Peat-derived hard carbon electrodes with superior capacity for sodium-ion batteries

Herein we demonstrate how peat, abundant and cheap biomass, can be successfully used as a precursor to synthesize peat-derived hard carbons (PDCs), applicable as electrode materials for sodium-ion batteries (SIB). The PDCs were obtained by pre-pyrolysing peat at 300–800 °C, removing impurities with base–acid solution treatment and thereafter post-pyrolysing the materials at temperatures (T) from 1000 to 1500 °C. By modification of pre- and post-pyrolysis temperatures we obtained hard carbons with low surface areas, optimal carbonization degree and high electrochemical Na⁺ storage capacity in SIB half-cells. The best results were obtained when pre-pyrolysing peat at 450 °C, washing out the impurities with KOH and HCl solutions and then post-pyrolysing the obtained carbon-rich material at 1400 °C. All hard carbons were electrochemically characterized in half-cells (vs. Na/Na⁺) and capacities as high as 350 mA h g⁻¹ at 1.5 V and 250 mA h g⁻¹ in the plateau region (E < 0.2 V) were achieved at charging current density of 25 mA g⁻¹ with an initial coulombic efficiency of 80%.

A synthesis method has been developed to turn peat, cheap biomass into hard carbons that demonstrate high capacity and excellent sodium storage capability as anode material in sodium-ion batteries.     

Silver-modified porous polystyrene sulfonate derived from Pickering high internal phase emulsions for capturing lithium-ion

Adsorption separation based on porous polystyrene sulfonate is an important method of extracting lithium ion (Li⁺). In this work, silver-modified porous polystyrene sulfonate (PHIPEs-SS-Ag) derived from Pickering high internal phase emulsions was fabricated for the selective binding of Li⁺. PHIPEs-SS-Ag possessed porous polymer matrix, sufficient sulfonic acid functional groups, and uniformly immobilized silver particles, which were beneficial for improving mass transfer, binding amount and antifouling performance. In batch mode experiments, the adsorption capacity reached a maximum value (i.e. 14.09 mg g⁻¹) under alkaline conditions, and the adsorption mechanism between PHIPEs-SS-Ag and Li⁺ was electrostatic attraction. PHIPEs-SS-Ag exhibited fast binding kinetics at 25 °C (i.e. 300 min), and the maximum monolayer adsorption amount from the Langmuir model for Li⁺ are 59.85 mg g⁻¹, 35.06 mg g⁻¹, and 27.09 mg g⁻¹ at 15 °C, 25 °C, and 35 °C, respectively. Moreover, PHIPEs-SS-Ag displayed excellent selectivity for Li⁺ in the presence of K⁺, Mg²⁺, and Na⁺, and maintained 80.71% of the initial adsorption capacity after seven sequential cycles of adsorption–regeneration. Therefore, this work opened up a universal route for the development of composite adsorbents for the specific separation of Li⁺.

Adsorption separation based on porous polystyrene sulfonate is an important method of extracting lithium ion (Li⁺).     

Enhanced sodium ion conductivity in Na3VS4 by P-doping

All-solid-state sodium-ion batteries are promising candidates for renewable energy storage applications, owing to their high safety, high energy density, and the abundant resources of sodium. The critical factor for an all-solid-state battery is having a sodium solid electrolyte that has high Na ion conductivity at room temperature and outstanding thermal stability, low flammability, and long battery lifespan. Herein, a new Na ion solid-state electrolyte, Na₃VS₄, is prepared by a solid state reaction. It shows conductivity of ∼1.16 × 10⁻⁸ to 1.46 × 10⁻⁶ S cm⁻¹ from 25 to 100 °C. The sodium ion conductivity was enhanced to ∼1.49 × 10⁻⁷ to 1.20 × 10⁻⁵ S cm⁻¹ through P substitution for V in the composition Na₃P_0.1V_0.9S₄. Such sodium ion conduction enhancement could be attributed to P substitution for V leading to a wider Na migration path and the generation of sodium vacancies.

