Oxygen In Alkaline Solution Research Articles

Extent of pyrite oxidation by dissolved oxygen in alkaline solutions including purified sodium bentonite

Ferrous iron-bearing minerals such as pyrite are promising reducing agents for the consumption of atmospheric oxygen in repositories used for the geological disposal of radioactive waste. Thus, the consumption of dioxygen (O2) by pyrite around repositories is essential for assessing atmospheric O2 which may be dissolved into underground water during installation of the repository. However, quantitative evaluation of the long-term oxidation of pyrite by dissolved oxygen (DO) has rarely been attempted. In particular, few observations of the particle morphology and internal inhomogeneity during the oxidation of pyrite have been recorded. Our study presents a quantitative investigation of the internal morphology of pyrite after approximately five years of oxidation by DO in carbonate-buffered solutions at varying ionic strengths. The effects of ionic strength (by applying various concentrations of sodium chloride (NaCl)) and of purified sodium bentonite (SB) on pyrite oxidation were studied. We observed that the surface of oxidized pyrite was covered with Fe(III) oxyhydroxides, which did not passivate the pyrite against further oxidation, and the interior of pyrite generated numerous flow-path-like voids in random directions during long-term oxidation. The oxidation of pyrite by DO was accelerated with increasing pH (9.3 ≤ pH ≤ 10.9) but was not associated with the increase in ionic strength by the addition of NaCl. The presence of SB increased pyrite oxidation when the pH was 10 or higher, while there was no effect when pH was 9.6 or lower. These observations suggest that pyrite can effectively consume O2 trapped underground in enclosed radioactive waste repositories.

Eco-friendly extraction of arsenic and tungsten from hazardous tungsten residue waste by pressure oxidation leaching in alkaline solutions: Mechanism and kinetic model

Tungsten residue waste (TRW), considered an environmental burden due to high content and excessive leaching toxicity of arsenic (As), are also secondary tungsten (W) resources. A novel method for simultaneous extraction of arsenic and tungsten from TRW via alkaline pressure oxidative leaching was proposed. The results show that As in the TRW mainly exists in the form of As coprecipitated with Mn(Ⅱ) oxides and FeAsS. In addition, As coprecipitated with Mn(Ⅱ) oxides and W are encapsulated in Fe, Mn oxides. The structure of Fe, Mn oxides with dense surface can be destroyed and the chemically stable arsenopyrite can be efficiently oxidized by oxygen in alkaline solutions. The leaching efficiency of As and S reached 97% and 99% at 80 min, respectively, while that of W reached 82% at 10 min. The leaching rate of As and S is controlled by diffusion with the apparent activation energies of 16.67 kJ/mol and 15.66 kJ/mol, respectively. Compared with TRW, the leaching toxicity of As in the leach residue decreased from 10.2 mg/L to only 0.071 mg/L. The new process suggests new possibilities for removal and recovery of As and W from TRW that will contribute to circular economy and environmental protection.

Carbon black modified with silver and low concentration of palladium as effective catalysts for electroreduction of oxygen in alkaline solutions

Carbon black modified with silver and low concentration of palladium as effective catalysts for electroreduction of oxygen in alkaline solutions

Electroreduction of oxygen in alkaline solution on iron phthalocyanine modified carbide-derived carbons

Carbide-derived carbons (CDC) are porous carbon materials with tunable pore structure, very high specific surface area and of great potential for electrochemical applications. In this work CDC-supported transition metal macrocyclic electrocatalysts are prepared using two different type of CDC materials and iron phthalocyanine (FePc). Herein, we report the superior electrocatalytic properties of FePc/CDC catalysts fabricated via simple pyrolysis approach. The morphology, composition and structural features of these CDC-based non-noble metal catalysts are evaluated using scanning and transmission electron microscopies, X-ray photoelectron spectroscopy, N2 physisorption and X-ray diffraction analysis. The electrochemical oxygen reduction reaction (ORR) behavior of FePc/CDC catalysts is evaluated employing the rotating disk electrode (RDE) method. FePc modified CDC materials demonstrate a superior ORR electrocatalytic activity in alkaline conditions, showing onset potential of −0.05 V (vs. SCE) close to that of commercial Pt/C. Thus, the RDE results show great potential of these non-Pt catalysts as cathode materials in metal-air batteries and alkaline membrane fuel cells.

