Electrochemical Growth Process Research Articles

NIR-ViS-UV broadband absorption in ultrathin electrochemically-grown, graded index nanoporous platinum films.

Nanoporous platinum broadband absorber has attracted interest in thermosensorics and IR photodetection due to its unique properties. In this work we report the physical mechanism underlying broadband absorption in electrochemically-grown, nanoporous Pt films by analyzing NIR-ViS-UV spectral ellipsometry data of nanoporous Pt films in dependence on the Pt film thickness (27, 35, 38, 48nm). For the two thinner films a single layer model with a graded optical index Pt surface layer was used. For the two thicker films a two-layer optical model with a constant optical index Pt substrate layer and a graded optical index Pt surface layer was used. The graded optical index of the Pt surface layer reduces surface reflectivity and the constant optical index Pt substrate layer supports multiple reflections in the Pt film. Finally, we relate the thickness dependent optical index with the nanostructure of the nanoporous Pt film, which can be controlled in the electrochemical growth process. We observed that while in the transverse plane the multilayer exhibits graded refractive index, in the top horizontal planes the multilayer assembly exhibits discontinuous refractive index values due to the distribution of platinum crystal islands in air, which allows a metamaterial behavior of the whole system.

Electrochemical Nucleation and Growth: A Multimicroscopy Approach at the Same Scale

Electrodeposition is a critical electrochemical reaction with broad applications in technology. This demands a comprehensive understanding of the electrochemical nucleation and growth process (EN&G), and the different factors driving the formation of a new phase on a given substrate. Our understanding of the role of the substrate and the real nature of active sites still remains elusive due to the challenge of probing specific sites and bringing a statistical interpretation of the nucleation process. Moreover, conventional macroscopic approaches often record electrochemical magnitudes over large areas (cm2) which are then correlated with surface characterizations obtained from a vastly different scale (~μm2), correlations, which are not necessarily representative of the macroscopic surface. In order to establish meaningful and unambiguous correlations, it becomes necessary to employ techniques capable of surveying the surface with a high spatial-temporal resolution, such as scanning probe techniques, capable of recovering information in a scale closer to the growth of the new phase, i.e., local scale1. To address these challenges, we employed Scanning Electrochemical Cell Microscopy (SECCM), to study the EN&G of Cu on a glassy carbon substrate at a scale closer to the initial stages of the electrodeposition2. SECCM can be combined with other imaging methods such as scanning electron microscopy (SEM) to recover information from the deposited nanostructures at the same scale as the electrochemical response3. This so-called multimicroscopy approach allows us establishing direct correlations between the EN&G and the morphological, structural, and compositional features of the substrate and deposit. As a result, new insights that are not available with conventional macro-electrochemical analysis can be gained, such as the time-, potential-, and site-dependent nature of the EN&G process with a statistical perspective. This approach provides a new avenue for developing novel analysis strategies to understand the real nature of active sites for nucleation.References M. Bernal, D. Torres, S. S. Parapari, M. Čeh, K. Ž. Rožman, S. Šturm, and J. Ustarroz, Electrochim. Acta, 445, 142023 (2023).D. Torres, M. Bernal, A. Demaude, S. Hussain, L. Bar, P. Losada-Pérez, F. Reniers, and J. Ustarroz, J. Electrochem. Soc., 169, 102513 (2022).D. Torres, M. Bernal Lopez, and J. Ustarroz, Electrochemical nucleation and growth: A multimicroscopy Approach at the same scale, In preparation. (2023). Figure 1

Temperature Dependent Nanochemistry and Growth Kinetics Using Liquid Cell Transmission Electron Microscopy.

Liquid cell transmission electron microscopy has become a powerful and increasingly accessible technique for in situ studies of nanoscale processes in liquid and solution phase. Exploring reaction mechanisms in electrochemical or crystal growth processes requires precise control over experimental conditions, with temperature being one of the most critical factors. Here we carry out a series of crystal growth experiments and simulations at different temperatures in the well-studied system of Ag nanocrystal growth driven by the changes in redox environment caused by the electron beam. Liquid cell experiments show strong changes in both morphology and growth rate with temperature. We develop a kinetic model to predict the temperature-dependent solution composition, and we discuss how the combined effect of temperature-dependent chemistry, diffusion, and the balance between nucleation and growth rates affect the morphology. We discuss how this work may provide guidance in interpreting liquid cell TEM and potentially larger-scale synthesis experiments for systems controlled by temperature.

