Low Conductivity Research Articles

NH2-MIL-125(Ti) and its functional nanomaterials - a versatile platform in the photocatalytic arena.

Titanium (Ti)-based MOFs are promising materials known for their porosity, stability, diverse valence states, and a lower conduction band (CB) than Zr-MOFs. These features support stable ligand-to-metal charge transfer (LMCT) transitions under photoirradiation, enhancing photocatalytic performance. However, Ti-MOF structures remain a challenge owing to the highly volatile and hydrophilic nature of ionic Ti precursors. The discovery of MIL-125 marked a breakthrough in Ti-cluster coordination chemistry. Combining it with NH2 chromophores to form NH2-MIL-125 enhanced its structural design and extended its activity into the visible light region. This review delves into the high-performance photocatalytic properties of NH2-MIL-125, focusing on its applications in H2O2 and H2 production, CO2 and N2 reduction, drug and dye degradation, photocatalytic sensors, and organic transformation reactions. The discussion considers the influence of the Ti precursor, coordination environment, synthesis process, and charge transfer mechanisms. Numerous strategic methods have been discussed to improve the performance of NH2-MIL-125 by incorporating linker modification, metal node modification, encapsulation of active species, and post-modification for enhancing light absorption ability, promoting charge separation, and improving photocatalytic efficiency. Moreover, future perspectives include methods to investigate how the efficiency of NH2-MIL-125-based materials can be planned in promoting research by highlighting their versatility and potential impacts in the area of photocatalysis.

Towards Solid-State Batteries Using a Calcium Hydridoborate Electrolyte.

Solid-state batteries created from abundant elements, such as calcium, may pave the way for cheaper and safer electrical energy storage. Here we report a new type of solid calcium hydridoborate electrolyte, Ca(BH4)2·2NH2CH3, with a high ionic conductivity of σ(Ca2+) ~ 10-5 S cm-1 at T = 70 °C, which is assigned to a relatively open and flexible structure with apolar moieties and weak dihydrogen bonds that facilitate migration of Ca2+ ions in the solid state. The compound display a low electronic conductivity, providing an ionic transport number close to unity (tion = 0.9916). Calcium plating is observed for a Ca|Ca(BH4)2·2NH2CH3|Pt electrochemical cell and the electrodes are investigated using scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS) that reveal a rugged Ca anode surface owing to the stripping process and the presence of Ca-containing domains on the Pt working electrode from the plating process. Improved electrochemical reversiblity was achieved in a three-electrode cell configuration using a CaxSn counter and reference electrode and a Sn working electrode, CaxSn|Ca(BH4)2·2NH2CH3|Sn, providing reversible Ca plating and stripping.

Features of the Defect Structure of the Compositionally Homogeneous Crystal LiNbO3:Er3+(3.1 wt%) and the Gradient Crystal LiNbO3:Er3+ and Their Manifestation in the IR Transmission Spectra in the Region of Stretching Vibrations of Hydrogen Atoms of OH−-Groups

Based on the analysis of the IR transmission spectra in the region of stretching vibrations of hydrogen atoms of OH−-groups, it was established that the oxygen-octahedral МеО6 clusters (Ме-Li+, Nb5+, vacant octahedron V, impurity ion) of the structure of the compositionally homogeneous crystal LiNbO3:Er3+(3.1 wt%) and the gradient crystal LiNbO3:Er3+(congruent composition by the main components, Er gradient of 0.55 at%/cm) have a shape close to the regular one. In this case, the value of R = [Li]/[Nb] ≈ 1, and in the structure of both crystals, there are practically no point defects in NbLi responsible for the photorefraction effect. By using the IR transmission spectra and Klauer’s method, it was found that the volume concentration of OH−-groups in the gradient crystal LiNbO3:Er3+ is almost an order of magnitude lower than in the compositionally homogeneous LiNbO3:Er3+(3.1 wt%) crystal. This fact explains the lower hydrogen conductivity of the gradient crystal LiNbO3:Er3+ and the lower photorefraction effect compared to the compositionally homogeneous LiNbO3:Er3+(3.1 wt%) crystal. The results obtained are important for the development of materials for active nonlinear laser media and for the conversion of laser radiation.

