Conducting polymer layers

A more favourable approach is the incorporation of the active species in an electrically conducting polymer layer which then acts as an (electrical) intermediate between the electrode surface and the catalyst. Polypyrrole is considered to be especially suitable because it is acceptably stable under ambient conditions (2), has a high conductivity and can be easily prepared electrochemically from a great variety of solvent systems, including aqueous solutions (3-5). The catalytic species that have been applied in such polypyrrole-based systems comprise metal particles (6-9), metal chelates (10-13) (with anionic side groups) and enzymes (14-18). 

Polymer film electrodes are prepared either by evaporation technique or by -> electropolymerization. Redox polymers that are usually synthesized chemically are dissolved in a suitable solvent, placed as a droplet on the surface of a metal (or dip-coating, spin-coating techniques are applied) and the solvent is subsequently left to evaporate. The electrode can be used in other solvents in which the polymer is insoluble. Conducting polymer layers are usually developed by electropolymerization directly on the surface of the metal. 

UV-Vis spectra of a conducting polymer layer of poly(2-propylaniline) deposited on a gold-sputtered glass slide OTE, Esce = -300 to+600 mV (first to last trace)... 

Schuhmann, W. (1995) Electron-transfer pathways in amperometric biosensors -ferrocene-modified enzymes entrapped in conducting-polymer layers. Biosensors ef Bioelectronics, 10 (1-2), 181-193. 

As mentioned previously a hybridization of an insulating PED film and a conductive polymer layer is quite attractive when they are applied to an electric device. In this case a hybridized multi-layered structure is expected to be fabricated, and the throwing power of the PED film can conveniently be utilized for this purpose. Additionally the photoelectrochemical area-selective doping and/or undoping of a polypyrrole film as dascrivec. earlier in this section encourage us to pursue this objective. The key problem in the fabrication of a hybridized multi-layered structure is hov to control the deposition of a PED overcoat onto polypyrrole layer and. vice versa. Figure 5 shows... 

The immobilization of an active species into a conducting polymer layer allows one to obtain active electrodes for the reduction of various organic halides. Polypyrrole containing viologen electrodes appear to be active for the reduction of alkyl dibromide [177] or hexachloroacetone [178], Cobalt-bipyridyl-polypyrrole films are active electrodes for the reduction of alkyl chloride [107], The mechanism of this reaction is similar to that observed in the homogeneous phase. This confinns one of the major interests of the modified conductive polymer electrodes, i,e. the possibility of performing catalytic reactions with smaller amounts of active catalyst in comparison to homogeneous catalysis, and then to avoid problems related to the separation of products from the solution which contains this catalyst. 

Figure 7.6 Spatial distribution of metallic particles electrodeposited in CPs. (Adapted with permission from V. Tsakova, How to affect number, size and location of metal particles deposited In conducting polymer layers, J. Solid State Electrochem., 12, 1421-1434 (2008). Copyright (2008) Springer)...

With PPy as the substrate, Yan ef al. noticed interesting GMR behavior with a value of 4% in cobalt and copper multilayers, as shown in Figure 12.14 [65]. The copper layer serves as a spacer for cobalt layers, similar to a conventional metal electrode system. However, there is no report regarding conductive polymer layers as ferromagnetic layer spacers. The reported value is lower than that of the pure metal system. There were three proposed reasons for the difference the quality of the cobalt layer (with more copper in the ferromagnetic cobalt layers with a PPy substrate) the roughness of the PPy thin film (rougher compared than conventional metal) and the low conductivity of the PPy film used. 

Adsorption of small redox-active molecules (e.g. ferrocene [326]) on ITO can be used to probe changes in electrochemical activity of ITO surface as a function of surface pretreatment [314]. Adsorption of ferrocene dicarboxylic add (Fc(COOH)2) and 3-thiophene acetic acid (3-TAA) onto ITO was achieved by soaking ITO in a 1 mM solution of these small molecules in pure ethanol for 10 min and then rinsing briefly with acetonitrile [314-316]. To ensure reproducibility, the adsorption of Fc(COOH)2 on pretreated ITO was repeated a minimum of three times on three separate ITO samples, for each pretreatment condition [314]. Chemisorbed small molecules on ITO will provide for better direct contact of added conducting polymer layers and/or hole transport layers (HTLs) in the devices [316],... 

Electrochemical Impedance Spectroscopy of Twin Working Electrodes Bridged with Conducting Polymer Layer, Electrochim. Acta 40, 1857-1862. 

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