Challenges in Understanding Electrochemical Growth

Over the past 100 years, electrodeposition has matured to an important method with numerous industrial applications, up to processes in micro- and nanofabrication. Knowledge on electrochemical processes on the atomic scale is still limited, however. While for vapor deposition under vacuum conditions the evolution of the deposit morphology can nowadays be predicted with high precision, a similar predictive understanding of electrodeposition is missing so far. A key issue here is the electrochemical interface where this growth occurs. The structural complexity of this interface on the one hand makes understanding of the elemental processes in nucleation and growth difficult. On the other hand, it is just this complexity that allows to tune electrodeposition processes in ways that are not possible for deposition in vacuum and thus make them attractive for many applications.In this talk, I will discuss current challenges in developing a true microscopic picture of electrodeposition processes, using examples from us and other groups. The focus will be on puzzling experimental observations and fundamental aspects that we do not yet understand and thus provide a rich field for future research. These include the mechanisms of elemental steps in electrochemical growth processes, such as ion transfer, intra- and interlayer surface diffusion, and the resulting development of the deposit morphology. Of particular interest is how these events are influenced by the electric field and electrolyte species in the electrochemical double layer, which is of key relevance for understanding the effects of overpotential and additives. A further challenge is to extend the insights obtained for electrodeposition of metals to the electrochemical growth of compound materials, such as oxides.

The Distribution of Nucleation Activities: A New Local Perspective with Scanning Electrochemical Cell Microscopy

Electrodeposition is a convenient strategy for the synthesis of functional nanostructures, for which electrochemical nucleation and growth (EN&G) processes need to be well understood [1]. As a heterogenous process, understanding the distribution of nucleation sites on a substrate is fundamental to relate the microscopic events to the macroscopic properties of the new deposit. In this work, we have explored the EN&G process on a glassy carbon substrate with a local electrochemical approach based on the Scanning Electrochemical Cell Microscopy (SECCM), using copper as a case of study [2]. Since the studies of EN&G are extremely sensitive to the state of the surface, the diversity of the nucleation process is revealed by performing hundreds of spatially resolved experiments on the heterogeneous surface of the glassy carbon [2,3]. The spatially-resolved characterization opens up the opportunity to correlate the electrochemical information to the local surface state, which can be modified with common surface pretreatments (i. e., polishing and preanodization). This unique perspective of the EN&G can help to deconvolute the individual contributions to the overall process, bringing forward information on nucleation sites that is unavailable with the conventional macroscopic approach.[1] J. Ustarroz, Current atomic-level understanding of electrochemical nucleation and growth on low-energy surfaces, Curr. Opin. Electrochem. 19 (2020) 144–152.[2] D.Torres, M. Bernal, J. Ustarroz, distribution of copper nucleation activities on glassy carbon: a new local perspective, to be submitted 2022[3] M. Bernal, D. Torres, S. Semsari, M. Čeh, K. Žužek Rožman, S. Šturm, J. Ustarroz, Diversity matters: Influence of surface heterogeneities in the electrochemical nucleation and dissolution of Au nanoparticles, under revision. Figure 1

(Keynote) Developments in Visualizing Electrochemistry in Action with Liquid Cell Electron Microscopy

