Arrhenius Analysis Research Articles

Kinetics of Oxygen Evolution Reaction in Soluble Lead Flow Batteries

Abstract Kinetics of oxygen evolution reaction (OER) on PbO2 deposited glassy carbon disk electrode in methane sulfonic acid (MSA) is analyzed with cyclic voltammetry and electrochemical impedance spectroscopy, for soluble lead flow battery applications. The effect of concentration of active species (Pb2+), and the electrolyte (MSA) on the OER at the deposited PbO2 layer is investigated. The apparent activation energy of the OER on PbO2, deposited at various overpotential, is obtained from the Arrhenius and Eyring analysis. The apparent activation energy follows a special trend that it increases with overpotential, reaches a maximum and decreases thereafter. This is consistent with the PbO2 specifically deposited from low concentration of MSA (<1M), where the gel layer composed of hydrated PbO(OH)2 is also found. It is observed that low MSA concentration is preferred for limiting the OER at the positive electrode.

Large-Scale Analysis on Accelerated Aging of Pentaerythritol Tetranitrate (PETN) Powders in Detonators.

Pentaerythritol tetranitrate (PETN) has been used extensively in commercial detonators and other explosive applications for many decades. Here, we show the results of a comprehensive 1.5 year aging study of PETN in commercial detonators, addressing batch-to-batch variations, surface area changes, and comparisons of aged loose powders side-by-side with identically aged detonators. Function time analysis of the aged detonators has also been provided and discussed in the context of powder aging. This large-scale, statistically relevant study addresses long-standing questions on PETN aging without the complications from making comparisons between multiple batches of material. We have evaluated the aging time required to reach the maximum measured amount of PETN coarsening and estimated an activation barrier of ∼123 kJ mol-1, which is higher than literature values reported by Gee et al. It is possible that this discrepancy is due to the fact that that this study cannot quantify the relative contributions of surface diffusion versus sublimation processes. At the lower temperatures of 50 and 60 °C, we assume that surface diffusion dominates over sublimation processes, even at longer aging times. At the higher temperature of 75 °C, we assume that both surface diffusion and sublimation contribute at the early time points, which are included in the Arrhenius analysis for coarsening.

Densities, Viscosities, and Self-Diffusion Coefficients of Octan-1-ol and Related Ether-Alcohols.

Density, viscosity, and self-diffusion coefficients are reported for octan-1-ol and the related ether-alcohols 2-pentoxy-ethan-1-ol, 3-butoxypropan-1-ol, 4-propoxybutan-1-ol, 5-ethoxypentan-1-ol, and 6-methoxyhexan-1-ol covering temperature ranges from 298.15 to 359.15 K. These new data reveal structure-property relationships affected by the presence and the position of the ether moiety in the molecular structure of the ether-alcohols. Compared to octan-1-ol, the presence of the ether moiety causes an increase in intermolecular hydrogen bonding interactions, resulting in higher densities. The increase in density is less pronounced for those ether-octanols that engage in intramolecular hydrogen bonding. As for the effects of the ether moiety on the dynamics, these are generally faster for the ether-alcohols compared to octan-1-ol, suggesting that hydrogen bonding between ether oxygen and hydroxy hydrogen is weaker compared to hydrogen bonding between two hydroxy groups. The activation energies obtained from an Arrhenius analysis are higher for translational motion than for momentum transfer for all alcohols. There are additional finer details across the ether alcohols for these activation barriers. These differences cancel out for the mathematical product of self-diffusion coefficient and viscosity (Dη). The effect of water impurities on the studied properties was also investigated and found to lead to small increases in densities for all alcohols. Viscosities decrease for octan-1-ol and 2-pentoxyethan-1-ol but increase for the other ether-alcohols that can engage in intramolecular hydrogen bonding.

