Oxygen Gas Evolution Research Articles

Influence of ph on the reduction of thick anodic oxide films on gold

The reduction of thick oxide films, produced anodically on gold under constant potential conditions in the oxygen gas evolution region, was examined as a function of sweep-rate in both acid and base. Although peak maxima potential values for the reduction reactions were not totally independent of sweep-rate, even at very low values of the latter, the earlier assumption that the film is composed of at least two (and in some cases, according to the present results, as many as five) different oxygold species was shown to be a reasonable one. The other assumption, namely that the hydrous film in the case of gold is anionic (due to excess hydroxide-ion incorporation) was also shown to be a reasonable one by comparison with recent work with hydrous nickel oxide films for which structural data is available. In these systems counterbalancing cations (H +, Na +, etc.) are assumed to be present in water contained in pores or layers in the structure. Furthermore, the unusual potential-pH dependence of the hydrous film reduction process can easily be explained in terms of the excess hydroxide incorporation model.

Formation of hydrous oxide films on cobalt under potential cycling conditions

Subjecting a cobalt electrode in base to repetitive triangular potential sweeps over the range 0–1.2 V(RHE) resulted in the formation of a thick hydrous oxide film. The electrochemical behaviour of the system is complicated due to metal dissolution over the first few cycles (this reaction was less important with thicker films due to the passivating nature of the latter) and and the variety of oxidation states (0, II, III and IV) accesible to this element within the range 0–1.5 V(RHE). As with rhodium, the rate of oxide growth on cycling and the general reactivity of the film decreased with decreasing hydroxide ion concentration. A notable feature of the cobalt system is that enhanced oxide growth was observed using a lower limit at which Co(II)—rather than the base metal—is thermodynamically stable. However, since Co(OH) 2 is slightly soluble, the reduced form of the hydrous oxide is non-protective and further oxidation of the metallic substrate can occur during the subsequent anodic sweep. A considerable proportion of the cations present in the surface layer did not participate in the redox reactions, especially at high sweep rates. Slight enhancement of oxygen gas evolution rates was observed with a hydrous film present on a cobalt anode in base. An advantage of cobalt (relative to RuO 2) is that it retains its low Tafel slope behaviour for oxygen gas evolution in base to quite high current densities.

Radiolytic Gas Generation and Oxygen Depletion in Ion Exchange Materials

ABSTRACTThe process of ion exchange is used extensively throughout numerous industries where water of extremely high purity is required. Government and commercial nuclear power facilities are typical of this, and have applied ion exchange processes for the removal of radioactive ions from aqueous solutions. When water is decontaminated in this fashion the ion exchange medium becomes saturated with the radioactive ions from solutions, and is then stored as radioactive waste in standard burial facilities. During this indefinite storage period, the chemical changes which occur in the ion exchange medium may result in oxygen depletion and gas generation within the storage vessel, and subsequent loss of integrity. It is the object of this work to investigate the early phases of radiolytic oxygen depletion and gas evolution through experimental procedure and observation. The results of this work will then be analyzed with respect to applications for the storage of radioactive ion exchange waste.

Thick oxide growth on gold in base

The formation of thick oxide films (ca. 100 monolayer equivalents at 2.3 V) on a gold anode was observed under steady-state polarization conditions in base. As reported by other authors for acid, the layer produced was of duplex character with a compact, largely anhydrous inner film at the metal surface, and a much thicker, porous, highly hydrated outer film at the oxide-solution interface. These deposits were readily distinguished, and quantified coulometrically, due to differences in reduction potential under cathodic sweep conditions. The onset of thick film growth occurred in a potential region where linear Tafel behaviour is observed for oxygen gas evolution on gold, and changes in oxygen coordination of cations in the outer region of the compact layer under these conditions is assumed to enhance the conversion of material in the outer region of the latter to the more hydrated form. As compared with acid, oxide growth was much slower (and reached a limiting value) in base, the outer film was reduced less readily and inhibition of oxygen gas evolution in the thick film region (at ca. 2.35 V) was observed. The results were accounted for by assuming increasing hydroxide ion coordination by cations in the hydrous layer with increasing pH — the more highly coordinated species being thermodynamically more stable but kinetically less capable of rearranging to form a crystalline product. The relationship between the hydrous film on gold and those produced on a wide range of other transition metals is briefly outlined.

