Scanning electrochemical microscopy: using the potentiometric mode of SECM to study the mixed potential arising from two independent redox processes

M. Serrapede, G. Denuault, M. Sosna, G.L. Pesce, R.J. Ball

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Abstract

This study demonstrates how the potentiometric mode of the scanning electrochemical microscope (SECM) can be used to sensitively probe and alter the mixed potential due to two independent redox processes provided that the transport of one of the species involved is controlled by diffusion. This is illustrated with the discharge of hydrogen from nanostructured Pd hydride films deposited on the SECM tip. In deareated buffered solutions the open circuit potential of the PdH in equilibrium between its β and α phases (OCPβ∼a) does not depend on the tip-substrate distance while in aerated conditions it is found to be controlled by hindered diffusion of oxygen. Chronopotentiometric and amperometric measurements at several tip-substrate distances reveal how the flux of oxygen toward the Pd hydride film determines its potential. Linear sweep voltammetry shows that the polarization resistance increases when the tip approaches an inert substrate. The SECM methodology also demonstrates how dissolved oxygen affects the rate of hydrogen extraction from the Pd lattice. Over a wide potential window, the highly reactive nanostructure promotes the reduction of oxygen which rapidly discharges hydrogen from the PdH. The flux of oxygen toward the tip can be adjusted via hindered diffusion. Approaching the substrate decreases the flux of oxygen, lengthens the hydrogen discharge, and shifts OCPβ∼a negatively. The results are consistent with a mixed potential due to the rate of oxygen reduction balancing that of the hydride oxidation. The methodology is generic and applicable to other mixed potential processes in corrosion or catalysis.

LanguageEnglish
Pages8341-8346
Number of pages6
JournalAnalytical Chemistry
Volume85
Issue number17
Early online date6 Aug 2013
DOIs
StatusPublished - 2013

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Microscopic examination
Microscopes
Oxygen
Scanning
Hydrogen
Hydrides
Substrates
Fluxes
Dissolved oxygen
Voltammetry
Catalysis
Oxidation-Reduction
Nanostructures
Polarization
Corrosion
Oxidation
Networks (circuits)

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Scanning electrochemical microscopy : using the potentiometric mode of SECM to study the mixed potential arising from two independent redox processes. / Serrapede, M.; Denuault, G.; Sosna, M.; Pesce, G.L.; Ball, R.J.

In: Analytical Chemistry, Vol. 85, No. 17, 2013, p. 8341-8346.

Research output: Contribution to journalArticle

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