Evidence of gas phase nucleation of nanodiamond in microwave plasma assisted chemical vapor deposition

The mechanism of ballas-like nanodiamond formation still remains elusive, and this work attempts to analyze its formation in the framework of activation energy (Ea) of nanodiamond films grown from a H2/CH4 plasma in a 2.45 GHz chemical vapor deposition system. The Ea was calculated from the Arrhenius equation corresponding to the thickness growth rate using substrate temperature (∼1000−1300 K) in all the calculations. While the calculated values matched with the Ea for nanodiamond formation throughout the literature, these values of ∼10 kcal/mol were lower compared to ∼15–25 kcal/mol for standard single crystal diamond (SCD) formation, concluding thus far that the energetics and processes involved were different. Further, the substrate preparation and sample collection method were modified while keeping the growth parameters constant. Unseeded Si substrate was physically separated from the plasma discharge by a molybdenum disk with a pinhole drilled in it. Small quantity of a sample substance was collected on the substrate. The sample was characterized by electron microscopy and Raman spectroscopy, confirming it to be nanodiamond, thus suggesting that nanodiamond self-nucleated in the plasma and flowed to the substrate that acted as a mere collection plate. It is hypothesized then, if nanodiamond nucleates in gas phase, gas temperature has to be used in the Arrhenius analysis. The Ea values for all the nanodiamond films were re-calculated using the simulated gas temperature (∼1500−2000 K) obtained from a simple H2/CH4 plasma model, giving new values within the range characteristic to SCD formation. Based on these findings, a unified growth mechanism for nanodiamond and SCD is proposed, concluding that the rate-limiting reactions for nanodiamond and SCD formation are the same.

Temperature-Dependent Frictional Behavior of MoS2 in Humid Environments: Insights from Water Molecule Adsorption and DFT Analyses.

This study investigates the temperature-dependent frictional behavior of MoS2 in humid environments within the context of a long-standing debate over increased friction due to oxidation processes or molecular adsorption. By combining sliding friction experiments and density functional theory (DFT)-based first-principles simulations, it aims to clarify the role of water molecule adsorption in influencing frictional properties of MoS2, addressing the challenge of identifying interfacial bonding behavior responsible for friction in such conditions. Sliding experiments revealed that magnetron-sputtered MoS2 exhibits a reduction in the coefficient of friction (COF) with an increase in temperature from 25 to 100 °C under 20 and 40% relative humidity. This change in the COF obeys the Arrhenius law, presenting an energy barrier of 0.165 eV, indicative of the temperature-dependent nature of these frictional changes and suggests a consistent frictional mechanism. DFT simulations showed that H2O molecules are adsorbed at MoS2 vacancy defects with adsorption energies ranging from -0.56 to -0.17 eV, which align with the experimentally determined energy barrier. Adsorptive interactions, particularly the formation of stable H···S interfacial hydrogen bonds at defect sites, increase the interlayer adhesion and impede layer shearing. TEM analysis confirms that although MoS2 layers align parallel to the sliding direction in humid conditions, the COF remains at 0.12, as opposed to approximately 0.02 in dry air. This demonstrates that parallel layer alignment does not notably decrease the COF, underscoring humidity's significant role in MoS2's COF values, a result also supported by the Arrhenius analysis. The reversibility of the physisorption process, demonstrated by the recovery of the COF in high-temperature humid environments, suggests its dynamic nature. This study yields fundamental insights into MoS2 interfaces for environments with variable humidity and temperature, crucial for demanding tribological applications.

Coverage-dependent desorption kinetics of water on a well-ordered alumina thin film surface.

We have developed an experimental and analytical setup for thermal desorption spectroscopy of solid water films on surfaces. We obtain the coverage-dependent desorption kinetics of water molecules from a well-defined ultra-thin alumina/NiAl(110) surface in the coverage range of 0-2 monolayers. We use a novel deconvolution technique to eliminate the pumping delay of water vapor in the vacuum system, which has previously hindered the accurate estimation of desorption kinetic parameters, such as activation energy and pre-exponential factor. The coverage-dependent Arrhenius analysis reveals that the desorption activation energy decreases with increasing coverage in the sub-monolayer range, indicating that the water-water interaction is not attractive. We also find that the pre-exponential factor for the second layer is higher than that for the sub-monolayer. We explain this difference in terms of transition state theory and propose that entropic effects play a significant role in water desorption kinetics.

