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Supercapacitor electrodes: Is nickel foam the right substrate for active materials?
Get PDFNi foam is an extensively used current collector and substrate in investigations of electrochemically active materials such as supercapacitors and electrocatalysts for oxygen and hydrogen evolution reactions. This material is relatively cheap, porous, and conductive and has a large specific surface area, all of which make it a good substrate. We investigated Ni-Mg ferrites and NiMn2O4 as active materials for electrochemical energy storage. These materials, when loaded on Ni foam, gave promising capacitance values: 172 F/g (at 2 mV/s) for NiMn2O4 in 6 M KOH and 242 F/g (at 2 mV/s) for MgFe2O4 in 3 M KOH. Nevertheless, during the authors’ work, many experimental problems occurred. Inconsistencies in the results directed further investigation towards measuring the capacitance of the active materials using GCE and platinum electrodes as substrates to discover if Ni foam was the culprit of the inconsistencies. When non-nickel substrates were used, both NiMn2O4 and MgFe2O4 showed reduced capacitance. Experimental problems associated with the utilization of Ni foam as a substrate for active materials in supercapacitor electrodes are discussed here, combined with other problems already addressed in the scientific literatur
Anatomical Characteristics and Assessment of Wood Fibers Quality of Mature Pedunculate Oak (Quercus robur L.) Trees Grown in Different Environmental Conditions
Get PDFFrom productive and ecological point of view, Quercus robur L. is an extremely important species and the investigation of its anatomical properties is very significant in terms of its technical and technological utilization. The paper deals with the analysis of the wood fiber characteristics (fiber length, fiber lumen width, double-cell wall thickness, Runkel ratio) of mature pedunculate oak trees in the non-flooded (Management Unit "Vinična-Žeravinac-Puk") and flooded area (Management Unit "GVO 83 b"). One of the aims of the study is to determine the wood fiber quality and the possibility of use in paper and pulp production. When the mean values of the analysed anatomical characteristics are compared, the results show slightly higher values in the non-flooded area, except for the Runkel ratio. The radial pattern of the investigated characteristics depending on the age shows growth in the non-flooded area, while the same tendency in the flooded area was found for the fiber length only. It was recorded that fiber lumen width, double-cell wall thickness and Runkel ratio decreased in the final annual rings. The wood fiber quality for use in pulp and paper production is the greatest in the juvenile zone, unlike sapwood zone, regardless of the site conditions
Use of sodium oxalate and calcium formate for chemical activation of high volume fly ash (HVFA) binders
Get PDFThis study investigates hydration mechanism of a high volume fly ash (HVFA) binder, comprising 70 wt.% of fly ash (FA), chemically activated by using sodium oxalate (Na2C2O4) and calcium formate (Ca(HCOO)2). Prior to the binder synthesis, mechanical activation of FA was employed. Effects of the activators on the properties of the HVFA binders were determined by measuring setting times and compressive strength of the binders. Heat of hydration, pore solution composition, bound water and portlandite content, mineral composition, and microstructure of HVFA binder pastes were analyzed in order to compare the hydration mechanisms of the HVFA binders activated with the selected activators. The obtained results indicated that using of the two different activators led to the enhancement of the properties of the HVFA binders, but it was achieved in two distinct ways. It was found that the use of Ca(HCOO)2 mitigated adverse effects of the high alkalinity of the pore solution of chemically activated HVFA binder on hydration process and strength development in the later period. Therefore, it was concluded that Ca(HCOO)2 was more suitable for chemical activation of HVFA binders, compared to Na2C2O4
The use of HOA (Hemiptera-Orthoptera-Aves) Indicators to formulate the Serbian Climate Change Index (SCCI)
No full textThe study aimed to provide data on three faunistic groups (Hemiptera, Orthoptera and birds) used as indicators of climate change as well as to formulate area-specific climate change index (the Serbian Climate Change Index - SCCI). Based on the data obtained, a total of 56 indicator taxa (10 hemipteran, 21 orthopteran and 25 bird species) belong to 17 families were included from the entire territory of Serbia. The SCCI is based on the statement that these species have expanded their distribution ranges and population density throughout Serbia during last decade (2012 2022) as well as predictions to inhabitat still inhabitable habitats in the Peripannonian and Pannonian regions. Some of species, predominantly hemipteran and orthopteran, had acquired new habitat preference (e. g. expanded to urban areas) moving northwardly with their range and abundance expansion. On the other hand, as consequence of climate change and global warming, some species were found to be indicators of environmental degradation and habitat fragmentation
Data-driven prediction of fracture toughness size effect in ductile-to-brittle transition using Two-Step-Scaling procedure
