Anodization Temperature Research Articles

Development of Novel Surface-Enhanced Raman Spectroscopy-Based Biosensors by Controlling the Roughness of Gold/Alumina Platforms for Highly Sensitive Detection of Pyocyanin Secreted from Pseudomonas aeruginosa.

Pyocyanin is considered a maker of Pseudomonas aeruginosa (P. aeruginosa) infection. Pyocyanin is among the toxins released by the P. aeruginosa bacteria. Therefore, the development of a direct detection of PYO is crucial due to its importance. Among the different optical techniques, the Raman technique showed unique advantages because of its fingerprint data, no sample preparation, and high sensitivity besides its ease of use. Noble metal nanostructures were used to improve the Raman response based on the surface-enhanced Raman scattering (SERS) technique. Anodic metal oxide attracts much interest due to its unique morphology and applications. The porous metal structure provides a large surface area that could be used as a hard template for periodic nanostructure array fabrication. Porous shapes and sizes could be controlled by controlling the anodization parameters, including the anodization voltage, current, temperature, and time, besides the metal purity and the electrolyte type/concentration. The anodization of aluminum foil results in anodic aluminum oxide (AAO) formation with different roughness. Here, we will use the roughness as hotspot centers to enhance the Raman signals. Firstly, a thin film of gold was deposited to develop gold/alumina (Au/AAO) platforms and then applied as SERS-active surfaces. The morphology and roughness of the developed substrates were investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The Au/AAO substrates were used for monitoring pyocyanin secreted from Pseudomonas aeruginosa microorganisms based on the SERS technique. The results showed that the roughness degree affects the enhancement efficiency of this sensor. The high enhancement was obtained in the case of depositing a 30 nm layer of gold onto the second anodized substrates. The developed sensor showed high sensitivity toward pyocyanin with a limit of detection of 96 nM with a linear response over a dynamic range from 1 µM to 9 µM.

Non-Isothermal Operation of Membrane Electrode Assembly-Based CO2 Electrolyzer for Enhanced Energy Efficiency

The utilization of membrane electrode assemblies (MEA) in carbon dioxide (CO2) electrochemical conversion showcases the promising potential for stable and scalable industrial applications in fuel production, attributed to efficient gas diffusion and minimized system resistance. The electrochemical performance of MEA-based CO2 electrolyzers relies on the chemical reactivity and product selectivity optimization which is dependent on three factors: CO2 mass transport, charge transport, and ionic transport. Elevating the overall system temperature benefits the performance of the oxygen evolution reaction (OER) at the anode. Furthermore, the elevated temperature enables higher conductivity of anion exchange membranes (AEM), thereby further diminishing cell voltage. However, the downside emerges as CO2 solubility decreases at higher temperatures, fostering a scenario where the catalytic reaction leans toward hydrogen evolution, thereby undermining product selectivity.Herein, we propose an innovative approach involving thermal management for separate temperature control for the anode and cathode, forming a non-isothermal MEA by maintaining an elevated anodic temperature while cooling the cathode. This approach simultaneously addresses the need for a high-temperature anode and a low-temperature cathode. This study exhibits a temperature gradient of approximately 20°C between the anodic and cathodic planes achieved through efficient thermal modulation of water cooling and heating within the electrode plates.We showcase the benefit of non-isothermal operation with an Ag-based cathode and IrO2-based anode using 1 M KOH as the anolyte for CO2 conversion into CO. The non-isothermal condition, i.e., maintaining an anodic temperature of 80°C and a cathode temperature of 60oC, demonstrated a 65% enhancement in CO partial current density (j co), 195.6 mA cm-2, compared to the isothermal 80°C condition, 118.6 mA cm-2. The optimal performance across all temperature regimes is found to be the non-isothermal condition with anode temperature at 60°C and cathode temperature at 40 oC, yielding a j co of 243.5 mA cm-2 at 3.25 V, marking a 13.3% improvement over the isothermal 60°C condition (j co = 214.9 mA cm-2). The increase in the j co can be attributed to the lower temperature at the cathode (40 oC for the non-isothermal condition vs. 60oC for the isothermal ccondition) resulting in higher CO faradaic efficiency.The CO faradaic efficiency remained above 80% (cell potential < 2.7V) for the non-isothermal 60°C condition, whereas it dropped below 80% throughout the entire region cell potential range for the isothermal 60°C condition. This study presents a novel non-isothermal operation for advanced thermal management for MEA-based CO2 electrolyzers for simultaneous enhancement in anode activity as well as cathode selectivity. We believe this thermal management strategy is promising for engineering high-performing MEA-based CO2 electrolyzers at industrial scales.

