Aluminum Anode Research Articles

Features of the porous morphology of anodic alumina films at the initial stage of disordered growth

A characteristic feature of disordered porous anodic film growth at the initial stage of aluminum anodizing was revealed by varying the electrolyte type and anodizing voltage. The samples were obtained by the electrochemical oxidation of thin aluminum films (100 nm thick) on SiO2/Si substrates in a 0.3 M oxalic acid at 10–50 V and were studied by SEM. The ImageJ analysis of the images revealed the simultaneous development of two large groups of pores: major pores with a large diameter and minor pores with a smaller diameter. When anodizing in oxalic acid at 10–50 V, it has been shown that the ratio of the diameters of the major and minor pores remains constant and is about 1.17. Using a geometric model, we demonstrated that the centers of the minor pores are located inside the elementary hexagonal cell formed by the centers of the major pores. Moreover, our results are very close to the theoretical value of 2/√3. At the initial stage of disordered pore growth, the development of minor pores rather than major pores is not a random process and is determined by energy-efficient conditions for the development of pores inside the hexagonal cells formed by the major pores. The increase in compressive mechanical stress in the anodic film leads to an interruption in the development of such pores.

Removal of COD and TSS from tomato ketchup industrial wastewater using cylindrical electrocoagulation method

Tomato ketchup industrial sector is associated with various environmental problems including high concentration wastewater containing organic pollutant and suspended solid. While the industry always considers from an economic point of view, electrocoagulation can be the best alternative of treat wastewater which has the advantage easy in operation, minimum space requirements, low volumes of sludge produced, and can be used in high concentration wastewater. This paper investigated the effect of pH and current electricity on performance of removal of COD and TSS in tomato ketchup wastewater treatment. The research was conducted in continuous flow using cylindrical reactor with rod aluminum anode dan helical stainless-steel cathode, while the pH and current variations were 6, 7, 8 and 30 A, 35 A, and 40 A respectively. Based on analyzed data, aluminum has an effectiveness in COD and TSS removal. On the other hand, pH and current has a significant role on the process of removing COD and TSS. The best removal of COD and TSS was under the 35 A and pH 8 condition with 81,86 % (103.24 gCOD) and 82.61% (6.48 gTSS).

Ultrahigh Energy Density and Long-Life Cyclic Stability of Surface-Treated Aluminum-Ion Supercapacitors.

In this study, aluminum-graphene supercapacitors (denoted as aluminum-ion supercapacitors; ASCs), consisting of a battery-type aluminum anode, a capacitor-type graphene cathode, and ionic liquid 1-ethyl-3-methylimidazolium chloride (EMImCl) and aluminum chloride (AlCl3) electrolyte, were prepared. This study primarily aimed to investigate the enhanced electrochemical performance of ASCs arising from changes in the surface oxide layer and morphology via electrochemical surface treatments, including electropolishing and electrodeposition of aluminum anodes. The ASC devices based on an electrodeposited anode at a current density of 3 A g-1 exhibited a high specific capacity of 211 F g-1 compared to that of the electropolished anode (∼186 F g-1); these were 20 and 5.7%, respectively, higher than that of the pristine aluminum anode. In particular, the electrodeposited ASC delivered an energy density of 151 W h kg-1 at a power density of 3,390 W kg-1. Furthermore, a maximum power density of 11,104 W kg-1 was achieved at an energy density of 124.3 W h kg-1. These values are among the best as compared to those of previously reported aluminum-based supercapacitors, suggesting the potential feasibility of these ASCs with outstanding energy and power densities for next-generation energy storage devices.