Differences in Photophysical Properties and Photochemistry of Ru(II)-Terpyridine Complexes of CH3CN and Pyridine.

A series of 22 Ru(II) complexes of the type [Ru(tpy)(L)(L')]n+, where tpy is the tridentate ligand 2,2';6,2″-terpyridine, L represents bidentate ligands with varying electron-donating ability, and L' is acetonitrile (1a-11a) or pyridine (1b-11b), were investigated. The dissociation of acetonitrile occurs from the 3MLCT state in 1a-11a, such that it does not require the population of a 3LF state. Electrochemistry and spectroscopic data demonstrate that the ground states of these series do not differ significantly. Franck-Condon line-shape analysis of the 77 K emission data shows no significant differences between the emitting 3MLCT states in both series. Arrhenius analysis of the temperature dependence of 3MLCT lifetimes shows that the energy barrier (Ea) to thermally populating a 3LF state from a lower energy 3MLCT state is significantly higher in the pyridine than in the CH3CN series, consistent with the photostability of complexes 1b-11b, which do not undergo pyridine photodissociation under our experimental conditions. Importantly, these results demonstrate that ligand photodissociation of pyridine in 1b-11b does not take place directly from the 3MLCT state, as is the case for 1a-11a. These findings have potential impact on the rational design of complexes for a number of applications, including photochemotherapy, dye-sensitized solar cells, and photocatalysis.

Storage Stability of Atheroglitatide, an Echogenic Liposomal Formulation of Pioglitazone Targeted to Advanced Atheroma with a Fibrin-Binding Peptide.

We have conducted a stability study of a complex liposomal pharmaceutical product, Atheroglitatide (AGT), stored at three temperatures, 4, 24, and 37 °C, for up to six months. The six parameters measured were functions of liposomal integrity (size and number), drug payload (loading efficiency), targeting peptide integrity (conjugation efficiency and specific avidity), and echogenicity (ultrasound-dependent controlled drug release), which were considered most relevant to the product's intended use. At 4 °C, liposome diameter trended upward, indicative of aggregation, while liposome number per mg lipid and echogenicity trended downward. At 24 °C, peptide conjugation efficiency (CE) and targeting efficiency (TE, specific avidity) trended downward. At 37 °C, CE and drug (pioglitazone) loading efficiency trended downward. At 4 °C, the intended storage temperature, echogenicity, and liposome size reached their practical tolerance limits at 6 months, fixing the product expiration at that point. Arrhenius analysis of targeting peptide CE and drug loading efficiency decay at the higher temperatures indicated complete stability of these characteristics at 4 °C. The results of this study underscore the storage stability challenges presented by complex nanopharmaceutical formulations.

Direct alkylation of benzene with branched alkanes using solid acids: Unexpected product selectivity based on the tertiary carbon position

The direct alkylation of benzene with alkanes offers significant advantages, such as the use of simple alkanes readily available from petroleum and natural gas, and no formation of byproducts containing halogens. In this study, the direct alkylation of benzene with branched alkanes was investigated using solid acid catalysts. The solid acid-catalyzed reaction of benzene with 2-methylhexane was significantly accelerated by the addition of hydrotalcite-supported Pt nanoparticles (Pt/HT). The highest alkylation product yield was approximately 20 % in the presence of H-beta and Pt/HT. The main products from the reaction of benzene and 2-methylhexane were heptylbenzenes (Ph-C7). In contrast, when 3-methylhexane was used as the branched alkane, the main products were pentylbenzenes (Ph-C5). The reaction with 3-methylhexane proceeded well with only the solid acid catalyst, whereas the acceleration effect of Pt/HT was limited. Analysis of the reaction intermediate and reaction pathway revealed that the acid-catalyzed cracking of 3-methylhexane to 2-pentene occurred, followed by benzene alkylation to afford Ph-C5. Arrhenius analysis of the alkylation of benzene with 2-methylhexane, 3-methylhexane, and n-heptane indicated that the activation energy of the reaction using 3-methylhexane was approximately 15–18 kJ mol−1 lower than those of 2-methylhexane and n-heptane, demonstrating the different alkylation pathways.

