Electrochemically Activated Screen-Printed Carbon Sensor Modified with Anionic Surfactant (aSPCE/SDS) for Simultaneous Determination of Paracetamol,Diclofenac and Tramadol

In this work, an electrochemically activated screen-printed carbon electrode modified with sodium dodecyl sulfate (aSPCE/SDS) was proposed for the simultaneous determination of paracetamol (PA), diclofenac (DF), and tramadol (TR). Changes of surface morphology and electrochemical behaviour of the electrode after the electrochemical activation with H₂O₂ and SDS surface modification were studied by scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The influence of various parameters on the responses of the aSPCE/SDS such as pH and concentration of the buffer, SDS concentration, and techniques parameters were investigated. Using optimised conditions (E_acc. of −0.4 V, t_acc. of 120 s, ΔE_A of 150 mV, ν of 250 mV s⁻¹, and t_m of 10 ms), the aSPCE/SDS showed a good linear response in the concentration ranges of 5.0 × 10⁻⁸–2.0 × 10⁻⁵ for PA, 1.0 × 10⁻⁹–2.0 × 10⁻⁷ for DF, and 1.0 × 10⁻⁸–2.0 × 10⁻⁷ and 2.0 × 10⁻⁷–2.0 × 10⁻⁶ mol L⁻¹ for TR. The limits of detection obtained during the simultaneous determination of PA, DF, and TR are 1.49 × 10⁻⁸ mol L⁻¹, 2.10 × 10⁻¹⁰ mol L⁻¹, and 1.71 × 10⁻⁹ mol L⁻¹, respectively. The selectivity of the aSPCE/SDS was evaluated by examination of the impact of some inorganic and organic substances that are commonly present in environmental and biological samples on the responses of PA, DF, and TR. Finally, the differential pulse adsorptive stripping voltammetric (DPAdSV) procedure using the aSPCE/SDS was successfully applied for the determination of PA, DF, and TR in river water and serum samples as well as pharmaceuticals.     

Direct Electrochemistry and Electrocatalysis of Horseradish Peroxidase Immobilized in a DNA/Chitosan-Fe3O4 Magnetic Nanoparticle Bio-Complex Film

A DNA/chitosan-Fe₃O₄ magnetic nanoparticle bio-complex film was constructed for the immobilization of horseradish peroxidase (HRP) on a glassy carbon electrode. HRP was simply mixed with DNA, chitosan and Fe₃O₄ nanoparticles, and then applied to the electrode surface to form an enzyme-incorporated polyion complex film. Scanning electron microscopy (SEM) was used to study the surface features of DNA/chitosan/Fe₃O₄/HRP layer. The results of electrochemical impedance spectroscopy (EIS) show that Fe₃O₄ and enzyme were successfully immobilized on the electrode surface by the DNA/chitosan bio-polyion complex membrane. Direct electron transfer (DET) and bioelectrocatalysis of HRP in the DNA/chitosan/Fe₃O₄ film were investigated by cyclic voltammetry (CV) and constant potential amperometry. The HRP-immobilized electrode was found to undergo DET and exhibited a fast electron transfer rate constant of 3.7 s⁻¹. The CV results showed that the modified electrode gave rise to well-defined peaks in phosphate buffer, corresponding to the electrochemical redox reaction between HRP(Fe^(III)) and HRP(Fe^(II)). The obtained electrode also displayed an electrocatalytic reduction behavior towards H₂O₂. The resulting DNA/chitosan/Fe₃O₄/HRP/glassy carbon electrode (GCE) shows a high sensitivity (20.8 A·cm⁻²·M⁻¹) toward H₂O₂. A linear response to H₂O₂ measurement was obtained over the range from 2 μM to 100 μM (R² = 0.99) and an amperometric detection limit of 1 μM (S/N = 3). The apparent Michaelis-Menten constant of HRP immobilized on the electrode was 0.28 mM. Furthermore, the electrode exhibits both good operational stability and storage stability.     

