Issue 14, 2007

On the use of electrokinetic phenomena of the second kind for probing electrode kinetic properties of modified electron-conducting surfaces

Abstract

The electrokinetic features of electron-conducting substrates, as measured in a conventional thin-layer electrokinetic cell, strongly depend on the extent of bipolar faradaic depolarisation of the interface formed with the adjacent electrolytic solution. Streaming potential versus applied pressure data obtained for metallic substrates must generally be interpreted on the basis of a modified Helmholtz–Smoluchowski equation corrected by an electronic conduction term—non linear with respect to the lateral potential and applied pressure gradient—that stems from the bipolar electrodic behavior of the metallic surface. In the current study, streaming potential measurements have been performed in KNO3 solutions on porous plugs made of electron-conducting grains of pyrite (FeS2) covered by humic acids. For zero coverage, the extensive bipolar electronic conduction taking place in the plug—depolarized by concomitant and spatially distributed oxidation and reduction reactions of Fe2+ and Fe3+ species—leads to the complete extinction of the streaming potential over the entire range of applied pressure examined. For low to intermediate coverage, the local electron-transfer kinetics on the covered regions of the plug becomes more sluggish. The overall bipolar electronic conduction is then diminished which leads to an increase in the streaming potential with a non-linear dependence on the pressure. For significant coverage, a linear response is observed which basically reflects the interfacial double layer properties of the humics surface layer. A tractable, semi-analytical model is presented that reproduces the electrokinetic peculiarities of the complex and composite system FeS2/humics investigated. The study demonstrates that the streaming potential technique is a fast and valuable tool for establishing how well the electron transfer kinetics at a partially or completely depolarised bare electron-conducting substrate/electrolyte solution interface is either promoted (catalysis) or blocked (passivation) by the presence of a discontinuous surface layer.

Graphical abstract: On the use of electrokinetic phenomena of the second kind for probing electrode kinetic properties of modified electron-conducting surfaces

Article information

Article type
Paper
Submitted
29 Nov 2006
Accepted
30 Dec 2006
First published
19 Feb 2007

Phys. Chem. Chem. Phys., 2007,9, 1713-1729

On the use of electrokinetic phenomena of the second kind for probing electrode kinetic properties of modified electron-conducting surfaces

J. F. L. Duval, E. Sorrenti, Y. Waldvogel, T. Görner and P. De Donato, Phys. Chem. Chem. Phys., 2007, 9, 1713 DOI: 10.1039/B617422A

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