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A novel self-healing coating with photothermal and pH dual-responsive properties has been designed to protect carbon steel against corrosion by loading the stimuli-responsive microcapsules into a shape memory epoxy coating. The sandwich-like microcapsules were based on reduced graphene oxide/mesoporous silica (rGO@MS) assembled with a pH-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) layer, and were loaded with benzotriazole (BTA) inhibitors (abbreviated as rGO@MS-P-BTA). Under near-infrared (NIR) light irradiation, the prominent photothermal effect of rGO could not only elevate the coating temperature to activate the shape memory effect and close the coating scratch, but also facilitate the release of corrosion inhibitors to suppress the corrosion activity. Moreover, the PDMAEMA as a pH-driven “gatekeeper” realized the controlled release of BTA from microcapsules at acid conditions. The surface morphology analysis, electrochemical impedance spectroscopy (EIS), and scanning electrochemical microscopy (SECM) were performed to evaluate the self-healing performance of the composite coatings. The results showed that the combination of NIR light and pH-responsive self-healing effects endowed the coating with short healing time and prominent healing efficiency.

In this study, a new self-healing strategy that can simultaneously recover the corrosion resistance and the adhesion strength of coatings was introduced. The coating was based on a shape memory epoxy resin containing ethylene vinyl acetate (EVA) microspheres loaded with Ce(NO3)3 inhibitors, and was cured at a relatively high temperature to facilitate the fusion of adjacent microspheres for a strengthened self-healing effect. The electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) results demonstrated that the shape memory effect of epoxy matrix, the filling of molten EVA microspheres as well as the release of Ce(NO3)3 inhibitors contributed synergistically to suppress the corrosion reaction at the coating damage. After healing, the low frequency impedance modulus of the coatings containing Ce(NO3)3-EVA microspheres was three orders of magnitude higher than that of the blank epoxy coating. The adhesion strength of the coatings containing Ce(NO3)3-EVA microspheres on the metal substrate was also largely repaired thanks to the strong bonding effect of the EVA microspheres.

Development of reaction-tailored electrocatalysts is becoming increasingly important as energy and environment are among key issues governing our sustainable future. Electrocatalysts are inherently optimized for application towards reactions of interest in renewable energy, such as those involved in water splitting and artificial photosynthesis, owing to its energy efficiency, simple fabrication, and ease of operation. In this view, it is important to secure logical design principles for the synthesis of electrocatalysts for various reactions of interest, and also understand their catalytic mechanisms in the respective reactions for improvements in further iterations. In this review, we introduce several key methods of scanning electrochemical microscopy (SECM) in its applications towards electrocatalysis. A brief history and a handful of seminal works in the SECM field is introduced in advancing the synthetic designs of electrocatalysts and elucidation of the operating mechanism. New developments in nano-sizing of the electrodes in attempts for improved spatial resolution of SECM is also introduced, and the application of nanoelectrodes towards the investigation of formerly inaccessible single catalytic entities is shared.

High-entropy alloys (HEAs), as a special heterostructure, possesses many exclusive advantages, including the inherited merits from each component and the synergistic regulation of electronic properties, which has a great potential for catalyzing complicated redox conversions. Herein, we reveal that the synthesized nano-HEA plays a unique role in the multi-electron and multiphase conversions of lithium polysulfides (LiPSs) in lithium-sulfur batteries (Li-S). Owing to the strong affinity with LiPSs, nano-HEA enriches the activity of LiPSs around the electrode more than 17 times higher than that of the control sample (without nano-HEA addition), significantly reducing the concentration polarization. In addition, the activation polarization was greatly suppressed by the nano-HEA catalyst, which is demonstrated by the lower Tafel slope, higher exchange current density, and the larger current response from the scanning electrochemical microscopy (SECM). Besides, the smooth and continuous redistribution of surface charge is further revealed by DFT calculation, benefiting the multi-electron reactions of LiPSs. As a result, Li-S batteries assembled with nano-HEA modified separators delivered outstanding capacity retention rates of 83.3% (2 C after 500 cycles in coin cell) and 82% (0.1 C 150 cycles in pouch cell), respectively.

The behaviors and kinetics of hydrogen evolution reaction (HER) on pure aluminum with passive film in the presence and absence of chloride ion are quantitatively investigated by using the tip generation/substrate collection mode of scanning electrochemical microscopy (SECM) with dual Al/Pt ultramicroelectrode (UME) as tip electrode and Pt UME as substrate electrode. The standard rate constants k0 and transfer coefficients αH of HER in ClO4−- and Cl−-containing solution are 6.9 × 10−7 cm/s and 0.22, 7.1 × 10−6 cm/s and 0.19, respectively. Results show that the kinetic of HER is slow and the destruction of Cl− on passive film can significantly promote the HER on Al surface. Moreover, these αH far less than commonly used 0.5 in corrosion research, can explain the great difference between theoretical Tafel slopes and experimental results. Besides, the existence of current plateau in Al electrode explains the large difference in corrosion potential during parallel testing.

The influence of heat treatment on the corrosion behavior of rolled Mg5Gd alloys in 3.5 wt.% NaCl solution saturated with Mg(OH)2 was characterized by immersion test, electrochemical test, scanning electrochemical microscopy (SECM) and corrosion morphology analysis in order to improve the corrosion resistance of Mg alloys. The results showed that solution treatment reduced the corrosion rate of the Mg5Gd significantly, resulting in relatively uniform corrosion and shallow corrosion cavities due to the dissolution of Cd-containing particles. The following aging process could further decrease the corrosion rate. Precipitation of nano-sized Cd-containing particles did not cause apparent micro-galvanic corrosion, which could be attributed to the formation of a protective corrosion product film fully covering the particles.

