Step Anodization Research Articles

Improving photoelectrochemical performance of transferred TiO2 nanotubes onto FTO substrate with Mo2C and NiS as Co-catalyst

The photoelectrochemical (PEC) performance of titanium dioxide nanotube (TiO2 NT) photoelectrodes for sustainable hydrogen production has garnered significant research interest. Despite the advantages of TiO2 NT fabricated via anodization of titanium metal, such as their well-ordered vertical structure, challenges persist including the thick oxide barrier layer, limited optical transparancy, and the wide energy band gap (∼3.0 eV), which constrain their practical efficiency in PEC applications. This study addresses these limitations by introducing a novel approch to transfer TiO2 NT onto a fluorine-doped tin oxide (FTO) substrate. TiO2 NTs were synthesized with varying anodization times and steps to achieve optimal free-standing structures. To further enhance PEC performance, co-catalyst including molybdenum carbide (Mo2C) and nickel sulfide (NiS) were incorporated using immersion and successive ionic layer adsorption reaction (SILAR) methods, respectively. Comprehensive characterization using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), ultraviolet–visible–near infrared (UV–Vis–NIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) provided insights into the crystal phase, morphological structure, band gap, and elemental composition of the photoelectrodes. Photoelectrochemical and photostability evaluations were conducted through linear scan voltammetry (LSV) and chronoamperometry under dark and light conditions. Results indicate that transferring TiO2 NTs onto FTO significantly enhanced photocurrent density, achieving a 2.5-fold increase at 0.7 V versus a TiO2 NT/Ti substrate. The incorporating of co-catalysts Mo2C, NiS and the combined NiS/Mo2C further enhanced the photocurrent density to 2.20, 3.00 and 8.00 mA cm−2 respectively, with a remarkable 31-fold enhancement compared to the TiO2 NT/Ti substrate. This findings underscore the potential of the TiO₂ NT/FTO photoelectrode with optimized co-catalyst integration for advanced photoelectrochemical applications.

Designing bipolar anodizing towards white anodic aluminum oxide (AAO)

Obtaining white anodic aluminum oxide (AAO) is a major challenge in the surface finishing industry. The present work presents a cost-effective route to design light-scattering morphologies through submicrometric hollows homogeneously dispersed in the depth of the oxide layer, created by localized hydrogen evolution. To this end, cathodic steps are added in alternance with anodic steps in a bipolar pulse anodizing process performed in 2 M sulfuric acid. The mechanisms of nucleation and growth of the targeted hollows within the AAO are highlighted by combining in situ electrochemical measurements and high magnification SEM observations. The aesthetic performances in terms of white color, evaluated by reflectance spectroscopy in comparison with a white reference, are directly related to the size, shape and distribution of the hollows, controlled by both the parameters of the cathodic step and the thickness of the unit anodic oxide layers.

Electroactive self-standing polyester membranes prepared using magnetite/poly(3,4-ethylenedioxythiophene) core-shell particles

In this work hybrid magnetite (Fe3O4)/poly(3,4-ethylenedioxythiophene) (PEDOT) core-shell particles are used to produce electro-responsive self-standing polycaprolactone (PCL) membranes with many potential applications. For this purpose, Fe3O4/PEDOT core-shell particles with different magnetite contents are prepared by combining chemical precipitation and emulsion polymerization. After chemical, morphological and physical characterization, the electrochemical response of the hybrid particles is analyzed and compared with that of PEDOT nanoparticles. In all cases, Fe3O4/PEDOT core-shell particles are more electroactive than PEDOT particles, with the electrochemical response of the former increasing with the content of magnetite. Composite membranes were prepared by spin-coating a mixture of polycaprolactone (PCL) and Fe3O4/PEDOT particles. The resulting Fe3O4/PEDOT-PCL membranes, which maintained the magnetic behavior, were transformed into electro-responsive by incorporating a PEDOT surface layer through anodic polymerization, which was possible thanks to the role of Fe3O4/PEDOT particles as polymerization nuclei. One of the potential applications of self-supported electro-responsive Fe3O4/PEDOT-PCL/PEDOT membranes was illustrated through a proof-of-concept. Specifically, a wide-spectrum antibiotic, chloramphenicol, was loaded into the membranes during the anodic polymerization step promoted by the hybrid Fe3O4/PEDOT particles and, subsequently, completely released by electrical stimulation. Overall, Fe3O4/PEDOT core-shell particles allowed us to obtain self-standing membranes with electric and magnetic properties, as promising candidates for many technological applications.

