One of the greatest limitations in electrochemical collision/ nanoimpact methods is the inability to quantify the size of colliding species due to the uneven current distribution on a disk ultramicroelectrode UME (so-called edge effect). This phenomenon arises since radial diffusion is greater at the edge than the center of the active electrode surface. One method of solving this problem is fabrication of a hemispherical UME. We describe the fabrication of a hemispherical Hg UME on a disk UME by a solution-based electrochemical method, chronocoulometry. The use of hemispherical Hg UME to detect collisions of individual amine-functionalized polystyrene beads removes the "edge effect" and enables simultaneous measurements of the concentration and the size distribution of colloids in suspension. Using finite element simulations, we deduce a quantitative relation between the distribution of current step size and the size distribution of the bead. The frequency of collision measured for a given size of bead is then converted into a concentration (in mol/L) by a quantification of the relative contributions of migration and diffusion for each size of bead. Under our experimental conditions (low concentration of supporting electrolyte), migration dominates the flux of bead. The average size of polystyrene beads of 0.5 and 1 μm radius obtained by electrochemistry and scanning electron microscopy (SEM) differs by only −8% and −9%, respectively. The total concentration of polystyrene beads of 0.5 and 1 μm radius obtained by electrochemistry is found in close agreement (<10% of error) with their nominal concentrations (25 and 100 fM).

 Electrochemical blocking is sensitive enough to sense individual proteins.  Single entity electrochemistry may be used to detect sub-attomolar concentrations of particles.  The size of spherical particles can be estimated within about 10% of error by electrochemical blocking.

Aqueous zinc-ion batteries (ZIBs) have attracted considerable attention because of their low cost, high intrinsic safety, and high volumetric capacity. However, unexpected dendrite growth and side reactions that arise at the Zn anode can severely hinder the mass adoption of ZIBs in practical applications. Herein, we report a dendrite-free ZIB anode via the hybridization of a eutectic ZnAl alloy with a copper mesh (denoted as ZnAl@Cu-mesh). The eutectic structure of the ZnAl alloy is composed of alternating Zn blocks and Al nanoflakes. The Al nanoflakes sacrificially consume the oxygen in the electrolyte to form an Al 2 O 3 /Al shell−core structure, which in turn guides the Zn deposition process by restraining the lateral diffusion of zinc ions and hence reducing the extent of dendrite formation. This process can synergistically reduce the likelihood of Zn passivation, which allows the Zn region to remain electrochemically active for the Zn stripping/plating process. Meanwhile, a copper mesh is used as a scaffold to provide uniform electric field distribution.

Nanoparticles interact with a variety of interfaces, from cell walls for medicinal applications to conductive interfaces for energy storage and conversion applications. Unfortunately, quantifying dynamic changes of nanoparticles near interfaces is difficult. While optical techniques exist to study nanoparticle dynamics, motions smaller than the diffraction limit cannot be quantified. Single entity electrochemistry has high sensitivity, but the technique suffers from ambiguity in the entity's size, morphology, and collision location. Here, we combine optical microscopy, single entity electrochemistry, and numerical simulations to elucidate the dynamic motion of graphene nanoplatelets at a gold ultramicroelectrode (radius ~ 5 m). The approach of conductive graphene nanoplatelets, suspended in 10 M NaOH, to an ultramicroelectrode surface was tracked optically during the continuous oxidation of ferrocenemethanol. Optical microscopy confirmed the nanoplatelet size, morphology, and collision location on the ultramicroelectrode. Nanoplatelets collided on the ultramicroelectrode at an angle, θ, enhancing the electroactive area, resulting in a sharp increase in current. After the collision, the nanoplatelets reoriented to lay flat on the electrode surface, which manifested as a return to the base-line current in the amperometric i-t response. Here, we report the coupled optoelectrochemical observation of single graphene nanoplatelet collision events under amperometric conditions. Through correlated Multiphysics simulations, the dynamics of these collision events and subsequent reorientation processes can be extracted to reveal angular velocity on the order of 0.5 to 2 °/ms. This simulation driven approach can be extended to a wide range of asymmetric single entities including nanorods, planar nanoflakes, and nanoparticle clusters for robust and unambiguous determination of collision dynamics on electrified interfaces one entity at a time.

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Contact-less interactions of micro/nano-particles near electrochemically or chemically active interfaces are ubiquitous in chemistry and biochemistry. Forces arising from a convective field, an electric field or chemical gradients act on...