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. 2023 Mar 6;1(3):205–219. doi: 10.1021/cbmi.2c00008

Imaging Analysis of Scanning Electrochemical Microscopy in Energy Catalysis

Xinfang Zhang †,‡, Ce Han †,*, Weilin Xu †,‡,*
PMCID: PMC11504021  PMID: 39473695

Abstract

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Scanning electrochemical microscopy (SECM) is a scanning probe technology based on Faraday current changes when an ultramicroelectrode is moved across a sample surface, which can directly reflect the surface topography and electrochemical information on the sample through imaging. This Review briefly introduces the basic SECM, including its developmental history and working mode. The application of SECM imaging in energy catalysis is mainly introduced, and the development trend of SECM is described briefly.

Keywords: scanning electrochemical microscopy, oxygen evolution reaction, oxygen reduction reaction, hydrogen evolution reaction, hydrogen oxidation reaction, operating mode, screening, kinetics, imaging

Introduction

Reactions involving hydrogen and oxygen including oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and hydrogen oxidation reaction (HOR) are important electrochemical reactions in hydrolytic systems1,2 and many new green energy conversion storage systems, such as fuel cells3−5 and metal–air batteries (lithium–air batteries,6−8 aluminum–air batteries,9,10 zinc–air batteries,7,11,12 etc.). Due to the increasingly serious energy consumption and environmental pollution, the design of efficient and cheap electrocatalysts for different electrocatalytic reactions is becoming more and more important, which is an important part of sustainable development in the future. Electrocatalysts have inherent advantages for applications in important reactions in the field of renewable energy, such as water electrolysis13,14 and artificial photosynthesis,15 due to their high energy efficiency, simple fabrication, and ease of operation. Many test methods, such as cyclic voltammetry, linear scanning, or timed current, are used in conjunction with a rotating ring-disk electrode to measure the catalytic performance of the sample as a whole. It is very important to understand and explore the micro-electrochemical properties of catalytic materials from the microscopic point of view and to clarify the structure-activity relationship between them and the physical morphology of materials to further construct high-performance catalytic materials for oxygen reactive electrodes. Therefore, it is extremely important to explore the catalytic mechanism of electrocatalysts in their respective reactions for subsequent improvement. In this Review, we present the history of the scanning electrochemical microscopy (SECM) field and the application of SECM image analysis in the study of energy catalysis (OER, ORR, HER, HOR, and some other energy catalyzed reactions) to advance the synthetic design of electrocatalysts and elucidate their working mechanisms.

Basic Information on SECM

SECM is a kind of scanning probe microscopy technology, which uses an ultramicroelectrode (UME) probe to obtain the microtopography and chemical information on the surface of the substance by recording the Faraday current or some other electrochemical parameters on the sample surface in electrolyte solution around the electrode. In 1986, the first study of electrochemical diffusion layers using ultramicroelectrodes was carried out by Engstrom et al.,16 which laid the foundation of SECM. In the same year, Bard et al.17 reported a scanning electrochemical device for high-resolution detection of electrode surfaces in solution and proposed the concept of SECM for the first time in 1989.18 Most solid surface characterization methods, such as scanning electron microscopy (SEM) or various electron spectrometers, require samples to be placed in an ultra-high vacuum (UHV) environment and are not suitable for in situ electrochemical studies. Optical technology, such as fluorescence probe technology, can improve the resolution through super-resolution technology, such as stimulated emission depletion (STED), but there are also problems such as bleaching. SECM, which can characterize the morphology and electrochemical information on a solid surface with high resolution in a solution environment, fills this gap. SECM can not only directly analyze the local chemical activity on the sample surface and screen the active center but also be used to study the surface reaction intermediates and their kinetics. SECM is mainly composed of four electrodes (tip electrode, counter electrode, reference electrode, and substrate electrode), a controllable bipotentiostat, a computer, and a piezoelectric controller (Figure 1). The controllable bipotentiostat is used to accurately measure and control the potential and current of the substrate and tip. The piezoelectric controller is used to precisely move the probe in the x, y, and z axes. As an imaging technology, spatial resolution is very important to SECM. The imaging resolution of SECM mainly depends on the size of the tip electrode and tip–substrate distance.19 The smaller UME and more accurate bipotentiostat and piezoelectric controller make the resolution and detection limit of SECM continuously improve.20,21 In order to achieve nanoscale resolution, Bard’s group stabilized the nanoscale gap between the tip and the substrate, synchronized the movement of the SECM tip with the electrochemical response, and avoided the damage of the electrochemical tip during the SECM experiment by building an equivalent greenhouse, modifying the code, and modifying the bipotentiostat.22

Figure 1.

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Simple schematic diagram of SECM (RE: reference electrode; CE: counter electrode).

From the initial direct mode to the generation–collection mode, the recent surface interrogation mode, and redox competition mode, SECM is constantly developing. Here, we mainly introduce the direct mode, feedback mode, generation–collection mode, surface interrogation mode, and redox competition mode.

Direct Mode

The direct mode is often used for surface modification of samples, such as local etching,23 electrodeposition,24 and modification25 of sample surfaces. In this working mode (Figure 2A), the sample is usually used as the working electrode, and the tip is used as the counter electrode. The metal salt in solution can be electrodeposited on the local surface of the sample very close to the scanning tip head under a certain voltage. Or the metal sample oxidizes under certain voltage conditions, and the local area close to the probe is modified and etched. Grisotto et al. used 4-nitrobenzenediazonium tetrafluoroborate (DNB) as an initiator for the polymerization of acrylic acid on the surface of the substrate and obtained very interesting patterns (Figure 2B).26

Figure 2.

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(A) Diagram of SECM operating in direct mode. (i) Electrodeposited metals onto the substrate. (ii) The metal substrate is etched. (B) (i) Diagram of different electrochemical and chemical reactions occurring at the tip–substrate. (ii) “Madeleine” by Henri Matisse (illustration) printed on gold backing by SECM. Adapted from ref (26). Copyright 2011 American Chemical Society.

Generation–Collection (G-C) Mode

The generation–collection modes include substrate generation–tip collection (SG-TC) and tip generation–substrate collection (TG-SC) modes (Figure 3A). The G-C mode operates under a four-electrode system with both the SECM tip and the substrate as working electrodes. If the reactants react at the tip of the needle to generate new species and then the new species diffuse to the substrate and are collected by the substrate, it is called tip generation–substrate collection. Otherwise, it is substrate generation–tip collection.27 TG-SC mode has a smaller background current and is suitable for studying reaction kinetics,28−30 while SG-TC mode is more suitable for measuring the chemical flux or concentration profiles from the substrate.31,32

Figure 3.

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(A) Diagram of SECM generation–collection mode. (i) Substrate generation–tip collection. (ii) Tip generation–substrate collection. O and R represent oxidized and reduced species. (B) (i) Schematic diagram of the tip collection of [DMPO–OH]· adduction formed by spin trapping of ·OH radical generated on a boron-doped diamond (BDD) electrode at different application potentials. (ii) In the absence and presence of 10 mm DMPO, different potentials were applied to the BDD electrode immersed in 0.1 M Na2SO4 (pH = 4), and the tip collection experiment was carried out. (iii) When the BDD electrode was turned on and off, the ESR spectra of a solution containing 10 mM DMPO and 0.1 M Na2SO4 (pH 4) were collected near the BDD electrode surface. Adapted from ref (33). Copyright 2022 American Chemical Society. (C) (i) Schematic diagram of the electrochemical classification of the SECM strategy. (ii, iii) H2 was generated and collected in a single Pt cluster using SECM at 10.8 μm (ii) and 46 nm (iii) distances in an oxygen-free 500 mM HClO4 solution, rNP = 1.8 nm. Adapted from ref (34). Copyright 2017 American Chemical Society.

Barroso-Martínez et al. developed a technique that enables real-time monitoring of newly generated ·OH on the electrode surface, using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to react with ·OH to form a long-lived adduct and then collecting the adduct produced on the electrode surface through a needle tip (Figure 3B).33 Ma et al. measured the size of the Pt nanoparticle (NP) at nanometer resolution by in situ SECM.34 In a high-concentration HClO4 solution, the tip generated hydrogen instead of bubbles by controlling the tip–substrate distance in TG-SC mode (Figure 3C), so as to obtain the steady-state current of Pt NP deposition at the tip and thus measure the size of Pt NP.

