Scanning Electrochemical Cell Microscopy Research Articles

Spatially Confined Microcells: A Path toward TMD Catalyst Design.

With the ability to maximize the exposure of nearly all active sites to reactions, two-dimensional transition metal dichalcogenide (TMD) has become a fascinating new class of materials for electrocatalysis. Recently, electrochemical microcells have been developed, and their unique spatial-confined capability enables understanding of catalytic behaviors at a single material level, significantly promoting this field. This Review provides an overview of the recent progress in microcell-based TMD electrocatalyst studies. We first introduced the structural characteristics of TMD materials and discussed their site engineering strategies for electrocatalysis. Later, we comprehensively described two distinct types of microcells: the window-confined on-chip electrochemical microcell (OCEM) and the droplet-confined scanning electrochemical cell microscopy (SECCM). Their setups, working principles, and instrumentation were elucidated in detail, respectively. Furthermore, we summarized recent advances of OCEM and SECCM obtained in TMD catalysts, such as active site identification and imaging, site monitoring, modulation of charge injection and transport, and electrostatic field gating. Finally, we discussed the current challenges and provided personal perspectives on electrochemical microcell research.

Simultaneous Mapping of Electrocatalytic Activity and Selectivity via Hybrid Scanning Electrochemical Probe Microscopy.

Nanoscale scanning electrochemical probe microscopy started to elucidate the heterogeneity of electrocatalytic activity at electrode surfaces. However, understanding the heterogeneity in product selectivity, another crucial aspect of interfacial reactivity, remains challenging. Herein, we introduce a method combining scanning electrochemical microscopy (SECM) and scanning electrochemical cell microscopy (SECCM) to enable the spatially resolved mapping of both activity and selectivity in electrocatalysis. A dual-channel nanopipette probe was developed: one channel for activity mapping and the other for product detection with a high collection efficiency (>95%) and sensitivity. Simultaneous mapping of activity and selectivity in the oxygen reduction reaction (ORR) is demonstrated. Combined with colocalized crystal orientation mapping, we uncover the local electrocatalytic performance of ORR at different facets on polycrystalline Pt and Au. The high-resolution selectivity mapping enabled by our method with colocalized structural characterization can provide structure-activity-selectivity relationships that are often unavailable in ensemble measurement, holding promise for understanding key structural motifs controlling interfacial reactivity.

Selective Initiation of Corrosion Pits in Stainless Steel Using Scanning Electrochemical Cell Microscopy.

Scanning electrochemical cell microscopy is a useful technique for determining variations in corrosion behavior across a surface. However, the numerous options for experimental parameters and little understanding of their effect on the corroding system render comparisons of results between studies difficult. Herein, we explore changes in corrosion behavior of two martensitic stainless steels, a cast CA6NM and a wrought S41500, as a result of the chosen experimental parameters, including scan rate, approach potential, surface oil immersion, and tip aperture diameter. The study demonstrates that these experimental parameters can be controlled to probe oxide passivation kinetics and single pitting events by changing the surface state and cathodic currents. We measured the pitting and repassivation kinetics of a single pit and determined the compositional change of the Al2O3 inclusion site initiation point. Hundreds of data points were measured within 17 h of experimental time on the stainless steel samples, allowing statistical averages of corrosion and pitting values. This work will open new avenues for fine-tuning various corrosion aspects at the microscale, thereby contributing to a deeper understanding of the corrosion processes and mechanisms of diverse materials.

Local electrochemiluminescence imaging using scanning electrochemical cell microscopy

In this communication, local electrochemiluminescence (ECL) imaging is achieved using scanning electrochemical cell microscopy (SECCM) to create a localized region for the occurrence of ECL reaction. The system is demonstrated using a droplet at the micropipette that is contact with the prepared Ru-Silica@Au particles at indium tin oxide (ITO) slide. Tri-n-propylamine (TPrA) in the droplet reacts with ruthenium complex in a 10 μm-diameter-region to produce ECL emission, which is recorded by photo multiplier tube (PMT) underneath the ITO slide. By contacting each local region consecutively, the distribution of steady-state current and the related ECL emission at the ITO surface is imaged. The local ECL intensity show an approximately linear dependence with the current, but obvious deviation from the linear curve is observed at some regions. This result suggests that the ECL emission is not only determined by the transferred electron number in the electrochemical reaction, and also affected by local environments at ITO surface. As compared with the traditionally used ECL imaging in the bulk solution, this strategy avoids the cross-talking of ECL emission from nearby regions, and could offer a new way to unveil more molecular mechanism in the ECL reaction.

