Nucleation Rate Constant Research Articles

Effect of Impurities on Solubility and Metastable Zone Width of Manganese Sulfate Monohydrate

AbstractRecovering manganese from waste batteries is an important issue to promote the development of new energy. Herein, nickel sulfate and cobalt sulfate, representative impurities in waste battery leachate, are selected to examine their influence on the crystallization thermodynamics and crystal nucleation of manganese sulfate monohydrate. This work assessed alterations in solubility and metastable zone width (MSZW) due to the presence of impurities. The results showed a decrease in manganese sulfate monohydrate solubility in water with increasing impurity concentrations of either nickel sulfate or cobalt sulfate. The effects of initial concentration, heating rate, and impurity concentration on MSZW demonstrated a consistent increase in MSZW as these factors increased. The MSZW data are fitted using the self‐consistent Nývlt‐like model and the classical 3D nucleation theory model. The results revealed a general increase in the nucleation rate constant, K, with increasing saturation temperature or decreasing nickel sulfate concentration. Conversely, the solid‐liquid interface energy, γ, generally decreases with increasing saturation temperature or decreasing nickel sulfate concentration. Based on the influence observed on the interface energy, a possible mechanism is proposed that suggests that impurities inhibit crystal nucleation through adsorption.

Physicochemical mechanisms of aggregation and fibril formation of α-synuclein and apolipoprotein A-I.

Deposition and accumulation of amyloid fibrils is a hallmark of a group of diseases called amyloidosis and neurodegenerative disorders. Although polypeptides potentially have a fibril-forming propensity, native proteins have evolved into proper functional conformations to avoid aggregation and fibril formation. Understanding the mechanism for regulation of fibril formation of native proteins provides clues for the rational design of molecules for inhibiting fibril formation. Although fibril formation is a complex multistep reaction, experimentally obtained fibril formation curves can be fitted with the Finke-Watzky (F-W) two-step model for homogeneous nucleation followed by autocatalytic fibril growth. The resultant F-W rate constants for nucleation and fibril formation provide information on the chemical kinetics of fibril formation. Using the F-W two-step model analysis, we investigated the physicochemical mechanisms of fibril formation of a Parkinson's disease protein α-synuclein (αS) and a systemic amyloidosis protein apolipoprotein A-I (apoA-I). The results indicate that the C-terminal region of αS enthalpically and entropically suppresses nucleation through the intramolecular interaction with the N-terminal region and the intermolecular interaction with existing fibrils. In contrast, the nucleation of the N-terminal fragment of apoA-I is entropically driven likely due to dehydration of large hydrophobic segments in the molecule. Based on our recent findings, we discuss the similarity and difference of the fibril formation mechanisms of αS and the N-terminal fragment of apoA-I from the physicochemical viewpoints.

Phase stability and nucleation kinetics of salts in confinement

Of fundamental importance to energy storage, electrochemistry and separation processes, ionic liquids in confinement exhibit unexpected thermodynamic behaviors. Such complex behaviors highlight the need for multi-scale descriptions of the thermodynamics and dynamics of nanoconfined ionic liquids. Here, we probe the impacts of confinement on the freezing point and nucleation kinetics of a simple molten salt which shares important features with ionic liquids. Using molecular modeling techniques, the melting temperature of salt in confinement is found to be larger than its bulk counterpart. Relying on conventional thermodynamic models (Clapeyron and Gibbs-Thomson equations), we capture the crystal/liquid coexistence in bulk and confinement with simple parameters derived from molecular simulations. Then, by considering different nucleation mechanisms – bulk, surface, and confined nucleation, the metastability barrier upon salt formation is shown to decrease upon confinement, therefore providing theoretical insight into the larger nucleation rate constants observed in experiments on nanoconfined ionic liquids. We also discuss the effects of wettability on capillary freezing of ionic liquids at various confining surfaces through varying the contact angle. These findings provide a practical means to predict the melting point, wettability, and freezing kinetics of ionic liquids at various surface conditions from simple thermodynamic data.