Metabolic analysis in animals is usually either evaluated as whole-body measurements or in isolated tissue samples. To reveal tissue specificities in vivo, this study uses scanning electrochemical microscopy (SECM) to provide localized oxygen consumption rates (OCRs) in different regions of single adult Caenorhabditis elegans individuals. This is achieved by measuring the oxygen reduction current at the SECM tip electrode and using a finite element method model of the experiment that defines oxygen concentration and flux at the surface of the organism. SECM mapping measurements uncover a marked heterogeneity of OCR along the worm, with high respiration rates at the reproductive system region. To enable sensitive and quantitative measurements, a self-referencing approach is adopted, whereby the oxygen reduction current at the SECM tip is measured at a selected point on the worm and in bulk solution (calibration). Using genetic and pharmacological approaches, our SECM measurements indicate that viable eggs in the reproductive system are the main contributors in the total oxygen consumption of adult Caenorhabditis elegans. The finding that large regional differences in OCR exist within the animal provides a new understanding of oxygen consumption and metabolic measurements, paving the way for tissue-specific metabolic analyses and toxicity evaluation within single organisms., Graphical abstract Image 1, Highlights • In vivo, tissue-specific, oxygen consumption rate over a single worm is measured using scanning electrochemical microscopy. • Respiration along the body of a Caenorhabditis elegans is found to be heterogenous. • The worm reproductive system respiration is 3-fold that of the head, alluding to the high energetic cost of reproduction. • Embryonating eggs are the biggest contributors to the reproductive system high respiration rate. • Smart SECM measurement protocols in tandem with numerical simulations enabled high-throughput quantitative analyzes.

Hypothesis: The anodic dissolution of chalcopyrite (CuFeS2) encounters the problem of surface passivation, which significantly affects the copper extraction efficiency. So far, there is no agreement on the passivation mechanism and composition of passive layer, which could be studied by using in-situ scanning electrochemical microscopy (SECM). Experiments: SECM was applied for the in-situ probing of chalcopyrite dissolution under mild oxidation potentials. The surface hydrophobicity and nanoscale distribution of hydrophobic domains were analyzed by static water contact angle measurement and atomic force microscope (AFM) force mapping, respectively. The surface conductivity was characterized by SECM feedback mode. Findings: The concentrations of released species Fe2+, Cu2+ and soluble copper sulfide species (CuxS) generally increased with the potential of chalcopyrite. In the active region (low potentials), Fe2+ was preferentially released, and the metal-deficient sulfide layer that was rich in copper relative to iron started to form as the passive layer. While the release of Fe2+ and Cu2+ was impeded in the passive region, the detected CuxS became pronounced in this region and the following transpassive region, which suggested that the existence of CuxS was a result of passive layer dissolution. The nanoscale distribution of hydrophobic domains suggested that the formation of hydrophobic passive layer initiated in the active region and this layer almost completely covered the chalcopyrite surface at the beginning of passive region. The surface conductivity of chalcopyrite decreased with potential due to the formation of less conductive metal-deficient sulfide layer and possibly insulating elemental sulfur (in the transpassive region). This work provides a new approach for the in-situ probing of chalcopyrite dissolution and useful insights into its dissolution kinetics and passivation mechanisms, with implications for similar electrochemical processes of other mineral surfaces.

For the analysis of corrosion and hydrogen production inhibition, we have synthesized Guar gum and methylmethacrylate (GG-MMA) composite. The synthesized composite was used as an eco-friendly corrosion inhibitor for P110 steel in 3.5% NaCl solution saturated with carbon dioxide at 50 °C. The primary corrosion techniques like weight loss, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) was used to analyze the corrosion inhibition process. EIS study reveals the kinetically controlled corrosion inhibition process. The results of PDP proposed that GG-MMA composite is the cathodic type of inhibitor. The corrosion inhibition performance of GG-MMA alone is 90% at 400 mg/L, and that of formulation with KI (5 mM) + GG-MMA (300 mg/L) is 96.8%. The adsorption of GG-MMA over P110 steel is spontaneous and mixed type i.e., both physical and chemical. The conformation of GG-MMA molecule adsorption was done using a scanning electron microscope (SEM), Contact angle measurement, Atomic force microscopy (AFM), Scanning Electrochemical Microscopy (SECM) and X-ray photoelectron spectroscopy studies.

Scanning electrochemical microscopy is a family of techniques that probes the local electrochemical surface environments with micrometer- and nanometer-scale space resolution and sub-picoampere chemical sensitivity. A recent growing trend uses these probes to investigate surface systems related to lithium-ion batteries, yielding a prodigious amount of new information. In this review, we give an overview of the recent progress on the scanning electrochemical microscopy and related techniques’ breakthroughs on lithium-ion battery electrodes research.

Single-cell analysis is important for understanding fundamental biological processes and mechanisms. Scanning electrochemical microscopy and scanning ion conductance microscopy as two kinds of scanning probe microscopy, with high temporal and spatial resolutions as well as in situ and noninvasive characterization capabilities, emerge as strong tools for single-cell analysis. In this review, we introduce the latest advances of scanning electrochemical microscopy and scanning ion conductance microscopy for single-cell analysis, including characterizations of cell morphology dynamics, membrane properties and mechanics, and monitoring cell surface charge, extracellular pH, and intracellular substances.

Single-atom catalysis has emerged as a cutting-edge field in heterogeneous catalysis. Considerable efforts have been devoted to developing versatile methodologies for synthesizing single-atom catalysts, however, the main thrust in this field is to fundamentally understand the intricacies of a catalyst and their performance on a specific reaction by complimenting different techniques. Here we demonstrate a supramolecular hydrogel strategy to effectively isolate copper atoms on interconnected carbon fibers as efficient electrocatalysts for the alkaline oxygen reduction reaction (ORR). The Cu–N2 coordination state and the atomic dispersion were confirmed by X-ray absorption spectroscopy and aberration-corrected scanning transmission electron microscopy. Additionally, the atom utilization (ηatom), which is the ratio between Cu(I) sites participating in the catalysis and the total Cu(I) sites available, has been investigated via surface-interrogation scanning electrochemical microscopy (SI-SECM) technique. The over 90% atom utilization of the synthesized Cu SACs is very close to the theoretical value (100%) for SACs, implying the proposed supramolecular approach can enable the ultrahigh exposure of Cu sites. The in situ time-resolved titration of SI-SECM and first-principal calculations further support the remarkable ORR activity on isolated Cu–N2 sites.

