Increasing Electrolysis Time Research Articles

The stability of NiCoZn electrocatalyst for hydrogen evolution activity in alkaline solution during long-term electrolysis

The long-term stability of NiCoZn coating for hydrogen evolution reaction (HER) was investigated in 1 M KOH solution under 100 mA cm −2 current density at room temperature. The effect of electrolysis on the corrosion behavior of NiCoZn coating was also studied. The alloy prepared on a copper electrode (Cu/NiCoZn) was etched in a concentrated alkaline solution (30% NaOH) to produce a porous and electrocatalytic surface suitable for use in the HER. The bulk and surface compositions of coating before and after alkaline leaching were determined by atomic absorption spectroscopy (AAS) and energy dispersive X-ray (EDX) analysis. The surface morphologies of freshly prepared and aged electrodes were investigated by scanning electron microscopy (SEM). Their catalytic activity towards the HER was assessed by recording cathodic current–potential curves and electrochemical impedance spectroscopy (EIS) techniques. It was found that the NiCoZn coating has a compact and porous structure. The long-term operation at 100 mA cm −2 current density showed that the electrochemical activity of Cu/NiCoZn electrode increased slightly with increasing electrolysis time. The activation of electrode related to the removal of any existing corrosion products and accumulations from the pores and formation of cracks during hydrogen gas evolution. The corrosion tests showed that the corrosion resistance of Cu/NiCoZn electrode changed after electrolysis.

The influence of F − doping on the activity of PbO 2 film electrodes in oxygen evolution reaction

The PbO 2 and F −-doped PbO 2 (F-PbO 2) film electrodes have been prepared by an electrodeposition process onto platinum substrate. The changes of their electrochemical activity for oxygen evolution (OE) reaction with accelerated electrolysis time have been studied. The results show that the activity of the electrodes decreases with increasing electrolysis time. This can be attributed to the conductivity variations, which are caused by the decrease of the oxygen vacancy concentration in PbO 2 films during OE. The mechanism of the decrease of the oxygen vacancies has been investigated. For F-PbO 2 film electrodes, though its electrochemical activity is somewhat lower than that of undoped one, its activity stability is much higher in comparison with that of PbO 2. The influence of F − doping on the activity of PbO 2 film electrodes has been also discussed.

Electrochemical Inactivation of Triclosan with Boron Doped Diamond Film Electrodes

This research investigated an electrochemical method for inactivating contaminated stockpiles of the biocidal agent, triclosan. The goal of the electrolysis was to produce products that were amenable to treatment in conventional activated sludge treatment systems. Triclosan oxidation in electrochemical cells with boron doped diamond (BDD) film anodes was investigated in aqueous solutions at a pH value of 12. Chronoamperometry experiments showed that direct oxidation of triclosan occurred at potentials below those for H2O, Cl-, or OH- oxidation. Measurable rates of triclosan oxidation began at potentials above 0.4 V with respect to the standard hydrogen electrode (SHE), while potentials of 0.5, 1.3, and 1.8 V were required to obtain measurable oxidation rates of H2O, Cl-, and OH-, respectively. At anode potentials below 2 V, the dominant electrode reaction involved direct triclosan oxidation, while indirect oxidation was the dominant pathway at higher potentials. However, cyclic voltammetry experiments showed that direct oxidation of triclosan resulted in the formation of a passivating film on the electrode that could only be removed by oxidation at potentials above 3 V. Direct triclosan oxidation showed a very weak potential dependence, suggesting that its oxidation was limited by chemical dependent factors rather than by an outer-sphere electron transfer reaction. Organic triclosan oxidation products consisted primarily of chlorinated acetic acids and chlorinated phenolic compounds. Although the byproducts of triclosan oxidation became increasingly less reactive with increasing electrolysis time, triclosan could be completely oxidized to CO2 at current densities above 2 mA/cm2. Microtox testing indicated that residual triclosan accounted for nearly all the toxicity in the treated water, despite the fact that chlorinated byproduct concentrations were significantly higher than those of triclosan itself.

Electrochemical degradation of chlorophenoxy and chlorobenzoic herbicides in acidic aqueous medium by the peroxi-coagulation method

The degradation of 4-chlorophenoxyacetic acid (4-CPA), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) as chlorophenoxy herbicides, as well as of 3,6-dichloro-2-methoxybenzoic acid (dicamba) as chlorobenzoic herbicide, has been studied by peroxi-coagulation. This electrochemical method yields a very effective depollution of all compounds in acidic aqueous medium of pH 3.0 working under pH regulation, since they are oxidized with hydroxyl radicals produced from Fenton’s reaction between Fe 2+ and H 2O 2 generated by the corresponding Fe anode and O 2-diffusion cathode. Their products can then be removed by mineralization or coagulation with the Fe(OH) 3 precipitate formed. Both degradative paths compete at low currents, but coagulation predominates at high currents. The peroxi-coagulation process of dicamba at I⩾300 mA leads to more than 90% of coagulation, being much more efficient than its comparative electro-Fenton treatment with a Pt anode and 1 mM Fe 2+, where only mineralization takes place. For the chlorophenoxy compounds, electro-Fenton gives a slightly lower depollution than peroxi-coagulation, because more easily oxidable products are produced. Oxidation of chlorinated products during peroxi-coagulation is accompanied by the release of chloride ion to the solution. The efficiency of this method decreases with increasing electrolysis time and current. The decay of all herbicides follows a pseudo-first-order reaction, with a similar constant rate for 4-CPA, MCPA, 2,4-D and 2,4,5-T, and a higher value for dicamba.

