Scanning Electrochemical Microscopy:  Approach Curves for Sphere-Cap Scanning Electrochemical Microscopy Tips

Abstract

In sampled-current voltammetry (SCV) current transients acquired after stepping the potential along the redox wave of interest are sampled at a fixed time to produce a sigmoidal current-potential curve akin to a pseudo steady state voltammogram. Repeating the sampling for different times yields a family of sampled-current voltammograms, one for each timescale. The concept has been used to describe the current-time-potential relationship at planar electrodes but rarely employed as an electroanalytical method except in normal pulse voltammetry where the chronoamperograms are sampled once to produce a single 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 58 59 60 2 diffusion at short times to hemispherical diffusion at long times. We also combine microdisk sampled-current voltammetry (MSCV) with a conditioning waveform to produce voltammograms where each data point is recorded with the same electrode history and demonstrate that the waveform is crucial to obtaining reliable sampled-current voltammograms below 100 ms. To facilitate qualitative analysis of the voltammograms we convert the current-potential data recorded at different timescales into a unique sigmoidal curve which clearly highlights kinetic complications. To quantitatively model the MSCVs we derive an analytical expression which accounts for diffusion regime and kinetic parameters.The procedure is validated with the reduction of Ru(NH 3 ) 6 3+ , a model one electron outer sphere process, and applied to the derivation of the kinetic parameters for the reduction of Fe 3+ on Pt microdisks. The methodology reported here is easily implemented on computer controlled electrochemical workstations as a new electroanalytical method to exploit the unique properties of microelectrodes, in particular at short times.

Analytical Expressions for Quantitative Scanning Electrochemical Microscopy (SECM)

“…[38], Table 1 gives A,B,C,D values for discrete values of H and R g = 10, and Table 2 gives parameters for discrete values of R g and H = 1.…”

“…In this study, as already described, a reasonably accurate analytical approximation of the current was proposed (see Figure 4 a). However the mathematical expression introduces a new notation, i k S , defined in Equation (38) [see Eq. (6 b) in ref.…”

“…Using Equation (38) to extract a so-called substrate current value may lead to quantitatively erroneous further studies (see for example Figure 5 in ref. [44]) since tip and substrate currents are equal.…”

Ex Situ Scanning Electrochemical Microscopy (SECM) Investigation of Bismuth‐ and Bismuth/Lead Alloy Film‐Modified Gold Electrodes in Alkaline Medium

“…The deposition was performed under potentiostatic conditions at À0.1 V against an Ag/AgCl reference electrode in a plating solution consisting of 5 mmol L À1 Hg 2 (NO 3 ) 2 in 1 mol L À1 KNO 3 acidified with nitric acid to pH < 1. The mercury microelectrode was characterised for voltammetric and SECM measurements as reported in refs [36,37].…”

In Situ Scanning Electrochemical Microscopy (SECM) Detection of Metal Dissolution during Zinc Corrosion by Means of Mercury Sphere‐Cap Microelectrode Tips

“…[41][42][43][44][45][46][47] Moreover, the functions to predict diffusioncontrolled steady-state currents [48] and approach curves at sphere-cap tips for both negative and positive feedback conditions are available. [49] Mercury sphere-cap microelectrodes can be fabricated onto microdisks of platinum by electrodeposition from mercury-ion solutions; the deposits adopt sphere-cap geometry. [36] Such protruding tips provide a larger electrode area than the basal disks onto which they are fabricated, yet they allow the sample surface to be approached more closely.…”