High Cell Potential Research Articles

Insights into self-discharge processes of Al-graphite batteries

Aluminum graphite dual ion batteries (AGDIB) have been widely explored thanks to abundant electrode materials, a long cycle life and high power density. However, the shelf life of AGDIBs is so far barely understood. This work's detailed self-discharge investigations allow the quantification of capacity losses for up to 4 weeks, confirm a deintercalation mechanism by Raman spectroscopy and X-ray diffraction, and furthermore give insight to influence factors. While a cell employing typical materials such as a natural graphite cathode, Mo current collector and AlCl3/[EMIm]Cl=1.5 ionic liquid electrolyte exhibits a capacity loss of 10 % in 24 h, this value can be significantly reduced to 3 % in 24 h when using a glassy carbon current collector and AlCl3/Et3NHCl=1.5 electrolyte instead. Iron impurities within the electrolyte do not affect battery capacities or self-discharge, since it is deposited on the Al anode within the battery soon after assembly. In general, the instability of the current collector material, gas evolution due to electrolyte oxidation at high cell potentials, and cationic electrolyte species greatly influence the self-discharge independently. Electrolyte speciation changes directly related to self-discharge processes are revealed by IR spectroscopy.

Simulation of Proton Exchange Membrane Durability Under Fuel Cell Vehicle Operation – a Fundamental Study

Proton exchange membrane fuel cells (PEMFCs) have been proven to be a promising candidate to replace combustion engines due to their zero-carbon emission and high power densities. Despite the recent success in PEMFC commercialization, a number of challenges such as high cost and difficulty in lifetime estimation still hinder their further development. PEMFC durability tests require a long time to complete; therefore, durability predicting models are increasingly important as a supporting tool for further development and implementation.Fuel cell membranes undergo a variety of dynamic conditions during regular operation such as varying temperature, humidity, current density, and cell potential. The cyclic variations of humidity and temperature (hygrothermal variations) during dynamic operation lead to swelling and contraction of the membrane. The fluctuating stress caused by the continuous expansion and contraction of the membrane when confined within the cell leads to mechanical membrane degradation. The recurring swelling and contraction of the membrane which stem from water content changes in the membrane cause fatigue and creep and ultimately the formation of pinholes, cracks, and tears [1-2].Chemical membrane degradation occurs when radicals such as hydroxyl and hydroperoxyl are formed and attack the membrane and is escalated by high operating cell potentials. Chemical degradation results in decay in the ionomer chemical structure, membrane thinning, increased gas crossover, and potential electrode shorting [3]. The outcomes of such degradation are aggravated in the presence of mechanical degradation [4]. Hence, the study of combined chemo-mechanical membrane degradation is crucial for overall fuel cell membrane durability [5].The objective of the present work is to establish a predictive membrane lifetime simulation tool designed to represent chemo-mechanical membrane degradation under various operating conditions for automotive fuel cell applications. To this end, a statistical model is developed based on the membrane fibrillar morphology presented by El Hannach et al. [6-7]. A network of fibre bundles is generated to represent the membrane structure where any bundle is assumed as the primary building block of the membrane [8-10]. Each bundle contains an aggregate of backbone chains with typical mechanical and chemical properties. Mechanical and chemical degradation rates are separately studied and coupled in the model. The thermally activated breaking rate of each fibre is calculated to evaluate the mechanical degradation rate at any given time. In order to calibrate the mechanical degradation rate in the model, the mechanical degradation of a reinforced membrane under cross-pressure accelerated mechanical stress tests ( p-AMST) [11] is investigated to obtain the membrane fatigue lifetime for a variety of cross pressures and temperatures. Then, the genetic algorithm is successfully applied to optimize the experimental parameters considering the least squares method. Furthermore, accelerated membrane durability tests (AMDT) carried out by Macauley et al. [12] are considered to calibrate the chemical degradation rate parameter in the model. Finally, the fully calibrated model is used to estimate the membrane lifetime under realistic fuel cell vehicle operating conditions (e.g. drive cycles).Fuel cell components experience different degradation mechanisms. In this regard, this modelling framework on the membrane lifetime can be used in conjunction with other methodologies on the cathode catalyst lifetime such as [13-14] to scrutinize the key factors and their impacts on fuel cell durability under similar operating conditions. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Research Chairs, and Simon Fraser University Community Trust Endowment Fund.

