Anodic Oxidation Process Research Articles

Electrolyte pH and operating potential: critical factors regulating the anodic oxidation and zinc storage mechanisms in aqueous zinc ion battery

The complicated multi-electron reactions and electrochemical/chemical evolution of vanadium oxides in zinc ion batteries make the detailed reaction mechanism difficult to understand. Here, we show that these reactions can be easily interpreted from the reliable potential–V-species (electrochemical) and pH–V-species (chemical) relationships. A systematic investigation of several low-valence vanadium oxides (V6O13, VO2, and V2O3) is conducted to study the detailed reaction mechanisms upon the anodic oxidation and routine zinc storage process. Vanadium oxides are thermodynamically converted to layered zinc pyrovanadate Zn3V2O7(OH)2·2H2O (ZVOH) in a certain range of pH (4.0–8.5) and operating potential following the VOx oxidation →V-species dissolution →ZVOH precipitation processes. The establishment of pH–V-species and potential–V-species relationships can well explain the reaction mechanisms not only in anodic oxidation but also in routine zinc insertion/extraction processes with the combination of electrochemical and chemical reactions. Moreover, due to the favorable open and stable crystal framework and unique Zn2+ storage mechanism, the obtained ZVOH exhibits a highly improved capacity of 492.7 mAh/g within the voltage window of 0.3–1.4 V. Our work highlights the critical roles of operating potential and electrolyte pH in zinc ion battery and offers new knowledge and practices for its commercialization.

A PEDOT-Pt-TiO2 hybrid material synthesized by the casting method for photocatalytic hydrogen generation

This study describes the synthesis and characterisation of a hybrid material consisting of titanium dioxide nanotube arrays (TiO2 NTs) modified by platinum nanoparticles (Pt-TiO2 NTs) via radiolysis and a conductive poly(3,4-ethylenedioxythiophene) (PEDOT) layer, for the first time. The NTs were fabricated by a two-step anodic oxidation process and exhibited different morphologies using electrolyte solutions with different water contents (2–10 vol%). The polymer layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was coated on the Pt-TiO2 scaffold using the casting method. The PEDOT:PSS-PT-TiO2 NTs exhibited stability in the photocatalytic process after additional calcination which was carried out to remove the PSS part; the nanotubes with lengths of ∼3 μm exhibited the highest photocatalytic activity (∼4.5 × 10−3 μmol cm−2 of H2). Additionally, the samples obtained from electrolyte solutions containing 5 and 10 vol% water exhibited nanostructures with the highest catalytic activity.

A Superhydrophobic Anti-Icing Surface with a Honeycomb Nanopore Structure

Recently, the icing disaster of transmission lines has been a serious threat to the safe operation of the power system. A superhydrophobic (SHP) anti-icing surface with a honeycomb nanopore structure was constructed using anodic oxidation technology combined with a vacuum infusion process. When the current density was 87.5 mA/cm2, the honeycomb porous surface had the best superhydrophobic performance (excellent water mobility), lowest ice-adhesion strength (0.7 kPa) and best anti-frosting performance. Compared with other types of alumina surfaces, the ice-adhesion strength of the SHP surface (87.5 mA/cm2) was only 0.2% of that of the bare surface. The frosting time of the SHP surface (87.5 mA/cm2) was 150 min, which was much slower. The former is attributed to the air cushion within the porous structure and the stress concentration, and the latter is attributed to the self-transition of the droplets and low solid–liquid heat transfer area. After 100 icing or frosting cycles, the SHP surface (87.5 mA/cm2) maintained a low ice-adhesion strength and superhydrophobic performance. This is because the anodic oxidation process forms a hard porous film, and the nano porous structure with a high aspect ratio can store modifiers to realize self-healing. The results indicate that the SHP surface with a honeycomb nanopore structure presents excellent anti-icing performance and durability.

