Electrochemical systems can be characterized by the molecular reactivity, denoted by x, related to the molecules participating in t he el ect r ode r ea ct ion, under electron transfer (ET), and by the collective properties, denoted by X, related to the g en er a l pr op er t ies of the electrochemical system, depending on electrode characteristics (ECS) as well as on properties of the near electrode space, volume characteristics (VCS). The ECS and VCS are determined by the electrode material, its structure, the electrode potential, the solvent, electrolyte and electrolyte concentration, temperature, pressure, etc.