In situ transmission electron microscopy (TEM) can provide unparalleled structural and compositional information with high spatial and temporal resolution and is a standard tool for understanding and quantifying electrochemical nucleation and growth processes. Both solid state reactions and processes involving liquids can be examined. However, liquid phase reactions require particular care since the liquid needs to be confined in a thin layer and protected from the vacuum in the microscope. This problem is solved in the technique of electrochemical liquid cell TEM by confining the liquid between microfabricated electron transparent membranes on which the electrodes are patterned. Electrochemical liquid cell TEM has enabled quantification of nucleation and growth phenomena, dendrite formation, additive effects on morphology and SEI formation. Recent experimental developments have broadened the application space, but many more opportunities remain to be explored. Here we discuss how the existing strategies for electrochemical liquid cell TEM experiments can be adapted to allow quantitative data acquisition under an expanded range of electrochemical conditions. We first discuss the control of temperature, an important parameter in electrochemical systems such as batteries and fuel cells. Increasing the temperature while simultaneously applying a bias is achieved by customizing liquid cell chips to incorporate an electrically isolated heater strip beneath the electrodes. We find, as expected, that elevated temperature increases the rates of deposition and etching reactions and we discuss potential applications in electrocatalysis and codeposition. We then address the limitations of image resolution in liquid cell experiments. For nucleation and growth processes that take place on the surface of the electrode, the electrode materials such as Au or Pt often used in microfabricated liquid cells contribute strongly to electron scattering and thereby reduce the signal to noise ratio in the images. We show how few-layer graphene can be added to liquid cell chips to produce electrodes with minimal scattering, resulting in nucleation and growth movies with improved discrimination between nucleus shapes. We next consider the exciting consequences of instrumental improvements in microscopy - aberration correction, energy filtering and efficient electron detectors - in improving the resolution and lowering the dose required for imaging. Electron beam effects are unavoidable, however, and we discuss how the chemical changes caused by the beam can be modeled and perhaps mitigated for different electrolyte compositions and as a function of temperature. More speculative developments in liquid cell technique may allow us to measure stress, electrolyte composition and even the electrochemical double layer. Although a lot of work remains to be done, I hope to convince you that electrochemical TEM of liquids can address grand challenge questions in nucleation and growth through its unique view of electrochemical processes.

Effect of Ni addition on CPP-GMR response in electrodeposited Co-Ni/Cu multilayered nanocylinders with an ultra-large aspect ratio

Effect of Co–Ni alloy composition on the current perpendicular-to-plane giant magnetoresistance (CPP-GMR) response of electrochemically synthesized Co–Ni/Cu multilayered nanocylinders was studied using anodized aluminum oxide membranes (AAOM) with nanochannel diameter D ∼67 nm and length L ∼70 μm. Co–Ni/Cu multilayered nanocylinders, which have an aspect ratio L/D of ∼1,045, were fabricated in the AAOM nanochannel templates by utilizing a pulse-current electrochemical growth process in an electrolytic bath with Co2+, Ni2+ and Cu2+ ions. Co–Ni/Cu alternating structure with Co84Ni16 alloy layer-thickness of 9.6 nm and Cu layer-thickness of 3.8 nm was clearly observed in a nanocylinder with a diameter of 63 nm. The alternating structure was composed from crystalline layers with preferential orientations in hcp-CoNi (002) and fcc-Cu (111). The Co–Ni/Cu multilayered nanocylinders were easily magnetized in the long axis direction because of the extremely large aspect ratio L/D. In Co84Ni16/Cu multilayered nanocylinders, the coercivity and squareness were ∼0.46 kOe and ∼0.5, respectively. The CPP-GMR value was achieved up to 22.5% (at room temperature) in Co84Ni16/Cu multilayered nanocylinders.

Kinetic Process of an Alkaline Earth Metal Ion Transmembrane through ZIF-8.

The confinement effect of biological ion channels regulates the transport of molecules and ions due to angstrom-sized pores. The structure of the potassium channel has a selection region (3-4 Å), a cavity (10 Å), and a gated region, while ZIF-8 has intrinsic pores with a 3.4 Å aperture and an 11.6 Å cavity similar to those of the potassium channel. Inspired by this, we constructed the glass/ZIF-8 hybrid membrane through an electrochemical growth process to explore the kinetics of the ion transmembrane by I-V curves and electrochemical impedance spectroscopy. These complementary approaches yield highly correlated results that show that ion transportation of the ZIF-8 membrane follows Arrhenius behavior. The rates of ions are controlled by the transmembrane activation energy, in which the ionic charge and radius play an important role.