Mutual independence of water and n-nonane nucleation at low temperatures.

The interaction of water with different substances in the earth's atmosphere lies at the heart of many processes that influence our climate. However, it is still unclear how different species interact with water on the molecular level and in which ways this interaction contributes to the water vapor phase transition. Here, we report the first measurements of water-nonane binary nucleation in the 50-110K temperature range, along with unary nucleation data of both. The time-dependent cluster size distribution in a uniform post-nozzle flow was measured by time-of-flight mass spectrometry coupled with single-photon ionization. From these data, we extract experimental rates and rate constants for both nucleation and cluster growth. The observed mass spectra of water/nonane clusters are not or only slightly affected by the introduction of the other vapor, and the formation of mixed clusters was not observed during nucleation of the mixed vapor. Additionally, the nucleation rate of either substance is not much affected by the presence (or absence) of the other species, i.e., the nucleation of water and nonane proceeds independently, indicating that hetero-molecular clusters do not play a role during nucleation. Only at the lowest temperature of our experiment (i.e., 51K) do the measurements suggest that interspecies interaction slows water cluster growth. The findings here are in contrast to our earlier work in which we showed that vapor components in other mixtures, e.g., CO2 and toluene/H2O, can interact to promote nucleation and cluster growth in a similar temperature range.

Physical, Static, and Kinetic Analysis of the Electrochemical Deposition Process for the Recovery of Heavy Metal from Industrial Wastewater.

Through the electrodeposition technique, toxic metals in wastewater can be removed and deposited on a chosen substrate with excellent selectivity. In this work, we use this technique to extract lead cations from simulated wastewater by using fluorine-doped tin oxide (FTO) substrate at various temperatures. In situ tracking of lead nucleation at advanced stages has been achieved by chronoamperometry. According to the experimental results, the theoretical models developed to study the kinetic growth of lead deposits in 2D and 3D are in good agreement. Nucleation rate and growth rate constants, for example, were found to be strongly influenced by temperature. Cottrell's equation is used to calculate the diffusion coefficient. X-ray diffraction, scanning electron microscopy, and energy-dispersiveX-ray techniques were used to investigate and characterize the lead deposits. The reported results could provide insight into the optimization of electrodeposition processes for heavy metal recovery from wastewater and electronic wastes.

PH Dependence of Amyloid-β Fibril Assembly Kinetics: Unravelling the Microscopic Molecular Processes.

Central to Alzheimer's disease (AD) is the assembly of the amyloid-beta peptide (Aβ) into fibrils. A reduction in pH accompanying inflammation or subcellular compartments, may accelerate fibril formation as the pH approaches Aβ's isoelectric point (pI). Using global fitting of fibril formation kinetics over a range of pHs, we identify the impact net charge has on individual fibril assembly microscopic rate constants. We show that the primary nucleation has a strong pH dependence. The titration behaviour exhibits a mid-point or pK a of 7.0, close to the pK a of Aβ histidine imidazoles. Surprisingly, both the secondary nucleation and elongation rate constants are pH independent. This indicates the charge of Aβ, in particular histidine protonation, has little impact on this stage of Aβ assembly. These fundamental processes are key to understanding the forces that drive the assembly of Aβ into toxic oligomers and fibrils.

PH Dependence of Amyloid-β Fibril Assembly Kinetics: Unravelling the Microscopic Molecular Processes.

Central to Alzheimer's disease (AD) is the assembly of the amyloid-beta peptide (Aβ) into fibrils. A reduction in pH accompanying inflammation or subcellular compartments, may accelerate fibril formation as the pH approaches Aβ's isoelectric point (pI). Using global fitting of fibril formation kinetics over a range of pHs, we identify the impact net charge has on individual fibril assembly microscopic rate constants. We show that the primary nucleation has a strong pH dependence. The titration behaviour exhibits a mid-point or pKa of 7.0, close to the pKa of Aβ histidine imidazoles. Surprisingly, both the secondary nucleation and elongation rate constants are pH independent. This indicates the charge of Aβ, in particular histidine protonation, has little impact on this stage of Aβ assembly. These fundamental processes are key to understanding the forces that drive the assembly of Aβ into toxic oligomers and fibrils.