First Screen-Printed Sensor (Electrochemically Activated Screen-Printed Boron-Doped Diamond Electrode) for Quantitative Determination of Rifampicin by Adsorptive Stripping Voltammetry

In this paper, a screen-printed boron-doped electrode (aSPBDDE) was subjected to electrochemical activation by cyclic voltammetry (CV) in 0.1 M NaOH and the response to rifampicin (RIF) oxidation was used as a testing probe. Changes in surface morphology and electrochemical behaviour of RIF before and after the electrochemical activation of SPBDDE were studied by scanning electron microscopy (SEM), CV and electrochemical impedance spectroscopy (EIS). The increase in number and size of pores in the modifier layer and reduction of charge transfer residence were likely responsible for electrochemical improvement of the analytical signal from RIF at the SPBDDE. Quantitative analysis of RIF by using differential pulse adsorptive stripping voltammetry in 0.1 mol L⁻¹ solution of PBS of pH 3.0 ± 0.1 at the aSPBDDE was carried out. Using optimized conditions (E_acc of −0.45 V, t_acc of 120 s, ΔE_A of 150 mV, ν of 100 mV s⁻¹ and t_m of 5 ms), the RIF peak current increased linearly with the concentration in the four ranges: 0.002–0.02, 0.02–0.2, 0.2–2.0, and 2.0–20.0 nM. The limits of detection and quantification were calculated at 0.22 and 0.73 pM. The aSPBDDE showed satisfactory repeatability, reproducibility, and selectivity towards potential interferences. The applicability of the aSPBDDE for control analysis of RIF was demonstrated using river water samples and certified reference material of bovine urine.     

Enhanced Structural Stability and Electrochemical Performance of LiNi0.6Co0.2Mn0.2O2 Cathode Materials by Ga Doping

Structural instability during cycling is an important factor affecting the electrochemical performance of nickel-rich ternary cathode materials for Li-ion batteries. In this work, enhanced structural stability and electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂ cathode materials are achieved by Ga doping. Compared with the pristine electrode, Li[Ni_0.6Co_0.2Mn_0.2]_0.98Ga_0.02O₂ electrode exhibits remarkably improved electrochemical performance and thermal safety. At 0.5C rate, the discharge capacity increases from 169.3 mAh g⁻¹ to 177 mAh g⁻¹, and the capacity retention also rises from 82.8% to 89.8% after 50 cycles. In the charged state of 4.3 V, its exothermic temperature increases from 245.13 °C to more than 271.24 °C, and the total exothermic heat decreases from 561.7 to 225.6 J·g⁻¹. Both AC impedance spectroscopy and in situ XRD analysis confirmed that Ga doping can improve the stability of the electrode/electrolyte interface structure and bulk structure during cycling, which helps to improve the electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂ cathode material.     

A Study of Methylcellulose Based Polymer Electrolyte Impregnated with Potassium Ion Conducting Carrier: Impedance,EEC Modeling,FTIR, Dielectric,and Device Characteristics

In this research, a biopolymer-based electrolyte system involving methylcellulose (MC) as a host polymeric material and potassium iodide (KI) salt as the ionic source was prepared by solution cast technique. The electrolyte with the highest conductivity was used for device application of electrochemical double-layer capacitor (EDLC) with high specific capacitance. The electrical, structural, and electrochemical characteristics of the electrolyte systems were investigated using various techniques. According to electrochemical impedance spectroscopy (EIS), the bulk resistance (R_b) decreased from 3.3 × 10⁵ to 8 × 10² Ω with the increase of salt concentration from 10 wt % to 40 wt % and the ionic conductivity was found to be 1.93 ×10⁻⁵ S/cm. The dielectric analysis further verified the conductivity trends. Low-frequency regions showed high dielectric constant, ε′ and loss, ε″ values. The polymer-salt complexation between (MC) and (KI) was shown through a Fourier transformed infrared spectroscopy (FTIR) studies. The analysis of transference number measurement (TNM) supported ions were predominantly responsible for the transport process in the MC-KI electrolyte. The highest conducting sample was observed to be electrochemically constant as the potential was swept linearly up to 1.8 V using linear sweep voltammetry (LSV). The cyclic voltammetry (CV) profile reveals the absence of a redox peak, indicating the presence of a charge double-layer between the surface of activated carbon electrodes and electrolytes. The maximum specific capacitance, C_s value was obtained as 118.4 F/g at the sweep rate of 10 mV/s.     

