Electrochemical Pre-oxidation Research Articles

Controlling Nucleation Sites for Metal Oxide Film Growth on Glassy Carbon via Electrochemical Preoxidation.

Coating electrode materials with metal oxide thin films can improve the performance of electrocatalysts and charge storage materials. Atomic layer deposition (ALD) enables the deposition of conformal, uniform films on a wide range of electrodes; however, an even film depends on the availability of nucleation sites directly on the electrode surface. Here, we show that the electrochemical oxidation of glassy carbon electrodes prior to the deposition of alumina thin films by ALD leads to more uniform electrochemically passivating films. Cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) demonstrate that film uniformity increases with the increasing potential of preoxidation until 2.50 V versus Ag/AgCl, at which point the films are fully passivating and appear continuous by SEM. Further increasing the potential of preoxidation leads to uniform but less consistently passivating alumina films. These findings show that electrochemical preoxidation is a rapid and readily tunable strategy for controlling oxygenic nucleation sites and therefore the growth of thin metal oxide films on glassy carbon electrodes.

Effect of borate on the corrosion behaviors of Ni11Fe10Cu anode in molten carbonate

Borates are an excellent electrolyte modifier for molten carbonate electrolyzers, which modulate electrode reactions. However, the addition of borate in molten carbonate causes the degradation of the Ni11Fe10Cu anode. Herein, the corrosion behaviors of Ni, Fe, Cu and Ni11Fe10Cu electrodes in molten Na2CO3-K2CO3 with/without borates were studied at different temperatures, gas atmospheres, and pre-oxidation conditions. The in situ formed acidic borate at the anode accelerates the dissolution of the oxide scale, which can be suppressed by increasing temperature or decreasing CO2 partial pressure. The corrosion resistance of the Ni11Fe10Cu anode can be further enhanced by preparing a NiFe2O4 scale through electrochemical pre-oxidation.

Effect of Electrochemical Pre-Oxidation for Mitigating Ultrafiltration Membrane Fouling Caused by Extracellular Organic Matter

Algal extracellular organic matter (EOM) will cause grievous membrane fouling during the filtration of algae-laden water; hence, boron-doped diamond (BDD) anodizing was selected as the pretreatment process before the ultrafiltration, and the EOM fouling mitigation mechanism and the purification efficiency were systematically investigated. The results showed that BDD oxidation could significantly alleviate the decline of membrane flux and reduce membrane fouling, and the effect was more notable with an increase in oxidation time. Less than 10% flux loss happened when oxidation duration was 100 min. The dominant fouling model was gradually replaced by standard blocking. BDD anodizing preferentially oxidizes hydrophobic organic matter and significantly reduces the DOC concentration in EOM. The effluent DOC was reduced to less than 1 mg/L when 100 min of BDD anodizing was applied. After the pre-oxidation of BDD, the zeta potential and interfacial free energy, including the cohesive and adhesive free energy, were all constantly increasing, which implied that the pollutants would agglomerate and deposit, and the repulsion between foulants and the ultrafiltration membrane was augmented with the extensive oxidation time. This further confirms the control of BDD on membrane fouling. In addition, the BDD anodizing coupled ultrafiltration process also showed excellent performance in removing disinfection by-product precursors.

Pre-oxidation of refractory gold concentrate by electrochemical methods in alkaline electrolyte

Pretreatment has been the focus of refractory gold concentrate, and many methods were developed. Pre-oxidation by electrochemical methods is environmentally friendly. The reaction mechanism of electrochemical oxidation of gold ore in an alkaline electrolyte at pH 10 was studied in this paper. The results suggest that the refractory gold concentrate electrochemical oxidation was divided into two different stages according to different oxidation products. The first one is passive-film-forming stage below 0.7 V (vs. SCE), when products are ferric hydroxide and high-sulfur products, including elemental sulfur or polysulfides, which form a passive film that hinders the further oxidation. Another is conventional continuous-oxidation mechanism, and products are soluble sulfate when the potential is maintained higher potentials. By the aid of ion beam etching (IBE), SEM and linear EDS scanning, a clear sulfur-rich outer ring structure morphology image caused by the electrochemical oxidation has been obtained in electrode surface. For pyrite-encapsulated gold deposits, it is important to provide a potential higher than 0.7 V (vs. SCE) for gold enrichment, when electrochemical pre-oxidation is employed.