No full textThe fracture properties of ferritic steels in transition temperature region are usually statistically treated by models that presuppose the existence of various forms of quenched disorder (critical cleavage triggers). In this study, the fracture toughness from the Euro fracture toughness dataset (stress intensity factor used in the master curve KJc) for reactor steel 22NiMoCr37 is used with the aim of outlining a methodology for using the recently proposed two-step scaling (2SS) method. Three widely different temperatures ( 154 ºC, -91 ºC, and 0 ºC), which cover the entire range from lower shelf to upper shelf fracture, are selected to demonstrate the accuracy of extrapolation and interpolation of the fracture toughness CDF (cumulative distribution function) and the pertinent issues related to the procedure application. The obtained predictions at the two lower temperatures are in good agreement with the experimental results and well within the inherent experimental data scatter, while 2SS method is shown not to be applicable in upper-shelf transition region. Special attention is devoted to the effect of statistical sample size on prediction accuracy/reliability along with the minimum sample size requirement. Moreover, the reduction in random sample size affects the Weibull parameters, which in turn impacts the accuracy of predictions, introducing a degree of uncertainty and highlighting limitations in the method
Structural, microstructural and multiferroic properties of yttrium manganite ceramics co-doped with titanium and rare-earth metals
No full textHexagonal manganites, RMnO3 (R- rare-earth element or yttrium), are multiferroic materials
with ferroelectric and antiferromagnetic ordering, that open the possibility of coupling
between them i.e. the opportunity of switching magnetization by an electric field and/or
electric polarization by a magnetic field. Hexagonal YMnO3 is the most commonly investigated
hexagonal manganite, with a high ferroelectric Curie temperature (TC ≈ 900 K) and a low Néel
temperature (TN ≈ 75 K). At room temperature, it exhibits a non-centrosymmetric structure
with space group P63cm. Microcracking and porosity observed in YMnO3 ceramics limit
application possibilities. The presented results indicated the influence of partial substitution of
Y3+ with La3+, Gd3+, Er3+ and Yb3+, and Mn3+ with Ti4+, on the properties of YMnO3 ceramics. The
Y1–xRxMn0.90Ti0.10O3+δ (R = La; Gd; Er; Yb and x = 0.005; 0.01; 0.02; 0.05) powders were synthesized
using the sol-gel, polymerization complex method from citrate precursors, and then calcinated
at 900 °C for 4 h. The ceramic samples were obtained after sintering at 1380, 1400 or 1420 °C
for 2 h, depending on the type of dopant and its concentration. All doped samples crystallized
in rhombohedral 1×1×3 superstructure with R3c space group, without the presence of
secondary phases. The morphology of the samples revealed non-uniform grain shapes and wide
ranges of grain sizes, with a mostly low concentration of microcracks and inter- and
intragranular pores. The ferroelectric response of doped samples did not significantly improve
relative to YMn0.90Ti0.10O3+δ, but they showed a reduction of the leakage current density. The
magnetic behavior of the ceramic samples indicated suppression of antiferromagnetic ordering,
observed through the shape of hysteresis curves and the increase in magnetization, which can
be attributed to the weakening of geometrical frustration. The observed enhancement of weak
ferromagnetism in samples depended on the dopant type and concentration
Hybrid supercapacitors with nickel manganite as a cathode and sodium alginate-derived carbon as an anode material
No full textElectric energy storage (EES) devices are mainly batteries and supercapacitors. Each have their own set of characteristics. While batteries store energy via diffuse-controlled, Faradaic redox processes, supercapacitors store energy by rapidly forming electrostatic double-layer. Batteries exhibit high energy density, while supercapacitors exhibit high power density. [1] Supercapacitors can have hundreds of thousands life cycles while lithium ion batteries, for example, have around 1000 of them. Hybrid supercapacitors are relatively novel devices that tend to combine advantages of both batteries and supercapacitors while overcoming their disadvantages. Hybrid supercapacitors employ both types of electric energy storage mechanisms, Faradaic redox and capacitive processes. [2] One electrode, typically composed of metal oxides, hydroxides, or phosphates, stores energy through redox reactions, while the other electrode, typically constructed from carbonaceous materials, stores energy through capacitive processes.
Nickel manganite, NiMn2O4, is a versatile transition metal oxide, with interesting electrical and magnetic properties. Its inverse cubic spinel structure indicates that it contains a variety of nickel and manganese ions at different sites in different oxidation states. This unique arrangement enables high electrical conductivity [3]. NiMn2O4 has been in the focus of electric energy storage research along with other transition metal oxides in order to downsize the production of cobalt- and lithium-derived oxides in devices that are already commercially used.
Sodium alginate is a polysaccharide naturally found in brown algae. It can be used to synthesize carbonaceous materials [4].
The work presented contains reports on synthesis, characterization and EES properties of nano-sized nickel manganite synthesized via electrospinning and glycine-nitrate sol-gel combustion processes followed by calcination at 400 and 800 °C to obtain pure spinel oxide. Amorphous carbon was also synthesized via pyrolitic carbonization of lyofilized sodium-alginate hydrogel. Nickel manganite and amorphous carbon were tested in 6 M KOH, 2 M LiOH, 1 M Na2SO4 and 1 M H2SO4 in a three-electrode cell via cyclic voltammetry and galvanostatic chronopotentiometry. NiMn2O4 showed the highest activity in alkaline electrolytes, while amorphous carbon showed capacitive-type energy storage performance in both alkaline and acidic electrolytes. Standard two-electrode sandwich cell was formed with NiMn2O4 as a cathode and amorphous carbon as an anode material. The cell performance was evaluated via cyclic voltammetry and galvanostatic chronopotentiometry followed by stability tests. Considerable capacitance values of the formed hybrid supercapacitor devices were obtained.