Bimetallic Co-Based (CoM,M = Mo,Fe, Mn) Coatings for High-Efficiency Water Splitting

Bimetallic cobalt (Co)-based coatings were prepared by a facile, fast, and low-cost electroless deposition on a copper substrate (CoFe, CoMn, CoMo) and characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction analysis. Prepared coatings were thoroughly examined for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution (1 M potassium hydroxide, KOH) and their activity compared to that of Co and Ni coatings. All five coatings showed activity for both reactions, where CoMo and Co showed the highest activity for HER and OER, respectively. Namely, the highest HER current density was recorded at CoMo coating with low overpotential (61 mV) to reach a current density of 10 mA·cm⁻². The highest OER current density was recorded at Co coating with a low Tafel slope of 60 mV·dec⁻¹. Furthermore, these coatings proved to be stable under HER and OER polarization conditions.     

Hazardous Petroleum Sludge-Derived Nitrogen and Oxygen Co-Doped Carbon Material with Hierarchical Porous Structure for High-Performance All-Solid-State Supercapacitors

Rational design and sustainable preparation of high-performance carbonaceous electrode materials are important to the practical application of supercapacitors. In this work, a cost-effective synthesis strategy for nitrogen and oxygen co-doped porous carbon (NOC) from petroleum sludge waste was developed. The hierarchical porous structure and ultra-high surface area (2514.7 m² g⁻¹) of NOC electrode materials could provide an efficient transport path and capacitance active site for electrolyte ions. The uniform co-doping of N and O heteroatoms brought enhanced wettability, electrical conductivity and probably additional pseudo-capacitance. The as-obtained NOC electrodes exhibited a high specific capacitance (441.2 F g⁻¹ at 0.5 A g⁻¹), outstanding rate capability, and cycling performance with inconspicuous capacitance loss after 10,000 cycles. Further, the assembled all-solid-state MnO₂/NOC asymmetrical supercapacitor device (ASC) could deliver an excellent capacitance of 119.3 F g⁻¹ at 0.2 A g⁻¹ under a wide potential operation window of 0–1.8 V with flexible mechanical stability. This ASC device yielded a superior energy density of 53.7 W h kg⁻¹ at a power density of 180 W kg⁻¹ and a reasonable cycling life. Overall, this sustainable, low-cost and waste-derived porous carbon electrode material might be widely used in the field of energy storage, now and into the foreseeable future.     

Modified Activation Process for Supercapacitor Electrode Materials from African Maize Cob

In this work, African maize cobs (AMC) were used as a rich biomass precursor to synthesize carbon material through a chemical activation process for application in electrochemical energy storage devices. The carbonization and activation were carried out with concentrated Sulphuric acid at three different temperatures of 600, 700 and 800 °C, respectively. The activated carbon exhibited excellent microporous and mesoporous structure with a specific surface area that ranges between 30 and 254 m²·g⁻¹ as measured by BET analysis. The morphology and structure of the produced materials are analyzed through Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Boehm titration, X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. X-ray photoelectron spectroscopy indicates that a considerable amount of oxygen is present in the materials. The functional groups in the activated carbon enhanced the electrochemical performance and improved the material’s double-layer capacitance. The carbonized composite activated at 700 °C exhibited excellent capacitance of 456 F g⁻¹ at a specific current of 0.25 A g⁻¹ in 6 M KOH electrolyte and showed excellent stability after 10,000 cycles. Besides being a low cost, the produced materials offer good stability and electrochemical properties, making them suitable for supercapacitor applications.     

Silver Nanoparticles Embedded on Reduced Graphene Oxide@Copper Oxide Nanocomposite for High Performance Supercapacitor Applications

In this work, silver (Ag) decorated reduced graphene oxide (rGO) coated with ultrafine CuO nanosheets (Ag-rGO@CuO) was prepared by the combination of a microwave-assisted hydrothermal route and a chemical methodology. The prepared Ag-rGO@CuO was characterized for its morphological features by field emission scanning electron microscopy and transmission electron microscopy while the structural characterization was performed by X-ray diffraction and Raman spectroscopy. Energy-dispersive X-ray analysis was undertaken to confirm the elemental composition. The electrochemical performance of prepared samples was studied by cyclic voltammetry and galvanostatic charge-discharge in a 2M KOH electrolyte solution. The CuO nanosheets provided excellent electrical conductivity and the rGO sheets provided a large surface area with good mesoporosity that increases electron and ion mobility during the redox process. Furthermore, the highly conductive Ag nanoparticles upon the rGO@CuO surface further enhanced electrochemical performance by providing extra channels for charge conduction. The ternary Ag-rGO@CuO nanocomposite shows a very high specific capacitance of 612.5 to 210 Fg⁻¹ compared against rGO@CuO which has a specific capacitance of 375 to 87.5 Fg⁻¹ and the CuO nanosheets with a specific capacitance of 113.75 to 87.5 Fg⁻¹ at current densities 0.5 and 7 Ag⁻¹, respectively.     

