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Operando wide‐field optical microscopy imaging yields a wealth of information about the reactivity of metal interfaces, yet the data are often unstructured and challenging to process. In this study, the power of unsupervised machine learning (ML) algorithms is harnessed to analyze chemical reactivity images obtained dynamically by reflectivity microscopy in combination with ex situ scanning electron microscopy to identify and cluster the chemical reactivity of particles in Al alloy. The ML analysis uncovers three distinct clusters of reactivity from unlabeled datasets. A detailed examination of representative reactivity patterns confirms the chemical communication of generated OH− fluxes within particles, as supported by statistical analysis of size distribution and finite element modelling (FEM). The ML procedures also reveal statistically significant patterns of reactivity under dynamic conditions, such as pH acidification. The results align well with a numerical model of chemical communication, underscoring the synergy between data‐driven ML and physics‐driven FEM approaches. [ABSTRACT FROM AUTHOR]

This work proposes a novel method for measuring the intrinsic activity of single metal‐based nanoparticles towards water reduction in neutral media at industrially relevant current densities. Instead of using gas nanobubbles as proxy, the method uses optical microscopy to track the local footprint of the reaction through the precipitation of metal hydroxide, which is associated to the local pH increase during electrocatalysis. The results show the electrocatalytic activities of different types of metal nanoparticles and bifunctionnal core‐shell nanostructures made of Ni and Pt, and demonstrate the importance of metal hydroxide nano‐shells in enhancing electrocatalysis. This method should be generalizable to any electrocatalytic reaction involving pH changes such as nitrate or CO2 reduction. [ABSTRACT FROM AUTHOR]

The formation of metal nanoparticles (NPs) on surfaces by electrodeposition is of significant interest, particularly with a view to understand the early stages of nucleation and growth. Here, the combination of scanning electrochemical cell microscopy (SECCM) and interference reflection microscopy (IRM) is demonstrated to be a compelling approach for real‐time monitoring of NP dynamics within the SECCM meniscus‐electrode wetted area, through synchronous monitoring in the millisecond range of the electrochemical and optical signatures. Diffraction‐limited entities, undergoing phase changes at the electrode substrate, are readily highlighted and tracked in time, including the onset time for the appearance of NPs and their movement over time. The results strongly implicate the rapid formation, surface diffusion and aggregation of smaller entities (not detectable optically) to produce the larger electrodeposited NPs. By applying SECCM tips of different size, it is also possible to understand how the wetted area (meniscus size) plays a key role in the number of NPs formed, with small tip sizes allowing the formation of single NPs. The SECCM‐IRM approach is expected to be a powerful platform for the study of myriad phase‐formation processes at the nanoscale, particularly by drawing on the possibility of making hundreds or thousands of measurements in fresh surface locations through SECCM technology. [ABSTRACT FROM AUTHOR]

Nanoimpact electrochemistry (NIE) is a straightforward analytical technique to study at high throughput the reactivity of single nanoparticles (NPs) colliding with a biased ultramicroelectrode (UME). As NIE can reveal both NP size and catalytic activity, this strategy can be employed to establish relationships between these two NP descriptors. Herein, it is shown that the electrode material is crucial for visualizing simultaneously electrocatalytic processes and NP transformation, which can size the NPs. UMEs made of gold (Au) or glassy carbon (GC), were employed to study the reduction of AgBr NPs and the electrocatalytic activity of the resulting Ag NPs for the oxygen reduction reaction (ORR). With Au UME, only the transformation process is probed, allowing a quantitative analysis of the overpotential effect on the reduction dynamics of the AgBr NPs. When a GC UME is employed, the AgBr NPs reduction and subsequent ORR activity can be quantified for the very same NPs. [ABSTRACT FROM AUTHOR]