From gradient-index to step-index filters: A switch between the two types of photonic crystals induced by the amplitude and period of sinusoidal function applied during high-temperature anodisation of aluminium

Porous anodic alumina (PAA) holds promise for the realisation of high-quality optical filters with first-order photonic stop-bands (PSBλ1) located in the infrared spectral region, thereby expanding the possibility of its application in photonics and light-based industries. High-temperature (30 °C) sinusoidal pulse anodisation (SPA) of aluminium was applied to fabricate PAA with PSBλ1 in the range of 800–2500 nm. The systematic increase in the anodisation period (tp) and amplitude (A) caused a significant change in the optical properties of the PAAs, which were monitored by both transmittance and reflectance measurements. A switch from gradient-index to step-index optical filters was observed when A and tp were increased from the lowest (5 V and 100 s, respectively) to the highest (15 V and 300 s, respectively) values. The switch was ascribed to the transition between different self-ordering regimes. The finest filtering properties (PSBλ1 reflectance close to 100 %) were achieved when the SPA proceeded between diffusion and kinetic regimes, providing a better porosity/refractive index contrast within the periodic structure. The analysis under polarised light confirmed both the excellent filtering properties of the PAAs and the asymmetrical light reflectance produced through the robust and cost-effective SPA process.

Chain-like carbon nano-onions from candle flame combustion as a high-performance cathode for aluminum-air batteries

A positive air electrode capable of a high‑oxygen reduction reaction (ORR) from chain-like carbon nano-onions (CLCNOs) was synthesized directly onto the surface of nickel foam using candle flame combustion. The 50 s synthesis positive air electrode with a carbon loading of 0.49 mgcm−2 provides higher ORR catalytic capability than that of other time synthesizers in natural pH electrolytes. Increasing the cathode-to-anode ratio increases the cell voltage from 0.41 to 0.53 V, causing the specific capacity to reach 1108 mAhg−1. In addition, a positive air electrode can work continuously for 14 days, even after repeated use and replacement of new aluminum anodes several times.

Flexible Electroflotocoagulation Reactor: New Design and Testing in Treatment of Real Surface Water

A novel continuous and flexible electroflotocoagulation (EFC) reactor was built using concentric cylindrical Al and Fe electrodes, which can be operated either as anodes or cathodes linked to a DC connection. The reactor was operationally assessed related to various cell configurations that assured the required stages of coagulant dosage, mixing, reaction, and settling or flotation. The effects of several design variables and operational parameters (such as the electrode position that determines the reactor configuration, current density (i), flow rate (F), and the electrode area-treated volume ratio (Sel/V)) on the specific energy consumption versus the aluminum dose and charge loading rate were investigated. The most energy-efficient cell configuration using an aluminum anode and iron cathode was tested for the treatment of surface water (Bega river, Timisoara city, Romania) rich in hydrophobic natural organic matter (8.3 mg C∙L−1 and specific UV absorbance parameter of 3.9 L∙m−1∙mg−1) and with a high turbidity of 92 NTU, under flood conditions. The best results that assured 97% turbidity removal, 87% for absorbance recorded at 254 nm, and 60% for DOC removal, through enhanced electroflotocoagulation, were achieved for an operational current density of 10 A∙m−2 with specific energy and electrode consumption of 0.1 kW h∙m−3 and 0.017 kg Al∙m−3, respectively.

New insight into anodization of aluminium with focused ion beam pre-patterning

The self-ordered anodic aluminium oxide (AAO) structure consists of micron-scale domains—defect-free areas with a hexagonal arrangement of pores. A substantial increase in domain size is possible solely by pre-patterning the aluminium surface in the form of a defect-free hexagonal array of concaves, which guide the pore growth during subsequent anodization. Among the numerous pre-patterning techniques, direct etching by focused gallium ion beam (Ga FIB) allows the preparation of AAO with a custom-made geometry through precise control of the irradiation positions, beam energy, and ion dosage. The main drawback of the FIB approach includes gallium contamination of the aluminium surface. Here, we propose a multi-step anodizing procedure to prevent gallium incorporation into the aluminium substrate. The suggested approach successfully covers a wide range of AAO interpore distances from 100 to 500 nm. In particular, anodization of FIB pre-patterned aluminium in 0.1 M phosphoric acid at 195 V to prepare AAO with the interpore distance of about 500 nm was demonstrated for the first time. The quantification of the degree of pore ordering reveals the fraction of pores in hexagonal coordination above 96% and the in-plane mosaicity below 3° over an area of about 1000 μm2. Large-scale defect-free AAO structures are promising for creating photonic crystals and hyperbolic metamaterials with distinct functional properties.

