Electrochemical Impedance Spectroscopy Studies Research Articles

Correlating Solid-Electrolyte Interface Composition to Charge Transfer Resistance for Improved Low-Temperature Performance of Lithium-Ion Batteries

The adverse impact of low temperatures on Li-ion batteries (LIBs) is a well known challenge. Currently, at subfreezing temperatures, the efficiency of conventional LIBs greatly decreases compared to their room temperature performance, which of course severely limits the performance of applications using LIBs in the colder regions on the planet. From a fundamental perspective, the causes of such performance decreases are yet to be fully understood, but are believed to be related to the ability of ions to move through the various phases (as well as move across phase interfaces) that exist in the battery.Several studies have been conducted to improve the low-temperature performance of LIBs, most of them focusing on using solvents with lower viscosity and higher dielectric constant to promote transport through the electrolyte at the lower temperatures so as to achieve lower bulk resistance (Rbulk) of the cell. However, our Electrochemical Impedance Spectroscopy (EIS) studies at low temperatures have indicated that it is the charge transfer resistance (Rct) that grows exponentially as we go to sub-zero Celsius temperatures and is responsible for the increase in the total resistance of the cell. EIS on 3-electrode cells have shown that the anode side (Gr) is predominantly responsible for the poor cell performance, necessitating our focus on the charge transfer process in the Gr-electrolyte interface. We observe that the Rct is not only related to the Li-solvation shell but also to the composition of the Solid Electrolyte Interface (SEI). By modifying the electrolyte, such as by changing the salt concentration, adding additives, and changing the solvent, significant changes in the interface and hence in the RSEI and Rct of the cell have been observed. By combining EIS with various techniques like mass spectrometry, differential capacity analysis and SEM, we have been able to better understand the SEI composition and its impact on interfacial resistances. We specifically focus on the influence of SEI composition on the charge-transfer resistance of the cell, correlating the effect of amounts of LiF and carbonates in the SEI with the interfacial performance of the cell. Through these relations, we aim to facilitate the development of electrolytes by having a better understanding of the solvation shells and the SEI composition for low temperature performance.

(Invited) Clay: A Ubiquitous Sustainable Material for Energy Applications

Silicates and their precursors make up the majority of the land mass on Earth in the form of inorganic components of soil, silt, and sediment. Clay minerals, essentially hydrous silicates or aluminosilicates, are widely used in a variety of applications and industries, including ceramic goods, cement, drilling fluids, molding sands, anti-corrosion paints, paper manufacturing process, water treatment, polymer-clay composites for automotive industries, and even in medicine and pharmaceutical applications. Lately, it has found use in developing cost-effective ink, drug delivery, food packaging using oxygen barrier properties, and battery separators.Structure-property features of clays reveal that one can functionalize clays leveraging their porous structures, tunable surface areas, remarkable thermal and mechanical stabilities, and abundant reserves, which make clay one of the cheapest natural materials from a sustainable source and one of the most sought-after materials for a variety of applications. Clays generally have layered structures with the possibility of interchangeable intercalated ions and tunable chemical properties. They are composed of alternating tetrahedral silica (T) and octahedral alumina (O) sheets arranged in a 1:1 ratio (T-O). The tetrahedral sheets are formed from Si4+ ions coordinated with oxygen; however, the Al3+ metal ion is the central atom in the octahedral sheet. Bentonite or Montmorillonite is one of the most used clay minerals owing to its abundance and low cost. Notably, naturally occurring Bentonite has some octahedral sites occupied by the Mg2+ and Fe2+ ions. The presence of these ions allows tuning chemical properties and mechanical strength by functionalizing with organic molecules within the octahedral layers. Over the decades, polymer-based clay composites have been developed using this technique. Herein, we shed light on a new strategy to create hybrid clay films made from small organic molecules with charges at two ends, known as zwitter ions. Using this novel approach, we have developed cost-effective, environmentally benign, and biocompatible clay films with unique physical and chemical properties, where the clay galleries are infused with intercalating zwitter ions. The insertion of these ions increases the interlayer spacing while simultaneously allowing the formation of mechanically robust and thermally and chemically durable clay films. These hybrid clay films can be used as membranes and have been characterized using powder X-ray diffraction, X-ray photoelectron spectra, rheology, ATR-IR spectra, DSC-TGA, dynamic mechanical analyses, and imaging techniques. The effect of varying the carbon chain length and changing functional groups in these zwitter ion species has been verified to significantly impact the clay slurry's rheology and control the clay films' interlayer spacing. Electrochemical impedance spectroscopy studies of the hybrid films confirm that intercalation of zwitter ions in the clay structures leads to improved ionic conductivity of the clays. A series of impedance spectroscopy experiments conducted using various electrolytes reveal remarkable improvements in the ionic conductivity of the hybrid clay films. Contrary to metal ion batteries due to dendritic growth causing thermal degradation of the batteries, the hybrid clay films possess high thermal and mechanical stability that makes them versatile for energy materials. A cost-effective solution to engineering such hybrid films provides an efficient and recycle-free avenue to develop a new generation of materials from sustainable sources for energy applications, especially for battery separators and capacitors for the future.

