Oxygen Gas Evolution Research Articles

Enhanced water electrolysis: Electrocatalytic generation of oxygen gas at manganese oxide nanorods modified electrodes

This study is concerned with the electrocatalytic evolution of oxygen gas at manganese oxide nanorods modified Pt, Au and GC electrodes in 0.5 M KOH solution. The electrochemical measurements revealed a significant enhancement of the electrocatalytic activity of the Pt, Au and GC electrodes towards the oxygen evolution reaction (OER) upon the electrodeposition of manganese oxide nanoparticles (nano-MnO x ), that is, the onset potentials of the OER at the modified Pt, Au and GC electrodes are more negative by about 300, 550 and 300 mV, respectively, compared with the bare (i.e., unmodified) electrodes. MnO x is electrodeposited in a porous nano-texture structure which covers the entire surface of the substrates homogeneously. The MnO x of a single crystalline manganite phase (γ-MnOOH) plays a vital role as a catalytic mediator, which facilitates the charge transfer during the water oxidation into molecular oxygen and thus the OER is accomplished at less positive potentials.

Effect of electric fields on oxygen exchange reactions during sodium perchlorate thermolysis

Alkali metal perchlorates are known as oxidizers widely used in propellants, pyrotechnics, catalysts, and other fields [1]. These compounds contain significant proportions of oxygen, so they can also be successfully employed as solid oxidizers in the self-propagating high-temperature synthesis (SHS) of functional oxide materials (ferrites, ferroelectrics, high- T c superconductors, and others) [2]. In the combustion synthesis of complex oxides, the quality of the ultimate product is significantly affected by the degree of coincidence of the peak of perchlorate decomposition with oxygen gas evolution and the peak of metal fuel oxidation [3]. Usually, numerous test-and-trial experiments are needed to solve this problem and to find an optimal batch composition. In this context, it is pertinent to search for means of controlling such processes, especially for distant control means. It was discovered that, for example, strong electric fields generated by a condenser under SHS conditions substantially change the combustion process parameters [4]. The magnetic parameters of some ferrites are substantially modified during SHS in electric fields. To explain the effect of external physical actions on combustion and phase formation during the synthesis of complex oxide materials, it was hypothesized that electromagnetic fields applied to the zone of intense chemical reactions affect the kinetics of the decomposition of solid intrareaction oxidizers [5]. In addition, it cannot be ruled out that such actions affect oxygen exchange during the formation of complex oxides. In order to elucidate possible effects of electric fields, we believed it important to recognize the major SHS stages and to analyze the field effects on each stage. In this context, by way of example we studied the decomposition kinetics in electric fields for pure sodium perchlorate. The experimental setup used to study sodium perchlorate thermolysis (Fig. 1) was a vertical furnace equipped with a kanthal wire heater, with two tubular chambers 20 mm in inner diameter. The furnace was mounted between two copper plates, which were isolated with Teflon liners 1 mm thick and to which voltage up to 25 kV could be applied. Crucibles 18 × 24 mm in size, one containing powdered sodium perchlorate and the other containing a reference (NaCl), were simultaneously inserted into the chambers preheated to the required temperature ( 750°C ). Chromel‐ Alumel thermocouples were embedded beforehand into the powder to a depth of about 3 mm. Thermocouple signals were recorded with a potentiometer equipped with an xy plotter. Sodium perchlorate (99+%) from Acros Organics pounded in an agate mortar with a pestle was used in the experiments.

Numerical and experimental study of the effect of gas evolution in electrolytic pickling

As part of a progressive approach to model the electrolytic pickling process, this paper focuses on the important aspect of hydrogen and oxygen gas evolution on the electrodes and on the steel strip being pickled. The system considered consists of type 316 stainless steel pickled in aqueous sodium sulphate, with lead anodes and stainless steel cathodes. The mathematical model is two-dimensional steady-state, and includes the differential equations describing the effect of migration, giving the potential and current fields, and the Tafel kinetic rate expressions for hydrogen and oxygen gas generation. Experiments were conducted to obtain a better understanding of the process and for model validation. Good agreement between the experimental measurements of the global current efficiency and the model predictions was obtained.