Anodising of aluminium in formate solutions with formation of porous alumina arrays

ABSTRACT New applications of porous anodic aluminium oxide (alumina) structures for the fabrication of photonic devices, etching masks, and periodic pore templates with prospective magnetic, photoluminescent, anti-reflecting properties recently are of high interest. In this respect, new anodising processes for controllable formation of periodic structures in unconventional solutions at low voltages might be challenging. In this study, the anodic behaviour of aluminium in aqueous formate solutions was studied within a wide range of concentrations, pH, electrolyte temperatures, anodising times, and voltages. It was established that the thickness of porous anodic films depended on the concentration of solution applied (c), pH, bath temperature (T), and voltage (U a) increasing with increase in c, U a, and T. The thickest films were formed in the solution containing 0.2 mol L−1 formic acid at a pH of 2.5. These films contained up to 5.8 at% of entrapped carbon. The transition of porous anodising to the ‘burning’ type occurred at 22–25 V. Under appropriate anodising conditions ordered hexagonal cell arrays can be formed.

Development of metal oxide incorporated Al-Zn-Sn sacrificial anodes processed by stir casting and heat treatment

Aluminum sacrificial anodes are currently the first choice for cathodic protection in numerous applications. The galvanic performance of aluminum-based sacrificial anodes is considerably enhanced by addition of certain alloying elements called activators. Recent researches proved that incorporation of specific metal oxides like MnO2, CeO2, RuO2, and IrO2 into the aluminum matrix could enhance the galvanic efficiency of aluminum anodes; however, the mechanism by which metal oxides improve galvanic properties of aluminum is still subject to discussion. The present work investigates the effect of incorporating commercially available low-cost manganese dioxide concentrate into Al-5Zn-0.1Sn sacrificial anodes in different volume fractions. It also studies the influence of heat treatment on anode’s galvanic performance by performing solution treatment at 3 different temperatures (250 °C, 400 °C, 550 °C). The electrochemical testing results proved an increase in efficiency of anodes incorporated with metal oxides and solution treated at 550 °C. The SEM imaging and EDX elemental mapping declared that the presence of SiO2 particles in the anode matrix which might cause effective and uniform corrosion of Al anodes and decreased non-coulombic losses.Graphical abstract

High-Productivity Single-Pass Electrochemical Birch Reduction of Naphthalenes in a Continuous Flow Electrochemical Taylor Vortex Reactor.

We report the development of a single-pass electrochemical Birch reduction carried out in a small footprint electrochemical Taylor vortex reactor with projected productivities of >80 g day–1 (based on 32.2 mmol h–1), using a modified version of our previously reported reactor [Org. Process Res. Dev.2021, 25, 7, 1619–1627], consisting of a static outer electrode and a rapidly rotating cylindrical inner electrode. In this study, we used an aluminum tube as the sacrificial outer electrode and stainless steel as the rotating inner electrode. We have established the viability of using a sacrificial aluminum anode for the electrochemical reduction of naphthalene, and by varying the current, we can switch between high selectivity (>90%) for either the single ring reduction or double ring reduction with >80 g day–1 projected productivity for either product. The concentration of LiBr in solution changes the fluid dynamics of the reaction mixture investigated by computational fluid dynamics, and this affects equilibration time, monitored using Fourier transform infrared spectroscopy. We show that the concentrations of electrolyte (LiBr) and proton source (dimethylurea) can be reduced while maintaining high reaction efficiency. We also report the reduction of 1-aminonaphthalene, which has been used as a precursor to the API Ropinirole. We find that our methodology produces the corresponding dihydronaphthalene with excellent selectivity and 88% isolated yield in an uninterrupted run of >8 h with a projected productivity of >100 g day–1.

