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Probing Second Harmonic Components of pH‐Sensitive Redox Processes in a Mesoporous TiO 2 ‐Nafion Film Electrode with Fourier‐Transformed Large‐Amplitude Sinusoidally Modulated Voltammetry
Author(s) -
Milsom Elizabeth V.,
Bond Alan M.,
O'Mullane Anthony P.,
Elton Darrell,
Lee ChongYong,
Marken Frank
Publication year - 2009
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/elan.200804391
Subject(s) - cyclic voltammetry , nafion , materials science , electrode , redox , analytical chemistry (journal) , ferrocene , electron transfer , mesoporous material , voltammetry , capacitance , chemistry , inorganic chemistry , electrochemistry , organic chemistry , catalysis
Electrochemical processes in mesoporous TiO 2 ‐Nafion thin films deposited on indium tin oxide (ITO) electrodes are inherently complex and affected by capacitance, Ohmic iR ‐drop, RC ‐time constant phenomena, and by potential and pH‐dependent conductivity. In this study, large‐amplitude sinusoidally modulated voltammetry (LASMV) is employed to provide access to almost purely Faradaic‐based current data from second harmonic components, as well as capacitance and potential domain information from the fundamental harmonic for mesoporous TiO 2 ‐Nafion film electrodes. The LASMV response has been investigated with and without an immobilized one‐electron redox system, ferrocenylmethyltrimethylammonium + . Results clearly demonstrate that the electron transfer associated with the immobilized ferrocene derivative follows two independent pathways i) electron hopping within the Nafion network and ii) conduction through the TiO 2 backbone. The pH effect on the voltammetric response for the TiO 2 reduction pathway (ii) can be clearly identified in the 2 nd harmonic LASMV response with the diffusion controlled ferrocene response (i) acting as a pH independent reference. Application of second harmonic data derived from LASMV measurement, because of the minimal contribution from capacitance currents, may lead to reference‐free pH sensing with systems like that found for ferrocene derivatives.