Influence of Anodization Mode and Temperature on the Optical Properties of Photonic Crystals Based on Porous Anodic Alumina

Porous anodic alumina (PAA) with periodic structure was produced by sinusoidal pulse anodization (SPA) of aluminum under time-controlled voltage (U t ), time-controlled current density (j t ), and charge density-controlled voltage (U q ) modes. The effect of anodizing temperature and the modes on the optical properties of PAA-based photonic crystals (PCs) was analyzed in detail. It was shown that depending on the anodizing temperature, either broad or narrow bandpass filters can be produced with variable optical quality that depends strongly on the anodization mode and the parameters of the SPA function. Broad bandpass PCs (Q-factor < 10) tend to form during high-temperature SPA, with the first order photonic stop band (λ 1) at near infrared (NIR) region and almost 100% reflectivity and 0% transmittivity at the λ 1 in the PC produced under the U t mode. At these electrochemical conditions, the λ 1 peak broadens and become less intensive in the PCs formed under the U q , and j t modes. At low temperature, narrow bandpass filters are produced (Q-factor > 10), with the highest Q-factor (67) and PSB at NIR obtained during high-field SPA under the j t mode. The most intensive λ 1 was, however, attained during the high-field SPA under the U q mode, after post-process pore widening.

Abrasive Wear Resistance and Tribological Characteristics of Pulsed Hard Anodized Layers on Aluminum Alloy 1011 in Tribocontact with Steel and Ceramics in Various Lubricants

Based on the analysis of known methods of surface hardening of aluminum alloys (chromium plating, plasma electrolytic oxidation, hard anodizing), the prospects for pulsed hard anodizing are shown both for improving the functional characteristics of alloys and for large-scale implementation of this method. The purpose of this work is to show the possibility of pulsed hard anodizing to improve the serviceability of low-strength aluminum alloy 1011 under conditions of abrasive and sliding wear. The influence of the pulsed anodizing temperature on the phase-structural state of the synthesized layers, their abrasive wear resistance, and tribological characteristics in various lubricants were established, and the mechanism of wear of these layers was proposed. It is shown that with an increase in the temperature of pulsed anodizing, the wear resistance of the synthesized layers increases, and their abrasive wear resistance decreases. The negative effect of lubricating media on the wear resistance of the synthesized layers compared to tests under dry conditions was shown, and an explanation for this phenomenon is proposed. A significant (up to 40 times) increase in wear resistance in dry friction of anodized low-strength aluminum alloy 1011 compared to high-strength aluminum alloy 1050 was shown.

Optical and structural characterization of one-dimensional porous silicon photonic crystals made in single and double electrochemical cells: Study on the back contact effect

One-dimensional porous silicon photonic crystals with microcavity were fabricated using single and double electrochemical cells and the same electrochemical parameters. Devices with better optical quality can be achieved when liquid acids are used as back contacts for current flow. Optical analysis of them shows that devices with less rough interfaces and layers with negligible in-depth inhomogeneities are formed. However, the etch rate and porosity depend strongly on the acid strength, the diffusion of the acid species from the liquid bulk to the interface, and the anodization temperature. Strong acids promote a higher etch rate. Thinner films with lower porosity and rougher interfaces are observed for devices fabricated in substrates with aluminum or platinum as solid ohmic contacts compared to devices fabricated in unmetallized substrates, as shown by optical analysis, such that devices with aluminum as the ohmic contact have about 80% of the reflectance, while with platinum shows 94%.