A microscopic view on the electrochemical deposition and dissolution of Au with scanning electrochemical cell microscopy – Part II: Potentiostatic dissolution and correlation with in-situ EC-TEM

The electrochemical oxidation of gold nanoparticles (NPs) has been examined in H2SO4 and acidified NaCl by combining multiple techniques including scanning electrochemical cell microscopy (SECCM) and in-situ electrochemical transmission electron microscopy (EC-TEM). Our findings provide novel insights into the intricate oxidation dynamics of Au NPs, which are determined by the interplay between passivation and dissolution. SECCM chronoamperometric measurements in the Cl− containing electrolyte reveal distinct current peak events during the dissolution process. We attribute these events to delayed one-by-one NP dissolution following the rapid breakdown of the passive layer formed during the initial stages of anodic polarization, and exposure of the metallic gold core to Cl− ions. Statistical analysis of these peak events further uncovers relationships between the applied potential and the distribution of the peak descriptors over time. The analysis of the charge consumed during each event indicates that NPs undergo partial dissolution interrupted by rapid re-passivation. As the potential increases, the peak current rises and the duration of the peak events decreases due to intensified dissolution and faster re-passivation. The onset time of the peak events displays a highly stochastic nature. In-situ EC-TEM measurements support these findings by confirming that Au NPs dissolve one-by-one at different time intervals and stages, revealing a core-shell structure during the dissolution process. The shell, which is more resistant, leads to a delayed, particle-by-particle dissolution once it is broken down. Quantification of the EC-TEM video allows recreating an equivalent current-time transient which presents peak events similar to these measured by SECCM. These findings contribute to our understanding of the complex and stochastic behavior of nanoparticle dissolution, which cannot be fully explained by traditional (macro) electrochemistry alone. The combination of SECCM and EC-TEM offers high potential to understand complex nanomaterial degradation pathways, essential for the design of durable electrocatalysts for electrochemical conversion and storage applications.

A simple approach for effectively improving the resolution of scanning electrochemical cell microscopy

The high-resolution scanning electrochemical cell microscopy (SECCM) is a powerful tool that can directly explore the structure-property correlation of materials at nanometer scale. However, so far, the attainable maximum resolution is still restricted by the diameter of the droplet probe. Here, we report a simple and effective approach that can highly reduce the effective size of a nanopipette probe in SECCM. The effective working size was reduced to tens of nanometers by using the conventional droplet probe with an opening size of ∼129 nm through one-step oil coating. Furthermore, both the topographical and electrochemical activity of the Au nanoplate were simultaneously recorded successfully at the pixel size of sub-10 nm in the x-axis direction, meaning the potential to achieve a sub-10 nm resolution. Finally, the modified probe displays excellent applicability with acidic, neutral and alkaline electrolytes. The method retains the advantages of the droplet probe and breaks the limitation of its opening size on the SECCM imaging resolution, opening a broad avenue for both further rapid commercialization and broad applications of SECCM.

Emergence of electrochemical catalytic activity via an electrochemical-probe on defective transition metal dichalcogenide nanosheets

Two-dimensional transition metal dichalcogenides (2D TMDs) have shown exceptional electrochemical catalytic activity for the efficient generation of hydrogen through electrochemical water splitting. In the case of molybdenum disulfide (MoS2), a prominent member of 2D TMDs, the electrochemically active sites primarily reside at the edges, while the basal plane, which constitutes the majority of the MoS2 structure, remains relatively inactive. In this study, we aimed to activate the inert sites of the basal plane with some defective structure for hydrogen evolution reaction (HER) by employing an electrochemical-probe in combination with voltage sweeping. The initiation of HER at these previously inactive sites was visualized and confirmed using scanning electrochemical cell microscopy (SECCM). Our findings reveal that the enhanced HER activity originates from surface defects induced by the probing process.

Revealing the Heterogeneous Bubble Nucleation at Individual Silica Nanoparticles.

Deep understanding of the bubble nucleation process is universally important in systems, from chemical engineering to materials. However, due to its nanoscale and transient nature, effective probing of nucleation behavior with a high spatiotemporal resolution is prohibitively challenging. We previously reported the measurement of a single nanobubble nucleation at a nanoparticle using scanning electrochemical cell microscopy, where the bubble nucleation and formation were inferred from the voltammetric responses. Here, we continue the study of heterogeneous bubble nucleation at interfaces by regulating the local nanostructures using silica nanoparticles with a distinct surface morphology. It is demonstrated that, compared to the smooth spherical silica nanoparticles, the raspberry-like nanoparticles can further significantly reduce the nucleation energy barrier, with a critical peak current about 23% of the bare carbon surfaces. This study advances our understanding of how surface nanostructures direct the heterogeneous nucleation process and may offer a new strategy for surface engineering in gas involved energy conversion systems.

