Electrochemical behaviour of palladium in acidic and alkaline solutions of heavy and regular water

• Published in: International journal of hydrogen energy 1993-02, Vol.18 (2), p.111-124
• Main Authors: Jaksic, M.M., Johansen, B., Tunold, R.
• Format: Article
• Language: English
• Subjects: Alternative fuels. Production and utilization; Applied sciences; Energy; Exact sciences and technology; Fuels; Hydrogen
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/0360-3199(93)90197-I

The behaviour of palladium as an electrode for hydrogen (protium and deuterium) and oxygen evolution in both alkaline and acidic, heavy and regular water solutions has been investigated primarily by cyclic voltammetry. The main features, such as adsorption and underpotential deposition of hydrogen, both protium and deuterium, as well as the specific multilayer (monolayer α- succeeded by multilayer β-phase) oxide growth preceding hydrogen and oxygen evolution, respectively, with characteristic desorption peaks, were more or less marked in both electrolytes. Some distinctly different behaviours have been observed, however, revealing that heavy and regular water behave almost as different solvent ambients. The hydrogen evolution reaction (H.E.R.) in heavy water occurs at substantially more negative potentials, while oxygen evolution becomes shifted to considerably more positive potential values. The latter effect enables one to record on voltammograms the multilayer oxide (β-phase) growth in alkaline heavy water, as distinctly indicated by corresponding continuously growing characteristic potentiodynamic waves scanned with cyclization. Hydrogen absorption, both protium and deuterium, has been clearly marked by the continuously growing charge capacity of the diffusional desorption peak, which exceeds one-to-one H(D)/Pd atom coverage on the exposed palladium surface and is related to the corresponding adsorption wave for its underpotential deposition. In addition, the hydrogen oxidation peak immediately following its desorption (in particular from acidic heavy water) has also been distinctly scanned on voltammograms. Oxide formation usually starts at more anodic potentials together with deuterium oxidation and, specifically in acidic media, proceeds vigorously with higher and continuously growing rates, while the evolving oxygen thereby arising is shifted to more positive potential values. These features reveal that, due to distinctly different steric factors, heavy water, in particular in acidic media, behaves as a stronger oxidizing agent than regular water. Some discernible properties of the interplay between hydrogen and oxygen on palladium electrodes in both electrolytes along the potential axis have been clearly marked and pointed out.