Design, characterization, and modeling of flexible supercapacitors

Superkondenzatori su uređaji za skladištenje energije sa mnogo većom gustinom energije od klasičnih kondenzatora dok znatno brže skladište i predaju energiju potrošaču u poređenju sa baterijama. Mogu da trpe znatno veći broj ciklusa punjenja/pražnjenja bez opadanja kapacitivnosti, tj. imaju mnogo duži vek trajanja od baterija. U okviru ove disertacije razvijen je nov fleksibilni samonosivi uglјenični tanak film za elektrode superkondenzatora sa velikom zapreminskom i površinskom kapacitivnošću. Povećanje kapacitivnosti postiže se uvođenjem kanala u uglјenični tanak film korišćenjem tehnologije jonskih tragova (ion-track technology). U prvom koraku sinteze, latentni tragovi se utiskuju u polazni polimer bombardovanjem brzim i teškim jonima. U sledećem koraku cilindrični kanali se formiraju selektivnim hemijskim ecovanjem duž ovih tragova. Naknadnom karbonizacijom i aktivacijom, dobijaju se fleksibilne elektrode od aktiviranog ugljenika velike specifične površine. Razvijeni novi materijal nazvan je aktivirani ugljenk sa jonskim tragovima (Activated Ion-Track Carbon A-ITC). Od serije sintesanih uzoraka, najveću površinsku (494 mF/cm2), zapreminsku (224 F/cm3) i gravimetrijsku (178 F/g) kapacitivnost ima uzorak hemijski ecovan u dužini od 40 min. Kao posledica formiranja kanala povećana je brzina superkondenzatora dok je tokom testiranja od 10 000 ciklusa punjenja i pražnjenja pokazana izuzetna stabilnost kapacitivnosti. Kroz ovu disertaciju istaknut je značaj interdisciplinarnog pristupa koji povezuje znanja iz nauke o materijalima i elektrohemije sa elektrotehnikom zarad dizajna novih uređaja za buduće primene u fleksibilnoj elektronici. Posebna vrednost ovog doktorata je razvijeni laboratorijski prototip fleksibilnog kondenzatora sa A-ITC elektrodama.Supercapacitors are energy storage devices with a much higher energy density than conventional capacitors and much faster storage and delivery of energy to the consumer compared to batteries. They can endure a significantly larger number of charge/discharge cycles without a decrease in capacitance, ie. they have a much longer lifespan then batteries. Within this dissertation, a new flexible self-supporting carbon thin film for supercapacitor electrodes with large volumetric and areal capacitance has been developed. The increase in capacitance is achieved by introducing channels into the carbon thin film using ion-track technology. In the first step of the synthesis, latent traces are imprinted into the starting Kapton polymer by bombardment with swift and heavy ions. In the next step, cylindrical channels are formed by selective chemical etching along these traces. With subsequent carbonization and activation, flexible activated carbon electrodes with large specific surface area are obtained. The developed new material is called Activated Ion-Track Carbon (A-ITC). Of the series of synthesized samples, the largest areal (494 mF/cm2), volumetric (224 F/cm3) and gravimetric (178 F/g) capacitance was obtained for the sample chemicaly etched for 40 min. As a consequence of the formation of channels, the speed of the supercapacitor was increased, while during the testing of 10 000 charge and discharge cycles, exceptional capacitance stability was shown. Through this dissertation, the importance of an interdisciplinary approach that combines knowledge from materials science and electrochemistry with electrical engineering for the design of new devices for future applications in flexible electronics is emphasized. A special value of this doctorate is the developed laboratory prototype of a flexible capacitor with A-ITC electrodes

The in vitro antioxidative and cytotoxic effects of selected Salvia species water extracts