Anodizing-induced cracking in the preparation of TiO2 nanotube arrays

Understanding structural integrity of physical structures in chemical and electrochemical systems/environments is of practical importance in analyzing and predicting the reliability and lifespan of the physical structures. In this work, we systematically investigate the crack growth in the TiO2 layers with TiO2 nanotube arrays during electrochemical anodization of Ti plates without external mechanical loading. There exists the combinational effects of the anodization voltage and the anodization temperature on the crack growth. A simple relationship between the growth rate of the areal crack density, the anodization temperature and the anodization voltage are proposed and supported by the experimental results. The growth rate of the areal density of the surface cracks increases with the increase of the anodization voltage and the anodization temperature. The nominal activation energy is a decreasing function of the anodization voltage, suggesting that increasing the anodization voltage promotes fast growth of the surface cracks in the TiO2 oxide layer.

Experimental Study on Electrochemical Desulfurization of Coal Liquefaction Residue

The occurrence of sulfur in coal direct liquefaction residue affects its further high quality and high value utilization. Electrochemical desulfurization is characterized by mild reaction conditions, simple operation, easy separation of sulfur conversion products and little influence on the properties of the liquefied residue. An anodic electrolytic oxidation desulphurization experiment was carried out on the liquefaction residue of the by-product of a coal-to-liquid enterprise in the slurry state. An electrochemical test and material characterization of raw materials before and after electrolysis showed that electrolytic oxidation can desulfurize the liquefaction residue under an alkaline condition. Linear sweep voltammetry (LSV) was used for the electrolysis experiments to obtain the optimal slurry concentration of 60 g/L. On this basis, the reaction kinetics were calculated, and the minimum activation energy in the interval at 0.9 (V vs. Hg/HgO) was 19.71 kJ/mol. The relationship between the electrolytic desulfurization of the liquefied residue and energy consumption was studied by the potentiostatic method. The influence of anodic potential and electrolytic temperature on the current density, cell voltage, desulfurization rate and energy consumption was investigated. The experimental results showed that the desulfurization rate and total energy consumption increase positively with the increase in reaction temperature and electrolytic potential in a certain range. The influence of the reaction temperature on the desulfurization rate and total energy consumption is more prominent than that of electrolytic potential, but the energy consumption of sulfur removal per unit mass does not show a positive correlation. Therefore, with the energy consumption per unit mass of sulfur removal as the efficiency index, the optimal experimental results were obtained: under the conditions of 0.8 (V vs. Hg/HgO) anode potential, 50 °C electrolytic temperature, 60 g/L slurry concentration and 14,400 s electrolytic time, the desulfurization rate was 18.85%, and the power consumption per unit mass of sulfur removal was 5585.74 W·s/g. The results of XPS, SEM, BET and IC showed that both inorganic and organic sulfur were removed by electrolytic oxidation, and the morphology, pore structure and chemical bond of the liquefied residue were affected by electrolytic oxidation. The research method provides a new idea and reference for the efficiency evaluation of desulfurization and hydrogen production from coal liquefaction residue.

Дослідження впливу температури електроліту при імпульсному анодуванні на властивості поверхневих шарів технічного алюмінію