Bismuth/Porous Graphene Heterostructures for Ultrasensitive Detection of Cd (II)

Heavy metals pollution is one of the key problems of environment protection. Electrochemical methods, particularly anodic stripping voltammetry, have been proven a powerful tool for rapid detection of heavy metal ions. In the present work, a bismuth modified porous graphene (Bi@PG) electrode as an electrochemical sensor was adopted for the detection of heavy metal Cd²⁺ in an aqueous solution. Combining excellent electronic properties in sensitivity, peak resolution, and high hydrogen over-potential of bi-continuous porous Bi with the large surface-area and high conductivity on PG, the Bi@PG electrode exhibited excellent sensing ability. The square wave anodic stripping voltammetry response showed a perfect liner range of 10⁻⁹–10⁻⁸ M with a correlation coefficient of 0.9969. The limit of detection (LOD) and the limit of quantitation (LOQ) are calculated to be 0.1 and 0.34 nM with a sensitivity of 19.05 μA·nM⁻¹, which is relatively excellent compared to other carbon-based electrodes. Meanwhile, the Bi@PG electrode showed tremendous potential in composite detection of multifold heavy metals (such as Pb²⁺ and Cd²⁺) and wider linear range.     

Dendritic Iron(III) Carbazole Complexes: Structural,Optical, and Magnetic Characteristics

This paper focuses on the synthesis, structural characterization, and study of the optical, magnetic, and thermal properties of novel architectures combining metal ions as magnetoactive centers and photoactive blocks formed by carbazole units. For this purpose, a series of azomethine complexes of the composition [Fe(L)₂]X (L = 3,6-bis[(3′,6′-di-tert-butyl-9-carbazol)-9-carbazol]benzoyloxy-4-salicylidene-N′-ethyl-N-ethylenediamine, X = NO₃⁻, Cl⁻, PF₆⁻) were synthesized by the reaction of metal salts with Schiff bases in a mixture of solvents. The UV–Vis absorption properties were studied in dichloromethane and rationalized via time-dependent density functional theory (DFT) calculations. Upon excitation at 350 nm, the compounds exhibited an intense dual fluorescence with two emission bands centered at ~445 and ~485 nm, which were assigned to π_carb–π* intraligand and π_carb–d_Fe ligand-to-metal charge-transfer excited states. EPR spectroscopy and SQUID magnetometry revealed solid-state partial spin crossover in some compounds, and antiferromagnetic interactions between the neighboring Fe(III) ions.     

Study of Overprotective-Polarization of Steel Subjected to Cathodic Protection in Unsaturated Soil

Various electrochemical methods were used to understand the behavior of steel buried in unsaturated artificial soil in the presence of cathodic protection (CP) applied at polarization levels corresponding to correct CP or overprotection. Carbon steel coupons were buried for 90 days, and the steel/electrolyte interface was studied at various exposure times. The coupons remained at open circuit potential (OCP) for the first seven days before CP was applied at potentials of −1.0 and −1.2 V vs. Cu/CuSO₄ for the remaining 83 days. Voltammetry revealed that the corrosion rate decreased from ~330 µm yr⁻¹ at OCP to ~7 µm yr⁻¹ for an applied potential of −1.0 V vs. Cu/CuSO₄. CP effectiveness increased with time due to the formation of a protective layer on the steel surface. Raman spectroscopy revealed that this layer mainly consisted of magnetite. EIS confirmed the progressive increase of the protective ability of the magnetite-rich layer. At −1.2 V vs. Cu/CuSO₄, the residual corrosion rate of steel fluctuated between 8 and 15 µm yr⁻¹. EIS indicated that the protective ability of the magnetite-rich layer deteriorated after day 63. As water reduction proved significant at this potential, it is proposed that the released H₂ bubbles damage the protective layer.     

