Simple Fabrication Method of Needle‐Type Carbon‐Disk Microelectrodes Using Conductive Thermoplastics

Chemical vapor deposition of pyrolytic carbon on carbon substrates: I: Effect of substrate surface characteristics on the kinetics of deposition

The scanning electrochemical microscope (SECM) is used to image the activity of enzymes immobilized on the surfaces of disk-shaped carbon-fiber electrodes. SECM was used to map the concentration of enzymatically produced hydroquinone or hydrogen peroxide at the surface of a 33-microm diameter disk-shaped carbon-fiber electrode modified by an immobilized glucose-oxidase layer. Sub-monolayer coverage of the enzyme at the electrode surface could be detected with micrometer resolution. The SECM was also employed as a surface modification tool to produce microscopic regions of enzyme activity by using a variety of methods. One method is a gold-masking process in which microscopic gold patterns act as mask for producing patterns of chemical modification. The gold masks allow operation in both a positive or negative process for patterning enzyme activity. A second method uses the direct mode of the SECM to produce covalently attached amine groups on the carbon surface. The amine groups are anchors for attachment of glucose oxidase by use of a biotin/avidin process. The effect of non-uniform enzyme activity was investigated by using the SECM tip to temporarily damage an immobilized enzyme surface. SECM imaging can observe the spatial extent and time-course of the enzyme recovery process.

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

The deposition of pyrolytic carbon in silica reactors

The infiltration of carbon fiber felts and composites by pyrolytic carbon deposition from propylene

Enhancing inward and outward mass transport during chemical vapor deposition of pyrolytic carbon for better synthesis of ZTC

Scanning electrochemical microscopy (SECM) is a powerful technique for mapping surface reactivity and investigating heterogeneous processes on the nanoscale. Despite significant advances in high-resolution SECM and photo-SECM imaging, they cannot provide atomic scale structural information about surfaces. By correlating the SECM images with atomic scale structural and bonding information obtained by transmission electron microscopy (TEM) techniques with one-to-one correspondence, one can elucidate the nature of the active sites and understand the origins of heterogeneous surface reactivity. To enable multitechnique imaging of the same nanoscale portion of the electrode surface, we develop a methodology for using a TEM finder grid as a conductive support in SECM and photo-SECM experiments. In this paper, we present the results of our first nanoscale SECM and photo-SECM experiments on carbon TEM grids, including imaging of semiconductor nanorods.

Double layer effects in voltammetric measurements with scanning electrochemical microscopy (SECM)

To understand the metal oxide coating effect on battery performance, the following two techniques are required: 1) constructing a flat thin-film electrode surface to realize a well-defined interface and 2) analyzing the electrode/electrolyte interface reaction with nanoscale resolution. We previously studied flat LiCoO2 thin-film electrodes using in situ surface-sensitive X-ray absorption spectroscopy (XAS) and reported that Co reduction at the LiCoO2 surface resulting from electrolyte contact caused the initial degradation. We also showed that the ZrO2 layer successfully prevented physical contact between LiCoO2 and the electrolyte. And it confirmed that a thicker ZrO2 layer (above 2 nm) increased the diffusion resistance of the lithium ions in the ZrO2 layer. However, since XAS lacks in-plane resolution and provides only averaged information, it is impossible to analyze the ZrO2 morphology in detail. Recently, Taguchi et al. investigated a thin Li-Zr-layer (ca. 2 nm) on a LiCoO2 composite electrode by transmission electron microscopy (TEM). They suggested that this thin layer could improve the durability. However, it is difficult to analyze the electrochemical properties using TEM. To evaluate the intrinsic mechanism of the metal oxide coating effect, it is necessary to develop a novel in-situ method that can analyze the surface morphology with high spatial resolution and simultaneously determine the local electrochemical properties. Scanning electrochemical microscopy (SECM) is a powerful technique for linking the surface morphology of a sample to its electrochemical properties. For the battery materials, the SECM feedback mode is effective in monitoring solid electrolyte interphase formation. To directly and quantitatively investigate spatially resolved ionic processes, mercury-capped platinum ultramicroelectrodes were developed and employed for Li+ imaging based on Li stripping. However, it is difficult to visualize the Li+ flux in battery materials at the sub-micrometer scale by SECM. Scanning electrochemical cell microscopy (SECCM), which uses a nanopipette as a probe and forms a local electrochemical cell, is effective in characterizing surface reactivity. We recently applied SECCM for visualization of electrochemical activities on a lithium-ion battery cathode material at sub-micrometer resolution. The SECCM was applied to collect or provide Li in specified area confined by the nanopipette. Further, it collection visualized the electrochemical properties by scanning the nanopipette as an image. There are some strong advantages in SECCM for battery material research such as its high spatial resolution, small capacitive current, and isolated electrochemical cell. In this report, we applied SECCM to characterize a ZrO2-coated LiCoO2 thin-film electrode prepared by pulsed laser deposition. Local cyclic voltammetry (CV) and galvanostatic charge/discharge were performed to characterize the cycle durability and rate performance of ZrO2-coated LiCoO2 thin-film electrodes and to reveal the relationship between the ZrO2 morphology and thickness.

