Scanning Electrochemical Microscopy. 46. Shielding Effects on Reversible and Quasireversible Reactions

Abstract

An approximate theory for the feedback mode of the scanning electrochemical microscope (SECM) is developed to interpret the effects of substrate shielding on an ultramicroelectrode tip during a recording of iT versus d curves (approach curves) for reversible and quasireversible kinetics at a substrate surface. The resulting expressions for the tip current, iT, show a good fit to more accurate SECM simulations as well as to the experimental response of a reversible and quasireversible reaction. SECM shielding experiments thus give an interesting new insight into SECM approach curves over electrodes at different potentials, which suggest possible applications to measuring heterogeneous kinetics for fast reactions and diffusion coefficient determination.

Ordered Array Electrodes Fabricated by a Mask‐Assisted Electron‐Beam Method as Platforms for Studying Kinetic and Mass‐Transport Phenomena on Electrocatalysts

“…As the kinetics of FcMeOH oxidation is fast on most conductive materials, the behavior of the Au/Rh microstructured electrode is similar to that of continuous conductive RDE where Levich equation ( i L,RDE = A G Bω 1/2 ) is accomplished . This was verified by fitting the i L,RDE ( ω ) data with Levich equation (dashed line), resulting a slope of 5.4×10 −7 A rpm −1/2 , which leads to B =1.72×10 −5 A cm −2 rpm −1/2 , quite close to the expected value B ≅1.6×10 −5 A cm −2 rpm −1/2 calculated with parameters for the 1 mM FcMeOH solution . On the other hand, as PMMA is insulating, the response of the PMMA‐coated electrodes is sensitive to the microelectrode sizes and to f G .…”

“…[25] This was verified by fitting the i L,RDE (w) data with Levich equation (dashed line), resulting a slope of 5.4 10 À7 A rpm À 1 = 2 , which leads to B = 1.72 10 À5 A cm À2 rpm À 1 = 2 , quite close to the expected value Bffi1.6 10 À5 A cm À2 rpm À 1 = 2 calculated with parameters for the 1 mM FcMeOH solution. [26] On the other hand, as PMMA is insulating, the response of the PMMA-coated electrodes is sensitive to the microelectrode sizes and to f G . Moreover, by using a proper analytical model to correlate the i L,array (w) dependences, it should be possible to obtain the value of f G for the studied 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 electrode.…”

Rapid and Direct Determination of Diffusion Coefficients Using Microelectrode Arrays

“…The surface, or substrate, and the UME, or tip, are used as a generator and a collector electrode and typically biased so that opposing reactions are happening at each electrode. [34][35][36][37][38][39] SECM is typically used for surface imaging of electrode arrays and thin flim studies, which both make use of the fact that the tip can be moved and gives spatial data about the resistive Figure 2. Chronoamperometric transients for the ETOF experiment in ferricyanide: the ferricyanide reduction current at the generator (red curve and axis) and the ferrocyanide reoxidation current at the collector (blue curve and axis).…”

Analysis of the hydrogen electrode reaction mechanism in thin-layer cells. 1. Theory

“…(19). However, the analysis over the full potential range requires the modeling of the shielding of H + concentration due to consumption at the substrate at slightly negative g S values [31,32]. So far a first approximation could be done by calculating the diffusion limiting tip current (I T,L ) with Eq.…”