Electrodeposition of Manganese-Nickel Oxide Films on a Graphite Sheet for Electrochemical Capacitor Applications

Manganese-nickel (Mn-Ni) oxide films were electrodeposited on a graphite sheet in a bath consisting of manganese acetate and nickel chloride, and the structural, morphological, and electrochemical properties of these films were investigated. The electrodeposited Mn-Ni oxide films had porous structures covered with nanofibers. The X-ray diffractometer pattern revealed the presence of separate manganese oxide (γ-MnO₂) and nickel oxide (NiO) in the films. The electrodeposited Mn-Ni oxide electrode exhibited a specific capacitance of 424 F/g in Na₂SO₄ electrolyte. This electrode maintained 86% of its initial specific capacitance over 2000 cycles of the charge-discharge operation, showing good cycling stability.     

Weight Goals,Disordered Eating Behaviors,and BMI Trajectories in US Young Adults

BackgroundCommunity sample data indicate that weight control efforts in young adulthood may have associations with greater increases in body mass index (BMI) over time.ObjectiveTo determine the prospective associations between weight goals and behaviors in young adults and BMI trajectories over 15-year follow-up using a nationally representative sample.DesignLongitudinal cohort data collected from 2001 to 2018 of the National Longitudinal Study of Adolescent to Adult Health.ParticipantsYoung adults aged 18–26 years old at baseline stratified by gender and BMI category.Main MeasuresPredictors: weight goals, any weight loss/maintenance behaviors, dieting, exercise, disordered eating behaviors. Outcomes: BMI at 7- and 15-year follow-up.Key ResultsOf the 12,155 young adults in the sample (54% female, 32% non-White), 33.2% reported a goal to lose weight, 15.7% to gain weight, and 14.6% to maintain weight. In unadjusted models, all groups have higher mean BMI at 7- and 15-year follow-up. In mixed effect models, goals to lose weight in men with BMI < 18.5 (5.94 kg/m²; 95% CI 2.58, 9.30) and goals to maintain weight in men with BMI ≥ 25 (0.44; 95% CI 0.15, 0.72) were associated with greater BMI increase compared to no weight goal. Engaging in disordered eating behaviors was associated with greater BMI increase in men with BMI < 18.5 (5.91; 2.96, 8.86) and women with 18.5 ≤ BMI < 25 (0.40; 0.16, 0.63). Dieting (− 0.24; − 0.41, − 0.06) and exercise (− 0.31; − 0.45, − 0.17) were associated with lower BMI increase in women with 18.5 ≤ BMI < 25. In women with BMI < 18.5, dieting was associated with greater BMI increase (1.35; 0.33, 2.37).ConclusionsWeight control efforts may have variable effects on BMI over time by gender and BMI category. These findings underscore the need to counsel patients on the effectiveness of weight control efforts and long-term weight management.KEY WORDS: BMI, weight goals, disordered eating behaviors, young adult, weight trajectories     

Effect of Mucin and Bicarbonate Ion on Corrosion Behavior of AZ31 Magnesium Alloy for Airway Stents

The biodegradable ability of magnesium alloys is an attractive feature for tracheal stents since they can be absorbed by the body through gradual degradation after healing of the airway structure, which can reduce the risk of inflammation caused by long-term implantation and prevent the repetitive surgery for removal of existing stent. In this study, the effects of bicarbonate ion (HCO₃⁻) and mucin in Gamble’s solution on the corrosion behavior of AZ31 magnesium alloy were investigated, using immersion and electrochemical tests to systematically identify the biodegradation kinetics of magnesium alloy under in vitro environment, mimicking the epithelial mucus surfaces in a trachea for development of biodegradable airway stents. Analysis of corrosion products after immersion test was performed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). Electrochemical impedance spectroscopy (EIS) was used to identify the effects of bicarbonate ions and mucin on the corrosion behavior of AZ31 magnesium alloys with the temporal change of corrosion resistance. The results show that the increase of the bicarbonate ions in Gamble’s solution accelerates the dissolution of AZ31 magnesium alloy, while the addition of mucin retards the corrosion. The experimental data in this work is intended to be used as foundational knowledge to predict the corrosion behavior of AZ31 magnesium alloy in the airway environment while providing degradation information for future in vivo studies.     