An Ultrahigh Rate and Stable Zinc Anode by Facet-Matching-Induced Dendrite Regulation.

Resource-abundant metal (e.g., zinc) batteries feature intrinsic advantages of safety and sustainability. Their practical feasibility, however, is impeded by the poor reversibility of metal anodes, typically caused by the uncontrollable dendrite enlargement. Significant effort is exerted to completely prevent dendrites from forming, but this seems less effective at high current densities. Herein, this work presents an alternative dendrite regulation strategy of forming tiny, homogeneously distributed, and identical zinc dendrites by facet matching, which effectively avoids undesirable dendrite enlargement. Confirmed by multiscale theoretical screening and characterization, the regularly exposed Cu(111) facets at the ridges of a copper nanowire are capable of such dendrite regulation by forming a low-mismatched Zn(002)/Cu(111) interface. Consequently, reversible zinc electroplating/stripping is achieved at an unprecedentedly high rate of 100mA cm-2 for over 30000 cycles, corresponding to an accumulative areal capacity up to 30 Ah cm-2 . A full cell using this anode shows a high capacity of 308.3 mAh g-1 and a high capacity retention of 91.4% after 800 cycles. This strategy is also viable for magnesium and aluminum anodes, thus opening up a promising and universal avenue toward long-life and high-rate metal anodes.

Nanoporous Anodic Alumina Photonic Crystals for Sunlight Harvesting Applications: A Perspective

Nanoporous anodic alumina (NAA) fabricated by anodization of aluminum is a versatile platform material with tailorable geometric, optical, and chemical features for specific light‐based technologies and applications. Recent advances in anodization technology have enabled a new generation of NAA‐based photonic crystals (PCs)—periodic dielectric nanoporous structures that selectively allow, forbid, and confine the flow of incoming electromagnetic waves of specific wavelengths across their structure. NAA–PCs provide exciting new opportunities to engineer light–matter interactions with versatility across the broad spectrum, from UV to IR. But despite these fundamental advances, demonstrations of sunlight‐harvesting technologies based on NAA–PCs are still limited. Herein, an up‐to‐date summary of recent advances in NAA–PC technology is provided, and proof‐of‐concept demonstrations and future pathways to propel this versatile platform material across sunlight‐harvesting technologies such as photocatalysis, photoelectrocatalysis, photothermal energy conversion, and solar cells are discussed.

Anode passivation mitigation by homogenizing current density distribution in electrocoagulation

Electrode passivation is the most challenging technical problem in electrocoagulation (EC) water treatment process, but research on understanding and mitigating passivation evolution are still lacking. Herein, homogenization of current density (CD) distribution was found to be a critical factor in alleviating the anode passivation during EC process. Decreasing electrode area decelerated the growth of passivation layer on anode through homogenizing CD distribution, which was quantified by the ratios of CD distributed at the electrode edges and centers. When aluminum anode area decreased from 8 cm2 to 2 cm2 with a constant CD, the homogenization degree increased by 24.0%, and passivation was reduced by 24.3%. The depth profiles of passivated anodes confirmed the inhomogeneity of the anode passivation. Thicker passivation layers were observed at edges due to high CD distributions, which originated from the “edge effect” of electric field distribution between parallel plate electrodes. A facile strategy to homogenize CD distribution by splitting electrodes into smaller electrodes is then proposed for passivation mitigation, which can save energy consumption by 21.8% with unchanged removal efficiency. This study provides a unique insight into anode passivation mitigation and a feasible electrode design in EC.

