Roles of adsorbed OH and adsorbed H in the oxidation of hydrogen and the reduction of UO2+2 ions at Pt electrodes under non-conventional conditions

Abstract

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 H 3 BO 3 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-OH ad plays a significant role in the passivation reaction in the potential range from 0.60 to 0.75 V SHE . From the analyses of the experimental results for the electrochemical reduction of UO 2 2+ ions on Pt surface in a 1.0 M HClO 4 solution, it is recognised that the reduction reaction of UO 2 2+ to U 4+ 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-H ad is also proposed.

Potential Correction Technique for Ag/AgCl Reference Electrode Using UV/VIS Absorbance of Internal Electrolyte

“…This effect is more pronounced at lower concentrations of KCl. 4 Therefore, when using TPMe as a spectrally active material for the correction of the potential of an Ag/AgCl electrode, the concentration of KCl should be between 0.01and 0.1 M due to the effects of KCl on the UV/VIS absorbance and of TPMe on the potential of the electrode.…”

“…In our previous study, 4 we established a correction technique based on the relationship between the electrical conductivity and the KCl concentration to enhance the long-term performance of Ag/AgCl electrodes. The applicability of the electrical conductivity technique was confirmed for aqueous media containing H 3 BO 3 .…”

“…In both academia and industry, Ag/AgCl and calomel electrodes have been commonly used as reference electrodes for a long time. [1][2][3][4][5] As the potentials of both types of electrodes depend only on the chemical activity of KCl in the internal electrolyte, [6][7][8][9] the KCl concentration of the electrolyte should be kept at a constant level to ensure the long-term performance of the reference electrodes. For this reason, many technologies have been developed to minimize the leakage and dilution of the internal electrolyte of the electrode.…”

“…This new approach is focused not on the suppression of the leakage of the internal electrolyte but on the estimation of the leakage so that the electrode can be used even if the internal electrolyte is diluted to some extent. Yun et al 4 established a correction technique for the potential of Ag/AgCl electrodes based on the linear relationship between the KCl concentration of the electrolyte and its electrical conductivity. This technique was able to effectively correct the potential of Ag/AgCl electrodes in aqueous solutions with low electrical conductivity, such as demineralized water and natural water.…”

A calibration technique for an Ag/AgCl reference electrode utilizing the relationship between the electrical conductivity and the KCl concentration of the internal electrolyte

“…For these reasons, the Ag/AgCl electrode has long been used to provide a reliable potential monitoring in aqueous solutions [1][2][3][4][5][6][7][8]. As the potential of the Ag/AgCl electrode is determined by the activity of the Cl -ions [9][10][11], it is important to maintain the Cl -ions at a constant concentration in the internal electrolyte of the reference electrode.…”