Effects of casting temperature of Pb-Sb-Sn grid alloy on the polarization potential of oxygen evolution of lead acid batteries

The electrochemical polarization potential of oxygen evolution at the surface of lead-antimony-tin alloy is varied in different casting temperature of electrode production, which is used in the most of battery manufacturer. Effect of the casting temperature on the polarization potential of oxygen evolution and electrochemical behavior of lead-antimony-tin alloy in low antimony grid (1.7%) of lead acid battery is studied by using cyclic voltammetry and linear sweep voltammetry in aqueous sulfuric acid solution. The grid morphology is studied by using scanning electron microscopy and optical microscopy at the different casting temperatures. Cyclic voltammograms of the Pb-Sb-Sn and lead-antimony electrodes are similar, and both alloys show the anodic excursion peak under the same experimental conditions. The oxidation of tin is done at the formation potential of PbO. The results show the polarization potential for oxygen gas evolution to vary with casting temperature for production of lead-antimony electrodes.

Oxygen Gas Evolution on Boron-Doped Diamond Electrode in Molten Chloride Systems

Faradaic oxygen gas evolution occurred without dissolution of anode material according to the reaction O 2 - → 1 2O 2 ∩ + 2e - when a boron-doped diamond electrode is anodically polarized at a potential of 2.5 to 3.5 V vsLi + /Li in a LiCl-KCl melt containing Li 2 O at 723 K.

Formation of oxygen bubbles and its influence on current efficiency in micro-arc oxidation process of AZ91D magnesium alloy

Micro-arc oxidation (MAO) of metals is a complicated process combining concurrent partial process of oxide film formation, dielectric breakdown, dissolution of pre-existing film and anodic gas evolution. The probability of domination for any of these partial processes in the overall process depends on the nature of the substrate metal, the constituents and concentration of the electrolyte, as well as on the applied current density. Thus, MAO is an energy-consumption process, always accompanied by plasma chemical, electrochemical and physics chemical reactions in the micro-arc discharge channels. Under those circumstances the subject of current efficiency becomes very important. The primary objective of this study is to evaluate the oxide film growth efficiency during MAO process. A series of experiments based on different operating conditions have been performed and the current efficiency has also been calculated. The possible reasons leading to the low current efficiency have also been evidenced as anodic oxygen gas evolution, metal anodic dissolution and chemical dissolution of pre-existing oxide films in the electrolyte. Among these reasons oxygen gas evolution associated with electronic current during sparking is considered to be the dominating one for the low current efficiency, and the factors contributing to formation of oxygen bubbles have also been categorized.

Preparation and sintering behaviour of spinel-type Co xNiMn 2− xO 4 (0.2 ≤ x ≤ 1.2) by the ethylene glycol–metal nitrate polymerized complex process

Spinel-type powders of composition Co x NiMn 2− x O 4 (0.2 ≤ x ≤ 1.2) were prepared by auto-combustion of ethylene glycol–metal nitrate polymerized gel precursors. A pure spinel-type phase, with no intermediate compounds, was attained from the burning of the polymerized gel precursor and subsequent calcining at 600–700 °C. The formation, the structural evolution of the spinel-type phase, and calcined powder characteristics have been studied by using different techniques, having found that the properties were strongly dependent of the chemical composition. Sintering of the Co x NiMn 2− x O 4 powders have been studied by both the constant rate of heating (CRH) and the conventional ramp-and-holding methods. Density increased with the increasing of the Co content, and theoretically dense bodies (≥99.9% of the theoretical density) with submicronic average grain sizes were obtained at a temperature as low as 1050 °C for 6 h in the case of the Co 1.2NiMn 0.8O 4 composition. Above that temperature, a slow bloating phenomena as consequence of the evolution of oxygen gas with the corresponding decreasing in density, and the beginning of an exaggerated grain growth in the sintered samples was present. Microstructure of the sintered samples has also been studied.