Exploring the Electrochemical Properties of Ultrathin LiMn1.5Ni0.5O4 Films at High and Low Current Rates for Lithium-Ion Micro Battery Applications

The development in the miniaturized - smart electric and electronic gadgets with the advancement in technologies has dramatically enhanced the demand for cobalt free-high energy density batteries. Among various choice of high-performance cathode materials Ni substituted LiMn2O4 spinel of composition LiMn1.5Ni0.5O4 (LMNO) has proved to be one of the solutions to yield a high-performance high-energy density battery which can operate at a higher potential window. Ultra - thin films of LMNO fabricated by Pulsed laser deposition method at 600 °C substrate temperature using 2000 pulses. LMNO films fabricated on SrTiO3 (STO) and stainless steel (SS) substrates are employed for a detailed structural and electrochemical performance analysis. Disordered phase corresponding to fd3m space group of LMNO thin film exhibits better electrochemical performance compared to the ordered phase. Phase formation of LMNO thin films are studied employing X-ray diffraction and Raman spectroscopy methods. The morphology obtained for the film of thickness 41.63 nm identified from the scanning electron microscopy (SEM) images clearly reveals the effect of growth conditions such as substrate temperature and base pressure on the growth behavior of these films. Since the electrochemical data obtained for the films are area limited, the capacity of the ultra-thin film is significantly low and can be ameliorate by controlling the area. Kinetic study of LMNO film reveals that the lithium diffusion during the charge storage mechanism resembles to a diffusion-limited process similar to a faradic process. The cycling stability and rate capability at different current densities of LMNO thin film electrodes are further investigated. Charge discharge profile for both higher (25, 50, 75, 100 and 125 mA) and lower (5, 10, 15, 20, and 25 mA) current densities are obtained and subjected for 500 cycles. The thin film electrode shows a stable profile for 500 cycles. Areal discharge capacity of 1.3 μAh/cm2 is observed at a higher current density while at lower current density an areal discharge capacity obtained is 2.13 μAh/cm2 with a coulombic efficiency of around 80% and 96% respectively. Electrochemical impedance spectroscopy studies carried out on LMNO films before and after cycle shows a strong contribution of charge-transfer resistance along with film resistance and solution resistance and the equivalent circuit model for the same is evolved. Present studies indicates that LMNO ultra-thin films can be employed as a cathode layer for fabricating the all-solid thin film micro-batteries for energy applications. Figure 1

Flattening of a Bent Sulfonated MOF Linker: Impact on Structures, Flexibility, Gas Adsorption, CO2/N2 Selectivity, and Proton Conduction.