Recent Advances in Transition Metal Chalcogenides Electrocatalysts for Oxygen Evolution Reaction in Water Splitting

Rapid industrial growth has overexploited fossil fuels, making hydrogen energy a crucial research area for its high energy and zero carbon emissions. Water electrolysis is a promising method as it is greenhouse gas-free and energy-efficient. However, OER, a slow multi-electron transfer process, is the limiting step. Thus, developing efficient, low-cost, abundant electrocatalysts is vital for large-scale water electrolysis. In this paper, the application and progress of transition metal chalcogenides (TMCs) as catalysts for the oxygen evolution reaction in recent years are comprehensively reviewed. The key findings highlight the catalytic mechanism and performance of TMCs synthesized using single or multiple transition metals. Notably, modifications through recombination, heterogeneous interface engineering, vacancy, and atom doping are found to effectively regulate the electronic structure of metal chalcogenides, increasing the number of active centers and reducing the adsorption energy of reaction intermediates and energy barriers in OER. The paper further discusses the shortcomings and challenges of TMCs as OER catalysts, including low electrical conductivity, limited active sites, and insufficient stability under harsh conditions. Finally, potential research directions for developing new TMC catalysts with enhanced efficiency and stability are proposed.

Study on the Preparation and Electrochemical Properties of LiFe0.4Mn0.6PO4 Coated with Bamboo Shaving-Based Carbon.

LiFe1-xMnxPO4 (0 < x < 1) has a high operating voltage range and theoretical energy density, but its actual capacity decreased due to its low electronic conductivity. To overcome this problem, we successfully prepared LiFe0.4Mn0.6PO4/C (LFMP/C) with a uniform carbon coating by a one-step solvothermal method using bamboo shavings as the carbon source. The results showed that heating at a reaction temperature of 180 °C for 18 h was the optimal synthesis condition to obtain LFMP/C. The addition of bamboo shaving-based carbon was effective in inhibiting excessive grain growth and reducing particle size. The disordered carbon layer enhanced the surface conductivity by connecting the surfaces of the particles. The synergistic effect of the nanoparticle size and the pores distributed around the particles increased the specific surface area and thus improved the contact area between the active substance and the electrolyte. Furthermore, there were improvements in electronic conductivity and ionic mobility. LFMP/C-16 showed initial discharge capacities of 150.1 and 143.5 mAh·g-1 at rates of 0.1 and 0.2C, respectively, with a capacity retention rate of 97.73% after 100 cycles, indicating excellent cyclic performance.

Effects of Unit Cell Size on Thermal Conductivity in Two Different Polymorphs of Niobium Diselenide.

2D materials possess weak inter-layer van der Waals bonding, allowing them to exist as different polymorphs depending on the stacking sequence of the layers. Herein, the thermal conductivities of the 2H-NbSe2 and 2H-3R-NbSe2 polymorphs by conducting experimental measurements and theoretical analysis are comparatively studied. Owing to its 1.8 times larger unit cell, 2H-3R-NbSe2 has a considerably greater number of optical phonon branches than does 2H-NbSe2, suggesting that 2H-3R-NbSe2 absorbs thermal energy rather than transporting it. In addition, scattering is more likely to occur in 2H-3R-NbSe2 because a far greater number of states satisfy the selection rule. As a result of these, the 2H-3R-NbSe2 has considerably lower thermal conductivity than that of the 2H-NbSe2. The results highlight how the size of the unit cell affects the thermal conductivities of polymorphs.

Nanomaterials for Zinc Batteries—Aerogels

Aqueous zinc batteries, mainly including Zn-ion batteries (ZIBs) and Zn–air batteries (ZABs), are promising energy storage systems, but challenges exist at their current stage. For instance, the zinc anode in aqueous electrolyte is impacted by anodic dendrites, hydrogen and oxygen precipitation, and some other harmful side reactions, which severely affect the battery’s lifespan. As for traditional cathode materials in ZIBs, low electrical conductivity, slow Zn2+ ion migration, and easy collapse of the crystal structure during ion embedding and migration bring challenges. Also, the slower critical oxygen reduction reaction (ORR), for example, in ZABs shows unsatisfactory results. All these issues greatly hindered the development of zinc batteries. Aerogel materials, characterized by their high specific surface area, unique open-pore structure formed by nanoporous structures, and excellent physicochemical properties, have a positive role in cathode modification, electrode protection, and catalytic reactions in zinc batteries. This manuscript provides a systematic review of aerogel materials, highlighting advancements in their preparation and application for zinc batteries, aiming to promote the future progress and development of aerogel nanomaterials and zinc batteries.

