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This paper is concerned with long-distance interactions between an unbiased metal nanoparticle (NP) and a nanoelectrode employed as a tip in the scanning electrochemical microscope (SECM). A NP immobilized on the inert substrate acts as a bipolar electrode, producing positive SECM feedback. The tip current magnitude depends strongly on the ratio of the particle and tip radii and the heterogeneous charge-transfer kinetics. The onset of electron tunneling was observed at very short separation distances (<2–3 nm) at which the NP behaves as a part of the tip electrode. The rate constant of the electron-transfer (ET) or electrocatalytic reaction at the NP can be extracted from either feedback or tunneling current. The tunneling mode of SECM can be used to investigate heterogeneous reactions occurring at a single NP without making an ohmic contact with it. This technique can also help elucidate nanoparticle/electrode interactions in various electrochemical systems ranging from NPs immobilized on the electrode surface to nanoimpact collision events.
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Why Measure Particle-by-Particle Electrochemistry? A Tutorial and Perspective
Single-particle electrochemistry has become an important area of research with the potential to determine the rules of electrochemical reactivity at the nanoscale. These techniques involve addressing one entity at the time, as opposed to the conventional electrochemical experiment where a large number of molecules interact with an electrode surface. These experiments have been made feasible through the utilization of ultramicroelectrode (UMEs), i.e., electrodes with at least one dimension, e.g., diameter of 30 μm or less. This paper provides a theoretical and practical introduction to single entity electrochemistry (SEE), with emphasis on collision experiments between suspended NPs and UMEs to introduce concepts and techniques that are used in several SEE experimental modes. We discuss the intrinsically small currents, below 1 nA, that result from the electroactive area of single entities in the nanometer scale. Individual nanoparticles can be detected using the difference in electrochemical reactivity between a substrate and a nanoparticle (NP). These experiments show steady-state behavior of single NPs that result in discrete current changes or steps. Likewise, the NP can have transient interactions with the substrate electrode that result in current blips. We review the effect of diffusion, the main mass transport process that limits NP/electrode interactions. Also, we pointed out the implications of aggregation and tunneling in the experiments. Finally, we provid a perspective on the possible applications of single-element electrochemistry of electrocatalyst.
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- Award ID(s):
- 2108462
- PAR ID:
- 10494561
- Publisher / Repository:
- Mexican Chemical Society
- Date Published:
- Journal Name:
- Journal of the Mexican Chemical Society
- Volume:
- 67
- Issue:
- 4
- ISSN:
- 1870-249X
- Page Range / eLocation ID:
- 566 to 580
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Electrochemical experiments at individual nanoparticles (NPs) can provide new insights into their structure–activity relationships. By using small nanoelectrodes as tips in a scanning electrochemical microscope (SECM), we recently imaged individual surface‐bound 10–50 nm metal NPs. Herein, we introduce a new mode of SECM operation based on tunneling between the tip and a nanoparticle immobilized on the insulating surface. The obtained current vs. distance curves show the transition from the conventional feedback response to electron tunneling between the tip and the NP at separation distances of less than about 3 nm. In addition to high‐resolution imaging of the NP topography, the tunneling mode enables measurement of the heterogeneous kinetics at a single NP without making an ohmic contact with it. The developed method should be useful for studying the effects of nanoparticle size and geometry on electrocatalytic activity in real‐world applications.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.29356/jmcs.v67i4.2014