Cu-catalyzed asymmetric regiodivergent electrosynthesis and its application in the enantioselective total synthesis of (-)-fumimycin

Quaternary amino acids are one of the essential building blocks and precursors of medicinally important compounds. Various synthetic strategies towards their synthesis have been reported. On the other hand, developing core-structure-oriented cross-dehydrogenative coupling (CDC) reactions, is a largely unsolved problem. Herein, we describe a copper-catalyzed regiodivergent electrochemical CDC reaction of Schiff bases and commercially available hydroquinones to obtain three classes of chiral quaternary amino acid derivatives for the efficient assembly of complex scaffolds with excellent stereocontrol. The electrochemical anodic oxidation process with slow releasing of quinones serves as an internal syringe pump and provides high levels of reaction efficiency and enantiomeric control. The utility of this strategy is highlighted through the synthetic utility in the asymmetric total synthesis of (-)-fumimycin.

Sequential anodic oxidation and cathodic electro-Fenton in the Janus electrified membrane for reagent-free degradation of pollutants

Electrified membrane technologies have recently demonstrated high potential in tackling water pollution, yet their practical applications are challenged by relying on large precursor doses. Here, we developed a Janus porous membrane (JPEM) with synergic direct oxidation by Magnéli phase Ti4O7 anode and electro-Fenton reactions by CuFe2O4 cathode. Organic pollutants were first directly oxidized on the Ti4O7 anode, where the extracted electrons from pollutants were transported to the cathode for electro-Fenton production of hydroxyl radical (·OH). The cathodic ·OH further enhanced the mineralization of organic pollutant degradation intermediates. With the sequential anodic and cathodic oxidation processes, the reagent-free JPEM showed competitive performance in rapid degradation (removal rate of 0.417 mg L−1 s−1) and mineralization (68.7 % decrease in TOC) of sulfamethoxazole. The JPEM system displayed general performance to remove phenol, carbamazepine, and perfluorooctanoic acid. The JPEM runs solely on electricity and oxygen that is comparable to that of PEM relies on large precursor doses and, therefore, operation friendly and environmental sustainability. The high pollutant removal and mineralization achieved by rational design of the reaction processes sheds light on a new approach for constructing an efficient electrified membrane.

Investigation of Anodic Bond Formation Process and Potential Use of the Results

Anodic bonding of glass to silicon wafers is an essential step in microsystems manufacturing, combining reliable process setup with robust process control and providing very strong and hermetic wafer bonds. It is general accepted that the bond formation is based on anodic oxidation processes, but it is still under debate where the oxygen originates from and how far the oxidation can be driven. The oxidation mechanism during anodic bonding has been studied using sequential and one-step bonding procedures. It can be concluded that the oxygen for the oxidation originates from the glass. It is therefore possible to completely oxidise sputtered aluminium between two glass wafers during bonding, resulting in a nearly optically transparent bond of both wafers. By understanding the oxidation processes, it is possible to predict which surface layers will bond well (silicon, silicon dioxide, aluminium) and which will be hardly or impossible to bond (silicon nitride, gold). These predictions have been tested and confirmed by experimental results.

Efficient degradation of refractory pollutant boosted by combining heterogeneous electro-Fenton on the hydrophobic modified gas diffusion electrode with anodic oxidation

To boost refractory pollutant removal over a broad pH range, we here proposed an integrated electrocatalytic process combining electrochemical anodic oxidation (AO) with cathodic electro-Fenton (EF) based on a hydrophobic modified gas diffusion electrode and heterogeneous Fenton catalyst of FeOCl. Total organic carbon (TOC) removal of refractory levofloxacin by EF + AO process was 85% in 120 min under the applied potential of −0.6 V and pH ∼6.7, obviously higher than that of only AO (22%) or EF (62%) process. Significantly, EF+AO process was demonstrated to be efficient and stable for actual wastewater treatment that chemical oxygen demand (COD) value of refinery wastewater after EF + AO treatment was steadily met the discharge standard (GB 18918–2002) for sewage treatment plants in China (I-A: COD < 50 mg/L) during 100 h of consecutive runs. Our results provide new insights into developing an energy-efficient electrocatalytic technology for enhancing refractory pollutant removal.