Accumulation of Liquid Byproducts in an Electrolyte as a Critical Factor That Compromises Long-Term Functionality of CO2-to-C2H4 Electrolysis.

Electrochemical conversion of CO2 using Cu-based gas diffusion electrodes opens the way to green chemical production as an alternative to thermocatalytic processes and a storage solution for intermittent renewable electricity. However, diverse challenges, including short lifetimes, currently inhibit their industrial usage. Among well-studied determinants such as catalyst characteristics and electrode architecture, possible effects of byproduct accumulation in the electrolyte as an operational factor have not been elucidated. This work quantifies the influence of ethanol, n-propanol, and formate accumulation on selectivity, stability, and cell potential in a CO2-to-C2H4 electrolyzer. Alcohols accelerated flooding by degrading the hydrophobic electrode characteristics, undermining selective and stable ethylene formation. Furthermore, high alcohol concentrations triggered the catalyst layer's abrasion and structural disfigurements in the Nafion 117 membrane, leading to high cell potentials. Therefore, continuous removal of alcohols from the electrolyte medium or substantial modifications in the cell components must be considered to ensure long-term performing CO2-to-C2H4 electrolyzers.

Treatment of aqueous solutions of oxytetracycline by different electrochemical approaches: anodic oxidation, pressurized electro‐Fenton and oxidation by electrogenerated active chlorine

AbstractThe tetracycline group (TCs) includes the most common antibiotics for treatment of both human and animal infections. TCs are resistant to biological degradation; hence, conventional wastewater treatments are unable to remove these contaminants. Here, the utilization of different electrochemical processes, such as electro‐Fenton (EF), direct anodic oxidation (AO) and indirect oxidation by electrogenerated active chlorine (EAC), for the treatment of aqueous solutions of oxytetracycline (OTC), which is one of the TCs, was studied. The effect of various operating conditions was evaluated to optimize the selected processes. EAC gave the fastest abatement of OTC, but the lowest removal of TOC and formation of chlorate. However, the utilization of carbon felt cathodes allowed the formation of chlorate to be reduced. AO gave the highest TOC removals, but it required the use of an expensive anode, as BDD, and high cell potentials. EF performed with pressurized‐air (5–10 bar) presented intermediate removals of OTC and TOC with respect to AO and EAC and consumed the least energy. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Surplus charge injection enables high-cell-potential stable 2D polyaniline supercapacitors

The extraordinary pseudocapacitance of polyaniline (PANI) can be only realized in acid electrolytes with a limited potential window of 0.6∼0.8 V. As the potential further increases, PANI will suffer from the hydrolysis issue, leading to molecular-chain fracture and oxidative failure. In this work, we propose a strategy of surplus electron injection to stabilize the molecular chain of PANI at high cell potential. The surplus electron injection in 2D PANI is realized by exceeding the stable potential induced by an asymmetric supercapacitor structure design. As excessive charges are poured, supramolecular hydrogen bonds presented at 2D PANI capture them and generate additional redox reaction, which suppresses the damage of 2D PANI molecular structure and simultaneously strengthens its capacitive behavior. This effect is vividly demonstrated by the modulated electronic structure as indicated by shifting up the Fermi level, shifting down the work function and increasing the electrical conductivity. Consequently, high cell potential (1.2 V) 2D PANI supercapacitors with sulfuric acid electrolyte deliver a much longer cycling lifetime (76.8% vs. 45.1% after 10,000 cycles) and a much higher energy density (19.9 vs. 7.53 Wh kg‒1) than that of low cell potential (0.8 V) 2D PANI counterpart. This work guides to a novel way to design high cell potential aqueous-solution supercapacitors.

