Presence Of Transition Metal Ions Research Articles

Solvation structure design for stabilizing MXene in transition metal ion solutions

AbstractAlthough MXene has attracted great interest in diverse fields, it is susceptible to oxidation in water (H2O) with transition metal ions such as Co2+, Fe2+, and Cu2+, which is pronounced at high temperatures. This impedes the preparation of MXene‐based composites and their functional applications. Here, this study revealed that Co2+ increases the maximum and average atomic charge of H in H2O to improve the reactivity of H2O, which leads to the fact that Co2+ catalyzes the oxidation of Ti3C2Tx MXene. Furthermore, the addition of N,N‐dimethyl formamide (DMF) reduces the H2O activity and improves the oxidation stability of Ti3C2Tx in the presence of Co2+ via preferentially forming coordination bonds with Co2+. This strategy is also effective in enhancing the oxidation tolerance of Ti3C2Tx to Fe2+ in H2O. Moreover, it is feasible to enhance the oxidation stability of Ti2CTx MXene in H2O with the existence of Co2+. By virtue of these, the CoO/Ti3C2Tx composite was successfully prepared without obvious Ti3C2Tx oxidation, which is desirable to harness the advantages of Ti3C2Tx as the complementary component for lithium‐ion batteries. This work provides a straightforward paradigm to enhance the oxidation resistance of MXene in H2O in the presence of transition metal ions and at high temperatures, which opens a new vista to use MXene for target applications.

The Influence of Cathode Degradation Products on the Anode Interface in Lithium-Ion Batteries.

Degradation of cathode materials in lithium-ion batteries results in the presence of transition metal ions in the electrolyte, and these ions are known to play a major role in capacity fade and cell failure. Yet, while it is known that transition metal ions migrate from the metal oxide cathode and deposit on the graphite anode, their specific influence on anode reactions and structures, such as the solid electrolyte interphase (SEI), is still quite poorly understood due to the complexity in studying this interface in operational cells. In this work we combine operando electrochemical atomic force microscopy (EC-AFM), electrochemical quartz crystal microbalance (EQCM), and electrochemical impedance spectroscopy (EIS) measurements to probe the influence of a range of transition metal ions on the morphological, mechanical, chemical, and electrical properties of the SEI. By adding representative concentrations of Ni2+, Mn2+, and Co2+ ions into a commercially relevant battery electrolyte, the impacts of each on the formation and stability of the anode interface layer is revealed; all are shown to pose a threat to battery performance and stability. Mn2+, in particular, is shown to induce a thick, soft, and unstable SEI layer, which is known to cause severe degradation of batteries, while Co2+ and Ni2+ significantly impact interfacial conductivity. When transition metal ions are mixed, SEI degradation is amplified, suggesting a synergistic effect on the cell stability. Hence, by uncovering the roles these cathode degradation products play in operational batteries, we have provided a foundation upon which strategies to mitigate or eliminate these degradation products can be developed.

Effects of transition-metal ions on the reduction of N-nitrosodimethylamine in water by zinc

The influencing factors, products and mechanism of N-nitrosodimethylamine (NDMA) reduction by zinc (Zn) in the presence of transition-metal ions (Mn2+, Co2+ and Ni2+), were investigated. The NDMA removal by Zn was significantly improved by them, and the promoting effect of Co2+ and Ni2+ were better than Mn2+. With the decrease of pH values and dissolved oxygen concentrations, the removals of NDMA were enhanced in all reaction systems. NDMA was mainly reduced to unsymmetrical dimethylhydrazine (UDMH) in Zn and Zn/Mn2+ systems. It was mainly reduced to dimethylamine (DMA) and ammonium (NH4+) in Zn/Co2+ and Zn/Ni2+ systems. There were undetected products in all reaction systems. Catalytic hydrogenation was the main mechanism, and active hydrogen atom was the main active species. The presence of Mn2+, Co2+ and Ni2+ promoted the corrosion of Zn and changed the surface morphology of Zn. The formation of type I film on Zn surface was promoted in the presence of Co2+ and Ni2+, which was conducive to the continuous corrosion of Zn and hydrogen generation. While type II film which would inhibit the corrosion of Zn formed on Zn surface in the presence of Mn2+. MnO2, Co3O4 and Ni(OH)2 were formed in Zn/Mn2+, Zn/Co2+ and Zn/Ni2+ systems, respectively. They would facilitate more generation of active hydrogen atoms.

