Scanning Electrochemical Microscopy. 60. Quantitative Calibration of the SECM Substrate Generation/Tip Collection Mode and Its Use for the Study of the Oxygen Reduction Mechanism
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- 作者：Carlos M. Sá ; nchez-Sá ; nchez ; Joaquí ; n Rodrí ; guez-Ló ; pez ; Allen J. Bard
- 刊名：Analytical Chemistry
- 出版年：2008
- 出版时间：May 1, 2008
- 年：2008
- 卷：80
- 期：9
- 页码：3254 - 3260
- 全文大小：262K
- 年卷期：v.80,no.9(May 1, 2008)
- ISSN：1520-6882
文摘
The substrate generation/tip collection (SG/TC) mode ofscanning electrochemical microscopy (SECM) coupledwith linear voltammetry is proposed as a way to quantifyreaction intermediates generated in the solution at smallsubstrates (100 
m diameter). The collection efficiency(CE) for SG/TC mode depends on the collector tip radius(a), the tip/substrate distance (d), and the size of theinsulating glass sheath surrounding the collector tip (RG).In this work, we present experimental and simulatedcalibration CE values for different SG/TC geometries.Results of digital simulations in axial 2-D symmetry withthe tip approaching a planar substrate are shown and fitexperimental results obtained using ferrocenemethanolas a redox mediator very well. This model assumes thatthe mediator reacts under stationary-state conditions andundergoes diffusion-controlled electron transfer withoutany heterogeneous or homogeneous kinetic complications. Empirical equations for all SG/TC geometriesreported here are provided as a convenient way to predictthe maximum CE value for any given distance within thecalibration range. Hydrogen peroxide quantification during the oxygen reduction reaction (ORR) at a Hg on Auelectrode in acid pH was carried out using the SG/TCmode of SECM to demonstrate the utility of this techniquein determining the number of electrons transferred (n)in the ORR. The results (n = 2.12-2.19) clearly pointout the predominance of the two-electron pathway overthe four-electron pathway when ORR takes place at thiselectrode material. Therefore, this work presents a powerful alternative to the rotating ring-disk electrode (RRDE)as means of obtaining mechanistic information by calculating the number of electrons transferred during anelectrochemical reaction.
m diameter). The collection efficiency(CE) for SG/TC mode depends on the collector tip radius(a), the tip/substrate distance (d), and the size of theinsulating glass sheath surrounding the collector tip (RG).In this work, we present experimental and simulatedcalibration CE values for different SG/TC geometries.Results of digital simulations in axial 2-D symmetry withthe tip approaching a planar substrate are shown and fitexperimental results obtained using ferrocenemethanolas a redox mediator very well. This model assumes thatthe mediator reacts under stationary-state conditions andundergoes diffusion-controlled electron transfer withoutany heterogeneous or homogeneous kinetic complications. Empirical equations for all SG/TC geometriesreported here are provided as a convenient way to predictthe maximum CE value for any given distance within thecalibration range. Hydrogen peroxide quantification during the oxygen reduction reaction (ORR) at a Hg on Auelectrode in acid pH was carried out using the SG/TCmode of SECM to demonstrate the utility of this techniquein determining the number of electrons transferred (n)in the ORR. The results (n = 2.12-2.19) clearly pointout the predominance of the two-electron pathway overthe four-electron pathway when ORR takes place at thiselectrode material. Therefore, this work presents a powerful alternative to the rotating ring-disk electrode (RRDE)as means of obtaining mechanistic information by calculating the number of electrons transferred during anelectrochemical reaction.