Thick oxide growth on gold in base

The formation of thick oxide films (ca. 100 monolayer equivalents at 2.3 V) on a gold anode was observed under steady-state polarization conditions in base. As reported by other authors for acid, the layer produced was of duplex character with a compact, largely anhydrous inner film at the metal surface, and a much thicker, porous, highly hydrated outer film at the oxide-solution interface. These deposits were readily distinguished, and quantified coulometrically, due to differences in reduction potential under cathodic sweep conditions. The onset of thick film growth occurred in a potential region where linear Tafel behaviour is observed for oxygen gas evolution on gold, and changes in oxygen coordination of cations in the outer region of the compact layer under these conditions is assumed to enhance the conversion of material in the outer region of the latter to the more hydrated form. As compared with acid, oxide growth was much slower (and reached a limiting value) in base, the outer film was reduced less readily and inhibition of oxygen gas evolution in the thick film region (at ca. 2.35 V) was observed. The results were accounted for by assuming increasing hydroxide ion coordination by cations in the hydrous layer with increasing pH — the more highly coordinated species being thermodynamically more stable but kinetically less capable of rearranging to form a crystalline product. The relationship between the hydrous film on gold and those produced on a wide range of other transition metals is briefly outlined.

Polyacetylene film: A new electrode material for photoenergy conversion

Polyacetylene films were characterized as an electrode material in aqueous solutions. The trans polyacetylene films behaved as electrodes under reducing conditions. Oxygen gas evolution was greatly retarded under oxidizing conditions, primarily due to the high reactivity with oxygen. Visible light illumination resulted in a positive shift in electrode potential. The electrode developed photopotential reversibly in accord with illumination. The polyacetylene electrode gave cathodic photocurrent when contacted with a deoxygenated acetate buffer. The cathodic photocurrent increased with decreasing pH, ranging from 0 to 5.5 × 10 −6 A/cm 2. The possible use of polyacetylene electrodes for photoenergy conversion is discussed.

Oxygen gas evolution on hydrous oxides — An example of three-dimensional electrocatalysis?

Oxygen gas evolution on hydrous oxides — An example of three-dimensional electrocatalysis?

Oxygen gas evolution on hydrous oxides — an example of three-dimensional electrocatalysis?

Oxygen gas evolution on hydrous oxides — an example of three-dimensional electrocatalysis?

Electrode reactions of various electric conductive materials in some molten glasses

Anodic dissolution, passivation and cathodic deposition of electric conductive materials were investigated by linear potential sweep method in molten glasses. Na 2O·2B 2O 3 and F8 lead glass were selected as sample glasses. As the electrodes, the materials such as Pt, Ni, Fe, Mo, graphite and stannic oxide were selected. Some examples of the results obtained in Na 2O·2B 2O 3 at 900°C by anodic polarization are summarized as follows: By anodic potential sweep of the Pt electrode, S-shape current-potential curves are obtained. This limiting current may be attributed to the diffusion current of oxygen ions. By applying more anodic potential than about 3V the oxygen gas evolution is observed. Pt acts as an insoluble electrode. The Ni electrode readily dissolves as soon as the potential is applied, but the dissolution current decreases by further anodic polarization because of the oxide film formed by Ni + O 2− = NiO + 2 ρ on the electrode surface. There are no any peak on the current-potential curves for Fe and W electrodes. Fe and W readily dissolve. The order of increase of electrolytic current density at 3V in Na 2O·2B 2O 3 is: W > Fe ⪢ Mo > Co > Ni > Cr ⋍ graphite ⋍ Pt > stannic oxide .

導電性固体材料とＮａ?S２?TＯ・２Ｂ?S２?TＯ?S３?Tガラス融液との分極下における反応について

In the previous paper, the results of the studies on anodic dissolution, passivation and catholic deposition of some metals such as Pt, Ni and Fe in molten sodium diborate glass had been reported.In this paper, the electrochemical behaviors of other electric conductive materials such as Co, graphite, W and Cr were investigated in the same melt by the linear potential sweep method and potential step chronoamperometry. Current-potential curves were obtained at various potential sweep rates (5∼0.5V/sec) and various potential spans between 0 and 5V for anodic polarization and between 0 and -4V for cathodic polarization. All the measurements were carried out under N2 atmosphere at 900°C.By anodic potential sweep of a Co electrode, the current-potential curve having a large current peak at ca. 1V was obtained. Such a passivation phenomenon may be explained with the oxide film formation on the electrode surface by the reaction, Co+O2-=CoO+2e. By applying higher potential than 3V, a plateau accompanied by small vibrating waves resulting from the oxygen gas evolution was observed on the current-potential curve. A graphite electrode showed a S-shape current-potential curve by anodic polarization in the same way as Pt. Graphite acted as an insoluble electrode, but a marked gas evolution was observed at the anodic potential more than 3V. A W electrode readily dissolved, and no peak was observed. A Cr electrode showed a broad and weak current peak during anodic polarization. As the current density for the Cr electrode on applying further potential was as small as the value for Pt, it seemed that Cr acted as an insoluble electrode.