Sculpting liquid metal stabilized interfaces: a gateway to liquid electronics.

Liquid electronics have potential applications in soft robotics, printed electronics, and healable electronics. The intrinsic shortcomings of solid-state electronics can be offset by liquid conductors. Alloys of gallium have emerged as transformative materials for liquid electronics owing to their intrinsic fluidity, conductivity, and low toxicity. However, sculpting liquid metal or its composites into a 3D architecture is a challenging task. To tackle this issue, herein, we explored the interfacial chemistry of metal ions and tannic acid (TA) complexation at a liquid-liquid interface. First, we established that an MIII-TA network at the liquid-liquid interface could structure liquid in liquid by jamming the interfacial film. The surface coverage of the droplet largely depends on the concentration of metal ions, oxidation state of metal ions and pH of the surrounding environment. Further extending the approach, we demonstrated that TA-functionalized gallium nanoparticles (Ga NPs) can also sculpt liquid droplets in the presence of transition metal ions. Finally, a mold-based free-standing 3D architecture is obtained using the interfacial reaction and interfacial crowding of a metal-phenolate network. Conductivity measurement reveals that these liquid constructs can be used for low-voltage electronic applications, thus opening the door for liquid electronics.

Synthesis, characterization, and biological evaluation of Ni, Co, and Cu Metal Complexes with Heterocyclic Compounds

Two new clinically active Schiff bases and their transition metal complexes were synthesized and studied by different spectroscopic and physicochemical methods like NMR, IR, UV-Visible, ESR, TGA, XRD, mass, elemental analysis, molar conductivity and magnetic character. Synthesized complexes and Schiff bases were assessed for invitro antituberculosis activity for Mycobacterium tuberculosis (ATCC–27294) and for antimicrobial activity against drug resistant ESBL (Extended Spectrum β-lactamase) and MBL (Metallo β-lactamase) producing microbial strains. The biological activity of Schiff base was found to improve in presence of transition metal ions. Among the studied metal complexes, copper complexes displayed superior biological activity against all of the microbial strains. Binary complexes of Cu(II), Ni(II), and Co (II) ions have been synthesized by reacting metal salts with a Schiff base, 2-((E)-(5-methylisoxazol-3-ylimino)methyl)-4-methoxyphenol (MIIMMP) in an alcoholic medium. All the metal complexes and schiff base have been characterized by using elemental analysis, IR, UV-VIS, 1H-NMR, 13C-NMR, Mass, ESR spectral data, magnetic moments, TG, and DTA studies. Based on the analytical, spectral data and molecular modeling studies, Ni (II) and Co (II) metal complexes have octahedral geometry, whereas Cu(II) complex has tetragonal geometry. The antimicrobial and cytotoxic activities of the Schiff base and its metal complexes were studied on bacteria, fungi, and human cervical carcinoma cells (HeLa).

Photocatalytic Degradation of Malachite Green Dye with UV/H2O2 System in presence of Transition Metal Ions

The chemical degradation of Malachite Green dye has been studied by using UV/H2O2 system in presence of transition metal ions (Fe2+, Mn2+ and Ti2+). The degradation reaction was carried out by circulating the aqueous dye solution in a custom-made UV reactor with the help of a variable speed peristaltic pump. The effects of initial concentration of dye, concentration of Hydrogen peroxide, operating temperature, pH, Ultrasound vibrations and transition metal ions were investigated on the time required for complete degradation of the dye. It has been found that under optimum conditions the dye could be degraded in minimum possible time especially in presence of transition metals like iron. The intermediate products obtained during the degradation process were subjected to FTIR spectroscopy for structural analysis. The residue spectra did not show any band revealing the presence of any aromatic ring. To check the completion of the reaction the final residue was analyzed for total organic carbon (TOC). All such tests indicated that the dye has been completely degraded leaving no detectable residue

