Synergistic effects of zirconium- and aluminum co-doping on the thermoelectric performance of zinc oxide

This work aims to explore zirconium as a possible dopant to promote thermoelectric performance in bulk ZnO-based materials, both within the single-doping concept and on simultaneous co-doping with aluminum. At 1100–1223 K mixed-doped samples demonstrated around ∼2.3 times increase in ZT as compared to single-doped materials, reaching ∼0.12. The simultaneous presence of aluminum and zirconium imposes a synergistic effect on electrical properties provided by their mutual effects on the solubility in ZnO crystal lattice, while also allowing a moderate decrease of the thermal conductivity due to phonon scattering effects. At 1173 K the power factor of mixed-doped Zn0.994Al0.003Zr0.003O was 2.2–2.5 times higher than for single-doped materials. Stability tests of the prepared materials under prospective operation conditions indicated that the gradual increase in both resistivity and Seebeck coefficient in mixed-doped compositions with time may partially compensate each other to maintain a relatively high power factorpublishe

Exploring tantalum as a potential dopant to promote the thermoelectric performance of zinc oxide

Zinc oxide (ZnO) has being recognised as a potentially interesting thermoelectric material, allowing flexible tuning of the electrical properties by donor doping. This work focuses on the assessment of tantalum doping effects on the relevant structural, microstructural, optical and thermoelectric properties of ZnO. Processing of the samples with a nominal composition Zn1-xTaxO by conventional solid-state route results in limited solubility of Ta in the wurtzite structure. Electronic doping is accompanied by the formation of other defects and dislocations as a compensation mechanism and simultaneous segregation of ZnTa2O6 at the grain boundaries. Highly defective structure and partial blocking of the grain boundaries suppress the electrical transport, while the evolution of Seebeck coefficient and band gap suggest that the charge carrier concentration continuously increases from x = 0 to 0.008. Thermal conductivity is almost not affected by the tantalum content. The highest ZT~0.07 at 1175 K observed for Zn0.998Ta0.002O is mainly provided by high Seebeck coefficient (-464 µV/K) along with a moderate electrical conductivity of ~13 S/cm. The results suggest that tantalum may represent a suitable dopant for thermoelectric zinc oxide, but this requires the application of specific processing methods and compositional design to enhance the solubility of Ta in wurtzite lattice

Prospects for electrical performance tuning in Ca3Co4O9 materials by metallic Fe and Ni particles additions

This work further explores the possibilities for designing the high-temperature electrical performance of the thermoelectric Ca3Co4O9 phase, by a composite approach involving separate metallic iron and nickel particles additions, and by employing two different sintering schemes, capable to promote the controlled interactions between the components, encouraged by our recent promising results obtained for similar cobalt additions. Iron and nickel were chosen because of their similarities with cobalt. The maximum power factor value of around 200 µWm−1K−2 at 925 K was achieved for the composite with the nominal nickel content of 3% vol., processed via the twostep sintering cycle, which provides the highest densification from this work. The effectiveness of the proposed approach was shown to be strongly dependent on the processing conditions and added amounts of metallic particles. Although the conventional one-step approach results in Feand Ni-containing composites with the major content of the thermoelectric Ca3Co4O9 phase, their electrical performance was found to be significantly lower than for the Co-containing analogue, due to the presence of less-conducting phases and excessive porosity. In contrast, the relatively high performance of the composite with a nominal nickel content of 3% vol. processed via a two-step approach is related to the specific microstructural features from this sample, including minimal porosity and the presence of the Ca2Co2O5 phase, which partially compensate the complete decomposition of the Ca3Co4O9 matrix. The obtained results demonstrate different pathways to tailor the phase composition of Ca3Co4O9 -based materials, with a corresponding impact on the thermoelectric performance, and highlight the necessity of more controllable approaches for the phase composition tuning, including lower amounts and different morphologies of the dispersed metallic phases.publishe

Strontium titanate and zinc-oxide-based materials for high-temperature thermoelectric harvesting