The scanning electrochemical microscope (SECM) is used to form and characterize patterns of oxides on glassy carbon (GC) surfaces. Chemically specific imaging of oxides present on these surfaces was demonstrated by taking advantage of differential heterogeneous electron-transfer rates for the Fe(II/III) reaction occurring at unoxidized and oxidized GC electrodes. Localized generation of surface oxides was demonstrated using both the microreagent and direct modification modes of the SECM. The microreagent mode was used to perform a chemical oxidation of the surface by generating the strong oxidant Ag(II) at the ultramicroelectrode tip while positioned close to the carbon surface. However, this technique had poor reproducibility. Direct mode oxidation was much more versatile toward generating complex patterns of oxides on carbon surfaces. The reproducibility of the direct mode technique depended heavily on the solution resistance. “Charge dose” studies, followed by reaction-rate imaging, qualitatively show that the electron-transfer rate for the Fe(II/III) system scales with the amount of charge “injected” in each oxidation experiment, indicating a correlation between surface oxide density and electron-transfer rate. © 2003 The Electrochemical Society. All rights reserved.

Bubbles are ubiquitous in many natural phenomena and industry processes, particularly in the water electrolysis. Due to the development of gas evolving electrocatalysis and energy conversion technology, a deep understanding of gas bubble behaviors at the electrode surface is highly desirable. This review summarizes the recent methodology and process for the study of gas nanobubbles at the electrode surface. We first introduce the electrochemical measurement of gas bubbles using disk nanoelectrodes and scanning electrochemical cell microscopy, and analyze the dynamic equilibrium for their stability. We then discuss the visualization of gas bubble behaviors from electrogeneration using scanning electrochemical microscopy and optical microscopy. Finally, the main challenges and future research concerning are proposed.

The requirement to separate topographical effects from surface electrochemistry information is a major limitation of scanning electrochemical microscopy (SECM). With many applications of SECM involving the study of (semi)conducting electrode surfaces, the hybridisation of SECM with scanning tunnelling microscopy (STM) or a surface conductance probe would provide the ultimate topographical imaging capability to SECM, but previous attempts are limited. Here, the conversion of a general scanning electrochemical probe microscopy (SEPM) platform to facilitate contact electrical conductance (C)‐ and electron tunnelling (T)‐SECM measurements is considered. Measurements in air under ambient conditions with a Pt/Ir wire tip are used to assess the performance of the piezoelectric positioning system. A hopping‐mode imaging protocol is implemented, whereby the tip approaches the surface at each pixel until a desired current magnitude is exceeded, and the corresponding z position (surface height) is recorded at a set of predefined xy coordinates in the plane of the surface. At slow tip approach rates, the current shows an exponential dependence on tip‐substrate distance, as expected for electron tunnelling. For measurements in electrochemical environments, in order to overcome well‐known problems with leakage currents at coated‐wire tips used for electrochemical STM, Pt‐sensitised carbon nanoelectrodes are used as tips. The hydrogen evolution reaction on 2D Au nanocrystals serves as an exemplar system for the successful simultaneous mapping of topography and electrochemical activity.

Microelectrode-based hydrogen peroxide detection during oxygen reduction at Pt disk electrode

Permeable porous 1–3 nm thick overoxidized polypyrrole films on nanostructured carbon fiber microdisk electrodes

Pyrolytic carbon layers—an electron spin resonance analysis