Feedback Mode

Feedback mode is one of the most common operation modes of SECM, which is often used to study reaction kinetics and local imaging.35−37 When a sufficient positive/negative potential is applied to the tip, the medium will be oxidized/reduced. When the tip is far away from the substrate, the tip current is not affected by the substrate and is the steady-state diffusion current iT,∞,

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where n is the number of electron transfers of the electrode reaction, D is the diffusion coefficient of the medium, F is the Faraday constant (96485 A·s·mol–1), c is the bulk concentration of the medium, and a is the radius of the UME tip. When the tip is near the conductive or electrochemically active substrate (Figure 4A), the product formed at the tip diffuses into the substrate and is reduced/oxidized to the medium. The flux from the medium to the tip increases, and iT (tip electrode current) > iT,∞. This phenomenon is called “positive feedback”. On the other hand, if the substrate surface is an insulator, the product cannot be reduced/oxidized to a medium on the substrate surface. Since the tip–substrate distance d is small, the medium cannot effectively diffuse to the tip surface, iT < iT,∞, which is called “negative feedback”.24 Under steady-state conditions, the normalized current IT (= iT/iT,∞) of the tip depends only on the tip–substrate distance d. The tip electrode current (iT) was recorded as a function of the distance between the tip and the substrate, and an approach curve could be obtained after fitting. The relationship between the normalized current IT and the normalized distance L (L = d/a) is as follows,

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where IT,C and IT,ins are the tip currents controlled by diffusion when the substrate is a conductor and an insulator, respectively. The feedback mode can be used to adjust the distance between the tip and the substrate, characterize the morphology of the sample, and quantitatively analyze the kinetic parameter kf of the sample reaction interface.

Figure 4.

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(A) SECM feedback mode diagram. (i) Positive feedback. (ii) Negative feedback. (B) (i) Diagram of mechanically induced defects (not to scale) on the graphene electrode. (ii) SECM images of mechanically induced defective graphene. (iii) SECM images of mechanically induced defects after four cycles of electropolymerization of o-phenylenediamne. Adapted from ref (38). Copyright 2012 American Chemical Society. (C) (i) Diagram of SECM experiment. (ii–v) Normalized SECM approach curve in the feedback mode. (ii) BiVO4 film with 2 mM [Fe(CN)6]3–, (iii) BiVO4 film with 2 mM [Fe(CN)6]4–, (iv) BiVO4/NiFe-LDH film with 2 mM [Fe(CN)6]3–, and (v) BiVO4/NiFe-LDH film with 2 mM [Fe(CN)6]4–. Adapted from ref (39). Copyright 2021 American Chemical Society.

Tan et al. studied monolayer chemical-vapor deposited graphene defects by the SECM feedback mode (Figure 4B), and the results showed that the reactivity of graphene defect sites to electrochemical reactions was about one order of magnitude higher than that of more primitive graphene surfaces.38 Yu et al. investigated the effect of NiFe layered double hydroxide (LDH) cocatalyst on BiVO4 photoanode by SECM feedback mode (Figure 4C).39 Studies on the photocatalyst and redox reaction of BiVO4/NiFe-LDH show that the rate constant of the photoluminescent hole (kh+0) and electron (ke–0) is five times larger than that of BiVO4 under illumination.

Redox Competition (RC) Mode

The redox competition mode was developed by Schuhmann’s research group in 2006 to minimize the impact of the large background current of the sample on the scanning results when studying the catalytic activity of various metal catalysts.40−44 At the double constant potentials, the same reactant will be electrocatalyzed simultaneously on the tip and the substrate (Figure 5A). This working mode was initially used to detect the oxygen reduction performance of platinum and gold particles deposited on glass carbon by pulse electrochemical deposition. Its working principle is to apply a pulse potential to the scanning probe. When the polarization potential of the sample is low, oxygen will only reduce on the tip surface. When the polarization of the sample increases negatively, the sample starts to show catalytic activity for the oxygen reduction reaction, and the oxygen reduction current detected on the tip decreases. According to the current detected by the probe, the oxygen reduction catalytic performance of the sample can be evaluated. The lower the oxygen reduction current measured by the probe, the better is the catalytic activity of the sample. By the above methods, the catalytic activities of different materials can be semiquantitatively studied.

Figure 5.

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(A) SECM redox competition mode diagram. (B) (i) Schematic diagram of the RC-SECM mode. (ii) Local ORR activity of octahedral CoS2 catalysts. Adapted with permission from ref (45). Copyright 2018 Royal Society of Chemistry. (C) (i) HER schematic diagram of the redox competition SECM model. (ii) Diagram showing the change in tip current when a cathode potential is applied to the base electrode. Adapted with permission from ref (46). Copyright 2022 Wiley-VCH GmbH.

Singh et al. visualized the local catalytic activity of octahedral CoS2 by RC mode (Figure 5B) and demonstrated that the active site distribution of electrocatalytic ORR was uniform.45 Liberman et al. used RC mode to accurately obtain the catalytic onset potential of the MOF (Figure 5C).46

Surface Interrogation (SI) Mode

The surface interrogation mode (SI-SECM) is a new in situ electrochemical technology based on the transient feedback mode developed by Bard and his colleagues,47 which can be used to detect and quantify the surface species adsorbed on the electrode.48−50 The reversible redox medium reacts on the SECM tip to generate a titrant, which reacts chemically with electrogenerated or chemically adsorbed material on a substrate of the same size as the tip (Figure 6A). First, a potential is applied to the substrate to oxidize and form adsorbed species, and the tip open circuit (OC) is maintained with the solution containing only oxidized state mediator O. Then, the substrate is kept open; a pulse voltage is applied to the tip, and the oxidized mediator O is reduced to the reduced state R on the tip surface. The reduced state R diffuses between the substrate and the tip and contacts and reacts with the adsorbed species A to regenerate the oxidized state O, and species A transforms the final product P. Ideally, O can only be regenerated by reacting with A adsorbed on the substrate, and the system presents positive feedback. When A is completely depleted, the reaction rate of O at the tip is hindered by the diffusion control of the tip–substrate gap, and the system presents a negative feedback. By means of SI-SECM, the Bard research group measured the kinetic constants of the adsorption of intermediate materials on the electrode surface.48,50 Initially, Rodríguez-López used this model to study the electrogenerated oxides stabilized on Au and Pt surfaces (Figure 6B) and obtained the evidence of the formation of so-called singly oxygenated species or “ incipient oxides”.47

Figure 6.

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(A) Diagram of SECM surface interrogation mode. (B) Results for the comparison of substrate voltammetry to the interrogation of Au (i–iii) and Pt (iv–vi) in 0.3 M PBS, pH 7, with Ru(NH3)62+. All potentials versus NHE. (i, iv) Voltammetry of the Au and Pt substrate. (ii, v) Spectrum of tip scans for the interrogation of Au and Pt electrodes taken to different potential limits. (iii) Isotherm for oxygen on gold. (vi) In independent experiments, the comparison between the integral charge found by the inquiry technique and the oxide electroreduction results. Adapted from ref (47). Copyright 2008 American Chemical Society.

In short, the direct mode is often used for sample surface modification. The G-C mode is often used for imaging and reaction kinetics research. The feedback mode is most commonly used to extract kinetics information, and the tip–substrate distance is generally determined and adjusted by the feedback mode. The RC mode is characterized by reducing the influence of the large background current of the sample on the scanning results and is used for qualitative and semi-quantitative comparison of the electrochemical activity of different samples. The SI mode is characterized by the same size of the tip and the substrate, which can be used to detect and quantify the surface species adsorbed on the electrode.

Application of SECM in OER Research

The development of catalysts requires a large number of experiments, which leads to long cycles and high research costs. Bard’s group proposed a new method to rapidly screen OER electrocatalysts by using SECM.51 Pure IrO2 and Sn1–xIrxO2 combinatorial mixtures were prepared by the sol-gel route to form electrocatalyst spot arrays. The electrocatalyst libraries were screened by SECM in SG-TC imaging mode under the condition that the entire array could carry out OER. It can be viewed from Figure 7A that, when the shield is “on”, the background current decreases and the image contrast is improved. Figure 7Aii shows that the current increases monotonously with Ir content, indicating that the activity of the Sn1–xIrxO2 composite is positively correlated with Ir content. Subsequently, they prepared the electrocatalyst arrays of photochemical (PEC) water oxidation on a metal oxide semiconductor electrode and studied it with the improved SECM.52 The current increases with the increase of Co and Pt content, indicating that Co and Pt oxide electrocatalysts have good catalytic activity for PEC water oxidation (Figure 7B).

Figure 7.