MXene Nanoribbon Aerogel-Based Gradient Conductivity Electromagnetic Interference Shields with Unprecedented Combination of High Green Index and Shielding Effectiveness.

The desire to reduce secondary pollution from shielded electronics devices demands electromagnetic interference (EMI) shields with high green index (GI), which is the ratio of absorbance over reflectance. Achieving high GI values simultaneously with high shielding effectiveness (SE) over 50dB is a serious unresolved challenge. Reducing the impedance mismatch between the shield and free space is the key to reducing the reflection of incoming radiation and enabling more penetration into the body of the shield for absorption. Here a sandwich structure with gradient conductivity is introduced that achieves a combination of high GI (≈2) and SE (70dB). The top layer deliberately uses an aerogel of low conductivity MXene nanoribbon in PEDOT:PSS polymer to boost the GI. The aerogel also reduces the permittivity of the shield, as another way to reduce the impedance mismatch for a nonmagnetic material. The bottom layer consists of a MXene nanosheet-polymer with its high metal-like conductivity to provide high SE. This successful demonstration is expected to lead to other novel ways to create conductivity gradient EMI shields.

Oligomeric Carbazole Phosphonic Acid as Hole‐Transporting Layer for Organic Solar Cells With Efficiency of 19.63%

AbstractA class of self‐assembly monolayers, distinguished by a carbazole‐conjugated backbone pendant with phosphonic acid (PA) side units, are widely used as hole‐transporting layers (HTL) in organic solar cells (OSCs). However, challenges such as pronounced aggregation tendency and low conductivity have hindered their widespread applications. This study addresses these limitations by introducing novel oligomeric PA designs to overcome the drawbacks associated with monolayer HTLs. The newly synthesized oligomer integrates carbazole backbones and PA side units through Suzuki polymerization, showing absorption characteristics similar to small molecules, but with reduced aggregation and improved hole transport properties. OSCs using such a HTL achieve an impressive efficiency of 19.63% with remarkable stability. These results highlight the potential of oligomeric HTLs as promising materials for realizing efficient OSCs.

Modelling the effect of deposited grid material on the power coupling of radio frequency ion thrusters

For radio-frequency(RF) ion thrusters, under nominal operating conditions, sputtering of the screen grid can lead to the formation of a conductive film of the grid material on the inner walls of the discharge chamber which leads to a decrease in RF coupling to the plasma. When the ion beam becomes unfocused, either due to off nominal operating conditions or as a result of lifetime degradation, this process can be accelerated. An RF ion thruster performance model is developed, which can quantitatively simulate the performance degradation caused by sputter deposition on the thruster. This model couples an RF power transmission model, a zero-dimensional thruster discharge chamber model, and a sputter deposition model. An experiment that intentionally enhances the erosion of the accelerator grid to accelerate the formation of the conductive film confirms the power transmission process described by the model. As a result, the deposition on the discharge chamber walls primarily originates from the sputtering of the accelerator grid by the ion beam. At a xenon flow rate of 0.63 sccm and RF power of 42 W, a 2.015 μm copper film deposited on the walls resulting in a decrease in thruster screen grid current. The simulated results indicate that the power absorbed by the plasma decreases after deposition, which is the primary cause of the screen grid current reduction. Using materials with low conductivity for the deposition layer in the construction of the accelerator grids can reduce the impact of the deposition layer on the thruster screen grid current.