A new sodium ion conductor Na₃VS₄ was prepared and its conductivity improved by substitution of V with P.     

Formation and dissociation of synthetic hetero-double-helix complex in aqueous solutions: significant effect of water content on dynamics of structural change

A 1 : 1 mixture of the ethynylhelicene pseudoenantiomers (M)-tetramer and (P)-pentamer, which possess hydrophilic terminal tri(ethyleneglycol) (TEG) groups, changes their structures in the water–THF (10 μM) solvent system between dissociated random-coils and an associated hetero-double-helix upon heating and cooling. A small change in water content between 30 and 33% significantly affects the dynamics of structural changes. At 30% water content, heating to 60 °C causes rapid formation of random-coil and cooling to 10 °C causes the rapid formation of hetero-double-helix, accompanied by repeated changes in Δε at 369 nm between 0 and −2000 cm⁻¹ M⁻¹. Heating and cooling experiments at constant rates between 60 and 10 °C resulted in sigmoidal curves in Δε/temperature profiles, which indicate rapid structural changes. Different phenomena occurred at 33% water content. Heating to 60 °C and cooling to 0 °C initially induced changes in Δε between 0 and −2000 cm⁻¹ M⁻¹, and repeated cycles gradually reduced the range between 0 and −500 cm⁻¹ M⁻¹. Heating and cooling experiments at constant rates between 60 and 10 °C caused small changes in Δε, and repeated cycles at 10 °C gradually increased Δε to −500 cm⁻¹ M⁻¹. These phenomena involved rapid changes in molecular structure and slow structural changes in the water–THF solvent system. The sharp switching of the dynamics of structural changes at water content between 30 and 33% indicated discontinuous structural changes in the hydration of TEG and/or in water clusters in the vicinity of oligomer molecules.

Significant structural changes by small change in water content from 30 to 33%.     

Hydrothermal synthesis of a novel nanolayered tin phosphate for removing Cr(iii)

In this work, an outstanding nanolayered tin phosphate with 15.0 Å interlayer spacing, Sn (HPO₄)₂·3H₂O (SnP–H⁺), has been synthesized by conventional hydrothermal method and first used in the adsorptive removal of Cr(iii) from aqueous solution. A number of factors such as contact time, initial concentration of Cr(iii), temperature, pH, and ionic strength on adsorption were investigated by batch tests. Moreover, the isothermal adsorption characteristics and kinetic model of Cr(iii) onto SnP–H⁺ were studied. The results showed that the adsorption of Cr(iii) by SnP–H⁺ was in accordance with the Langmuir adsorption isotherm model and the pseudo-second-order kinetic model. The adsorption capacity of Cr(iii) onto SnP–H⁺ at temperature 40.0 °C and pH 3.0 could reach 81.1 mg g⁻¹. And the distribution coefficient K_d was 23.0 g L⁻¹. Overall, experiments certified that SnP–H⁺ was an excellent adsorbent that can effectively remove Cr(iii) from aqueous solution.

In this work, an outstanding nanolayered tin phosphate with 15.0 Å interlayer spacing, Sn (HPO₄)₂·3H₂O (SnP–H⁺), has been synthesized by conventional hydrothermal method and first used in the adsorptive removal of Cr(iii) from aqueous solution.     

MoO3−x-deposited TiO2 nanotubes for stable and high-capacitance supercapacitor electrodes

Here we report the supercapacitive properties of a novel MoO_3−x/TiO₂ nanotube composite prepared by a facile galvanostatic deposition technique and subsequently thermal treatment in an argon atmosphere between 350 °C and 550 °C. X-ray diffraction and X-ray photoelectron spectroscopy confirm the existence of MoO_3−x. The MoO_3−x/TiO₂ electrode prepared at 550 °C exhibits a high specific capacitance of 23.69 mF cm⁻² at a scan rate of 10 mV s⁻¹ and good cycling stability with capacitance retention of 86.6% after 1000 cycles in 1 M Na₂SO₄ aqueous solution. Our study reveals a feasible method for the fabrication of TiO₂ nanotubes modified with electroactive MoO_3−x as high-performance electrode materials for supercapacitors.