二，三の金属とＮａ?S２?TＯ・２Ｂ?S２?TＯ?S３?Tガラス融液との分極下における反応について

The knowledge about the electrochemical behavior of various metals in molten glasses during voltage application is essential to electric melting of glass.In this paper, the anodic dissolution, passivation and cathodic deposition of metals were investigated in molten sodium diborate glass by linear potential sweep method. As the electrodes, metals such as Pt, Ni and Fe were selected. The relationship between current and applied potential was determined at various linear potential sweep rates (0.001∼5V/sec) between 0∼±5V by using platinum wire as a reference electrode and an auxiliary electrode under N2 atmosphere.By anodic potential sweep of Pt electrode, S shape current-potential curves were obtained at various potential sweep rates. This limiting current might be attributed to the diffusion current of oxygen ions. When the applied potential was more than ca. 3V, the oxygen gas evolution was observed because of electrolysis of the solvent glass. Pt electrode acted as an insoluble electrode.Due to anodic polarization, Ni electrode dissolved as soon as a potential was applied, but the dissolution current decreased suddenly at a certain voltage. The respective plots of the peak currents and peak potentials against (potential sweep rates)1/2 were shown to be straight lines. These phenomena can be explained by coverage of the electrode surface by poor conductive oxide films formed by the reaction, Ni+O2-=NiO+2e. There was no peak on the current-potential curve for Fe electrode and Fe dissolved rapidly.

Calculation of equlibrium composition in more concentrated systems H2O2-KOH (or NaOH)-H2O

From relations for acid-base equilibria in more concentrated systems H2O2-KOH (or NaOH)-H2O equations were derived for the calculation of the concentrations of OH- and HO2- ions and undissociated H2O2 during preparation of hydrogen peroxide by cathodic reduction of oxygen in alkali hydroxide solution and during spontaneous decomposition of alkaline hydrogen peroxide solutions. Mass changes of the solutions due to the consumption or evolution of gaseous oxygen were taken into account. The role of various parameters is discussed.

Optical and electrical experiments at some transition-metal oxide foil-electrolyte interfaces†

Metal oxide layers formed from transition-metal foils oxidized by heating in air have been examined for their photoelectrolytic response. The metals examined are Y, Ti, Zr, Hf, V, Nb, Ta, Mo, W, and Pt. Weak photoeffects are observed for oxide layers of all of these metals. Sizable light-dependent oxygen gas evolution rates are found in Ti and also in W oxides. The spectral dependence of the oxygen response in these compounds is investigated, and interpretation is given of these experiments.

Thermal studies of the reactions of vanadium(V) oxide with other transition metal oxides

Studies of the thermal behaviour of binary oxide mixtures containing vanadium(V) oxide (V2O5-TiO2, V2,O5- MoO3, V2,O5-ZrO2 and V2O5-ZnO) have shown that the evolution of gaseous oxygen at fairly low temperatures is characteristic of those systems which are eflective catalysts for the oxidation of hydrocarbons. No weight changes were observed with V2, O5-ZnO mixtures under these conditions and, in accordance with this, zinc(II) oxide does not enhance the catalytic activity of vanadium(V) oxide. In V2O5-containing systems, evolution of oxygen occurs during the reduction of V2O5 to V2O4. This process is accelerated in the presence of certain metal oxides and such acceleration may be caused by structural interactions at the interface of the oxides. Among the systems studied, the formation of compounds such as Mo6V9O40 is thought to be of little significance from the catalytic point of view.