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(A) SECM images of Sn1–xIrxO2 mixed oxide electrocatalytic spot arrays. The Au shield is “off” when an open circuit (i) and “on” when a potential of −0.1 V vs RHE is applied (ii). Adapted from ref (51). Copyright 2008 American Chemical Society. (B) SECM images of (i) Ir/Co oxide array and (ii) Pt array on the BiVW-O film under UV-visible and visible light irradiation. Pt points were prepared by photoreduction of Pt precursor through an optical fiber for 20, 30, and 40 min (from left to right) under UV-visible light irradiation. Adapted from ref (52). Copyright 2011 American Chemical Society. (C) SECM pseudo-color image of a 3 mm boron-doped diamond (BDD) disk electrode. (i) Feedback mode (EUME = 0.5 V). (ii, iii) Hydrodynamic SG-TC mode (frot = 25 s–1) in 0.2 M HClO4 during amperometric OER, substrate = 2.8 V (ii) and substrate = 3.4 V (iii). Adapted with permission from ref (53). Copyright 2018 Elsevier Ltd. (D) SECM studies of the karst NF. (i, ii) The description of the SG-TC model of SECM experiments (i) and 3D surface topography (ii) of the karst NF. (iii, iv) 3D current image of (iii) HER and (iv) OER. Adapted with permission from ref (54). Copyright 2020 Royal Society of Chemistry. (E) (i) Scanning image and (ii) corresponding 3D image of LDH-ppy, Etip = −0.6 V vs Ag/AgCl, Esub = 0.9 V vs Ag/AgCl. (iii, iv) Height image (iii) and the scanning image (iv) of LDH. (v) Current profile along the lines marked in (i) and (iv). Adapted from ref (55). Copyright 2021 American Chemical Society.

Conventional detection methods can detect the overall catalytic performance of the catalyst but ignore the local differences of different structures or components in the catalyst. Matysik et al. used hydrodynamic SECM to study the generation of reactive oxygen species (ROS) on Pt and BDD macroelectrodes during oxygen evolution reactions (OERs).53 In Figure 7Cii, a large amount of H2O2 is generated in the region with low feedback current. In Figure 7Ciii, both positive and negative currents are present, and the negative current coincides with the bright area in Figure 7Cii, indicating that ROS is mainly produced in the region where ·OH evolution decreases. This observation suggests that H2O2 and reducible ROS are produced simultaneously in different regions of BDD during OER. Gao et al. studied nickel foam with typical karst landform characteristics by peak force scanning electrochemical microscopy (PF-SECM) to obtain the correlation between surface morphology and electrocatalytic activity.54 The karst landform-featured electrode is composed of a Ni/α-Ni(OH)2 heterostructure in the tower area and nickel in the valley area. The peak currents of HER (dark area in Figure 7Dii and blue and white area in Figure 7Diii) and OER (bright area in Figure 7Dii and pink area in Figure 7Div) are observed in the valley area and tower area, respectively. The importance of different reaction sites to HER and OER is proven in this in situ SECM observation.

Yang et al. prepared LDH-ppy (polypyrrole) hybrid catalyst through a simple ICPS process by utilizing the complementary charge of the LDH main layer and py-COOH monomer in alkaline solution.55 The OER activity of LDH-ppy was visualized at subnanometer resolution by SG-TC mode, and the reduction current collected by the tip on the LDH-ppy (∼−5.3 nA, Figure 7Ei,ii,iv) was much greater than that in the OER noble gold substrate region (∼−1.7 nA) and the original NiFe LDH (∼−2.7 nA, Figure 7Eiii–v), which confirms that the conductive polymers greatly improve the catalytic performance of LDH.

Application of SECM in ORR Research

In recent years, more and more attention has been paid to the method of comparing and rapidly screening catalysts by SECM imaging. Bard et al. electrodeposited a series of bimetallic arrays on the glassy carbon electrode, such as Pd–Co, Pd–W, Au–V, Ag–V, Pd–Mn, and Pd–V, and used rapid screening SECM technology to determine the electrocatalytic activity.56−58 Compared with pure metals, bimetallic catalysts show stronger electrocatalytic activity, even comparable to commercial Pt catalysts.

Xin et al. successfully synthesized 3D rosebud-like nanometer MoSe2@rGO by a simple hydrothermal method and used RC-SECM technology to compare the ORR catalytic activities of MoSe2@rGO, pure MoSe2, rGO, and physical mixed MoSe2 and rGO at different polarization potentials.59 The SECM image shows the decrease of ORR current recorded at the tip (Δi) after deducting the background current. The images (Figure 8A) showed that all four samples showed good ORR electrocatalytic activity at lower potentials, but as the potential increases, Δi of MoSe2@rGO is significantly larger than that of the other three samples, which indicates that MoSe2@rGO has better ORR catalytic activity.

Figure 8.

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(A) Optical photograph of spots of MoSe2@rGO, MoSe2, MoSe2+rGO, and rGO loaded on GC. (ii–iv) Scanning images of the corresponding RC-SECM regions of the catalysts spots; different potentials are applied to GCE (Esub): (ii) 0.57 V, (iii) 0.62 V, and (iv) 0.67 V. Tip potential: 0.17 V (vs. RHE). Adapted with permission from ref (59). Copyright 2016 Tsinghua University Press and Springer-Verlag Berlin Heidelberg. (B) Scanning images for ORR over NCS-800 in 0.1 M NaOH electrolyte with available dissolved oxygen. Adapted with permission from ref (31). Copyright 2017 Royal Society of Chemistry. (C) Scanning images and current distribution of (i) Fe-clusters/NAC and Pt; (ii) Fe clusters/NAC and AC; (iii) Pt and AC. Adapted with permission from ref (60). Copyright 2020 Royal Society of Chemistry.

Alkaline ORR has a lower overpotential, but the viscous resistance of highly alkaline medium interferes with SECM imaging. Nagaiah et al. prepared a nitrogen-containing carbon sphere (NCS) catalyst by the soft template method and imaged ORR catalytic activity of the NCS catalyst in highly alkaline medium with high resolution through RC-SECM.31 The SECM image (Figure 8B) shows that the catalyst surface is uniformly red, indicating that the active centers are evenly distributed. The reduction current at the tip of the catalyst surface is significantly lower than that around it, indicating that the ORR activity is higher in highly alkaline medium. This is the first report of visualization of local electrocatalytic activity on ORR in a highly alkaline medium.

It is very important to study the electrochemical process from the microscopic point of view to understand the properties and the mechanism of the catalysts. Huang et al. synthesized new Fe clusters/NAC and NAC (nitrogen doped activated carbon) catalysts by the ball milling method and compared the catalytic activities of Fe clusters/NAC, AC, and Pt in pairs by SECM.60 Compared with AC and Pt, as Figure 8C shows, the Fe cluster/NAC catalyst can generate higher current, which indicates that the Fe cluster/NAC catalyst has better ORR catalytic activity.

Application of SECM in HER Research

Hydrogen is an ideal and pollution-free renewable energy source, and HER is an important reaction in the preparation of green hydrogen. Due to the low reserve and high price of precious metal platinum, it is a hot topic to find suitable alternative materials. Recently, nanostructured MoS2 has been shown to be a good catalyst for HER. Compared with the thermodynamic stable semiconductor (2H) phase, HER is enhanced on the MoS2 nanoflake metal (1T) phase.

In order to measure this difference, Sun et al. used SECM to conduct high-resolution imaging of the surface catalytic activity of mixed-phase and pure 2H MoS2 nanosheets.61Figure 9Ai shows significant HER activity at the edge of the 2H flake. A high-resolution map (Figure 9Aiii) obtained using the smaller tip shows that HER activity is limited to the edge of the sheet, with a reaction width of about 50 nm. Due to the diffusion, the true width of the reaction edge may be much narrower than in the figure. Activity maps of mixed-phase MoS2 nanosheets obtained by feedback mode in Fc redox mediator (Figure 9Aiv–vi) indicate the presence of a 1T phase. Line profiles were extracted using the SG-TC mode (Figure 9Avii) to quantify HER activity in the mixed-phase MoS2 nanosheet region. By comparing Figure 9Avi,vii, it can be seen that HER is much faster on the edge of 2H than on the plane and has high activity in the whole part of 1T.

Figure 9.

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(A) (i) SG/TC image of HER over a 2H MoS2 flake. (ii) Feedback mode image of the boundary between 2H MoS2 and ITO. (iii) SG/TC mode (HER activity) images of the boundary between 2H MoS2 and ITO. (iv) 3D Feedback mode image of mixed-phase MoS2 nanosheets on ITO obtained by Fc redox mediator and (v) the corresponding two-dimensional color graph. (vi) The magnified area showing a more detailed picture of boundaries between ITO, 2H MoS2, and 1T MoS2 based on the feedback current of Fc. (vii) HER SG/TC line profiles across the same substrate area as in (vi). Adapted with permission from ref (61). Copyright 2019 Royal Society of Chemistry. (B) SEM and SECM images of MoS2 before (i–iii) and after (iv–vi) HER. (i, iv) SEM images. (ii, v) Feedback SECM images. (iii, vi) SG/TC SECM images. Adapted with permission from ref (62). Copyright 2022 Elsevier Inc. (C) (i, iii, v, vii, ix) SECM feedback mode in 1 mM Fc and 0.1 M KCl. (ii, iv, vi, viii, x) SG-TC mode SECM in 0.5 mM Fc, 0.1 M KCl, and 10 mM HClO4. Adapted with permission from ref (63). Copyright 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (D) (i) SECM schematic diagram. (ii–v) SG/TC SECM image on HOPG NiCoP@MXene for HER at different temperatures. (vi) Arrhenius diagram of the reciprocal of the logarithm of temperature and tip current obtained for NiCoP@MXene. Adapted from ref (64). Copyright 2022 American Chemical Society.