Here we report the supercapacitive properties of a novel MoO_3−x/TiO₂ nanotube composite prepared by a facile galvanostatic deposition technique and subsequently thermal treatment in an argon atmosphere between 350 °C and 550 °C.     

The effect of guest cations on proton conduction of LTA zeolite

Zeolites as important crystalline microporous materials have been widely used as catalysts, sorbents and ion-exchangers. In such materials, the guest ions in the pores can not only balance the charge of the framework but also make a difference to the pore environment and the resulting performance. In this work, we focus on the proton conduction properties of zeolites, and have comprehensively studied for the first time the effect of guest ions on proton conduction. To this end, aluminosilicate NaA zeolite (LTA) and ion-exchanged NaA zeolites by different guest ions (i.e. Li⁺, K⁺, Mg²⁺, Ca²⁺ and Sr²⁺) have been successfully synthesized. The study indicates that the guest ions could affect the proton conduction properties through the synergistic effect between the pore features (e.g. pore size, pore polarity, etc.) and guest ions, the ionic concentrations, and the interference between different ions. Among various guest ions, the existence of Na⁺ ions can greatly promote the proton conduction properties. The proton conductivity of NaA can reach 1.98 × 10⁻³ S cm⁻¹ (100% RH) at room temperature and 9.12 × 10⁻³ S cm⁻¹ (80 °C) under the condition of 100% RH. In addition, guest monovalent ions (Li⁺, Na⁺ and K⁺) exhibit better proton conductivity than divalent ions (Mg²⁺, Ca²⁺ and Sr²⁺). The distinct effect of these guest ions enables zeolites with tunable proton conductivity, which will provide more opportunities to design zeolitic proton conducting materials.

The as-synthesized NaA zeolite with the proton conductivity of 9.12 × 10⁻³ S cm⁻¹ (80 °C, 100% RH) can show unique cations effects on proton conduction property with different guest cations substituted (e.g. Li⁺, K⁺, Mg²⁺, Ca²⁺ and Sr²⁺).     

A technology for strongly improving methane production from rice straw: freeze–thaw pretreatment

Overcoming the complex three dimensional structure of biomass is a major challenge in enhancing anaerobic digestion (AD) efficacy. Freeze–thaw pretreatment was proposed herein in order to improve methane production from rice straw. The effect was notable: average methane content for group-A (−4 °C) and -B (−20 °C) were A1 (−4 °C, 12 h): 40.0%, A2 (−4 °C, 24 h): 40.5%, A3 (−4 °C, 48 h): 42.2%; B1 (−20 °C, 12 h): 44.2%, B2 (−20 °C, 24 h): 45.7%, B3 (−20 °C, 48 h): 46.0%, the increases were 88.8–99.1% and 108.8–117.2%, respectively, compared with control (CK) (21.2%). Total methane production for group-A and -B were A1: 22.8 mL g⁻¹ TS, A2: 24.7 mL g⁻¹ TS, A3: 27.8 mL g⁻¹ TS; B1: 29.9 mL g⁻¹ TS, B2: 31.3 mL g⁻¹ TS, B3: 32.0 mL g⁻¹ TS, compared with CK (7.6 mL g⁻¹ TS), the increases were 200.0–265.8%, 293.4–321.1%, respectively. The technical digestion time (T₈₀) was shortened by 8 days. Therefore, the maximum methane production was obtained under conditions of −20 °C and 48 h. This study proposed an efficient pretreatment method that broadens the horizon of improving biomass conversion into bioenergy.

Overcoming the complex three dimensional structure of biomass is a major challenge in enhancing anaerobic digestion (AD) efficacy.     