Realized potential as neutral pH flow batteries achieve high power densities

High power density operation of redox flow batteries (RFBs) is essential for lowering system costs, but until now, only acid-based chemistries have achieved such performance, primarily due to rapid membrane proton (H + ) transport. Here, we report a neutral pH RFB using the highly reducing Cr-(1,3-propylenediaminetetraacetate) (CrPDTA) complex that achieves acid-like power performance while utilizing potassium ion (K + ) transport. We investigate RFB resistance components and demonstrate the high and consistent K + conductivity of the Fumasep E-620(K) membrane. When combined with a robust bismuth electrocatalyst, this membrane enables constant voltage efficiency operation of a CrPDTA|Fe(CN) 6 RFB for 200 cycles. An optimized CrPDTA|Fe(CN) 6 RFB, which combines a high cell potential with a low area-specific resistance (0.46 Ω cm 2 ), demonstrates a maximum discharge power density of 1.63 W cm −2 and an average discharge power density over 500 mW cm −2 while maintaining 80% round-trip energy efficiency cycling, which are records for non-acid-based RFBs. • High-power flow battery operates at neutral pH with potassium membrane transport • Record discharge-power performance for a flow battery not using proton transport • Inexpensive membrane provides high conductivity and constant efficiency cycling • Chelated metal electrolyte enables high voltage battery and high-power operation High-power flow battery operation lowers system costs but has previously required proton transport. By combining high voltage with low resistance from a highly selective and conductive membrane, Robb et al. demonstrate an aqueous flow battery that achieves record non-acidic power performance while utilizing potassium membrane transport at neutral pH.

Conjugated Bipolar Redox-Active Electrolyte for Symmetric Redox Flow Battery

Organic non-aqueous redox-flow batteries (O-NRFBs) are gaining traction as viable alternatives for long-term, low-cost stationary energy storage with a wide potential window.[1] The symmetric O-NRFBs with single bipolar electrochemically active molecule as both anolyte and catholyte (i.e. bipolar redoxmer) helps to mitigate permanent cross-contamination and capacity fading.[2] However, symmetric O-NRFBs with bipolar molecules are hampered by the scarcity of redox active molecules capable of serving as a stable bipolar redoxmer with high cell potential and unpredictable side reactions.[3] This study proposes the π-conjugation of electrochemical active electron donors and electron acceptor which leads to the possible control over direct electronic perturbation between acceptor-donor to form new type of redox molecules. This study aims designing of benzothiadiazole based conjugated bipolar redox-active molecule with high potential window and high stability.[1]. M. Li, S. A. Odom, A. R. Pancoast, L. A. Robertson, T. P. Vaid, G. Agarwal, H. A. Doan, Y. Wang, T. M. Suduwella, S. R. Bheemireddy, R. H. Ewoldt, R. S. Assary, L. Zhang, M. S. Sigman, and S. D. Minteer, “Experimental protocols for studying organic non-aqueous redox flow batteries,” ACS Energy Lett., 2021, 6, 11, 3932–3943.[2]. M. Li, J. Case, and S. D. Minteer, “Bipolar redox-active molecules in non-aqueous organic redox flow batteries: status and challenges,” ChemElectroChem, 2021, 8, 1215–123.[3] M. Li, G. Agarwal, I. A. Shkrob, R. T. VanderLinden, J. Case, M. Prater, Z. Rhodes, R. S. Assary and S. D. Minteer, “Critical role of structural order in bipolar redox-active molecules for organic redox flow batteries,” J. Mater. Chem. A, 2021, 9, 23563-23573.

Membrane-Assisted Electrochlorination for Zero-Chemical-Input Point-of-Use Drinking Water Disinfection.

Due to the challenges of providing centralized drinking water infrastructure in low-income and rural settings, point-of-use (POU) disinfection systems are an attractive option for enhancing access to safe drinking water. Electrochlorinators offer an easily scalable and adaptable alternative to POU disinfection systems that require frequent replenishment and accurate dosing of chlorine, but they also require addition of salts on a regular basis. To address this need, we developed an electrochemical disinfection system that efficiently produces chlorine without any chemical inputs. To convert the low concentration of chloride in source waters (i.e., 10-200 mg L-1) to free chlorine (i.e., HOCl/OCl-), an anion exchange membrane was positioned between two electrodes, creating two separate chambers. By providing continuous water flow through the catholyte while operating the anolyte in the batch mode, chloride was concentrated into the anolyte, where it was more efficiently converted into chlorine. This approach allowed us to produce chlorine at rates that were about 50% faster than that of an undivided cell operating under similar conditions. Chlorate production was approximately 20% slower in the separated cell compared to an undivided cell; concentrations in finished water never exceeded the World Health Organization's provisional guideline value of 0.7 mg L-1. The performance of the system was further improved by retaining some of the anolyte between operating cycles. This helped avoid periods of high cell potential before salts were concentrated in the anolyte chamber. Use of an anion exchange membrane and a recycled anolyte mode of operation reduced energy consumption by 30%-70% relative to an undivided cell. The energy required to disinfect water ranged from approximately 0.05 to 1 kWh m-3, depending on the chloride content and conductivity of the source water.