Influence of Pre-Adsorbed TiO2 Particles on the Nucleation and Growth Mechanism of Ni in Deep Eutectic Solvent Electro-Codeposition

Electrodeposition holds excellent potential for creating controllable nanoscale functional interfaces. However, the key characteristics of these processes remain elusive, especially the composite electrodeposition processes involving inert nanoparticles. Herein, the pre-adsorption of inert particles is considered in detail in electro-codeposition. The nucleation and growth mechanism of nickel nanoparticles under the influence of pre-adsorbed inert particles is studied in a choline chloride–ethylene glycol deep eutectic solvent (DES). Cyclic voltammetry results show that pre-adsorbed TiO2 particles can significantly increase the cathodic reduction current, while codeposited TiO2 particles hinder the reduction process. Chronoamperometry analysis demonstrates that pure Ni electrodeposition in a DES follows the mechanism of instantaneous nucleation and tridimensional growth at a high potential, while the Ni electrodeposition deviated from the instantaneous nucleation model due to the pre-adsorption of TiO2 particles. Moreover, considering the classical model description of multiphase 3D nucleation and diffusion-controlled growth, the typical kinetic parameters such as nucleation rate constant and diffusion coefficient were investigated under different applied potentials. It was found that the nucleation rate constant of Ni electrodeposition increased significantly in the presence of pre-adsorbed TiO2 particles. These findings are of great significance for understanding and perfecting the electro-codeposition process containing inert nanoparticles.

Single Molecule Study of the Polymerization of RecA on dsDNA: The Dynamics of Individual Domains.

In the Escherichia coli, RecA plays a central role in the recombination and repair of the DNA. For homologous recombination, RecA binds to ssDNA forming a nucleoprotein filament. The RecA-ssDNA filament searches for a homologous sequence on a dsDNA and, subsequently, RecA mediates strand exchange between the ssDNA and the dsDNA. In vitro, RecA binds to both ssDNA and dsDNA. Despite a wide range of studies of the polymerization of RecA on dsDNA, both at the single molecule level and by means of biochemical methods, important aspects of this process are still awaiting a better understanding. Specifically, a detailed, quantitative description of the nucleation and growth dynamics of the RecA-dsDNA filaments is still lacking. Here, we use Optical Tweezers together with a single molecule analysis approach to measure the dynamics of the individual RecA domains on dsDNA and the corresponding growth rates for each of their fronts. We focus on the regime where the nucleation and growth rate constants, k n and k g, are comparable, leading to a coverage of the dsDNA molecule that consists of a small number of RecA domains. For the case of essentially irreversible binding (using ATPγS instead of ATP), we find that domain growth is highly asymmetric with a ratio of about 10:1 between the fast and slow fronts growth rates.

Nucleation and crystal growth kinetic parameter optimization of a continuous Poiseuille flow struvite crystallizer using a discretized population balance and dynamic fluid model

Struvite crystallization is an important process in recovering phosphorus from waste streams, but kinetic parameters involve significant uncertainty. In this research a model is developed which includes population balance, fluid flow equations, and kinetic relations. Power law rate coefficients for struvite nucleation (knuc=7.509×107L-1.min-1) and growth (kg=16.72μm.min-1) are optimised by combining a Poiseuille flow reactor model (PFR) and experimental data for phosphorus concentration and particle size distribution (PSD) at the reactor outlet. Nucleation and crystal growth rates were optimized using both filtered and sonicated PSD samples. The model incorporated three key aspects: non-ideal thermodynamics; Poiseuille fluid flow (including advection, diffusion and reaction); and a discretized population balance model (PBM). Sensitivity analysis using deltas (min/max) showed diffusion effects to be negligible and indicated that power law rate constants for both nucleation and growth were more influential on PSD and phosphorus concentration than the associated rate orders. Optimized parameters agreed reasonably well with a previous study conducted by our group under different conditions, using a different model, providing confidence in results. The optimized nucleation rate, knuc, was only 12% lower than that found using a similar model for a seeded system, where secondary nucleation is dominant. Additionally, a primary nucleation model provided a poor fit to experimental data. These two factors indicate that secondary nucleation is an influential mechanism. A 2nd order growth model provided a better fit to data than a previously suggested 5th order growth model. The optimized growth rate coefficient, kg, was higher than in any previous studies, an effect attributed to sonication, which eliminated aggregates.