Minority Carrier Traps Induced by Neutron Reactions with 4H-SiC

This work presents the characterization of minority carrier traps in epitaxial n-type 4H-SiC after high fluence neutron irradiation using minority carrier transient spectroscopy (MCTS) in a temperature range of 20 K to 660 K. Three minority carrier trap levels are reported, labelled as X, B and Y, whose activation energies were estimated by Arrhenius analysis and where the B level is assigned to substitutional boron (BSi). The dynamic behaviour of the trap levels was studied by consecutive temperature scans.

Aldol Cleavage in Water and the Power of Citrate Lyase as a Catalyst.

Citrate lyase allows Klebsiella aerogenes to grow anaerobically on citrate as the sole carbon source. Arrhenius analysis of experiments at high temperatures indicates that citrate is cleaved nonenzymatically to acetate and oxaloacetate with a t1/2 of 6.9 million years in neutral solution at 25 °C, while malate cleavage occurs even more slowly (t1/2 = 280 million years). However, t1/2 is only 10 days for the nonenzymatic cleavage of 4-hydroxy-2-ketoglutarate, indicating that the introduction of an α-keto group enhances the rate of aldol cleavage of malate by a factor of 1010. The aldol cleavages of citrate and malate, like the decarboxylation of malonate (t1/2 = 180 years), are associated with a near-zero entropy of activation, and their extreme differences in rate reflect differences between their heats of activation. Citrate lyase enhances the rate of substrate cleavage 6 × 1015-fold, comparable in magnitude with the rate enhancement produced by OMP decarboxylase, although these enzymes are strikingly different in their mechanisms of action.

Liquid crystalline electrolytes derived from the 1,12-disubstituted [closo-CB11H12]– anion

A new approach to anisotropic liquid electrolytes is explored. Thus, a non-ionic liquid crystalline host exhibiting SmC and N phases is doped with a lithium salt containing an anion structurally similar to the host and derived from the weakly-nucleophilic [closo-CB11H12]– cluster. The resulting unaligned 5, 10, and 15 mol% solutions of the lithium salt in the host were investigated by optical, thermal, powder XRD and impedance spectroscopy methods in a broad temperature range. The results showed that the increasing concentration of the ionic additives essentially does not affect the mesophase stability, but expands the lamellar SmA phase possessing ion conducting channels. At the same time ionic conductivity, σ, monotonically increases from 10-8 to 10-4 S cm−1 with increasing temperature (20–120 °C) and with increasing Li+ ion concentration. The Arrhenius analysis of the conductivity data revealed progressively decreasing activation energy EaIC from crystalline (∼102 kJ mol−1), to SmA (∼70 kJ mol−1) and to nematic (∼30 kJ mol−1) phases. The electrochemical stability window of the 15 mol% electrolyte was determined as 1.3–4.6 V vs Li metal anode.

Weak Temperature Dependence of the Relative Rates of Chlorination and Hydrolysis of N2O5 in NaCl–Water Solutions