Synthesis and sintering behaviour of spinel-type Co xNiMn 2− xO 4 (0.2 ≤ x ≤ 1.2) prepared by the ethylene glycol–metal nitrate polymerized complex process

Co x NiMn 2− x O 4 (0.2 ≤ x ≤ 1.2) spinel-type powders were prepared by auto-combustion of ethylene glycol–metal nitrate polymerized gel precursors. A pure spinel-type phase, with no intermediate compounds, was attained from the burning of the polymerized gel precursor and subsequent calcining at 600–700 °C. The formation and the structural evolutions of the spinel-type phase have been studied by simultaneous thermogravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Powder characteristics such as particle size and specific surface areas of the calcined powders were dependent of the chemical compositions. In the same way, the crystalline structure of the synthesized spinel-type phases was strongly dependent of the Co content, and a tentative cationic distribution is proposed. Sintering of the Co x NiMn 2− x O 4 oxides have been studied by both the constant rate of heating (CRH) and the conventional ramp-and-holding methods. Density increased with the increasing of the Co content, and theoretically dense bodies (≥99.9% of the theoretical density) with submicronic average grain sizes were obtained at a temperature as low as 1050 °C for 6 h in the case of the Co 1.2NiMn 0.8O 4 composition. Above that temperature, and coinciding with the apparition of an amorphous cobalt oxide liquid-phase, a slow bloating phenomena as consequence of the evolution of oxygen gas with the corresponding decreasing in density and the beginning of an exaggerated grain growth in the sintered samples was present. Microstructural evolution of the samples as a function of the sintering temperature has also been studied.

Flux and chemical vapor transport growth and characterization of [formula omitted]- and [formula omitted]-VO[formula omitted] single crystals

Differential thermal and thermogravimetric analysis investigations of VO(PO3)2 at elevated temperatures shows that the substance melts at 1035∘C incongruently with decomposition in two condensed phases and evolution of gaseous oxygen. In order to grow single crystals at lower temperature two techniques were used: flux and chemical vapor growth. α- and β-VO(PO3)2 single crystals were grown from V–P–O flux and by vapor transport mediated by TeCl4. Because of a high viscosity of the flux the crystallized material contains inclusions of flux. Vapor transport growth leads to crystals of a higher quality. The crystals contain no inclusions of foreign phases and contaminations of Te and Cl which might be introduced by transport agent. Magnetic susceptibility measurements of β-VO(PO3)2 single crystals indicate a quasi one-dimensional system with weak antiferromagnetic interactions. The temperature dependence of the magnetic susceptibility shows the parameters of the interaction (intra and interchain) to be essentially similar with the previously published parameters of α-phase.

Synthesis and thermoanalytical characterization of samarium peroxocarbonate

This paper presents the samarium peroxocarbonate synthesis and the data collected by thermogravimetry (TG)–differential thermogravimetry (DTG), active oxygen determination via iodine generation and total oxide content by gravimetry and elemental analysis of CHN by microanalyses. By thermal analysis (DTG), a mass loss corresponding to volatile components and water, equivalent to 29.22% of the total mass was observed. This value is in accordance with the mass loss of the compound when it was fired at 900 °C toward the Sm 2O 3 oxide. With the DTG program a process of thermodecomposition in multisteps, was observed, corresponding to the loss of water (up to 200 °C), evolution of oxygen gas from the peroxide compound and a partial decomposition to CO 2 (200–550 °C) and a second evolution of CO 2 (from 500 to 900 °C). This final evolution of CO 2 probably came from the intermediary compound Sm 2O 2CO 3. By microanalyses the carbon and hydrogen contents were 4.7 and 1.0%, respectively. In summary, the analytical data collected allowed one to conclude that the stoichiometric formula for the studied compound is Sm 2O 2(CO 3) 2·2H 2O.