References
1. T. S. Mathis, N. Kurra, X. Wang, D. Pinto, P. Simon, Y. Gogotsi, Adv. Energy Mater. 9 (2019) 1902007 https://doi.org/10.1002/aenm.201902007
2. M. Z. Iqbal, U. Aziz, J. Energy Storage 46 (2022) 103823 https://doi.org/10.1016/j.est.2021.103823
3. M.P. Dojcinovic,Z.Z. Vasiljevic, J. Kovac, N.B. Tadic, M.V. Nikolic, Chemosensors 9 (2021) 241 https://doi.org/10.3390/chemosensors9090241
4. L. Liu, Y. Lu, D. Qiu, D. Wang, Y. Ding, G. Wang, Z. Liang, Z. Shen, A. Li, X. Chen, H. Song, J. Colloid Interface Sci. 620 (2022), 284-292 https://doi.org/10.1016/j.jcis.2022.04.022
Response of maize (Zea mays L.) on yield, physiology and stomatal behaviour under two different elevated CO2 concentrations. Do these anatomical changes affect the physiology of the C4 crop plant under high CO2 conditions?
No full textRising CO2 concentration in the atmosphere is a matter of global concern and poses apprehension about how plants will adapt to the changing environment. Various studies have proved that under high CO2 levels, plant physiology alters and affects plant functioning. However, under elevated CO2, the stomatal characters and their relation with physiological responses are still not yet clear. To find out these changes in the stomatal parameters at ambient and two elevated CO2 (550 ppm and 700 ppm) levels, four genotypes of maize (Zea mays L.) viz. DHM-117, Harsha, Varun and M-24 were grown in open-top chambers. In the study, it was observed that the stomatal density increased, stomatal size altered, stomatal conductance (gs) and transpiration rate (Tr) decreased under elevated CO2 (eCO2) while photosynthetic rate (Pn), water use efficiency (WUE), yield and biomass, of which especially the reproductive biomass increased. Under eCO2, stomatal and physiological changes were genotypic and CO2 concentration specific. Increased stomatal density at eCO2 was mainly due to increased abaxial stomatal density. The improved Pn and reduced Tr at 550 ppm
improved the WUE in the plants, while this response was not observed at 700 ppm. These results elucidate that this C4 crop responded positively to up to 550 ppm of CO2 concentrations, and beyond this, the impact was minimal
Exploring the link between microplastic and genotoxicity in fish
No full textWorldwide, reports of MPs in various environmental compartments have been growing. Despite the fact that rivers are thought to be one of the main sources of plastic waste, not much is known about them. Fishes are one the most valuable sources to estimate the level of MP pollution in rivers due to their position in the food chain. Here, we aimed to connect ingested MPs in the intestine to other environmental factors and their effects on genotoxicity in fish blood. A total of 15 specimens of common bream (Abramis brama) were collected during 2022 from the Danube River in Belgrade, in the area where the river receives untreated communal and wastewater. Tissue samples were collected: blood for genotoxicity analysis (comet assay) and gastrointestinal tract for MP analysis. After digestion with KOH 10%, the digests were filtered using a vacuum filtration system with a 50 μm stainless steel
mesh. The particles were directly visualised under a light stereomicroscope to classify and identify the MPs found according to their shape, colour, and size. A total of 21 MP particles were found in 11 specimens (73%). Regarding the MP shapes, it was identified 20 microfibers (95%) and 1 fragment (5%). Concerning the colour, it seems that blue microfibers were dominant (66.67%), followed by black (9.52%) and purple microfibers (9.52%), followed by red (4.76%) and brown microfibers (4.76%), and white fragment (4.76%). The size of the microfibers ranged between 135.81 μm and 2516.73 μm, with an average of 677.94±337.13 μm. DNA damage in blood ranged between 9.76 and 46.03 TI, with an average of 25.18±13.32 TI. Although there was no direct positive correlation between the number of MPs particles and DNA damage in samples, the high number of MPs could be interpreted as an indirect link to river pollution pressure and strong genotoxic potential
Pathobiome and Microbial Community Shifts Associated with Vegetable, Fruit, and Cereal Crops
No full textIt is estimated that by 2050, world food production must increase by 40% to meet the growing food needs, while food security and crop protection are concerns of utmost significance. Plant pathogens represent an insidious threat to agriculture, and they are accounted for a loss of more than 15% of global crop yield annually. However, agriculture still relies on massive consumption of chemical pesticides. Furthermore, between 2000 and 2020, the total agricultural use of inorganic fertilizers (nitrogen, phosphorus, and potassium) increased in all world regions, reaching 201 million tonnes in 2020. The prosperity of sustainable agriculture will only be possible if the integration of biotechnology is combined with traditional agricultural practices. We are aware that an increase in crop yields and disease resistance can be achieved by genetic engineering. Therefore, it is important to acknowledge that plants harbour complex microbial communities known as microbiomes that play a crucial role in plant productivity, health, and stress tolerance