High-specific-capacitance electrolytic capacitors based on anodic TiO2 nanotube arrays

Electrolytic capacitors have been increasingly used in almost all electronic devices because of their large specific capacitance, broad operating voltage range and good price to performance ratio. To satisfy the continuing miniaturization trend of electronic devices, researchers have continuously maintained efforts to increase the specific capacitance of electrolytic capacitors. Herein, we report a novel way to achieve high-specific-capacitance electrolytic capacitors starting from titanium dioxide nanotube arrays (TDNAs) formed by anodization. The anodized TDNAs are first transformed into titanium nitride nanotube arrays (TNNAs) by nitridation. Then TNNAs covered with a BaTiO3 film (BaTiO3@TNNAs) are obtained through electrochemical deposition and subsequent annealing. Thus, the fabricated BaTiO3@TNNAs are employed as anode of an electrolytic capacitor. The capacitor cathode is also derived from the anodized TDNAs by an electrochemical doping approach. The capacitor made of the BaTiO3@TNNAs anode and TDNAs cathode shows excellent electrical properties with a high specific capacitance of 292.8 μF cm−2, considerably higher than previously reported values for the modified aluminum anode foils. This study can provide new directions in increasing specific capacitance of electrolytic capacitors.

Development of hybrid aluminum-air battery fuel-cell system

Industrial 4.0 accelerates the need to introduce clean energy to accommodate the increase in electricity demand globally without causing environmental issues. Metal-air battery is a new type of energy storage system in which the metal anode is consumed to generate electricity through the electrochemical reaction. Among various types of the metal anode, aluminum is a promising energy carrier. Aluminum-air battery shows advantages such as high capacity, abundance, low cost, and being environmentally friendly. Traditional aqueous aluminum-air battery experiences restriction from application due to its self-corrosion issues. In this study, instead of reducing or limiting the self-corrosion issues, a different approach is proposed so to make use of the self-corrosion issues of the aluminum-air battery. By incorporating an additional hydrogen-air subcell to the aluminum-air battery, this hybrid system turned the self-corrosion issue into a beneficial reaction by utilizing the hydrogen gas produced from the aluminum anode as the fuel to power the hydrogen-air fuel cell and improving the overall power performance. The electrical performance of each system is studied experimentally using potassium hydroxide electrolytes. The hybrid system shows a great improvement as compared to a single system. The maximum power is improved by more than 40%. This study shows that the hybrid design is feasible in enhancing the aluminum-air battery performance and yet, maintaining low cost and low weight in nature.

A cradle-to-grave life cycle assessment of high-voltage aluminum electrolytic capacitors in China

Aluminum electrolytic capacitors (AECs) are widely used in electric circuits with various functions of filtering, power storage, decoupling, and circuit smoothing. High-voltage AECs can meet the requirements of high-voltage circuit applications, but they also aggravate the energy and environmental burden on capacitor production and use. The environmental performance of high-voltage AECs has not been well investigated, which weakens the manufacturers' ability to continuously reduce their negative environmental impacts. A cradle-to-grave life cycle assessment (LCA) of high-voltage AECs was performed to evaluate the environmental impacts and identify the corresponding environmental hotspots. According to the ReCiPe2016 method, fossil depletion, climate change, and photochemical ozone formation (ecosystems) are the main contributors to their environmental problems. The electricity used (798,545 kWh per 100,000 capacitors) and the raw material aluminum ingots (5130 kg per 100,000 capacitors) are the environmental hotspots for high-voltage AECs’ life cycle, which account for 94.1% of fossil consumption, 94.7% of greenhouse gas emission, and 94.9% of photochemical smog. It is of great significance to improve the area-specific capacitance of aluminum anode foil and the comprehensive electrical performance of high-voltage AECs to reduce their environmental impacts. This work would provide a benchmark to make informed eco-design decisions regarding the environmental consequences of alternative materials, design, manufacturing, and application for high-voltage AECs in the future.