Electrochemical reduction of oxygen in alkaline solution on Pd/C catalysts prepared by electrodeposition on various carbon nanomaterials

Electrochemical deposition by applying potential steps between −0.25 (or 0V) and 0.85V (vs SCE) was used to deposit Pd on different nanocarbon substrates. Influence of overpotential on the electrodeposition process was observed. Obtained Pd/C catalysts were studied with scanning electron microscopy and electrochemically in alkaline solution. Specific activity for the oxygen reduction reaction (ORR) of the catalysts was determined using the rotating disc electrode method. The ORR on all the studied Pd/C catalysts proceeded through a 4-electron pathway with a rate-limiting step of the first electron transfer to the O2 molecule. Pd catalysts deposited on graphene nanosheets showed highest specific activities for the ORR. The prepared catalysts showed higher specific activities than commercial Pd/C catalysts, which can be due to electrodeposition process proceeding without the presence of intrusive additives used in chemical synthesis of nanoparticles. Electrochemical activation was employed to improve the electrocatalytic activity of carbon nanotube-supported Pd catalysts for ORR.

Development of Nanostructured-Carbon-Supported Gold Nanoparticles As Catalysts for Electroreduction of Oxygen and Carbon Dioxide

There has been growing interest in the field of oxygen electroreduction, particularly with respect to potential applications in the science and technology of low-temperature fuel cells.. Obviously, many efforts have been made to develop suitable alternative electrocatalysts efficient enough to replace electrocatalysts based on scarce strategic elements such as platinum-group metals. Despite intensive research in the area, there are still a number of fundamental problems to be resolved, and the practical oxygen reduction catalysts still utilize systems based on platinum. Various homogeneous and heterogeneous catalytic systems have been proposed to induce the CO2 reduction and, depending on reaction conditions (applied potential, strength of the electrolyte, local pH, local concentration of CO2 and the catalyst applied), various products can be obtained. Because the CO2 molecule is very stable, its electroreduction would be characterized by large over-potentials. In this respect, behavior of carbon dioxide resembles that of dioxygen. In both cases, the limiting steps involve protonation of the respective species. The present study refers to a novel and unique approach of fabrication and deposition of gold nanoparticles on the surfaces of reduced graphene oxide and multi-walled carbon nanotubes. Among important issues is application of inorganic (rather than organic) capping ligand, heteropolymolybdate, to modify and stabilize (as well as probably also to link with the oxygen or hydroxyl groups on graphene surfaces) gold nanoparticles. During operation in alkaline medium or neutral media, polyoxometallates disappear but catalytically highly active gold remains and it exhibits excellent stability. The resulting material has occurred to show highly potent electrocatalytic properties toward electroreductions of carbon dioxide in neutral medium and oxygen in alkaline solution. What is even more important is that both carbon nanotubes and graphene have occurred to act effectively as carriers for gold nanostructures. Mutual activating interactions are feasible. The conclusions are reached on the basis of diagnostic electrochemical (e.g. rotating ring disk voltammetry), spectroscopic (FTIR) and microscopic (SEM, TEM) experiments. A series of comparative experiments with different carbon carriers and model catalytic materials (e.g. Vulcan-supported platinum) have also been performed. With respect to oxygen reduction, our diagnostic experiments at different concentrations of H2O2, support a view that the effect of the fast following chemical (H2O2-reductive-decomposition) reaction could be the dominating factor in explaining the observed positive potential shift observed during the oxygen reduction. The fact, that the optimum graphene-based catalytic system produced the oxygen reduction peak current comparable to that observed at the model platinum containing catalyst, would imply the efficient four-electron-type reduction mechanism.

Carbon-Supported Gold and Silver Nanoparticles As Catalysts for Electroreduction of Oxygen in Alkaline Media

