Diffusion Digital electronics

Attempts to develop a model for the digital simulation of the cyclic voltammetric behaviour of PVF films on platinum62 electrodes required inclusion of the following features (a) environmentally distinct oxidized and reduced sites within the film (b) interconversion of the above sites and interaction between them (c) rate of electrochemical reactions to depend on the rate of interconversion of redox sites, the rate of heterogeneous electron transfer between film and substrate, intrafilm electron transfer and the rate of diffusion of counter ions and (d) dependence on the nature of the supporting electrolyte and the spacing of electroactive groups within the film. 

With a potentiostat the potential at the working electrode is linearly increased from 1.0 to 1.6 V and then decreased back to 0 V. In the first interval 1 is oxidized to the radical cation l+ with a peak potential of p.a = 1-38 V. 1 is stable in this solvent and is reduced in the reverse scan back to 1 at p,c = 1-32 V. The ratio of the current for reduction and oxidation ip c-ip.a = 1 indicates the stability of the radical cation. All of 1, that is formed by oxidation of 1 is reduced back to 1. This behavior is termed chemically reversible. Upon addition of 2,6-lutidine, the radical cation 1 reacts with the nucleophile to afford 2 , which is further oxidized to a dication, which yields the dication with 2,6-lutidine. This can be seen in the decrease of /p,c fp,a and an increase of due to the transition from an le to a 2e oxidation. From the variation of the ratio ip.c-ip,n with the scan rate, the reaction rate of the radical cation with the nucleophile can be determined [9]. This can also be aehieved by digital simulation of the cyclovoltammogram, whereby the current-potential dependence is calculated from the diffusion coefficients, the rate constants for electron transfer and chemical reactions of substrate and intermediates at the electrode/electrolyte interface [10]. With fast cyclovoltammetry [11] scan rates of up to 10 Vs- can be achieved and the kinetics of very short-lived intermediates thus resolved. 

This first chapter to Volume 2 Interfadal Kinetics and Mass Transport introduces the following sections, with particular focus on the distinctive feature of electrode reactions, namely, the exponential current-potential relationship, which reflects the strong effect of the interfacial electric field on the kinetics of chemical reactions at electrode surfaces. We then analyze the consequence of this accelerating effect on the reaction kinetics upon the surface concentration of reactants and products and the role played by mass transport on the current-potential curves. The theory of electron-transfer reactions, migration, and diffusion processes and digital simulation of convective-diffusion are analyzed in the first four chapters. New experimental evidence of mechanistic aspects in electrode kinetics from different in-situ spectroscopies and structural studies are discussed in the second section. The last... 

A novel method for the study of diffusion through catalytic layers has been recently proposed by Novak et al. [20]. The authors predicted the effective dififusivity by employing a detailed pore scale model. This model is based on the digital reconstruction of the porous layers as 3D matrices using the information from cross-section electron microscopy and particle size analysis. 

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