We have measured the temperature dependence of the ClNO2 product yield in competition with hydrolysis following N2O5 uptake to aqueous NaCl solutions. For NaCl-D2O solutions spanning 0.0054-0.21 M, the ClNO2 product yield decreases on average by only 4 ± 3% from 5 to 25 °C. Less reproducible measurements at 0.54-2.4 M NaCl also fall within this range. The ratio of the rate constants for chlorination and hydrolysis of N2O5 in D2O is determined on average to be 1150 ± 90 at 25 °C up to 0.21 M NaCl, favoring chlorination. This ratio is observed to decrease significantly at the two highest concentrations. An Arrhenius analysis reveals that the activation energy for hydrolysis is just 3.0 ± 1.5 kJ/mol larger than for chlorination up to 0.21 M, indicating that Cl- and D2O attack on N2O5 has similar energetic barriers despite the differences in charge and complexity of these reactants. In combination with the measured preexponential ratio favoring chlorination of 300-200+400, we conclude that the strong preference of N2O5 to undergo chlorination over hydrolysis is driven by dynamic and entropic, rather than enthalpic, factors. Molecular dynamics simulations elucidate the distinct solvation between strongly hydrated Cl- and the hydrophobically solvated N2O5. Combining this molecular picture with the Arrhenius analysis implicates the role of water in mediating interactions between such distinctly solvated species and suggests a role for diffusion limitations on the chlorination reaction.

Enzyme Kinetics Features of the Representative Engineered Recombinants of Chondroitinase ABC I.

Chondroitinase ABC I (cABC I) from Proteus vulgaris is an important enzyme in medicinal biotechnology due to its ability to help axon regeneration after spinal cord injury. Its practical application involves solving several problems at the molecular and cellular levels. Structurally, most residues at the C-terminal domain of cABC I are arranged as organized strands, and only a small fraction of residues have helical conformation. The structural and functional features of modified residues on two specific helix fragments have previously been reported. The single mutant M889K has been combined with L679S and L679D mutants to make enzyme variants containing simultaneously modified helix. Here, the pH stability and temperature-based analysis of the transition state structure for the catalysis reaction were investigated. We found that double mutant L679D/M889K is the better choice to use in physiological conditions due to its higher pH stability at physiological pH as well as its different optimum temperature as compared with the (wild-type) WT protein. According to Arrhenius's analysis, the values of the Gibbs free energy of the transition state (∆G#) are not changed upon mutation. However, the relative contribution and absolute values of the enthalpy and entropy change to the total value of ∆G#, varied between the WT and mutants.

Crystallization Kinetics of Vitreous Magnesium Sulfate Hydrate and Implications for Europa’s Surface

Brines consistent with that expected for Europa’s global subsurface ocean have been shown to form vitreous salt hydrates when frozen. We report experiments examining the crystallization kinetics of vitreous MgSO4 hydrate in order to better understand the stability of such materials on the surface of Europa. Vitreous MgSO4 hydrates formed from a 2 M parent solution were found to crystallize into MgSO4·11H2O (meridianiite) upon annealing at 195–225 K. Raman spectroscopy was used to monitor the crystallization and reaction rates were determined from the growth of the crystalline fraction as a function of time. Arrhenius analysis yielded an activation energy of 60 ± 9 kJ mol−1 for the vitreous to crystalline transition, implying that such transformation does not occur spontaneously at Europa’s surface temperatures. If emplacement processes favor the formation of vitreous salt hydrates, they are likely to still be stable and could be an important non-ice component on Europa at present day.

Thermal aging management of underground power cables in electricity distribution networks: a FEM-based Arrhenius analysis of the hot spot effect

Thermal aging management of underground power cables in electricity distribution networks: a FEM-based Arrhenius analysis of the hot spot effect

Acetonitrile Ligand Photosubstitution in Ru(II) Complexes Directly from the 3MLCT State.

The excited states of the series [Ru(tpy)(L)(CH3CN)]n+ (1-11) (n = 1, 2) containing bidentate ligands L with varying electron-donating ability were characterized through Arrhenius analysis of the temperature dependence of their excited-state lifetimes. Complexes 1-11 undergo photoinduced CH3CN dissociation upon 450 nm irradiation with ligand exchange quantum yields that increase with the energy barrier to populating a dissociative triplet ligand field (3LF) state from the lowest-energy triplet metal-to-ligand charge transfer (3MLCT) excited state. Combined with DFT calculations, the data indicate that ligand photodissociation in 1-11 occurs directly from the 3MLCT state instead of a 3LF state. This finding is in contrast to the generally accepted mechanism for ligand photodissociation in Ru(II) complexes and indicates that alternative pathways for photoinduced ligand dissociation are available. These results can widely impact design principles for applications that require ligand photodissociation, such as photochemotherapy and photocatalysis, as well as for those where photosubstitution is undesirable, such as solar energy conversion.