Scanning electrochemical microscopy (SECM) and scanning vibrating electrode technique (SVET) were used to investigate the electrochemical behaviour of the top surface of the 2098-T351 alloy welded by friction stir welding (FSW). The SVET technique was efficient in identifying the cathodic and anodic weld regions. The welding joint (WJ), which comprises the thermomechanically affected zone (TMAZ) and the stir zone (SZ), was cathodic relative to the heated affected zone (HAZ) and the base metal (BM). The reactivities of the welding joint at the advancing side (AS) and the retreating side (RS) were analyzed and compared using SECM technique in the competition mode by monitoring the dissolved oxygen as a redox mediator in 0.005 mol L−1 NaCl solution. The RS was more electrochemically active than the AS, and these results were correlated with the microstructural features of the welded alloy.

3D-printing (also known as additive manufacturing) has recently emerged as an appealing technology to fight against the mainstream use of carbon-based fossil fuels by the large-scale, decentralized, and sustainable manufacturing of 3D-printed electrodes for energy conversion devices. Although promising strides have been made in this area, the tunability and implementation of cost-effective metal-based 3D-printed electrodes is a challenge. Herein, a straightforward method is reported to produce bimetallic 3D-printed electrodes with built-in noble metal catalysts via galvanic replacement. For this goal, a commercially available copper/polylactic acid composite filament has been exploited for the fabrication of Cu-based 3D-printed electrodes (3D-Cu) using fused filament fabrication (FFF) technology. The subsequent electroless deposition of an active noble metal catalyst (viz. Pd) onto the 3D-Cu surface has been carried out via galvanic exchange. A detailed electrochemical study run by scanning electrochemical microscopy (SECM) has revealed that the resulting bimetallic 3D-PdCu electrode exhibits enhanced capabilities by energy conversion related reactions -hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR)- when compared with the monometallic 3D-Cu counterpart. Thus, this simple functionalization approach provides a custom way for manufacturing functional metal-based 3D-printed electronics harboring noble metal catalysts to improve energy-converting applications on-demand and beyond.

A bifunctional N-glycoside namely N,N′-Diglycidyl-1,6-hexanediamine (DHA) was synthesized by the facile reaction of 1,6-hexamethylene diamine and glucose and its corrosion inhibition behavior was evaluated on copper in 3.5% NaCl solution for the first time. A detailed electrochemical study using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and scanning electrochemical microscopy (SECM) was carried out to understand the mechanism of corrosion inhibition shown in the present work. The DHA showed a corrosion inhibition efficiency of >95% at a concentration of 0.27 mmol L−1. The adsorption of DHA over copper surface followed the Langmuir isotherm. The surface and the electrochemical reactivity of the inhibitor-modified Cu samples in 3.5% NaCl solution was examined by the SECM technique, demonstrating the formation of a thin inhibitor film with exposure/immersion time in solution containing DHA molecules. The results of surface analysis using scanning electron microscopy (SEM) and ATR-IR spectroscopy supported the adsorption of inhibitor molecules over copper surface. The quantum chemical parameters and molecular electrostatic potential were evaluated using density functional theory, further supported the experimental findings.

We report the controllable fabrication of defective single-layer graphene and the investigations on kinetic rates (k0) of heterogeneous electron transfer (HET). Electron beam lithography (EBL) and Ar+ plasma treatment were employed to fabricate graphene patterns with different defect density. Raman spectroscopy, scanning electrochemical microscopy (SECM) and finite element simulations were performed to correlate the HET kinetic rate to the defect density (nD) and defect distance (LD) of single-layer graphene. The results showed that k0 is linearly increased with nD initially and then increased rapidly with nD, which would be attributed to the density dependent interactions between defects. The facilitated HET results from the increased electronic density of states near the Dirac point of graphene, and the enlarged overlap of electronic states between graphene and redox. Increasing the defect density larger than 7.73 × 1012 cm−2 (LD

Catalyst deactivation derived from slow conversion of Fe(III)/Fe(II) is the critical problem restricting catalytic efficiency of advanced oxidation. Herein, a novel multichannel healing strategy is proposed for fast healing structural damage by designing rationally smart platform (TiO2-CDs-FeOOH hollow sandwich hybrid). This ingenious system shows remarkable catalytic activity (0.77 min−1) and stability towards the removal of organic contaminants. Systematic studies confirm that the excellent catalytic activity is attributed to multiple electron transfer (MET) behavior at interface between photocatalytic substrate and FeOOH, leading to highly efficient interfacial charge separation and then fast recovery of Fe(II) on FeOOH surface during H2O2 activation process. Notably, multichannel healing procedure and MET kinetic information are unveiled by UV–vis/scanning electrochemical microscopy (SECM) through an in situ probe scanning technique. A higher ET rate constant keff (0.92 × 10-2 cm s-1) was revealed over TiO2-CDs-FeOOH, two times that of TiO2-FeOOH, further confirming that multi-channel electron transfer could achieve fast Fe(III)/Fe(II) conversion. This work offers a new insight to design highly efficient catalysts for the practical applications of sustainable environmental remediation and energy conversion.

A PEDOT-modified Pt microelectrode was used in SECM for DNA biosensing and combined with long self-assembled DNA concatemers to realize dual signal amplification. The approach curve could also be plotted for tip location using this modified microelectrode with no impact on the catalytic effect so that both signal amplification and tip locating were achieved in one single tip. The detection limit of this method reached 0.076 fM, providing an ultra-sensitive DNA biosensing platform. Furthermore, this strategy could be applied in scanning a DNA chip, showing great potential in high-throughput bioanalysis with high sensitivity.

Alternating hydrostatic pressure (AHP) is the main cause of the marine coating failure of deep-sea tools and equipment. Herein, we synthesized a novel nanostructure, namely, graphene oxide–mesoporous silicon dioxide layer–nanosphere structure loaded with tannic acid (GSLNTA), as a self-healing coating additive. The anti-corrosion and anti-AHP performance and the self-healing capability of GSLNTA coating were evaluated through electrochemical impedance spectroscopy, field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, and alternating current scanning electrochemical microscopy (AC-SECM). Results showed that the nanolayer structure of GSLNTA effectively inhibited corrosion mass transmission under simulated deep-sea AHP. The nanospheres of GSLNTA released inhibitors to form a ferric tannate film on the exposed metal surface under AHP. The nanolayer and nanosphere of GSLNTA self-healing coating exerted a synergistic effect on anti-corrosion and anti-AHP performance and blocked corrosion factor transmission and coating failure in deep-sea applications. AC-SECM revealed the advantages of local impedance complementation of different electrochemical parameters (|Z| and –phase) to monitor the self-healing of coatings with GSLNTA. This work also investigated the self-healing performance of alkyd varnish coating embedded with synthetic GSLNTA in protecting steel surfaces. Self-healing materials have an “active healing” capability to prolong the life of organic coatings after unwanted external damage in deep-sea environments.