Quantifying Nucleation Rates in Phase-Transforming Metal-Ion Intercalation Materials Based on Cyclic Voltammetry and Chronoamperometry Data

Phase-transforming cathode materials with a wide miscibility gap have been extensively studied for both Li-ion (LiFePO4, Li4Ti5O12) and Na-ion (Na3V2(PO4)3) batteries. In particular, LiFePO4 material has become a model system for the investigation of intercalation induced phase transformation mechanisms.1 Most of the state-of-the-art research on the phase-separating intercalation materials focuses on the elucidation of phase transformation mechanisms as well as on the theoretical assessment of the nucleation barrier heights based on the evidence from structural investigation and microscopic single particle-level experiments.2 In this work, we show that the new phase nucleation appears to be a characteristic rate-determining step for a wide range of intercalation materials (LiFePO4, V2O5, cation-rich Prussian blue analogues, Na3V2(PO4)3). We demonstrate that the nucleation rates (probabilities of critical nucleus formation) can be straightforwardly determined from the electrochemical experimental data. A simple experimental approach is proposed based on the classical nucleation theory toward interpreting electrochemical cyclic voltammetry and chronoamperometry data for phase-transforming electrodes.3 The new methodology provides for a facile assessment of the influence of various experimental factors (particle size, defect concentration, solvent nature, and surface coating) on the nucleation-controlled phase-transformation rates in intercalation materials.4 Experimental data analysis illustrates the validity of the applied approaches, which allows developing diagnostic criteria for distinguishing slow nucleation rate control from other possible rate-determining steps as well as obtaining quantitative estimates of the nucleation rate constants. R e f e r ence s 1. Malik, R.; Abdellahi, A.; Ceder, G. J. Electrochem. Soc. 2013, 160, A3179.2. Bai, P.; Bazant, M. Z. Nat. Commun. 2014, 5, 3585.3. Vassiliev, S.Yu.; Levin, E.E; Presnov, D.E; Nikitina, V.A. J. Electrochem. Soc. 2019, 166, A829.4. Iarchuk, A.R.; Nikitina, V.A.; Karpushkin, E.A.; Sergeyev, V.G.; Antipov, E.V.; Stevenson, K.J.; Abakumov, A.M. ChemElectroChem 2019, 6, 5090. Figure 1

Kinetics of Aggregation using Single-Molecule Fluorescence Techniques to Determine Nucleation and Elongation Rate Constants of Amyloid Growth

Elucidation of the underlying mechanisms of amyloid aggregation of proteins is critical in understanding the development of many neurodegenerative diseases. Self-assembly of the monomeric proteins to fibrillar forms are considered to proceed via both primary nucleation and secondary nucleation processes followed by elongation of the nuclei. However, determination of the rate constants of these microscopic processes using ensemble measurements are difficult. We have used two single-molecule sensitive techniques, viz, cuvette-FCS and total internal reflection fluorescence microscopy (TIRFM) for real time monitoring of amyloid aggregation. Analysis of the fluorescence bursts of thioflavinT arising from the protofibrils or the fibrils of amyloid-β (Aβ) in Cuvette-FCS allows measurements of concentration of the fibrils, size distribution of the fibrils and total aggregation both under quiescent conditions and in presence of stirring. Thus, cuvette-FCS allows characterization of the early aggregates and direct measurement of the nucleation and elongation rate constants. Additionally, we have established a TIRFM based approach to visualize time dependent growth of the individual amyloid fibrils. While both the techniques provide estimation of the rate constants of elongation and nucleation, TIRFM provides measurements of the heterogeneity of the various rate constants. Furthermore, TIRFM enables characterization of the parallel pathways of aggregation. However, ability to measure both fibril concentration and total aggregation at the same time in the single molecule experiments makes the measurements of the rate constants robust. For example, we find that while kinetics of the overall aggregation depend highly on sample preparation, the elongation rate constant remains almost invariable. Taken together, single molecule measurements of amyloids can be used to evaluate individual rate constants of both primary and secondary processes of amyloid aggregation.