Vertical Graphene Growth on LDH Nanosheets and Carbon Cloth Nanofibers with NiCo Nanoparticles as a Freestanding Host for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur batteries have been recognized as one of the excellent candidates for next-generation energy storage batteries because of their high energy density and low cost and low pollution. However, lithium-sulfur batteries have been challenged by low conductivity, low sulfur utilization, poor cycle life, and the shuttle effect of polysulfides. To address these problems, we report here an independent mixed sulfur host. First, NiCoAl-layered double hydroxide (LDH) nanosheets were uniformly grown on carbon cloth (CC) by a hydrothermal method. Then, vertical graphene (VG) was uniformly vertically grown on the composite structures to form VG@LDH/CC by a plasma enhanced chemical vapor deposition (PECVD) method. Graphene and LDH nanosheets forming a three-dimensional mesh structure can effectively physically block lithium polysulfides, store singlet sulfur, and improve the conductivity of the cathode. In addition, during the growth of graphene, the Ni and Co ions in the LDH nanosheets are reduced to NiCo nanoparticles, which can enhance the chemical adsorption of polysulfides, thus effectively mitigating the "shuttle effect" and improving the electrical conductivity of the material. The lithium sulfur batteries with derived sulfur anodes (VG@LDH/CC-S) exhibited excellent electrochemical properties, including excellent rate performance (780.8 mAh g-1 at 3C) and impressive cycling stability (capacity decay of about 0.0755% per cycle after 750 cycles at 0.5C).

Optimization strategies for high-performance aqueous zinc-sulfur batteries: challenges and future perspectives

Aqueous zinc-sulfur batteries (AZSBs) have emerged as promising candidates for high-energy density, cost-effective, and environmentally sustainable energy storage systems. Despite their potential, several challenges hinder the realization of high-performance AZSBs, including sluggish reaction kinetics, disproportionation reactions of ZnS in water, low conductivity and volume expansion of the sulfur cathode, poor wetting properties, and dendrite growth issues of the zinc anode. This review comprehensively summarizes optimization strategies for overcoming these challenges. We discuss cathode modification approaches, such as sulfur/carbon composites, sulfide composites, and catalytic sulfur matrices, which address low conductivity and volume expansion while enhancing sulfur conversion reaction kinetics. Additionally, electrolyte engineering strategies, including the use of iodide-based additives and co-solvent modifications, are examined for their effectiveness in improving reaction kinetics and wetting properties. Despite these advancements, AZSBs still face issues with long-cycle stability. Therefore, this review proposes future perspectives for the development of AZSBs. We aim to provide valuable insights into sulfur-based cathode materials and advance the achievement of high-performance AZSBs.

Characterization of phase-changing materials as stabilized thermal energy storage in impregnated biomaterial

In recent years, impregnation of biomaterial (wood veneers) with eutectic phase change materials (PCM) has been investigated to increase the thermal capacity of bio-based materials, which significantly affects the thermal capacity, especially in building applications requiring low heat. In this study, four eutectic phase change materials were prepared using three different fatty acids and impregnated on two wood veneers (oak and ash). The structural characterization of the prepared eutectic mixtures was examined using FT-IR, while the morphological properties of the wood veneers were examined by scanning electron microscopy (SEM). The thermal performance was analyzed via differential scanning calorimetry (DSC) and their thermo-mechanical properties by dynamic mechanical analysis (DMA). Additionally, the thermal conductivity ( k values) was determined. From the results obtained, it was possible to prepare eutectic mixtures with melting temperatures around 30°C with heat capacities up to 225.5 J/g. It was also generally determined that eutectic PCM, prepared from mixtures of lauric acid and palmitic acid, have lower thermal conductivity but show higher storage and loss modulus for the wood coatings leading to a balance between mechanical and thermal properties.

Multifunctional Polar Polymer Boosting PEO Electrolytes toward High Room Temperature Ionic Conductivity, High-Voltage Stability, and Excellent Elongation.

Poly(ethylene oxide) (PEO) has been widely studied as an electrolyte owing to its excellent lithium compatibility and good film-forming properties. However, its electrochemical performance at room temperature remains a significant challenge due to its low ionic conductivity, narrow electrochemical window, and continuous decomposition. Herein, we prepare a multifunctional polar polymer to optimize PEO's electrochemical properties and cycling stability. PEO's crystallinity is disrupted with the addition of polar polymer, and the amorphous polymer segments create more transfer pathways for Li-ion. More importantly, the polar groups enhance PEO's Li-ion transference number by facilitating lithium salt dissociation through Lewis acid-base interactions and weaken the coordination between Li-ion and ether oxygen, thereby expediting Li-ion migration. In addition, the trifluoromethyl groups promote TFSI- defluorination, forming LiF-rich solid electrolyte interphase layers that prevent continuous decomposition of PEO. The resulting composite electrolyte exhibits excellent room temperature ionic conductivity (2.06 × 10-4 S cm-1) and Li-ion transference number (0.30) and outstanding voltage (4.9 V). The assembled symmetric lithium battery could perform stably for 620 h at 0.1 mA cm-2. Li||LiFePO4 cells exhibit excellent capacity retention (87.81%) and Coulombic efficiency (100.0%) at 0.5 C over 700 cycles.