Interfacial and rheological properties of long-lived foams stabilized by rice proteins complexed to transition metal ions in the presence of alkyl polyglycoside

HypothesisTransition-metal coordination complexes are hopeful to make advanced structural materials, since the metal-coordination bonds, unlike typical covalent bonds, can regenerate after rupture, allowing for dynamic, tunable, and reversible mechanical characteristics. Integration of metal-coordinate crosslinking in foam material has rarely been reported. ExperimentsWe developed the hydrolyzed rice proteins (HRP) as the building block for amphiphilic transition-metal coordination complexes that could be used to make long-lived foams with high yield stress. Surface properties of the foaming solution were determined using equilibrium and dynamic tensiometers. Structural information of aggregates in the foaming solution was detected by small-angle X-ray scattering (SAXS) and Cryo-Tem. Visualization of liquid flow in the interfacial liquid film was studied by the reflective optical interference technique. Rheological response of liquid foam was characterized by a rheometer with amplitude-sweep and frequency-sweep modes. FindingsIn the presence of transition metal ions, HRP formed a mechanically strong rigid film. In the absence of transition metal ions or the addition of alkyl polyglycoside (APG), HRP was desorbed to produce a mobile film with a detergent state. The two interfacial states could be actively switched based on facile changes in bulk solution composition (metal ions or alkyl glycoside or chelating agent), and the switching between the two states led to the formation of extremely stable foam with high yield stress or the collapse of foam with a significant decrease in yield limit. The transition-metal coordination complexes adsorbed on the surface of the liquid film could increase the elastic modulus of liquid foam by more than an order of magnitude without increasing the viscosity of the foaming solution. We further revealed the origin of foam stability/instability and used other well-characterized proteins to prepare transition-metal coordination complexes to make long-lived foams. The cases described in this work illustrate the universal nature of the strategy, which in principle can be extended to many types of protein.

Assessing Free Radical Scavenging Activity of Various Cerium Materials for Proton Exchange Membrane Fuel Cells Using Fluorescence Spectroscopy Presentation Format

Proton-exchange membrane fuel cells (PEMFCs) are an electrochemical energy conversion device that only has water vapor as an emission. During fuel cell operation, the PEM undergoes mechanical, thermal, and chemical degradation. The chemical degradation is attributed to reactive oxygen species (ROS) that are generated in situ through both chemical and electrochemical pathways during fuel cell operation. Hydrogen peroxide (H2O2) is a reactive oxygen species (ROS) and is often an intermediate formed in the presence of transition metal ion like Fe2+ or Fe3+. The free radical ROS mainly hydroxyl and hydroperoxyl radicals initiate oxidative degradation of both the PEM backbone and the side chains that contain ionic groups that are essential for ion conduction. In this study, various types of free radical scavenger (FRS) additives’ free radical scavenging activity are assessed using ex-situ and in-situ fluorescence spectroscopy(1, 2). Some of FRS materials studied are cerium oxide and doped ceria salts. The scavenging ability of the FRS materials were related to their physio-chemical properties – which were assessed by XPS, SEM, and dynamic light scattering (zetasizer). V. Prabhakaran, C. G. Arges and V. Ramani, Proceedings of the National Academy of Sciences of the United States of America, 109, 1029 (2012).V. Prabhakaran, C. G. Arges and V. Ramani, Phys Chem Chem Phys, 15, 18965 (2013).

