated functional groups in the cured GNP and CNT coatings fosters improved hydrophilicity, promoting water intercalation within the nanostructures. The hybrid cured GNP/CNT coating demonstrates superior nucleate boiling performance compared to individual cured GNP and CNT coatings, owing to complementary mechanisms. Cured CNT facilitate efficient water permeation by enabling water molecules to infiltrate through their inner cores and intertwining tube spaces, while cured GNP offer an escape route for trapped water molecules and absorbed latent heat due to their layer-by-layer arrangement of graphene sheets with broadened interlayers. As compared to the bare copper surface, the LED cooled using the hybrid cured GNP/CNT coating exhibits a maximum temperature drop of 20.7 °C and an enhancement up to 1212 % in heat transfer coefficient, surpassing the cured GNP and CNT coatings. Moreover, the hybrid cured GNP/CNT coating improves the LED illuminance by 16.6 %, validating its potency in improving cooling performance. These findings highlight the potential of GNP/CNT hybrid coatings in advancing nucleate boiling cooling technologies and offer valuable insights into optimizing LED performance for high-quality lighting solutions.

Oxygen Hole Formation Controls Stability in LiNiO2 Cathodes: DFT Studies of Oxygen Loss and Singlet Oxygen Formation in Li-Ion Batteries

Ni-rich cathode materials achieve both high voltages and capacities in Li-ion batteries but are prone to structural instabilities and oxygen loss via the formation of singlet oxygen. Using ab initio molecular dynamics simulations, we observe spontaneous O2 loss from the (012) surface of delithiated LiNiO2, singlet oxygen forming in the process. We find that the origin of the instability lies in the pronounced oxidation of O during delithiation, i.e., O plays a central role in Ni-O redox in LiNiO2. For LiNiO2, NiO2, and the prototype rock salt NiO, density-functional theory and dynamical mean-field theory calculations based on maximally localised Wannier functions yield a Ni charge state of ca. +2, with O varying between –2 (NiO), –1.5 (LiNiO2) and –1 (NiO2). Predicted XAS Ni K and O K-edge spectra are in excellent agreement with experimental XAS spectra, confirming the predicted charge states. The calculations also show that a high-voltage O K-edge feature at 531 eV previously assigned to lattice O-redox processes could alternatively arise from O-redox induced water intercalation and O–O dimer formation with lattice O at high states of charge. The O2 surface loss route observed here consists of 2 surface O•– radicals combining to form a peroxide ion, which is oxidised to O2, leaving behind 2 O vacancies and 2 O2– ions: effectively 4 O•– radicals disproportionate to O2 and 2 O2– ions. The reaction liberates ca. 3 eV per O2 molecule. Singlet oxygen formation is caused by the singlet ground state of the peroxide ion, with spin conservation dictating the preferential release of 1O2, the strongly exergonic reaction providing the free energy required for the formation of 1O2 in its excited state.

Swelling of Ti3 C2 Tx MXene in Water and Methanol at Extreme Pressure Conditions.

Pressure-induced swelling has been reported earlier for several hydrophilic layered materials. MXene Ti3C2Tx is also a hydrophilic layered material composed by 2D sheets but so far pressure-induced swelling is reported for this material only under conditions of shear stress at MPa pressures. Here, high-pressure experiments are performed with MXenes prepared by two methods known to provide "clay-like" materials. MXene synthesized by etching MAX phase with HCl+LiF demonstrates the effect of pressure-induced swelling at 0.2GPa with the insertion of additional water layer. The transition is incomplete with two swollen phases (ambient with d(001) = 16.7Å and pressure-induced with d(001) = 19.2Å at 0.2GPa) co-existing up to the pressure point of water solidification. Therefore, the swelling transition corresponds to change from two-layer water intercalation (2L-phase) to a never previously observed three-layer water intercalation (3L-phase) of MXene. Experiments with MXene prepared by LiCl+HF etching have not revealed pressure-induced swelling in liquid water. Both MXenes also show no anomalous compressibility in liquid methanol. The presence of pressure-induced swelling only in one of the MXenes indicates that the HCl+LiF synthesis method is likely to result in higher abundance of hydrophilic functional groups terminating 2D titanium carbide.