Aqueous supercapacitors based on carbonized silk electrodes

Graphitic nitrogen-doped hierarchical porous carbon nanosheets for supercapacitor application were derived from an easily obtained and green silk by simultaneous ZnCl₂ activation and FeCl₃ graphitization at different heating temperatures. By increasing the heating temperature from 700 to 850 °C, the degree of graphitization and BET surface area rose to their highest levels, while the nitrogen doping content was maintained at 2.24 wt%. Carbonized silk at 850 °C displays a nanosheet morphology and a considerable specific surface area (1285.31 m² g⁻¹), and it was fabricated into a supercapacitor as an electrode material, exhibiting superior electrochemical performance with a high specific capacitance of 178 F g⁻¹ at 0.5 A g⁻¹ and an excellent rate capability (81% capacitance retention ratio even at 20 A g⁻¹) in 1 mol L⁻¹ H₂SO₄ electrolyte. A symmetric supercapacitor using carbonized silk at 850 °C as the electrodes has an excellent specific energy of 14.33 W h kg⁻¹ at a power density of 251 W kg⁻¹ operated over a wide voltage range of 2.0 V in aqueous neutral Na₂SO₄ electrolyte.

An aqueous symmetrical supercapacitor was achieved by assembling SC-850 electrodes, which possess a specific energy of 14.33 W h kg⁻¹ at a power density of 251 W kg⁻¹ operated over the wide voltage range of 2.0 V in aqueous neutral Na₂SO₄ electrolyte.     

Ultrathin δ-MnO2 nanoflakes with Na+ intercalation as a high-capacity cathode for aqueous zinc-ion batteries

Pristine δ-MnO₂ as the typical cathode for rechargeable zinc-ion batteries (ZIBs) suffers from sluggish reaction kinetics, which is the key issue to prepare high-performance manganese-based materials. In this work, Na⁺ incorporated into layered δ-MnO₂ (NMO) was prepared for ZIB cathodes with high capacity, high energy density, and excellent durable stability. By an effective fabricated strategy of hydrothermal synthesis, a three-dimensional interconnected δ-MnO₂ nanoflake network with Na⁺ intercalation showed a uniform array arrangement and high conductivity. Also, the H⁺ insertion contribution in the NMO cathode to the discharge capacity confirmed the fast electrochemical charge transfer kinetics due to the enhanced ion conductivity from the insertion of Na⁺ into the interlayers of the host material. Consequently, a neutral aqueous NMO-based ZIB revealed a superior reversible capacity of 335 mA h g⁻¹, and an impressive durability over 1000 cycles, and a peak gravimetric energy output of 459 W h kg⁻¹. As a proof of concept, the as-fabricated quasi-solid-state ZIB exhibited a remarkable capacity of 284 mA h g⁻¹ at a current density of 0.5 A g⁻¹, and good practicability. This research demonstrated a significant enhancement of the electrochemical performance of MnO₂-based ZIBs by the intercalation of Na⁺ to regulate the microstructure and boost the electrochemical kinetics of the δ-MnO₂ cathode, thus providing a new insight for high-performance aqueous ZIBs.

Sodium-ion intercalated δ-MnO₂ nanoflakes are applied in an aqueous rechargeable zinc battery cathode with high energy density and excellent durable stability.     

Large-scale and fast synthesis of nano-hydroxyapatite powder by a microwave-hydrothermal method

A microwave-hydrothermal (M-H) method assisted with ultrasonic atomization precipitation was developed for large-scale and fast synthesis of nano-hydroxyapatite (nano-HAP) powder. This technology combines the uniform mixing effect of ultrasonic atomization precipitation at high concentration with the rapid and uniform heating effect of the M-H method, aiming to obtain a high quality product with low agglomeration, homogeneous size distribution, accurate stoichiometry, and high purity while improving the yield. The influences of reaction temperature, reaction time and reactant concentration on the formation of nano-HAP were investigated. The results show that the crystallinity increases significantly and the diameter of nano-HAP increases to some extent, but the length does not change obviously while the reaction temperature increase from 60 °C to 160 °C and the reaction time increases from 1 minute to 40 minutes respectively. The crystallinity, dispersion and crystal size of nano-HAP do not change obviously while the concentration of Na₂HPO₄·12H₂O increases from 0.06 mol L⁻¹ to 0.4 mol L⁻¹. When the reaction temperature is 160 °C, the reaction time is 40 min, and the concentration of Na₂HPO₄·12H₂O is 0.4 mol L⁻¹, the yield of nano-HAP powder achieved a maximum yield (0.033 kg L⁻¹). The obtained nano-HAP powder exhibits a uniform size and good dispersibility, with a size of 87.62 ± 22.44 nm and crystallinity of 0.92, respectively. This study indicates that the M-H method assisted with ultrasonic atomization precipitation is a facile one-pot method for the rapid and large-scale synthesis of highly crystalline, dispersible nano-HAP particles.