The SiCp/Al composites was modified by electroless nickel plating, the corrosion behavior of Ni-coated SiCp/Al composites in 0.05 M NaCl solution was investigated by situ electrochemical techniques. The surface properties of the Ni-coated SiCp/Al composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectrometer (EDS). The results showed that: The Ni-P layer is the most uniform with a thickness of 15 μm after electroless nickel plating for 60 min; Soak in 0.05 M NaCl solution, Ni-coated SiCp/Al composites exhibits higher corrosion potential and impedance values than non-coated SiCp/Al composite, showed that a greater corrosion resistance of Ni-coated SiCp/Al composite, and the corrosion resistance of SiCp/Al composite is the best after 60 min nickel plating. The Scanning Electrochemical Microscopy (SECM) measurements showed that the formation of the corrosion-resistant passive film in the Ni-coated SiCp/Al composites are easier, and the main corrosion mechanism of composites is local corrosion. The nickel phosphorus compound is easily produced on the surface of Ni-coated SiCp/Al composites after polarizing 1 h, which inhibits the corrosion of the composite. Thus, the Ni-coated SiCp/Al composite has greater corrosion resistance in a chloride-containing environment than the SiCp/Al composite.

The topic of intermolecular interactions enhancing electron tunneling between protein residues on biofilm surface has been investigated by some theoretical studies. However, few of experimental studies could confirm this viewpoint. In this work, the Mercaptopropionic acid self-assembled monolayer (MPA SAM) with terminal carboxyl groups was constructed, as a simplified model for functionalized biomimic membrane. The electron tunneling rate constant of ferrocenylmethanol redox process on SAM was obtained from experimental results of scanning electrochemical microscopy. It is found that the electron tunneling across MPA SAM is faster than that of contrastive Methyl mercaptopropionate SAM. This result is attributed to the intermolecular interactions between the redox and MPA molecules. The conditions of lower pH and weaker ion pair effect all benefit the formation of the intermolecular interactions, resulting the enhancement of electron tunneling more obvious. Based on this, this kind of intermolecular interaction is inferred to be intermolecular hydrogen bond. Our work may have contributions to exploring electron tunneling between protein residues on biofilm surface.

The emergence of antibiotics in the environment, especially in drinking water, poses potential harm to human health. It’s urgent to develop effective methods to remove antibiotics in drinking water. In this work, a series of mesoporous MnxCo3−xO4 nanoparticles with high surface area were successfully synthesized and firstly used as effective stable electro-Fenton catalysts to degrade ciprofloxacin (CIP). The removal of CIP achieved to 100% within 5 h. Experimental and density functional theory (DFT) studies verified the existence of redox pairs of Mn2+/Mn3+ and Co2+/Co3+. Scanning electrochemical microscopy (SECM) results suggested that the redox reaction capacity of MnCo2O4 was enhanced and the electron transfer rate on the surface of this bimetallic oxide was 2.67 and 1.6 times the number of MnO2 and Co3O4, respectively. The effective degradation of CIP was mainly associated with the increased electron transfer rate and advanced redox reactivity owing to the synergistic effect of manganese and cobalt entrapped in the matrix of mesoporous structure which provided more accessible active sites. The degradation intermediates and possible process mechanism were investigated in detail. The reusability of MnCo2O4-CF cathode was evaluated five cycles with minimal ion leaching which the concentration of Mn and Co in the system was lower than 2.5 and 3.4 ppm, respectively. This work provides further understanding for removal process of organic pollutants by investigation of redox couple and electron transfer rate of the promising MnCo2O4-CF cathode.

The electrochemical reactivity of a defect in organic coating was investigated by electrochemical noise (EN) and scanning electrochemical microscopy (SECM). Time dependent EN spectra and SECM image on a metal with defective organic coating was measured, and corresponding EN frequency domain spectra and probe approach curves (PACs) were used to obtain electrochemical reactivity information within the coating defects. All time domain and frequency domain analyses, and SECM measurements were successful indicators of corrosion intensity within the defect. The amplitude of electrochemical current noise (ECN) and the low-frequency plateau of the power spectral density (PSD) WL increased significantly with corrosion intensity.

The development of bifunctional oxygen electrodes is a key factor for the envisaged application of rechargeable metal-air batteries. In this work, we present a simple procedure based on pyrolysis of polybenzoxazine/metal metalloid nanoparticles composites into efficient bifunctional oxygen reduction and oxygen evolution electrocatalysts. This procedure generates nitrogen-doped carbon with embedded metal metalloid nanoparticles exhibiting high activity towards both, oxygen reduction and oxygen evolution, in 0.1 M KOH with a roundtrip voltage of as low as 0.81 V. Koutecký-Levich analysis coupled with scanning electrochemical microscopy reveals that oxygen is preferentially reduced in a 4e− transfer pathway to hydroxide rather than to hydrogen peroxide. Furthermore, the polybenzoxazine derived carbon matrix allows for stable catalyst fixation on the electrode surface, resulting in unattenuated activity during continuous alternate polarisation between oxygen evolution at 10 mA cm−2 and oxygen reduction at −1.0 mA cm−2.

The conversion of photon energy to chemical energy and vice versa requires the close arrangement of absorber/emitters and (electro)chemical reactions sites. This review considers local measurement techniques aiding in the design of efficient oxide systems for the utilization of light as energy source and as efficient detection principle. Artificial photoelectrochemical systems are often build on oxides as they are abundant and have semiconducting properties. However, no single oxide fulfills all requirements for an efficient conversion of sunlight to chemical energy and thus complex oxides are explored. These oxides might be obtained by doping oxides with other metal cations or by combining different oxides for absorbance and catalyzing the desired reaction, mainly water splitting. Due to the enormous amount of possible combinations combinatorial search for new material systems has been pursued and accelerated around the world making use of local photoelectrochemical characterization techniques in the screening step. Local detection schemes based on scanning electrochemical microscopy and scanning electrochemical cell microscopy also provide details about the kinetics for heterogeneous charge transfer and the release of soluble reaction products. During the recent years the scanning probe methods have been complemented by local detection of fluorescent reaction products that are formed by heterogeneous electron transfer reactions from and non-fluorescent precursor molecules. Such detection is possible with single molecule sensitivity and spatial resolution exceeding the diffraction limit (superresolution). Such approaches enabled the discovery of population within ensembles of metal oxide nanoparticles that are distinguished by the location and reactivity of their reaction sites. Optical techniques for measuring Faradaic currents hold great promise for the measurement of very low currents beyond the study of photoelectrochemistry of metal oxides.