Preparation and Electrochemical Properties of LiNi2/3Co1/6Mn1/6O2 Cathode Material for Lithium-Ion Batteries

The cathode material LiNi_2/3Co_1/6Mn_1/6O₂ with excellent electrochemical performance was prepared successfully by a rheological phase method. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy and charge-discharge tests. The results showed that both calcination temperatures and atmosphere are very important factors affecting the structure and electrochemical performance of LiNi_2/3Co_1/6Mn_1/6O₂ material. The sample calcinated at 800 °C under O₂ atmosphere displayed well-crystallized particle morphology, a highly ordered layered structure with low defects, and excellent electrochemical performance. In the voltage range of 2.8–4.3 V, it delivered capacity of 188.9 mAh g⁻¹ at 0.2 C and 130.4 mAh g⁻¹ at 5 C, respectively. The capacity retention also reached 93.9% after 50 cycles at 0.5 C. All the results suggest that LiNi_2/3Co_1/6Mn_1/6O₂ is a promising cathode material for lithium-ion batteries.     

The Optical and Electrical Performance of CuO Synthesized by Anodic Oxidation Based on Copper Foam

Metal oxide semiconductor materials have a wide range of applications in the field of solar energy conversion. In this paper, CuO was prepared directly on copper foam substrate by anodic oxidation. The effects of current density and anodizing temperature on sample preparation and performance were studied. Field emission scanning electron microscopy (FESEM) and X-ray diffractometer (XRD) had been used to determine the morphology and phase structure of the sample, and its optical and electrical properties were discussed through UV-vis spectrophotometer and electrochemical tests. In addition, the influences of experimental conditions such as current density and reaction temperature on the morphology and properties of CuO were systematically discussed. The FESEM images showed that as the anodic oxidation temperature increase, the morphology of the prepared sample changed from nanowires to leaf-like CuO nanosheets. According to the results of XRD, the structure of prepared CuO was monoclinic, and the intensity of diffraction peaks gradually increased as anodizing temperature increased. We found that the optimum current density and anodizing temperature were 20 mA cm⁻² and 60 °C, respectively. The results of electrochemical indicated that the CuO electrode based on copper foam (CuO/Cu foam) prepared at the optimum exhibited the highest specific capacitance (0.1039 F cm⁻²) when the scan rate was 2 mV s⁻¹.     

Genuine divalent magnesium-ion storage and fast diffusion kinetics in metal oxides at room temperature

Rechargeable magnesium batteries represent a viable alternative to lithium-ion technology that can potentially overcome its safety, cost, and energy density limitations. Nevertheless, the development of a competitive room temperature magnesium battery has been hindered by the sluggish dissociation of electrolyte complexes and the low mobility of Mg²⁺ ions in solids, especially in metal oxides that are generally used in lithium-ion batteries. Herein, we introduce a generic proton-assisted method for the dissociation of the strong Mg–Cl bond to enable genuine Mg²⁺ intercalation into an oxide host lattice; meanwhile, the anisotropic Smoluchowski effect produced by titanium oxide lattices results in unusually fast Mg²⁺ diffusion kinetics along the atomic trough direction with a record high ion conductivity of 1.8 × 10⁻⁴ S ⋅ cm⁻¹ on the same order as polymer electrolyte. The realization of genuine Mg²⁺ storage and fast diffusion kinetics enabled a rare high-power Mg-intercalation battery with inorganic oxides. The success of this work provides important information on engineering surface and interlayer chemistries of layered materials to tackle the sluggish intercalation kinetics of multivalent ions.