luminum alloys are characterized by low abrasive wear resistance, which significantly restricts their wide use in technological environments, especially if they contain abrasive particles. The method of pulse anodizing, which consists in periodically changing the current density, allows to improve the hardness and abrasive wear resistance. However, the influence of temperature on these processes has not been sufficiently studied. The process of pulsed hard anodizing was carried out in a 20% aqueous H2SO4 solution at a current density of 1.4 A/dm2 with a frequency of 100 Hz and a sparability of 75%. The temperature of the electrolyte during the formation of layers was maintained at -5°±1С, 0°С±1, +5°С±1, +10°С±1. The duration of synthesis was 60 minutes. At low temperatures of less than -5С due to the low speed of electrochemical processes, oxide layers with reduced microhardness and thickness are synthesized. At the same time, the phase analysis recorded the synthesis of an oxide layer based on aluminum with the content of two phases: the synthesis of the anodized layer begins with the formation of hydrated aluminum oxide Al2O3•H2O. As the anodizing temperature increases, the rate of electrochemical processes increases, which leads to an increase in the thickness of the anodized layer and its microhardness. At temperatures of 0С and -5С, the anodized layer contains only one phase - Al2O3 H2O, (boehmite) with one water molecule. At anodizing temperatures of +5С and -8С, the anodized layer is formed again in the form of two phases - Al2O3 3H2O (gibbsite) and Al2O3H2O (boehmite) and at a temperature of +10С only Al2O3 3H2O (gibbsite). At a temperature lower than –10°C, the electrolyte turns into a gel-like substance in which electrochemical reactions practically stop, so the synthesis of a pulsed solid anodized layer at a temperature of –5°C was started. However, as a result of the synthesis at T = –5 С and then even higher (up to 0С), the average thickness of the pulsed hard anodized layer increased from 83 μm to 110 μm. With further increase in the temperature of the electrolyte, the thickness decreased and at an electrolyte temperature of +10 С it was 80 μm. Such a change in the thickness of the anodized layer depending on the synthesis temperature was explained by two opposing processes that occur during anodization. As the temperature of the electrolyte increases, the process of synthesis of the layer intensifies first of all, and therefore the thickness of the obtained layer should constantly increase with the increase of the synthesis temperature. However, an increase in the temperature of the electrolyte also intensifies the surface dissolution of the anodized layer, which is aimed at reducing the thickness of the anodized layer. And when the rate of dissolution of the anodized layer begins to exceed the rate of its synthesis, its thickness begins to decrease. Conclusions: 1) The more water and sulfur molecules in the anodized layer, the lower its microhardness and abrasive wear resistance. 2) The minimum wear of the anodized layer, which means the highest wear resistance, was recorded for layers synthesized at an anodization temperature of -8ºС, and the maximum wear and lowest wear resistance at an anodization temperature of -5ºС. 3) High wear resistance of anodized layers synthesized at electrolyte temperatures from -8 to +10ºС under conditions of friction without lubrication is caused by the presence of crystalline water in the anodized layer.

In-situ fabrication of superhydrophobic surface on copper with excellent anti-icing and anti-corrosion properties

The accumulation of ice on electrical construction works not only leads to the reduced efficiency of power supply and heat exchangers, but also increases the energy losses and even brings about serious disasters. Therefore, it is essential to reduce or eliminate the issue of ice accumulation on metal constructions. Nowadays, superhydrophobic surfaces have received lots of attentions for their outstanding hydrophobicity. In this study, Cu(OH)2 nano grass was firstly in-situ constructed on copper surface via simple anodization, then superhydrophobic CuO nano needles were obtained after the dehydration of Cu(OH)2 and modification with fluoro-alkyl silanes. The results showed that when the anodic oxidation temperature was 20 °C and the current density was 2 mA·cm−2, nano-needle-like multistage micro-nano structures can be obtained. The as-prepared superhydrophobic surface showed the water contact angle as large as 162° and sliding angle lower to 4°. Additionally, the as-prepared superhydrophobic surface displayed outstanding anti-icing property, delaying icing substantially even under − 10 °C environment regardless of droplet volume and type. Moreover, it also revealed good anti-corrosion property with a corrosion current density of 2.2 × 10−8 Ω·cm2 and the corrosion resistance of 1.55 × 106 Ω·cm2 which is about three order of magnitudes than that of bare copper. We prospect that this easily prepared surface can provide a solution of anti-icing and anti-corrosion for electrical construction works and large-scale metals.