Cerium-based metal–organic framework as an electrocatalyst for the reductive detection of dopamine

Thin films of a chemically stable and electrochemically active cerium(IV)-based metal–organic framework (MOF), Ce-MOF-808, are capable of electrocatalyzing the reduction of dopaquinone (DAQ) generated by the electrochemical pre-oxidation of dopamine (DA) present in 3-(N-morpholino)propanesulfonic acid buffer solutions. As the first study reporting the use of pristine cerium-based MOFs in electrochemical DA detection, the stability of the MOF during electrochemical operations, optimized thin-film loading, and the electrocatalytic mechanism are investigated. By utilizing the cathodic Faradaic responses for the reduction of the electrochemically pre-generated DAQ as a probe to detect DA in the electrolyte, the interference signals from the commonly coexisting ascorbic acid and uric acid can be effectively reduced.

An Electrochemical Process Comparison of As(III) in Simulated Groundwater at Low Voltage in Mixed and Divided Electrolytic Cells

A relatively low voltage can be favor of e- transfer and peroxide generation from dominant 2e--reduction of O2 on carbon materials as cathode, with low energy loss. In this study the conversion of As(III) in simulated high arsenic groundwater at low voltage was compared in a mixed and a anode–cathode separated electrolytic system. With applied voltages (the potential difference between cathode and anode) from 0.1 V to 0.8 V, As(III) was found to be efficiently converted to As(V) in the mixed electrolytic cells and in separated anodic cells. The complete oxidation of As(III) to As(V) at 0.1–0.8 V was also achieved on graphite in divided cathodic cells which could be long-running. The As(III) conversion process in mixed electrolytic cells, anodic cells and cathodic cells all conformed to the pseudo first-order kinetics equation. The energy consumed by As(III) conversion was decreased as the applied voltage declined. Low voltage electrolysis is of great significance for saving energy consumption and improving the current efficiency and can be applied to in-situ electrochemical pre-oxidation for As(III) in high arsenic groundwater.

High-efficient and environmentally friendly enrichment of semiconducting single-walled carbon nanotubes by combining short-time electrochemical pre-oxidation and combustion

High purity semiconducting single-walled carbon nanotubes (s-SWCNTs) have bright prospects in the field of microelectronics, but their enrichment processes are usually very complicated and cost time and energy, which represent a major impediment for their future applications. Here, we report on a new efficient covalent modification enrichment approach that tackles this problem. Our method is to first selectively functionalize the surface of arc-discharge metallic single-walled carbon nanotubes (m-SWCNTs) rapidly by electrochemical pre-oxidation at 7.0 V in 0.1 M KCl aqueous solution, and subsequently followed up by removing the m-SWCNTs with a short-time combustion process at 600 °C for 30 s to enrich high purity s-SWCNTs. Although the surface of the s-SWCNTs was functionalized and heat-treated, the intrinsic tubular structure and electronic characteristics were well maintained. Besides, our approach, without any complex equipment or toxic reagents, is energy and time saving and can be easily scaled up. Milligrams of high-quality s-SWCNTs with high purity of more than 95 wt% can be easily obtained in only several minutes. The retention rate of s-SWCNTs after combustion is as high as 61 wt%.

CaCO3scaling of oilfield produced water in “electrochemical pre-oxidation–coagulation sedimentation–filtration” process: reason, mechanism, and countermeasure

AbstractChemical stability of oilfield injection water is a critical factor to avoid corrosion and scaling of water treatment devices and pipelines. Especially, Guangli oilfield (a branch of Shengli Oilfield) has achieved remarkable success in anti-corrosion by applying an electrochemical pre-oxidation process into strong corrosive wastewater treatment, while scaling was aggravated therefore. XRD, SEM, EDS, and chemical analysis demonstrated the major component of the scale deposit was calcite. Succeedingly, chemical analysis of produced water along the process showed that pH, concentration of calcium ions, bicarbonate ions, and suspended solids changed remarkably before and after the mixing reactor. Further studies revealed that the addition of water treatment chemicals (Na2CO3) in the mixing reactors induced the precipitates of CaCO3, which could serve as crystal seeds and resulted in the continuous precipitation of calcium ions. Moreover, calcite saturation ratio increased from 0.97 to 3.94 could contr...