The current paper presents antioxidant and cytotoxic activities and total phenolic and flavonoid content of the selected species of genus Salvia (Lamiaceae) growing wild in Macedonia (S. jurisicii Košanin, S. amplexicaulis Lam., S. ringens Sibth. & Sm.) and Libya (S. fruticosa Mill. and S. lanigera Poir.). Crude water extracts, obtained from aerial parts, were yielded from 6.50 to 14.32%. Total phenolic content was the highest in water extracts of S. amplexicaulis and S. ringens (226.30 and 189.01 mg GAE/g, respectively), while the flavonoids were the most abundant in S. jurisicii extract (32.36 mg QE/g). Antioxidant activities of extracts were measured using DPPH, ABTS and FRAP assays. S. amplexicaulis and S. ringens extracts showed the strongest antioxidant activity, measured using DPPH (14.21 and 23.44 μg/mL, respectively) and ABTS assays (2.91 and 2.42 mg AAE/g, respectively). In FRAP assay, S. amplexicaulis and S. fruticosa extracts exhibited strongest activity (1406.73 and 1191.51 µmol Fe(II)/g). Water extract of S. amplexicaulis and S. ringens performed the strongest cytotoxic activity against K562 cells (151.07 and 173.06 μg/mL, respectively). Based on these findings, it can be concluded that S. amplexicaulis and S. ringens water extracts could be considered as possible source of antioxidant and cytotoxic agents

Investigation of tungsten-carbide-oxideas the anode catalysts supports for the proton exchange membrane fuel cells

A significant research efforts are directed towards the development of compact energy supply devices, so-called stacks of fuel cells, which might be located near or at the point of energy consumption. For widespread use, the most practical are fuel cells with proton exchange membrane, which produce clean electricity, heat and water, at low temperatures. The price of the catalyst limits the mass production and large-scale utilization of fuel cells. Within our research, non-stoichiometric tungsten-carbide-oxide (WxCyOz) were developed as support for catalysts based on PtRu for PEM fuel cells. The conductivity, morphology and structure of the synthesized catalysts were investigated. Cyclic voltammetry, linear scan voltammetry and rotating disk electrode voltammetry were used to determine performance of obtained PtRu/WxCyOz catalysts. Special attention was given to the analysis of CO poisoning. The catalyst with the best performance (30% PtRu/WxCyOz) has higher number of active sites for HOR and the highest interfacial region which contributes the improved CO tolerance, in relation to the other tested catalysts. By testing this catalyst as an anode catalyst in a single PEM fuel cell, a significantly lower power drop was obtained (16,3%) compared to a single fuel cell that uses commercial catalysts (35,3%). These results highlight the potential of PtRu/WxCyOz catalysts in mitigating performance degradation caused by CO poisoning in PEM fuel cells

In-situ grafting of Fe and Cu nanoparticles on carbon for electrolytic hydrogen production

In order to reduce air pollution by green-house gases released during fossil fuels combustion, hydrogen has been suggested as an alternative, clean fuel [1]. The most promising method of obtaining green hydrogen (and oxygen) is electrolytic water splitting [2]. For splitting process to be efficient, it is necessary to useelectrocatalysts with high activity, but they should also be economically accessible. Ionic liquids are used in the most diverse fields of sciencedue to their unique physical and chemical properties, and in this regard, they can be used for the development of electrocatalystsby direct carbonization [3]. Within this study, carbon catalysts doped with iron and copper (Fe/C, Cu/C and FeCu/C) were prepared by carbonization of ionic liquids containing the corresponding metal and characterized for the hydrogen evolution reaction (HER) in alkaline (8 M KOH) media. Electrochemical measurements were made by cyclic voltammetry (CV), linear cyclic voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). All electrocatalysts showed good activity for HER. Tafel slope (b) values of -132, 155 and -151 mV dec-1 (Table 1) were obtained for HER at 25 oC for Fe/C, Cu/C and FeCu/C, respectively. Also, the exchange current density (j0) was determined and the values ranged from 1.28 to 2.94 10-2 mAcm-2. The results (Table 1) show that Fe/C, Cu/C and FeCu/Care promisingelectrocatalysts for hydrogen gas production by water splitting.Ninth Symposium Chemistry and Environmental Protection : June 4-7, Kladovo, 2023

Enhanced Catalytic Activity and Energy Savings with Ni-Zn-Mo Ionic Activators for Hydrogen Evolution in Alkaline Electrolysis