Development of the anodized aluminum substrates for thermoelectric energy converters

Operation of the thermoelectric converters requires hot- and cold-side insulating plates with low thermal resistance. In this work, we developed anodized aluminum substrates with physical properties accommodated for thermoelectric converters, which can be a possible alternative to the expensive and brittle commercial ceramics. The XRD, SEM, and EDS analyses were employed to investigate the quality of the prepared samples. The thermal resistance of the developed substrates shows much lower values compared with the commercial ceramics indicating the beneficial effect of the anodized aluminum substrates on the heat transfer through the thermoelectric module. The temperature-dependent breakdown voltage of the Al2O3 anodic layer was estimated as a key parameter that defines the thermoelectric module's workability. For the measurement of the thermal breakdown voltage of dielectric layers, the temperature-controlled testing setup was developed. With the help of the Walther-Fock theory and the measured data, the analytical expression that determines the thickness of the Al2O3 dielectric layer as a function of the anodization voltage and temperature is proposed. Considering Seebeck voltage generated by a thermoelectric module, the desired thickness of the Al2O3 layer can be defined to prevent the destruction of the dielectric substrate during the thermoelectric module operation. The application of the presented results can significantly accelerate the development of mechanically strong, low-cost, and highly efficient thermoelectric energy converters.

Photoreduction of Cr(VI) in wastewater by anodic nanoporous Nb2O5 formed at high anodizing voltage and electrolyte temperature.

In this study, nanoporous anodic film was produced by anodization of niobium, Nb in a fluoride ethylene glycol electrolyte. The effect of anodization voltage and electrolyte temperature was studied to find an optimum condition for circular, ordered, and uniform pore formation. The diameter of the pores was found to be larger when the applied voltage was increased from 20 to 80V. The as-anodized porous film was also observed to comprise of nanocrystallites which formed due to high field-induced crystallization. The nanocrystallites grew into orthorhombic Nb2O5 after post-annealing treatment. The Cr(VI) photoreduction property of both the as-anodized and annealed Nb2O5 samples obtained using an optimized condition (anodization voltage: 60V, electrolyte temperature: 70°C) was compared. Interestingly, the as-anodized Nb2O5 film was found to display better photoreduction of Cr(VI) than annealed Nb2O5. However, in terms of stability, the annealed Nb2O5 presented high photocatalytic efficiency for each cycle whereas the as-anodized Nb2O5 showed degradation in photocatalytic performance when used continually.

Effect of the Anodizing Temperature on Microstructure and Tribological Properties of 6061 Aluminum Alloy Anodic Oxide Films

Anodizing a simple and effective method to improve the wear resistance of 6061 aluminum alloy. In this study, the microstructure of 6061 aluminum alloy oxide films (AAO) was adjusted by changing the electrolyte temperature (5, 15, and 25 °C) using 160 g/L sulfuric acid as the electrolyte. The phase composition, microstructure, and morphological characteristics of the specimens were detected using X-ray diffractometer and field emission scanning electron microscopy (SEM). The hardness, elastic modulus, and tribological properties of the films were examined using hardness testers and a rotary friction tester. The results showed that as the temperature of the electrolyte increases, the surface of the oxide films changes from uniformly distributed small-sized pores to a coral-like loose porous structure, and the thickness of the films increases. The electrolyte temperature has a significant effect on the friction performance of the AAO films. When the solution temperature decreases from 25 to 5 °C, the steady-state friction coefficient decreases from 0.46 to 0.39. According to the morphology of the wear tracks, it can be determined that the main wear mechanism of AAO films gradually changes from delamination wear to abrasive and adhesive wear, and the wear rate drops by ~69%.

Morphological and Optical Characterization of Colored Nanotubular Anodic Titanium Oxide Made in an Ethanol-Based Electrolyte.