Molecular Diffusion and Self-Assembly: Quantifying the Influence of Substrate hcp and fcc Atomic Stacking.

Molecular diffusion is a fundamental process underpinning surface-confined molecular self-assembly and synthesis. Substrate topography influences molecular assembly, alignment, and reactions with the relationship between topography and diffusion linked to the thermodynamic evolution of such processes. Here, we observe preferential adsorption sites for tetraphenylporphyrin (2H-TPP) on Au(111) and interpret nucleation and growth of molecular islands at these sites in terms of spatial variation in diffusion barrier driven by local atomic arrangements of the Au(111) surface (the 22× √3 “herringbone” reconstruction). Variable-temperature scanning tunnelling microscopy facilitates characterization of molecular diffusion, and Arrhenius analysis allows quantitative characterization of diffusion barriers within fcc and hcp regions of the surface reconstruction (where the in-plane arrangement of the surface atoms is identical but the vertical stacking differs). The higher barrier for diffusion within fcc locations underpins the ubiquitous observation of preferential island growth within fcc regions, demonstrating the relationship between substrate-structure, diffusion, and molecular self-assembly.

The Dissociation of Gallium–Hydrogen Pairs in Crystalline Silicon during Illuminated Annealing

Hydrogen‐rich crystalline Si samples are produced by coating Ga‐doped Czochralski‐grown silicon wafers with SiNx:H and subsequent rapid thermal anneal. This procedure introduces H2 dimers into the bulk, which enables the formation of gallium–hydrogen pairs (GaH). The change in pair concentration can be determined by change in resistivity, as pair formation consumes holes. During illumination at elevated temperature (180 °C), some of the previously formed GaH pairs dissociate into H and/or H2 within hours. A subsequent anneal step forms the pairs again. If illumination is prolonged to days at 180 °C, a second dissociation phase occurs after which GaH pairs do not form again in the dark. Therefore, probably two processes are ongoing: a reversible (fast) one and an irreversible (slow) dissociation of GaH pairs in crystalline silicon. The fraction of dissociated pairs and rate of dissociation depend on temperature and excess charge carrier concentration. This suggests an electron‐driven, thermally activated back reaction into either H dimers or atomic hydrogen. An Arrhenius analysis reveals a possibly injection‐dependent activation energy of the reversible dissociation process in the range of 0.64–0.71 eV. Lifetime measurements reveal a drastic increase in effective defect density during the second decrease in pair concentration.

Preparation and characterization of vanadium-implanted silicon for intermediate band solar cell applications

The research of intermediate band solar cells has become a hot spot in the field of photovoltaics. The preparation of intermediate band materials is a key for intermediate band solar cell applications. In this paper, we attempted to prepare the intermediate band photovoltaic materials with supersaturated vanadium-doped silicon by ion implantation and rapid thermal treatment (RTP). The results show that the RTP technique can recover the damage to the lattice and morphology caused by ion implantation and can promote carrier activation and mobility. Moreover, the near infrared absorption of the samples is significantly enhanced, which indicates that some subband absorptions have been implemented in the samples. Furthermore, the minority carrier lifetime increases with increasing the dose of vanadium ion. This agrees with the intermediate-band prediction, suggesting an intermediate band is formed in the vanadium-doped silicon. In addition, the Arrhenius analysis shows that the intermediate band is located at about 0.43 eV below the conduction band edge of silicon. Our results indicated that the IB photovoltaic materials can be effectively prepared by vanadium-implantation in silicon and RTP technique.