Rational design of organic building blocks provides opportunities to control and tune various physicochemical properties of metal-organic frameworks (MOFs), including gas handling, proton conduction, and structural flexibility, the latter of which is responsible for new adsorption phenomena and often superior properties compared to rigid porous materials. In this work, we report synthesis, crystal structures, gas adsorption, and proton conduction for a flexible two-dimensional cadmium-based MOF (JUK-13-SO3H-SO2) containing a new sulfonated 4,4'-oxybis(benzoate) linker with a blocking SO2 bridge. This two-dimensional (2D) MOF is compared in detail with a previously reported three-dimensional Cd-MOF (JUK-13-SO3H), based on analogous, but nonflat, SO2-free sulfonated dicarboxylate. The comprehensive structure-property relationships and the detailed comparisons with insights into the networks flexibility are supported by five guest-dependent structures determined by single-crystal X-ray diffraction (XRD), and corroborated by spectroscopy (IR, 1H NMR), powder XRD, and elemental/thermogravimetric analyses, as well as by volumetric adsorption measurements (for N2, CO2, H2O), ideal adsorbed solution theory (IAST), density-functional theory (DFT+D) quantum chemical and grand-canonical Monte Carlo (GCMC) calculations, and electrochemical impedance spectroscopy (EIS) studies. Whereas both dynamic MOFs show moderate proton conductivity values, they exhibit excellent CO2/N2 selectivity related to the capture of CO2 from flue gases (IAST coefficients for 15:85 mixtures are equal to ca. 250 at 1 bar and 298 K). The presence of terminal sulfonate groups in both MOFs, introduced using a unique prechlorosulfonation strategy, is responsible for their hydrophilicity and water-assisted proton transport ability. The dynamic nature of the MOFs results in the appearance of breathing-type adsorption isotherms that exhibit large hysteresis loops (for CO2 and H2O) attributed to strong host-guest interactions. Theoretical modeling provides information about the adsorption mechanism and supports interpretation of experimental CO2 adsorption isotherms.

Size dependent electrochemical properties of green synthesized NiO nanoparticles as a supercapacitor electrode

The nickel oxide nanoparticles (NiO NPs) are synthesized by a green method using the leaf extract of Ocimum sanctum (OS) as a reducing agent. The NiO NPs of different sizes are synthesized using various concentrations of leaf extract of OS. The average crystallite size and particle size of the NiO NPs is measured using XRD and Transmission electron microscope (TEM) respectively. The size of NiO NPs is observed to decrease from ∼ 17 nm to ∼ 13 nm with increase in concentrations of leaf extract of OS. The morphology and elemental analysis of the NiO NPs is carried out using Field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray (EDX) analysis respectively. The cyclic voltammetric (CV) studies on electrode of NiO NPs showed a pseudocapacitive behavior with a specific capacitance of 100 Fg−1 at a scan rate of 100 mV/sec for the particles with the size of ∼ 13 nm. The Galvonostatic charge–discharge studies showed a prolonged discharge time for the electrode of NiO NPs with size of ∼ 13 nm for a current density of 5 A/g. The electrochemical impedance spectroscopy (EIS) studies of electrodes of NiO NPs indicate the electric double layer capacitance (EDLC) and diffusion controlled pseudo capacitance behavior. The synthesized electrode shows capacitance retention of 84 % for 2500 cycles, is chosen for designing a supercapacitor device for glowing 10 red light emitting diodes (LEDs). Therefore, the use of leaf extract of OS is an ecofriendly alternative for synthesis of NiO NPs of different sizes that has applications in energy storage devices.

Development of Novel Cobalt Tungstate Anchored on MCM-41 for Sensitive Detection of Dopamine in Human Urine Samples

In this study, MCM-41/CoWO4 nanocomposite has been used for electrochemical detection of dopamine neurotransmitters. The cobalt tungstate nanoparticles (CoWO4) were synthesized through facile hydrothermal method and MCM-41/CoWO4 nanocomposite was prepared by ultrasonication method. The as-synthesized MCM-41/CoWO4 nanocomposite was characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman techniques. The electrochemical performance of the nanocomposite was examined using electrochemical impedance spectroscopy, cyclic voltammetry, and differential pulse voltammetry studies. The GCE/MCM-41/CoWO4 electrode exhibited a linear range, better sensitivity, and limit of detection (LOD) of 10–170 μM, 0.3361 μA μM−1 cm−2 and 7.2 nm, respectively. Moreover, the GCE/MCM-41/CoWO4 electrode demonstrated good repeatability, reproducibility, and stability. In addition to that, the real sample analysis was conducted using human urine with excellent recovery and RSD percentage.