Microphase Separation of Cationic Homopolymers Bearing Alkyl Ammonium Salts into Sub-4 nm Lamellar Materials with Water Intercalation Channels

Microphase Separation of Cationic Homopolymers Bearing Alkyl Ammonium Salts into Sub-4 nm Lamellar Materials with Water Intercalation Channels

Hard X-ray photoelectron spectroscopy reveals self-organized structures of electrocatalytic nickel oxy-hydroxides

Alkaline water electrolysis represents one of the simplest methods employed for renewable hydrogen production, reaching high conversion efficiency utilizing cheap and abundant transition metals such as nickel and its alloys. The outstanding properties of Ni-materials do not arise from the metallic host, rather from the surface passivated with various oxidized compounds formed during the electrochemical process. This newly formed layer is responsible for the catalytic properties of the system, therefore the investigation of its evolution as function of potential and time is crucial for a deeper understanding of the overall electrochemical process. However, the characterization of the chemical environment at the topmost layer, as well as the underlying layers, is complex and requires surface sensitive techniques. Here, we show that while ambient pressure soft X-ray photoelectron spectroscopy (APXPS) allows to follow the changes of the topmost layer, characterization of the deeper layers modifications occurring during electrocatalysis requires a combination of soft- and hard X-ray photoelectron spectroscopy (XPS/HAXPES), coupled with electrochemical impedance spectroscopy (EIS). The findings show how the high electrocatalytic activity of Ni (oxy)-hydroxides is directly related to the increasing water intercalation into the passivation layer, which supports the long-debated hypothesis of a water mediated OH− diffusion mechanism. High performance of the electrode is promoted by the peculiar structure of the surface, which self-organizes during the initial formation of the passivation layer enabling self-healing during electro-catalysis. Ultimately, we show how the investigation at different depths by means of XPS/HAXPES in combination with EIS allows a better understanding of the chemical changes occurring throughout the passivation layer, signaling a paradigm shift from the traditional explanation of electro-catalysis by a simple electrode material with a stable nanostructure, to a concept leaning towards a dynamic electrochemical interface.

Evidence for Charging and Discharging of MoS2 and WS2 on Mica by Intercalating Molecularly Thin Liquid Layers

Transition metal dichalcogenides (TMDCs) are often mechanically exfoliated on mica and examined under ambient conditions. It is known that above a certain relative humidity, a molecularly thin layer of water intercalates between the mica and the TMDC. Herein, the effect of molecularly thin liquid layers on the optical spectra of MoS2 and WS2 exfoliated on dry mica and exposed to the vapors of water, ethanol, and tetrahydrofuran (THF) is investigated. Photoluminescence and differential reflectance (ΔR/R) spectra on the TMDCs on dry mica show dominant trion emission due to n‐doping. Intercalation of water removes charge doping and results in purely neutral exciton emission, while an ethanol layer, which can be reversibly exchanged with water, does not completely suppress charge. Similarly, THF intercalates between TMDC and mica, as shown by atomic force microscopy, but it does not suppress the charging of mica. In MoS2 bi‐ and trilayers, an intercalated water layer leads to a near doubling of the intensity of the indirect band transition. The described charging/discharging of TMDCs by molecular thin liquid layers can provide important clues to better control the optical properties of TMDCs under environmental conditions.

Effect of water intercalation into tungsten trioxide structure (WO3·xH2O) (x = 0,1,2): Correlation between structure and photocatalytic performances

Tungsten oxide (WO3) is a potential photoanode material for water oxidation, however, its employment is still restricted by its limited light absorption (Eg ∼ 2.75 eV). A particular interest was devoted to tuning its electronic structure and optical bandgap in order to enhance its photocatalytic performance in hydrogen production as well as in advanced oxidation process. One of the promising alternatives for the enhancement of these photocatalytic performances, is the introduction of guest molecules into the tungsten oxide structure. In this paper, the photocatalytic performances of tungsten trioxide were highly improved by the intercalation of water into its structure. The intercalated compounds of chemical formula WO3·xH2O were prepared and characterized by TGA-DSC, PXRD, FT-IR, Raman spectroscopy, SEM-EDS and XPS. The structures of intercalated materials were refined using Rietveld method and the electronic proprieties including bandgap energy, CB and VB edges were estimated using UV–visible reflectance spectroscopy. The obtained results show that the intercalation of water molecules into tungsten oxide structure reduces the gap energy of the WO3 (2.4 eV) to 2.16 eV for WO3∙H2O and to 2.31 eV for WO3∙2H2O. The photocatalytic efficiency of the obtained materials was studied through oxygen evolution reaction tests in the presence of an electron acceptor (Ag+) and the oxidative photodegradation of the orange G dye pollutant. We found that intercalated samples exhibit the highest efficiencies compared with anhydrous samples. These findings are correlated with the increase in the average W-O-W tilt angle in WO3∙2H2O and WO3∙H2O compared to that of WO3. This improvement in the tilt angle induces the shrinkage of the energy bandgap and increases the photocatalytic performance. Furthermore, the stability of the investigated materials was studied as a function of pH, the results reveal that the intercalation of water molecules is beneficial for the chemical stability of the hydrated tungsten oxides. These findings shed light on new alternatives for band-gap engineering and improvement of materials stability through intercalation with water molecules.