The electrochemical active surface area (EASA) of polycrystalline boron-doped diamond (BDD) electrodes is heterogeneous and can be affected by numerous factors. There is a strong need for proper consideration of BDD heterogeneity in order to improve this material's range of application in electrochemistry. Localized changes in surface termination due to the influence of oxidation agent result in increased surface resistance. The observed behavior of this characteristic feature varies among individual grains, depending on their crystallographic orientation. Still, there is not much information about this key factor in terms of its influence on the electrochemical response of BDD. In this study we compared two approaches towards BDD surface oxidation, namely: anodic polarization at potentiostatic and potentiodynamic conditions. The surface impedance measurements via Nanoscale Impedance Microscopy (NIM) allowed the confirmation of diversified propensity for the modification of surface termination in BDD. We showed that the NIM studies provide a deep understanding on the electrical characterization and variation of surface resistance in BDD electrodes. In order to evaluate the actual heterogeneity of electrochemical activity distribution, voltammetry, dynamic electrochemical impedance spectroscopy (DEIS) and scanning electrochemical microscopy (SECM) studies were performed. For each investigated electrode, departure from the Randles-Sevcik equation was observed, with its level depending on the surface heterogeneity and oxidation treatment, justifying the standardization of pre-treatment procedure and development of non-standard model for diffusion transport in proximity of BDD electrode.

In this research, we are reporting the application of microorganisms modified by a conducting polymer – polypyrrole (Ppy) – for the improvement of microbial biofuel cells. The synthesis of polypyrrole was assisted by metabolic and other biochemical processes that occur in microorganisms. Therefore, in this research the reported Ppy formation method can be recognized as environmentally friendly. During herein reported synthesis of Ppy, the cell walls and some other structures of Aspergillus niger and Rhizoctania sp selected for this research were modified by the formed Ppy, which facilitated the transfer of electrical charge generated by microorganisms towards an electrode. Two electrochemical methods: (i) amperometric measurements at constant potential and (ii) scanning electrochemical microscopy (SECM) were applied for the evaluation of charge transfer efficiency and for the determination of electrochemical activity of Ppy-modified and non-modified cells. Two mediators (1,10-phenanthroline-5,6-dione (PD) or 9,10-phenanthrenequinone (PQ) and potassium ferricyanide (K3[Fe(CN)6])) based redox system was applied for the assessment of charge transfer from above mentioned living cells. The amperometric signals registered for electrodes based on Ppy modified cells were over six times higher in comparison to that of electrodes based on non-modified cells. This effect is assigned to advanced electrical conductivity of Ppy-modified cell wall and/or to better permeability of charge transfer mediators through the membrane and/or cell wall of Ppy-modified cells. Fungi of Aspergillus niger, which showed few times higher electrochemical activity in comparison to Rhizoctania sp., were investigated by SECM. Electrochemical differences between Ppy-modified and non-modified cells have been confirmed by SECM results. Therefore, this eco-friendly Ppy-formation technique seems effective in improving the performance of electrochemical devices such as microbial fuel cells and/or cell-based biosensors.

Alternating current-intermittent contact-scanning electrochemical microscopy (AC-IC-SECM) technique is used for the first time for simultaneous mapping of local electrochemical activity and topography of as-polished, passivated and pickled 304L SS-Zr-4 dissimilar weld joint (explosive welded) surfaces in fresh water at open circuit potential (OCP) without redox mediator. The local surface activity showed good contrast and uniformity, even when the surfaces are in tilted condition and topographic resolution is in good agreement with contact and non-contact profilometry. The difference in current and impedance values on SS and Zr-4 surfaces were ∼100 nA and 200 kΩ, respectively. The images acquired on pickled 304L SS and Zr-4 surfaces after immersion in HNO3+HF exhibited a relatively higher current and lower impedance compared to as-polished and passivated surfaces. XPS analysis of Zr-4 pickled surface revealed the presence of ZrOF2, ZrO2 and Zr, while pickled 304L SS showed a higher metallic to oxide ratio, indicating less protective thinner passive films, resulting in a relatively higher electrochemical activity. Though 304L SS in passivated condition revealed Cr-oxide enrichment, the higher metallic concentration on 304L SS, resulted in similar electrochemical activity as in as-polished condition. The quantitative XPS analysis corroborated the local electrochemical activity results obtained from AC-SECM technique.

The influence of D-cysteine (D-cys) on the microbiologically influenced corrosion (MIC) of 304 stainless steel caused by Pseudomonas aeruginosa was investigated in this work. Immersion tests in the sterile and P. aeruginosa-inoculated culture media with different D-cys concentrations were carried out. The results showed that the addition of D-cys inhibited the formation of P. aeruginosa biofilms on stainless steel surfaces. D-cys itself did not affect the corrosion of stainless steel but could decrease the corrosion rate of MIC of stainless steel caused by P. aeruginosa. X-ray photoelectron spectroscopy (XPS) analysis and scanning electrochemical microscopy (SECM) analysis indicated that the biofilm inhibition effect of D-cys greatly reduced the destructive effect of the adhered P. aeruginosa cells on the passive film of the stainless steel, thus inhibiting the MIC of the stainless steel.

A new hybrid of favorable orientated cytochrome c (cyt c) and a 1-Pyreneacetic acid (PA) functionalized graphene (Gr) on Au electrode (AuE) was prepared. In the hybrid system, Gr was functionalized with (PA) molecule through π-π interaction (PA-Gr). Afterward the PA-Gr attached to the AuE via Thionalide self-assembled monolayer (SAM), then conjugated with cyt c. The AuE/SAM/PA-Gr/cyt c hybrid system was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) techniques. SECM approach curves were applied to measure the standard tunneling electron transfer (ET) and bimolecular rate constants which were 56.6 s-1 and 1×109cm3mol-1s-1, respectively.