Rechargeable multivalent metal-ion batteries are promising energy sources that can potentially satisfy the existing demand for high-energy density electrochemical energy storage devices (1, 2). The electrochemical discharge and charge reactions in these batteries involve multiple electron transfers per ion, which may significantly increase the ion storage capacity relative to that of monovalent batteries. Among the studied systems, Mg-ion batteries utilizing divalent magnesium ions (Mg²⁺) as charge carriers are considered the most viable option. In addition to their numerous advantages such as abundant Mg resources, low fabrication cost, and environmental friendliness, these batteries exhibit dendrite-free Mg plating and stripping during electrochemical cycling, which ensure high operational safety. Furthermore, the volumetric capacity of Mg anodes (3,833 mAh ⋅ cm⁻³) is almost twice as large as that of Li anodes (2,062 mAh ⋅ cm⁻³) (3–5). Unfortunately, it is very difficult to realize genuine storage and fast transport of Mg²⁺ ions in solids (especially in inorganic oxides) at low temperatures due to their high degree of polarization and charge density. The charge of the Mg²⁺ ion is two times larger than that of the Li⁺ ion, although the ionic radius of Mg²⁺ (0.72 Å) is close to that of Li⁺ (0.76 Å). As a result, Mg²⁺ ions are more likely to form strong covalent bonds with electrolytes (such as Mg–Cl bonds in the commonly used all-phenyl complex electrolytes) with very high dissociation energy. Meanwhile, the strong electrostatic interactions between Mg²⁺ ions and solid host lattices significantly inhibit their diffusion kinetics in these lattices. Resultantly, the migration barrier for Mg²⁺ ions is usually higher than that for Li⁺ ions in the same cathode material (6–8).To overcome the Mg bond dissociation barrier and enhance Mg-ion diffusion kinetics, intercalation chemistries based on solvated Mg²⁺ as the intercalating cation species, including Mg(DME)₃²⁺, Mg(H₂O)_x²⁺, and MgCl⁺, have been established (9–11). These complex ions lower the charge density by either increasing the ionic radius or decreasing the net charge. Although the storage of these complex ions alleviates the drawbacks related to the dissociation and diffusion of bare Mg²⁺ ions, it produces several challenges. The practical energy densities at the cell level for the hybrid battery based on such intercalation chemistry are lower than that of the battery exclusively involving Mg²⁺ storage. Additionally, the coinsertion of these bulky solvent molecules induces significant volume changes of the electrode, thereby limiting its cycle life. Recently, a two-pronged approach has been developed to overcome these challenges (12). It involved the storage of exclusively Mg²⁺ ions and their fast solid-state diffusion in an organic cathode fabricated from pyrene-4,5,9,10-tetraone. Heterogeneous enolization redox chemistry was utilized to avoid the bond cleavage and reformation; meanwhile, an electrolyte comprising weak-coordinated anions in an ethereal solvent blend was employed to increase the bulk ion mobility and promote Mg²⁺ desolvation on the electrode surface. However, it still remains a critical challenge in inorganic materials to overcome the two important problems: the ion dissociation in the conventional Mg chloride complex electrolyte and solid-state ion diffusion. The development of rechargeable inorganic cathodes for Mg batteries using a rational structural design is the major limiting factor of this promising post–Li-ion battery technology.Metal oxides are the most promising electrode materials for Li-ion batteries, taking advantage of their excellent chemical and thermal stabilities; however, this is not always true for Mg-ion batteries. Compared to sulfides and selenides, most metal oxides suffer from low reversible capacities and slow diffusion kinetics, owing to the higher strength of the Mg–O bond as compared with those of the Mg–S and Mg–Se bonds (7, 13). Furthermore, the reaction of Mg ions with highly polarizable O²⁻ ions often leads to MgO formation rather than Mg²⁺ intercalation, making it almost impossible to achieve reversibility in oxide-based cathodes (14). Therefore, the development of rechargeable metal-oxide electrode materials for Mg-ion batteries characterized by genuine Mg²⁺ storage, fast solid-state diffusion kinetics, and excellent cycling performance (especially at room and low temperatures) remained an unsurmountable challenge.In the present study, genuine Mg²⁺ intercalation/deintercalation and fast diffusion in oxide lattices were realized not only at room temperature but also at subzero temperatures. These outstanding results were achieved by placing protons on negatively charged metal-deficient oxide sheets and disorderly stacking these sheets over a certain distance (this strategy is schematically illustrated in Fig. 1). The stripping of Cl⁻ ions was facilitated by the presence of protons between the sheets, while fast Mg²⁺ diffusion was ensured by the extension of the wavefunction along an atomic trough on the unique sheet surface due to the anisotropic Smoluchowski effect. This induced the formation of flat potential-energy surfaces and diffusion highways, which gave a record high Mg-ion conductivity of 1.8 × 10⁻⁴ S ⋅ cm⁻¹. As a result, the fabricated Mg-ion cell exhibited a high-power density of 7.4 kW ⋅ kg⁻¹ while maintaining an energy of 113.0 Wh ⋅ kg⁻¹. Practically, the cell battery, which was charged in 55 s, could be gradually discharged for a stable long run of ∼4.5 h. Even at a subzero temperature of −15 °C, the electrode capacity remained above 55%, and the diffusion coefficient was in the range of 10⁻⁹ tο 10⁻¹¹ cm² ⋅ s⁻¹ (10⁻⁸ to 10⁻¹⁰ cm² ⋅ s⁻¹ at room temperature). The proposed strategy is generic and can be easily applied to other two-dimensional electrode materials, including titanium oxide, manganese oxide, and oxyanion-terminated titanium carbide.Open in a separate windowFig. 1.Schematic illustration. The genuine Mg²⁺ storage mechanism and fast diffusion in the oxide electrode, which were studied using PhMgCl–AlCl₃ electrolyte. The protons efficiently stripped Cl ions from the electrolyte complex, ensuring the genuine Mg²⁺-intercalation chemistry. The anisotropic Smoluchowski effect or wavefunction extension along the atomic troughs on the surface created pathways for the unusually fast diffusion of Mg²⁺ species.     