Novel Superaerophobic Anode with Fern‐Shaped Pd Nanoarray for High‐Performance Direct Formic Acid Fuel Cell

AbstractDirect formic acid fuel cells (DFAFCs) possess the advantages of high power density and theoretical cell potential. Exploring robust catalysts for electrochemical formic acid electro‐oxidation (FAO) is greatly essential for the wide spread uptake of DFAFCs. However, many electrodes with attractive catalysts suffer limited mass transport due to sluggish CO2 bubble growth and departure steps on its surface. In this study, a superaerophobic electrode is developed by depositing fern‐shaped palladium nanostructured arrays on the carbon paper (Pd‐nanoarray@CP). Its unique superaerophobic feature successfully facilitates the CO2 bubble releasing from the catalyst surface in a significantly small size. With the merits of specific nanoarray morphology, superior under water superaerophobicity, and rapid gas bubble release, the Pd‐nanoarray@CP shows fast charge/mass transport rate, high electrocatalytic activity, and great stability for FAO. A direct formic acid fuel cell equipped with the Pd‐nanoarray@CP anode is successfully fabricated on a microfluidic platform. A peak power density of 35.8 mW cm−2 and limiting current density of 173.3 mA cm−2 are obtained, respectively, which are 49.2% and 33.0% higher than that of conventional Pd‐black anodes. The electrode with superaerophobic interface allows deeper insight into the mechanism of FAO efficiency and holds promise for possible applications of commercially viable DFAFCs.

Comparative Study for the Production of Sustainable Electricity from Marine Sediment Using Recyclable Low‐Cost Solid Wastes Aluminum Foil and Graphite Anodes

AbstractThe influence of low‐cost anode materials, aluminum, and graphite on the sediment microbial fuel cell (SMFC) performance is investigated. The cathode in both cells is a high‐conductive pencil electrode. The open‐circuit potentials of the graphite sediment microbial fuel cell (CSMFC) and the aluminum sediment microbial fuel cell (ASMFC) are 600 mV and 1103 mV, respectively. The microbial metabolic activity in polluted marine sediment creates a large potential difference at the marine sediment/seawater interface. The sustainable electrical power from CSMFC and ASMFC are 680 mW.m−2 and 930 mW.m−2 respectively. The high cell potentials of both cells are achieved at ambient temperature. The designed SMFCs could power oceanographic instruments and biosensors in the coastal ocean. The total viable bacterial count (TVBC) and biological parameters of pore water are related to the high cell potential. The higher open‐circuit potential of ASMFC than CSMFC is mainly attributed to the lower charge transfer resistance of aluminum than graphite. This high performance is confirmed by using electrochemical impedance spectroscopy (EIS). The charge transfer resistance (Rct) of aluminum and graphite are 1600 and 2050 Ohm.cm2, respectively. The electrical conductivity of a thin film of aluminum and graphite are 40.1 104 and 9.99 103 Siemens/cm, respectively. The electrical resistivity of the ASMFC and CSMFC are 1.506×10−5 and 2.25661×10−5 Ω.m, respectively. These results strongly suggest that ASMFC has a higher electrical power density than CSMFC due to the lower charge transfer resistance, the good electrical conductivity of aluminum, and the lower electrical resistivity of ASMFC.