Electrochemical Pre-Oxidation of Drinking Water by On-Site Electro-Generation of Hydrogen Peroxide

Hydrogen peroxide is a green oxidizer. On-site electrochemical production of hydrogen peroxide has potential to become a new way for raw water pre-oxidation. The performance of electro-generation hydrogen peroxide was studied in the electrochemical reactor equipped with graphite felt as cathode and RuO2-IrO2-coated titanium mesh as anode. The effect of water flow rate, air flow rate and current density on concentration of hydrogen peroxide and energy consumption was studied. Results indicate that the optimal condition for the lowest energy consumption is to directly produce 5 mg/L of hydrogen peroxide as compared with producing high concentration followed by dilution. It was found that electrochemical pre-oxidation technology had a good effect on sterilization and removing turbidity and stink for raw water.

Laboratory study of the electrochemical pre-oxidation for improving thermodynamic stability of an oilfield produced water

Currently, oilfield produced water (OPW) in Haoxian Station, Shengli Oilfield was only treated in a simple physical procedure including sterilization, sedimentation and filtration. The thermodynamic stability of the treated OPW was not satisfied. The concentration of the suspended solid (SS) in the treated OPW would gradually increase in the process of OPW transportation from the station to injection wells. The concentration was over than 32 mg/L in some injection wells. This paper presented a new technology of electrochemistry pre-oxidation for OPW disposal. The effects of pre-oxidation electrical voltage and the pH on the actual treatment result and the corrosion rate of the OPW were investigated, and the optimal conditions were decided as an electrical voltage of 10 V and pH of 7.0. The indexes of the OPW treated with the new technology could completely meet the requirements of C1 grade in the SY/T 5329-94 standard (a criterion of China Petroleum Industry). The concentration of the SS in the OPW did not increase with time and corrosive rate of the treated OPW was only 0.044 millimeter per year (mm/a), less than 0.076 mm/a required by SY/T 5329-94, which implied improvement of the thermodynamic stability. Moreover, the compatibility of the treated OPW with the formation water was greatly improved after pre-oxidation treatment, thus less of formation damage would be made when the OPW was used for waterflooding.

A novel method for photodegradation of high-chroma dye wastewater via electrochemical pre-oxidation

A new two-step process involving the electrocatalytic (EC) pre-oxidation and the following photoelectrocatalytic synergistic (PEC) oxidation is proposed to treat the high concentration and high-chroma methyl orange dye wastewater, which cannot be degraded by photocatalytic oxidation (PC) directly. The SnO 2/TiO 2-NTs/Ti electrode simultaneously possessing the outstanding PC oxidation properties of TiO 2-NTs and the excellent EC oxidation abilities of the Sb doped SnO 2 was synthesized by impregnating Sb doped SnO 2 nanoparticles into TiO 2-NTs. In the pre-oxidation process as the first stage, the high-color dye wastewater is decolorized with electrochemical method to some extent. Then, the wastewater becomes a light transmission system. It provides a suitable condition for PC oxidation reaction in the second stage. The synergistic effects of PC and EC oxidation led to the high PEC efficiency and the complete mineralization of dye wastewater is achieved. This two-step process is fast and efficient, which is worthy to study and explore in the practical environmental treatment.