Development of Thermally Insulating Nonwovens from Milkweed Fibers Using an Air-Laid Spike Process

Milkweed (MW) fiber is a natural fiber that provides tremendous thermal insulation properties due to its lightweight hollow structure. This study aimed to investigate the effect of milkweed fiber as a thermal fiber in nonwovens. Milkweed fibers were blended with a low-melt fiber consisting of a polyethylene terephthalate core, a polyolefin sheath (LM 2.2), and polylactic acid (PLA) fiber. Nonwovens with different fiber contents were manufactured using an air-laid Spike process to determine their effect on thermal and mechanical properties. Then, the nonwovens were compared with Thinsulate® and Primaloft®, two commercially synthetic insulation products. Structural properties, including mass per unit area, thickness, and porosity and thermal properties were studied. Furthermore, compression and short-term compression recovery were also evaluated. The results revealed that milkweed-based nonwovens that contained 50 wt% or 70 wt% of milkweed presented a lower thermal conductivity than synthetic nonwovens. Milkweed nonwovens of the same thickness provided identical thermal resistance as Thinsulate® and Primaloft. Sample 3, composed of 50 wt% MW, 20 wt% LM 2.2, and 30 wt% PLA, demonstrated the same thermal insulation as Thinsulate® with a weight three times lighter. Milkweed nonwovens presented higher moisture regain values than Thinsulate® and Primaloft®, without affecting thermal conductivity.

α-ZnO Manipulated Growth of Ag Gird on AgNWs Enables High Conductive Flexible Electrode for Large-Area Monolithic Organic Photovoltaics.

The conductivity of AgNWs electrodes can be enhanced by incorporating Ag grids, thereby facilitating the development of large-area flexible organic solar cells (FOSCs). Ag grids from vacuum evaporation offer the advantages of simple film formation, adjustable thickness, and unique structure. However, the complex 3D multi-component structure of AgNWs electrodes will exacerbate the aggregation of large Ag particles, causing the device short circuits. To address this issue, the relationship between the surface energy of modification layers and the morphology and conductivity of ultrathin Ag on AgNWs is studied. The amorphous ZnO (α-ZnO) layer promotes Ag growth from Volmer-Weber (VW) to Frank-Van der Merwe (FM), reducing particle aggregation. The 1µm thick PET/AgNWs/Ag grid electrode with α-ZnO exhibited low contact resistance and high conductivity. As a result, 1cm2 FOSCs with Ag grids achieve a power conversion efficiency (PCE) of 16.01%. As the area increased to 4 and 9cm2, the performance of the monolithic FOSCs is 14.70% and 12.69%, showing less efficiency loss during upscaling. The 8 and 16cm2 modules constructed by series and parallel connection of the monolithic devices yield PCEs of 14.47% and 12.92%, respectively. This study offers valuable insights into constructing Ag grids on AgNWs electrodes for highly efficient large-area FOSCs.

A Review of the Application of Metal-Based Heterostructures in Lithium–Sulfur Batteries

Lithium–sulfur (Li-S) batteries are recognized as a promising alternative in the energy storage domain due to their high theoretical energy density, environmental friendliness, and cost-effectiveness. However, challenges such as polysulfide dissolution, the low conductivity of sulfur, and limited cycling stability hinder their widespread application. To address these issues, the incorporation of heterostructured metallic substrates into Li-S batteries has emerged as a pivotal strategy, enhancing electrochemical performance by facilitating better adsorption and catalysis. This review delineates the modifications made to the cathode and separator of Li-S batteries through metallic heterostructures. We categorize the heterostructures into three classifications: single metals and metal compounds, MXene materials paired with metal compounds, and heterostructures formed entirely of metal compounds. Each category is systematically examined for its contributions to the electrochemical behavior and efficiency of Li-S batteries. The performance of these heterostructures is evaluated in both the cathode and separator contexts, revealing significant improvements in lithium-ion conductivity and polysulfide retention. Our findings suggest that the strategic design of metallic heterostructures can not only mitigate the inherent limitations of Li-S batteries but also pave the way for the development of high-performance energy storage systems.