The nanostructuration of an electrochemical interface dictates its micro‐ and macroscopic behavior. It is generally highly complex and often evolves under operating conditions. Electrochemistry at these nanostructurations can be imaged both operando and/or ex situ at the single nanoobject or nanoparticle (NP) level by diverse optical, electron, and local probe microscopy techniques. However, they only probe a tiny random fraction of interfaces that are by essence highly heterogeneous. Given the above background, correlative multimicroscopy strategy coupled to electrochemistry in a droplet cell provides a unique solution to gain mechanistic insights in electrocatalysis. To do so, a general machine‐vision methodology is depicted enabling the automated local identification of various physical and chemical descriptors of NPs (size, composition, activity) obtained from multiple complementary operando and ex situ microscopy imaging of the electrode. These multifarious microscopically probed descriptors for each and all individual NPs are used to reconstruct the global electrochemical response. Herein the methodology unveils the competing processes involved in the electrocatalysis of hydrogen evolution reaction at nickel based NPs, showing that Ni metal activity is comparable to that of platinum. [ABSTRACT FROM AUTHOR]

Energy storage provides flexibility to an energy system and is therefore key for the incorporation of renewable energy sources such as wind and solar into the grid. Aqueous Zn–MnO2 batteries are promising candidates for grid‐scale applications due to their high theoretical capacity (616 mAh g–1) and the abundance of their components in the Earth's crust. However, they suffer from low cyclability, which is probably linked to the dramatic pH variations induced by the electrochemical conversion of MnO2. These pH variations are known to trigger the precipitation/dissolution of zinc hydroxide sulfate (Zn4(OH)6SO4. xH2O, (ZHS)), which might have an influence on the conversion of MnO2. Herein, optical reflectometry is used to image and quantitatively monitor the MnO2 electrode's charge and discharge in situ and under operation. It emphasizes how solid‐phase ZHS rules the dynamics of both charge and discharge, providing a comprehensive picture of the mechanism at play in aqueous Zn–MnO2 batteries. If the precipitation of ZHS might impede the MnO2 electrode's discharge, it is a crucial pH buffer delaying the occurrence of the competing oxidation of water on charge. [ABSTRACT FROM AUTHOR]

Electrodeposition of earth‐abundant iron group metals such as nickel is difficult to characterize by simple electrochemical analyses since the reduction of their metal salts often competes with inhibiting reactions. This makes the mechanistic interpretation sometimes contradictory, preventing unambiguous predictions about the nature and structure of the electrodeposited material. Herein, the complexity of Ni nanoparticles (NPs) electrodeposition on indium tin oxide (ITO) is unraveled operando and at a single entity NP level by optical microscopy correlated to ex situ SEM imaging. Our correlative approach allows differentiating the dynamics of formation of two different NP populations, metallic Ni and Ni(OH)2 with a <25 nm limit of detection, their formation being ruled by the competition between Ni2+ and water reduction. At the single NP level this results in a self‐terminated growth, an information which is most often hidden in ensemble averaged measurements. [ABSTRACT FROM AUTHOR]

Herein we report the first example of using scanning electrochemical microscopy (SECM) to quantitatively analyze O2 reductive activation in organic media catalyzed by three different Fe porphyrins. For each porphyrin, SECM can provide in one single experiment the redox potential of various intermediates, the association constant of FeII with O2, and the pKa of the FeIII(OOH−)/ FeIII(OO2−) couple. The results obtained can contribute to a further understanding of the parameters controlling the catalytic efficiency of the Fe porphyrin towards O2 activation and reduction. [ABSTRACT FROM AUTHOR]

Herein we report the first example of using scanning electrochemical microscopy (SECM) to quantitatively analyze O2 reductive activation in organic media catalyzed by three different Fe porphyrins. For each porphyrin, SECM can provide in one single experiment the redox potential of various intermediates, the association constant of FeII with O2, and the pKa of the FeIII(OOH−)/ FeIII(OO2−) couple. The results obtained can contribute to a further understanding of the parameters controlling the catalytic efficiency of the Fe porphyrin towards O2 activation and reduction. [ABSTRACT FROM AUTHOR]