The obtained nano-HAP still has high crystallinity, uniform size and good dispersibility when the concentration of Na₂HPO₄ is 0.4 mol L⁻¹.     

Improved performance of a samarium-doped ceria interlayer of intermediate temperature solid oxide electrolysis cells by doping the transition metal oxide Fe2O3

The ionic conductivity of the interlayer in the intermediate temperature solid oxide electrolysis cell (IT-SOEC) affects the polarization resistance of the oxygen electrode. Improving the ionic conductivity of the interlayer can improve the performance of the oxygen electrode. In this work, the ionic conductivity of a samarium-doped ceria (SDC) interlayer is improved by doping the transition metal oxide Fe₂O₃. The experimental results show that the oxygen electrode polarization resistance of the symmetrical cell based on the SDC-Fe₂O₃ interlayer is 0.09 Ω cm⁻² at 800 °C and under the open circuit voltage, which is obviously lower than that of the symmetrical cell based on an SDC interlayer (0.22 Ω cm⁻²). Besides, the electrolysis current of the SOEC based on the SDC-Fe₂O₃ interlayer is 0.5 A cm⁻² at 800 °C and 1.5 V, which is higher than that of the SOEC based on the SDC interlayer (0.3 A cm⁻²). The above results show that improving the ionic conductivity of the SDC interlayer in the SOEC by doping Fe₂O₃ can reduce the polarization resistance of the oxygen electrode and enhance the performance of the SOEC. Thus, this work provides an effective way for improving the performance of the SDC interlayer in the IT-SOEC.

Improving the ionic conductivity of the SDC interlayer in an SOEC by doping Fe₂O₃ can reduce the polarization resistance of the oxygen electrode and enhance the performance of the SOEC.     

Molecular dynamics simulations of Y(iii) coordination and hydration properties

Y mainly exists in ionic rare-earth resources. During rare-earth carbonate precipitation, rare-earth ion loss in the precipitated rare-earth mother liquor often occurs due to CO₃²⁻ coordination and Y(iii) hydration. Microscopic information on the coordination and hydration of CO₃²⁻ and H₂O to Y(iii) has not yet been elucidated. Therefore, in this study, the macroscopic dissolution of Y(iii) in different aqueous solutions of Na₂CO₃ was studied. The radial distribution function and coordination number of Y(iii) by CO₃²⁻ and H₂O were systematically analyzed using molecular dynamics (MD) simulations to obtain the complex ion form of Y(iii) in carbonate solutions. Density functional theory (DFT) was used to geometrically optimize and calculate the UV spectrum of Y(iii) complex ions. This spectrum was then analyzed and compared with experimentally determined ultraviolet-visible spectra to verify the reliability of the MD simulation results. Results showed that Y(iii) in aqueous solution exists in the form of [Y·3H₂O]³⁺ and that CO₃²⁻ is present in the bidentate coordination form. In 0–0.8 mol L⁻¹ CO₃²⁻ solutions, Y(iii) was mainly present as the 5-coordinated complex [YCO₃·3H₂O]⁺. When the concentration of CO₃²⁻ was increased to 1.2 mol L⁻¹, [YCO₃·3H₂O]⁺ was converted into a 6-coordinated complex [Y(CO₃)₂·2H₂O]⁻. Further increases in CO₃²⁻ concentration promoted Y(iii) dissolution in solution in the form of complex ions. These findings can be used to explain the problem of incomplete precipitation of rare earths in carbonate solutions.