Practical guidelines for the use of scanning electrochemical cell microscopy (SECCM).

Scanning electrochemical cell microscopy (SECCM) has emerged as a transformative technology for electrochemical materials characterisation and the study of single entities, garnering global adoption by numerous research groups. While details on the instrumentation and operational principles of SECCM are readily available, the growing need for practical guidelines, troubleshooting strategies, and a systematic overview of applications and trends has become increasingly evident. This tutorial review addresses this gap by offering a comprehensive guide to the practical application of SECCM. The review begins with a discussion of recent developments and trends in the application of SECCM, before providing systematic approaches to (and the associated troubleshooting associated with) instrumental set up, probe fabrication, substrate preparation and the deployment of environmental (e.g., atmosphere and humidity) control. Serving as an invaluable resource, this tutorial review aims to equip researchers and practitioners entering the field with a comprehensive guide to essential considerations for conducting successful SECCM experiments.

Structure-dependent CO2 reduction on molybdenite (MoS2) electrocatalysts.

Scanning electrochemical cell microscopy (SECCM) is employed to directly identify the structure-dependent electrochemical CO2 reduction reaction (eCO2RR) activity of molybdenite (MoS2) electrocatalysts in an aqueous imidazolium-based aprotic ionic liquid electrolyte. Nanoscale defects, where the edge plane (EP) is exposed, are directly targeted, revealing heightened overall activity (eCO2RR + the competing hydrogen evolution reaction, HER) over the relatively inactive basal plane (BP). In addition, certain types of defects (e.g., step edges) only exhibit heightened activity under a CO2 atmosphere (i.e., compared to N2), indirectly confirming higher selectivity at these surface sites. Overall, this work will guide the bottom-up design of earth-abundant electrocatalysts for use in large-scale CO2 electrolysis.

Antimicrobial effects of silver nanoparticle-microspots on the mechanical properties of single bacteria.

Silver nanoparticles (AgNPs) conjugated with polymers are well-known for their powerful and effective antimicrobial properties. In particular, the incorporation of AgNPs in biocompatible catecholamine-based polymers, such as polydopamine (PDA), has recently shown promising antimicrobial activity, due to the synergistic effects of the AgNPs, silver(I) ions released and PDA. In this study, we generated AgNPs-PDA-patterned surfaces by localised electrochemical depositions, using a double potentiostatic method via scanning electrochemical cell microscopy (SECCM). This technique enabled the assessment of a wide parameter space in a high-throughput manner. The optimised electrodeposition process resulted in stable and homogeneously distributed AgNP-microspots, and their antimicrobial activity against Escherichia coli was assessed using atomic force microscopy (AFM)-based force spectroscopy, in terms of bacterial adhesion and cell elasticity. We observed that the bacterial outer membrane underwent significant structural changes, when in close proximity to the AgNPs, namely increased hydrophilicity and stiffness loss. The spatially varied antimicrobial effect found experimentally was rationalised by numerical simulations of silver(I) concentration profiles.

Long-Range SECCM Enables High-Throughput Electrochemical Screening of High Entropy Alloy Electrocatalysts at Up-To-Industrial Current Densities.

High-entropy alloys (HEAs), especially in the form of compositional complex solid solutions (CCSS), have gained attention in the field of electrocatalysis. However, exploring their vast composition space concerning their electrocatalytic properties imposes significant challenges. Scanning electrochemical cell microscopy (SECCM) offers high-speed electrochemical analysis on surface areas with a lateral resolution down to tens of nm. However, high-precision piezo positioners often used for the motion of the tip limit the area of SECCM scans to the motion range of the piezo positioners which is typically a few tens of microns. To bridge this experimental gap, the study proposes a long-range SECCM system with a rapid gas-exchange environmental cell for high-throughput electrochemical characterization of 100mm diameter HEA thin-film material libraries (ML) obtained by combinatorial co-sputtering. Due to the gas-liquid interface at the positioned SECCM droplet on the sample, high-throughput evaluation under industrial current density conditions becomes feasible. This allows the direct correlation between electrocatalytic activity and material composition with high statistical reliability. The multidimensional data obtained accelerates materials discovery, development, and optimization.