The present study refers to a novel and unique approach of fabrication and deposition of gold nanoparticles on the surfaces of reduced graphene oxide and multi-walled carbon nanotubes. Among important issues is application of inorganic (rather than organic) capping ligand, heteropolymolybdate, to modify and stabilize (as well as probably also to link with the oxygen or hydroxyl groups on graphene surfaces) gold nanoparticles. During operation in alkaline medium or neutral media, polyoxometallates disappear but catalytically highly active gold remains and it exhibits excellent stability. The resulting material has occurred to show highly potent electrocatalytic properties toward electroreductions of carbon dioxide in neutral medium and oxygen in alkaline solution. What is even more important is that both carbon nanotubes and graphene have occurred to act effectively as carriers for gold nanostructures. Mutual activating interactions are feasible. The conclusions are reached on the basis of diagnostic electrochemical (e.g. rotating ring disk voltammetry), spectroscopic (FTIR) and microscopic (SEM, TEM) experiments. A series of comparative experiments with different carbon carriers and model catalytic materials (e.g. Vulcan-supported platinum) have also been performed. With respect to oxygen reduction, our diagnostic experiments at different concentrations of H2O2, support a view that the effect of the fast following chemical (H2O2-reductive-decomposition) reaction could be the dominating factor in explaining the observed positive potential shift observed during the oxygen reduction. The fact, that the optimum graphene-based catalytic system produced the oxygen reduction peak current comparable to that observed at the model platinum containing catalyst, would imply the efficient four-electron-type reduction mechanism. Graphene and other distinct carbon nanostructures are explored as supports (carriers) for dispersed metallic silver nanocenters which exhibit electrocatalytic activity toward reduction of oxygen in alkaline media. To facilitate fabrication, immobilization and distribution of Ag(0) nanoparticles, various types of graphene (e.g. reduced graphene oxide, RGO, and CFx graphene with carbon black) have been modified with the silver analogue of polynuclear Prussian Blue, namely with ultra-thin silver(I) hexacyanoferrate(II,III) layers. Following the heat-treatment step at temperatures as high as 400-600oC, some thermal decomposition of the cyanometallate network occurs and, consequently, metallic silver sites are generated. Their formation and distribution are facilitated by the voltammetric potential cycling in KOH electrolyte. The most promising electrocatalytic results with respect to the reduction of oxygen (the highest currents and the most positive electroreduction potentials) have been obtained when graphene nanostructures are combined or intermixed with Vulcan XC-72R nanoparticles. What is even more important that, due to the presence of the polynuclear cyanoferrate modifier or linker, the amounts of the undesirable hydrogen peroxide intermediate are significantly decreased.

Porous Carbon-Supported Gold Nanoparticles for Oxygen Reduction Reaction: Effects of Nanoparticle Size.

Porous carbon-supported gold nanoparticles of varied sizes were prepared using thiolate-capped molecular Au25, Au38, and Au144 nanoclusters as precursors. The organic capping ligands were removed by pyrolysis at controlled temperatures, resulting in good dispersion of gold nanoparticles within the porous carbons, although the nanoparticle sizes were somewhat larger than those of the respective nanocluster precursors. The resulting nanocomposites displayed apparent activity in the electroreduction of oxygen in alkaline solutions, which increased with decreasing nanoparticle dimensions. Among the series of samples tested, the nanocomposite prepared with Au25 nanoclusters displayed the best activity, as manifested by the positive onset potential at +0.95 V vs RHE, remarkable sustainable stability, and high numbers of electron transfer at (3.60-3.92) at potentials from +0.50 to +0.80 V. The performance is comparable to that of commercial 20 wt % Pt/C. The results demonstrated the unique feasibility of porous carbon-supported gold nanoparticles as high-efficiency ORR catalysts.

An RDE Investigation of NaOH Effect on Electrosynthesis of Lead Dioxide in Alkaline Solution

An electrochemical investigation of NaOH concentration on electrosynthesis of lead dioxide in alkaline solutions was performed using rotating disk electrodes (RDE). The results show that Pb(II) does not modify the evolution of oxygen in alkaline solutions, and the reaction taking place at 0.84 VSHE is under the mixed control of ionic transport and charge transfer. The Koutechy-Levich equation was used to calculate the value of diffusion coefficient D and apparent heterogeneous rate constant k of the PbO2 electrodeposition process at 0.84 VSHE. The results indicate that NaOH has a negative influence on the diffusion of Pb(II) within a NaOH concentration range of 2.5 ∼ 4.5 M. In addition, NaOH has a positive influence on the apparent heterogeneous rate constant of Pb(II) oxidation reactions within a NaOH concentration range of 2.5 ∼ 3 M, but a negative influence within a NaOH concentration range of 3 ∼ 4.5 M. XRD and SEM were employed to investigate the effects of NaOH concentration on phase composition and surface microstructures of deposits. The results show that PbO2 synthesized in an alkaline solution consists of pure α phase. The deposits are all composed of rounded nanocrystallites, except for the deposit synthesized in a solution of 3 M NaOH, which exhibited rod-like crystallite.