Electrochemical Detection of Metol through the Cobalt Nickel Oxide Nanosheets Incorporated with MCM-41 Nanospheres Composites Modified Glassy Carbon Electrode

In this study, contaminations of metol (or Elon) in environmental water and industrial wastewater are the major causes of toxicity, which is very harmful to human health and other living things. Hence the determination of metol in high demand is more important. Further, the Mobil Composition of Matter (MCM-41) mesoporous silica nanoparticles incorporated with cobalt nickel oxide (CoNiO2) complex to form MCM-41/CoNiO2 composite modifying the glassy carbon electrode (GCE) used for metol detection. The MCM-41/CoNiO2 composite coated on the GCE surface exhibited fast electron transfer kinetics, improved conductivity, a large surface area, active stability, and improved catalytic efficiency. The structural morphology of the MCM-41/CoNiO2 composite was investigated using several spectroscopic and microscopic techniques. Here, the MCM-41/CoNiO2 composite was verified using different characterization studies such as Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, Energy Dispersive X-ray Analysis, X-ray Diffraction Analysis, and X-ray Photoelectron Spectroscopy. Additionally, the electrochemical investigations have included Electrochemical Impedance Spectroscopy, Cyclic Voltammetry, and Differential Pulse Voltammetry studies. The GCE/MCM-41/CoNiO2 electrode shows a low detection limit of 10 nM and the LOQ value is 0.1 μM with a broad linear response range of 0.1–750 μM, and greater sensitivity of 0.411 μA μM−1 cm−2 under optimal voltammetry.

Espial: Electrochemical Soil pH Sensor for In Situ Real-Time Monitoring.

We present a first-of-its-kind electrochemical sensor that demonstrates direct real-time continuous soil pH measurement without any soil pre-treatment. The sensor functionality, performance, and in-soil dynamics have been reported. The sensor coating is a composite matrix of alizarin and Nafion applied by drop casting onto the working electrode. Electrochemical impedance spectroscopy (EIS) and squarewave voltammetry (SWV) studies were conducted to demonstrate the functionality of each method in accurately detecting soil pH. The studies were conducted on three different soil textures (clay, sandy loam, and loamy clay) to cover the range of the soil texture triangle. Squarewave voltammetry showed pH-dependent responses regardless of soil texture (while electrochemical impedance spectroscopy's pH detection range was limited and dependent on soil texture). The linear models showed a sensitivity range from -50 mV/pH up to -66 mV/pH with R2 > 0.97 for the various soil textures in the pH range 3-9. The validation of the sensor showed less than a 10% error rate between the measured pH and reference pH for multiple different soil textures including ones that were not used in the calibration of the sensor. A 7-day in situ soil study showed the capability of the sensor to measure soil pH in a temporally dynamic manner with an error rate of less than 10%. The test was conducted using acidic and alkaline soils with pH values of 5.05 and 8.36, respectively.

Selective Perchlorate Sensing Using Electrochemical Impedance Spectroscopy with Self-Assembled Monolayers of semiaza-Bambusurils.

In the last two decades, perchlorate salts have been identified as environmental pollutants and recognized as potential substances affecting human health. We describe self-assembled monolayers (SAMs) of novel semiaza-bambus[6]urils (semiaza-BUs) equipped with thioethers or disulfide (dithiolane) functionalities as surface-anchoring groups on gold electrodes. Cyclic voltammetry (CV) with Fe(CN)6 3-/4- as a redox probe, together with X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and ellipsometry, were employed to characterize the interactions at the interface between the anchoring groups and the metal substrate. Data showed that the anion receptors' packing on the gold strongly depends on the anchoring group. As a result, SAMs of BUs with lipoic amide side chains show a concentration-dependent layer thickness. The BU SAMs are extremely stable on repeated electrochemical potential scans and can selectively recognize perchlorate anions. Our electrochemical impedance spectroscopy (EIS) studies indicated that semiaza-BU equipped with the lipoic amide side chains binds perchlorate (2-100 mM) preferentially over other anions such as F- , Cl- , I- , AcO- , H2 PO4 - , HPO4 2- , SO4 2- , NO2 - , NO3 - , or CO3 2- . The resistance performance is 10 to 100 times more efficient than SAMs containing all other tested anions.

