Relationship between permselectivity and the acidity of polyphenols pertaining to the pH response of Pt/polyphenol electrode

The permselectivity of Pt/polyphenols has been investigated. The selective permeability is found to be different for various polyphenols. Relationships of the diffusion rates, the limiting currents for the reduction of H+ ions and the pKa values of the polyphenols have been established. Electron-withdrawing substituents increase the diffusion rate of the H+ ions with increasing acidity of the polyphenol; whereas electron-donating groups bring out the reverse effect. Poly(p-cyanophenol) and poly(2,6-dichlorophenol) are found to be better candidates to modify a Pt electrode for application as pH sensor than existing polyphenol and poly(2,6-dimethylphenol) films.