Effect of interlayer K ordering on water intercalation behavior in δ-type layered manganese dioxide

Layered manganese dioxide (birnessite) that contains K cations and water molecules in between the MnO2 layers exhibits reversible heat storage properties via a water-intercalation mechanism (0.5 mol H2O per K0.33MnO2). However, a certain amount of an irreversible capacity of water intercalation is observed after the initial thermal cycle, which limits the reversibly available energy density of the material for the subsequent cycles. In this study, we analyzed crystal structures of the K-containing birnessite, K0.33MnO2, before and after heat treatment, by electron diffraction and atomic-resolution scanning transmission electron microscopy, to elucidate the origin of the initial irreversible capacity (0.83 mol per K0.33MnO2). The K-containing birnessite synthesized by thermal decomposition of KMnO4 was found to basically possess a superstructure of tripled periodicity along the in-plane direction due to an ordered arrangement of the interlayer K cations, while the stacking periodicity of the interlayer K cations along the out-of-plane direction was partially lost. The K cations preferentially occupy the 2c site (space group P63/mmc), which is the most stable position as confirmed by ab initio calculations. The K cations occupy every third 2c site in almost all the interlayers after heat treatment, although the K cations in the as-synthesized state are randomly arranged in some of the interlayers because excess water molecules prevent the interlayer K cations from occupying the most stable 2c site. Thus, the ordering of the K cations once occurring without the water molecules during heat treatment hinders the excess water initially included to re-intercalate in the subsequent cycle process.

The Evolution of MXenes Conductivity and Optical Properties Upon Heating in Air.

MXenes, a family of 2D transition-metal carbides and nitrides, have excellent electrical conductivity and unique optical properties. However, MXenes oxidize in ambient conditions, which is accelerated upon heating. Intercalation of water also causes hydrolysis accelerating oxidation. Developing new tools to readily characterize MXenes' thermal stability can enable deeper insights into their structure-property relationships. Here, in situ spectroscopic ellipsometry (SE) is employed to characterize the optical properties of three types of MXenes (Ti3 C2 Tx , Mo2 TiC2 Tx , and Ti2 CTx ) with varied composition and atomistic structures to investigate their thermal degradation upon heating under ambient environment. It is demonstrated that changes in MXene extinction and optical conductivity in the visible and near-IR regions correlate well with the amount of intercalated water and hydroxyl termination groups and the degree of oxidation, measured using thermogravimetric analysis. Among the three MXenes, Ti3 C2 Tx and Ti2 CTx , respectively, have the highest and lowest thermal stability, indicating the role of transition-metal type, synthesis route, and the number of atomic layers in MXene flakes. These findings demonstrate the utility of SE as a powerful in situ technique for rapid structure-property relationship studies paving the way for the further design, fabrication, and property optimization of novel MXene materials.

Intercalated water-induced hysteretic friction behavior of graphene, h-BN, and MoS[formula omitted

Two-dimensional (2D) materials have extraordinary properties that promise significant advancement of electronic, mechanical, and electrochemical devices. However, these properties are often measured in ideal, clean states, absent from contamination from their surrounding environment. Here we study the impact of water intercalation on the mechanical and lubricating properties on 2D nanofilms of graphene, h-BN, and MoS2 using atomic force microscopy (AFM) and molecular dynamics (MD) simulations. Comparing the performance of pristine 2D nanofilms and those with water intercalated between the substrate and the 2D nanofilm, we observed higher friction in intercalated samples than in pristine samples. In load dependent friction measurements, we also observed that the friction hysteresis varied from pristine samples to those with water intercalated. MD simulations suggest that this difference was a result of a decrease in the apparent out-of-plane mechanical stiffness of the 2D nanofilm and a reduction in the adhesive interaction between substrate and nanofilm that occurred when water was intercalated between the 2D material and the substrate, allowing for a change in the out-of-plane deformation behavior of the supported 2D nanomaterial. These observations suggest that 2D materials experience performance degradation when exposed to ambient conditions.

Novel Pr-Doped BaLaInO4 Ceramic Material with Layered Structure for Proton-Conducting Electrochemical Devices

One of the urgent tasks of applied materials science is the creation of novel high-effective materials with target properties. In the area of energy systems, there is a problem in the conversion of chemical energy to electricity without mechanical work. Hydrogen energy provides a way using electrochemical devices such as protonic ceramic fuel cells. Novel advanced proton-conducting materials with the top characteristics of target properties are strictly needed. Layered perovskites are a novel and promising class of protonic conductors. In this work, the layered perovskite BaLa0.9Pr0.1InO4 was obtained and investigated as a protonic conductor for the first time. The possibility for water intercalation and proton transport is proved. It was shown that isovalent doping Pr3+ → La3+ leads to an increase in the crystal lattice size, proton concentration and proton mobility. The proton conductivity value for doped BaLa0.9Pr0.1InO4 composition is 18 times greater than for undoped BaLaInO4 composition. Layered perovskites based on BaLaInO4 are promising materials for application in proton-conducting electrochemical devices.