Enhanced performance of Al-0.02Mg-0.01Sn-0.004Bi-0.003In alloy as novel anode for Al-air batteries in alkaline electrolyte

In this paper, aluminum alloy doped with Mg, In, Sn and Bi (Al-0.02Mg-0.01Sn-0.004Bi-0.003In) is prepared via melting and casting process. The influence of rare earth elements Bi and In on electrochemical performance of aluminum alloy anode is studied. The self-corrosion of hydrogen evolution and the electrochemical performance are investigated for the prepared alloy in 4 M NaOH electrolyte. The scanning electron microscope is used to study the surface morphology of the prepared alloy after discharge. It shows that synergistic effect between the alloy elements significantly reduces the self-corrosion rate of aluminum anode. Discharge experiments display that the prepared alloy outputs high capacity density and energy density of 2857.14 A h kg−1 and 4805.71 W h kg−1 at a high discharge rate (50 mA cm−2), respectively. It can also obtained considerable anodic utilization of 95.94 %. The prepared aluminum alloy is a desirable candidate anode material for the high-performance Al-air battery.

Unusual Size Effect in Ion and Charge Transport in Micron‐Sized Particulate Aluminum Anodes of Lithium‐Ion Batteries

Aluminum is a promising anode material for lithium-ion batteries owing to its high theoretical capacity, excellent conductivity, and natural abundance. An anomalous size effect was observed for micron-sized aluminum powder electrodes in this work. Experimental and theoretical investigations reveal that the insulating oxide surface layer is the underlying cause, which leads to poor electrical conductivity and limited capacity utilization when the particle is too small. Additionally, poor electrolyte wettability also accounts for the hindered reaction kinetics due to the weak polarity feature of the oxide layer. Surface grafting of polar amino groups was demonstrated to be an effective strategy to improve electrolyte wettability. The present work revealed the critical limitations and underlying mechanisms for the aluminum anode, which is crucial for its practical application. Our results are also valuable for other metallic anodes with similar issues.

Unusual Size Effect in Ion and Charge Transport in Micron‐Sized Particulate Aluminum Anodes of Lithium‐Ion Batteries

AbstractAluminum is a promising anode material for lithium‐ion batteries owing to its high theoretical capacity, excellent conductivity, and natural abundance. An anomalous size effect was observed for micron‐sized aluminum powder electrodes in this work. Experimental and theoretical investigations reveal that the insulating oxide surface layer is the underlying cause, which leads to poor electrical conductivity and limited capacity utilization when the particle is too small. Additionally, poor electrolyte wettability also accounts for the hindered reaction kinetics due to the weak polarity feature of the oxide layer. Surface grafting of polar amino groups was demonstrated to be an effective strategy to improve electrolyte wettability. The present work revealed the critical limitations and underlying mechanisms for the aluminum anode, which is crucial for its practical application. Our results are also valuable for other metallic anodes with similar issues.

Anodic Layer Growth on 1050 and 2024 Aluminium Alloys in Presence of Etidronic Acid : Changes in Morphology and Structure

Anodic layer growth during anodization is a well-known phenomenon, used to increase the thickness of the natural layer present on the surface of metals for corrosion resistance. In the case of pure aluminum and its alloys, the porous oxide layer leading to a regular structures with nanopores arrangements, which provides interesting corrosion resistance and mechanical performances. The most frequent electrolytes (sulfuric, oxalid or phosphoric acid) induce low current/voltage at direct or pulsed modes to elaborate the oxide layer according to the different electrochemical windows. If the anodic oxide film elaborated in the first moment is soluble into the electrolyte, a porous structure take place with pores oriented perpendicular to the metal surface. The formation of the barrier layer occurs at the interface between the metal and the porous layer, but is thin enough to allow a continuous ionic flow which lead to a continuous film growth.The present work deals with aluminum anodization in etidronic acid (HEDP) at very high voltages for aluminum 1050 and 2024 alloys. It appears that the oxide layer growth, studied by XRD and SEM pictures of cross section obtained by ionic polishing, differs clearly for the reason that pores formations not only starts from the barrier layer, but also at different locations such as the oxide layer/electrolyte interface. The final result consist in an oxide layer with excellent functional properties.