Fluidised-bed anodic dissolution of chalcocite

The anodic dissolution of chalcocite (Cu 2S) has been investigated using a fluidised-bed anode technique. Results obtained for a variety of electrolytes and experimental conditions indicate that the fluidised-bed anodic dissolution of chalcocite occurs via the formation of an intermediate copper sulphide, viz., “blue-remaining” covellite, Cu 1.1 S. In sulphuric acid electrolyte the dissolution of chalcocite is inhibited after about 50% copper extraction by the vigorous evolution of oxygen gas at the platinum feeder anode. In both sulphuric acid-sodium chloride and sulphuric acid-potasium bromide electrolytes, the dissolution of chalcocite occurs to 95% copper extraction in two stages. The first stage involves the formation of Cu 1.1 S, as is the case for the sulphuric acid electrolyte, while the second stage is attributed to the reaction between chloride (or bromide) and Cu 1.1 S.

Photochemical decomposition of sodium chlorate

The photolysis of powdered NaClO3 exposed to 254 nm light has been investigated using unirradiated crystals and material subjected to 60Co gamma−ray irradiation. Pressure versus time curves for all samples increase monotonically and eventually exhibit a constant rate of oxygen gas evolution. The curves appear to contain one saturating exponential component and one linear component. This final stage approximates a second order dependence on light intensity. This dependence can be attributed to the photolytic generation of additional decomposition sites. Gamma−ray irradiation increases the variation from the observed almost second order dependence, decreases the magnitude of the exponential component, and decreases the time required to reach the final stage and the steady state rate. Irradiation also produces color centers and a shift in the apparent optical absorption edge. These observations are consistent with a previously developed phenomenological theory.

The Acid-catalyzed Bromination of Aromatic Compounds with Potassium Bromate in Aqueous Acetic Acid

Abstract Bromobenzene is obtained in a 64% yield when an aqueous acetic acid solution containing a catalytic amount of sulfuric acid is slowly added to an aqueous acetic acid solution of benzene and potassium bromate at 60°C. It seems, according to the synthetic data, that the formation of bromobenzene is accelerated by an electron-releasing group. The rate of the consumption of active oxygen has been expressed as follows: v=k_2[BrO_3^-][C_6H_6]+k_3[BrO_3^-][C_6H_6]^2 Here, both k2 and k3 gave a straight line against −log(CBH+⁄CB), with a slope of ca. −2. The reaction is accelerated by sulfuric acid and does not occur at all in the absence of the acid. The evolution of oxygen gas was not observed during the reaction, but the presence of peroxyacetic acid and/or acetyl peroxide in the reaction mixture was indicated by paper chromatography. A mechanism which involves the rate-determining attack of protonated hypobromous acid and/ or protonated acetyl hypobromite on benzene has been suggested.

Temperature Dependence of Magnetic Susceptibilities of KClO3, KBrO3, and KIO3

Magnetic susceptibilities of crushed samples of KClO 3 , KBrO 3 and KIO 3 were measured with a recording magnetic balance which was operated by the Faraday method. The temperature was elevated at a constant rate, 250°C per hour. It was found that, being heated, KClO 3 showed irregular paramagnetic susceptibilities in the solid or liquid state, before the evolution of oxygen gas at 500°C. A possible explanation for the irregular paramagnetic behaviors is suggested. On the contrary, KBrO 3 and KIO 3 showed the diamagnetic susceptibilities, which were independent of temperature below the temperatures of the evolution of oxygen gas, 370° and 550°C, respectively.

Ionic nature of liquid iron-silicate slags

Measurements of current efficiency on iron-silicate slags in iron crucibles showed that conduction is about 10 pct ionic in slags with less than 10 pct silica and about 90 pct ionic in slags with more than 34 pct silica, increasing linearly in the intermediate range. The balance of the conduction is electronic in character. Silicate ions are discharged at the anode with the evolution of gaseous oxygen. Transport experiments show that the ionic current is carried almost entirely by ferrous ions, which may be assigned a transport number of one.

Anode Polarization Effects of Nickel in Sulfuric Acid

The electrochemical polarization effects at nickel anodes in 2N sulfuric acid were studied to determine the nature of the electrode reactions involved. Current densities below and above that required to passivate a nickel anode were used. There was evidence of an anodic film forming at the active nickel surface prior to the onset of passivity. In the passive state, the anode reaction was the discharge of hydroxyl ions and subsequent evolution of oxygen gas and formation of a nickel oxide. The presence of chloride ions had the effect of raising the minimum current density required to passivate a nickel anode and delaying the onset of passivity above this current density. The nickel oxide formed anodically was soluble in the acid solution and controlled the rate of polarisation decay.