(Digital Presentation) Cathodic Exfoliation of Few-Layer Tellurium As Electrocatalyst Support for Hydrogen Evolution

Few-layer tellurium represents the two-dimensional (2D) form of tellurium crystal with the majority of the Te atoms exposed on its surface. Recent studies demonstrated that 2D Te has good environmental stability and high charge carrier mobility, making it suitable electrocatalyst support to host active sites and assist electron transfer between the electrode and the sites [1]. Yet, its mass production for electrocatalysis application remains challenging.In this study, we present a simple cathodic exfoliation method to exfoliate commercially available Te crystal directly into few-layer tellurium with exceptionally high yield [2] (see Figure 1A). Using alkaline aqueous electrolyte (1.0 M KOH), Te nanosheets with the thickness of 7~10 nm and lateral size of 1~4 µm were produced at an applied potential of −0.42 V (vs. RHE). Combining in situ Raman spectroscopy and ex situcharacterization results, we were able to reveal the exfoliation mechanism, where the in situ generated ditelluride (Te2 2−) anions on the nanosheets played the critical role of separating nanosheets from the bulk crystal (see Figure 1B).At the presence of transition metal ions in the electrolyte, such as Pt2+ and Ni2+, simultaneous surface doping of Te nanosheets was enabled by the interaction between Te2 2− anions and metal ions, producing Pt/Ni-doped Te with tunable doping level. Such doped nanosheets exhibited high stability and hydrogen evolution reaction (HER) activity. Particularly at high potential, Pt-doped Te nanosheets outperformed both polycrystalline Pt and commercial Pt/C catalysts (see Figure 1C). We suggested a collaborative hydrogen production mechanism via Volmer–Heyrovsky pathway to justify such unusual activity. In short, at HER conditions, the surface Te atoms of Pt-doped Te nanosheets are reduced to Te2 2− anions. Such species can help attract protons and assist their transfer to adjacent Pt atoms, where the protons are reduced to form hydrogen (see Figure 1D). Figure 1 (A) Experimental setup and photos of the electrochemical exfoliation of Te crystal; (B) Exfoliation mechanism; (C) HER performance and relative energy of Pt-doped Te with various doping levels; (D) Collaborative HER mechanism. Reference: Shi, Z.; Cao, R.; Khan, K.; Tareen, A. K.; Liu, X.; Liang, W.; Zhang, Y.; Ma, C.; Guo, Z.; Luo, X.; Zhang, H., Nano-Micro Lett. 2020, 12 (1), 99. Zheng, W.; Li, Y.; Liu, M.; Lee, L. Y. S., Small 2021, 17 (18), e2007768. Figure 1

Effect of gamma rays on Zn/Cu doped strontium borate glass system for dosimetric applications

Abstract Two alkali strontium borate glasses containing Cu2+ or Zn2+ ions (0.15 mol%) has been prepared by melting annealing method. Some of the glasses dosimetric measurements have been performed; they were checked by ultraviolet-visible light measurement showing the specific peaks of Cu+/Cu2+ and Zn2+ ions. Upon γ-rays, glasses are sensitive to the absorbed dose in the range 0.4–15 kGy, revealing their light absorption. A gradual decrease in optical absorbance and DC electrical conductivity was detected with progressive irradiation. While a gradual increase in optical energy bandgap (Eopt) and electron paramagnetic resonance (EPR) was observed. The presence of transition metal ion (TM) with their variable configurations helps to trap the radiolytic electrons or holes during the color center recovery rates. UV–Vis and EPR dosimetric characteristics have high color stability with excellent short and long-term stability revealing their possible use as glass dosimeters in medical sterilization and food irradiation processing.

Theoretical insight into the catalytic effect of transition metal ions on the aquathermal degradation of heavy oil: A DFT study of cyclohexyl phenyl amine cleavage