Electrochemically Induced DNA Cleavage by Copper-Phenanthroline Complex

The interaction of copper-1,10-phenanthroline (phen) complex with calf thymus DNA has been investigated by cyclic voltammetry and differential pulse voltammetry at gold electrode. DNA can be efficiently cleaved by electrochemically reduced Cu(phen) complex at −0.5 V (vs. Ag/AgCl) in the presence of oxygen without addition of extra reductive agent. Oxygen is required for electrochemically induced DNA cleavage by Cu(phen) complex because it serve as a precursor formation of hydrogen peroxide. DNA cleavage is inhibited by bathocuproine and hydroxyl radical scavenges. These results reveal Cu(I) complex and hydroxyl radical are involved in DNA cleavage reaction. The percentage of DNA cleavage is enhanced with increasing electrolysis time and is also dependent on the ratio of Cu(phen) to DNA concentration. The cleaved DNA fragments are separated by high performance liquid chromatography (HPLC). The experimental results indicate that the method for electrochemically induced DNA cleavage by Cu(phen) is simple and efficient.

Aniline degradation by Electro-Fenton ® and peroxi-coagulation processes using a flow reactor for wastewater treatment

The degradation of 10–30 l of a 1000 ppm aniline solution in 0.050 M Na 2SO 4+H 2SO 4 at pH 3.0 and 40 °C by Electro-Fenton ® and peroxi-coagulation processes at constant current until 20 A has been studied using a pilot flow reactor in recirculation mode with a filter-press cell containing an anode and an oxygen diffusion cathode, both of 100 cm 2 area. H 2O 2 is produced by the two-electron reduction of O 2 at the cathode, being accumulated with a current efficiency between 60% and 80% at the first stages of electrolyses performed with a Ti/Pt anode. In the presence of 1 mM Fe 2+, less H 2O 2 is accumulated, but it is not detected using an Fe anode. The Electro-Fenton ® process with 1 mM Fe 2+ and a Ti/Pt or DSA ® anode yields an insoluble violet polymer, while the soluble total organic carbon (TOC) is gradually removed, reaching 61% degradation after 2 h at 20 A. In this treatment, pollutants are preferentially oxidized by hydroxyl radicals formed in solution from reaction of Fe 2+ with H 2O 2. The peroxi-coagulation process with an Fe anode has higher degradation power, allowing to remove more than 95% of pollutants at 20 A, since some intermediates coagulate with the Fe(OH) 3 precipitate formed. Both advanced electrochemical oxidation processes (AEOPs) show moderate energy costs, which increase with increasing electrolysis time and applied current.

Relationship between hydrocarbon production in the electrochemical reduction of CO2 and the characteristics of the Cu electrode

Abstract The distribution of H 2 , CO, CH 4 and C 2 H 4 produced by electrochemical reduction of CO 2 in aqueous KHCO 3 solution at Cu electrodes has been studied in combination with the electrode surface analysis by X-ray photoelectron spectroscopy. Electrolytes were performed mainly at 1.9 V vs. SCE with Cu electrodes pretreated in various ways: ultrasonically cleaned, air-oxidized and electrolytically cleaned. The product distribution depended drastically on the pretreatment method and the electrolysis time. The heavily oxidized electrode surface produced H 2 predominantly, while the surface with a relatively large amount of metallic Cu gave preferential CO production. The surface with metallic Cu, Cu oxide and much adsorbed oxygen had an enhanced activity for hydrocarbon production. The oxide film at the surface was gradually reduced to bare Cu metal with increasing electrolysis time, resulting in a variation of the product distribution.

Electrometallurgy of copper refinery anode slimes

High-selenium copper refinery anode slimes form two separate and dynamically evolving series of compounds with increasing electrolysis time. In one, silver is progressively added to non-stoichiometric copper selenides, both those originally present in the anode and those formed subsequently in the slime layer, and in the other, silver-poor copper selenides undergo a dis-continuous crystallographic sequence of anodic-oxidative transformations. The silver-to-selenium molar ratio in the as-cast anode and the current density of electrorefining can be used to construct predominance diagrams for both series and, thus, to predict the final bulk “mineralogy” of the slimes. Although totally incorrect in detail, these bulk data are sufficiently accurate to provide explanations for several processing problems which have been experienced by Kidd Creek Division, Falconbridge Ltd., in its commercial tankhouse. They form the basis for a computer model which predicts final cathode quality from chemical analyses of smelter feed.