Green hydrogen produced by alkaline electrolysis is a promising solution to address the world’s increasing energy demand while mitigating greenhouse gas emissions. However, the efficient and cost-effective production of green hydrogen via alkaline electrolysis requires improvements. This paper presents an in situ activation process that simplifies the alkaline electrolysis technology while enhancing the catalytic activity of electrodes for the hydrogen evolution reaction. The aim of this research is to enhance the energy efficiency of alkaline electrolysis and decrease the energy consumption for hydrogen production. To achieve this goal, ionic activators comprising Ni, Zn, and Mo were incorporated into the standard electrolyte solution. Our results demonstrate that the anticipated improvement in the catalytic activity of the d-metal combination, surpassing even that of precious metals, has been successfully attained. As a result, a 20% reduction in energy consumption (REC) for the hydrogen produced has been observed. The catalytic activity of the added activators for the hydrogen evolution reaction was discussed by analyzing the mechanism of the reaction via Tafel analysis and EIS techniques. These findings offer a promising approach to improve alkaline electrolysis and enhance the production of green hydrogen

Polyphenolic Content and Biological Activities of Post-Distillation Waste of Three Sage Species from the Republic of Macedonia

This research was aimed at investigating polyphenolic content, antioxidant and anti-neurodegenerative activities of post-distillation waste extracts of Macedonian Salvia amplexicaulis, S. jurisicii and S. ringens, for the first time. Total phenolic and flavonoid contents varied in a broad range (3.92-146.49 mg GAE/g and 7.11-67.51 mg QE/g, respectively), with the highest values obtained for S. amplexicaulis and S. ringens extracts. Certain S. amplexicaulis and S. ringens extracts neutralized more than 80% of DPPH radicals at the highest concentration, while S. amplexicaulis extracts showed up to ≈50% inhibition of β-carotene oxidation in β-carotene/linoleic acid assay. Post-distillation waste extracts inhibited acetylcholinesterase (25.94-38.15%) and tyrosinase (18.84-59.52%), with the strongest inhibition of S. amplexicaulis extracts. The obtained results suggest that post-distillation waste of tested species, especially of S. amplexicaulis, show antioxidant and anti-neurodegenerative activities and could be considered as potential raw material rich in polyphenols

Micromorphological and anatomical characteristics of Salvia amplexicaulis Lam., S. jurisicii Košanin and S. ringens Sibth. & Sm. (Lamiaceae)

In this study, we examined Salvia amplexicaulis Lam., S. jurisicii Košanin and S. ringens Sibth. & Sm. collected in the Republic of North Macedonia, which are for the first time subjected to detailed micromorphological and structural analysis using light and scanning electron microscopy. The nutlets and mucilage were additionally subjected to spectroscopic analysis using Raman and Attenuated Total Reflectance Fourier Transform Infrared spectroscopy. The anatomical structure of stems and leaves is described and compared. The stems, leaves and calyces bear numerous one- and multi-cellular nonglandular trichomes, and various peltate, capitate and digitiform glandular trichomes. The nutlets differ in size and shape, as well as in myxocarpy. The nutlets predominantly contained α-linolenic and linoleic acid, whereas the mucilages are primarily formed of polysaccharides. The results obtained in this study confirmed the importance of micromorphological and anatomical analysis of Salvia L. spp. plant parts, particularly trichomes and nutlets, and hence contributing to the knowledge about the variety of micromorphological characteristics within the genus Salvia L.This is the peer-reviewed version of the article: Alimpić-Aradski, A.; Janosević, D.; Pećinar, I.; Budimir, S.; Dajić-Stevanović, Z.; Matevski, V.; Marin, P. D.; Duletić-Lausević, S. Micromorphological and Anatomical Characteristics of Salvia Amplexicaulis Lam., S. Jurisicii Kosanin and S. Ringens Sibth. & Sm. (Lamiaceae). Plant Biosystems 2021, 155 (1). [https://doi.org/10.1080/11263504.2020.1727976]