The enhanced electrocatalytic activity of graphene co-doped with chlorine and fluorine atoms

Graphene co-doped with fluorine and chlorine heteroatoms was prepared through a one-step synthesis and was investigated as the oxygen reduction electrocatalysts. Voltammetric measurements show that fluorine and chlorine co-doped graphene has remarkable catalytic activity toward the electrochemical reduction of oxygen in alkaline solution. Besides having a high tolerance to methanol crossover effect, the co-doped graphene also showed a better stability than that of commercial Pt/C electrocatalysts and of the chlorine-doped graphene that was prepared by the same approach. The charge transfer resistance of the co-doped graphene was substantially lower than that of the chlorine-doped graphene, suggesting that there may exist a synergistic interaction between fluorine and chlorine dopants. The rapid synthetic method reported here provides an effective approach for future investigation of halogen (co-) doped graphene.

Mechanism of alcohol-enhanced lucigenin chemiluminescence in alkaline solution.

The chemiluminescence (CL) of lucigenin (Luc(2+)) can be enhanced by different alcohols in alkaline solution. The effect of different fatty alcohols on the CL of lucigenin was related to the carbon chain length and the number of hydroxyl groups. Glycerol provides the greatest enhancement. UV/Vis absorption spectra and fluorescence spectra showed that N-methylacridone (NMA) was produced in the CL reaction in the presence of different alcohols. The peak of the CL spectrum was located at 470 nm in all cases, indicating that the luminophore was always the excited-state NMA. The quenching of lucigenin CL by superoxide dismutase (SOD) and the electron spin resonance (ESR) results with the spin trap of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) demonstrated that superoxide anions (O2 (•-)) were generated from dissolved oxygen in the CL reaction and that glycerol and dihydroxyacetone (DHA) can promote O2 (•-) production by the reduction of dissolved oxygen in alkaline solution. It was assumed that the enhancement provided by different alcohols was related to the solvent effect and reducing capacity. Glycerol and DHA can also reduce Luc(2+) into lucigenin cation radicals (Luc(•+) ), which react with O2 (•-) to produce CL, and glycerol can slowly transform into DHA, which is oxidized quickly in alkaline solution.

Effect of Cu Ad-layers deposited onto Gold Electrodes Surfaces on the Electrocatalytic Reduction of Oxygen in Alkaline Solution: a Rotating Ring-Disk Electrode Hydrodynamic Voltammetry Study

Effect of Cu Ad-layers deposited onto Gold Electrodes Surfaces on the Electrocatalytic Reduction of Oxygen in Alkaline Solution: a Rotating Ring-Disk Electrode Hydrodynamic Voltammetry Study

Oxygen Electroreduction on Multi-Walled Carbon Nanotube Supported Metal Phthalocyanines and Porphyrins in Alkaline Media

Metal phthalocyanine and porphyrin modified electrodes were prepared using multi-walled carbon nanotubes (MWCNTs) as a support material. The catalyst materials were heat-treated before electrochemical testing. X-ray photoelectron spectroscopic study was carried out in order to examine the surface composition. The electroreduction of oxygen has been investigated on Fe phthalocyanine/MWCNT, Co phthalocyanine/MWCNT, Fe porphyrin/MWCNT and Co porphyrin/MWCNT catalysts. Electrochemical experiments were carried out in 0.1 M KOH employing the rotating disk electrode (RDE) method. The glassy carbon (GC) disk electrodes were modified with MN4 macrocycle/MWCNT catalysts using Tokuyama AS-4 ionomer. Electrochemical characterization of the materials showed that all the MN4 macrocycle/MWCNT modified GC electrodes are highly active for the reduction of oxygen in alkaline solutions. Particularly high electrocatalytic activity was observed for porphyrin-based electrodes heat-treated at 800 degrees C. The RDE results obtained are significant for the development of alkaline membrane fuel cells.

Influence of surfactants on the solubility of oxygen in alkaline solutions

It is established that the structure of the hydrophilic part of surfactant molecules affects the solubility of oxygen in alkali solutions: the presence of anionic groups lowers the solvation ability of the system, and the presence of alcoholic hydroxyls raises the sorption capacity of solutions. An original method is proposed for experimental estimation of the concentration of surfactants in alkaline solutions at the gas-liquid interface.

Efficient Oxygen Reduction Reaction Using Ruthenium Tetrakis(diaquaplatinum)Octacarboxyphthalocyanine Catalyst Supported on MWCNT Platform

AbstractElectrocatalytic reduction of molecular oxygen in alkaline solution using a novel ruthenium tetrakis(diaquaplatinum)octacarboxyphthalocyanine (RuOCPcPt) electrocatalyst supported on multi‐walled carbon nanotube electrode has been described. We show that the oxygen reduction activity follows a direct 4‐electron transfer process at high kinetic rate constant, 3.57×10−2 cm s−1.