Thermoanalytical characterization of neodymium peroxicarbonate

This paper presents the data collected for the neodymium peroxicarbonate by thermogravimetry (TG)–differential thermogravimetry (DTG), active oxygen determination via iodine generation and total oxide content by gravimetry and elementary analysis of CHN by microanalyses. By thermal analysis (DTG) a mass loss corresponding to volatile components and water, equivalent to 27.65% of the total mass was observed. This value is in accordance with the mass loss of the compound when it was fired at 900 °C toward the Nd 2O 3 oxide. With the DTG program a process of thermodecomposition in multisteps, was observed, corresponding to the loss of water (up to 250 °C), evolution of oxygen gas from the peroxide compound and a partial decomposition to CO 2 (250 to 600 °C) and a second evolution of CO 2 (from 600 to 900 °C). This final evolution of CO 2 probably came from the intermediary compound Nd 2O 2CO 3. By microanalyses the carbon and hydrogen contents were 4.8 and 1.0%, respectively. In summary, the analytical data collected allowed one to conclude that the stoichiometric formula for the studied compound is Nd 2O 2(CO 3) 2·2H 2O.

A Colorful Catalysis Demonstration

A simple, yet colorful, homogeneous catalysis demonstration is reported. When concentrated H2O2 is added to a yellow-orange aqueous solution of Fe3+, the solution turns black in color. After a brief induction period, exothermic decomposition of H2O2 ensues with the evolution of oxygen gas. As the reaction subsides, the solution returns to the original yellow-orange color. These color changes demonstrate one of the most important (and often most misunderstood by first-year students) concepts of catalysis—although a catalyst may be altered as it participates in a reaction, it is not consumed.

Wastes Treatment: Hydrothermal electrolytic oxidation of wastewater

Electrochemical evolution of hydrogen gas, oxygen gas and chlorine at the electrodes is the usual reaction in conventional electrolysis of aqueous salt solution. However, here we demonstrate that the electrolysis governing reaction in hydrothermal solutions is different from the electrolysis performed at atmospheric pressure and temperatures up to 100°C. Experimental electrolytic reaction of aqueous salt solution carried out inside a sealed 300-mL batch autoclave showed that; accumulation of hydrogen gas, oxygen gas and chlorine is highly suppressed under hydrothermal (250°C and 7 MPa) conditions. We have also observed that, when organics are present in the aqueous salt solution being hydrothermally electrolyzed, an effective oxidation of organics is accomplished. Furthermore, for hydrothermal electrolytic oxidation (HEO) with oxygen gas added, experimentally observed TOC removal profile demonstrates apparent anodic oxidation electrical current efficiency of almost 200% for highconcentrated acetic acid solutions.

Sintering Behavior, Microstructure, and Phase Composition of Sr(Fe,Co)O3−δ Ceramics

SrFe1−xCoxO3−δ (x= 0, 0.33) ceramics have been prepared in the temperature interval 900–1350°C in air, nitrogen, and oxygen atmosphere. The effect of cation nonstoichiometry on densification behavior, microstructure, and phase composition has been investigated. Densification of Sr‐deficient SrFeO3−δ initiates at a lower temperature than near stoichiometric SrFeO3−δ probably due to enhanced diffusion of Sr. However, for Sr‐deficient samples Sr4Fe6O13 is formed above ∼775°C, causing a significant decrease in the sintering rate. It is therefore necessary to avoid Sr deficiency to obtain dense SrFeO3−δ ceramics. The densification rate was significantly increased by Co substitution. Dense ceramics (>95% of theoretical density) of Sr‐excess and Co‐substituted SrFeO3−δ were obtained by sintering in the temperature region 1000–1200°C. The grain size increases by increasing temperature, decreasing partial pressure of oxygen and Co substitution. Exaggerated grain growth in the Co‐substituted material occurred at high temperatures. Sintering above 1200°C caused all materials, apart from Co‐substituted SrFeO3−δ in oxygen, to swell and develop a porous microstructure. The swelling mechanism was related to heterogeneous phase equilibria, which is reductive in nature and leads to evolution of oxygen gas. The phase equilibria are governed by the cation nonstoichiometry of the materials. The present findings demonstrate the importance of controlling the cation stoichiometry of ternary transition‐metal oxides to achieve ceramics with the desired homogeneous microstructure. The mixed valence state of the transition metal may lead to both swelling during sintering and cracking during cooling due to reduction/oxidation during heating/cooling.

