title: Impact of Adsorption on Scanning Electrochemical Microscopy Voltammetry and Implications for Nanogap Measurements.
abstract: Scanning electrochemical microscopy (SECM) is a powerful tool that enables quantitative measurements of fast electron transfer (ET) kinetics when coupled with modeling predictions from finite-element simulations. However, the advent of nanoscale and nanogap electrode geometries that have an intrinsically high surface area-to-solution volume ratio realizes the need for more rigorous data analysis procedures, as surface effects such as adsorption may play an important role. The oxidation of ferrocenylmethyl trimethylammonium (FcTMA(+)) at highly oriented pyrolytic graphite (HOPG) is used as a model system to demonstrate the effects of reversible reactant adsorption on the SECM response. Furthermore, the adsorption of FcTMA(2+) species onto glass, which is often used to encapsulate ultramicroelectrodes employed in SECM, is also found to be important and affects the voltammetric tip response in a nanogap geometry. If a researcher is unaware of such effects (which may not be readily apparent in slow to moderate scan voltammetry) and analyzes SECM data assuming simple ET kinetics at the substrate and an inert insulator support around the tip, the result is the incorrect assignment of tip-substrate heights, kinetics, and thermodynamic parameters. Thus, SECM kinetic measurements, particularly in a nanogap configuration where the ET kinetics are often very fast (only just distinguishable from reversible), require that such effects are fully characterized. This is possible by expanding the number of experimental variables, including the voltammetric scan rate and concentration of redox species, among others.
authors.affiliation: Department of Chemistry, University of Warwick , Coventry, West Midlands CV4 7AL, United Kingdom.|School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
authors.forename: Sze-yin
authors.initials: SY
authors.lastname: Tan
authors.affiliation: School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.affiliation: School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
authors.forename: Alan M
authors.initials: AM
authors.lastname: Bond
authors.affiliation: Department of Chemistry, University of Warwick , Coventry, West Midlands CV4 7AL, United Kingdom.
authors.forename: Julie V
authors.initials: JV
authors.lastname: Macpherson
authors.affiliation: Department of Chemistry, University of Warwick , Coventry, West Midlands CV4 7AL, United Kingdom.
authors.forename: Patrick R
authors.initials: PR
authors.lastname: Unwin