Insights on the Performance of Nickel Foam and Stainless Steel Foam Electrodes for Alkaline Water Electrolysis Ana L. Santos, Maria João Cebola, Jorge Antunes, Diogo M. F. Santos Sustainability Switzerland, 2023 Green hydrogen production seems to be the best route to achieve a sustainable alternative to fossil fuels, as hydrogen has the highest energy density on a mass basis and its combustion does not produce greenhouse gases. Water electrolysis is the method of choice for producing green hydrogen. Among commercially available water electrolysis systems, alkaline water electrolysis (AWE) is the most well-established technology, which, nevertheless, still needs to improve its efficiency. Since the electrodes’ performance is of utmost importance for electrolysis efficiency, nickel foam (NF) and stainless steel foam (SSF) electrodes were analyzed via voltammetry to validate their catalytic activity toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 30 wt.% NaOH electrolyte solution. Moreover, at a current density of 50 mA cm−2, the NF and the SSF exhibited good stability, with the potential for HER and OER stabilizing at −0.5 V and 1.6 V vs. reversible hydrogen electrode. A lab-scale electrolyzer attained current densities of 10, 20, and 50 mA cm−2 at small cell voltages of 1.70 V, 1.80 V, and 1.95 V. The results validated NF and SSF as electrodes for a high-performance AWE electrolyzer, especially at higher temperatures. They ensured the progress for the project’s next stage, i.e., constructing an electrolyzer at a pilot scale.
Towards the hydrogen economy—a review of the parameters that influence the efficiency of alkaline water electrolyzers Ana L. Santos, Maria-João Cebola, Diogo M. F. Santos Energies, 2021 Environmental issues make the quest for better and cleaner energy sources a priority. Worldwide, researchers and companies are continuously working on this matter, taking one of two approaches: either finding new energy sources or improving the efficiency of existing ones. Hydrogen is a well-known energy carrier due to its high energy content, but a somewhat elusive one for being a gas with low molecular weight. This review examines the current electrolysis processes for obtaining hydrogen, with an emphasis on alkaline water electrolysis. This process is far from being new, but research shows that there is still plenty of room for improvement. The efficiency of an electrolyzer mainly relates to the overpotential and resistances in the cell. This work shows that the path to better electrolyzer efficiency is through the optimization of the cell components and operating conditions. Following a brief introduction to the thermodynamics and kinetics of water electrolysis, the most recent developments on several parameters (e.g., electrocatalysts, electrolyte composition, separator, interelectrode distance) are highlighted.
Green extraction of Sambucus nigra L. For potential application in skin nanocarriers Ana Henriques Mota, Joana Marçalo Andrade, Epole N Ntungwe, Paula Pereira, Maria João Cebola, et al. Green Materials, 2020 Sambucus nigra L. is a well-known species with a wide range of medicinal properties. In this work, supercritical fluid extracts were obtained from fresh and dried elderberries of S. nigra L.: A (dried berries, ethanol (C2H5OH) absolute), B (dried berries, ethanol 96%), C (dried berries, ethanol 70%) and D (fresh berries, ethanol 96%). Evaluation of the in vitro enzymatic activities and antioxidant activity (AA) of the extracts and a preliminary assessment of their safety were carried out. The most promising extracts were selected for encapsulation in polymeric nanoparticles (NPs). All extracts demonstrated low to moderate AA, and they did not reveal any antimicrobial activity against the bacteria and yeasts tested. No toxic effect in the Artemia salina model was observed. Due to the moderate or good AA, anti-collagenase and anti-elastase activities, A and C extracts were selected and then successfully encapsulated into poly(lactide-co-glycolide) (PLGA) NPs. According to morphological analysis, empty PLGA NPs had a rounded irregular shape and seemed somewhat collapsed, while PLGA NPs loaded with extract A or C exhibited a spherical shape with a smooth surface. The encapsulation process produced a slight increase in the NP size. Further studies will include the optimization of extract conditions in order to improve the yield of extraction, as well as the in vivo evaluation of these nanocarriers.