Nucleation and growth mechanism of tellurium electrodeposited on tin-doped indium oxide substrate

The mechanism of electrochemical deposition of tellurium on tin-doped indium oxide (ITO) substrate from a nitric acid solution containing telluryl ion (HTeO2+) has been studied in this work. The investigation, using cyclic voltammetry and chronoamperometry, shows that the electrodeposition of Te at a negative potential around − 0.42 V versus saturated calomel electrode (SCE) is a quasi-reversible reaction controlled by the diffusion process. Furthermore, by chronoamperometry, the measured current transient curves were compared with the theoretical models, proposed by Scharifker–Hills and Heerman–Tarallo models. It was found that the nucleation and growth mechanism of Te on ITO substrate changed with increasing the concentration of HTeO2+, it can be instantaneous for 2.10−2 mol L−1 or progressive for 2.10−3 mol L−1. The quantitative analysis (nonlinear fitting) shows that the diffusion coefficient remains between 7.10−6 and 9.10−6 cm2 s−1, the nucleation rate constant A and the number density of active sites N0 were growth with the increase of the concentration and the deposition potential. The thin tellurium layers, electrodeposited by chronoamperometry, are characterized by X-ray diffraction. It has been identified that all the films were polycrystalline type hexagonal crystal structure with preferred orientation of (1 0 0) and (1 1 0) planes to growth. The SEM analysis reveals that the morphology of the resulting deposits is depending on the type of electrodeposition mechanism.

A new hydration kinetics model of composite cementitious materials, part 1: Hydration kinetic model of Portland cement

AbstractThis work is the first part of an overall research project that aims to model the hydration kinetics of modern composite cementitious materials. The aim of this part is to build a hydration kinetic model to characterize the hydration behavior of cement at all ages. In this paper, the nucleation and growth of CSH and the diffusion of water are described by a modified BNG model and a modified Jander's model. The kinetic parameters are obtained by simulative fitting of the model to the experimental data. The linear functions between the nucleation and growth rates and the W/C ratios are given in this paper. The apparent activation energy of the nucleation rate constant, growth rate constant, and generalized diffusion constant are approximately 36.0, 37.5, and 42.0 kJ/mol, respectively. Finally, the phase compositions of hardened cement paste are calculated according to the kinetic model and the reaction formula of cement.

Reaction coordinates and rate constants for liquid droplet nucleation: Quantifying the interplay between driving force and memory

In this work, we revisit the classic problem of homogeneous nucleation of a liquid droplet in a supersaturated vapor phase. We consider this at different extents of the driving force, or equivalently the supersaturation, and calculate a reaction coordinate (RC) for nucleation as the driving force is varied. The RC is constructed as a linear combination of three order parameters, where one accounts for the number of liquidlike atoms and the other two for local density fluctuations. The RC is calculated from biased and unbiased molecular dynamics (MD) simulations using the spectral gap optimization approach "SGOOP" [P. Tiwary and B. J. Berne, Proc. Natl. Acad. Sci. U. S. A. 113, 2839 (2016)]. Our key finding is that as the supersaturation decreases, the RC ceases to simply be the number of liquidlike atoms, and instead, it becomes important to explicitly consider local density fluctuations that correlate with shape and density variations in the nucleus. All three order parameters are found to have similar barriers in their respective potentials of mean force; however, as the supersaturation decreases, the density fluctuations decorrelate slower and thus carry longer memory. Thus, at lower supersaturations, density fluctuations are non-Markovian and cannot be simply ignored from the RC by virtue of being noise. Finally, we use this optimized RC to calculate nucleation rates in the infrequent metadynamics framework and show that it leads to a more accurate estimate of the nucleation rate with four orders of magnitude acceleration relative to unbiased MD.