Based on MD results, DFT was used to geometrically optimize and calculate the UV spectrum of Y(iii) complex ions. Data validation was further performed using UV-vis experiments to reveal Y(iii) coordination and hydration properties.     

Experimental and model research on chloride ion gas–solid distribution in the process of desulfurization wastewater evaporation

In this paper, research on chloride ion gas–solid distribution in the process of desulfurization wastewater evaporation was carried out. The factor analysis of temperature, pH, and concentrations of Cl^– Na⁺, Ca²⁺ and Mg²⁺ was explored by orthogonal experiments. Results show that the distribution coefficient increases with increasing temperature and Mg²⁺ concentration and decreasing pH, but decreases with increasing concentrations of Cl⁻, Ca²⁺ and Na⁺; The interaction and significance of each factor were compared and analyzed, and the order of influence significance on the chloride ion gas–solid distribution coefficient is listed as: temperature (0.781) > pH (0.611) > Cl⁻ concentration (0.366 ) > Mg²⁺ concentration (0.211) > Ca²⁺ concentration (0.079) > Na⁺ concentration (0.03). A chloride ion gas–solid phase distribution coefficient model ranging from 180 °C to 380 °C was built based on phase equilibrium theory and state equations. The study clarifies the gas phase transformation mechanism of chloride ions, and achieves the quantification and prediction of chloride ion volatilization under different environmental and water quality parameters; an important theoretical and practical reference for the application of high temperature flue gas evaporation technology is provided through the research.

In this paper, research on chloride ion gas–solid distribution in the process of desulfurization wastewater evaporation was carried out.     

Low-temperature all-solid-state lithium-ion batteries based on a di-cross-linked starch solid electrolyte

The preparation of a low-temperature solid electrolyte is a challenge for the commercialization of the all-solid-state lithium-ion battery (ASSLIB). Here we report a starch-based solid electrolyte that displays phenomenal electrochemical properties below room temperature (RT). The starch host of the electrolyte is synthesized by two cross-linking reactions, which provide sufficient and orderly binding sites for the lithium salt to dissolve. At 25 °C, the solid electrolyte has exceptional ionic conductivity (σ, 3.10 × 10⁻⁴ S cm⁻¹), lithium-ion transfer number (t⁺, 0.82) and decomposition potential (dP, 4.91 V). At −20 °C, it still has outstanding σ (3.10 × 10⁻⁵ S cm⁻¹), t⁺ (0.72) and dP (5.50 V). The LiFePO₄ ASSLIB assembled with the electrolyte exhibits unique specific capacity and long cycling life below RT, and the LiNi_0.8Co_0.1Mn_0.1O₂ ASSLIB can operate at 4.3 V and 0 °C. This work provides a solution to solve the current challenges of ASSLIBs to widen their scope of applications.

The all-solid-state lithium battery based on di-cross-linked starch electrolyte is applicable at low temperature.     

Hierarchical porosity via layer-tunnel conversion of macroporous δ-MnO2 nanosheet assemblies

This work reports the layer-tunnel conversion of porous dehydrated synthetic alkali-free δ-MnO₂ analogs prepared by exfoliation, flocculation, and heat treatment of nanosheets derived from highly crystalline potassium birnessite. High surface area porous solids result, with specific surface areas of 90–130 m² g⁻¹ and isotherms characteristic of both micro and macropores. The microstructures of the re-assembled floccules are reminiscent of crumpled paper where single and re-stacked nanosheets form the walls of interconnected macropores. The atomic and local structures of the floccules heat treated from 60–400 °C are tracked by Raman spectroscopy and synchrotron X-ray total scattering measurements. During heating, the nanosheets comprising the pore walls condense to form tunnel-structured fragments beginning at temperatures below 100 °C, while the microstructure with high surface area remains intact. The flocc microstructure remains largely unchanged in samples heated up to 400 °C while an increasing fraction of the sample is transformed, at least locally, to possess 1D tunnels characteristic of α-MnO₂. Cyclic voltammetry in Na₂SO₄ aqueous electrolyte reflects the nanoscale structural evolution, where intercalative pseudocapacitance diminishes with the degree of transformation. Collectively, these results demonstrate that it is feasible to tailor the materials for applications incorporating nanoporous solids and nanofluidics, and specifically imply strategies to maintain a kinetically accessible interlayer contribute to Na intercalative pseudocapacitance.