In this paper, the possibility of color controlling anodic titanium oxide by changing anodizing conditions of titanium in an ethanol-based electrolyte is demonstrated. Colored anodic titanium oxide was fabricated in an ethanol-based electrolyte containing 0.3 M ammonium fluoride and various amounts of deionized water (2, 3.5, 5, or 10 vol%), at voltages that varied from 30 to 60 V and at a constant anodization temperature of 20 °C. Morphological characterization of oxide layers was established with the use of a scanning electron microscope. Optical characterization was determined by measuring diffusion reflectance and calculating theoretical colors. The resulting anodic oxides in all tested conditions had nanotubular morphology and a thickness of up to hundreds of nanometers. For electrolytes with 3.5, 5, and 10 vol% water content, the anodic oxide layer thickness increased with the applied potential increase. The anodic titanium oxide nanotube diameters and the oxide thickness of samples produced in an electrolyte with 2 vol% water content were independent of applied voltage and remained constant within the error range of all tested potentials. Moreover, the color of anodic titanium oxide produced in an electrolyte with 2 vol% of water was blue and was independent from applied voltage, while the color of samples from other electrolyte compositions changed with applied voltage. For samples produced in selected conditions, iridescence was observed. It was proposed that the observed structural color of anodic titanium oxide results from the synergy effect of nanotube diameter and oxide thickness.

Investigations of anodization parameters and TiCl4 treatments on TiO2 nanostructures for highly optimized dye-sensitized solar cells

In this research, effects of anodization parameters on the growth behavior and top morphology of TiO2 nanotubes are investigated. Five TiO2 nanostructures with different top morphologies, including nanopores, nanotubes, nanohexagons, nanonet and nanograss, are obtained through an electrochemical anodization of Ti foil, by varying the anodization parameters, e.g., anodization time, anodization temperature and deionized water contents. Dye sensitized solar cells (DSSC) based on the photoanodes fabricated with the TiO2 nanohexagon morphology show the highest power conversion efficiency of 5.29% with N719 Dye. Moreover, to further enhance the efficiency of DSSC, modifications of the TiO2 nanohexagons with TiO2 nanoparticles derived from TiCl4 with different molar concentrations are also explored. It is observed that the TiO2 nanohexagons based photoanode treated with 0.2 M TiCl4 shows a maximum efficiency of 6.64% with N719 Dye and incident photon-to-current efficiency (IPCE) of 68%, due to the increased effectiveness in electronic transport and enhanced surface area for N719 dye-adsorption.

Morphological Characterization of Porous Anodic Alumina Membranes Prepared in Sulphuric, Oxalic, Chromic and Phosphoric Acids

Porous Anodic Alumina membranes (PAAM) have a significant role in nanoscale devices due to their easily tunable structural aspects and variety of applications in nanotechnology. The variable process parameters in the synthesis of PAAM were anodization potential, temperature, duration and nature of electrolyte concentration. Pores of different sizes and geometry were obtained by varying these anodization parameters. In the present work, PAAM were prepared in 0.3 M of sulphuric, oxalic, chromic and phosphoric acids as electrolyte and with anodization potentials (20, 40, 50 and 90 V) at a temperature of 8 °C. Field-emission Scanning Electron Microscopy investigations confirm the pore formation in PAAM layers. Pore ordering was calculated using the Fast Fourier transform (FFT) of top view SEM micrographs. Pore arrangement analysis of PAAM was studied using Image-J and WSxM software. Morphological features of PAAM such as pore diameter, interpore distance, porosity and pore density were calculated in all electrolytes. Results show that, PAAM formed in oxalic acid having high regularity ratio and circularity compared with other cases.