In order to replace platinum as catalyst in the hydrogen evolution reaction, in addition to catalytic activity, the stability of the catalyst is also an important parameter. Wert analyzed the corrosion degree caused by HER on a MoS2 crystal, and its influence on the micro level of material morphology and electrochemical activity.62 There is no significant difference between the SEM images of MoS2 before and after HER (Figure 9B). In addition, the SG/TC and feedback mode recorded before and after HER are highly similar, which indicates that the MoS2 crystal has good stability for HER.

MXenes are a family of two-dimensional transition metal carbides and nitrides, which have shown excellent electrocatalytic performance in HER. Studies on carbide MXenes have been widely reported, while nitride MXenes are less well known. Djire et al. prepared a series of mixed metal nitride MXenes, characterized the electrochemical activity of a single MXene flake with SECM, and provided experimental evidence for the first time that MXene substrate catalyzed HER.63 Due to the sluggish regeneration rate of Fc mediator on MXene nanoflake in comparison to the ITO surface, the current on the MXene nanoflake is lower than that on the ITO surface as displayed in Figure 9Ci,iii,v,vii,ix. However, in the corresponding SG-TC images, prominent signals can only be detected on the V–Ti4N3TX and Cr–Ti4N3TX, which suggests the improved electrocatalytic activity against HER.

Heterogeneous interfaces can greatly reduce the kinetic energy barrier (Ea) by adjusting the adsorption energy of intermediates in the transition state. Niu et al. anchored NiCoP grains (about 5 nm in size) on a Ti3C2Tx MXene monolayer (about 1 nm in thickness) and investigated the thermal effect of HER reaction kinetics on NiCoP@MXene thin slices by SECM.64 The tip current increases with the increase of temperature (Figure 9D), indicating that the reaction rate is accelerated. Ea was obtained by fitting the Arrhenius diagram. Ea (31.4–31.9 kJ mol–1) of NiCoP@MXene is significantly lower than that of NiCoP (40.3 kJ mol–1).

Application of SECM in HOR Research

HOR is the anode reaction of the hydrogen fuel cell. The development of high-performance HOR catalyst is necessary for the large-scale application of the hydrogen fuel cell.

SECM has been proven to be a reliable technology for screening catalysts. Weng et al. optimized the composition of Pt–Pd, Pt–Ru, and Pt–Ir bimetallic systems used for hydrogen oxidation reactions by a combination screening method.65 The catalytic activity of these catalyst arrays for HOR was characterized by TG-SC. In Figure 10A, the sample points with higher catalytic HOR current are darker brown, while the sample points with lower current are darker green. Within a wide potential range, Pt4Pd6, Pt9Ru1, and Pt3Ir7 indicate the highest HOR activity with proper atomic ratio.

Figure 10.

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(A) (i) Scheme showing the spot distribution pattern of the atomic ratio of Pt to Pd in different columns and SECM image of Pt–Pd electrocatalyst array for H2 oxidation at 0.4, 0.5, 0.6, 0.7, and 0.8 V in 0.1 M H2SO4 solution. Adapted with permission from ref (65). Copyright 2011 Elsevier Ltd. (B) (i) The SECM image for H+/H2 coupling, representing three different positions of first, third, and fourth Pt NPs. (ii) Cross section current response at each different position in the SECM image in the panel. Adapted from ref (66). Copyright 2016 American Chemical Society. (C) (i) SECM tip current diagram of HOR on the surface of polycrystalline Pt substrate, which plots the grain boundary. (ii) Corresponding EBSD IPF diagram. (iii–xii) SECM tip current image of the same region of the Pt substrate biased toward HOR at different potentials and MSE. Adapted with permission from ref (67). Copyright 2020 the Electrochemical Society.

Understanding the structure-activity relationship of catalytic metal nanoparticles is very important for achieving more efficient electrocatalytic devices. However, it is still a great challenge to study these relationships at the individual NP level. In order to solve this challenge, Kim et al. developed a method for the geometric properties and catalytic activity of single Pt NPs in HOR.66 Pt NPs with a radius of tens to a hundred nanometers were directly electrodeposited on highly oriented HOPGs. It can be observed (Figure 10B) that the current of three different Pt NPs is the same, which means that H2 generated at the Pt tip is oxidized immediately when it diffuses to the surface of Pt NPs, and the reaction is controlled by diffusion. Assuming the existence of a Butler–Volmer relation, the lower limit of the heterogeneous effective rate constant of HOR can be extracted, keff0 ≥ 2 cm/s, α = 0.5, and potential difference (E – E0′) ≈ 250 mV.

Wang et al. first proposed a method to study the activity of HOR catalysts with a high index using SECM imaging technology.67 The grain boundaries derived from an electron backscatter diffraction (EBSD) inverse pole (IPF) diagram were plotted on a SECM diagram (Figure 10C) to facilitate the comparison of catalytic activities of different crystal surfaces. Grains 4 and 5 have (111) symmetric steps with 5 atomic widths and different ladder symmetries. Grain 4 has a single atom (100) step, while grain 5 has a single atom high (110) orientation step. It can be seen from Figure 10Ci that the grain 5 with a (110) step site has higher catalytic activity than grain 4. Grain 6 without any (110) orientation step has the lowest electrocatalytic activity for HOR. In short, the surface catalytic activity of the crystal is Pt(111) > Pt(110) > Pt(100). When the biased substrate potential increases from −0.75 to +0.8 V, the tip current decreases and the HOR rate decreases. This may be due to the blocking effect of anion adsorption on the surface of platinum substrate and the growth of platinum oxide. When the substrate potential is biased from +0.1 to −0.5 V, the total tip current increases, which indicates the reversible reduction of Pt/O species.

In addition to OER, ORR, HER, and HOR, many energy-related catalytic reactions have been extensively studied. Perales-Rondón investigated the effect of Pb adsorption atoms on formic acid oxidation reaction (FAOR) on Pt NPs.68 In the SECM image (Figure 11A), brown in the figure corresponds to the background current and green indicates the increased oxidation current due to the oxidation of HCOOH on the electrode. Under the two potentials studied, the current of Pb–Pt is much higher than that of Pt, indicating that the FAOR activity of Pb modified Pt NPs is much stronger than that of the original platinum electrode. Díaz-Real synthesized TiO2 nanotube film (TNM) and modified it with Pt–Ru electrocatalyst.69 Its photocatalytic activity for methanol (MeOH) oxidation was evaluated by SECM. As shown in Figure 11B, the current of Pt–Ru/TNM (Figure 11Bv,vi) is significantly higher than that of TNM (Figure 11Biii,iv) in the acidic medium with 0.5 M MeOH, indicating that Pt–Ru modified TMN had photocatalytic activity for MeOH oxidation. Gupta synthesized nitrogen-doped carbon nanotubes (NCNTs) and modified them with PtRu nanoparticles.70 With the increase of oxidation current, the image color changes from blue to red. For Figure 11Ci, if the tip current is large, the sample current is small, and the methanol oxidation activity of the sample is low. The tip current of the PtRu/NCNT-400 area is significantly smaller than that of PtRu/OCNT, indicating that PtRu/NCNT-400 has better methanol oxidation activity. In Figure 10Ciii, the CO oxidation current of PtRu/NCNT-400 is less than that of PtRu/OCNT, which indicates that PtRu-NCNT produces less CO during methanol oxidation.

Figure 11.

Figure 11

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(A) SECM image of the MD/SC mode showing the substrate current collected for HCOOH oxidation with different potentials in degassed 0.5M H2SO4 solution. Adapted with permission from ref (68). Copyright 2017 Elsevier B.V. (B) (i) Distribution of Pt–Ru catalyst on the TNM surface. (ii) SECM experimental diagram. SECM image of TNM obtained with 0.5 M methanol/0.5 M H2SO4: (iii) no UV light; (iv) UV light; (v) Pt–Ru nanoparticles and no UV light; (vi) Pt–Ru nanoparticles and UV light on an area of 300 × 300 μm. Adapted with permission from ref (69). Copyright 2018 Elsevier B.V. (C) (i) RC-SEM 3D images of PtRu/OCNT and PtRu/NCNT-400 catalyst spots in 1 M CH3OH+0.5 M H2SO4. (ii) Inverted image of (i). (iii) SECM 3D image of the SG-TC mode of CO oxidation. Adapted with permission from ref (70). Copyright 2021 Royal Society of Chemistry.