This work reports the layer-tunnel conversion of porous dehydrated synthetic alkali-free δ-MnO₂ analogs prepared by exfoliation, flocculation, and heat treatment of nanosheets derived from highly crystalline potassium birnessite.     

The rapid microwave-assisted hydrothermal synthesis of NASICON-structured Na3V2O2x(PO4)2F3−2x (0 < x ≤ 1) cathode materials for Na-ion batteries

NASICON-structured Na₃V₂O_2x(PO₄)₂F_3−2x (0 < x ≤ 1) solid solutions have been prepared using a microwave-assisted hydrothermal (MW-HT) technique. Well-crystallized phases were obtained for x = 1 and 0.4 by reacting V₂O₅, NH₄H₂PO₄, and NaF precursors at temperatures as low as 180–200 °C for less than 15 min. Various available and inexpensive reducing agents were used to control the vanadium oxidation state and final product morphology. The vanadium oxidation state and O/F ratios were assessed using electron energy loss spectroscopy and infrared spectroscopy. According to electron diffraction and powder X-ray diffraction, the Na₃V₂O_2x(PO₄)₂F_3−2x solid solutions crystallized in a metastable disordered I4/mmm structure (a = 6.38643(4) Å, c = 10.62375(8) Å for Na₃V₂O₂(PO₄)₂F and a = 6.39455(5) Å, c = 10.6988(2) Å for Na₃V₂O_0.8(PO₄)₂F_2.2). With respect to electrochemical Na⁺ (de)insertion as positive electrodes (cathodes) for Na-ion batteries, the as-synthesized materials displayed two sloping plateaus upon charge and discharge, centered near 3.5–3.6 V and 4.0–4.1 V vs. Na⁺/Na, respectively, with a reversible capacity of ∼110 mA h g⁻¹. The application of a conducting carbon coating through the surface polymerization of dopamine with subsequent annealing at 500 °C improved both the rate capability (∼55 mA h g⁻¹ at a discharge rate of 10C) and capacity retention (∼93% after 50 cycles at a discharge rate of C/2).

NASICON-structured Na₃V₂O_2x(PO₄)₂F_3−2x (0 < x ≤ 1) solid solutions have been prepared using a microwave-assisted hydrothermal (MW-HT) technique.     

Cu(i) substituted wurtzite ZnO: a novel room temperature lead free ferroelectric and high-κ giant dielectric

Semiconducting wurtzite ZnO, with the highest incipient piezoelectricity is an attractive alternative choice with doping transition metal ions in the host lattice to develop novel binary ferroelectric materials that can be easily fabricated in any device architecture. Up to 8% Cu⁺ ion substitution on Zn²⁺ sites in the ZnO lattice was achieved by careful selection of raw material and adaptation of a low temperature sol–gel synthesis route for the preparation of bulk material. Phase purity and substitution of Cu⁺ ions in the ZnO lattice along with oxide-ion vacancy formation was confirmed using Powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray analysis (EDX), X-ray Photoelectron Spectroscopy (XPS) and Magnetic property measurement system (MPMS) studies. A giant dielectric constant (∼6300) was observed at 600 °C for Zn_0.95Cu_0.05O_1−δ pellets at 100 kHz frequency. Bulk Zn_0.95Cu_0.05O_1−δ also exhibits ferroelectricity at room temperature with remnant polarization P_r and V_c equal to 9.60 × 10⁻³ μC cm⁻² and 3.83 × 10² V cm⁻¹ respectively.