Catalytic Internal Reforming, Electrochemical Performance and Thermal Effect of Large-Scale SOFC Single Cell Using Oxygen-Bearing Low-Concentration Coal Mine Methane

Coal mine methane is one kind of clean fuel with the global resource quantity of 260×1012 m3, however more than 230×108 m3 low concentration coal mine methane (LC-CMM) is directly emitted to the atmosphere annually in China, causing the severe energy loss and global warming effect. We proposed to utilize the LC-CMM through SOFC for realizing the efficient and clean conversion of LC-CMM. In this paper, the catalytic internal reforming efficiency, electrochemical performance and thermal effect of the large-scale 10cm × 10cm single cell were investigated using the oxygen-bearing LC-CMM as fuel. The results show that the peak power density and open circuit voltage can respectively reach 1.13 V and 100 mW cm-2 using the simulated LC-CMM (12.2 % CH4-4% O2) under 780 oC. Importantly, the stable discharging for nearly 400h using the oxygen-bearing LC-CMM were also be achived based on the large-scale single cell. The CH4 conversion and CO selectivity can also respectively reach 68.5% and 97.9%. The anodic temperature distribution of the large-scale single cell were tested, which implied that the exothermic oxidation reaction happen in the inlet side of anode, causing the higher tempeature of the area. However, the largest temperature gap in the whole large anode is smaller than 5oC, which cannot lead to the thermal distress. Therefore, above experimental results demonstrated the feasibility of efficient oxygen-bearing LC-CMM utilization through SOFC, which might create the opportunity to greatly improve the utilization ratio of LC-CMM and prevent the fuel waste and greenhouse effect by LC-CMM direct emission.

Resolving Anodic Current and Temperature Distributions in a Polymer Electrolyte Membrane Water Electrolysis Cell Using a Pseudo-Two-Phase Computational Fluid Dynamics Model

Expanding upon our prior experimental work, we constructed a three-dimensional model of a polymer electrolyte membrane water electrolyzer using computational fluid dynamics. We applied the assumption of pseudo-two-phase flow, the flow of two phases with equal velocity. Experimental data were used to obtain parameters and to determine the conditions under which this model was valid. Anodic distributions of current density, temperature, liquid saturation, and relative humidity were obtained at various flow rates. The overall current density and temperature difference from inlet to outlet at the anode agreed strongly with experimental measurements under most circumstances. This verification allowed us to further examine the apparent gas coverage calculated from experimental and model temperature data. Results suggested a low liquid saturation and low relative humidity at the anode due to the consumption of liquid water and water vapor. However, we questioned the accuracy of the pseudo-two-phase assumption at low water feed rates. We concluded that the model was applicable to systems with liquid water feed rates greater than 0.6 ml min−1 cm−2. Therefore, it is a fair screening method that can advise which operating conditions lead to excessive temperatures or drying at the anode, thereby promoting the longevity of the membrane and catalyst.

Improvement of corrosion properties of plasma in an aluminum alloy 6061-T6 by phytic acid anodization temperature

We report on the formation of anodic aluminum oxide (AAO) film using phytic acid (C6H18O24P6), a naturally obtainable and non-toxic organic acid electrolyte. When the temperature of the phytic acid electrolytes changes from 0 °C to 20 °C, the pore size increases, and the AAO film becomes less dense because the growth rate of the AAO film increases. In particular, when the temperature of the phytic acid electrolyte is above 15 °C, the AAO film changes dramatically. According to XRD analysis, the alpha-alumina intensity was relatively higher in the AAO film grown at low-temperatures (0, 5, 10 °C) than high-temperatures (15, 20 °C). It was possible to obtain a result that the properties were better. The microstructural change of the AAO film according to the temperature of the phytic acid electrolytes affected the breakdown voltage and the number of contamination particles that are generated, which are important properties for plasma corrosion protection coating materials. The AAO film grown in the low-temperature has the most suitable properties for use as a plasma corrosion protection coating material. Notably, the breakdown voltage of the AAO film is 0.45 kV at 14.9 μm thickness, with no observable crack on its surface after the plasma corrosion test. These findings provide significant evidence to support the application of phytic acid as an electrolyte to grow AAOfilms, and the AAOfilm grown in a phytic acid bath can be applied as a plasma corrosion protection coating material.

The Optical and Electrical Performance of CuO Synthesized by Anodic Oxidation Based on Copper Foam.