Humidity-Sensing Properties of an 1D Antiferromagnetic Oxalate-Bridged Coordination Polymer of Iron(III) and Its Temperature-Induced Structural Flexibility

A novel one-dimensional (1D) oxalate-bridged coordination polymer of iron(III), {[NH(CH₃)(C₂H₅)₂][FeCl₂(C₂O₄)]}_n (1), exhibits remarkable humidity-sensing properties and very high proton conductivity at room temperature (2.70 × 10⁻⁴ (Ω·cm)⁻¹ at 298 K under 93% relative humidity), in addition to the independent antiferromagnetic spin chains of iron(III) ions bridged by oxalate groups (J = −7.58(9) cm⁻¹). Moreover, the time-dependent measurements show that 1 could maintain a stable proton conductivity for at least 12 h. Charge transport and magnetic properties were investigated by impedance spectroscopy and magnetization measurements, respectively. Compound 1 consists of infinite anionic zig-zag chains [FeCl₂(C₂O₄)]_nⁿ⁻ and interposed diethylmethylammonium cations (C₂H₅)₂(CH₃)NH⁺, which act as hydrogen bond donors toward carbonyl oxygen atoms. Extraordinarily, the studied coordination polymer exhibits two reversible phase transitions: from the high-temperature phase HT to the mid-temperature phase MT at T ~213 K and from the mid-temperature phase MT to the low-temperature phase LT at T ~120 K, as revealed by in situ powder and single-crystal X-ray diffraction. All three polymorphs show large linear thermal expansion coefficients.     

New O3-Type Layer-Structured Na0.80[Fe0.40Co0.40Ti0.20]O2 Cathode Material for Rechargeable Sodium-Ion Batteries

Herein, we formulated a new O3-type layered Na_0.80[Fe_0.40Co_0.40Ti_0.20]O₂ (NFCTO) cathode material for sodium-ion batteries (SIBs) using a double-substitution concept of Co in the parent NaFe_0.5Co_0.5O₂, having the general formula Na_1-x[Fe_0.5–x/2Co_0.5–x/2M⁴⁺_x]O₂ (M⁴⁺ = tetravalent ions). The NFCTO electrode delivers a first discharge capacity of 108 mAhg⁻¹ with 80% discharge capacity retention after 50 cycles. Notably, the first charge–discharge profile shows asymmetric yet reversible redox reactions. Such asymmetric redox reactions and electrochemical properties of the NFCTO electrode were correlated with the phase transition behavior and charge compensation reaction using synchrotron-based in situ XRD and ex situ X-ray absorption spectroscopy. This study provides an exciting opportunity to explore the interplay between the rich chemistry of Na_1–x[Fe_0.5–x/2Co_0.5–x/2M⁴⁺_x]O₂ and sodium storage properties, which may lead to the development of new cathode materials for SIBs.