A Study of Electrode Passivation during Aqueous Phenol Electrolysis

Publisher Website
Google Scholar
Abstract
The process of electrode passivation during phenol electrolysis at a platinum electrode was studied in a sulfuric acid electrolyte (pH0‐1). Passive film growth and the effects of concentration and potential were investigated using chronoamperometry, x‐ray photoelectron spectroscopy, and gel permeation chromatography. The main products of the phenol oxidation are oligomers/polymers with weight‐averaged molecular weights typically around 1000 g/mol after a 30 ms anodic pulse. X‐ray photoelectron spectroscopy shows that the passivating polymer film is oxidized incompletely with many hydroxyl groups present. Increased potential increased the polymerization rate, but above 1.0 V vs. SCE film decomposition reactions also occurred. Increased phenol concentration increased the charge required to initiate passivation. Potential steps to the open‐circuit potential or to more cathodic values can interfere with the passivation process. Chronoamperometric results show that the current decay at the passivated electrode is roughly inversely proportional to time and that the currents for a fixed amount of polymerization reaction follow a Tafel relationship. This type of decay is not due to a limitation caused by reactant diffusion through, nor IR drop across, a growing film but is more characteristic of electron tunneling through a growing insulating barrier layer. The model proposed for the observed behavior involves the formation of a region of high molecular weight, oxidized material at the electrode surface which blocks further reaction at the electrode. The rate‐determining step at the passivated electrode is therefore electron tunneling through this unreactive material.

This publication has 0 references indexed in Scilit: