Quantitative Feedback Referencing for Improved Kinetic Fitting of Scanning Electrochemical Microscopy Measurements

Abstract

Scanning electrochemical microscopy (SECM) has matured as a technique for studying local electrochemical processes. The feedback mode is most commonly used for extracting quantitative kinetic information. However, approaching individual regions of interest, as is commonly done, does not take full advantage of the spatial resolution that SECM has to offer. Moreover, fitting of experimental approach curves remains highly subjective due to the manner of estimating the tip-to-substrate distance. We address these issues using negative or positive feedback currents as a reference to calculate the tip-to-substrate distance directly for quantitative kinetic fitting of approach curves and line profiles. The method was first evaluated by fitting simulated data and then tested experimentally by resolving negative feedback and intermediate kinetics behavior in a spatially controlled fashion using (i) a flat, binary substrate composed of Au and SiO2 segments and (ii) a dual-mediator system for live-cell measurements. The methodology developed herein, named quantitative feedback referencing (QFR), improves fitting accuracy, removes fitting subjectivity, and avoids substrate–microelectrode contact.

Imaging Analysis of Scanning Electrochemical Microscopy in Energy Catalysis

“…Feedback mode is one of the most common operation modes of SECM, which is often used to study reaction kinetics and local imaging. − When a sufficient positive/negative potential is applied to the tip, the medium will be oxidized/reduced. When the tip is far away from the substrate, the tip current is not affected by the substrate and is the steady-state diffusion current i T,∞ , i normalT , ∞ = 4 n D F c a where n is the number of electron transfers of the electrode reaction, D is the diffusion coefficient of the medium, F is the Faraday constant (96485 A·s·mol –1 ), c is the bulk concentration of the medium, and a is the radius of the UME tip.…”

Effect of Redox Mediators on Corrosion Behavior and Scanning Electrochemical Microscopy Response

“…Electroactive regions that may play a role in local breakdown tend to present positive feedback behavior. Established analytical approximations can be used to relate the tip-to-substrate distance and the measured current to the RM’s kinetic rate constant at the substrate’s surface, where efforts have been made to ensure the accuracy of the fitting procedure . SECM in feedback mode has been used to estimate rate constants at distinctive features, detect surface heterogeneities, , and reveal passive film formation. , …”

“…Established analytical approxima- tions can be used to relate the tip-to-substrate distance and the measured current to the RM's kinetic rate constant at the substrate's surface, 26 where efforts have been made to ensure the accuracy of the fitting procedure. 27 SECM in feedback mode has been used to estimate rate constants at distinctive features, 28 detect surface heterogeneities, 29,30 and reveal passive film formation. 31,32 Despite their popularity in corrosion science, utilizing the analytical approximations for feedback mode has some fundamental assumptions that may be compromised when studying an actively corroding substrate.…”

Temperature Effect on the Electrochemical Current Response during Scanning Electrochemical Microscopy of Living Cells

“…Various research groups conducted nonbiological temperature-related studies using SECM, which demonstrates the importance of integrating temperature control units into SECM apparatus and understanding the effect of temperature on SECM sample resolution. − Researchers have also discussed the importance of convective heat transfer during SECM and how SECM data are influenced by temperature by using numerical modeling. ,− Other groups have proposed the use of hot-tip SECM , and hot-wire electrochemistry with SECM to perform temperature-dependent studies. Biological SECM studies for live cells have been conducted by numerous researchers at room/ambient temperature ,,− ,− as well as physiological temperature (37 °C), − whereby it is not always clear whether the temperature was monitored throughout an experiment or just at the beginning of the imaging procedure.…”