Conclusions

In this Review, we summarized and elaborated the basic principle of SECM and the application of ORR, OER, HER, HOR, and some energy catalysis related reactions in image analysis and research. Particularly, the application of SECM in the rapid screening of catalysts and the study of the surface structure-activity relationship of catalysts were particularly discussed, which benefit from the high-resolution scanning characteristics of SECM, but it is not without shortcomings. Because the signal is very sensitive to the tip–catalyst distance and the exact same distance cannot be guaranteed in any two experiments, it is difficult to repeat the SECM results. Reducing the scanning rate and using smaller step size and probe can improve the resolution. However, this may greatly prolong the experimental time. Therefore, it is challenging to optimize the resolution and shorten the scanning time at the same time.

In recent years, with the continuous development of SECM technology, its application scope has been rapidly expanded to charge transfer,71,72 solar cells,73−75 heterogeneous catalysis,76,77 biological analysis,78,79 and many other fields. With the progress of technology and equipment, SECM is often combined with other multifunctional technologies, such as a single molecule fluorescence microscope,80,81 AFM,82−84 and SICM,85−87 to obtain more useful information. With the continuous expansion and deepening of research, a single technology is increasingly unable to meet the needs of scientific research. It can be predicted that multi-technology combinations will become particularly important. With the development of technology, the research scope of SECM is also expanding and will play a greater role in the energy field.

Acknowledgments

The authors are grateful to the financial support from the by the National Natural Science Foundation of China (Nos. 21721003, 22102172, 22072145, 22005294, and 21925205).

Glossary

Vocabulary

UME

Ultramicroelectrode, a small electrode with a diameter of less than 100μm.

MOF

Metal-organic framework refers to crystalline porous materials with a periodic network structure formed by self-assembly of transition metal ions and organic ligands.

LDH

Layered double hydroxide is the general name of hydrotalcite (HT) and hydrotalcite-like compounds (HTLCs). A series of supramolecular materials assembled by these compounds are called hydrotalcite-like intercalation materials (LDHs).

ROS

Reactive oxygen species refers to free radicals and non-free radicals from oxygen sources, including superoxide anion (O2–), hydrogen peroxide (H2O2), hydroxyl radical (OH–), ozone (O3), and singlet oxygen (1O2). As they contain unpaired electrons, they have high chemical reactivity.

BDD

Pure diamond is an insulator, while diamond incorporated with a certain amount of boron (boron doped diamond, BDD) impurity later becomes a p-type semiconductor or even a conductor, and the change in the concentration of boron incorporation directly affects its own electrical performance.

EBSD

Electron back scatter diffraction is a technique for identifying the crystallographic orientation of a sample using a diffracted electron beam. It can be used to determine grain boundary, phase identification, orientation, texture, and strain.

The authors declare no competing financial interest.

