Analytical Expressions for Quantitative Scanning Electrochemical Microscopy (SECM)

Abstract

Scanning electrochemical microscopy (SECM), is a recent analytical technique in electrochemistry, which was developed in the 1990s and uses microelectrodes to probe various surfaces. Even with the well-known disc microelectrodes, the system geometry is not as simple as in regular electrochemistry. As a consequence even the simplest experiments, the so-called positive and negative feedback approach curves, cannot be described with exact analytical expressions. This review gathers all the analytical expressions available in the SECM literature in steady-state feedback experiments. Some of them are claimed as general expressions, other are presented as approximate. Their validity is discussed in the light of the current understanding and computer facilities.

Topographical and electrochemical nanoscale imaging of living cells using voltage-switching mode scanning electrochemical microscopy

“…1B) were used to produce theoretical approach curves for the same tip geometric parameters. The current profiles were fitted to established theoretical curves for a simple disk geometry (30)(31)(32). Good correlation was observed between theory and experiment.…”

“…The set point was typically in the range 75-90% of the reference current, I REF , which was the steady-state current measured in bulk solution. The corresponding tip/substrate distance could then be estimated by reference to theoretical approach curves for the characteristic electrode (30)(31)(32). The probe position was controlled by a XY and Z piezoelectric translation stage (Physik Instrumente, 621.2CL and 621.ZCL), using an amplifier module (Physik Instrumente, E-503.00).…”

The role of titanium in the initiation of localized corrosion of stainless steel 444

“…30 The PAC measurements were repeated over different inclusions and passivated areas to obtain a standard deviation and associated error of local reactivity across the SS 444 (SI Figure S12). Analytical approximations have been developed and are frequently used to extract the local heterogeneous rate constant from a PAC, 31 but the majority of these assume a uniformly reacting substrate. 2D-axisymmetric finite element simulations have previously been employed to study conductive inclusions in otherwise insulating substrates for Al and Ti alloys, 32,33 but the high symmetry requirements make these entirely unsuitable for highly heterogeneous systems such as those here presented.…”

Probing Passivating Porous Films by Scanning Electrochemical Microscopy

“…In pure negative feedback, the current reduces to zero, whereas in pure positive feedback the current rises to infinity, when the electrode is short-circuited to the substrate provided the electrode surface is parallel to the substrate. This can be largely reproduced by analytical approximations, which were reviewed in detail by Lefrou and Cornut in 2010. 18 For comparability of currents between different microelectrodes, these mathematical expressions use tip currents (Ni T ) normalized to the steady state current in the bulk electrolyte with distances (L) and glass sheath radii (R g ) normalized to radius of the electroactive area of the microelectrode.…”

“…This can be largely reproduced by analytical approximations, which were reviewed in detail by Lefrou and Cornut in 2010. 18 For comparability of currents between different microelectrodes, these mathematical expressions use tip currents (Ni T ) normalized to the steady state current in the bulk electrolyte with distances (L) and glass sheath radii (R g ) normalized to radius of the electroactive area of the microelectrode. Normalized substrate rate constants (κ) are calculated by multiplying the substrate rate constant by the radius of the electroactive area and dividing by the diffusion coefficient of the redox mediator.…”