ELECTROCHEMICAL-BEHAVIOR OF IRIDIUM IN ALKALINE AND ACIDIC SOLUTIONS OF HEAVY AND REGULAR WATER

The behaviour of iridium as an electrode for hydrogen (protium and deu terium) and oxygen evolution in both alkaline and acidic, heavy and re gular water solutions has been investigated primarily by cyclic voltam metry. The main features, such as adsorption and underpotential deposi tion of hydrogen (both protium and deuterium), as well as the specific charge capacity for monolayer (alpha-phase) with subsequent multilaye r (beta-phase) oxide growth with successive increase in oxygen content , preceding hydrogen and oxygen evolution, respectively, with characte ristic desorption peaks, were more or less marked in both electrolytes . Some distinctly different behaviours, however, have been observed re vealing that heavy and regular water behave almost as different solven t ambients. In contrast to some other noble metals (Pt, Pd, Au, Re) an d in common with Rh, hydrogen and oxygen evolving limits for Ir keep t heir potential values unaltered in alkaline media of both heavy and re gular water. Hydrogen absorption, besides adsorption, of both protium and deuterium has been clearly marked by the continuously growing char ge capacity of the diffusional desorption peak, whose extent depends o n the evolving rate and contact time of hydrogen evolution and distinc tly exceeds one-to-one hydrogen (H/Ir or D/Ir) atom coverage on the ex posed Ir surface, and relative to the corresponding reversible adsorpt ion wave charge area for its underpotential deposition. In addition, a deuterium oxidation peak, immediately following its desorption (in pa rticular from acidic heavy water) has also been clearly marked on the voltammograms. A distinct merging and melding together of three initia l deuterium reversible desorption peaks into the diffusional desorptio n peak in acidic heavy water has been discernibly scanned upon the vol tammograms. Oxide formation usually starts at more anodic potentials t ogether with deuterium oxidation and, specifically in acidic media, pr oceeds vigorously with higher and continuously growing rates and merge s together with deliberation of molecular oxygen, while prevailing oxy gen evolution thereby arises shifted to more positive potential values . These features reveal that due to its distinctly different steric fa ctor, heavy water, in particular in acidic media, behaves as a stronge r oxidizing agent than regular water. Some discernible properties of t he interplay between hydrogen and oxygen on the Ir electrode in both e lectrolytes along the potential axis have been clearly marked and poin ted out. The Rowland or EDTA effect was much more pronounced on the po tentiodynamic and electrocatalytic features of the Ir electrode in alk aline solutions as compared with Pt and Pd, and therefore is displayed in more detail.