The recovery of oil deposits strongly depends on the flow characteristics. The degree of oil extraction can be substantially increased using the steam injection method, which can be further enhanced by catalytic upgrading of heavy oil fractions under conditions of aquathermolysis directly in the reservoir with the purpose to reduce viscosity. Transition metal ions, such as Fe(II), Co(II), Ni(II), and Cu(II), are capable of catalyzing the aquathermolysis reactions, but it is essential to better understand the mechanisms and kinetics of the catalytic aquathermolysis for effective selection and molecular design of catalysts for different types of heavy oil. In continuation of our previous theoretical efforts to clarify the catalytic mechanism and kinetics of the aquathermal cleavage of ether and sulfide heteroatomic linkages in heavy oil with use of quantum chemical tools, the thermochemical and kinetic parameters of catalytic aquathermolysis of cyclohexyl phenyl amine in the presence of transition metal ions are calculated by the DFT method based on the B3LYP, ωB97X-D, and M06-2X functionals. An analysis of the thermochemistry and kinetics of the aquathermolysis of model compound N-cyclohexyl aniline shows that the most probable mechanism of the aquathermal degradation proceeds through the heterolytic cleavage of the C–N bond with formation of cyclohexyl carbocation. According to the DFT calculation results, hydroxonium ions and transition metal ions, such as Fe(II), Co(II), and Ni(II), can substantially reduce the kinetic energy barrier of C–N bond breakage and, thereby, catalyze the aquathermal degradation of the model amine compound. However, the copper(II) ion stands out from other transition metals under study by stronger coordination bonds with amines, which leads to the self-poisoning of this catalyst by a reaction product, namely, aniline that is formed as a result of the aquathermolysis reaction. The catalytic effects of the hydroxonium ion and the iron(II), cobalt(II), and nickel(II) ions are comparable to each other and can be arranged in the following sequence in decreasing order of their catalytic strength: Ni2+ ≈ Co2+ > H3O+ > Fe2+.

Electrochemical sensitive detection of hydrazine through cobalt-doped cerium oxide nanostructured platform

Chemically synthesized cobalt-doped cerium oxide nanoparticles (CeO2: Co NPs) were successfully prepared by complexed based co-precipitation process. The structural, morphological, chemical composition, optical properties, and electrocatalytic properties were determined by X-ray diffraction pattern (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), UV/visible absorption spectroscopy, and cyclic voltammetry techniques. Owing to the wide-spread applications of CeO2 NPs in various fields of applied material sciences, transition metal ion-doped CeO2: Co NPs exhibited excellent electrocatalytic properties. Outstanding physiochemical properties of CeO2, such as reversible oxidation states, high ionic mobility, large oxygen storage ability, effective large specific surface area, and the excellent current response, were observed in the electrocatalytic oxidation of hydrazine. The presence of transition metal ions (cobalt) improves the oxidation potential of hydrazine. Cyclic voltammetry was analog with the electrochemical impedance spectroscopy results, which revealed the enhanced with rapid sensing response against hydrazine. The electrocatalytic results of the CeO2: Co NPs electrode exhibited excellent voltammetry and impedance spectroscopy performance towards the hydrazine oxidation. The fabricated chemical sensor shows a wide linear detection range from 7.18 to 1000 µM, a low detection limit 7.2 µM, and sensitivity of 2.42 µAmLµM−1 cm−2. The fabricated sensing electrode demonstrated long-term steadiness, resulting in high sensitivity, selectivity, repeatability/reproducibility, and rapid detection of hydrazine.

Peroxiredoxin 2 oxidation reveals hydrogen peroxide generation within erythrocytes during high-dose vitamin C administration

Intravenous infusion of high dose (>10 g) vitamin C (IVC) is a common alternative cancer therapy. IVC results in millimolar levels of circulating ascorbate, which is proposed to generate cytotoxic quantities of H2O2 in the presence of transition metal ions. In this study we report on the in vitro and in vivo effects of millimolar ascorbate on erythrocytes. Addition of ascorbate to whole blood increased erythrocyte intracellular ascorbate approximately 35-fold. Within 10 min of ascorbate addition, we detected increased oxidation of erythrocyte peroxiredoxin 2 (Prx2), a major thiol antioxidant protein and a sensitive marker of H2O2 production. Up to 50% of Prx2 was present in the oxidised form after 60 min. The presence of extracellular catalase, removal of plasma or the addition of a metal chelator did not prevent ascorbate-induced Prx2 oxidation, suggesting that the H2O2 responsible for Prx2 oxidation was generated within the erythrocyte. Ascorbate is known to increase the rate of haemoglobin autoxidation and H2O2 production. Through spectral monitoring of oxidised haemoglobin we estimated a generation rate of 15 μM H2O2/min inside erythrocytes. We also investigated changes in erythrocyte ascorbate concentration and Prx2 oxidation following IVC infusion in a cohort of patients with cancer. Plasma ascorbate levels ranged from 7.8 to 35 mM immediately post infusion, while erythrocyte ascorbate levels reached 1.5–3.4 mM 4 h after beginning infusion. Transient oxidation of erythrocyte Prx2 was observed. We conclude that erythrocytes accumulate ascorbate during IVC infusion, providing a significant reservoir of ascorbate, and this ascorbate increases H2O2 generation within the cells. The consequence of increased erythrocyte Prx2 oxidation warrants further investigation.