Broad societal needs have focused increased attention to providing a sustainable energy supply to the population, based on technologies with minimal environmental impact and reduced fossil fuels usage. One solution is to improve energy conversion efficiency in key consuming sectors. Since most of the energy (60-70%) used worldwide is discharged as waste heat, ”green” thermoelectric (TE) conversion has received considerable attention due to its intrinsic simplicity, employing no moving parts, silent operation, excellent scalability and reliability, and self-sufficiency to enable mobile or remote applications. In some energy-conversion scenarios, the cost and thermal stability requirements may dominate over efficiency issues, making abundant, high-temperature-stable and low-toxic oxides an interesting alternative TE material. This talk will feature some oxide-specific approaches towards tuning the thermoelectric performance in strontium titanate and zincoxide-based materials, including defects engineering and in-situ induced nanostructuring.publishe

The Immune Profile of the Endometrium in the "Uterine Factor" of Infertility

Background: This study aimed to investigate the endometrial characteristics (pathomorphological and immunological) of women with infertility. Methods and Results: Data from an immunohistochemical study of endometrial biopsies (TNF-α, IL-10, GM-CSF, CXCL16, BCA1, TGF-β1) collected during the “implantation window” and microbiota studied by real-time polymerase chain reaction in 171 patients (21 women with unexplained infertility, 36 - chronic endometritis, 74 - tubal-peritoneal infertility, 22 - external genital endometriosis, 8 - "thin" endometrium, and 10 healthy fertile women from the comparison group) were analyzed to identify molecular signatures. Chronic endometritis was verified morphologically and immunohistochemically. Each group revealed different immune endometrial phenotypes. The basis of the "normal" phenotype was a controlled immune inflammation and a Lactobacillus-dominant microbiota (LDM) type. In contrast to the comparison group, in the group with the phenotype of chronic inflammation, an excessive immune response (overexpression of TNF-α, GM-CSF, CXCL16, BCA1, and a decrease in IL-10 and TGF-β1 in glandular epithelium and stroma) was determined on the background of non-Lactobacillus-dominated microbiota (NLDM) type (63.3%) (P<0.001). The peculiar feature of a dysplastic phenotype was a "poor" immune response, with maximal TGF-β1 overexpression (P<0.001) and a NLDM type (47.1%). We determined an excessive immune response in the proliferative endometrial phenotype (GM-CSF overexpression by 1.2 times in the glandular epithelium and stroma [P<0.001 in both cases] and a decrease in IL-10 by 1.6 times in the glandular epithelium and 1.2 times in the stroma [P<0.001 in both cases]). Uterine microbiome disorders were detected less frequently than in patients with the inflammation phenotype (31.6%) (P=0.01). In the phenotype with impaired immune status, there was a decrease in GM-CSF, BCA1, CXCL16, TNF-α, and IL-10 markers in both endometrial compartments (P<0.001) with a LDM type (81.2%). Conclusion. The molecular signatures of the endometrium are due to the heterogeneity of immune factors and microbiota. Aberrant expression of immune factors may contribute to the formation of a microenvironment unfavorable for blastocyst implantation

Exploring the high-temperature thermoelectric performance of Al-doped ZnO ceramics prepared by in-situ aluminothermic reactions

Zinc oxide (ZnO) is a highly versatile and well-known material, widely used for its useful optoelectronic, catalytic, and photochemical properties [1]. In the search for alternative energy sources, ZnO-based ceramics emerge as promising materials for high-temperature thermoelectric (TE) applications [2], capable of direct conversion of (waste) heat to electricity, thanks to the Seebeck effect. Owing to the specific wurtzite crystal structure of this large band-gap semiconductor, donor substitutions are often performed/employed, for tailoring the electrical properties and, in this respect, aluminium is probably the most well-known and often used cation [3] for improving the charge carrier concentration and/or mobility. Additionally, nanostructuring approaches are also considered and implemented for the independent control of the different TE coefficients involved in the charge and heat transport [4], provided by their ability to promote the formation of specific microstructural features, capable of simultaneously enhancing the electrical conductivity and decreasing the lattice thermal conductivity. This work reports on the preliminary results of a combined charge carrier transport improvement / grain boundary tailoring scheme, involving the simultaneous increase in electron concentration/mobility (by doping with Al) and the engineering of defects between the highly packed grains characteristic for this material (by controlled aluminothermic reactions, providing in-situ redox conditions). The solubility of Al and the exothermic effects of aluminothermy are controlled by the careful choice of 3 different aluminium sources (for the targeted nominal composition Zn0.995Al0.005O) and a one stage sintering cycle, performed in air. The samples prepared from metallic micrometric and nanometric Al particles show the highest density values (around 96% of the theoretical value), compared with the conventional, reference Zn0.995Al0.005O samples prepared from Al2O3 (around 92% of the theoretical value). The Wurtzite phase has been found in all cases as the single phase, and the relevant microstructural changes/features, including defects formation at the grain boundaries, have only been observed for the samples prepared from the 2 different metallic aluminium sources, provided by the aluminothermic reactions. The electrical performance results show a dramatic increase in electrical conductivity, for the samples prepared from micro- and nano-sized aluminium particles, leading to a maximum power factor value of around 700 μW/K^2m, at 900 °C for the samples prepared from micrometric particles, being among the best values found in literature.Not Publishe