Metal oxide semiconductor materials have a wide range of applications in the field of solar energy conversion. In this paper, CuO was prepared directly on copper foam substrate by anodic oxidation. The effects of current density and anodizing temperature on sample preparation and performance were studied. Field emission scanning electron microscopy (FESEM) and X-ray diffractometer (XRD) had been used to determine the morphology and phase structure of the sample, and its optical and electrical properties were discussed through UV-vis spectrophotometer and electrochemical tests. In addition, the influences of experimental conditions such as current density and reaction temperature on the morphology and properties of CuO were systematically discussed. The FESEM images showed that as the anodic oxidation temperature increase, the morphology of the prepared sample changed from nanowires to leaf-like CuO nanosheets. According to the results of XRD, the structure of prepared CuO was monoclinic, and the intensity of diffraction peaks gradually increased as anodizing temperature increased. We found that the optimum current density and anodizing temperature were 20 mA cm−2 and 60 °C, respectively. The results of electrochemical indicated that the CuO electrode based on copper foam (CuO/Cu foam) prepared at the optimum exhibited the highest specific capacitance (0.1039 F cm−2) when the scan rate was 2 mV s−1.

(Invited) Formation Efficiency of Anodic Porous Alumina in Sulfuric Acid Containing Alcohol As Additives

The properties of anodic porous alumina films, which are generally formed by the anodization of aluminum in an acid electrolyte, are well known to be affected by the dimensions of their structure (e.g., pore diameter, pore density, and film thickness). For instance, to increase the hardness of anodic films on aluminum, the anodization is industrially carried out at low-temperature to avoid chemical dissolution of the formed oxide film during anodization. Anodization in an electrolyte containing organic compounds is also one approach for improving the performance of anodic oxide film not only for aluminum but also for other light metals such as titanium and magnesium (1).One such initiative is anodization of aluminum at a relatively high current density or high voltage using a common acidic electrolyte (e.g., sulfuric acid, oxalic acid, or phosphoric acid) with an alcohol added. In such studies, the effects of adding an alcohol are summarized as follows: i) the alcohol functions as an anti-freeze agent in the electrolyte, enabling the anodization temperature to be lowered; ii) the alcohol acts as a cooling agent—specifically, the vaporization of alcohol at the bottom of the pore channels removes the heat generated at the aluminum/oxide interface; and iii) nonuniform growth of the anodic film (i.e., burning) is effectively prevented, even during high-field anodization. However, these effects are observed not only for monohydric alcohols with a boiling point less than 100 °C (e.g., methanol and ethanol) but also for polyhydric alcohols with a boiling point greater than 100 °C (e.g., ethylene glycol and glycerol). Therefore, the effect of alcohol addition cannot be reasonably explained solely on basis of the boiling point of the alcohol used as an additive. Understanding the effects of alcohol addition necessitates a systematic investigation comparing types of alcohols, in addition to further fundamental studies.In this study, monohydric alcohols or polyhydric alcohols were added to the sulfuric-acid-based electrolyte to examine their effects on the anodization behavior of aluminum, the coating ratio, the porosity, the maximum attainable film thickness, and the resulting etching ability. Anodization was conducted in sulfuric acid solutions containing various alcohols with different physical properties under mild anodization conditions with a constant current of 100 A·m−2 at 20 °C (2, 3). The influence of the type and concentration of alcohol on the coulombic efficiency of film formation and the structure of the porous alumina under a constant electric charge was also investigated. In terms of basic research, the potential impact of alcohol addition in electrolytes will be discussed. H. Asoh, K. Asakura, H. Hashimoto, RSC Advances, 10, 9026-9036 (2020).H. Asoh, M. Matsumoto, H. Hashimoto, Surface and Coatings Technology, 378, 124947 (2019).M. Matsumoto, H. Hashimoto, H. Asoh, Journal of The Electrochemical Society, 167, 041504 (2020).