Study the effect of rGO on the porous binary Zn0.25Cu0.75S nanocomposite deposited on Ni-foam electrode for high performance energy storage devices

Supercapattery is the combination of battery and supercapacitor, which has the benefits of both devices like high power density, cycle stability, and greater energy density. Using a simple hydrothermal method, we synthesized zinc sulfide (ZnS), copper sulfide (CuS), and zinc copper sulfide (ZnCuS). The Zn0.25Cu0.75S@rGO nanocomposite electrode exhibited excellent electrochemical results, functioning at 1.4 A/g in a three-electrode assembly with an extraordinary specific capacitance of 2935 F/g. Brunauer-Emmett-Teller (BET) measurements and electrochemical impedance spectroscopy (EIS) studies show the improvement in surface area and electrochemical properties of the material. The hybrid device (Zn0.25Cu0.75S@rGO//AC) showed an extraordinary specific capacity of 150 C/g at 1.2 A/g with Pb of 2800 W/kg and Ed of 36.6 Wh/Kg. The supercapattery device exhibited an outstanding cyclic stability of 91 %. Our findings show that Zn0.25Cu0.75S@rGO is more suitable for storage devices as an electrode material.

Polymer‐derived SiOC ceramic coating for corrosion protection

AbstractIn the present study, a polymer‐derived silicon oxycarbide (SiOC) ceramic layer has been coated on stainless steel 304 (SS304) to improve corrosion resistance in a seawater environment. The surface of SS304 is dip‐coated with vinyl‐functionalized polysiloxane, followed by pyrolysis under argon at 800°C to obtain SiOC layer with a thickness of about 1 μm after two‐fold coating/pyrolysis steps. Structural characterization of the samples was performed by fourier transform infrared (FTIR), X‐ray diffraction, Raman spectroscopy, and scanning electron microscopy. Electrochemical characterization of SS304 and SiOC‐coated SS304 is performed in 0.6 M NaCl solution. Potentiodynamic polarization measurements showed improved corrosion resistance of SiOC‐coated SS304 with a very low corrosion current density of 4.14 × 10−9 A/cm2 whereas for uncoated SS304 corrosion current density of 4.56 × 10−7 A/cm2 was measured. Electrochemical impedance spectroscopic study confirmed superior corrosion resistance behavior of SiOC‐coated SS304 over uncoated SS304.

Molybdenum‐Incorporated O3‐type Sodium Layered Oxide Cathodes for High‐Performance Sodium‐Ion Batteries

Transition metal layered oxide materials with a general formula NaxMO2 (M = Ni, Mn, Co, Fe) are widely researched with various possible electrode configurations. Herein, O3‐type NaNi(1−x)/2Mn(1−x)/2MoxO2 (x = 0, 0.05,0.1) layered oxide cathode materials are synthesized by solid‐state reaction method, and its structural, thermal, and electrochemical performance in sodium ion battery is investigated. The structural analysis reveals that a single phase highly crystalline O3‐type cathode material with an irregular particle shape is formed. The introduction of molybdenum improves the thermal stability of cathode materials, which can be attributed to the improved TMO2 layers that provide stability to the material. The addition of Mo to Na‐layered oxide cathode materials enhances electrochemical performance. The developed cathode materials, the NaNi0.475Mn0.475Mo0.05O2, exhibit excellent specific discharge capacity (≈154 mAh g−1) at C/20 rate, (an increase of ≈20% when compared to the NaNi0.5Mn0.5O2) which can be attributed to the increased capacitance effect by the addition of Mo. The electrochemical impedance spectroscopy study reveals that the diffusion of Na+ into/from the host structure is rapid during the first cycle and then gradually reduces with subsequent cycling due to the formation of the solid electrolyte interface layer, which hinders Na+ migration. This has a potential effect on the improved electrochemical performance of the material.