Electrodeposition of nanostructured catalysts for electrochemical energy conversion: Current trends and innovative strategies

This review discusses the latest advances in electrodeposition of nanostructured catalysts for electrochemical energy conversion: fuel cells, water splitting, and carbon dioxide electroreduction. The method excels at preparing efficient and durable nanostructured materials, such as nanoparticles, single atom clusters, hierarchical bifunctional combinations of hydroxides, selenides, phosphides, and so on. Yet, in most cases, chemical composition cannot be decoupled from catalyst morphology. This compromises the rational design of electrodeposition procedures because performance indicators depend on both morphology and surface chemistry. We expect electrodeposition will keep unraveling its potential as the preferred method for electrocatalyst synthesis once a deeper understanding of the electrochemical growth process is combined with complex chemistries to have control of the morphology and the surface composition of complex (bifunctional) electrocatalysts.

Looking Deep inside the Cathode of Li-O2 Batteries: Unraveling the Local Distribution of Li2O2 with a Combined Experimental and Model-Based Approach

Carbon-based, high surface area gas diffusion electrodes (GDEs) are commonly used as cathodes in Li-O2 batteries. These GDEs provide an sufficient amount of active sites to deposit the main discharge product, Li2O2. Despite the fast electron transfer at the electrode surface to form Li2O2, experimental results show that the very high theoretical energy densities of Li-O2 batteries cannot be achieved at the moment. Instead of the desired formation of high amounts of soluble LiO2, predominantly insoluble Li2O2 precipitates at the active sites of the cathode during discharge. Unfortunately Li2O2 is poorly conductive for electrons, which leads to a low amount of deposited Li2O2 per active site and a fast passivation of the cathode. Thus, only the cathode surface area and not the pore volume is utilized by Li2O2, which explains the discrepancy between theory and experiments. Furthermore, the precipitation leads to continuous changes in porosity, available active surface area and predominant reaction pathway. For this reason a detailed analysis of the distribution of Li2O2 at all points in the GDE and of the factors that influence the Li2O2 morphology is needed to overcome performance limitations. [1]In this work, we elucidate how the local distribution of Li2O2 inside the GDE and its particle size evolve as a function of discharge current density. We apply a powerful combination of experimental and model-based analysis. To the best of our knowledge, this is the first study on the cathode surface utilization by Li2O2 and its particle sizes performed for different locations and states of discharge (SOD). The impact of the distribution and the resulting changes in transport resistance and active surface area on the battery performance are derived thereof.In the experimental part, decreasing capacities and Li2O2 particle sizes are observed for increasing discharge current densities (see SEM analysis of discharged battery cathodes in fig. 1 a)). Furthermore, the experimental results show that particle precipitation starts mainly at the side of the cathode that faces the oxygen reservoir of the battery (see fig. 1 b)). Discharging a battery at low current densities leads to a uniform cathode surface coverage by Li2O2 even at low SOD whereas discharging at high current densities yields a gradient of blocked active sites through the cathode.Simulations based on a physical GDE model show that a two-step reaction mechanism with the soluble species LiO2 as reaction intermediate can quantitatively explain the experimental findings. Depending on the current density, either a chemical or an electrochemical particle growth process predominates, which leads to the distinct different particle size distributions (see fig. 1 c) and d)). The strong dependence of capacity on the current density is related to different capacities per carbon cathode surface area at the end of discharge. At high discharge rates and thereby lowered potential more nucleation takes place. As a result, the particle number is higher and the average size smaller. Due to the surface volume ratio, smaller particles entail lower capacities per cathode surface area. The results point out that even at moderate current densities the battery capacity is limited by the surface area of the GDE and not by the concentration of dissolved O2 in the liquid electrolyte. Therefore, the solubility and reaction kinetics of the reaction intermediate LiO2 play a crucial role to enhance Li2O2 particle size and with it the obtainable discharge capacity.The presented results provide detailed insight into the cathode surface utilization and the underlying processes that limit the performance of GDEs in Li-O2 batteries. In the end, the study will help to achieve higher discharge capacities for this type of battery and thus will propel the ongoing research and the efforts in commercialization of metal-oxygen batteries.Acknowledgement:The authors are thankful for financial support by the BMBF (Federal Ministry of Education and Research) within the project “MeLuBatt” (03XP0110A).