Facile Fabrication of Hierarchical Structured Anodic Aluminum Oxide Molds for Large-Scale Production of Superhydrophobic Polymer Films.

Anodized aluminum oxide (AAO) molds were used for the production of large-area and inexpensive superhydrophobic polymer films. A controlled anodization methodology was developed for the fabrication of hierarchical micro-nanoporous (HMN) AAO imprint molds (HMN-AAO), where phosphoric acid was used as both an electrolyte and a widening agent. Heat generated upon repetitive high-voltage (195 V) anodization steps is effectively dissipated by establishing a cooling channel. On the HMN-AAO, within the hemispherical micropores, arrays of hexagonal nanopores are formed. The diameter and depth of the micro- and nanopores are 18/8 and 0.3/1.25 µm, respectively. The gradual removal of micropatterns during etching in both the vertical and horizontal directions is crucial for fabricating HMN-AAO with a high aspect ratio. HMN-AAO rendered polycarbonate (PC) and polymethyl methacrylate (PMMA) films with respective water contact angles (WCAs) of 153° and 151°, respectively. The increase in the WCA is 80% for PC (85°) and 89% for PMMA (80°). On the PC and PMMA films, mechanically robust arrays of nanopillars are observed within the hemispherical micropillars. The micro-nanopillars on these polymer films are mechanically robust and durable. Regular nanoporous AAO molds resulted in only a hydrophobic polymer film (WCA = 113-118°). Collectively, the phosphoric acid-based controlled anodization strategy can be effectively utilized for the manufacturing of HMN-AAO molds and roll-to-roll production of durable superhydrophobic surfaces.

New insights into aluminium anodizing in phosphonic acid

Aluminium anodizing in phosphonic acid is known to produce anodic aluminium oxide (AAO) honeycomb structures with large interpore distances. However, detailed information on two-stage anodizing in phosphonic acid and annealing conditions required for the crystallization of AAO cell walls have not been reported yet. Here, the kinetics of aluminium anodizing in 1 M phosphonic acid and the thermal behaviour of the resulting AAO have been studied in detail. The apparent activation energy of aluminium anodizing is 65 kJ mol–1 and the AAO growth rate reaches 15 µm h–1 before oxide “burning”. A universal approach for stable two-stage anodizing at high voltages allowing to prevent porous structure rearrangement in the upper part of AAO is proposed. It involves the preliminary formation of a dense barrier alumina layer by anodizing in a weak acid electrolyte before the second anodizing step in phosphonic acid. The crystallization pathways of AAO obtained in phosphonic acid electrolyte are revealed based on differential scanning calorimetry, X-ray diffraction, and solid-state nuclear magnetic resonance techniques. The designed annealing program allows one to preserve the honeycomb porous structure after the crystallization of AAO in corundum at 1310 °C for 60 h. AAO obtained in phosphonic acid possesses high thermal stability and, thus, is promising as a support for gas sensors and fuel cells.

Process for integrating multiple porous silicon membranes with variable characteristics into planar microfluidics

We present a fabrication process based on selective ion implantation to monolithically integrate several porous silicon membranes with different morphologies in the same planar fluidic chip through a single anodization step. By manipulating the dopant concentration of specific zones of a silicon on insulator wafer, the porous silicon elements formed through electrochemical anodization present different characteristics in terms of pore size and porosity. Using this technique, we are able to fabricate both lateral porous silicon membranes and standard porous silicon membranes with vertical pores that can be used in flow-through and flow-over configurations. Achieved mean pore sizes and porosities for the various membranes integrated in the same chip range from 25 nm to 50 nm, and 65–90 %, respectively. Because porous silicon membranes have been used for biosensing and for sample preparation in microfluidics devices, this method is foreseen to enable the use of porous silicon membranes to achieve all the functions involved in the analytical process on a single chip.