Optimization of Nb/Al-AlO x /Nb Josephson junctions through wafer-scale anodic oxidation: a systematic characterization and performance analysis

The Nb/Al-AlO x /Nb (SIS) Josephson junction is a crucial component in many types of superconducting devices. However, it can be easily damaged during the plasma fabrication processes. Anodic oxidation is an effective method for protecting SIS junctions by oxidizing Nb and Al from the junction profile. We used a custom wafer-scale anodic oxidation system and a neutral electrolyte to study the oxidation process of Nb films and Nb-Al(-AlO x )-Nb junctions. The oxidation process was thoroughly characterized by considering factors such as morphology and electrical properties. Anodization spectroscopy revealed varying oxidation sections from the top Nb layer to the bottom layer, extending across the Al-AlO x interlayer. This indicates that a 4 nm Al layer is sufficient to cover the surface of the bottom Nb film. High-resolution transmission electron microscopy and energy dispersive spectroscopy revealed that the Nb2O5 layer produced from the oxidation of the bottom Nb layer penetrated the Al2O3 layer and migrated to the top surface as the oxidation voltage increased. The top Nb layer of the SIS junction was also subjected to oxidation, despite the presence of a protective photoresist. Following the anodic oxidation process, the entire wafer surface was coated with an insulating Nb2O5 film. This film provided protection for the SIS junctions during the subsequent microfabrication process. The fabricated junction array, consisting of 128 junctions, demonstrated uniform electrical properties benefiting from the anodic oxidation process. This systematic analysis will further the research and practical applications of SIS junctions.

Removal of pharmaceuticals and personal care products from wastewater via anodic oxidation and electro-Fenton processes: current status and needs regarding their application.

This review provides a current opinion on the most recent works that have been published toward the application of electrochemical advance oxidation processes (EAOPs) for the degradation of pharmaceutical and personal care products (PPCPs) in water streams. Advances in the application of anodic oxidation (AO)- and electro-Fenton (EF)-based processes are reported, including operational conditions, electrode performance, and removal. Although AO- and EF-based processes can easily reach 100% removal of PPCPs, mineralization is desirable to avoid the generation of potential toxic byproducts. The following section exploring some techno-economic aspects of the application of EAOPs is based on electrode selection, operational costs as well as their use as cotreatments, and their synergistic effects. Finally, this short review ends with perspectives about the emerging topics that are faced by these technologies applied for the degradation of PPCPs in research and practice.

Defluorinative Thiolation of gem-Difluoroalkenes by Convergent Paired Electrolysis.

Herein, we have successfully developed a convergent paired electrolysis strategy for the defluorinative thiolation process utilizing thiols and gem-difluoroalkenes as precursors. This protocol exhibits remarkable tolerance toward a wide range of functional groups, as exemplified by the successful late-stage defluorothiolation of complex molecules. Additionally, this strategy is amenable to gram-scale synthesis, making use of both anodic oxidation and cathodic reduction processes in an efficient manner. Several control studies were conducted and suggested a convergent paired electrolysis mechanism.

Study of antiviral drug Famciclovir as a corrosion inhibitor for carbon steel in hydrochloric acid medium

A nucleoside antiviral drug namely 2-[2-(2-Amino-9H-purine-9-yl)ethyl]-1,3-propanediol Diacetate (Famciclovir, or FAM for short), is developed as a corrosion inhibitor of carbon steel in hydrochloric acid medium. The corrosion inhibition performance is explored using electrochemical measurement and detailed surface characterization techniques. The results indicate that the charge transfer resistance (Rct) values of carbon steel samples modified with FAM get a significant improvement, and the highest corrosion inhibition efficiency reached 96.87% at a concentration of 1.0 mM after soaking for 2 h at 298 K. When the solution temperature rises from 298 K to 318 K, the efficiency of the corrosion inhibitor with a concentration of 1.0 mM slightly decreases from 96.87% to 93.92% after soaking for 2 h. FAM presents a mixed corrosion inhibitor that simultaneously inhibits the anodic oxidation and cathodic reduction processes of carbon steel electrodes in hydrochloric acid medium. Adsorption of FAM on the surface of carbon steel is found to follow the Langmuir adsorption isotherm and it is mainly chemical adsorption. Confocal micrograph, X-ray diffraction analyzer (XRD) and X-ray photoelectron spectrometer (XPS) results further validate that FAM can adsorb on carbon steel surface, which inhibits the corrosion of HCl.