Novel polymer electrolyte derived from diazonaphthone monomers for an aqueous supercapacitor with high cell potential and superior safety

Supercapacitors have attracted considerable attention due to their high-power density and long cycle life. However, flexibility and safety have become new challenges encountered by supercapacitors with the further increase in their demand. Here, we have prepared a novel electrolyte which is further compounded by combining a polymer with a rigid main chain and a flexible side chain as a support matrix. It has more stable thermomechanical properties and mechanical strength compared to liquid and conventional solid polymer electrolytes. Furthermore, it demonstrates a high ionic conductivity of 3.2 × 10−2 S cm−1 at room temperature, and an extended electrochemical window of 2 V. Consequently, the assembled symmetric supercapacitors show acceptable electrochemical performance. We believe that this simultaneous introduction of rigid structures and flexible chain segments provides a novel and effective strategy for building solid polymer electrolytes that can be practically applied.

Chemically induced delithiation and phase change of lithium rich nickel manganese oxides

In this study, Li[Ni.25Li.167Mn.583]O2 (LLRNMO) was exposed to acidic solutions of H3PO4, H2SO4, HCl, and HNO3 in an attempt to chemically motivated the phase transformation analogous to the that encountered during electrochemically-driven delithiation. Powder X-ray diffraction and electrochemical data provide evidence of delithiation similar to a low cell potential charge (sub 4.5 V), but the data were not consistent with the phase change induced by the initial high cell potential (>4.5 V) charge. Repeated full cycling revealed that acidic treatments reduced sample capacity and cell potential. XRF and SEM data suggest the effects of acid treatment are not universal and are dependent on the acid used. To the best of our knowledge, this study marks the first time that a lithium-excess cobalt-free cathode was exposed to acidic solutions for this purpose. Our results demonstrate that these chemically induced phase transformations are a poor substitute for the electrochemically induced phase transformation. The possible reasons and consequences of this are discussed.

Novel Aluminum-Ion Based Non-Aqueous Redox Flow Battery

The global implementation of renewable energy technologies requires sustainable large-scale manufacturing by using locally available materials. The urgent need to achieve a climate-neutral society encouraged researchers to find sustainable and innovative ways to store electrical energy. Currently, Li-ion battery (LIB) technology is the largest implemented commercial level battery for energy systems. The LIBs' upstream supply chain comprises specific materials, including lithium, cobalt, iron, and phosphate. The latter poses a challenge as they are geographically limited to fewer countries. Therefore, as the LIB production growth rate increases rapidly, balancing the raw material supply and resource circulation is required.In contrast to the intercalation-based electrochemistry of the LIBs, the redox flow battery (RFB) store electrical energy in the form of chemical energy directly into the electrolyte. The amount of energy stored in the battery is proportional to the concentration of redox species or simply to the amount of the electrolyte used. The redox reactions happen at the electrode surface assembled inside the battery, and the electrolyte containing the active redox species flows across the electrodes from the adjacent reservoirs. Minimal single cell design variations are required to use different electrolyte chemistries, barring the widely and commonly used Vanadium redox ions. This flexibility enables adjusting the active redox species comprised on the electrolyte, with locally abundant transition metals. The redox potentials of the mentioned metallic compounds lie outside the electrochemical stability range of aqueous electrolytes. The research community addresses increment in electrochemical operation range by introducing the non-aqueous RFB (NAqRFB) technology.The latter allowed to explore more promising redox ions for NAqRFB. An ideal redox ion should i) have great abundancy; ii) be cheap, iii) provide fast multiple electron transfer per reacting molecule, and iv) possess reversible kinetics mechanisms, therefore not compromising the system's stability by generating irreversible side reactions. This thirst is quenched by Aluminum-ions (Al3+), which demonstrate the mentioned features besides having high energy density and high value of negative redox potential, i.e., -1.7 V vs. Ag/Ag+ allow higher cell potential. In this regard, an aluminum-ion-based non-aqueous redox flow battery was introduced in this study as a proof-of-concept. The aluminum redox ion is used as negolyte coupled with the posolyte based on the redox ions of metal acetylacetonates - M(acac) (where, M = Cr, Fe) - and Ferrocene (Fc). The insertion of the mentioned metals at the posolyte while keeping aluminum ion at the negolyte ensured the generation of novel chemistries for NAqRFBs, in detail Al||Cr, Al||Fc, and Al||Fe with cell potential differences of 3.2 V, 1.26 V, and 0.8 V, respectively.The reversibility of the redox ions in the electrolyte is compulsory and crucial for the operation of RFB. Cyclic voltammetry (CV) was performed for the non-aqueous electrolytes with acetonitrile as solvent and TEABF4 as supporting electrolyte. The redox ions of Al/Al3+, Cr4+/Cr5+, Fc/Fc+, and Fe3+/Fe4+ were used as active species and proved to be reversible on a glassy carbon working electrode (GCE); said attained redox couple potentials (vs. Ag/Ag+) were -1.7 V, 1.5 V, 0.1 V, and -0.9 V, respectively. Detailed electrochemical characterization was performed in a single NAqRFB, using polarization curve analysis, electrochemical impedance spectroscopy (EIS), and charge-discharge cycling (CDC) – Table 1. Post-mortem CVs of the electrolyte using GCE highlight the stability of the electrolyte after intensive CDC.The RFB assembled with Al||Cr offered the capacity and energy density performance. The CV results highlight that the redox reaction is quasi-reversible, affecting the battery performance and stability. The RFB composed of Al||Fc offers the highest capacity and energy density than others and is three times more than reported Al||Cr NAqRFB. The post-mortem analyses on the posolyte signify that there was crossover through the membrane, which ended up with a contaminated electrolyte (mixture with negolyte chemistry) that affected the extended capacity of the cell. Reinforced membranes permit to decrease the permeability of the membrane toward smaller ions of Al3+ as compared to Fc+. Further optimization of the membrane is required to improve the promising Al||Fe RFB, perhaps to reach the energy efficiency of 90%. Furthermore, the Al||Fe battery demonstrated a stable performance up to 50 cycles and the second-highest energy density ca. 25.9 mWh.g-1 compared to other versions of aluminum-ion-based non-aqueous redox flow batteries. This work is still in progress for in-depth study covering other aspects and ascertaining the feasibility of Al based RFB to be the new generation of NAqRFBs. Figure 1