Reactive oxygen species (ROS) have gained much attention as they are related to cellular homeostasis and functions. New insights into physiology of cancer cells are anticipated from the analysis of their ROS evolution at single cancer cells level. Herein, a novel scanning electrochemical microscopy (SECM) detection strategy with self-designed multi-potential step waveform (MPSW) has been developed for in situ monitoring ROS with no interference of dissolved oxygen (DO) at the single cells level. Using MPSW, the signals of three different electrochemical molecules – FcMeOH, DO and ROS could be obtained simultaneously in a single imaging process. Images of FcMeOH were used to determine cell morphology. ROS released by normal and cancer cells without the interference of DO were imaged and quantitatively determined using MPSW. ROS released by cancer cells under different pHs was further investigated, suggesting that an acid environment could stimulate the release of ROS. Thus, this work provides a new way for sensing ROS released by cells without interference, and can be applied in the cancer research based on ROS releasing.

Cu corrosion is a major issue affecting the structural integrity and efficient performance of Cu components in several applications. In recent years, the utilization of metal oxide thin films on copper components is fascinated cumulative consideration particularly in the field of energy and electronic related materials like micro-electromechanical, energy storage and memory device components. Herein, we report the use of a rapid and reproducible approach of aerosol-assisted (AA) CVD for depositing bimetallic nickel-vanadium oxide (NiVOx) thin films directly on Cu substrates. NiVOx coatings were produced by increasing the deposition period from 1 to 3 h at a fixed temperature of 480 °C and were structurally characterized through XRD analysis, XPS, SEM/EDS, and AFM. Detailed characterization was performed for the as-prepared amorphous NiVOx binary films having a compact and dense microstructure at an elemental stoichiometry of Ni/V in 1:1 ratio. Corrosion analyses, including electrochemical frequency modulation, Tafel plot analysis, and dynamic electrochemical impedance spectroscopy, were performed to assess the corrosion resistance performance of binary films on Cu substrates in saline medium. Moreover, scanning electrochemical microscopy was accomplished to estimate the electrochemical stability of the as-processed binary films during the 24-h immersion period in NaCl.

In this article, we report that electrochemically generated quaternary ammonium polybromide (QBr2n+1) droplets can act not only as electrochemical reactors for the electro-oxidation of Br−, but also as tiny reductants for Br2 dissolved in an aqueous phase. We suggest two different theoretic models: Cloud and Droplet. In the Cloud model, we consider a cloud composed of small droplets located in the vicinity of a Pt ultramicroelectrode (UME). The positive feedback loop of the redox reaction is derived in the gap between the Cloud and the Pt UME, which leads to catalytic current enhancement, like the positive feedback mode of scanning electrochemical microscopy (SECM). In the Droplet model, a droplet adsorbed on the center of a Pt UME drives the catalytic feedback loop of the redox reaction. Next, we adopted the two theoretical models to explain the current amplification by QBr2n+1 observed in our experimental systems. In the early potential region for electro-oxidation of Br−, we found the QBr2n+1 droplets-Cloud model was a more reliable scenario for the catalytic current amplification. As the potential became more positively biased, stochastic collisions of QBr2n+1 droplets occurred on the Pt UME, and in this stage, we determined that the QBr2n+1-Droplet model was the main catalytic mechanism for Br− electro-oxidation in the presence of QBr in the solution.

Today the common view of the Neosepta membranes is that their material is electrically homogeneous, i.e. it does not include heterogeneities (except reinforcing fabric). However, there are a few publications, according to which their surface is not homogeneous geometrically and this fact has an important impact on the mass transfer rate. In this paper, we thoroughly study geometric heterogeneity of four commercial homogeneous Neosepta cation-exchange (CMX and CMX-Sb) and anion-exchange (AMX and AMX-Sb) membranes by applying optical microscopy, scanning electron microscopy, scanning electrochemical microscopy (SECM) and digital micrometer. It is found that the surface of all membranes is undulated: there are repeating hills and valleys due to the waved reinforcing fabric. The amplitude of undulation increases when swelling: in the case of dry samples, it varies from 10 (AMX-Sb) to 30 (CMX-Sb) microns, while for swollen samples, from 20 (AMX-Sb) to 55 (CMX) microns. These values are comparable to the diffusion layer thickness in industrial electrodialyzers, hence might make an essential impact in enhancement of mass transfer. The period of undulation is several hundreds of microns. Despite common use of micrometer, it gives overestimated membrane thickness since its measuring faces are applied only to the tops of the hills.

Spontaneously forming oxide film protects titanium containing medical implants against corrosion and it also mitigates the release of poisonous ionic species into the surrounding life tissues. The self-healing kinetics of the film that lost integrity upon some impact is an important feature. In this short paper, the recent results obtained investigating the formation of the oxide film using potentiometric SECM and electrochemical impedance spectroscopy is presented. Ti G4 dental root implant was used as sample surface immersed in PBS medium. SECM in potentiometric mode, using antimony microprobe was applied to monitor the pH change in different times over freshly polished G4 titanium by recording a series of consecutive line scans, to find out the mechanism of TiO2 formation. Impedance spectroscopic experiments were carried out to investigate how the corrosion resistance of freshly polished titanium G4 surface changes by the exposition time. Keywords: Ti G4 dental implant, SECM, Self-healing TiO2 formation, Antimony microelectrode, Kinetics of TiO2 formation

In this work the complementary characterization of pretreatment techniques for adhesive bonding of carbon fiber reinforced plastics (CFRP) is presented. Industrial CFRP plates were pretreated with laser, plasma, and corundum blasting abrasive techniques followed by chemical activation. The combined use of atomic force microscopy and chemical force microscopy enabled the characterization of the surface morphology and the specific adhesion force between a chemically functionalized cantilever and the pretreated surfaces simulating the adhesive bond. Complementary measurements with scanning electrochemical microscopy and X-ray photoelectron spectroscopy supported the experimental findings and delivered additional information about the chemical structure of the surfaces. A comparison of experimental data of mechanical tensile shear strength measurements and the applied analytical methods revealed a valid correlation of microscopic and macroscopic techniques.