DNA damage in a solution containing copper(II) ions and ascorbic acid: Effect of the presence of sulfite

Some antioxidant compounds have a pro-oxidant effect in the presence of transition metal ions, due to the reduction of Mn+ to M(n-1)+ with simultaneous formation of free radicals, which then promote DNA damage. In the present study, we evaluated the pUC19 DNA damage in a solution containing Cu(II) and ascorbic acid (AA) or S(IV) saturated with air by agarose gel electrophoresis. Our results showed that this damage decreases if AA and S(IV) are simultaneously added. This study also illustrates the importance of Cu(II) in this process, as no DNA damage was observed when AA or S(IV) were present in the absence of this metallic ion. Our data showed that DNA preservation depends on the concentration of AA and S(IV) and occurs when the [S(IV)]:[AA] ratio ranges from 1:1 to 20:1. Absorbance measurements and thermodynamic data show that no reaction occurs between AA and S(IV) when this mixture (pH 5.5) is added to pUC-19 DNA. The presence of dissolved oxygen may be the cause of AA consumption in the mixture of these two antioxidants, which subsequently decreases DNA damage.

Intramolecular H-bond stabilization of a primary hydroxylamine in salen-type metal complexes.

Primary hydroxylamines, RNHOH, decompose readily in the presence of transition metal ions. We show that this reactivity can be arrested by ligand design via an intramolecular hydrogen bond. Six metal complexes with an intact NHOH group were synthesized and crystallographically characterized. The Cu-hydroxylamine complexes can catalyze the aerobic oxidation of benzylic alcohols.

Metal doped titania nanoparticles as efficient photocatalyst for dyes degradation

Objectives: The present work aims at the synthesis of metal-doped and undoped titania photocatalysts for the degradation of methylene blue and neutral red dyes. Methods: Un-doped and metal-doped titania photocatalysts were synthesized by hydrothermal treatment, calcined at 673 K, and were evaluated by SEM, XRD, and XPS techniques for their phase composition. Results and conclusions: XPS studies of photo catalysts confirmed the presence of transition metal ions of Co, Ni, and Zn as dopants along with titania. XRD analysis indicated that all the synthesized photocatalysts were in the anatase phase. The morphology of prepared photocatalysts was confirmed through SEM analysis. The synthesized nanoparticle’s photocatalytic nature was examined through testing their degradation potentials of methylene blue and neutral red dyes under UV light irradiation. Under optimized conditions, like pH, contact time, initial dye concentration and catalyst amount metal-doped titania photocatalysts showed higher photodegradation efficiency than the pure parental material. Among the metal doped titania best results were obtained with Ni doped titania as 90% and 95% degradation were observed for neutral red and methylene blue dyes respectively. This photocatalyst can therefore be used successfully to degrade the selected dyes present in industrial effluents.

Evaluation of physical and radiation shielding properties of Bi2O3–B2O3 glass doped transition metals ions