Sintering of LaFeO3 Ceramics

The sintering of LaFeO3 has been studied in the temperature interval 1100–1600°C in air. The effect of cation nonstoichiometry on densification, microstructure, and phase composition is emphasized. La2O3 was observed to inhibit both sintering and grain growth. In Fe‐excess materials, exaggerated grain growth occurred, particularly above 1430°C, where a liquid phase was formed. Postsintering swelling was observed in Fe‐excess materials above 1430°C. The swelling mechanism is related to phase equilibria, which are reductive in nature and lead to the evolution of oxygen gas. The density in La‐excess materials remains high up to 1600°C, but the ceramics might disintegrate in air.

Oxygen stoichiometry and the problem of the growth of (VO) 2P 2O 7 single crystals

The crystal growth of (VO) 2P 2O 7 single crystals is discussed with respect to the formation of a high-temperature nonstoichiometric phase (VO) 2P 2O 7+x. The interaction between vanadyl pyrophosphate and oxygen was investigated in the temperature region 600–900°C. It was found that the decay of the high-temperature nonstoichiometric phase at lower temperature led to imperfections in crystals grown in an atmosphere with oxygen concentration higher than 0.2%. Two mechanisms for the decay are considered. The oxygen content of the crystals may be reduced at the surface by evolution of gaseous oxygen, whereas in the bulk the formation of an oxygen-enriched solid phase is observed.

Nanometer-thick oxide films produced by electrochemical anodizing of silicon

Electrochemical anodizing of silicon in dilute nitric acid was used to form nanometer-thick SiO2 films under galvanostatic conditions. The effects of current density and electrolyte temperature were studied. The evolution of gaseous oxygen was shown to essentially influence the process kinetics and qualitatively can account for all of the observed process features. At oxide thicknesses above 5 nm, the oxide becomes porous and its electrical characteristics are much worse than those of thermally grown SiO2.

The growth of a porous oxide film of a unique morphology by anodic oxidation of an Al-0.5 wt% Ni alloy

Porous anodic oxide film growth on an Al-0.5 wt% Ni alloy, containing finely dispersed Al 3Ni intermetallic particles, has been investigated by transmission electron microscopy of ultramicrotomed sections. It was found that film growth is influenced greatly by the localised processes proceeding at the intermetallic Al 3Ni particles, with consequent development of a unique film morphology, which has not been observed previously. At the initial stage of anodizing, the majority of the applied current is consumed by dissolution of the Al 3Ni particles at the alloy surface, accompanied by oxygen gas evolution, which leads to the suppression of the forming voltage, at 10 to 15 V, for a sufficiently long period until the particles are removed from the alloy surface. During this period, a thin porous film of fine dimensions, corresponding to the voltage of 10 to 15 V, is formed over the matrix surface generally. After the particles have been removed from the surface, the applied current is used for the growth of the porous oxide over the matrix surface as well as over the walls of cavities formed by dissolution of the particles. As the forming voltage increases, some of the pores grow further, at the expense of other pores in the immediate surrounding regions, with their dimensions controlled precisely by the increasing forming voltage, resulting in the formation of large pores of a ‘‘tear-drop’’ shape. Implications of these findings for forming porous anodic oxide films of controlled morphologies on aluminium and its alloys are discussed.

