Single Nanoparticle Growth from Nanoparticle Tracking Analysis: From Monte Carlo Simulations to Nanoparticle Electrogeneration

International audienceBy scrutinizing the trajectory of individual nanoparticles (NPs) in solution, NP tracking analysis (NTA) allows sizing individual NPs and providing meaningful complementary information to single NP electrochemistry.H erein, am odel is developed to extend NTAt oa llow dynamic NP sizing and to analyze the kinetics of growth of NPs in solution. Interpreting the NP trajectories as scaled Brownian motion, Monte Carlo simulations produce stochastic trajectories of growing NPs (under diffusion-controlled growth). These trajectories are grounds for determining as trategy to estimate the growth parameters of individual NPs from the time evolution analysis of the mean square displacement (MSD) curves. In particular,w ee valuate the accuracy and precision of the parameter estimates from MSD analysis. In addition, the strategy is illustrated to depict the homogeneous electrosynthesis of silver NPs from the oxidation of as acrificial Ag ultramicroelectrode (UME) in Fe 2 + solution

Are nanoparticles spherical or quasi-spherical?

The geometry of quasi-spherical nanoparticles is investigated. The combination of SEM imaging and electrochemical nano-impact experiments is demonstrated to allow sizing and characterization of the geometry of single silver nanoparticles

A perspective on heterogeneous catalysts for the selective oxidation of alcohols

Selective oxidation of higher alcohols using heterogeneous catalysts is an important reaction in the synthesis of fine chemicals with added value. Though the process for primary alcohol oxidation is industrially established, there is still a lack of fundamental understanding considering the complexity of the catalysts and their dynamics under reaction conditions, especially when higher alcohols and liquid-phase reaction media are involved. Additionally, new materials should be developed offering higher activity, selectivity, and stability. This can be achieved by unraveling the structure–performance correlations of these catalysts under reaction conditions. In this regard, researchers are encouraged to develop more advanced characterization techniques to address the complex interplay between the solid surface, the dissolved reactants, and the solvent. In this mini-review, we report some of the most important approaches taken in the field and give a perspective on how to tackle the complex challenges for different approaches in alcohol oxidation while providing insight into the remaining challenges

Electronic circuit simulations as a tool to understand distorted signals in single-entity electrochemistry

Electrochemical analysis relies on precise measurement of electrical signals, yet the distortions caused by potentiostat circuitry and filtering are rarely addressed. Elucidation of these effects is essential for gaining insights behind sensitive low-current and short-duration electrochemical signals, e.g., in single-entity electrochemistry. We present a simulation approach utilizing the Electrical Simulation Program with Integrated Circuit Emphasis (SPICE), which is extensively used in electronic circuit simulations. As a proof-of-concept, we develop a universal electrical circuit model for single nanoparticle impact experiments, incorporating potentiostat and electronic filter circuitry. Considering these alterations, the experimentally observed transients of silver nanoparticle oxidation were consistently shorter and differently shaped than those predicted by established models. This reveals the existence of additional processes, e.g., migration, partial or asymmetric oxidation. These results highlight the SPICE approach’s ability to provide valuable insights into processes occurring during single-entity electrochemistry, which can be applied to various electrochemical experiments, where signal distortions are inevitable

Operando studies of the electrochemical dissolution of silver nanoparticles in nitrate solutions observed with hyperspectral dark-field microscopy

Since nanoparticles are frequently used in commercial applications, there is a huge demand to obtain deeper insights into processes at the nanoscale. Especially, catalysis, chemical and electrochemical reaction dynamics are still poorly understood. Thus, simultaneous and coupled opto-and spectro-electrochemical dark-field microscopy is used to study $\textit {in situ}$ and $\it operando$ the electrochemically driven dissolution mechanism of single silver nanoparticles in the presence of nitrate ions as non-complexing counter-ions, herein. Hyperspectral imaging is used to probe the intrinsic localized surface plasmon resonance of individual silver nanospheres before, during and after their electrochemical oxidation on a transparent indium tin oxide (ITO) electrode. Furthermore, optical video imaging was performed for additional information. Based on the complete loss of spectral information and intensity, a dissolution of the particles during the reaction was concluded. This way it is revealed that the dissolution of individual particles proceeds over several seconds, indicating a hindrance by the nitrate ions. Only electrochemical analysis does not provide this insight as the measured current does not allow distinguishing between successive fast dissolution of one particle after another or slow dissolution of several particles in a concerted manner. For comparison, experiments were performed in the presence of chloride ions. It was observed that the silver chloride formation is an instantaneous process. Thus, it is possible to study and define the reaction dynamics on the single nanoparticle level in various electrochemical systems and electrolyte solutions. Accordingly, $\it operando$ opto- and spectro-electrochemical studies allow us to conclude, that the oxidation of silver to solvated silver cations is a kinetically slow process, while the oxidation to silver chloride is fast. We propose this approach as a new method to study electrocatalyst materials, their transformation and degradation under operando conditions