Electrochemical Pre-Oxidation of a Platinum / Graphitized-Carbon Catalyst for Improved PEM Fuel Cell Performance

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Evaluation of various strategies to formation of pH responsive hydroquinone-terminated films on carbon electrodes

Abstract The hydroquinone/quinone (H 2 Q/Q) redox system was tethered to glassy carbon surfaces using first an electrochemical pre-oxidation treatment to afford carboxylic acid functionalities followed by immobilizing the H 2 Q precursor, n -(2,5-dimethoxyphenyl)alkan-1-amine (general structure: H 2 N–(CH 2 ) n –C 6 H 3 (OCH 3 ) 2 , n = 1, 2, 4, 8, and 12), by carbodiimide chemistry and a final demethylation reaction. The resultant surfaces exhibited the expected chemical reversibility in aqueous solution with a pH-sensitive position of the formal potential (∼55 mV/pH unit), and an increase in the peak potential separation going from 0.02 V for n = 1 to 0.21 V for n = 12. The films were very robust and could withstand prolonged sonication and relatively large potential excursions. While the films followed the expected kinetic distance dependence for up to 4 methylene units the electrode kinetics was faster than expected for longer alkyl spacers. We suggest that film disorder, electrode-mediating effects, and a roughened electrode material could account for these apparent inconsistencies. To further understand such effects, two complementary electrode modification strategies leading to better film ordering on carbon were adapted; immobilizing a thin layer of benzoic acid by oxidative deposition of 4-aminobenzoic acid or employing a plasma deposition process to tether an acid analogue. Analysis of the various electrodes was accomplished by electrochemical methods, atomic force microscopy, and X-ray photoelectron spectroscopy.

Electrochemical Scanning Tunneling Microscopic Observation of the Preoxidation Process of CO on Pt(111) Electrode Surface

Presented are sequential images of CO on Pt(111), observed with electrochemical scanning tunneling microscopy, during its electrochemical preoxidation process. In the course of the well-known phase transition from the (2 x 2)-3CO-alpha structure to the (radical 19 x radical 19)R23.4 degrees-13CO structure, various structures were observed: (2 x 2)-3CO-beta (Chem. Comm. 2006, 2191-2193), (1 x 1)-CO, and (radical 13 x radical 13)R46.1 degrees-9CO. Based on an analysis of the populations of the structures averaged over imaging time and imaged location at the preoxidation potential range (0-0.25 V vs Ag/AgCl), the structures of CO domains changed sequentially in the order of (2 x 2)-3CO-alpha, (2 x 2)-3CO-beta, (1 x 1)-CO, (radical 13 x radical 13)R46.1 degrees-9CO, and (radical 19 x radical 19)R23.4 degrees-13CO as the potential shifted from 0 to 0.25 V. Such a sequential structural change demonstrates that the structures of (2 x 2)-3CO-beta, (1 x 1)-CO, and (radical 13 x radical 13)R46.1 degrees-9CO are transient ones during the preoxidation of CO on Pt(111). Discussed are the transient structures in terms of various aspects, such as the absence of CO in solution and the origin of compressed structures.

An Ellipsometric and Electrochemical Study of Microperoxidase-8 and -11 Adsorption on Platinum and Gold Surfaces

The adsorption of microperoxidase-8 and -11 (MP-8 and 11) on hydrophilic platinum and gold surfaces was studied by in situ ellipsometry. Neither peptide adsorbed on gold regardless of the composition of the aqueous solution. Electrochemical preoxidation of Pt decreased both the rate constant of adsorption (kads) and the maximum surface concentration (Γmax) of MP-8 by a factor of 2.7 and 1.6, respectively. Thus, the adsorption on Pt is chemical in nature. However, both kads and Γmax after rinsing (Γm) depend to a large degree on the pH-induced ionization of the MP-8 and -11 molecules, i.e., on the structure of the peptide chain. The experimental and calculated Γm values for the different pH-dependent species of heme peptides indicated formation of a monolayer. Electrochemical studies on Pt revealed that the protoporphyrin ring of the adsorbed heme peptides is involved in a multiple-electron oxidation reaction. In addition, the adsorbates exert a "blocking" effect on the electrochemical reactions of the Pt oxides and generation of "strongly bound" hydrogen layers. However, through the net charge of the adsorbed heme peptides, the adsorption of "loosely bound" oxygen and hydrogen is controlled by changing the concentration of H+ at the electrode surface.