Roles of adsorbed OH and adsorbed H in the oxidation of hydrogen and the reduction of UO 2 2+ ions at Pt electrodes under non-conventional conditions
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The roles of adsorbed hydroxyl radicals, OH, at a high temperature and adsorbed hydrogen atoms, H, in an acidic solution were investigated in the electrochemical reactions on Pt electrode by using potentiodynamic polarisation experiment, cyclic voltammetry and constant-potential electrolysis combined with UV/VIS analysis. From the analysis of the polarisation curves obtained from Pt electrode in a 0.185 M H3BO3 solution at 473 K, it was found that the reducing capability of dissolved hydrogen is significantly enhanced due to the increases of the mass transfer and the electron transfer rates. Especially, it is suggested that the stable Pt-OHad plays a significant role in the passivation reaction in the potential range from 0.60 to 0.75 VSHE. From the analyses of the experimental results for the electrochemical reduction of UO 2 2+ ions on Pt surface in a 1.0 M HClO4 solution, it is recognised that the reduction reaction of UO 2 2+ to U4+ ions is strongly dependent on the hydrogen atoms adsorbed on Pt electrode (indirect reduction of UO 2 2+ ) as well as on the electrons transferred from Pt electrode (direct reduction of UO 2 2+ ). In addition, the reduction mechanism of UO 2 2+ ions involved in Pt-Had is also proposed.
KeywordsAdsorbed hydrogen Adsorbed hydroxyl Passivation Pt electrode Reduction of UO22+
This work was supported by the Nuclear R&D Program of the Korean Ministry of Science and Technology (MOST). Incidentally, this work was partly supported by the Brain Korea 21 project. Furthermore, the authors are indebted to Mr. K.-N. Jung and Mr. K.-H. Na in CIERL at KAIST for their helpful comments.
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