Electrochemistry at One Nanoparticle

Abstract

Electrochemistry at metal nanoparticles (NPs) is of significant current interest because of its applications in catalysis, energy conversion and storage, and sensors. The electrocatalytic activity of NPs depends strongly on their size, shape, and surface attachment. The use of a large number of particles in most reported kinetic experiments obscured the effects of these factors because of polydispersity and different NP orientations. Recent efforts to probe electrochemistry at single NPs included recording of the catalytically amplified current produced by random collisions of particles with the electrode surface, immobilizing an NP on the surface of a small electrode, and delivering individual NPs to electrode surfaces. Although the signals recorded in such experiments were produced by single NPs, the characterization issues and problems with separating an individual particle from other NPs present in the system made it difficult to obtain spatially and/or temporally resolved information about heterogeneous processes occurring at a specific NP. To carry out electrochemical experiments involving only one NP and characterize such an NP in situ, one needs nanoelectrochemical tools with the characteristic dimension smaller than or comparable to those of the particle of interest. This Account presents fundamentals of two complementary approaches to studying NP electrochemistry, i.e., probing single immobilized NPs with the tip of a scanning electrochemical microscope (SECM) and monitoring the collisions between one catalytic NP and a carbon nanopipette. The former technique can provide spatially resolved information about NP geometry and measure its electron transfer properties and catalytic activity under steady-state conditions. The emphasis here is on the extraction of quantitative physicochemical information from nanoelectrochemical data. By employing a polished disk-type nanoelectrode as an SECM tip, one can characterize a specific nanoparticle in situ and then use the same NP for kinetic experiments. A new mode of SECM operation based on tunneling between the tip and nanoparticle can be used to image the NP topography with a lateral resolution of ∼1 nm. An alternative approach employs carbon nanoprobes produced by chemical vapor deposition of carbon into quartz nanopipettes. One metal NP is captured inside the carbon nanocavity to probe the dynamics of its interactions with the electrode surface on the microsecond time scale. The use of high-resolution transmission electron microscopy is essential for interpreting the results of single-NP collision experiments. A brief discussion of the nanoelectrochemical methodology, recent advances, and future directions is included.

Advanced electroanalytical chemistry at nanoelectrodes

“…26–29 For the third approach, metallic layers are deposited onto the nanoporous polymeric membrane or nanopipette to fabricate the nanoelectrode. 5,15,18,30–34 For example, a carbon nanoelectrode was fabricated by pyrolysis of a carbon source, such as methane, acetylene, and butane, inside capillaries. 35–37 Recently, chemical vapour deposition was used to facilitate the deposition of carbon inside the nanopipette (Fig.…”

“…1 Moreover, the smaller RC ( R = resistance; C = capacitance) time constant ( τ ) of nanoelectrodes ensures their ability to study transient electrochemical reactions. 4 Because of their advantages, nanoelectrodes have been widely applied in the characterization of single nanoparticles/molecules, 5,6 the construction of ultrasensitive and non-invasive electrochemical probes for the detection of a single living cell within its natural environment, 7 and incorporated with scanning electrochemical probe techniques to acquire highly resolved electrochemical imaging. 8,9 …”

Monitoring Simultaneous Electrochemical Reactions with Single Particle Imaging

“…[10] Recently, we showed how nanoscale heterogeneity of surface oxide layers impacts the kinetics and morphology of single Ag NPs during electrodissolution using dark-field microscopy. [11][12][13] Several other groups have also studied the oxidation of single Ag NPs using electrochemical, optical, and correlated electrochemical-optical methods . [11][12][13] Several other groups have also studied the oxidation of single Ag NPs using electrochemical, optical, and correlated electrochemical-optical methods .…”

Counting and Sizing of Single Vesicles/Liposomes by Electrochemical Events

“…Several excellent reviews have summarized the recent progress on single-entity analysis by using electrochemical techniques, [14][15][16][17][18][19][20][21][22][23] mainly focusing on strategies and methodologies for single-entity analysis, especially for hard particles. First, electrochemical experiments are conducted in solution, even in solutions with high salt concentrations, which can largely maintain the structures and properties of vesicles as in biological systems.…”