Polydopamine-Modified Carboxymethyl Cellulose as Advanced Polysulfide Trapping Binder

The search for a high-energy-density alternative to lithium-ion batteries has led to great interest in the lithium sulfur battery (LSB). However, poor cycle lifetimes and coulombic efficiencies (CEs) due to detrimental lithium polysulfide (LiPS) shuttling has hindered its widespread adoption. To address this challenge, a modified sodium carboxymethyl cellulose (CMC) polymer with integrated dopamine moieties and polydopamine nanoparticles was created through a facile one-pot dopamine (DOP) amidation reaction to strengthen noncovalent interactions with LiPSs and mitigate the shuttling effect. The resulting CMC-DOP binder improved electrode wettability, adhesion, and electrochemical performance. Compared to LSBs with a standard CMC binder, CMC-DOP 5:1 (with a 5:1 weight ratio of CMC to dopamine precursor) improves the specific capacity at cycle 100 by 38% to 552 mAh g−1 and CE from 96.8 to 98.9%. LSBs show good stability, even after 500 cycles. Post-mortem electrochemical impedance spectroscopy (EIS) and energy-dispersive spectroscopy (EDS) studies confirmed the effectiveness of the CMC-DOP in confining LiPS in the cathode. This simple but effective nature-inspired strategy promises to enhance the viability of LSBs without using harmful chemicals or adding excess bulk.

Controlled modulation of coating morphology, mechanical properties and anti-tarnishing response of nanocrystalline Au-Cu alloy coatings electrodeposited from a thiourea (TU)-based non-toxic cyanide-free bath: Effect of current density variation

In the present work, Au-Cu alloy coatings are prepared by pulse galvanostatic electrodeposition from a novel thiourea (TU)-based bath by varying the current density from 5 to 25 mA/cm2. The effect of the applied current density on the surface morphology, mechanical properties, and anti-tarnishing performance of the developed Au-Cu coatings is investigated. Linear sweep voltammetry (LSV) experiments from different bath compositions are carried out to explore the electroanalytical behaviour of Au and Cu in the system. The SEM and EDS investigations show a wide variation in the surface morphology and Cu content of the deposited coatings as the applied current density changes from 5 to 25 mA/cm2. As the current density increases, the hardness of the coatings escalates from 173 to 279 VHN. The electrochemical impedance spectroscopy (EIS) studies suggest that the severity of tarnishing decreases with the increase in the current density.

Decoration of spherical Sb2S3 over CuO nanoflakes for efficient photoelectrochemical hydrogen generation

Developing an efficient photocathode system from earth abundant materials is essential for effectual Photoelectrochemical (PEC) water splitting. Charge transfer between heterojunctions is important in fabricating a novel photocathode, keeping cost-effectiveness, abundance, and PEC performance in mind. The p-type narrow band gap photocathode, CuO (Eg = 1.5 eV) synthesized by hydrothermal method, was decorated with Sb2S3 Nanospheres (NSs) by adopting a facile chemical bath deposition (CBD) procedure to fabricate CuO/Sb2S3 NSs heterojunction. Fabricated heterojunction showed better PEC performance contrary to bare CuO, improvement in photocurrent density CuO/Sb2S3 NSs (J = −1 mA cm−2) than CuO (J = −0.3 mA cm−2) photoelectrode at 0 VRHE in 0.5 M Na2SO4 (pH 6.85) is due to enhanced charge carrier generation/separation. The photostability of CuO/Sb2S3 remains intact for 2.5 h with no degradation in photocurrent density. Sb2S3 works as a sensitizer, diminishing the recombination rate of the e−/h+ in CuO/Sb2S3 NSs. UV–Visible and photoluminescence(PL) emission spectra results suggested CuO/Sb2S3 enhanced absorption spectrum and reduced rate of recombination. Electrochemical impedance spectroscopy studies show less charge transfer resistance for CuO/Sb2S3 NSs than CuO. This finding will pave new path in developing novel photocathodic material configurations and heterojunction with Cu-based binary oxides/chalcogenides for solar harvesting.