Synthesis of Core-Shell Al/tiO2 Nanotube Composites by Electrochemical Methods

In many material applications such as energy storage, photovoltaic, optoelectronic devices, etc., there is a need for complex structures prepared with low cost and simple techniques such as electrochemical methods. In this paper, the electrochemical growth process of aluminium nanostructure on TiO2 nanotubes from room temperature ionic liquid containing AlCl3 electrolyte has been investigated. Firstly, the TiO2 nanotubes were formed by electrochemical anodization of Ti foil, and then the nanotubes coated with Al by electrodeposition, for the formation of Al/TiO2 nanotube nanocomposites. The effect of the AlCl3 concentration in electrolyte on the nucleation and growth process of Al has been studied. The loading of the deposit has been well controlled by the electrochemical charge measured during deposition process. The morphology, structure and compositions of the composites have been characterized by X-ray diffraction, Scanning Electronic Microscopy coupled with Energy Dispersive X-ray Spectroscopy, and Transmission Electronic Microscopy. It is shown that polycrystalline aluminium grains are successfully deposited on the surface of the nanotubes filling the spacing in-between nanotube walls. Since both Al and TiO2 nanotubes have several interesting properties, the synthesis of their nanocomposites expects to gain great interest of various technological applications.

Determination of Crystal Growth Geometry Factors and Nucleation Site Densities of Electrodeposited Ferromagnetic Cobalt Nanowire Arrays

The time-dependence of electrochemical reduction current, which was observed during the one-dimensional (1-D) crystal growth of ferromagnetic cobalt nanowire arrays, was analyzed by Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory. Textured hcp-Co nanowire arrays were synthesized by potentio-static electrochemical reduction of Co2+ ions in anodized aluminum oxide (AAO) nanochannel films. Crystal growth geometry factor n in the JMAK equation was determined to be ca. 1. Hence, the electrochemical crystal growth process of a numerical nanowires array can be explained by 1-D geometry. The crystal nucleation frequency factor, k in JMAK equation was estimated to be the range between 10−4 and 10−3. Our experimental results revealed that the crystal nucleation site density Nd increased up to 2.7 × 10−8 nm−3 when increasing the overpotential for cobalt electrodeposition by shifting the cathode potential down to −0.85 V vs. Ag/AgCl. The (002) crystal orientation of hcp-Co nanowire arrays was, remarkably, observed by decreasing Nd. Spontaneous magnetization behavior was observed in the axial direction of nanowires. By decreasing the overpotential for cobalt electrodeposition, the coercivity of the nanocomposite film increased and reached up to 1.88 kOe, with a squareness of ca. 0.9 at room temperature.

(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.

(Invited) Electrochemical Growth Mediated By Nanocluster Aggregation

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. However, the electrodeposition of nanostructures in a reproducible way requires a full understanding of the electrochemical nucleation and growth mechanisms at the nanoscale. Recently, we have developed an approach based on using carbon coated TEM grids as electrodes. 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 surface diffusion, aggregation and coalescence as important elementary steps of the electrochemical growth process [2,3]. Due to the high level of complexity of the problem and the small timescales and lengthscales which 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 [4]. 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, it is shown that a classical first-order nucleation kinetics equation cannot describe the evolution of the number of clusters with time, N(t), in potentiostatic electrodeposition. Instead, a more accurate representation of N(t) 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, can induce errors of several orders of magnitude in the determination of nucleation rate constants. These findings are extremely important towards evaluating the elementary electrodeposition processes, considering not only adatoms, but also nanoclusters as building blocks.