References

  1. Zhou B.; Gao R.; Zou J.-J.; Yang H. Surface Design Strategy of Catalysts for Water Electrolysis. Small 2022, 18 (27), 2202336. 10.1002/smll.202202336. [DOI] [PubMed] [Google Scholar]
  2. Wang X.; Zhou X.; Li C.; Yao H.; Zhang C.; Zhou J.; Xu R.; Chu L.; Wang H.; Gu M.; Jiang H.; Huang M. Asymmetric Co□N3P1 Trifunctional Catalyst with Tailored Electronic Structures Enabling Boosted Activities and Corrosion Resistance in an Uninterrupted Seawater Splitting System. Advanced Materials 2022, 34 (34), 2204021. 10.1002/adma.202204021. [DOI] [PubMed] [Google Scholar]
  3. Klingenhof M.; Hauke P.; Brückner S.; Dresp S.; Wolf E.; Nong H. N.; Spöri C.; Merzdorf T.; Bernsmeier D.; Teschner D.; Schlögl R.; Strasser P. Modular Design of Highly Active Unitized Reversible Fuel Cell Electrocatalysts. ACS Energy Letters 2021, 6 (1), 177–183. 10.1021/acsenergylett.0c02203. [DOI] [Google Scholar]
  4. Chao S.; Zhang Y.; Wang K.; Bai Z.; Yang L. Flower–like Ni and N codoped hierarchical porous carbon microspheres with enhanced performance for fuel cell storage. Applied Energy 2016, 175, 421–428. 10.1016/j.apenergy.2016.04.043. [DOI] [Google Scholar]
  5. Bezerra L. S.; Maia G. Developing efficient catalysts for the OER and ORR using a combination of Co, Ni, and Pt oxides along with graphene nanoribbons and NiCo2O4. Journal of Materials Chemistry A 2020, 8 (34), 17691–17705. 10.1039/D0TA05908K. [DOI] [Google Scholar]
  6. Liu B.; Sun Y.; Liu L.; Xu S.; Yan X. Advances in Manganese-Based Oxides Cathodic Electrocatalysts for Li–Air Batteries. Adv. Funct. Mater. 2018, 28 (15), 1704973. 10.1002/adfm.201704973. [DOI] [Google Scholar]
  7. Luo M.; Zhao Z.; Zhang Y.; Sun Y.; Xing Y.; Lv F.; Yang Y.; Zhang X.; Hwang S.; Qin Y.; Ma J.-Y.; Lin F.; Su D.; Lu G.; Guo S. PdMo bimetallene for oxygen reduction catalysis. Nature 2019, 574 (7776), 81–85. 10.1038/s41586-019-1603-7. [DOI] [PubMed] [Google Scholar]
  8. Jung J.-W.; Cho S.-H.; Nam J. S.; Kim I.-D. Current and future cathode materials for non-aqueous Li-air (O2) battery technology – A focused review. Energy Storage Materials 2020, 24, 512–528. 10.1016/j.ensm.2019.07.006. [DOI] [Google Scholar]
  9. Lu M.; An L.; Yin J.; Jin J.; Yang R.; Huang B.; Hu Y.; Zhao Y.-Q.; Xi P. Electronic engineering of amorphous Fe–Co–S sites in hetero-nanoframes for oxygen evolution and flexible Al–air batteries. Journal of Materials Chemistry A 2022, 10 (37), 19757–19768. 10.1039/D2TA00191H. [DOI] [Google Scholar]
  10. Nandan R.; Gautam A.; Tripathi S.; Nanda K. K. A comprehensive analysis and rational designing of efficient Fe-based oxygen electrocatalysts for metal–air batteries. Journal of Materials Chemistry A 2018, 6 (18), 8537–8548. 10.1039/C8TA01938J. [DOI] [Google Scholar]
  11. Zhou T.; Zhang N.; Wu C.; Xie Y. Surface/interface nanoengineering for rechargeable Zn–air batteries. Energy Environ. Sci. 2020, 13 (4), 1132–1153. 10.1039/C9EE03634B. [DOI] [Google Scholar]
  12. Yu P.; Wang L.; Sun F.; Xie Y.; Liu X.; Ma J.; Wang X.; Tian C.; Li J.; Fu H. Co Nanoislands Rooted on Co–N–C Nanosheets as Efficient Oxygen Electrocatalyst for Zn–Air Batteries. Advanced Materials 2019, 31 (30), 1901666. 10.1002/adma.201901666. [DOI] [PubMed] [Google Scholar]
  13. Jiao S.; Fu X.; Wang S.; Zhao Y. Perfecting electrocatalysts via imperfections: towards the large-scale deployment of water electrolysis technology. Energy Environ. Sci. 2021, 14 (4), 1722–1770. 10.1039/D0EE03635H. [DOI] [Google Scholar]
  14. An L.; Wei C.; Lu M.; Liu H.; Chen Y.; Scherer G. G.; Fisher A. C.; Xi P.; Xu Z. J.; Yan C.-H. Recent Development of Oxygen Evolution Electrocatalysts in Acidic Environment. Advanced Materials 2021, 33 (20), 2006328. 10.1002/adma.202006328. [DOI] [PubMed] [Google Scholar]
  15. Wan S.; Qi J.; Zhang W.; Wang W.; Zhang S.; Liu K.; Zheng H.; Sun J.; Wang S.; Cao R. Hierarchical Co(OH)F Superstructure Built by Low-Dimensional Substructures for Electrocatalytic Water Oxidation. Advanced Materials 2017, 29 (28), 1700286. 10.1002/adma.201700286. [DOI] [PubMed] [Google Scholar]
  16. Engstrom R. C.; Weber M.; Wunder D. J.; Burgess R.; Winquist S. Measurements within the diffusion layer using a microelectrode probe. Analytical Chemistry 1986, 58 (4), 844–848. 10.1021/ac00295a044. [DOI] [Google Scholar]
  17. Liu H. Y.; Fan F. R. F.; Lin C. W.; Bard A. J. Scanning electrochemical and tunneling ultramicroelectrode microscope for high-resolution examination of electrode surfaces in solution. J. Am. Chem. Soc. 1986, 108 (13), 3838–3839. 10.1021/ja00273a054. [DOI] [Google Scholar]
  18. Bard A. J.; Fan F. R. F.; Kwak J.; Lev O. Scanning electrochemical microscopy. Introduction and principles. Analytical Chemistry 1989, 61 (2), 132–138. 10.1021/ac00177a011. [DOI] [Google Scholar]
  19. Bard A. J.; Fan F.-R. F.; Pierce D. T.; Unwin P. R.; Wipf D. O.; Zhou F. Chemical Imaging of Surfaces with the Scanning Electrochemical Microscope. Science 1991, 254 (5028), 68–74. 10.1126/science.254.5028.68. [DOI] [PubMed] [Google Scholar]
  20. Chen R.; Balla R. J.; Lima A.; Amemiya S. Characterization of Nanopipet-Supported ITIES Tips for Scanning Electrochemical Microscopy of Single Solid-State Nanopores. Analytical Chemistry 2017, 89 (18), 9946–9952. 10.1021/acs.analchem.7b02269. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Wang X.; Han L.; Xin H.; Mirkin M. V. TEM-Assisted Fabrication of Sub-10 nm Scanning Electrochemical Microscopy Tips. Analytical Chemistry 2019, 91 (24), 15355–15359. 10.1021/acs.analchem.9b04316. [DOI] [PubMed] [Google Scholar]
  22. Kim J.; Renault C.; Nioradze N.; Arroyo-Currás N.; Leonard K. C.; Bard A. J. Nanometer Scale Scanning Electrochemical Microscopy Instrumentation. Analytical Chemistry 2016, 88 (20), 10284–10289. 10.1021/acs.analchem.6b03024. [DOI] [PubMed] [Google Scholar]
  23. Eckhard K.; Etienne M.; Schulte A.; Schuhmann W. Constant-distance mode AC-SECM for the visualisation of corrosion pits. Electrochemistry Communications 2007, 9 (7), 1793–1797. 10.1016/j.elecom.2007.03.035. [DOI] [Google Scholar]
  24. Bard A. J.; Denuault G.; Lee C.; Mandler D.; Wipf D. O. Scanning electrochemical microscopy - a new technique for the characterization and modification of surfaces. Acc. Chem. Res. 1990, 23 (11), 357–363. 10.1021/ar00179a002. [DOI] [Google Scholar]
  25. Hauquier F.; Matrab T.; Kanoufi F.; Combellas C. Local direct and indirect reduction of electrografted aryldiazonium/gold surfaces for polymer brushes patterning. Electrochimica Acta 2009, 54 (22), 5127–5136. 10.1016/j.electacta.2009.01.059. [DOI] [Google Scholar]
  26. Grisotto F.; Ghorbal A.; Goyer C.; Charlier J.; Palacin S. Direct SECM Localized Electrografting of Vinylic Monomers on a Conducting Substrate. Chem. Mater. 2011, 23 (6), 1396–1405. 10.1021/cm101563n. [DOI] [PubMed] [Google Scholar]
  27. Zhou F.; Unwin P. R.; Bard A. J. Scanning electrochemical microscopy. 16. Study of second-order homogeneous chemical reactions via the feedback and generation/collection modes. J. Phys. Chem. 1992, 96 (12), 4917–4924. 10.1021/j100191a036. [DOI] [Google Scholar]
  28. Kai T.; Zhou M.; Duan Z.; Henkelman G. A.; Bard A. J. Detection of CO2•– in the Electrochemical Reduction of Carbon Dioxide in N,N-Dimethylformamide by Scanning Electrochemical Microscopy. J. Am. Chem. Soc. 2017, 139 (51), 18552–18557. 10.1021/jacs.7b08702. [DOI] [PubMed] [Google Scholar]
  29. Kai T.; Zhou M.; Johnson S.; Ahn H. S.; Bard A. J. Direct Observation of C2O4•– and CO2•– by Oxidation of Oxalate within Nanogap of Scanning Electrochemical Microscope. J. Am. Chem. Soc. 2018, 140 (47), 16178–16183. 10.1021/jacs.8b08900. [DOI] [PubMed] [Google Scholar]
  30. Fernández J. L.; Bard A. J. Scanning Electrochemical Microscopy 50. Kinetic Study of Electrode Reactions by the Tip Generation–Substrate Collection Mode. Analytical Chemistry 2004, 76 (8), 2281–2289. 10.1021/ac035518a. [DOI] [PubMed] [Google Scholar]
  31. Tiwari A.; Singh V.; Mandal D.; Nagaiah T. C. Nitrogen containing carbon spheres as an efficient electrocatalyst for oxygen reduction: Microelectrochemical investigation and visualization. Journal of Materials Chemistry A 2017, 5 (37), 20014–20023. 10.1039/C7TA05503J. [DOI] [Google Scholar]