Evaluation of bioactivities and phenolic composition of extracts of Salvia officinalis L. (Lamiaceae) collected in Montenegro

Sage (Salvia officinalis) is the best-known species of the genus Salvia, due to its medicinal and flavouring properties. This research was conducted on samples of S. officinalis collected from Potoci (SOP) in the continental part of Montenegro and from Valdanos (SOV) and Luštica (SOL) in the country´s coastal region. Extracts prepared using 96% ethanol, 50% ethanol and hot distilled water were examined for phenolic composition, as well as for their antioxidant, enzyme-inhibiting and cytotoxic activities. The HPLC-DAD method was employed for quantitative-qualitative analysis of phenolic compounds in extracts, which confirmed the presence of rosmarinic and caffeic acids and luteolin-7-O-glucoside. Total phenolic and flavonoid contents, antioxidant activity, and inhibition of acetylcholinesterase and tyrosinase were measured spectrophotometrically. In the applied antioxidant tests (DPPH, FRAP and β-carotene/linoleic acid tests) and tests of inhibition of the enzymes acetylcholinesterase and tyrosinase, the SOP extracts showed stronger antioxidant and enzyme-inhibiting activities compared to SOV and SOL, while the most efficient solvent was 50% ethanol. The highest cytotoxic activity in the MTT test was recorded for 96% ethanol extracts, especially in the case of the SOL sample, against the A375 cell line. All of the tested bioactivities were more strongly correlated with total phenolic content than with flavonoid content. Differences in the tested bioactivities of extracts obtained from plants collected at ecologically different localities and with different extractio

Biological activities of Cretan Salvia pomifera extracts

The polyphenolic content and biological activities of dichloromethane, chloroform, ethyl acetate, and ethanol extracts of Cretan Salvia pomifera L. (Lamiaceae) were analysed. The ethyl acetate extract showed the highest content of total phenolics and total flavonoids. The ethanol extract exhibited the highest activity in the DPPH and FRAP assays, while the dichloromethane extract had the highest activity in the ABTS test. The ethyl acetate extract showed the highest activity in the β-carotene--linoleic acid system. The antioxidant activity of extracts was positively correlated with the total content of phenolics. Extracts demonstrated weak antibacterial activity. The ethyl acetate extract had the highest acethylcholinesterase inhibition at 50 μg/mL, while the ethanol and dichloromethane extracts showed the highest activity of tyrosinase inhibition at 25 μg/mL. In view of the significance of antioxidants in prevention and treatment of neurological diseases, the noticeable antioxidant and anti-neurodegenerative effects of the ethanol and ethyl acetate extracts recorded in this study make further research on S. pomifera seem promisin

Enzyme inhibitors as controllers of neurodegenerative diseases: An update of in vitro effects of medicinal plants

Considering the increase of the elderly population in recent years, the growing prevalence of age-related neurodegenerative diseases (NDDs), including Alzheimer's disease (AD) and Parkinson's disease (PD), has become one of the leading healthcare problems. Currently, available therapies for AD and PD are still limited, while medicinal plants used in traditional medicine for millennia can inhibit enzymes involved in the neurodegeneration processes in AD (acetylcholinesterase, AChE, and butyrylcholinesterase, BChE) and PD (tyrosinase, TYR), hence their inhibiting effects are continuously being investigated especially in the past decade. This study was aimed to review data on medicinal plants as potential cholinesterases and TYR inhibitors reported from January 2018 until May 2021. The literature search was performed using several online bibliographical databases (Scopus, Web of Science, Science Direct, Google Scholar, PubMed, and ResearchGate) and two websites. Data analysis showed that the highest number of representatives belongs to Lamiaceae family (up to 20%), followed by Asteraceae. Almost half of the tested samples were prepared from whole plant/aerial plant parts followed by leaves. The most frequently tested preparations were methanolic extracts (about 25% of the samples examined). Additionally, synergistic interactions between different herbs and/or isolated compounds were considered as a promising strategy for further research. The presented data showed that medicinal plants preparations represent an unlimited source for research of new and more effective AD and PD treatments. This review will provide a useful starting point for further research on this topic