Electroactive layers

Prussian blue, or ferric hexacyanoferrate, is definitely one of the most ancient coordination materials. The earliest announcements were from the very beginning of the eighteenth century [1, 2], However, a quite recent investigation by Neff [3], that Prussian blue forms electroactive layers after electrochemical or chemical deposition onto the electrode surface, has opened a new area in fundamental investigation of this unique inorganic polycrystal. 

P.L. He, N.F. Hu, and G. Zhou, Assembly of electroactive layer-by-layer films of haemoglobin and poly-cationic poly(diallyldimethylammonium). Biomacromolecules 3, 139-146 (2002). 

The speed of p- and n-type doping and that of p-n junction formation depend on the ionic conductivity of the solid electrolyte. Because of the generally nonpolar characteristics of luminescent polymers like PPV, and the polar characteristics of solid electrolytes, the two components within the electroactive layer will phase separate. Thus, the speed of the electrochemical doping and the local densities of electrochemically generated p- and n-type carriers will depend on the diffusion of the counterions from the electrolyte into the luminescent semiconducting polymer. As a result, the response time and the characteristic performance of the LEC device will highly depend on the ionic conductivity of the solid electrolyte and the morphology and microstructure of the composite. 

Bard, A.J. and Faulkner, L.R. (2001) Electrochemical Methods Electroactive Layers and Modified Electrodes, John Wiley and Sons, New York. 

Fig. 2.23 Schematics representation of the electroactive layer in the case of the electrochemical reduction of a solid when ion diffusion through the solid is allowed—electron diffusion is highly hindered...

To assess the electrochromic response of the bipyridinium dications embedded into multilayers of 7, we envisaged the possibility of assembling these films on optically transparent platinum electrodes.27d f Specifically, we deposited an ultrathin platinum him on an indium-tin oxide substrate and then immersed the resulting assembly into a chloroform/methanol (2 1, v/v) solution of 7. As observed with the gold electrodes (Fig. 7.5), the corresponding cyclic voltammograms show waves for the reversible reduction of the bipyridinium dications with a significant increase in 2p with the immersion time. In fact, is 0.8,1.5, and 3.1 nmol/cm2 after immersion times of 1, 6, and 72 h, respectively. Furthermore, the correlation between ip and v is linear after 1 h and deviates from linearity after 6 and 72 h. Thus, the bisthiol 7 can indeed form multiple electroactive layers also on platinum substrates. 

Considerable potential exists to design surface modified electrodes which can mimic the behaviour of electronic components. For example, a rectifying interface can be produced by using two-layer polymer films on electrodes. The electroactive species in the layers have different redox potentials. Thus electron transfer between the electrode (e.g. platinum) and the outer electroactive layer is forced to occur catalytically by electron transfer mediation through the inner electroactive layer. 

Electric double layer forces between polyelectrolyte and non-polymer surfaces in aqueous media have also been studied very intensively [371,394,400-402]. The adhesion between polyelectrolyte surfaces could be reduced considerably by increasing the ionic strength of the medium [400]. Using an electrochemical cell and a gold coated tip, the adhesion between electroactive layer of p oly( vinyl-ferrocene) was controlled through the selective oxidation or reduction of the polymer films [401]. 

Ren X, Pickup PG (2001) Simulation and analysis of the impedance behaviour of electroactive layers with non-uniform conductivity and capacitance profiles. Electrochim Acta 46 4177-83... 

This three-enzyme scheme suffers interference from endogenous creatine in the sample, requiring correction. Low concentrations of creatinine found in blood (<100p,moI/L) must be measured in the presence of oxidizable interfering substances, sometimes present at higher concentrations than the analyte. Special electroactive layers within the biosensor have been proposed to remove redox-active interfering substances. Since the useful life of the creatinine biosensor based on these reactions requires three enzymes to retain activity, reusable commercial biosensors for creatinine based on this measurement principle typically suffer from a short useful life of only a few days. 

Chapter 14. Electroactive Layers and Modified Electrodes Initial conditions must also be supplied, for example,... 

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