Fabrication and Magnetic Behavior of Jellyfish-Like Ni Nanowires Synthesized Using Bilayered Nanoporous Anodic Alumina Templates.

The potential to produce nanostructures with intricate shapes in large quantities holds promise for a range of applications in the fields of nanoelectronics and biomedicine. Here a method for fabricating jellyfish-like Ni nanowires (JFNWs) using bilayered nanoporous anodic alumina templates with through pores of varying diameters in each layer is presented. To assess the capabilities of this method,samples are created with different voltages during the second step of anodization, resulting in distinct geometrical characteristics of the second layer of the template,and subsequently synthesizeNiJFNWs. By employing magnetometry and first-order reversal curve (FORC)method, the magnetic properties are examined and a significant alteration in their magnetic behavior,attributed to the differing shapes of theJFNWsand the magnetostatic interactions within the array,is observed.The study utilizes magnetic force microscopy to evaluate the stray magnetic fields generated by the individualJFNWsand unveils their unusual and asymmetric distribution. Through simulations based on the experimental data, the study analyzes the field- andcurrent-induced domain wall movement in a singleJFNWand their array. The findings revealnon-trivial micromagnetic configurations in these structures, including a remarkable 'corkscrew' state, and allowfor an examination of the process of magnetization switching.

Cu microvia filling by pulse-reverse electrodeposition with a single accelerator

Cu electrodeposition processes are widely employed to achieve defect-free interconnections in electronic devices. Typically, combinations of three additives—an accelerator, a suppressor, and a leveler—are used for bottom-up filling of Cu in microscaled features. However, the use of multiple additives adds complexity to electrolyte maintenance and can lead to reliability issues in the process. To address this challenge, we have developed a single-accelerator filling technique using pulse-reverse electrodeposition for microvias. During pulse-reverse electrodeposition, the anodic steps produce a large amount of Cu+ ions near the electrode surface. These Cu+ ions can form complexes with Cl− ions or CuCl layers, thereby enhancing the adsorption of the accelerator, SPS. This phenomenon depends on the electrolyte convection. Under strong forced convection, Cu-Cl species are removed, leading to subsequent deactivation of SPS, whereas Cu-Cl species remain stable under mild convection conditions. Based on this convection-dependent behavior of SPS and Cl, Cu electrodeposition is promoted at the bottom of microvias while the SPS is selectively deactivated outside the microvias where the strong electrolyte motion exists. As a result, without any polymeric suppressor and organic leveler, the microvias are successfully filled with Cu.

Sculpting Tiered Micro‐Nanogradient Structure by Anisotropic Stepped Anodization for Mediating Water Distribution and Transportation

AbstractTiered micro‐nanogradient structures with custom‐tailored profiles and dimensions can be fabricated by the anisotropic electrochemical anodization of aluminum, where the micro and nanostructures are simultaneously formed. The microgradient structures can be sculpted by the chronological and spatial order of polymer masking followed by step anodization; the nanostructures can be controlled by electrochemical conditions in step anodization. Water spatial distribution and directional transportation abilities of the exemplified micro‐nanogradient structures (i.e., tiered micro symmetric circular structure, microasymmetric circular structure, and microrectangular step structure which are all integrated with nanotip‐capped nanopore structure) are studied under the fogging condition. It is found that despite the directional self‐jumping of the microdroplets caused by the cooperation of asymmetric structure and wind blowing, microdroplets can also be quickly gathered on the topper tier of the gradient structures to form large droplets and then roll away along the descending direction of the structures (also wind blowing direction), which sweep the microdroplets they passed by. These tiered micro‐nanogradient structures not only have potentials to become high efficiency fog collector but also could be a platform for the preparation of tiered micro‐nanogradient structures of various materials with advanced functions.