Experimental probes of silver metal nanoparticle formation kinetics: Comparing indirect versus more direct methods

AbstractThe kinetics of noble metal nanoparticle formation in bottom‐up syntheses are important for controlling and optimizing these methods. Hence, experimental probes that are easily accessible to most laboratories are also of interest. We collected kinetic curves for the formation of silver nanoparticles in a modified Turkevich method with citrate acting as the reducing and stabilizing agent by (i) measuring the change in silver nanoparticle surface plasmon resonance by UV‐visible spectroscopy, a somewhat indirect method, and then also by (ii) measuring the change in silver ion concentration by ion‐selective electrode potentiometry and/or atomic absorption spectroscopy, two more direct methods. The resulting sigmoidal kinetic curves were curvefitted with the Finke‐Watzky two‐step kinetic model of slow, continuous nucleation and fast autocatalytic growth to extract average rate constants. We found that the kinetic curves obtained by following the change in silver ion concentration were apparent mirror images of those constructed by following the change in nanoparticle surface plasmon resonance, and that their respective curvefits displayed the same sigmoidal characteristics. The resultant values of the rate constants for nucleation and growth overlapped within experimental error between the methods and showed similar trends over the range of citrate concentrations studied. The use of multiple probes in this work to follow the kinetics of nanoparticle formation helps fill a need for the comparison and evaluation of different methods available to scientists, particularly those considered easily accessible.

Measuring the activation energy barrier for the nucleation of single nanosized vapor bubbles

Heterogeneous bubble nucleation is one of the most fundamental interfacial processes that has received broad interest from diverse fields of physics and chemistry. While most studies focused on large microbubbles, here we employed a surface plasmon resonance microscopy to measure the nucleation rate constant and activation energy barrier of single nanosized embryo vapor bubbles upon heating a flat gold film with a focused laser beam. Image analysis allowed for simultaneously determining the local temperature and local nucleation rate constant from the same batch of optical images. By analyzing the dependence of nucleation rate constant on temperature, we were able to calculate the local activation energy barrier within a submicrometer spot. Scanning the substrate further led to a nucleation rate map with a spatial resolution of 100 nm, which revealed no correlation with the local roughness. These results indicate that facet structure and surface chemistry, rather than geometrical roughness, regulated the activation energy barrier for heterogeneous nucleation of embryo nanobubbles.

Constraining nucleation, condensation, and chemistry in oxidation flow reactors using size-distribution measurements and aerosol microphysical modeling

Abstract. Oxidation flow reactors (OFRs) allow the concentration of a given atmospheric oxidant to be increased beyond ambient levels in order to study secondary organic aerosol (SOA) formation and aging over varying periods of equivalent aging by that oxidant. Previous studies have used these reactors to determine the bulk OA mass and chemical evolution. To our knowledge, no OFR study has focused on the interpretation of the evolving aerosol size distributions. In this study, we use size-distribution measurements of the OFR and an aerosol microphysics model to learn about size-dependent processes in the OFR. Specifically, we use OFR exposures between 0.09 and 0.9 equivalent days of OH aging from the 2011 BEACHON-RoMBAS and GoAmazon2014/5 field campaigns. We use simulations in the TOMAS (TwO-Moment Aerosol Sectional) microphysics box model to constrain the following parameters in the OFR: (1) the rate constant of gas-phase functionalization reactions of organic compounds with OH, (2) the rate constant of gas-phase fragmentation reactions of organic compounds with OH, (3) the reactive uptake coefficient for heterogeneous fragmentation reactions with OH, (4) the nucleation rate constants for three different nucleation schemes, and (5) an effective accommodation coefficient that accounts for possible particle diffusion limitations of particles larger than 60 nm in diameter. We find the best model-to-measurement agreement when the accommodation coefficient of the larger particles (Dp > 60 nm) was 0.1 or lower (with an accommodation coefficient of 1 for smaller particles), which suggests a diffusion limitation in the larger particles. When using these low accommodation-coefficient values, the model agrees with measurements when using a published H2SO4-organics nucleation mechanism and previously published values of rate constants for gas-phase oxidation reactions. Further, gas-phase fragmentation was found to have a significant impact upon the size distribution, and including fragmentation was necessary for accurately simulating the distributions in the OFR. The model was insensitive to the value of the reactive uptake coefficient on these aging timescales. Monoterpenes and isoprene could explain 24 %–95 % of the observed change in total volume of aerosol in the OFR, with ambient semivolatile and intermediate-volatility organic compounds (S/IVOCs) appearing to explain the remainder of the change in total volume. These results provide support to the mass-based findings of previous OFR studies, give insight to important size-distribution dynamics in the OFR, and enable the design of future OFR studies focused on new particle formation and/or microphysical processes.