On the performance of liquid-liquid Taylor flow electrochemistry in a microreactor – A CFD study

A comprehensive understanding of the underlying phenomena (coupled fluid flow, charge transfer, mass transfer and chemical reaction) is fundamental for a proper design, analysis and scale-out of chemical reactors when carrying out multiphase electro-organic transformations. In this study, we have explored the novel combination of organic electrochemical synthesis and computational fluid dynamics (CFD) to perform a systematic theoretical investigation concerning the effect of different operational parameters on the performance of organic-aqueous Taylor flow in electrochemical microreactors. The results indicate that operating at high concentrations of the rate-limiting species (>5 mol⋅m−3 for Di≥10-9 m2⋅s−1; 500 mol⋅m−3 for Di~10-10 m2⋅s−1) is beneficial for the reactor performance. However, excessively high concentrations (>500 mol⋅m−3) do not result in a further improvement in mass transfer and current/voltage relation. Higher diffusivities are also beneficial, but even in this scenario limiting current densities can be found when working at low concentrations. Overall, keeping an internal:external phase electrical conductivity ratio > 1 improves the reactor performance. Working at lower velocities can be beneficial in some scenarios, since higher limiting current densities can be obtained. However, the velocity impact on the reactor performance is not significant in some operating conditions (e.g., at higher concentrations and diffusivities). Finally, working with higher cell potentials is beneficial, but limiting current densities can be encountered at lower concentrations and diffusivities. Variables such as internal phase volume fraction, droplet length and interelectrode distance also have relevant impact on the reactor performance, but are subjected to the same conditioning factors previously mentioned. A comprehensive potential balance was also conducted, showing the relative importance of the activation, Ohmic and concentration overpotentials under different operating conditions. We believe the insights gained herein will be of interest to researchers in both academia and industry to develop more efficient electrochemical flow reactors for liquid–liquid transformations.