Artemia species: An important tool to screen general toxicity samples Epole Ntungwe N, Eva M. Domínguez-Martín, Amilcar Roberto, Joana Tavares, Vera M. S. Isca, et al. Current Pharmaceutical Design, 2020 Medicinal plants are a good source of novel therapeutic drugs, due to the phytochemicals present. Artemia, commonly known as brine shrimp, is a tiny halophilic invertebrate belonging to class Crustacean, which plays an important role in saline aquatic and marine eco-systems. Besides its usage in aquaculture, it is also highly valued for its application in toxicity detection and it is used in areas such as Ecology, Physiology, Ecotoxicology, Aquaculture and Genetics. Furthermore, Artemia based lethality assay (brine shrimp lethality assay, BSLA) is rapid, convenient and low cost. Presently, brine shrimp lethality assays are enormously employed in research and applied toxicology. It has been used in the study of natural products as a preliminary toxicity assay to screen a large number of extracts and compounds for drug discovery in medicinal plants. The aim of this review paper is to collect, organize, select and discuss the existing knowledge about the different uses of Artemia salina as a bench-top bioassay for the discovery and purification of bioactive natural products.
Parvifloron D from plectranthus strigosus: Cytotoxicity screening of Plectranthus spp. extracts Catarina Garcia, Epole Ntungwe, Ana Rebelo, Cláudia Bessa, Tijana Stankovic, et al. Biomolecules, 2019 The Plectranthus genus is commonly used in traditional medicine due to its potential to treat several illnesses, including bacterial infections and cancer. As such, aiming to screen the antibacterial and cytotoxic activities of extracts, sixteen selected Plectranthus species with medicinal potential were studied. In total, 31 extracts obtained from 16 Plectranthus spp. were tested for their antibacterial and anticancer properties. Well diffusion method was used for preliminary antibacterial screening. The minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values of the five most active acetonic extracts (P. aliciae, P. japonicus, P. madagascariensis var. “Lynne”, P. stylesii, and P. strigosus) were determined. After preliminary toxicity evaluation on Artemia salina L., their cytotoxic properties were assessed on three human cancer cell lines (HCT116, MCF-7, and H460). These were also selected for mechanism of resistance studies (on NCI-H460/R and DLD1-TxR cells). An identified compound—parvifloron D—was tested in a pair of sensitive and MDR-Multidrug resistance cancer cells (NCI-H460 and NCI-H460/R) and in normal bronchial fibroblasts MRC-5. The chemical composition of the most active extract was studied through high performance liquid chromatography with a diode array detector (HPLC-DAD/UV) and liquid chromatography–mass spectrometry (LC–MS). Overall, P. strigosus acetonic extract showed the strongest antimicrobial and cytotoxic potential that could be explained by the presence of parvifloron D, a highly cytotoxic diterpene. This study provides valuable information on the use of the Plectranthus genus as a source of bioactive compounds, namely P. strigosus with the potential active ingredient the parvifloron D.
Extraction Optimization and Structural and Thermal Characterization of the Antimicrobial Abietane 7α-Acetoxy-6β-hydroxyroyleanone Carlos E. S. Bernardes, Catarina Garcia, Filipe Pereira, Joana Mota, P. Pereira, et al. Molecular Pharmaceutics, 2018 The abietane 7α-acetoxy-6β-hydroxyroyleanone (AHR), obtained from plant extracts, is an attractive lead for drug development, given its known antimicrobial properties. Two basic requirements to establish any compound as a new drug are the development of a convenient extraction process and the characterization of its structural and thermal properties. In this work seven different methods were tested to optimize the extraction of AHR from Plectranthus grandidentatus. Supercritical fluid extraction (SFE) proved to be the method of choice, delivering an amount of AHR (57.351 μg·mg-1) approximately six times higher than the second best method (maceration in acetone; 9.77 μg·mg-1). Single crystal X-ray diffraction analysis of the ARH molecular and crystal structure carried out at 167 ± 2 K and 296 ± 2 K showed only a single phase, here dubbed form III (orthorhombic space group P21212), at those temperatures. The presence of two other polymorphs above room temperature was, however, evidenced by differential scanning calorimetry (DSC). The three forms are enantiotropically related, with the form III → form II and form II → form I transitions occurring at 333.5 ± 1.6 K and 352.0 ± 1.6 K, respectively. The fact that the transitions are reversible suggests that polymorphism is not likely to be an issue in the development pharmaceutical formulations based on ARH. DSC experiments also showed that the compound decomposes on melting at 500.8 ± 0.8 K. Melting should therefore be avoided if, for example, strategies to improve solubility based on the production of glassy materials or solid dispersions are considered.