The local electroless deposition of gold on pyrite is studied by scanning electrochemical microscopy (SECM). The SECM and additional SEM experiments provide kinetic and mechanistic insights on the local galvanic replacement of pyrite by gold. We evidence that individual gold nanoparticles or full coverage of gold on the pyrite surface can be obtained by controlling either the deposition time or the flux of gold ions electrogenerated at the ultramicroelectrode. We also studied the influence of ferric ions, known to be implied on gold etching and pyrite corrosion and therefore, on the overall process of gold deposition on pyrite. We then demonstrate that the presence of ferric ions significantly modifies i) the thermodynamic of the gold electrodissolution, ii) the process of adsorption of auric ions on pyrite in the first instants, iii) the number of nucleation sites on the pyrite surface and, iv) the structure of the deposited gold layer. The electroless deposition of gold on pyrite is studied at the local scale by the scanning elextrochemical microscope. Herein, kinetic and mechanistic insights on the galvanic replacement of yrite by gold are provided. Additionally, it is demonstrated that the depositon of gold on pyrite is strongly affected by the presence of ferric ions. [ABSTRACT FROM AUTHOR]

By 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. Herein, a model is developed to extend NTA to allow 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 a strategy to estimate the growth parameters of individual NPs from the time evolution analysis of the mean square displacement (MSD) curves. In particular, we evaluate 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 a sacrificial Ag ultramicroelectrode (UME) in Fe2+ solution. Where next? The tracking of nanoparticles (NP) trajectories provides complementary size information to single NP electrochemistry. Monte Carlo simulations are extending such strategy to the case of NPs growing in solution. A strategy is proposed to estimate the growth rate of single NPs from mean square displacement curves. It is illustrated to depict the homogeneous electrosynthesis of silver NPs from the oxidation of a sacrificial Ag ultramicroelectrode. [ABSTRACT FROM AUTHOR]

Abstract: Electrodeposition of nanoparticles (NPs) is a promising route for the preparation of highly electroactive nanostructured electrodes. By taking advantage of progressive electrodeposition, disordered arrays with a wide size distribution of Ag NPs are produced. Combined with surface‐reaction monitoring by using highly sensitive backside absorbing‐layer optical microscopy (BALM), such arrays offer a platform for screening size‐dependent electrochemistry at the single NP level. In particular, this strategy allows rationalizing the electrodeposition dynamics at the single‐NP level (>10 nm), up to the point of quantifying the presence of metal nanoclusters (<2 nm), and probing easier NP oxidation with size decrease, either through electrochemical or galvanic reactions. [ABSTRACT FROM AUTHOR]

Single nanoparticle (NP) electrochemistry detection at a micro liquid|liquid interface (LLI) is exploited using the catalyzed oxygen reduction reaction (ORR). In this way, current spikes reminiscent of nanoimpacts were recorded, which corresponded to electrocatalytic enhancement of the ORR by Pt NPs. The nature of the LLI allows exploration of new phenomena in single NP electrochemistry. The recorded impacts result from a bipolar reaction occurring at the Pt NP straddling the LLI. O2 reduction takes place in the aqueous phase, while ferrocene hydride (Fc-H+; a complex generated upon facilitated interfacial proton transfer by Fc) is oxidized in the organic phase. Ultimately, the role of reactant partitioning, NP bouncing, or the ability of NPs to induce Marangoni effects, is demonstrated. [ABSTRACT FROM AUTHOR]

Electrodeposition, nanopipette, optical microscopy, SECCM, single nanoparticle Keywords: electrodeposition; nanopipette; optical microscopy; SECCM; single nanoparticle EN electrodeposition nanopipette optical microscopy SECCM single nanoparticle 1 1 1 05/04/23 20230502 NES 230502 B The Front Cover b draws a parallel between the hybrid scanning electrochemical cell microscopy-interference reflection microscopy (SECCM-IRM) technique, and its use to monitor the nucleation and growth of silver nanoparticles, and the recording of a performance by a rock band. The stage corresponds to the meniscus-electrode wetted area formed with the SECCM probe. [Extracted from the article]

The degradation of Prussian blue (PB) during H2O2 reduction is investigated by scanning electrochemical microscopy (SECM). Coupling SECM with optical microscopy allows quantitative assessment in situ of the effect of HO− on the dissolution of PB in lithographic experiments. The local production of HO− in the vicinity of PB is an easy way to pattern a PB layer; Such PB dissolution during H2O2 reduction leads to the release of soluble ferrocyanide and Fe2+. In the presence of H2O2, the latter initiate the Fenton reaction and the generation of highly reactive hydroxyl radicals HO.. This is revealed by the degradation of an organic layer immobilized on an ultramicroelectrode held in the vicinity of a PB layer during H2O2 reduction. The formation of such reactive species is of great importance to further understand the possible origin of the activity loss of sensors, batteries, and photovoltaic cells when composite materials based on PB or on its derivatives are used as catalysts for H2O2 or O2 reduction. [ABSTRACT FROM AUTHOR]

