Application of pattern recognition techniques to qualitative electrochemical analysis: Part I. Feature extraction of non-linear characteristics of the electrode process by the two-dimensional fast Hadamard transform

The feature extraction on non-linear characteristics of the electrode process is described. A model consisting of a linear element and a static non-linear element (ZNL=zero-memory non-linear system) is used to acquire the representation of the electrode process, from which the features of the electrode process should be extracted. That is, the electrode process is assumed to be composed of two processes, a solution process which has a dynamic characteristic due to the accumulation of materials in solution, and a surface process which has a non-linear characteristic like a kind of Butler's relation, etc. Previous work showed that a linear diffusion model with and without pseudo-first order chemical reactions made it possible to obtain the representation of the former process as a cross-power-spectral pattern (linear transfer function) between the current (I) and the surface concentration (c). For the latter process, it should be pointed out that its non-linear characteristics are nearly static due to the absence of material accumulation along the normal direction to the surface at the electrode surface. On the basis of this static non-linear model, this paper shows that the surface process can be represented by a pattern of a static curved surface, E-I-c (E= electrode potential) obtained by use of the computational measurements of the surface concentration. A two-dimensional fast Hadamard transform achieved high information compression in the feature extraction of the observed E-I-c pattern.