Elucidating Evidence for the In Situ Reduction of Graphene Oxide by Magnesium Hydride and the Consequence of Reduction on Hydrogen Storage

The current study highlights important information regarding how graphene oxide (GO) additive interacts with magnesium hydride (MgH2) and transforms to reduced graphene oxide (rGO). A mild reduction occurs during mechanical milling itself, whereas a strong reduction of GO happens concurrently with the oxidation of Mg formed during the dehydrogenation of MgH2. Owing to the in situ transformation of GO to rGO, the dehydrogenation temperature of MgH2 reduces by about 60 °C, whereas the hydrogen ab/desorption reaction kinetics of MgH2 increases by two orders of magnitude and the dehydrogenation activation energy decreases by about 20 kJ/mol. We have thoroughly scrutinized the transformation of GO to rGO by differential scanning calorimetry (DSC), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) techniques. Interestingly, the GO to rGO transformation triggered by magnesium hydride in the current study further paves the way for the facile preparation of rGO- and MgO-decked rGO composites, which are important materials for energy storage applications

Porous Carrageenan-Derived Carbons for Efficient Ciprofloxacin Removal from Water

Porous carbon materials derived from biopolymers are attractive sorbents for the removal of emerging pollutants from water, due to their high specific surface area, high porosity, tunable surface chemistry, and reasonable cost. However, carrageenan biopolymers were scarcely investigated as a carbon source to prepare porous carbon materials. Herein, hydrochars (HCs) and porous activated carbons (ACs) derived from natural occurring polysaccharides with variable sulfate content (&#954;-, &#953;- and &#955;-carrageenan) were prepared and investigated in the uptake of ciprofloxacin, which is an antibiotic detected in water sources and that poses serious hazards to public health. The materials were prepared using hydrothermal carbonization and subsequent chemical activation with KOH to increase the available surface area. The activated carbons were markedly microporous, presenting high specific surface area, up to 2800 m2/g. Activated carbons derived from &#954;- and &#955;-carrageenan showed high adsorption capacity (422 and 459 mg/g, respectively) for ciprofloxacin and fast adsorption kinetics, reaching the sorption equilibrium in approximately 5 min. These features place the ACs investigated here among the best systems reported in the literature for the removal of ciprofloxacin from water

Electrochemical behaviour of magnesium hydride-added titania anode for Li-ion battery

This work explores the electrochemical performance of a 10 wt.% MgH2 added titania anode for Li-ion half-cell batteries. We used a distribution function of relaxation times (DFRT) analysis to quantify the sources of polarisation losses from the impedance data. We observed a notable increase in both ohmic and polarisation resistance terms for the TiO2+10 wt.% MgH2 compared to the standard titania anode. Nonetheless, the modified electrode showed a significantly higher lithium diffusion coefficient than pure TiO2, with capacity retention reaching 300 mA h g−1 at 0.1C. Scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) reveals a higher surface coverage by secondary surface(s) upon lithium insertion for MgH2 added titania. Scanning Electron Microscopy (SEM) and atomic force microscopy (AFM) studies provide indirect evidence that different nanodomains with different conducting properties evolve at the anode side upon making various charging/discharging cycles.publishe