GROWTH OF THIN, HYDROUS OXIDE-FILMS AT PD ELECTRODES

The electrochemistry of polycrystalline Pd has been examined in alkali ne and acidic solutions, with the focus being on the growth and reduct ion of thin, hydrous Pd oxide (beta-oxide) films. In the first few cyc les 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. T his alpha-oxide film has been suggested to consist of mainly PdO and s ome PdO2 at potentials positive of ca. 1.5 V. When the alpha-oxide fil m is ca. five monolayers in thickness, the conversion of the alpha- to beta-oxide commences at certain sites, resulting in the development o f islands of alpha- and beta-Pd oxide. Evidence indicates that, with i ncreasing oxide growth, the coverage of the electrode surface by patch es of alpha-oxide of unchanged thickness decreases slowly, reaching a steady state, while the islands of beta-oxide lengthen in the form of columns.