This investigation aimed to study the influence of time of sandblasting, as a surface mechanical attrition treatment method, on the corrosion behavior of carbon steel in different solutions with different pHs. Optical microscopy, micro-hardness test, as well as Scanning Electrochemical Microscopy, were used to examine the affected area underneath the surface of the sandblasted specimens. The results of the electrochemical experiments showed significant improvement in corrosion resistance of the sandblasted specimens in the high alkaline solution. In neutral and acidic solutions, specimens sandblasted for 5 min showed superior corrosion resistance compared to the as-received and other specimens, sandblasted for longer period of time.

A protective passive layer is formed on the surface of embedded reinforcing carbon steel bar in the alkaline environment of concrete. Corrosion of steel in concrete environment is a function of formation, strengthen and stability of this layer. In this study, Scanning Electrochemical Microscopy (SECM) was exploited to study the kinetic and the formation of the passive layer in a simulated concrete pore solution. The specimen was cut, epoxy mounted and polished from a carbon steel reinforcing bar. Then, it was immersed in a concrete simulated pore solution containing 0.5 mM potassium ferrocyanide as a mediator for 48 h and amperometry SECM approach curves were recorded over the unbiased surface of the freshly polished surface. A platinum microelectrode tip with the diameter of 25 µm was used in the experiment. The effective heterogeneous electron rate coefficient (keff) variation for the mediator regenerating surface reaction was estimated during the time of exposure. Decreasing values of keff, throughout passivation period, indicates formation and increase in the strength of the passive layer formed on the surface of the steel in the alkaline environment in concrete pore solution.

Zeolitic imidazole framework (ZIF) is an emerging class of functional materials with promising nanostructures and applications in biomedicine and materials science. Herein we present a dynamic protective coating system with self-healing anticorrosion function, based on pH-responsive ZIF nanoparticles. Due to the advantage of high content of corrosion inhibitor in the ZIF-7 nanoparticles and its nature of pH-sensitivity, the ZIF-7 nanoparticles could quickly respond to the surrounding acid environment and release the linker as healing agent, led to a new barrier on scratched metal surfaces. The embedding and homogeneous distribution of the ZIF-7 nanoparticles in polymer coating system improved the corrosion resistance of carbon steel in 0.1 M hydrochloric acid solution in comparison to the control samples, as determined by electrochemical impedance spectroscopy (EIS). The self-healing anticorrosion property of dynamic polymer system was characterized during a simulated corrosion process by scanning electrochemical microscopy (SECM). The concentration of the embedded ZIF-7 nanoparticles was varied (0.5 − 7 wt %) to ascertain the optimum conditions for anticorrosion performance. The important effect of particle size and shape of ZIF-7 nanoparticles is discussed as well. The ZIF-7 based on dynamic protective polymer systems can interact with and adapt to the surrounding acid environment, leading to a new healed barrier on metal surfaces with anticorrosion functions.

This investigation analyses the use of the scanning electrochemical microscopy (SECM) to study the open porosity of PVD-coatings through electrochemical ion detection. CrN und TiN PVD coatings with artificially created permeable areas as well as without any mechanical damage were investigated. Furthermore, the thickness of the interlayers was also modified to increase the diffusion layer thickness. As a result, coatings with different protective effect were obtained and used for comparison purposes. The ion detection was done by means of a microelectrode located over the sample surface. It was used to oxidize ferrous Fe2+ ions coming from the substrate to ferric Fe3+ ions. The measurement of higher currents indicates higher anodic dissolution and consequently higher open porosity of the coating. The validity of the SECM measurements was supported by topographical analysis and optical evaluation of the samples after the measurements.

Summary Heated electrodes have been introduced a few decades ago to perform thermoelectrochemical investigations in a very flexible manner. This review considers unusual materials and devices that have been introduced recently to create new heated and also actively cooled electrodes: carbon paste with ionic liquids as binder, carbon nanotubes, iridium, Hg films, Bi films, Bi–Au alloys, gold nanostructures, and indium-doped tin oxide. Scanning electrochemical microscopy (SECM) based on thermocouple tips, as well as SECM of heated electrode arrays, and hot-tip-SECM have been proposed to study surfaces. Thermo-responsive layers allow for rapid switching of heated electrode surfaces. Recent years have seen a broad variety of thermoelectrochemical studies enabled by actively heated and cooled electrodes based on new materials. Very quick temperature changes and very high energy efficiency are two very distinct advantages of directly heated electrodes over both isothermal electrochemical cells and indirectly heated electrodes that suffer from high heat capacity.

The porphyrin aggregate is recognized as an attractive candidate for developing artificial light-harvesting systems. Using 5, 10, 15, 20-tetrakis-(4-carboxyphenyl) porphyrin (TCPP), the porphyrin aggregates with different morphologies (sphere, rod and flake) are controllably prepared by the surfactant-assisted self-assembly reaction, and then synthesize the ternary bionic-system (e.g. porphyrin composites). These composites are characterized by scanning-electron microscopy (SEM), atomic force microscope (AFM) and spectroscopic technology. The combinatorial technique consisted of ultraviolet–visible spectroscopy and scanning electrochemical microscopy (UV–vis/SECM) is used to record SECM approach curves of porphyrin photocatalysis under visible light illumination at the specific zones, where morphology-dependent porphyrin composite is recognized to be distributed evenly on ITO surface. Heterogeneous photoelectron transfer rates (keff) are given by simulating SECM approach curves. It is suggested that rod-like porphyrin aggregate composite has highest photocatalytic efficiency with the kinetics rate to be 8.624 × 10−2 cm s−1, the largest keff of which is obtained at the excitation wavelength of 469 nm. These findings are also proved by photocatalytic decomposition test of pollutants (methyl orange). It is indicated that one-dimensional nanostructure is advantageous for separation of electrons and holes and directional transmission of photoelectron.

Hydrodynamic scanning electrochemical microscopy (SECM) was applied for the characterization of Pt and boron-doped diamond (BDD) macroelectrodes operated in a potential region producing reactive oxygen species (ROS) during oxygen evolution reaction (OER). Forced convection introduced by high-precision stirring enabled the formation of a stable diffusion layer of electrochemically produced species and tip-substrate voltammetry was used for the detection of different ROS species produced during OER at BDD. Hydrodynamic SECM imaging in substrate generation/tip collection mode revealed local differences in the production of the ROS species across the BDD electrode surface.