Treatment of urban wastewater by coupling planted filters with anodic oxidation process

ABSTRACT The wastewater reuse strategy has the advantage of providing an effective resource to reduce water deficits, protect natural resources and alleviate future water shortages caused by climate change. In many arid and semi-arid regions, water reuse provides the majority of irrigation water, which is why appropriate treatment techniques are needed. These include planted filters, with restricted reuse of agricultural treated water. The main innovation is therefore to develop a new technique with reduced operating costs and increased efficiency for wastewater treatment that can be used in different sectors (household, industrial, washing centers…). The current work aimed to assess the performance of coupling planted Filters with anodic oxidation on platinum to remove contaminants and pathogens from urban wastewater effluents. To evaluate the efficiency of this hybrid process, urban sewage was first treated by filters planted with reeds, then by anodic oxidation on platinum using photovoltaic panels. Results showed that this treatment system allows a complete elimination of organic matter, ammonium nitrogen, and pathogenic bacteria. Removal rates were ~ 100% for COD, ~100% for BOD, ~100% for NH4 +, 93.24% for NO3 −, and ~100% for TC, FC, and FS. Due to the satisfactory performance, treated water can be reused without restriction in different sectors.

Anodizing model and CV simulation for etched aluminium foil for high voltage

The core of aluminium electrolytic capacitors anode foil is the pit distribution of etched foils and the specific capacitance of formed foils, there is still no well-developed system to evaluate both at once. In this study, a pit anodizing model and a method to simulate the CV value of high-voltage etched aluminium foil is proposed. The model processes scanning electron microscopy photographs of high-voltage etched aluminium foils, models the growth of alumina in the 200–600 V ranges, takes into account the pit clogging phenomenon of the anodic oxidation process by image processing, corrects and specifies the formation constants and dielectric constants of alumina at different formation voltages. The model can reflect the growth pattern of alumina in the standard process. With the model proposed in this work, the CV values of aluminium foils at each formation voltage are simulated. The simulated results have a mean deviation of 1.4% from the actual experimental values, which can accurately simulate the real performance of the etched foil. This simulation method can evaluate the performance of aluminium foil after anodizing by considering both the pit distribution and the anodizing environment. It can also be used to compare the applicable working voltage ranges of different etched foils. This can help factories and laboratories with etching foil selection, greatly reducing material and time consumption.

High-efficiency refractory organic pollutants removal boosted by combining heterogeneous electro-Fenton with electrochemical anodic oxidation over a broad pH range

Electrochemical anodic oxidation (AO) is a green and efficient treatment process for refractory pollutants degradation. The cathode in AO process generally serves as the counter electrode, and does not contribute significantly for pollutants removal. The heterogeneous electro-Fenton (EF) process uses the bifunctional catalytic material as cathode to produce H2O2 via 2e- oxygen reduction reaction and activate H2O2 decomposition to generate •OH for degrading pollutants. Herein, we investigated an integrated electrocatalytic process between heterogeneous EF and AO (EF+AO) to enhance refractory pollutants removal over a broad pH range without the production of iron-containing sludge. Total organic carbon removal of phenol by EF+AO was 98.2 % in 180 min under pH ∼5.9 and the applied current density of 1.0 mA cm−2, obviously higher than that of only EF (48.8 %) or AO (56.9 %). Significantly, EF+AO process can efficiently treat the actual coking wastewater that the chemical oxygen demand (COD) value gradually decreased from 312.3 mg L−1 to 47.8 mg L−1 with the low specific energy consumption of 14.0 – 25.7 kWh·(kg COD)−1. This process delivered excellent long-term durability in flow mode, retaining efficient degradation performance for phenol during 100 h of consecutive runs. Our results provide new insights into developing an energy-efficient electrocatalytic process for pollutants removal.

