ac6b04093_si_002.pdf (2.92 MB)
Cyclic Voltammetry Probe Approach Curves with Alkali Amalgams at Mercury Sphere-Cap Scanning Electrochemical Microscopy Probes
journal contribution
posted on 2017-02-13, 00:00 authored by Zachary
J. Barton, Joaquín Rodríguez-LópezWe
report a method of precisely positioning a Hg-based ultramicroelectrode
(UME) for scanning electrochemical microscopy (SECM) investigations
of any substrate. Hg-based probes are capable of performing amalgamation
reactions with metal cations, which avoid unwanted side reactions
and positive feedback mechanisms that can prove problematic for traditional
probe positioning methods. However, prolonged collection of ions eventually
leads to saturation of the amalgam accompanied by irreversible loss
of Hg. In order to obtain negative feedback positioning control without
risking damage to the SECM probe, we implement cyclic voltammetry
probe approach surfaces (CV-PASs), consisting of CVs performed between
incremental motor movements. The amalgamation current, peak stripping
current, and integrated stripping charge extracted from a shared CV-PAS
give three distinct probe approach curves (CV-PACs), which can be
used to determine the tip–substrate gap to within 1% of the
probe radius. Using finite element simulations, we establish a new
protocol for fitting any CV-PAC and demonstrate its validity with
experimental results for sodium and potassium ions in propylene carbonate
by obtaining over 3 orders of magnitude greater accuracy and more
than 20-fold greater precision than existing methods. Considering
the timescales of diffusion and amalgam saturation, we also present
limiting conditions for obtaining and fitting CV-PAC data. The ion-specific
signals isolated in CV-PACs allow precise and accurate positioning
of Hg-based SECM probes over any sample and enable the deployment
of CV-PAS SECM as an analytical tool for traditionally challenging
conditions.
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Keywords
amalgamation reactionsHg-based ultramicroelectrodeCV-PAS SECMCV-PAC dataprobe radiusHg-based SECM probesCyclic Voltammetry Probe Approach CurvesSECM probepotassium ionsmetal cationsscanning electrochemical microscopymethodprobe approach curvesside reactionscyclic voltammetry probe approach surfaces3 ordersUMEHg-based probeselement simulationspropylene carbonateion-specific signalsAlkali Amalgamsfeedback mechanismsmotor movementsMercury Sphere-Cap Scanning Electrochemical Microscopy Probesamalgam saturation
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