INFLUENCE OF TEMPERATURE ON THE THERMODYNAMICS AND KINETICS OF COBALT ELECTROCHEMICAL NUCLEATION AND GROWTH

From potentiodynamic and potentiostatic experiments, the cobalt electrochemical nucleation and growth process, onto the glassy carbon electrode surfaces, from an aqueous solution containing 10−2M CoCl2 and 1M NH4Cl (pH=4.66) at different temperatures (15–60°C) is reported. It was found that while the equilibrium potential moves to more negative values as the temperature of the system was increased, the contrary was observed for the nucleation overpotential, ηnucleation, required for the onset of cobalt nucleation onto the surfaces of vitreous carbon. From Tafel plots recorded at the different temperatures considered, both: the transfer coefficient, α, and the exchange current density, j0, associated with the Co(II)/Co(0) system were assessed, and from the Arrhenius plot (ln j0 vs. T−1) the activation energy for Co(II) reduction of (27.9±0.3) kJmol−1 was estimated. From analysis of the potentiostatic current density transients according with the formalism proposed by Palomar-Pardavé et al. (Electrochim. Acta 50 (2005) 4736-4745), the total current density was de-convoluted into individual contributions, due to formation of multiple mass-transfer controlled 3D Co nuclei and that associated to the proton reduction occurring simultaneously on the growing surface of the Co nuclei. The latter contribution was practically null at 10°C, however, it drastically increased as the temperature of the system did, provoking that the cathodic efficiency for Co deposition diminished. Furthermore, it was found that both the number density of active sites, N0, and the nucleation rate, A, for Co nucleation depend exponentially with ηnucleation, regardless of temperature, except at 60°C where N0 diminished linearly with ηnucleation. From variations of the Co(II) ions diffusion coefficient with temperature, a value of (8.5±0.2) kJmol−1 was obtained for the activation energy for bulk diffusion. SEM analysis showed that the cobalt nuclei are bigger as the temperature increases; however, the coverage of the electrode surfaces becomes lower.

Miniaturized Electrochemical Device from Assembled Cylindrical Macroporous Gold Electrodes

AbstractTo design original electrochemical devices, self‐assembly and growth processes can be coupled to create a wide range of sophisticated architectures with interesting functionalities. In this work, we present a convergent strategy for the fabrication of a miniaturized, macroporous, and coaxial two‐electrode electrochemical cell with tunable porosity, thickness, and distance between individually addressable macroporous electrodes. The assembly presents a platform that could be used for the fabrication of high‐performance electrochemical devices such as miniaturized (bio)fuel cells, sensors, and batteries.

Investigation of the electrochemical growth of a Cu–Zn–Sn film on a molybdenum substrate using a citrate solution

Cu–Zn–Sn (CZT) metallic films were electrodeposited on molybdenum-coated soda lime glass (Mo/SLG) substrates at a constant potential using an aqueous electrolyte solution containing Cu (II), Zn (II), Sn (II) ions, and tri-sodium citrate. The electrochemical growth process of the CZT film has been elucidated by analysis of the film thickness, charge consumption, elemental and phase composition, and surface morphology. Interestingly, it was found that only copper and tin were deposited in the initial stage (30 s) of electrodeposition, and after this zinc began to be incorporated into the film. Further study revealed that H2 evolution was responsible for the failed deposition of zinc on the Mo substrate. The grain size of the CZT film increased over the deposition time. It was also found that the film thickness (except for the first 1 min) increased linearly with the charge consumption, and the film grew at a constant rate. As a result, the composition of the CZT film remained constant throughout the deposition process and copper, tin, and zinc were distributed evenly in the film. Alloy phases of Cu6Sn5 and Cu5Zn8 were found in the CZT film and they were largely constant during the growth of the film. The new insight into the electrodeposition process of CZT films will be very useful for the production of high-quality solar active materials such as Cu2ZnSnS4 and Cu2ZnSnSe4.