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

Understanding the High Scan Rate PDP Curves Obtained By Seccm

Scanning electrochemical cell microscopy (SECCM) is progressively employed for investigating corrosion behaviors at localized sites on metal surfaces. Normally, hundreds of potentiodynamic polarization (PDP) measurements are conducted on the sample using a high potential scan rate to reduce the experimental duration. However, polarization curves obtained under such conditions would yield inaccurate Tafel kinetics. In this research, we performed PDP measurements on Al sample at various scan rates using SECCM and obtained reproducible results. The experimental polarization curves were successfully simulated by a high field model that accounted for the cathodic contribution from oxygen reduction reaction and the anodic contribution from Al oxide film growth. By utilizing this model, we were able to extract the true corrosion kinetic properties from the high scan rate polarization curves, which has not been reported previously. This study represents a significant contribution towards enhancing SECCM-based micro-polarization as a robust quantitative technique for corrosion study.

Resolving the Dependence of Aluminum Alloy Corrosion on Grain Orientation by Scanning Electrochemical Cell Microscopy

The study of grain-dependent corrosion behaviors of practical polycrystalline metals remains challenging due to the influences of other microstructural features, such as intermetallic particles and grain boundaries. In this work, we employed the oil-immersed scanning electrochemical cell microscopy (SECCM) to investigate the effect of grain orientations of a practical aluminum alloy AA7075-T73 on the surface electrochemical behaviors. Thousands of spatially resolved microscopic potentiodynamic polarization (PDP) measurements were performed, allowing the extraction of information only from grain interior areas excluding intermetallic particles and grain boundaries. The differences in the corrosion behaviors between grains were revealed. Cathodic currents exhibited a strong grain orientation dependence with a decreasing order of {101} > {001} > {111}, agreeing with the prediction from the order of atomic planar density. By contrast, the dependence of anodic currents on grain orientation was weak, and pitting was independent of grain orientation, which could be due to the limited mass transport of ions within the surface oxide film. This work highlights the capability of oil-immersed scanning electrochemical cell microscopy in resolving small electrochemical differences, which will greatly promote the study of grain-dependent behaviors of practical polycrystalline samples.

(Invited) High-Throughput Local Electrochemistry Coupled with (in-situ) microscopy to Advance on the Fundamentals of Electrochemical Nucleation and Growth

Electrochemical nucleation and growth (EN&G) are the cornerstone for many (nano)material growth routes and the main factor limiting battery durability. The in-depth experimental assessment of the process is very challenging due to the random nature of initiation events (nucleation), the heterogeneity of surfaces and the (very) fast kinetics across several length scales. For all that, our understanding of the mechanisms involved is inaccurate and incomplete [1].During the last years, we have developed an approach based on using carbon coated TEM grids as electrodes to combine ex-situ atomic-scale TEM characterization with electron tomography and macroscale electrochemical measurements [2,3]. This approach has brought valuable evidence of non-classical growth pathways such as growth mediated by nanocluster aggregation [3,4]. Yet, it does not capture the influence of the heterogeneous nature of the surface where EN&G proceeds, nor the dynamics before, during and after nucleation [5].In this contribution, we present our recent work in which we combine high-throughput local electrochemistry by Scanning Electrochemical Cell Microscopy (SECCM), with ex-situ and in-situ characterization, including electrochemical transmission electron microscopy (EC-TEM), to study the electrochemical nucleation and growth of metals on carbon surfaces [6,7].The spatially resolved electrochemical characterization enables a one-to-one correlation between the electrochemical data and the local surface properties, which can be evaluated by different surface analytical tools (SEM, AFM, ...) in identical locations to where the local electrochemical measurements have been performed. In addition, EC-TEM allows the study of the early-stage growth/dissolution dynamics of the metallic phase.The combination of both methods opens new opportunities for fully understanding the complex nature of EN&G phenomena. In the longer run, this can be exploited for the rational design (electrodeposition) of functional nanostructured materials considering the heterogeneous nature of the supports and the differences within nanomaterial ensembles.

(Invited) Insights into Processes at the Electrode/Electrolyte Interface of Battery Electrodes Via Scanning (Electrochemical) Probe Microscopy