Polyoxometalates (POMs) are attractive candidates for the rational design of multi-level charge-storage materials because they display reversible multi-step reduction processes in a narrow range of potentials. The functionalization of POMs allows for their integration in hybrid complementary metal oxide semiconductor (CMOS)/molecular devices, provided that fine control of their immobilisation on various substrates can be achieved. Owing to the wide applicability of the diazonium route to surface modification, a functionalized Keggin-type POM [PW11O39{Ge( p-C6H4-CC-C6H4- ${{\rm N}{{+\hfill \atop 2\hfill}}}$)}]3− bearing a pending diazonium group was prepared and subsequently covalently anchored onto a glassy carbon electrode. Electron transfer with the immobilised POM was thoroughly investigated and compared to that of the free POM in solution. [ABSTRACT FROM AUTHOR]

In the mechanism of reaction of Grignard reagent formation for alkyl halides (RX), it is generally assumed that the alkyl radical, formed by the electron transfer from the metal to this halide, reacts rapidly with the paramagnetic MgX• species. The previous comparisons of aryl halides reactivity toward magnesium and their reactivity toward a cathode strongly suggested that MgX• species are not, for the aryl halides, compulsory to rationalise the observed facts. The aryl radicals formed by electron transfer from the metal to the aryl halide would undergo a rapid second electron transfer to yield carbanions transformed into RMgX by reaction with MgX2. In contrast, for the alkyl halides, the reduction of the rapidly formed alkyl radicals into carbanions has seldom been discussed as a possible fate for these radicals, the main discussed fates being dimerisation, disproportionation, hydrogen abstraction from the solvent, rearrangement or coupling with MgX• radicals. Two main differences distinguish the reactivity of alkyl halides from their aryl halides counterpart. First, the radical anions of aryl halides may have a given lifetime whereas electron transfer to alkyl halides is concerted with the cleavage of the molecule. Second, the aryl radicals display far stronger oxidising properties than the alkyl radicals. The counterpart of this property is that aryl carbanions display weaker reducing properties than the alkyl ones. In this report, putting in perspective Grignard reaction and the experimental results obtained with identical radical clocks in electrochemistry, we tentatively provide an answer to the question raised in the title. The comparison of electrochemical patterns of reactivity of selected alkyl halides and the evolutions of yields in the preparation of Grignard reagent suggest a new explanation for the lower yields generally observed when alkyl iodides are the starting substrates. It involves an autocatalytic reaction where carbanionic species formed from the alkyl radicals and diffusing away from the metal surface, transfer one electron to the alkyl halide; the result would be the creation of two radicals leading to an increased amount of by-products. If the carbanionic mechanism were to be retained for the formation of alkyl Grignard reagent one would have to admit that the magnesium surface behaves as a cathode displaying high current densities reminiscent of microelectrodes. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Herein we report the first example of using scanning electrochemical microscopy (SECM) to quantitatively analyze O2 reductive activation in organic media catalyzed by three different Fe porphyrins. For each porphyrin, SECM can provide in one single experiment the redox potential of various intermediates, the association constant of FeII with O2, and the pKa of the FeIII(OOH−)/ FeIII(OO2−) couple. The results obtained can contribute to a further understanding of the parameters controlling the catalytic efficiency of the Fe porphyrin towards O2 activation and reduction. [ABSTRACT FROM AUTHOR]

Herein we report the first example of using scanning electrochemical microscopy (SECM) to quantitatively analyze O2 reductive activation in organic media catalyzed by three different Fe porphyrins. For each porphyrin, SECM can provide in one single experiment the redox potential of various intermediates, the association constant of FeII with O2, and the pKa of the FeIII(OOH−)/ FeIII(OO2−) couple. The results obtained can contribute to a further understanding of the parameters controlling the catalytic efficiency of the Fe porphyrin towards O2 activation and reduction. [ABSTRACT FROM AUTHOR]