Cu⁺ ion substituted ZnO, Zn_1−xCu_xO_1−δ have shown high dielectric constant (∼6300) at 600 °C at 100 kHz frequency and ferroelectricity at room temperature than for bulk Zn_0.95Cu_0.05O_1−δ samples.     

Arrangement of water molecules and high proton conductivity of tunnel structure phosphates,KMg1−xH2x(PO3)3·yH2O

A fast proton conductor was investigated in a mixed-valence system of phosphates with a combination of large cations (K⁺) and small cations (Mg²⁺), which resulted in a new phase with a tunnel structure suitable for proton conduction. KMg_1−xH_2x(PO₃)₃·yH₂O was synthesized by a coprecipitation method. A solid solution formed in the range of x = 0–0.18 in KMg_1−xH_2x(PO₃)₃·yH₂O. The structure of the new proton conductor was determined using neutron and X-ray diffraction measurements. KMg_1−xH_2x(PO₃)₃·yH₂O has a tunnel framework composed of face-shared (KO₆) and (MgO₆) chains, and PO₄ tetrahedral chains along the c-direction by corner-sharing. Two oxygen sites of water molecules were detected in the one-dimensional tunnel, one of which exists as a coordination water of K⁺ sites. Multi-step dehydration was observed at 30 °C and 150 °C from thermogravimetric/differential thermal analysis measurements, which reflects the different coordination environments of the water of crystallization. Water molecules are connected to PO₄ tetrahedra by hydrogen bonds and form a chain along the c-axis in the tunnel, which would provide an environment for fast proton conduction associated with water molecules. The KMg_1−xH_2x(PO₃)₃·yH₂O sample with x = 0.18 exhibited high proton conductivity of 4.5 × 10⁻³ S cm⁻¹ at 150 °C and 7.0 × 10⁻³ S cm⁻¹ at 200 °C in a dry Ar gas flow and maintained the total conductivity above 10⁻³ S cm⁻¹ for 60 h at 150 °C under N₂ gas atmosphere.

A fast proton conductor exhibiting high proton conductivity of 7.0 × 10⁻³ S cm⁻¹ at 200 °C in a dry Ar gas flow was developed by designing water chains in a rigid tunnel framework.     

MgTiO3:Mn4+ a multi-reading temperature nanoprobe

MgTiO₃ nanoparticles doped with Mn⁴⁺, with homogeneous size ranging about 63.1 ± 9.8 nm, were synthesized by a molten salt assisted sol gel method. These nanoparticles have been investigated as optical thermal sensors. The luminescence of tetravalent manganese ion in octahedral environment within the perovskite host presents drastic variations with temperature. Three different thermometry approaches have been proposed and characterized. Two luminescence intensity ratios are studied. Firstly between the two R-lines of Mn⁴⁺ emission at low temperature (−250 °C and −90 °C) with a maximal sensitivity of 0.9% °C⁻¹, but also secondly between ²E → ⁴A₂ (R-line) and the ⁴T₂ → ⁴A₂ transitions. This allows studying the temperature variation within a larger temperature range (−200 °C to 50 °C) with a sensitivity between 0.6% °C⁻¹ and 1.2% °C⁻¹ over this range. The last proposed method is the study of the lifetime variation versus temperature. The effective lifetime value corresponds to a combination of transitions from two excited energy levels of the tetravalent manganese (²E and ⁴T₂) in thermal equilibrium toward the fundamental ⁴A₂ state. Since the more energetic transition (⁴T₂ → ⁴A₂) is spin-allowed, contrary to the ²E → ⁴A₂ one, the lifetime drastically decreases with the increase in temperature leading to an impressive high sensitivity value of 4.1% °C⁻¹ at 4 °C and an exceptional temperature resolution of 0.025 °C. According to their optical features, MgTiO₃:Mn⁴⁺ nanoparticles are indeed suitable candidates for the luminescence temperature probes at the nanoscale over several temperature ranges.

Luminescence properties of MgTiO₃ nanoparticles doped with Mn⁴⁺ ions are investigated for precise temperature determination.