AN ELECTROCHEMICAL AND ELECTRON MICROSCOPIC STUDY OF ACTIVATION AND ROUGHENING OF PLATINUM ELECTRODES

The factors which govern the behavior of platinum electrodes during anodic-cathodic cycling in IM H2SO4 are examined. Cyclic voltammetry with linear potential sweep is found to be a sensitive criterion of the state of the electrode surface. With a new electrode, the shapes of these voltammograms change during the first few hundred cycles of any potential program in which a layer of adsorbed oxygen is periodically formed and reduced. These changes are considered to represent activation of the electrode and electron microscopy suggests that they are accompanied by surface structural changes in the form of shallow pitting. Further roughening occurs if the electrode is treated with a potential program fulfilling the conditions that (a.) the amount of adsorbed oxygen after the anodic cycle exceeds the equivalent of one oxygen atom per platinum atom and (b) the reduction cycle is fast. The rate of roughening is proportional to the amount of adsorbed oxygen. Smoothing oc curs when a program which does not fulfill conditions (a) and (b) is applied to an already roughened electrode. After extensive roughening, platinum can be detected in solution. The nature of the roughening process and also of the effects produced by flaming the electrode is examined by electron micros copy. It is suggested that activation and roughening occur through weakening of platinum interactions due to formation of the strong platinum-oxygen chemisorption bond. This allows rearrangement of platinum surface atoms and dissolution of a platinum-oxygen species. High energy platinum sites are probably lost in the initial activation process while a roughening program provides sufficient energy to dislodge atoms in more stable sites. © 1969, The Electrochemical Society, Inc. All rights reserved.