Electrocatalysis of oxygen reduction by quinones adsorbed on highly oriented pyrolytic graphite electrodes

The reduction of oxygen in alkaline solution has been studied on highly oriented pyrolytic graphite (HOPG) electrodes modified with various quinones using a rotating disk electrode (RDE). The electrode surface was modified by adsorption of quinones from a 0.1 M KOH solution. The oxygen reduction activity of these electrodes was considerably higher than that for unmodified HOPG and characteristic current maxima for oxygen reduction was observed. All quinones studied catalysed the two-electron reduction of oxygen to hydrogen peroxide. The peak potentials for oxygen reduction were in good correlation with the redox potentials of the quinones that were found from the cyclic voltammograms in oxygen-free solutions. The results obtained give further evidence that oxygen reduction is catalysed by the semiquinone radical and that the redox potential of the quinone is the most important factor determining its electrocatalytic activity for oxygen reduction.

Oxygen reduction on carbon nanomaterial-modified glassy carbon electrodes in alkaline solution

Electroreduction of oxygen in alkaline solution on glassy carbon (GC) electrodes modified with different carbon nanomaterials has been studied. Electrochemical experiments were carried out in 0.1 M KOH employing the rotating disk electrode and rotating ring-disk electrode methods. The GC disk electrodes were modified with carbon nanomaterials using polytetrafluoroethylene as a binder. Four different carbon nanomaterials were used: multiwalled carbon nanotubes, carbon black powder, and two carbide-derived carbons (CDC). For the first time, the electrocatalytic behavior of CDC materials toward oxygen reduction is explored. Electrochemical characterization of the materials showed that all the carbon nanomaterial-modified GC electrodes are highly active for the reduction of oxygen in alkaline solutions.

One-step through-mask electrodeposition of a porous structure composed of manganese oxide nanosheets with electrocatalytic activity for oxygen reduction

Potentiostatic electrolysis of a mixed aqueous solution of Bu 4NBr and MnSO 4 at +1.0 V (vs. Ag/AgCl) on Pt electrode led to the oxidation of Br − and Mn 2+ ions. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and X-ray diffraction (XRD) revealed that this anodic process was followed by the deposition of insulating crystals of bromide salt of Bu 4N + and the subsequent formation of layered manganese oxide in the interstitial spaces of the bromide grains already grown. Dissolution of the bromide crystals in water left a well-dispersed porous texture composed of manganese oxide nanosheets. The resulting MnO x -modified electrode exhibited a larger catalytic current for the reduction of oxygen in alkaline solution, compared to the bare Pt electrode.

Electrochemical synthesis of hydrogen peroxide: Rotating disk electrode and fuel cell studies

The electrochemical reduction of oxygen on various catalysts was studied using the thin-layer rotating disk electrode (RDE) method. High-surface-area carbon was modified with an anthraquinone derivative and gold nanoparticles. Polytetrafluoroethylene (PTFE) and cationic polyelectrolyte (FAA) were used as binders in the preparation of thin-film electrodes. Our primary goal was to find a good electrocatalyst for the two-electron reduction of oxygen to hydrogen peroxide. All electrochemical measurements were carried out in 0.1 M KOH. Cyclic voltammetry was used in order to characterise the surface processes of the modified electrodes in O2-free electrolyte. The RDE results revealed that the carbon-supported gold nanoparticles are active catalysts for the four-electron reduction of oxygen in alkaline solution. Anthraquinone-modified high-area carbon catalyses the two-electron reduction at low overpotentials, which is advantageous for hydrogen peroxide production.

Novel Pt-free catalyst for oxygen electroreduction

The tungsten carbide nanocrystals promoted Ag composite electrocatalysts have been firstly prepared and used for the electroreduction of oxygen in alkaline solution. These Pt-free electrocatalysts show high activities similar to those of Pt-based electrocatalysts. The kinetic parameters and the reaction mechanism for ORR are determined by RRDE. The enhancement of the activity is the evidence of synergetic effect. The novel electrocatalyst shows unique selectivity towards the electroreduction of oxygen and is immune to methanol, ethanol, isopropanol and glycerol. Such low cost electrocatalysts can be potentially applied to anion exchange membrane alcohol fuel cells, alcohol monitors and metal-air batteries.