Scanning (electrochemical) probe microscopy (SEPM) techniques such as atomic force microscopy (AFM), scanning electrochemical microscopy (SECM), nano-pipette derived scanning probe methods like scanning electrochemical cell microscopy (SECCM) and hybrid methods have recently been used to study interfacial processes occurring at solid/electrolyte interfaces of battery electrodes [1]. So far, mainly Lithium-ion battery (LIB) electrodes have been studied, such as the solid-electrolyte interphase formation at graphite anodes [2,3]. Next generation battery chemistries, using earth abundant elements like sodium (Na), potassium (K), aluminum (Al) improving sustainability still suffer from insufficient knowledge of processes occurring during cycling at the electrode/electrolyte interface such as interphase formation, as gained insights from Li batteries cannot simply be transferred to post-Li chemistries.In this contribution, an overview of the potential of SEPM techniques to gain insight in interfacial process of post-Li battery chemistries will be given, focusing mainly on the SEI formation on hard carbon composite anodes for Na-ion batteries (SIBs) [4]. The influence of the electrolyte composition along with the effects of additives on the SEI formation and the nanomechanical properties of the electrode will be presented. In addition, given the abundance of Al and the high theoretical volumetric capacity, makes Al a highly attractive battery chemistry [5]. Despite these advantages, there are several challenges like the Al2O3 passivating layer and the mostly used acidic ionic liquid (IL)-based electrolyte AlCl3/1-ethyl-3-methylimidazolium chloride [EMIm]Cl that leads to corrosion, which determines the plating and stripping efficiency and therefore the overall performance. First correlative SECCM/EDX/EBSD studies on Al anodes will be presented. Acknowledgement This work contributes to the research performed at CELEST (Center for Electrochemical Energy Storage Ulm - Karlsruhe) and was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy – EXC 2154 – Project number 390874152 (POLiS Cluster of Excellence).

Visualization and Location Determination of Pit Initiation Sites in Martensitic Stainless Steel during Corrosion-Fatigue Cyclic Plastic Deformation

Low-carbon martensitic stainless steels, such as 13%Cr4%Ni, are widely used in manufacturing hydraulic turbine runners. High tensile strength steel, such as cast CA6NM or wrought S41500 martensitic stainless steel, has an acceptable resistance to corrosion and cavitation, and reduces the weight and cost while offering a more efficient design. During operation, the combined effect of cyclic loading (fatigue) and corrosion reduces the fatigue strength and can initiate cracks at localized corrosion surface defects.In this study, we determined the bulk and localized corrosion behavior of wrought (S41500) and cast (CA6NM) 13%Cr4%Ni stainless steel before and after plastic deformation.Susceptibility to pitting corrosion was studied using open circuit potential and potentiodynamic polarization measurements in 0.020 M NaCl. Localized corrosion behavior was studied using a scanning droplet cell (SDC) and oil immersed scanning electrochemical cell microscopy (OI-SECCM). The bulk and localized electrochemical measurements after different surface preparation methods (mechanical polishing, followed by etching or electro-etching in different media) were compared.The surface defects including micro-voids and inclusions of different types were characterized. The location of pit initiation was then determined using scanning electron microscopy and profilometry imaging. A three-electrode microcell with a working electrode of 1 mm² was designed and hyphenated with optical microscope to allow in situ tracking of pit initiation and growth. Chronopotentiometry and chronoamperometry controlled pit initiation, while optical microscopy demonstrated dynamic release of corrosion products and measured oxide repassivation kinetics.Finally, the in situ technique was developed further to include a microtensiometer fatigue apparatus to study the synergy effect between corrosion and fatigue. Location of pit initiation was compared with and without plastic deformation. Videos of pit initiation and growth will be presented.

Minimize Surface Change for Corrosion Study Using a Chronopotentiometric Approach Method in SECCM

In the realm of single-channel scanning electrochemical cell microscopy (SECCM), two primary methods are utilized for approaching the micropipette onto the substrate surface, specifically the chronoamperometric and chronopotentiometric methods. The chronoamperometric method is typically employed in corrosion studies utilizing SECCM, although it has been observed that negative approach potentials can influence subsequent microscale electrochemical measurements as a result of cathodic degradation of the metal oxide film. In this study, we investigated the practicality and stability of utilizing the chronopotentiometric approach method in SECCM-based corrosion research, and we found that the metal surface change during the approach process can be reduced by applying a 0 A approach signal, allowing for the acquisition of primitive electrochemical information of the surface.

Bond coat assisted enhancement in microstructural, mechanical and corrosion behavior of AZ91 magnesium alloy cold spray coated with aluminum alloys

Cold spray coating technique was used to deposit coatings of AA6061 aluminum alloy on AZ91 magnesium alloy substrates. A bond coat of commercially pure aluminum was used to facilitate deposition of the AA6061 powders. Two cold spray coating iterations were conducted to optimize the coating’s microstructural features such as porosity, surface roughness, and interface microstructure. Mechanical properties such as hardness, wear resistance, and adhesion behavior were characterized and used as metrics to compare the coatings with the substrate. The corrosion behavior of the coated and uncoated samples was characterized using multiscale and multimodal corrosion measurements comprising macroscopic potentiodynamic polarization and scanning electrochemical cell microscopy. The coated substrates exhibited a significant improvement in mechanical and corrosion performance as compared to the uncoated substrate.