Bismuth borate glasses of formula 60% Bi2O3 and 40% B2O3 doped 0.7 wt % of one of the transition metal oxides; TiO2, Cr2O3, V2O5 or Fe2O3 were prepared using melting-annealing method. The glasses optical transmittance spectra have been studied and reveal UV transmission bands related to the different valence states of the doped transition metal ions. Electrical conductivity and many physical parameters of the glasses were also investigated such as; optical bandgap (Eopt), refractive index (n), reflection loss (RL), molar refractivity (Rm), molar polarizability (αm), dielectric constants (ε), optical transmission coefficient (T) and metallization criterion (M Criterion).The effectiveness of the glasses as radiation protective shield was evaluated and calculated by Monte Carlo N-Particle Transport Code (MCNP) using the Medical Internal Radiation Dose (MIRD) of male human model. Many shielding parameters have been also deliberated such as; linear attenuation coefficient, effective removal cross section (ΣR), radiation protective efficiency (RPE %), tissue weighting factors (Wt), in addition to a comparison between the experimental and the simulated linear gamma attenuation coefficients at numerous energies. The glasses reveal high stable optical and physical properties in addition to high radiation shielding efficiency against gamma irradiation. The high concentration of heavy Bi3+ ions and presence of transition metal ions with their variable configurations, provide the shielding behavior of the glasses and decreased the life time risk for cancer by about five times.

Physical Model of Catalyst Dissolution, Platinum Band Formation, Hydrogen Peroxide Production and Chemical Degradation of Proton Exchange Membrane in Low Temperature Fuel Cells

Low temperature fuel cells with perfluorinated proton exchange membrane (LT-PEMFC) are recognized as one of the most promising technologies for clean electricity production in automotive sector. Despite significant progress in their efficiency and reliability, the degradation of fuel cells still remains an important issue, significantly hindering their wider market adoption. Degradation processes can to some extent be avoided by the use of new, more durable materials and components, but also by properly managing the fuel cell operation and thus avoiding the conditions in which the fuel cell degradation is most pronounced. Fast and reliable computational models of fuel cell operation and degradation are crucial for efficient development of such mitigation strategies.The catalyst layer and the membrane are the components recognized as being most susceptible to degradation phenomena. In the catalyst layer, high temperature, electric potential and relative humidity lead to electrochemical corrosion of carbon support and dissolution of the catalyst, most commonly being platinum or platinum-based binary alloy. Dissolved platinum, diffusing into the membrane, plays an important role in its chemical and consequent mechanical degradation. The platinum particles in the membrane serve as the catalyst for hydrogen peroxide formation from crossover fluxes of hydrogen and oxygen, while the presence of transition metal ions, such as copper or cobalt, originating from the binary catalyst dissolution, initiate the decay of hydrogen peroxide into various radical species via Fenton-like reactions [1]. The radical’s attack on the perfluorinated chains and sulphonic groups leads to a reduction of membrane conductivity, thinning of the membrane and consequent increase in its susceptibility to mechanical degradation, caused by the swelling and shrinking of the membrane due to the changes in its humidity, which can result in formation of cracks and pinholes in the membrane.To properly model the entire causal chain of chemical membrane degradation, several individual processes mentioned above need to be coupled into a unified model. To achieve this, we present a physically based spatially and temporally resolved model of fuel cell operation, providing the detailed picture of species concentration and electric potential distribution in the fuel cell [2], coupled with innovative model of hydrogen peroxide formation, diffusion and decay into reactive radicals, causing the chemical degradation of the membrane. The model describes the electrochemical dissolution of binary alloy catalyst, its diffusion into the membrane and the formation of so-called Pt band. The hydrogen peroxide production is modeled by including both its formation in the catalyst layers and inside the Pt band by consistently taking into account the cross-over fluxes of reactants and local electric potential across the membrane [3]. The rate of radical formation (.H, .OH, .OOH) via Fenton-like reactions is modeled by considering the concentration of transition metal ions, originating from electrochemical dissolution of binary alloy catalyst and their diffusion into the membrane. The chemical degradation due to reactive radical’s attack on the membrane is described by recently developed 0-D reactor approach [4].The output of the model is a detailed spatially and temporally resolved profile of chemical groups concentration in the membrane, which enables the calculation of changes in both membrane thickness and proton conductivity. The results, indicating most pronounced membrane degradation in vicinity of Pt band, are compatible with the Raman measurements of chemical group concentrations in the aged membrane [5]. Furthermore, the testing of the model on long-term degradation experiments is used to identify the optimal fuel cell operating conditions in which the durability of the fuel cell membrane is maximized.[1] Strlič M, Kolar J, Šelih VS, Kočar D, Pihlar B. A comparative study of several transition metals in fenton-like reaction systems at circum-neutral pH, Acta Chim Slov 2003;50:619–32.[2] Tavčar G, Katrašnik T. A Real Time Capable Quasi 3D System Level Model of PEM Fuel Cells, Fuel Cells 2020;20:17–32.[3] Burlatsky SF, Gummalla M, Atrazhev V V., Dmitriev D V., Kuzminyh NY, Erikhman NS. The Dynamics of Platinum Precipitation in an Ion Exchange Membrane, J Electrochem Soc 2011;158:B322.[4] Frühwirt P, Kregar A, Törring JT, Katrašnik T, Gescheidt G. Holistic approach to chemical degradation of Nafion membranes in fuel cells: modelling and predictions, Phys Chem Chem Phys 2020;22:5647–66.[5] Ohma A, Yamamoto S, Shinohara K. Membrane degradation mechanism during open-circuit voltage hold test. J Power Sources 2008;182:39–47. Figure 1