Intermittent pulse amperometry as an effective electrochemical assay of 4-nitrophenol

4-nitrophenol (4-NP) is a precursor of many industrial products and drugs, an environmental pollutant, and is used as a reporter molecule in many enzyme assays and disease biomarker screens. Accordingly, 4-NP analysis is a cross-disciplinary requirement, and we propose intermittent pulse amperometry (IPA) as an alternative to spectrophotometric methods. The sensor signal is acquired by applying 0.5 s pulses of 0.95 V once every 99.5 s during continuous amperometric recordings at 0 V resting potential to drive intermittent 4-NP detection at a diffusion-limited rate. With IPA, sensor surface fouling by polymerization of radical intermediates formed in the anodic oxidation process, which is a severe problem in constant-potential amperometry and voltammetry of phenols, is kept at acceptable minimum by restriction of the time at the potential that produces contamination. Complex potential profiles with electrochemical activation steps and/or electrolyte supplementation with anti-fouling agents are not required. Calibration plots are linear up to 500 μM with a sensitivity of 35 nA μM−1 and a practical detection limit of 10 μM. Model samples of 100 μM 4-NP were assessed with suitable recovery rates, and in a proof-of-principle test as electrochemical readout of an enzyme assay, IPA accurately reported the time course of enzymic release of 4-NP from GlcNAc-4NP, a synthetic substrate of glucosaminidases. Simplicity and high performance are the major features of the proposed electrochemical 4-NP testing, and unless the analytical target is present only at trace levels, the technique is a promising alternative for the evaluation of 4-NP, either as a solution component or as a reporter molecule in enzyme assays.

Enhanced electrochemical oxidation of perfluorooctanoic acid on Ti/SnO2-Sb electrode by surface morphology regulation

Electrochemical oxidation is an effective method to degrade persistent organic pollutants. However, due to the limited catalytic activity of traditional thin film electrodes, the anodic oxidation process is slow and usually requires high energy consumption. Herein, Ti/SnO2-Sb electrode with regulated surface structure was reported to enhance the performance for electrochemical oxidation of persistent organic pollutants. The electrode deposited with SnO2-Sb nanoneedles (Ti/N-SnO2-Sb) showed higher oxidation activity. Its kinetic constant for perfluorooctanoic acid (PFOA) oxidation was 2.0 h−1 and the total organic carbon removal rate was 81.7% (4 h) at a relatively low current density of 6 mA/cm2. Compared with Ti/SnO2-Sb thin film and nanoparticles, Ti/N-SnO2-Sb significantly improved the electrochemical active area and •OH yield, and simultaneously reduced the electron transfer resistance, which enabled it to oxidize PFOA more rapidly even at a lower potential. This work provides a new strategy for promoting the electrochemical oxidation performance.

Synergistic activation of persulfate by ultrasound/PbO2 anodic oxidation system for effective degradation of naproxen, a toxic and bio-recalcitrant pollutant: Process optimization and application for pharmaceutical wastewater

Naproxen (NPX) is a widely used pain reliever that conventional treatment systems are unable to fully mineralize its residues in wastewater. The aim of this study is to develop a synergistic persulfate activation system based on ultrasound/PbO2 anodic oxidation process (US/PS/AO) for effective degradation of NPX and improving the biodegradability of pharmaceutical wastewater. PbO2 electrocatalyst was prepared by anodic deposition and then its characteristics were determined by FESEM, EDX and XRD techniques. Optimizing the effect of independent variables on NPX removal was done using an CCD method. The performance of the optimized US/PS/AO process for NPX degradation and TOC mineralization after 60 min of reaction was 98.5 % and 73.6 %, respectively. The reusability of the PbO2 electrocatalyst was maintained above 97 % in ten continuous oxidation cycles for NPX degradation. Also, the cumulative concentration of leaked lead (53 μg L−1) was within the permitted standard for discharging wastewater into the river. Using HPLC-mass spectrometer data, possible pathways for NPX mineralization were suggested. The biodegradability of pharmaceutical wastewater with the optimized US/PS/AO and PS/AO processes increased to above 0.4 after 100 and 150 min of treatment, respectively. However, the total energy consumption in the PS/AO process (US power = 0, EC = 83 kWh kg−1 COD) is significantly lower than the US/PS/AO (US power = 100 W, EC = 982 kWh kg−1 COD). The findings of the present study can contribute to the development of a cheap, safe, and effective integrated AOP for the treatment of pharmaceutical wastewater containing non-biodegradable compounds.