Anodic dissolution and cathodic hydrogen evolution behavior of pure Fe in 5 mM HClO4 solution was investigated via a modified tip generation/substrate collection mode using scanning electrochemical microscopy. The modified TG/SC mode of SECM could instantaneously divide the apparent current of Fe corrosion process into Fe oxidation and proton reduction process, and standard rate constants and transfer coefficients of hydrogen evolution and Fe oxidation are 9.2 × 10−6 cm/s and 0.27, 2.5 × 10−6 cm/s and 0.7, respectively, based on COMSOL simulation and Tafel linear fitting. Comparing with traditional polarization curve and electrochemical noise, the more accuracy corrosion current can be obtained in time.

Oxygen reduction reaction (ORR) is of great interest in various areas, including energy conversion. This paper presents the simple synthesis and characterization of one-dimensional silver halides nanowires (AgClNW and AgBrNW) as an electrocatalyst for ORR in alkaline media, as well as an investigation of the ORR pathway at AgCl. AgClNW and AgBrNW were prepared via a galvanic replacement reaction (GRR) between silver nanowires (AgNW) and a halide precursor. AgClNW exhibited excellent ORR catalytic activity that was comparable to or better than that for commercial Pt (20 wt% Pt loading on Vulcan carbon), demonstrating potential to replace Pt-based catalysts. A scanning electrochemical microscopy (SECM) analysis supports the existence of an associative ORR pathway at AgCl, and first-principles density functional theory (DFT) calculations suggest that the high ORR activity of AgCl is possibly attributed to the up-shifted Ag d-band center energy in AgCl as well as the assistance of adsorbed water molecules.

The evolution of the corrosion process on Cu-Ni-Zn alloy in alkaline chloride solution was investigated by in-situ scanning electrochemical microscopy, X-ray photoelectron spectroscopy, and ex-situ laser confocal microscopy, and the effects of ambient temperature and polarization time were also discussed. The results demonstrated a higher pitting nucleation rate and lower pit growth rate at low temperature. The ratio of pit depth to mouth diameter decreased with increasing pit volume and temperature, indicating that pits preferentially propagate in the horizontal direction rather than the vertical direction owing to the presence of corrosion products and deposited copper. The surface current was uniform and stabilized at approximately 2.2 nA during the passive stage, whereas the current increased after the pits were formed with the maximum approaching 3 nA. Increasing the temperature led to an increase in porous corrosion products (CuO, Zn(OH)2, and Ni(OH)2) and significantly increased the rate of transition from pitting to uniform corrosion. Dezincification corrosion was detected by energy dispersive spectrometry, and a mechanism for pitting transition into uniform corrosion induced by dezincification at the grain boundaries is proposed.

Major difficulties in nanoscale scanning electrochemical microscopy (SECM), resulting from the short tip-to-sample distance, are tilt misalignment and vertical thermal drift. This renders constant height mode nanoscale electrochemical imaging experimentally problematic. Nanoscale SECM also requires application of reliable nanoprobes. Although SECM nanotips are commercially available, they are rather disposable, fragile and their shelf-life is limited. Many SECM laboratories employ self-prepared nanoprobes, fabricated using advanced apparatus. In this paper, we employ a hopping mode approach to nanoscale electrochemical imaging, which resolves the mentioned common difficulties. The applied platinum nanoelectrodes, insulated with borosilicate glass, were prepared using affordable equipment and materials. They were applied for nanoscale mapping of redox mediator regeneration at a model interdigitated microsensor, composed of Pt microband electrodes, in a solution of ferrocene in viscous hydrophobic room temperature ionic liquid (RTIL) – 1-butyl-3-methylimidazoliumbis(trifluoro-methylsulfonyl)imide (C4mim N(Tf)2). The presented nanosensors were also characterized with cyclic voltammetry in aqueous electrolyte containing hexamineruthenium (III) chloride as redox mediator.

The effect of Ti interlayers on the corrosion resistance of TiN PVD coatings is investigated. The coatings were deposited using direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HIPIMS). Ti interlayers with different thicknesses but same composition and deposition parameters were studied. The barrier effect was investigated using potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) together with a chemical porosity test. Remarkable improvement of the corrosion resistance with increased thickness of the Ti interlayers was found. The results showed a good agreement between potentiodynamic polarization tests, EIS, SECM and the microscopic inspection.

Potentiometric Scanning Electrochemical Microscopy (SECM) allows the pH distribution at electrode/electrolyte interfaces to be mapped at the micrometer and submicrometer scale using ion-selective ultramicroelectrodes (UMEs) as scanning probes. However, this technique lacks precise control of the tip-to-substrate distance. Herein we propose a novel dual Pt-Pt/IrOx UME for local in situ pH visualization of 316L stainless steel (316L-SS) corrosion processes with precise tip–substrate distance control using both amperometric and potentiometric SECM modes. Simulations based on COMSOL and experimental approach curves obtained with this dual UME configuration are used to precisely establish the tip–substrate distance. Higher pH values were observed for smaller tip–substrate separations when this probe configuration is used with bulk electrolyte of the same pH. Furthermore, during the corrosion process local anodic and cathodic zones were observed to form, disappear and regenerate at a vertical tip–substrate distance of 12 μm as a result of the localized corrosion and repassivation of 316L-SS. Keywords: Dual UME, pH distribution, Combined mode, SECM, Stainless steel

TiO 2 nanotube membranes (TNM) were synthesized, separated (by electrochemical anodization) and modified with Pt-Ru electrocatalyst to assess their photoelectrocatalytic activity towards methanol (MeOH) oxidation. The feasibility of use of these composite materials was evaluated in different supports to observe the development of the electrochemical responses as a function of the nature of the electrical collecting substrate. The results suggested that, while the Pt-Ru decorated TMN present photoelectrocatalytic activity, the electrical contact in the back might be the limiting step in current collection. Such findings were demonstrated by performing scanning electrochemical microscopy SECM over the surface of the TNMs, where methanol was oxidized in the microelectrode tip of the SECM. This approach corroborated the suitability of TNMs to be modified with an electrocatalyst and its application in current technology such as microfluidic fuel cells.