PORTUGALIAE ELECTROCHIMICA ACTA Nanotoxicity -an electrochemist's perspective

Abstract This article highlights the fundamental role of mass-transport for interfacial reactions. First, the dissolution of particulate CaCO 3 is discussed demonstrating how the dimensions of the dissolving particle can 'switch' the reaction mechanism from being diffusion to surface controlled. Second, the influence of mass-transoprt on electrochemical reactions is considered, specifically considering how electrode modification can alter the observed voltammetric response in the absence of changing the electrochemical mechanism or the rate of electron transfer. Finally, these observations on the chemically controlling role of mass-transport are concluded by considering nanoparticle toxicity and how 'size effects' may be exhibited even in the absence of altered thermodynamics or interfacial kinetics of the reactions involved

Unveiling colloidal nanoparticle properties and interactions at a single entity level

Here, we discuss the capabilities of nanoimpact electrochemistry for studying properties of colloidal nanoparticles, electrocatalytic activity and particle reactivity at a single entity level, to gain better understanding of solid/liquid interfaces, which play a key role in various chemical and biological systems. The effect of particle properties like size, shape or composition, and particle-electrode interactions on the electrochemical signals and the resulting scientific insights are reviewed

Electrochemistry under confinement

Although the term 'confinement' regularly appears in electrochemical literature, elevated by continuous progression in the research of nanomaterials and nanostructures, up until today the various aspects of confinement considered in electrochemistry are rather scattered individual contributions outside the established disciplines in this field. Thanks to a number of highly original publications and the growing appreciation of confinement as an overarching link between different exciting new research strategies, ‘electrochemistry under confinement’ is the process of forming a research discipline of its own. To aid the development a coherent terminology and joint basic concepts, as crucial factors for this transformation, this review provides an overview on the different effects on electrochemical processes known to date that can be caused by confinement. It also suggests where boundaries to other effects, such as nano-effects could be drawn. To conceptualize the vast amount of research activities revolving around the main concepts of confinement, we define six types of confinement and select two of them to discuss the state of the art and anticipated future developments in more detail. The first type concerns nanochannel environments and their applications for electrodeposition and for electrochemical sensing. The second type covers the rather newly emerging field of colloidal single entity confinement in electrochemistry. In these contexts, we will for instance address the influence of confinement on the mass transport and electric field distributions and will link the associated changes in local species concentration or in the local driving force to altered reaction kinetics and product selectivity. Highlighting pioneering works and exciting recent developments, this educational review does not only aim at surveying and categorizing the state-of-the-art, but seeks to specifically point out future perspectives in the field of confinement-controlled electrochemistry

Why standard electrokinetic analysis often fails for nanostructured electrodes

The advancement of electrocatalysis from fundamental research to application is a process that requires researchers from different fields to co-work seamlessly to be effective. In this mini review, we highlight common problems that are faced when the complexity of novel electrode assemblies, consisting of nanostructured materials, is moved from a fundamental view towards an evaluation for application. When the classical kinetic descriptors such as Butler-Volmer kinetics are applied to complex electrode assemblies, a clear distinction and attribution of material properties versus electrode performance becomes challenging. We emphasize recent advancements to discern and analyse electrocatalysis at composite or nanostructured electrodes. We discuss the origins of inhomogeneities in the electrocatalytic activity of three-dimensional electrodes, how these can be detected and which necessary changes from the classical methods, such as Tafel analysis, can be performed to ensure a sound data acquisition and evaluation

Simultaneous Opto- and Spectro-Electrochemistry: Reactions of Individual Nanoparticles Uncovered by Dark-Field Microscopy

Despite the frequent use of silver nanoparticles in consumer products and medical treatments, their reactivity and degradation in aqueous suspensions are still under debate. Here we elucidate this reactivity by an <i>in situ</i> opto- and spectro-electrochemical approach. Using dark-field microscopy coupled to a spectrophotometer and to an electrochemical cell, redox reactions of individual silver nanoparticles are studied in the presence of chloride. The intensity and spectral position of the plasmon resonance of an individual particle are tracked simultaneously in real time during cyclic voltammetry. They both change almost instantaneously with the detected current in a chemically reversible way. Thus, it is evidenced that the intensity decrease of the optical signal at the silver peak position is caused by the reversible formation of silver chloride and not by dissolution of silver. Moreover, at large positive potentials, further transformation to silver oxide or chlorite is revealed spectroscopically, although the electrochemical current is hidden by water and chloride oxidation. Thus, the combination of electrochemistry with dark-field microscopy and hyperspectral imaging is introduced as a new tool for real-time analysis of (electro-)­chemical reactions of nanoparticles on a single-entity level