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Porphyrin molecules were immobilized on polycrystalline gold and glassy carbon by coordinating cobalt(II) 5,10,15,20-tetraphenyl-21H,23H-porphine to a 4-aminothiophenol self-assembled monolayer. The resulting electrocatalytic activity of the metalloporphyrin-modified substrates with regard to the oxygen reduction reaction was characterized by means of cyclic voltammetry and scanning electrochemical microscopy (SECM) using nanoelectrodes of well-defined geometry. From substrate generation tip collection (SG-TC) mode SECM measurements performed under steady-state conditions and at different applied substrate potentials, it is possible to extract kinetic information relevant to electrocatalyst substrates such as metalloporphyrin-modified gold and glassy-carbon electrodes. Such an approach allows for the isolation of the unique contribution of the electrocatalyst to the oxygen reduction reaction and peroxide formation.

The electrification of the transport sector has created an increasing demand for lithium‐ion batteries that can provide high power intermittently while maintaining a high energy density. Given the difficulty in designing a single redox material with both high power and energy density, electrodes based on composites of several electroactive materials optimized for power or capacity are being studied extensively. Among others, fast‐charging LiFePO4 and high energy Li(NixMnyCoz)O2 are commonly employed in industrial cell manufacturing. This study focuses on comparing different approaches to combining these two active materials into a single electrode. These arrangements were compared using standard electrochemical (dis)charge procedures and using synchrotron X‐ray fluorescence to identify variations in solution concentration gradient formation. The electrochemical performance of the layered electrodes with the high‐power material on top is found to be enhanced relative to its blended electrode counterpart when (dis)charged at the same specific currents. These findings highlight dual‐layer lithium‐ion batteries as an inexpensive way of increasing energy and power density of lithium‐ion batteries as well as a model system to study and exploit the synergistic effects of blended electrodes. [ABSTRACT FROM AUTHOR]

Keywords: electrode architecture; power density; fast charge; blended electrode; X-ray fluorescence EN electrode architecture power density fast charge blended electrode X-ray fluorescence 1 1 1 11/07/23 20231102 NES 231102 B The Front Cover b shows Li-metal cells which contain two active materials (red and blue). Front Cover: Exploring the Synergistic Effects of Dual-Layer Electrodes for High Power Li-Ion Batteries (ChemElectroChem 21/2023) Electrode architecture, power density, fast charge, blended electrode, X-ray fluorescence. [Extracted from the article]

The ionic liquid 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide was used in the scanning micropipette contact method to extend the electrochemical window of the electrolyte solution and enable the study of lithium‐ion battery materials with higher oxidation potential. Localized electrochemical measurements were performed on lithium iron phosphate particles that were drop‐cast onto a glassy carbon substrate. Investigation of the active materials occurred on a small scale (ca. 10 μm diameter), defined by the area of meniscus contact between the electrolyte solution in the micropipette and the substrate. Our studies showed that the SMCM probe is stable and can be used to analyze high energy lithium‐ion battery materials in the range of 2.5 to 5.1 V vs. Li/Li+. Extended potential, higher efficiency: Scanning micropipette contact method (SMCM) is extended to ionic liquid studies. The potential window for 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI TFSI) ionic liquid is suitable to examine high‐energy lithium‐ion battery materials. The electrochemical properties of lithium iron phosphate (LFP) particles drop‐cast onto a glassy carbon substrate are probed under inert atmosphere. SMCM‐coulombic efficiency of LFP particles in EMI TFSI is estimated to be higher than 90 %. [ABSTRACT FROM AUTHOR]

In scanning electrochemical microscopy (SECM), an approach curve performed in feedback mode involves the downward displacement of a microelectrode toward a substrate while applying a bias to detect dissolved electroactive species at a diffusion-limited rate. The resulting measured current is said to be at steady state. In order to reduce the required measurement time, the approach velocity can be increased. In this paper, we investigate experimentally and theoretically the combination of diffusion and convection processes related to a moving microdisk electrode during feedback approaches. Transient modeling and numerical simulations with moving boundaries are performed, and the results are compared to the experimental approach curves obtained in aqueous solution. The geometry and misalignment of the microelectrode influence the experimental approach curves recorded at high approach velocities. The effects are discussed through the decomposition of the current into transient diffusional, radial convectional, and axial convectional contributions. Finally a ready-to-use expression is provided to rapidly evaluate the maximal approach velocity for steady state measurements as a function of the microelectrode geometry and the physical properties of the media. This expression holds for the more restrictive case of negative feedback as well as other modes, such as SECM approach curves performed at substrates displaying first order kinetics. [ABSTRACT FROM AUTHOR]