Development and Evaluation of Corrosion Resistance and Hydrophobic Properties of Thermal Sprayed Coatings over Carbon Steel

Various industrial parts and equipment made of steel need to withstand demanding conditions. In order to increase performance and lifetime, surface processing and functional coatings can be applied. In this study we report on the evaluation of coated carbon steel with commercial corrosion-resistant powders Diamalloy 4276 and Woka 7502 by Oerlikon Metco, using thermal spraying. Further functionalization is performed by rendering thermal sprayed surfaces syperhydrophobic via gas phase deposition of trichloro-1H,1H,2H,2H-perfluorooctyl silane, (PFOTS). Electrochemical impedance spectroscopy, contact angle and water condensation studies reveal the protective properties of coatings prepared by both materials as well as the superiority of Diamalloy 4276 based coatings. Corrosion was evaluated under a harsh 20% w/w H2SO4 environment. Rendering the coating superhydrophobic improves water condensation under the tested conditions of high (80%) relative humidity.

Morphology-Dependent Immunomodulatory Coating of Hydroxyapatite/PEO for Magnesium-Based Bone Implants.

One of the most critical issues concerning orthopedic implants is the risk of chronic inflammation, which poses a threat to the bone healing process. Osteo-immunomodulation plays a pivotal role in implant technology by influencing proinflammatory and anti-inflammatory responses, ultimately promoting bone healing. This study aims to investigate the morphology-dependent osteo-immunomodulatory properties of a hydroxyapatite (HA)/plasma electrolytic oxidation (PEO)-coated WE43 alloy. In this context, following the PEO process with various operational parameters (duty cycles of 50-40, 50-20, 70-40%, and frequencies of 0.5, 0.8, and 1 kHz), a layer of HA was applied as the top coating using a straightforward hot-dip process. The results revealed the formation of the PEO layer with distinct morphologies and pore sizes, depending on the operational parameters. Specifically, a uniform PEO coating with small pore sizes (5.2-5.3 μm) led to the creation of plate-like HA particles, while a random-like HA structure formed on nonuniform surfaces with large pores (7.0-11.1 μm) of PEO. Moreover, it was observed that the plate-like HA coating exhibited higher adhesion strength than the random one (classified as class 2 vs class 3 based on cross-cut standards). Furthermore, electrochemical impedance spectroscopy (EIS) and polarization studies confirmed a substantial increase in the polarization resistance (680 kΩ) and total impedance (48 559.6 Ω) for the plate-like HA/PEO as compared to the substrate (an increase of 1511-fold and 311-fold, respectively) and the random HA/PEO samples (an increase of 85-fold and 18-fold, respectively). In addition, compared to random HA coatings, there was a significant enhancement in the viability (150% control vs 96% control), proliferation, and differentiation of MG63 cells when exposed to plate-like HA coatings. Moreover, surface morphology and chemistry pronouncedly impacted macrophages' viability, morphology, and phenotype. Notably, plate-like HA coatings resulted in a higher upregulation of BMP-2 and TGF-β than proinflammatory cytokines (IL-6 and M-CSF), indicating a polarization of macrophage type 1 (M1) toward type 2 (M2). In summary, the bilayer HA/PEO coating exhibited remarkable osteo-immunomodulatory activity, making it highly appealing for use in bone implant applications.

