Nation film-modified electrode

H.S. White, J. Leddy and A. Bard, Polymer films on electrodes. 8. Investigation of charge-transfer mechanism in Nation polymer modified electrodes, J. Am. Chem. Soc., 1982, 104, 4811-4817 F.C. Anson, D.N. Blauch, J.-M. Saveant and C.-F. Shu, Ion association and electric field effects on electron hopping in redox polymers. Application to the Os(bpy)33+/2+ couple in Nafion, J. Am. Chem. Soc., 1991, 113, 1922-1932. 

To build an efficient, high-quality microscale fuel cell, microfabrication techniques need to be combined with appropriate materials such as Nation based membrane electrode assemblies (MEAs). These techniques must be able to produce three-dimensional structures, allow reactant and product flow into and out of the device, process appropriate materials, and should be of low cost. Fortimately, traditional thin film techniques can be modified for microscale fuel cell fabrication, while maintaining their advantages of surface preparation, sensor integration, and finishing or packaging. In addition, other techniques are also available and are discussed in the following sections. 

The intercalation of cobaltocene and its ions into a range of materials have been considered e.g. into Cd2P2S6. Cobaltocenium salts have been used as redox labels in Nation films. The photochemical properties of metallocene redox diodes has been reported. Several electrochemical investigations have been carried out on cobaltocenes or cobaltocene modified electrodes. Rigid rod paraphenylene acetylenes have been introduced into metallocenes for non linear optic use. The crystal structure of cobaltocene has been redetermined " and the crystal structure of cobaltocenium bis[(4,5-dimercapto-S4,S5)-l,3-dithiolate-2-thionato] nickelate has been reported. Finally, cobaltocenium metallacarboranide mixed-sandwich salts have been prepared. ... 

The GC/Nafion/Co-(5-N02)TRP modified electrodes were stable in water/ethanol solution and presented only a reversible Ru(III/II) pair of waves at 0.8 V versus Ag/AgCl in the -1.0 to 1.0 V range. However, an irreversible reduction wave, whose intensity is linearly dependent on sulfite concentration in the 0.4 to 70 mg/L range, appeared at Epc = -0.52 V, confirming that tetramthenated porphyrins continue to be electrocatalytic active for reduction processes. The detection and quantification limits were estimated as 0.4 and 1.2 mg/L, respectively. The electrolysis at -0.65 V for 6 h produced thiosulfate and not dithionite, the conventional reduction product in acidic media. The modified electrodes exhibited high stability, and 4.1 % was the RSD measured for 10 independent electrodes stored for 90 days in open air. Rotating disk voltammetry experiments showed a linear Koutecky-Levich plot and the electrocatalytic oxidation of sulfite was limited by electron diffusion through the film. In fact, because of the presence of Co-(5-N02)TRP dispersed in nonelectroactive Nation, several processes such as (a) the mass transfer at film and electrode surface, (b) the electron and substrate diffusion... 

Equation 3 indicates that for redox-polymer mediated reactions that comply with "SR kinetics, fast mediator-substrate cross-reaction rates (large ik) and poor substrate permeation through the polymer phase (low is) will tend to decrease the thickness of the reaction zone. Situations may thus arise in which only the outermost layers of mediator sites attached to the coating participate in the reaction with substrate. Such a surface process is observed for the oxidation of catechol at a carbon electrode modified with a Nation film containing Fe(bipy)3 + as mediator. The homogeneous solution rate constant for the oxidation of catechol by Fe(bipy)3 is estimated a to be 2 x 10 and is roughly 1000 times... 

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