The development of a reproducible procedure for the fabrication of Pt disk-shaped microelectrodes with characteristic dimensions ranging from 50 nm to 1 μm in diameter was carried out using a laser pulling technique. The governing physical phenomena involved in their fabrication are discussed, and the importance of adding a critical quartz thinning step in the general procedure is demonstrated. The preparation of the microelectrodes involves sealing a platinum wire inside a quartz tubing using a pipet puller, thinning the composite material (platinum/quartz assembly), and laser pulling it to obtain two microelectrodes. The resulting microelectrodes display reproducible well-controlled geometry, which is important to downstream quantitative scanning electrochemical studies and imaging. Mechanical polishing of the microelectrode is required and remains the critical step in the fabrication of nanometer size electrodes. Following production, the microelectrodes are characterized by electron microscopy, scanning electrochemical microscopy, and cyclic voltammetry. Development of these microelectrodes is motivated by their subsequent application to electrocatalysis and their potential in theoretical study because of their well-defined geometry. [ABSTRACT FROM AUTHOR]

The article reports on the use of scanning electrochemical microscopy (SECM) as an analytical technique to monitor electrochemical activity of a surface. The fundamental element of SECM is a small-scale electrode that serves as high spatial resolution, recording alterations in electrochemical potential having remarkable sensitivity and mobile probe. SECM measurements fuse with other biosensing techniques can conduct multiple experiments on a living project.

Scanning electrochemical microscopy (SECM) has recently been reported as a convenient technique to characterize the apparent diffusion coefficients in porous media (D ⋆) such as lithium-ion battery electrodes. The technique relies on hemispherical diffusion at the probe in the presence and absence of porous media. However, transition towards cylindrical diffusion follows as the diffusion layer becomes comparable to the media thickness, gradually limiting direct correlation between D ⋆ and the SECM probe steady state current. In this work, we examine the experimental parameters that define this transitional frontier using simulations. A best practice thickness criterium is derived that ensures that the measured steady state current is ≳ 90% of that found in the ideal hemispherical case. Below this thickness limit the response was found to follow an empirical formulation with only two variables. Fundamentally, this quantifies diffusion in the transition regime between hemispherical and cylindrical transport. Practically, this correction formulation may be included into standard steady-state current expression to account for the deviation from hemispherical transport in "thin" electrodes. The analysis consolidates SECM as a reliable tool to characterize liquid phase mass transport within porous films over wide range of thicknesses, including films supported on blocking substrates, like lithium-ion battery electrodes. [Display omitted] • Scanning electrochemical microscopy (SECM) porous media electrolyte transport. • Thin/thick threshold for SECM measurement of lithium-ion battery electrodes. • Empirical expressions for SECM analysis of high power thin electrodes. [ABSTRACT FROM AUTHOR]

Maintaining a well-defined tip-to-substrate separation is a critical area of development in scanning electrochemical microscopy (SECM). One technique that provides topographic data independently to the electrochemical measurement is shear force (SF) SECM. SF measurements are highly sensitive to factors including the tip-to-substrate separation, experimental solution, and probe geometry. We present a procedure for the fabrication of highly reproducible electrochemical probes with an active electrode disc with radii between 3nm to 190nm. A systematic study of the SF characteristics of these nano electrodes provides details on how to achieve the highest sensitivity and stability of SF signals, and maximize the number of SF sensitive frequencies. A new methodology to identify SF sensitive frequencies without needing to immerse the probes in solution or approach the surface is presented. Furthermore, we demonstrate that the greatest source of error in achieving reproducible SF behavior lies in the positioning of the piezo electric components and the piezo-nano electrode interface. [ABSTRACT FROM AUTHOR]

Abstract: Scanning electrochemical microscopy (SECM) is increasingly applied to study and image live cells. To reduce the overall analysis time during live cell SECM measurements and maintain cell viability, the microelectrode scan rate can be increased. The use of increasing microelectrode scan rates is challenging because our understanding of the downstream convection effects is tied to the ill-defined topography of the imaged live cells. The present study investigates the effect of forced convection on the microelectrode current during SECM imaging of live cells, model non-planar substrates and planar surfaces. Experimentally, we demonstrate that during constant height imaging, the normalized peak current observed during line scans on all three substrates scales linearly with the microelectrode velocity. This quasi-linear relationship is corroborated by finite element simulations of non-planar substrates, which further reveal that the slope is closely related to the electrochemical activity of the substrate. [Copyright &y& Elsevier]

The effect of the insulator-mixed-material edge on the galvanic corrosion rate of magnesium alloy (AE44)-mild steel (MS) couple is experimentally studied using scanning vibrating electrode technique (SVET), profilometry, and classical electrochemistry. The local and average corrosion rates estimated from the experimental depth of anodic attack profile of AE44-MS couple are validated by 2D and 3D corrosion numerical models. Our study demonstrates experimentally and theoretically that the presence of the insulator edge increases the local current density, which enhances the corrosion rate. The extent of the local corrosion rate enhancement and its effect on the overall corrosion rate of the mixed material is discussed and depends on the mixed material's geometry and the edge type. [ABSTRACT FROM AUTHOR]