Investigation of the controlled growth of large undoped and Pt-containing YBCO pseudo-crystals

A thermal processing system incorporating four sets of independently controllable heating elements and a cold finger which generates uniform temperature gradients of up to 25 °C cm −1 has been developed and optimized to fabricate large undoped and Pt-containing YBCO pseudo-crystals by seeded peritectic solidification. Evolution of oxygen gas and loss of liquid during peritectic decomposition have been identified as key variables for the fabrication of large, single grain samples. The processing conditions associated with this system have been investigated for varying precursor body heating rate, undercooling, growth rate and sample thickness. Optimum values of these parameters were determined as heating rate: 10 °C h −1, undercooling: ≈ 15 °C and sample thickness: < 25 mm. A thermal profile for the optimized growth of large YBCO pseudo-crystals is proposed on the basis of these results. Single grain samples fabricated using this profile grow to within 2 mm of the bottom of the YBCO body and exhibit good morphology with 4-fold symmetry.

Solvent and structural effects on catalase-like function of binuclear manganese(II) compounds with μ-phenoxide bridge

The structures and ESR spectral properties of binuclear manganese(II) compounds which functionally mimic the bacterial dimanganese catalase enzyme have been developed. These compounds are formulated as [(L 1)Mn 2X 2]Y(XCl, Br, CH 3COO, C 6H 5COO, (C 6H 5) 2HCCOO; YClO 4, PF 6), [(L 2)Mn 2X 3] (XCl, Br), and [(L 2)Mn 2(benzoate) 2 (NCS)], where H(L 1)2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methyl-phenol and H(L 2)2,6-bis[N-(2-dimethylamino)ethyl]iminomethyl]-4-methyl-phenol. An X-ray diffraction structure determination of [(L 1)Mn 2Cl 2(CH 3OH) 2]PF 6 confirmed the anticipated N 6O septadentate coordination of the (L 1)-ligand, binuclear manganese(II) complex with μ-phenoxide, and two halogenide ions and two methanol molecules. In the crystal of [(L 2)Mn 2Cl 3]CH 3CN, there exists tetranuclear manganese(II) complex having center of symmetry. The terminal and central manganese(II) ions are bridged by phenoxide oxygen and a chloride ion (Mn…Mn = 3.440(1) Å, and two central atoms are bridged by two chloride ions with Mn…Mn distance of 3.804(1) Å. In acetonitrile solution, catalase-like function of the manganese(II) compounds with H(L 1)-ligand are found to be highly dependent the anions coordinating the Mn(II) ion; the activity of the XCl complex is much higher than those of the acetate and benzoate. On the other hand, the activity of [(L 2)Mn 2Cl 3] is slightly lower than that of the [(L 2)Mn 2(benzoate) 2(NCS)], where two manganese ions are bridged by benzoate anion. The Mn(II/III) complex of H(L 1), [(L 1)Mn 2(CH 3COO) 2] 2+ exhibits much higher activity than that of the corresponding Mn(II/III) complex, [(L 1)Mn 2(CH 3COO) 2] +. In dimethylformamide(dmf) solutions, an induction period (at least 30 minutes) is necessary before vigorous evolution of oxygen gas occurs for both the Mn(II) complexes with (L 1) and (L 2), however, some binuclear Mn 2(II/III) and Mn 2(III/III) complexes exhibited high catalase-like function in dmf. The latter fact may give a reasonable explanation for the fact that the manganese cluster in S 2-state of the Photosystem II shows a high catalase-like function instead of the negligible action in the S 1-state. Based on these facts, it is concluded that most important factor to control the catalase-like function of binuclear Mn(II) complex should be the oxidizable nature of the Mn(II) ion to a higher oxidation state, and the unusual behavior in dmf solution was accounted for on the assumption that dmf molecule may contribute to the activation of peroxide ion through interaction with an Mn(II)-peroxide adduct, leading to oxidation of the Mn(II) ion.