  32. Lee W.; Lee T.; Kim S.; Bae S.; Yoon J.; Cho K. Descriptive Role of Pt/PtOx Ratio on the Selective Chlorine Evolution Reaction under Polarity Reversal as Studied by Scanning Electrochemical Microscopy. ACS Appl. Mater. Interfaces 2021, 13 (29), 34093–34101. 10.1021/acsami.1c06187. [DOI] [PubMed] [Google Scholar]
  33. Barroso-Martínez J. S.; Romo A. I. B.; Pudar S.; Putnam S. T.; Bustos E.; Rodríguez-López J. Real-Time Detection of Hydroxyl Radical Generated at Operating Electrodes via Redox-Active Adduct Formation Using Scanning Electrochemical Microscopy. J. Am. Chem. Soc. 2022, 144 (41), 18896–18907. 10.1021/jacs.2c06278. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Ma W.; Hu K.; Chen Q.; Zhou M.; Mirkin M. V.; Bard A. J. Electrochemical Size Measurement and Characterization of Electrodeposited Platinum Nanoparticles at Nanometer Resolution with Scanning Electrochemical Microscopy. Nano Lett. 2017, 17 (7), 4354–4358. 10.1021/acs.nanolett.7b01437. [DOI] [PubMed] [Google Scholar]
  35. Zoski C. G.; Aguilar J. C.; Bard A. J. Scanning Electrochemical Microscopy. 46. Shielding Effects on Reversible and Quasireversible Reactions. Analytical Chemistry 2003, 75 (13), 2959–2966. 10.1021/ac034011x. [DOI] [PubMed] [Google Scholar]
  36. Skaanvik S. A.; Stephens L. I.; Gateman S. M.; Geissler M.; Mauzeroll J. Quantitative Feedback Referencing for Improved Kinetic Fitting of Scanning Electrochemical Microscopy Measurements. Analytical Chemistry 2022, 94 (40), 13852–13859. 10.1021/acs.analchem.2c02498. [DOI] [PubMed] [Google Scholar]
  37. Laforge F. O.; Velmurugan J.; Wang Y.; Mirkin M. V. Nanoscale Imaging of Surface Topography and Reactivity with the Scanning Electrochemical Microscope. Analytical Chemistry 2009, 81 (8), 3143–3150. 10.1021/ac900335c. [DOI] [PubMed] [Google Scholar]
  38. Tan C.; Rodríguez-López J.; Parks J. J.; Ritzert N. L.; Ralph D. C.; Abruña H. D. Reactivity of Monolayer Chemical Vapor Deposited Graphene Imperfections Studied Using Scanning Electrochemical Microscopy. ACS Nano 2012, 6 (4), 3070–3079. 10.1021/nn204746n. [DOI] [PubMed] [Google Scholar]
  39. Yu Z.; Huang Q.; Jiang X.; Lv X.; Xiao X.; Wang M.; Shen Y.; Wittstock G. Effect of a Cocatalyst on a Photoanode in Water Splitting: A Study of Scanning Electrochemical Microscopy. Analytical Chemistry 2021, 93 (36), 12221–12229. 10.1021/acs.analchem.1c01235. [DOI] [PubMed] [Google Scholar]
  40. Eckhard K.; Chen X.; Turcu F.; Schuhmann W. Redox competition mode of scanning electrochemical microscopy (RC-SECM) for visualisation of local catalytic activity. Phys. Chem. Chem. Phys. 2006, 8 (45), 5359–65. 10.1039/b609511a. [DOI] [PubMed] [Google Scholar]
  41. Chen X.; Eckhard K.; Zhou M.; Bron M.; Schuhmann W. Electrocatalytic Activity of Spots of Electrodeposited Noble-Metal Catalysts on Carbon Nanotubes Modified Glassy Carbon. Analytical Chemistry 2009, 81 (18), 7597–7603. 10.1021/ac900937k. [DOI] [PubMed] [Google Scholar]
  42. Nagaiah T. C.; Schäfer D.; Schuhmann W.; Dimcheva N. Electrochemically Deposited Pd–Pt and Pd–Au Codeposits on Graphite Electrodes for Electrocatalytic H2O2 Reduction. Analytical Chemistry 2013, 85 (16), 7897–7903. 10.1021/ac401317y. [DOI] [PubMed] [Google Scholar]
  43. Maljusch A.; Nagaiah T. C.; Schwamborn S.; Bron M.; Schuhmann W. Pt–Ag Catalysts as Cathode Material for Oxygen-Depolarized Electrodes in Hydrochloric Acid Electrolysis. Analytical Chemistry 2010, 82 (5), 1890–1896. 10.1021/ac902620g. [DOI] [PubMed] [Google Scholar]
  44. Zeradjanin A. R.; Schilling T.; Seisel S.; Bron M.; Schuhmann W. Visualization of Chlorine Evolution at Dimensionally Stable Anodes by Means of Scanning Electrochemical Microscopy. Analytical Chemistry 2011, 83 (20), 7645–7650. 10.1021/ac200677g. [DOI] [PubMed] [Google Scholar]
  45. Singh V.; Tiwari A.; Nagaiah T. C. Facet-controlled morphology of cobalt disulfide towards enhanced oxygen reduction reaction. Journal of Materials Chemistry A 2018, 6 (45), 22545–22554. 10.1039/C8TA06710D. [DOI] [Google Scholar]
  46. Liberman I.; Ifraemov R.; Shimoni R.; Hod I. Localized Electrosynthesis and Subsequent Electrochemical Mapping of Catalytically Active Metal–Organic Frameworks. Adv. Funct. Mater. 2022, 32 (19), 2112517. 10.1002/adfm.202112517. [DOI] [Google Scholar]
  47. Rodríguez-López J.; Alpuche-Avilés M. A.; Bard A. J. Interrogation of Surfaces for the Quantification of Adsorbed Species on Electrodes: Oxygen on Gold and Platinum in Neutral Media. J. Am. Chem. Soc. 2008, 130 (50), 16985–16995. 10.1021/ja8050553. [DOI] [PubMed] [Google Scholar]
  48. Arroyo-Currás N.; Bard A. J. Iridium Oxidation as Observed by Surface Interrogation Scanning Electrochemical Microscopy. J. Phys. Chem. C 2015, 119 (15), 8147–8154. 10.1021/acs.jpcc.5b00106. [DOI] [Google Scholar]
  49. Kim J. Y.; Ahn H. S.; Bard A. J. Surface Interrogation Scanning Electrochemical Microscopy for a Photoelectrochemical Reaction: Water Oxidation on a Hematite Surface. Analytical Chemistry 2018, 90 (5), 3045–3049. 10.1021/acs.analchem.7b04728. [DOI] [PubMed] [Google Scholar]
  50. Jin Z.; Bard A. J. Surface Interrogation of Electrodeposited MnOx and CaMnO3 Perovskites by Scanning Electrochemical Microscopy: Probing Active Sites and Kinetics for the Oxygen Evolution Reaction. Angew. Chem. Int. Ed Engl 2021, 60 (2), 794–799. 10.1002/anie.202008052. [DOI] [PubMed] [Google Scholar]
  51. Minguzzi A.; Alpuche-Aviles M. A.; López J. R.; Rondinini S.; Bard A. J. Screening of Oxygen Evolution Electrocatalysts by Scanning Electrochemical Microscopy Using a Shielded Tip Approach. Analytical Chemistry 2008, 80 (11), 4055–4064. 10.1021/ac8001287. [DOI] [PubMed] [Google Scholar]
  52. Ye H.; Park H. S.; Bard A. J. Screening of Electrocatalysts for Photoelectrochemical Water Oxidation on W-Doped BiVO4 Photocatalysts by Scanning Electrochemical Microscopy. J. Phys. Chem. C 2011, 115 (25), 12464–12470. 10.1021/jp200852c. [DOI] [Google Scholar]
  53. Iffelsberger C.; Raith T.; Vatsyayan P.; Vyskočil V.; Matysik F.-M. Detection and imaging of reactive oxygen species associated with the electrochemical oxygen evolution by hydrodynamic scanning electrochemical microscopy. Electrochimica Acta 2018, 281, 494–501. 10.1016/j.electacta.2018.05.115. [DOI] [Google Scholar]
  54. Gao X.; Chen Y.; Sun T.; Huang J.; Zhang W.; Wang Q.; Cao R. Karst landform-featured monolithic electrode for water electrolysis in neutral media. Energy Environ. Sci. 2020, 13 (1), 174–182. 10.1039/C9EE02380A. [DOI] [Google Scholar]
  55. Ju M.; Cai R.; Ren J.; Chen J.; Qi L.; Long X.; Yang S. Conductive Polymer Intercalation Tunes Charge Transfer and Sorption–Desorption Properties of LDH Enabling Efficient Alkaline Water Oxidation. ACS Appl. Mater. Interfaces 2021, 13 (31), 37063–37070. 10.1021/acsami.1c08429. [DOI] [PubMed] [Google Scholar]
  56. Walsh D. A.; Fernández J. L.; Bard A. J. Rapid Screening of Bimetallic Electrocatalysts for Oxygen Reduction in Acidic Media by Scanning Electrochemical Microscopy. J. Electrochem. Soc. 2006, 153 (6), E99. 10.1149/1.2186208. [DOI] [Google Scholar]
  57. Lin C.-L.; Sánchez-Sánchez C. M.; Bard A. J. Methanol Tolerance of Pd–Co Oxygen Reduction Reaction Electrocatalysts Using Scanning Electrochemical Microscopy. Electrochem. Solid-State Lett. 2008, 11 (8), B136. 10.1149/1.2931020. [DOI] [Google Scholar]
  58. Li W.; Fan F.-R. F.; Bard A. J. The application of scanning electrochemical microscopy to the discovery of Pd–W electrocatalysts for the oxygen reduction reaction that demonstrate high activity, stability, and methanol tolerance. J. Solid State Electrochem. 2012, 16 (7), 2563–2568. 10.1007/s10008-012-1775-7. [DOI] [Google Scholar]
  59. Xin S.; Liu Z.; Ma L.; Sun Y.; Xiao C.; Li F.; Du Y. Visualization of the electrocatalytic activity of three-dimensional MoSe2@reduced graphene oxide hybrid nanostructures for oxygen reduction reaction. Nano Research 2016, 9 (12), 3795–3811. 10.1007/s12274-016-1249-9. [DOI] [Google Scholar]
  60. Zhang X.; Guo X.; Wang Q.; Zhang R.; Xu T.; Liang P.; Huang X. Iron-based clusters embedded in nitrogen doped activated carbon catalysts with superior cathodic activity in microbial fuel cells. Journal of Materials Chemistry A 2020, 8 (21), 10772–10778. 10.1039/C9TA10797E. [DOI] [Google Scholar]