A Finite Element Simulation of the Electrochemical Growth of a Single Hemispherical Silver Nucleus

Understanding the early stages of electrochemical nucleation and growth is the cornerstone for nanoscale electrodeposition. Although studied since decades, the process is not yet fully understood. In this paper, we introduce a new modelling approach to study the growth of a single hemispherical nucleus: Multi-Ion Transport and Reaction Model (MITReM). This approach takes into account the transport driven by diffusion and migration of all species in the electrolyte together with the electrochemical reactions at the electrode boundary. A Finite Element Method (FEM) is used to solve the balance equations for the concentration of all the active species and the electrolyte potential. In contrast to analytical models or discrete scale modelling techniques, the strength of this approach is that no assumptions on the diffusional or kinetic limitations have to be made. In addition, this novel platform allows to add further levels of complexity, such as multiple nuclei, adatom surface diffusion, aggregation, particle detachment, etc. The simulation results prove that, the initial growth stage of a 10 nm single hemispherical silver nucleus always starts under kinetic control, regardless of concentration and electrode potential. Later on, a transition from kinetic to diffusion control takes place. The time of transition depends on the imposed concentration and electrode potential. Moreover, the simulations clearly show that the growth rate is strongly affected by the imposed concentration and electrode potential, as it has been proven experimentally in countless occasions. Numerical simulation by MITReM proves to be of great interest to gain knowledge towards unravelling the early stages of electrochemical nucleation and growth processes.

FFT-impedance spectroscopy analysis of the growth of magnetic metal nanowires in ultra-high aspect ratio InP membranes

This paper reports on the characterization of the electrochemical growth process of magnetic nanowires in ultra-high-aspect ratio InP membranes via in situ fast Fourier transform impedance spectroscopy in a typical frequency range from 75 Hz to 18.5 kHz. The measured impedance data from the Ni, Co, and FeCo can be very well fitted using the same electric equivalent circuit consisting of a series resistance in serial connection to an RC-element and a Maxwell element. The impedance data clearly indicate the similarities in the growth behavior of Ni, Co and FeCo nanowires in ultra-high aspect ratio InP membranes—the beneficial impact of boric acid on the metal deposition in ultra-high aspect ratio membranes and the diffusion limitation of boric acid, as well as differences such as passivation or side reactions.

Coupling Phenomena Between Micromorphological Evolution and Ionic Mass Transfer Rate during Ag Electrodeposition in AgNO3 Aqueous Solution

The rechargeable battery concept with maltreat tolerance and safety is essentially indispensable not only in the space application but also in terrestrial renewable energy storage systems. Higher energy density, power capability and longer life requirements make the targets more challenging. A better understanding of the electrolyte/electrode interface phenomena including electrode kinetics is crucial. “Electrochemical Nucleation & Growth” aspect is a fundamental approach how to control the coupling phenomena between nano-structural interface evolution and ionic mass transfer rate enclosed a meso-scale space filled with electrolyte. Such a research has not been frequently challenged in designing the longer life energy storage devices. Metal negative electrode surface shows various morphologies after repetition of electrodeposition and electrochemical dissolution reaction. Dendrite precursor is finally grown after electrochemical nucleation and growth process where the coupling phenomena govern. It is also indispensable for us to prolong the charging/discharging operation of secondary battery after longer term utilization under various environments. For liquid electrolyte, a precise study of these morphologies may be complicated by convective motion caused by gravitational force of buoyancy. Now the coupling phenomena are discussed in the case of silver because it has been employed as negative electrode in space application. 3M AgNO3 aqueous solution was contained in a quasi-2D cell. Holographic interferometry was employed to monitor the ionic mass transfer rate. The concentration profiles were formed around dendrite tips of silver electrodeposited at extremely high current densities. A uniform diffusion layer was formed along the cathode surface at the start of electrolysis. Following a certain incubation period, several dendrite tips began to protrude into the diffusion layer. The growth rates of these dendrites were related to concentration gradients around the tips, diffusivity, and transfer number of Ag+ ion. Giant-Macro step flow accompanied with Ag dendritic growth was dynamically observed with Laser Confocal Scanning Microscope. Transient current variation measurements are now engaged under the double pulse potential which introduces Ag nucleus on the foreign substrate in order to develop a multi-scale physical model of dendritic growth.