Nafion-coated electrodes

NADH, 121, 122, 180 Nafion coating, 118, 123, 124, 126 Nanometer electrodes, 116, 128 Nernst equation, 3, 15, 80 Nernstian behavior, 143 Nernst Planck equation, 5 Neuronal sensors, 188 Neurotransmitters, 40, 116, 124 Neutral carrier electrodes, 154 Nickel, 123... 

J. Hayon, D. Ozer, J. Rishpon, and A. Bettelheim, Spectroscopic and electrochemical response to nitrogen monoxide of a cationic iron porphyrin immobilized in nafion-coated electrodes or membranes. J. Chem. Soc.-Chem. Commun. 619-620 (1994). 

E.V. Gogol, G.A. Evtugyn, J.L. Marty, H.C. Budnikov, and V.G. Winter, Amperometric biosensors based on Nafion coated screen-printed electrodes for the determination of cholinesterase inhibitors. Talanta 53, 379-389 (2000). 

Application of a divided cell containing one pair of electrodes (Pt-coated Ti anode 316 type stainless steel cathode) with an effective area of 100 cm2. Nafion-324 was used as the membrane. Two 81 tanks contained anolyte (feed) and catholyte (caustic). A coil-type heat exchanger was used to maintain the heat... 

Another study compared the bulk gold electrode to Nafion coated gold electrodes using RRDE in 0.5 M H2S04. There were no significant differences observed in the reaction pathway or kinetics of ORR on the electrodes.213... 

Because Nafion film can preconcentrate organic cations at a substrate electrode surface, Nafion-coated electrodes can be used as sensitive and selective sensors for electroactive organic cations. The film-entrapped ion is then either oxidized or reduced and the resulting current is recorded and related to the concentration of ions in the aqueous solution (qualitatively similar to anodic stripping voltammetry). It was shown that ion-exchange voltammetric determination of the dication methyl viologen at a Nafion-film-coated electrode results in an improvement of three orders of magnitude in detection limit relative to an uncoated electrode.46... 

An improved adsorption of DNA bases has been observed at a chemically modified electrode based on a Nafion/ruthenium oxide pyrochlore (Pb2Ru2-x FhxOj-y modified GC (CME). Nafion is a polyanionic perfiuorosulfonated ionomer with selective permeability due to accumulation of large hydrophobic cations rather than small hydrophilic ones. The Nafion coating was demonstrated to improve the accumulation of DNA bases, while the ruthenium oxide pyrochlore proved to have electrocatalytic effects towards the oxidation of G and A. The inherent catalytic activity of the CME results from the Nafion-bound oxide surface being hydrated. The catalytically active centers are the hydrated surface-boimd oxy-metal groups which act as binding centers for substrates [50]. 

A. J. Cunningham and J. B. Justice, Jr., Approaches to Voltammetric and Chromatographic Monitoring of Neurochemicals in Vivo, J. Chem. Ed. 1987, 64, A34. Another Nafion-coated electrode can detect 10 10 mol of the neurotransmitter nitric oxide within a single cell [T. Malinski and Z. Taha, Nitric Oxide Release from a Single Cell Measured in Situ by a Porphyrinic-Based Microsensor, Nature 1992, 358, 676]. 

The potential danger associated with mercury has led to the development of other strategies that avoid the use of a mercury solution. These strategies use glassy carbon electrodes (GCE) coated with a mercury film modified with Nafion [3,4], cellulose acetate [5], naphthol derivative [6], etc., where mercury is generated in situ and this way avoiding the manipulation of mercury solutions as done previously. Composite electrode containing HgO as a built-in mercury precursor, which supply mercury-film formation, has even been reported to avoid the use of mercury solution [7]. 

Capelo, S., Mota, A.M. and Gongalves, M.L.S. (1995) Complexation of lead with humic matter by stripping voltammetry. Prevention of adsorption with Nafion-coated mercury film electrode. Electroanalysis, 7, 563-568. 

Gerhardt GA, Oke AF, Nagy G, Moghaddam B, Adams RN (1984) Nafion-coated electrodes with high selectivity for CNS electrochemistry. Brain Res 290(2) 390-395. 

Nafion film coated on an ITO electrode to understand the structural transformations of the dimer in the Nafion coating during the catalytic water oxidation process . The absorption spectral changes observed during the oxidation scan from 0.4 to 1.4 V (s. SCE) (Fig. lOA) showed a decrease in the absorbance at 655 nm with simultaneous increase in the absorbance at around 450 nm with clear isosbestic points at 430 and 545 nm. In the reductive scan from 1.4 to 0.4 V (vs. SCE) (Fig. lOB), the absorbance at 655 nm increased and a simultaneous decrease in the absorbance at 450 nm was observed with an isosbestic point at 555 nm. The absorbance at 655 nm was almost recovered back. Initially the oxidation of the dimer complex H20-Ru" -Ru "-0H2 leads to the formation of H20-Ru "-Ru -0H2 with an absorption maximum at around 450 nm and further oxidation at higher positive potentials must lead to Ru -Ru formation in a successive oxidation process. The Ru -Ru would be rapidly reduced by water molecules to produce H20-Ru -Ru -0H2 at pH 1. The same in situ spectrocyclic voltammetry experiments at pH 9.3 showed an absorption maximum at around 500 nm with the formation of H20-Ru" -Ru -OH in the Nafion film. In relevant to the absorbances at 450... 

However, Nafion-modified electrodes also exhibited several disadvantages. For example, the response time of the Nafion-coated sensors increases due to a reduced diffusion coefficient value in the film [7], This can pose a serious disadvantage for in vivo work where dopamine and other neurotransmitter releases often occur on a sub-second time scale. In addition, Nafion coatings perform well for applications such as stripping analysis, but their use for direct voltammetric analysis is complicated by slow equilibration of the film with solution species [5 7], Therefore, there is a need for a modification system that can allow for rapid and selective permeation of the ions of interest. 

Taylor et al.8 were the first to report an electrochemical method for preparation of MEAs for PEMFCs. In their technique, Pt was electrochemically reduced and deposited at the electrode membrane interface, where it was actually utilized as an electrocatalyst. Nation, which is an ion exchange polymer membrane, is first coated on a noncatalyzed carbon support. The Nafion-coated carbon support is then immersed into a commercial acidic Pt plating solution for electrodeposition. Application of a cathodic potential results in diffusion of platinum cations through the active Nation layer. The migrated platinum species are reduced and form Pt particle at the electrode/membrane interface only on the sites which are both electronically and ionically conductive. The deposition of Pt particles merely at the electrode/membrane interface maximizes the Pt utilization. The Pt particles of 2-3.5 nm and a Pt loading of less than 0.05 mg cm-2 were obtained employing this technique.8 The limitation of this method is the difficulty of the diffusion of platinum... 

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