Multiple Nucleation Processes during the Platinum Electrodeposition Onto Glassy Carbon Electrodes Influence of the Temperature

Introduction The deposition of noble metal particles on some substrates is a field of great interest due the resulting electrocatalytic properties [1, 2]. This is because these particles can exhibit a larger efficient surface area and higher activity [3]. In this sense, Pt nanoparticles deposited on carbon substrates are of special interest [4, 7] due to the low cost, performance and high efficiency. Pt has been electrodeposited onto carbon substrates including highly oriented graphite (HOPG) electrode [6], carbon nanotubes [7], carbon fiber [8], graphite [9], conducting polymers and macroporous carbon [10], glassy carbon [11, 12], among others. In the case of platinum electrodeposition process onto GCE, the information concerning kinetical of the nucleation and growth process is scarce. Therefore, in the present work, we carried out an electrochemical study, in order to understand the Pt electrodeposition process onto this system. Methodology Pt electrodeposits onto GCE were carried out from an aqueous solution containing 0.01 M K2PtCl4 at 25, 30, 35 and 40 oC. All solutions were prepared using analytic grade reagents with ultra pure water (Millipore-Q system) and were deoxygenated by bubbling N2 for 15 minutes before each experiment. A 3-compartment electrochemical cell was used in the electrochemical experiments. An Ag/AgCl and graphite bar served as the reference and counter electrode, respectively. A glassy carbon disk of 3 mm of diameter was used as working electrode and polished to mirror–like finish and ultrasonicated before each experiment. The three electrodes remained connected to an EPSILON potentiostat and a personal computer with the BASi-Epsilon-EC software during the experiments to keep them under control and obtain the results. Results and discussion Figure 1 shows a set of current density transients recorded at a potential value of -0.010 V at different temperature values. These transients were obtained applying an initial potential 0.600 V on the surface of the GCE electrode. In this Figure, it is possible to observe that at shorter times, there is a falling current transient that can be associated with a process that follows Langmuir adsorption-desorption kinetics [13]. After this falling current, in each case, the j-t plots pass through a first maximum (t < 5 s), and a second maximum (t > 5 s), which corresponds to a secundary nucleation and growth process. Also, note that for the transients obtained at 25 y 30 oC, there is a third maximum, which coresponds a new nucleation and growth process. These transients were fitted to a nucleation model which considers that the total current is given by jT=j1+j2+j3, where j1, j2, and j3 corresponds to the nucleation and growth process of the first, second and third maxima, respectively. Conclusions Pt electrodeposition on GCE was studied at different temperatures using potentiostatic and voltammetric techniques. The effect of the temperature effect on kinetics parameters such as diffusion coefficient, and charge transfer coefficient was analyzed. The values of nucleation rate and rate constant of the proton reduction reaction increased with the temperature increment and the applied overpotential. The values of the transfer coefficient was analyzed and a decrease in its value with the temperature increment is observed. Acknowledgements: LHMH gratefully acknowledges financial support from CONACYT (project CB2015-257823) and to the Universidad Autónoma del Estado de Hidalgo. References Spenadel and M. Boudart, J. Phys. Chem., 64 (1960) 204Gunasingbam and C.B. Tan, Analyst, 114 (1989) 695Dong, Q. Qiu, J. Electroanal. Chem., 314 (1991) 223Yin, S., Mu, S., Lv, H., Cheng, N., Pan, M., Fu, Z. Appl. Catal. B Environ. 2010, 93, 233–240He, M. Liu, J.L. Luo, A.R. Sanger, K.T. Chuang, J. Electrochem. Soc. 2002, 149, A808.Lu, G. Zangari, J Phys Chem B. 2005, 109(16), 7998.Zhang, Z. Fang, G.-C. Zhao, X.-W. Wei, Int. J. Electrochem. Sci., 2008, 3, 746.A. Islam, M. S. Islam, Engineering International, 2013, 1(2).Gloaguenb, J.M Légerb, C Lamyb, A Marmanna, U Stimminga, R Vogela. Electrochimica Acta, 1999, 44(11) 1805.Domínguez-Domínguez, S., Arias-Pardilla, J., Berenguer-Murcia, Á. et al. J Appl Electrochem (2008) 38: 259.Dong, Q. Qiu, J. Electroanal. Chem., 1991, 314, 223.-J. Feng, A-Q. Li, A.-J. Wang, Z. Lei, J.-R. Chen. Microchim Acta, 2011, 173, 383.H. Hölzle, U. Retter, and D. M. Kolb, J. Electroanal. Chem., 371, 101, 1994. Figure 1