Sustainable electricity production from seawater using Spirulina platensis microbial fuel cell catalyzed by silver nanoparticles-activated carbon composite prepared by a new modified photolysis method

A new and innovative microbial fuel cell of high energy conversion efficiency (with no heat emission or corrosion problems) was formulated using nanoparticles of dry biomass Spirulina platensis microalgae. High cell potential up to 1.0 V was obtained from this microbial fuel cell. The Spirulina platensis nanoparticles have been prepared using the top-down approach, then were sonicated to facilitate their digestion as a feedstock for the microorganisms in the seawater. The microorganisms in the polluted seawater at the deaerated anode chamber oxidized the organic matter producing electrons that transfer to the anode surface inside the microbial fuel cell via the microbial nanowires. These electrons (electric current) passed in the external circuit from the anode surface to the cathode surface. The microstructure of the bacterial biofilm on the anode surface was confirmed using the scanning electron microscope. The promising catalyst silver nanoparticles-activated carbon composite was prepared by a new modified photolysis method. The transmitting electron microscope micrograph of silver nanoparticles showed an average particle size of about 10 nm homogeneously loaded on the activated carbon matrix. The powder X-ray diffraction pattern of silver nanoparticles-activated carbon composite confirmed the formation of zero-valent metallic silver nanoparticles via the photoreduction of silver nitrate using low cost modified photolysis method. The composite efficiently catalyzed the slow oxygen reduction reaction at the cathode surface. The open cell potential of microbial fuel cell was 500 mV and 1000 mV and the corresponding power density up to 1.0 and 2.5 W. m−2 in the absence and the presence of silver nanoparticles-activated carbon composite, respectively. Both open-cell potential and the closed-cell potential were maximized in the presence of silver nanoparticles-activated carbon composite and remained unchanged for nearly one month of the cell operation.

On the road again: Establishment and maintenance of stemness in the neural crest from embryo to adulthood.

Unique to vertebrates, the neural crest (NC) is an embryonic stem cell population that contributes to a greatly expanding list of derivatives ranging from neurons and glia of the peripheral nervous system, facial cartilage and bone, pigment cells of the skin to secretory cells of the endocrine system. Here, we focus on what is specifically known about establishment and maintenance of NC stemness and ultimate fate commitment mechanisms, which could help explain its exceptionally high stem cell potential that exceeds the “rules set during gastrulation.” In fact, recent discoveries have shed light on the existence of NC cells that coexpress commonly accepted pluripotency factors like Nanog, Oct4/PouV, and Klf4. The coexpression of pluripotency factors together with the exceptional array of diverse NC derivatives encouraged us to propose a new term “pleistopotent” (Greek for abundant, a substantial amount) to be used to reflect the uniqueness of the NC as compared to other post‐gastrulation stem cell populations in the vertebrate body, and to differentiate them from multipotent lineage restricted stem cells. We also discuss studies related to the maintenance of NC stemness within the challenging context of being a transient and thus a constantly changing population of stem cells without a permanent niche. The discovery of the stem cell potential of Schwann cell precursors as well as multiple adult NC‐derived stem cell reservoirs during the past decade has greatly increased our understanding of how NC cells contribute to tissues formed after its initial migration stage in young embryos.

Experience in Clinical Application of Cryopreserved Placental Derivatives: Cells, Tissue, Membranes, Extract, and Cord Blood Serum

Background. The human placenta is a promising source of biomaterial for regenerative medicine. This is primarily due to the availability of a sufficient amount of material, low immunogenicity, a large number of stem cells, and high proliferative cell potential. The effectiveness of stem cells, their lysates, and conditioned media in various pathological conditions has been proven in many studies. Most studies are experimental, or are in different phases of clinical trials. At the same time, in Ukraine there is a wealth of experience of cli­nical using the cryopreserved placenta medico-immunobiological preparations, which can be the basis for further application of placental material.Objective. We aim to perform a critical analysis of data on the effectiveness and prospects of application of the cryo­preserved placenta preparations (cells, tissues, membranes, extract and cord blood serum) in clinical practice.Methods. The results of clinical application of 2,579 medical immunobiological Platex and Cryocell placenta preparations were analyzed. An attention was paid to the effectiveness, course of concomitant, comorbid pathology in patients, as well as the presence of negative responses and complications. The number of the preparations used and the one of the patients according to the nosological forms were counted.Results. The experience of application of medical immunobiological preparations of placental origin in obstetric-gynecological, therapeutic, neurological and endocrinological pathologies is analyzed in the work. The obtained data are compared with the research results in the corresponding model experiments of in vitro and in vivo systems. The positive effect of placental preparations on the course of miscarriage, climacteric syndrome, infertility, diabetes mellitus, coronary heart disease, multiple sclerosis, amyotrophic lateral sclerosis, trophic ulcers has been determined. Contraindications for placenta preparations are some malignancies and an infectious disease process without proper pathogen elimination.Conclusions. Cryopreserved placenta preparations are effective when used in obstetric, gynecological, neurological, endocrinological and therapeutic practice. Their effect is primarily observed in diseases, which are accompanied by autoimmune reactions, hormonal disorders, dysplastic or degenerative processes. The restric­ted application of placenta preparations is infectious disease process without proper pathogen elimination.

