ELECTROCHEMICAL-BEHAVIOR OF PLATINUM IN ALKALINE AND ACIDIC SOLUTIONSOF HEAVY AND REGULAR WATER

The behaviour of Pt as an electrode for hydrogen (protium and deuteriu m) 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 char ge capacity for monolayer oxide growth with successive increase in oxy gen content (preceding hydrogen and oxygen evolution, respectively, wi th characteristic desorption peaks), were more or less marked in both electrolytes. Some distinctly different behaviour, however, has been o bserved, revealing that heavy and regular water behave almost as diffe rent solvent ambients. The hydrogen evolution reaction (HER) particula rly in alkaline heavy water occurs at substantially more negative pote ntials, while oxygen evolution becomes shifted to considerably more po sitive potential values. Hydrogen absorption, besides adsorption, of b oth protium and deuterium, has been marked clearly by the continuously growing charge capacity of the diffusional desorption peak, whose ext ent depends on the evolving rate and contact time of hydrogen evolutio n and distinctly exceeds both one-to-one hydrogen to platinum (H/Pt or D/Pt) atom coverage on the exposed electrode surface, and relative to the corresponding reversible adsorption wave charge area for its unde rpotential deposition. In addition, the hydrogen oxidation peak immedi ately following its desorption (in particular from acidic heavy water) has also been clearly marked on voltammograms. A distinct merging and melding together of two initial deuterium reversible desorption peaks into the diffusional desorption peak in acidic heavy water has been d iscernibly scanned, too. Oxide formation usually starts at more anodic potentials together with deuterium oxidation and, specifically in aci dic media, proceeds vigorously with higher and continuously growing ra tes and merging together with evolving molecular oxygen, while the pre vailing oxygen evolution thereby becomes shifted to more positive pote ntial values. These features reveal that, owing to its distinctly diff erent steric factor, heavy water (in particular in acidic media) behav es as a stronger oxidizing agent than regular water. Some discernible properties of the interplay between hydrogen and oxygen on the Pt elec trode in both electrolytes along the potential axis have been clearly marked and pointed out. The Rowland or EDTA effect on the potentiodyna mic features of Pt has also been scanned and displayed.