Five Nitrogen Oxidation States from Nitro to Amine: Stabilization and Reactivity of a Metastable Arylhydroxylamine Complex.

Redox noninnocent ligands enhance the reactivity of the metal they complex, a strategy used by metalloenzymes and in catalysis. Herein, we report a series of copper complexes with the same ligand framework, but with a pendant nitrogen group that spans five different redox states between nitro and amine. Of particular interest is the synthesis of a unprecedented copper(I)-arylhydroxylamine complex. While hydroxylamines typically disproportionate or decompose in the presence of transition metal ions, the reactivity of this metastable species is arrested by the presence of an intramolecular hydrogen bond. Two-electron oxidation yields a copper(II)-(arylnitrosyl radical) complex that can dissociate to a copper(I) species with uncoordinated arylnitroso. This combination of ligand redox noninnocence and hemilability provides opportunities in catalysis for two-electron chemistry via a one-electron copper(I/II) shuttle, as exemplified with an aerobic alcohol oxidation.

Kinetic and Thermodynamic Study of Oxidative Decolourisation of a Typical Food Dye (Tartrazine) in an Aqueous Environment

The study was carried out to describe the kinetics and thermodynamics of hydrogen peroxide oxidation of a typical food dye (Tartrazine). The effect of different operational factors were investigated spectrophotometricallyat wavelength460 nm under pseudo first order reaction.These included concentration of the oxidant and the dye, the pH, ionic strength and temperature of the reacting medium and the presence of transition metal ion as homogenous catalyst. A complete and smooth decolourisation was observed. The results showed that the rate of oxidation of dye increased with increasing in concentration of substrate and oxidant. Increasing in temperature, ionic strength and pH of the basic reaction medium also raised the reaction rate. The rate of oxidation also increased with increasing in the concentration of Fe (III) ion. Pseudo second order rate constant (k2) obtained was 1.95 x 10-3 M-1s-1 and 3.8 x10-3M-1s-1 in the absence and presence of Fe (III) ion respectively. The Arrhenius activation energy for the oxidation in the absence and presence of Fe (III) ion were 47.23 kJmol-1 and 42kJmol-1 respectively. Other thermodynamic parameters showed entropy of activation (ΔS#), free energy of activation (ΔG#) and Enthalpy of activation of the reaction (ΔH#) in the presence of Fe (III) as -34.7 JK-1mol-1, 48.4 kJmol-1 and 40.30 kJmol-1 respectively. The results in the absence of Fe (III) ion were -24.6 JK-1mol-1, 51.2 kJmol-1 and 44.0 kJmol-1respectively. The relative lower activation energy (Ea),fairly higher negative value of (ΔS#) and higher (ΔG#) , with higher rate constant in the presence of Fe(III) ion showed Fe(III) ion enhancement of rate of decolourisation.
 Keywords: Tartrazine Food dye, Kinetics, Thermodynamics, Hydrogen Peroxidede colourisation,