Anodically Induced Chemical Etching of GaAs Wafers for a GaAs Nanowire-Based Flexible Terahertz Wave Emitter.

A generic top-down approach for the preparation of extended arrays of high-aspect ratio GaAs nanowires (NWs) with different crystallographic orientations (i.e., [100] or [111]) and morphologies (i.e., porous, nonporous, tapered, or awl-like NWs) is reported. The method is based on the anodically induced chemical etching (AICE) of GaAs wafers in an oxidant-free aqueous HF solution at room temperature by using a patterned metal mesh and allows us to overcome the drawbacks of conventional metal-assisted chemical etching (MACE) processes. Local oxidative dissolution of GaAs in contact with a metal is achieved by externally injecting holes (h+) into the valence band (VB) of GaAs through the metal mesh. It is found that injection of holes (h+) through direct GaAs contact, rather than the metal mesh, does not yield uniform nanowires but porosify GaAs wafers due to the high cell potential. On the basis of experiments and numerical simulation for the spatial distribution of an electric field, a phenomenological model that explains the formation of GaAs NWs and their porosification behaviors is proposed. GaAs NWs exhibit excellent terahertz (THz) wave emission properties, which vary with either the length or the shape of the nanowires. By taking advantage of controlled porosification and easy transfer of GaAs NWs to foreign substrates, a flexible THz wave emitter is realized.

Nickel catalyst migration in an anion exchange membrane fuel cell

Nickel materials have been widely studied as non-platinum group metal (non-PGM) cathode catalysts for anion exchange membrane fuel cells (AEMFC). Although the stability of Ni based catalysts has been tested by accelerated potential cycling, this analysis does not fully simulate the operating AEMFC conditions. For back-up power systems, the standby AEMFCs need to be held at a high steady state cell potential. For cathode catalysts, this may be more challenging than cycled potentials. As Ni dissolution has been reported from Ni and Ni alloyed catalysts under cycled cathode potentials, its stability under steady state potentials should be questioned. In this study, a Ni on Vulcan® XC72 carbon (Ni/C) was tested at the cathode of a simulated AEMFC, under a 0.9 V steady state cell potential for 1500 h. After operation, in addition to Ni oxidation at the cathode, Ni dissolution and migration was found resulting in cathode catalyst morphology changes and Ni(OH)2 deposits on the anode. These results were supported by scanning electron microscopy (SEM), scanning transmission electron microscopy (TEM), and X-ray Photoelectron Spectroscopy (XPS) analyses.

Compartmentalized desalination and salination by high energy density desalination seawater battery

A novel desalination seawater battery (DSWB) has been developed by adapting the design of a rechargeable seawater battery, which operates for both seawater desalination and energy storage. The DSWB system has a unique architecture composed of two subsystems used for desalination and salination during charging and discharging, respectively. A higher energy density (4010 Wh/kg) can be achieved at high nominal cell potential (EO = 3.46 V, pH 8.4) in the DSWB system throughout the charging (desalination) process which is much larger than those of any reported desalination battery system (< 78 Wh/kg and <1.25 V). In addition, the system provides a compartment for desalination, which is independent from the salination (discharging) process, enabling the salination process to be carried out without renewing the seawater for every step, which enables the proposed system to achieve high levels of seawater desalination (up to 84%). The results affirm that further optimization of the cell system will facilitate economical and practical desalination battery applications with high energy density.