  61. Sun T.; Zhang H.; Wang X.; Liu J.; Xiao C.; Nanayakkara S. U.; Blackburn J. L.; Mirkin M. V.; Miller E. M. Nanoscale mapping of hydrogen evolution on metallic and semiconducting MoS2 nanosheets. Nanoscale Horizons 2019, 4 (3), 619–624. 10.1039/C8NH00346G. [DOI] [Google Scholar]
  62. Wert S.; Iffelsberger C.; Novčić K. A.; Pumera M. Corrosion of catalyst in high resolution: Layered transition metal dichalcogenides electrocatalyse water splitting and corrode during the process. Journal of Catalysis 2022, 416, 85–91. 10.1016/j.jcat.2022.10.023. [DOI] [Google Scholar]
  63. Djire A.; Wang X.; Xiao C.; Nwamba O. C.; Mirkin M. V.; Neale N. R. Basal Plane Hydrogen Evolution Activity from Mixed Metal Nitride MXenes Measured by Scanning Electrochemical Microscopy. Adv. Funct. Mater. 2020, 30 (47), 2001136. 10.1002/adfm.202001136. [DOI] [Google Scholar]
  64. Niu H.-J.; Yan Y.; Jiang S.; Liu T.; Sun T.; Zhou W.; Guo L.; Li J. Interfaces Decrease the Alkaline Hydrogen-Evolution Kinetics Energy Barrier on NiCoP/Ti3C2Tx MXene. ACS Nano 2022, 16 (7), 11049–11058. 10.1021/acsnano.2c03711. [DOI] [PubMed] [Google Scholar]
  65. Weng Y.-C.; Hsieh C.-T. Scanning electrochemical microscopy characterization of bimetallic Pt–M (M=Pd, Ru, Ir) catalysts for hydrogen oxidation. Electrochimica Acta 2011, 56 (5), 1932–1940. 10.1016/j.electacta.2010.12.029. [DOI] [Google Scholar]
  66. Kim J.; Renault C.; Nioradze N.; Arroyo-Currás N.; Leonard K. C.; Bard A. J. Electrocatalytic Activity of Individual Pt Nanoparticles Studied by Nanoscale Scanning Electrochemical Microscopy. J. Am. Chem. Soc. 2016, 138 (27), 8560–8568. 10.1021/jacs.6b03980. [DOI] [PubMed] [Google Scholar]
  67. Wang Y.; Wipf D. O. Visualizing Hydrogen Oxidation Reaction Activity of Polycrystalline Platinum by Scanning Electrochemical Microscopy. J. Electrochem. Soc. 2020, 167 (14), 146502. 10.1149/1945-7111/abbf28. [DOI] [Google Scholar]
  68. Perales-Rondón J. V.; Solla-Gullón J.; Herrero E.; Sánchez-Sánchez C. M. Enhanced catalytic activity and stability for the electrooxidation of formic acid on lead modified shape controlled platinum nanoparticles. Applied Catalysis B: Environmental 2017, 201, 48–57. 10.1016/j.apcatb.2016.08.011. [DOI] [Google Scholar]
  69. Díaz-Real J. A.; Dubed-Bandomo G. C.; Galindo-de-la-Rosa J.; Ortiz-Ortega E.; Ledesma-García J.; Arriaga L. G. Evaluation of transferable TiO2 nanotube membranes as electrocatalyst support for methanol photoelectrooxidation. Applied Catalysis B: Environmental 2018, 222, 18–25. 10.1016/j.apcatb.2017.09.019. [DOI] [Google Scholar]
  70. Gupta D.; Chakraborty S.; Amorim R. G.; Ahuja R.; Nagaiah T. C. Local electrocatalytic activity of PtRu supported on nitrogen-doped carbon nanotubes towards methanol oxidation by scanning electrochemical microscopy. Journal of Materials Chemistry A 2021, 9 (37), 21291–21301. 10.1039/D1TA04962C. [DOI] [Google Scholar]
  71. Zhang B.; Zhang X.; Xiao X.; Shen Y. Photoelectrochemical Water Splitting System—A Study of Interfacial Charge Transfer with Scanning Electrochemical Microscopy. ACS Appl. Mater. Interfaces 2016, 8 (3), 1606–1614. 10.1021/acsami.5b07180. [DOI] [PubMed] [Google Scholar]
  72. Barman K.; Wang X.; Jia R.; Mirkin M. V. Mediated Charge Transfer at Nanoelectrodes: A New Approach to Electrochemical Reactivity Mapping and Nanosensing. J. Am. Chem. Soc. 2021, 143 (23), 8547–8551. 10.1021/jacs.1c02532. [DOI] [PubMed] [Google Scholar]
  73. Yuan D.; Xiao L.; Luo J.; Luo Y.; Meng Q.; Mao B.-W.; Zhan D. High-Throughput Screening and Optimization of Binary Quantum Dots Cosensitized Solar Cell. ACS Appl. Mater. Interfaces 2016, 8 (28), 18150–18156. 10.1021/acsami.6b06029. [DOI] [PubMed] [Google Scholar]
  74. Gao X.; He R.; Du J.; Zhou D.; Chen A.; Sun X. Recycling Solar Cells for Hydrogen Production Coupling Hydrazine Degradation with Entropy-Driven High-Chaos Nickel Molybdenum Phosphorus Sulfide Oxides. ACS Catal. 2022, 12 (22), 14387–14397. 10.1021/acscatal.2c04205. [DOI] [Google Scholar]
  75. Zhang B.; Yuan H.; Zhang X.; Huang D.; Li S.; Wang M.; Shen Y. Investigation of Regeneration Kinetics in Quantum-Dots-Sensitized Solar Cells with Scanning Electrochemical Microscopy. ACS Appl. Mater. Interfaces 2014, 6 (23), 20913–20918. 10.1021/am505569w. [DOI] [PubMed] [Google Scholar]
  76. Li P.; Jin Z.; Qian Y.; Fang Z.; Xiao D.; Yu G. Supramolecular confinement of single Cu atoms in hydrogel frameworks for oxygen reduction electrocatalysis with high atom utilization. Mater. Today 2020, 35, 78–86. 10.1016/j.mattod.2019.10.006. [DOI] [Google Scholar]
  77. Arrocha-Arcos A. A.; Cervantes-Alcalá R.; Huerta-Miranda G. A.; Miranda-Hernández M. Electrochemical reduction of Bicarbonate to Formate with Silver Nanoparticles and Silver Nanoclusters supported on Multiwalled Carbon Nanotubes. Electrochimica Acta 2017, 246, 1082–1087. 10.1016/j.electacta.2017.06.147. [DOI] [Google Scholar]
  78. Kisieliute A.; Popov A.; Apetrei R.-M.; Cârâc G.; Morkvenaite-Vilkonciene I.; Ramanaviciene A.; Ramanavicius A. Towards microbial biofuel cells: Improvement of charge transfer by self-modification of microoganisms with conducting polymer – Polypyrrole. Chemical Engineering Journal 2019, 356, 1014–1021. 10.1016/j.cej.2018.09.026. [DOI] [Google Scholar]
  79. Lin T.-E.; Bondarenko A.; Lesch A.; Pick H.; Cortés-Salazar F.; Girault H. H. Monitoring Tyrosinase Expression in Non-metastatic and Metastatic Melanoma Tissues by Scanning Electrochemical Microscopy. Angew. Chem., Int. Ed. 2016, 55 (11), 3813–3816. 10.1002/anie.201509397. [DOI] [PubMed] [Google Scholar]
  80. Boldt F.-M.; Heinze J.; Diez M.; Petersen J.; Börsch M. Real-Time pH Microscopy down to the Molecular Level by Combined Scanning Electrochemical Microscopy/Single-Molecule Fluorescence Spectroscopy. Analytical Chemistry 2004, 76 (13), 3473–3481. 10.1021/ac049635x. [DOI] [PubMed] [Google Scholar]
  81. Goines S.; Deng M.; Glasscott M. W.; Leung J. W. C.; Dick J. E. Enhancing scanning electrochemical microscopy’s potential to probe dynamic co-culture systems via hyperspectral assisted-imaging. Analyst 2022, 147 (11), 2396–2404. 10.1039/D2AN00319H. [DOI] [PMC free article] [PubMed] [Google Scholar]
  82. Kolagatla S.; Subramanian P.; Schechter A. Catalytic current mapping of oxygen reduction on isolated Pt particles by atomic force microscopy-scanning electrochemical microscopy. Applied Catalysis B: Environmental 2019, 256, 117843. 10.1016/j.apcatb.2019.117843. [DOI] [Google Scholar]
  83. Knittel P.; Mizaikoff B.; Kranz C. Simultaneous Nanomechanical and Electrochemical Mapping: Combining Peak Force Tapping Atomic Force Microscopy with Scanning Electrochemical Microscopy. Analytical Chemistry 2016, 88 (12), 6174–6178. 10.1021/acs.analchem.6b01086. [DOI] [PubMed] [Google Scholar]
  84. Shi X.; Qing W.; Marhaba T.; Zhang W. Atomic force microscopy - Scanning electrochemical microscopy (AFM-SECM) for nanoscale topographical and electrochemical characterization: Principles, applications and perspectives. Electrochimica Acta 2020, 332, 135472. 10.1016/j.electacta.2019.135472. [DOI] [Google Scholar]
  85. Morris C. A.; Chen C.-C.; Baker L. A. Transport of redox probes through single pores measured by scanning electrochemical-scanning ion conductance microscopy (SECM-SICM). Analyst 2012, 137 (13), 2933–2938. 10.1039/c2an16178h. [DOI] [PubMed] [Google Scholar]
  86. O’Connell M. A.; Lewis J. R.; Wain A. J. Electrochemical imaging of hydrogen peroxide generation at individual gold nanoparticles. Chem. Commun. 2015, 51 (51), 10314–10317. 10.1039/C5CC01640A. [DOI] [PubMed] [Google Scholar]
  87. Şen M.; Takahashi Y.; Matsumae Y.; Horiguchi Y.; Kumatani A.; Ino K.; Shiku H.; Matsue T. Improving the Electrochemical Imaging Sensitivity of Scanning Electrochemical Microscopy-Scanning Ion Conductance Microscopy by Using Electrochemical Pt Deposition. Analytical Chemistry 2015, 87 (6), 3484–3489. 10.1021/acs.analchem.5b00027. [DOI] [PubMed] [Google Scholar]

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