Exfoliated Graphene Oxide @ Sb2O3 Octahedrons as Alloy-Conversion Anode for High-Performance Na-Ion Batteries with P2-Type Na2/3Ni1/3Mn2/3O2 Cathode

Conversion–alloying–based anodes for sodium–ion batteries (SIBs) have attracted wide interest due to their high energy density and specific capacity. However, it suffers from volume expansion during operation, leading to poor cycling stability. This study introduces a novel carbon matrix, exfoliated graphene oxide (EGO), to alleviate the issues due to volume expansion in the antimony (III) oxide anode for SIBs. Four combinations of Sb2O3 with EGO were explored, and electrochemical performance was compared. An optimized combination (Sb–E1) showed a capacity of ∼100 mAh g–1 at a high current density of 1 A g–1 with good cycling stability. The results show that EGO can effectively buffer the volume expansion and promote fast kinetics. An in–situ electrochemical impedance spectroscopy study revealed that the exceptional charge-transfer resistance varies during the alloying reaction but not during the conversion reaction. The full-cell is fabricated with P2-type layered Na2/3Ni1/3Mn2/3O2 (NNMO) cathode. The Sb–E1/NNMO cell displayed an average operating potential of ∼2.95 V, a high capacity of ∼100 mAh g–1 at a current density of 1 A g–1, and a maximum energy density of ∼100 Wh kg–1.

Electrochemical Sensor Based on N–Doped Carbon Nanodots Derived from the Agro-Waste Cotton Boll Peel Extracts for Nano Molar Determination of an Anti-Cancer Drug, Pemetrexed

A green and facile one-step synthetic route was proposed for the synthesis of nitrogen-doped carbon nanodots (N-CDs) from agro-waste cotton boll peel extract as a natural carbon source and glycine as a nitrogen source. The prepared N-CDs were utilized further in the fabrication of an electrochemical sensor for the nanomolar determination of an anti-cancer drug, pemetrexed (PMT). The electrode material was characterized by XRD, FTIR, TEM, Raman, EDX, UV–vis, fluorescence, cyclic voltammetric and electrochemical impedance spectroscopic studies. The N-CDs drop-casted on the surface of glassy carbon electrode (GCE) served as a good sensing material and exhibited electrocatalytic activity as evident from ∼20-fold enhancement in the oxidation peak current of PMT at N-CDs/GCE with 130 mV lesser positive oxidation peak potential than that at bare GCE. This was attributed to excellent conductivity, higher electroactive surface area, graphitic cores of N-CDs besides the interactions between PMT and N-CDs via hydrogen bonding and π–π stacking. The sensing performance of the demonstrated electrode was optimized by varying the peak current dependant parameters and also by investigating the influence of interfering substances in the determination of PMT. The electrochemical behaviour of PMT at different pH revealed the adsorption controlled electrode process with the involvement of protons. Under optimized conditions, differential pulse voltammetric (DPV), square wave voltammetric (SWV) and adsorptive differential pulse voltammetric (AdSDPV) methods were developed for sensitive determination of PMT at nano molar level. Further, these developed analytical methods were applied successfully for the determination of PMT in analyte fortified human urine samples and pharmaceutical formulations.

Electrochemical study of carboxylated chitosan-graft-poly (Vinyl-2-Pyrrolidone) films for supercapacitor applications

ABSTRACT The present study aimed at preparing-grafted-poly(vinyl-2-pyrrolidone) film and carboxylated chitosan-grafted-po (vinyl-2-pyrrolidone) films using gamma irradiation. poly(vinyl-2-pyrrolidone was grafted onto carboxylated chitosan based on different concentrations of in-situ reaction media. Properties of films were characterized by various techniques of Fourier transform infrared (FTIR), scanning electron microscope (SEM) and energy dispersive X-ray (EDX). The energy storage capability of the films was tested using electrochemical analysis as it could act as electrodes for supercapacitors. Both NaOH and KOH have acted as devise electrolytes for comparison of electrodes performance. From cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy studies, carboxylated chitosan-grafted-poly(vinyl-2-pyrrolidone) films at concentration of N-vinyl-2-pyrrolidone was 20 (v/v)% that exposed the highest specific capacitance, energy density, and power density in NaOH. Results refer to the capability of the prepared films could be applied as electrodes in supercapacitor devices.