(Electrodeposition Division Early Career Investigator Award) Electrochemical Growth Mediated by Nanocluster Aggregation: Implications and Perspectives

Supported nanostructured electroactive materials are known to boost the efficiency of electrocatalytic processes. Although they can be fabricated by multiple methods, electrodeposition offers several advantages, since the nanostructures are grown on the final support. During the last years, we have developed an approach based on using carbon coated TEM grids (CCTGs) as electrodes to better understand electrochemical nucleation and growth mechanisms on the nanoscale. This way, by combining atomic-scale TEM characterization with electron tomography and electrochemical measurements, we have found evidence that has led us to suggest an electrochemical aggregative growth mechanism [1]. It includes nanocluster self-limiting growth, surface diffusion, aggregation and coalescence as important elementary steps of the electrochemical growth process [2,3]. In this context, we have employed the same approach to study the electrodeposition and electrochemical stability of dendritic nanoparticles with large surface areas [4,5], as well as electrochemical nucleation and growth phenomena in Deep Eutectic Solvents (DESs). Special attention is given to the interaction between the solvent and the electrodeposited phase and the role of water since DESs are highly hygroscopic and water cannot be completely removed [6-8]. Due to the high level of complexity of the electrodeposition process and the small timescales and lengthscales that need to be considered, electrochemical and surface characterization techniques feature inherent limitations. Therefore, a complementary approach based on numerical simulations is being evaluated. We have introduced a novel modelling approach that couples a Finite Element Method (FEM) with a random walk algorithm, to study the early stages of nanocluster formation, aggregation and growth, during electrochemical deposition. This approach takes into account different factors: not only the overpotential, but the transport of active species and electrochemical kinetics are also evaluated, together with the surface diffusion and aggregation of adatoms and small nanoclusters [9]. The combined analysis of experimental and simulated data reveals that the relative surface mobility of nanoclusters compared to this of the adatoms plays a crucial role in the early growth stages. The number of clusters, their size and size dispersion are influenced more significantly by nanocluster mobility than by the applied overpotential itself. As a result, an accurate representation of the number of clusters with time, N(t), in potentiostatic electrodeposition should consider, not only an induction time that precedes cluster formation, but also the balance between cluster formation and aggregation. We show that an evaluation of N(t), which neglects the effect of nanocluster mobility and aggregation, induces errors of several orders of magnitude in the determination of nucleation rate constants. These findings are highly important towards properly evaluating the elementary electrodeposition processes, considering not only adatoms, but also nanoclusters as building blocks.