GROWTH OF THIN, HYDROUS OXIDE-FILMS AT PD ELECTRODES

The electrochemistry of polycrystalline Pd has been examined in alkaline and acidic solutions, with the focus being on the growth and reduction of thin, hydrous Pd oxide (beta-oxide) films. In the first few cycles of potential between 0.47 and 2.8 V (reversible hydrogen electrode), the typical potential limits for beta-oxide growth employed in this work, a compact, anhydrous Pd oxide (alpha-oxide) film forms first. This alpha-oxide film has been suggested to consist of mainly PdO and some PdO2 at potentials positive of ca. 1.5 V. When the alpha-oxide film is ca. five monolayers in thickness, the conversion of the alpha- to beta-oxide commences at certain sites, resulting in the development of islands of alpha- and beta-Pd oxide. Evidence indicates that, with increasing oxide growth, the coverage of the electrode surface by patches of alpha-oxide of unchanged thickness decreases slowly, reaching a steady state, while the islands of beta-oxide lengthen in the form of columns.