Elimination of sulfamethoxazole by anodic oxidation using mixed metal oxide anodes

The degradation of sulfamethoxazole (SMX) was studied by anodic oxidation (AO) process using mixed metal oxide (MMO) electrodes with different Ru/Ir ratios. Each electrode was characterized morphological and electrochemically. The electrolyzes were performed in NaCl and Na2SO4 applying two current densities (10 and 50 mA cm−2). The electrode with the highest composition of Ir, Ru/Ir (30/70), showed greater SMX degradation and generation of oxidizing species and was used to treat the antibiotic by AO and AO assisted by solar energy in natural water and actual municipal wastewater effluents.The efficiency in SMX degradation depends on the type of electrode used (MMO) and electrolytic medium. All MMO electrodes, reached almost total degradation of SMX in chloride medium. However, 60 % degradation of SMX in sulfate medium was achieved with anode with lower Ru/Ir ratio. Additionally, degradation of SMX in complex matrices can be successfully carried out by solar-assisted AO and AO processes, without the need to adjust the pH, at room temperature and using anode with lower Ru/Ir ratio. Finally, the AO process assisted by solar energy reduced electrolysis times and the cell's potential, leading to lower energy consumption.

Highly sensitive NO2 sensor based on mesoporous ZrO2–WO3 nanotubes composite

In this study, two anodic oxidation processes were used to prepare ordered mesoporous zirconia nanotubes. Ammonium metatungstate was introduced into zirconia to obtain mesoporous ZrO2–WO3 composite nanotubes. We performed XRD, TEM, and SEM tests on the material. Furthermore, a mixed electromotive force–based NO2 sensor was fabricated using ZrO2–WO3 nanotubes as sensing materials. The sensor not only has a low working temperature (400°C) and high sensitivity (131.4 mV/decade) but also shows remarkable selectivity, stability, and repeatability. At 400°C, the polarity curve of the sensor in air and under different concentrations of NO2 was measured, which proves the mixed electromotive force mechanism. Moreover, the tubular structure of the mesoporous ZrO2–WO3 composite provides additional electrochemical active sites, improves the catalytic efficiency, enhances the diffusion of NO2, and reduces NO2 consumption in the diffusion process, thus essentially improving the performance of the sensor.

Corrosion behavior of self-organized TiO2 nanotubular arrays grown on Ti6Al4V for biomedical applications

The electrochemical interactions between a biomaterial and a human fluid are important to understand when developing surfaces on titanium biomedical composites to improve bone regeneration, healing times, and longevity. Electrochemical corrosion is a major problem in implant-tissue interaction in that environment. The purpose of this research is to use different electrochemical methods such as open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) to examine the effect of self-organized TiO2 nanotubular surfaces on the corrosion resistance of Ti6Al4V surface. The electrochemical behavior of polished Ti6Al4V (control), and anodized samples at a constant voltage of 30V and various time-periods of anodization, such as 3hr, 4hr, and 5hrs respectively is the main focus of our study. All the anodized samples were annealed at 500 °C for 3hr with preheating rate of 5 °C per minute. The resistance of the nanotubular structure is improved after annealing because the anatase phase is stabilised, and the fluoride ions are removed. The electrochemical behavior of the nanotubular surfaces were investigated by using the simulated body fluid (SBF, 7.4 pH) solution. Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), and a Drop Shape Analyzer were all used to investigate the nanotubular morphology, chemical compositions, and structure. According to the findings, the anodic oxidation process results in a nanotubular structure that improves the surface area and influences the surface's chemical composition. Surfaces with self-organized TiO2 nanotubular structures had greater corrosion resistance than polished Ti6Al4V because the passive film had a larger surface area and a more dispersed amorphous crystal structure. Finally, the physical condition of the post-electrochemical treated sample was evaluated by the SEM images and compositional analysis by the EDS and XRD. The PDP curves showed the corrosion rate of the samples polished Ti6Al4V, TiO2 30V 3hr, TiO2 30V 4hr, and TiO2 30V 5hrs are 0.39, 0.35, 0.09, and 0.24 mm per year respectively. Similarly, the efficiencies of the anodized samples TiO2 30V 3hr, 4hr, and 5hrs are 9.96, 76.44, and 38.30% respectively. When comparing all of the anodized samples, the overall corrosion resistance is improved by 2 times.