Synergistic Effects of Fe3O4/N-Doped Porous Carbon Nanospheres for Enhanced Oxygen Reduction Reaction.

Designing transition metal oxide (TMO)/porous carbon composite materials for the oxygen reduction reaction (ORR) is a promising strategy in high-performance fuel cell technology. In this study, we used the isolation effect and pore-creating properties of Zn2+ to fabricate a composite material comprising ultrasmall Fe3O4 particles anchored on hierarchically N-doped porous carbon nanospheres. This material, referred to as CPZ1.0-Fe0.1, serves as an efficient ORR electrocatalyst in alkaline fuel cells. CPZ1.0-Fe0.1 exhibits outstanding ORR catalytic activity with a half-wave potential of 0.86 V in a 0.1 M KOH solution, surpassing that of the Pt/C catalyst (0.82 V). Furthermore, CPZ1.0-Fe0.1 exhibited excellent stability with minimal current degradation after 18 h of continuous testing. The superior ORR catalytic performance can be attributed to the synergistic effect between the catalytic sites and the high conductivity of porous carbon. The porous carbon nanospheres effectively address the low conductivity of Fe3O4 nanoparticles, while the ultra-small Fe3O4 nanoparticles anchored on the carbon surface provide efficient catalytic sites for the ORR.

Lattice thermal conductivity in CrSBr: the effects of interlayer interaction, magnetic ordering and external strain.

With the continuous development of digital information and big data technologies, the ambient temperature and heat generation during the operation of magnetic storage devices play an increasingly crucial role in ensuring data security and device stability. In this study, we examined the lattice thermal conductivity of the van der Waals magnetic semiconductor CrSBr from bulk to monolayer structures using first-principles calculations and the phonon Boltzmann transport equation. Our results indicated that lattice thermal conductivity show anisotropy and CrSBr bilayer exhibits lower thermal conductivity at all temperatures. Through the analysis of phonon spectra. phonon lifetime, heat capacity, scattering probability, phonon-phonon interaction strength, we demonstrated that Cr-Br antisymmetrical stretching vibrations and phonon band gap are the main factors, which exhibit considerable dependence on layer number, magnetic ordering and strain effects. These results offer a comprehensive insight into phonon transport phenomena in van der Waals magnetic materials.&#xD.

Aortic Valve Surgery in Patients Over 75 Years Old: Early Results and Predictors of Hospital Mortality

Background: Aortic valve surgery is the most essential part of worldwide heart valve surgery. In recent decades, the patient profile has changed even in our country, with the age of patients undergoing aortic valve surgery increasing significantly. The primary objectives of this study are the early results of aortic valve replacement surgery in patients over 75 years old and the negative predictors that affect hospital mortality. Materials and Methods: This is a retrospective study of 73 patients over 75 who underwent aortic valve surgery in 2014-2021 in our Cardiac Surgery Service, University Hospital Center “Mother Theresa” in Tirana. The patients' data regarding demographic, preoperative, operative, and postoperative variables were collected from the hospital's medical records. The data are presented in mean values and standard deviation. T-test and chi-squared test are also used. Results: This study involved 73 patients, 50 males and 23 females. The age range was 75-85, averaging 77.12±2.31 years. Hospital mortality was 4.1%. The incidence of major perioperative complications such as low cardiac output, stroke, respiratory problems, bleeding, atrial fibrillation, wound infection, and conduction disturbances was 6.8%, 2.7 %, 4.1%, 2.7 %, 21.9 %, 2.6%, and 4.2 %. Conclusions: Aortic valve surgery for elderly patients over 75 can be performed well. Concomitant procedures, prolonged extracorporeal circulation, and emergency intervention expose the patient to a high operative risk.