Isotopic Tracer Study of Initiation of Porosity in Anodic Alumina Formed in Chromic Acid.

In this paper, we focused on the initiation of porosity in the anodic alumina under galvanostatic conditions in chromic acid, using an 18O isotope tracer. The general concept of the initiation and growth of porous anodic oxide films on metals has undergone constant development over many years. A mechanism of viscous flow of the oxide from the barrier layer to the pore walls has recently been proposed. In this work, two types of pre-formed oxide films were analysed: pure Al2O3 formed in chromic acid, and a film containing As ions formed in a sodium arsenate solution. Both were anodized in chromic acid for several different time durations. Both pre-formed films contained the oxygen isotope 18O. The locations and quantities of 18O and As were analysed by means of ion accelerator-based methods supported by transmission electron microscopy. The significant difference observed between the two oxide films is in the 18O distribution following the second step of anodization, when compared with galvanostatic anodization in phosphoric or sulfuric acid reported in previous works. From the current experiment, it is evident that a small amount of As in the pre-formed barrier layer appears to alter the ionic conductivity of the film; thus, somehow, it inhibits the movement of oxygen ions ahead of advancing pores during anodization in chromic acid. However, anodising pure alumina film under these conditions does not enhance oxygen movement within the oxide layer. In addition, the tracer stays in the outer part of the growing porous oxide film. A lower-than-expected value for pure alumina enrichment in 18O in the pre-formed films suggests, indirectly, that the pre-formed film may contain hydrogen species, as well as trapped electrons, since no Cr is detected. This may lead to the presence of space charge distribution, which has a dual effect: it both retards the ejection of Al3+ ions and prevents O2- ions from migrating inward. Thus, the negative- and positive-charge distributions might play a role in the initiation of pores via a flow mechanism.

An Electrocrystallization Approach for Modeling Protective Scale Formation in CO2 Corrosion of Carbon Steel

The CO2 corrosion of carbon steel has been extensively studied and many models have been developed to estimate the corrosion rate in various industrially relevant conditions [1]. These models agree moderately well in non-scaling environments but can produce significantly different results under higher temperature and higher pH conditions where protective scales of iron carbonate may be formed [2,3]. The scaling effect is typically incorporated in empirical models using a ‘scaling factor’ [2,3]. Nesic and co-workers developed a model that attempts to calculate the corrosion rate in scaled conditions from first principles [4,5,6], later including a numerical model to describe the formation kinetics and growth morphology of the surface layer [7]. In this and other models, the driving force for scaling is the degree of supersaturation (S) of FeCO3 at the steel surface, and it is generally assumed that protective films are formed by precipitation from solution, at a rate dependent on S [7,8,9].To investigate the formation and structure of these surface scales, Williams and colleagues [10-14] completed a series of experiments using in-situ synchrotron x-ray techniques. The majority of this work accelerated the corrosion process through the application of a small anodic potential step, and focused on solutions of moderate chloride content, saturated with CO2 at ~ 1 bar, pH adjusted to ~ 6 and at temperatures of ~ 80 °C. Small Angle X-Ray Scattering (SAXS) showed that the first stage in scaling was the formation of a precipitated layer of Amorphous Ferrous Carbonate (AFC) [13], while X-Ray Diffraction (XRD) revealed that the reduction of corrosion rate was associated with the slower formation of crystalline siderite (FeCO3) and sometimes chukanovite (Fe2(OH)2CO3) (see Figure 1). Hassan et al [14] then developed a model for this process in which the protective scale forms directly on the steel surface by an electrocrystallization mechanism, using an Avrami model to describe the crystal nucleation and growth. The relative volume of siderite as a function of time was fitted with an Avrami-like equation. The anodic current transients formed during potentiostatic experiments (see Figure 1) were then fitted with separate components due to iron dissolution and electrocrystallization, allowing various kinetic parameters to be extracted from the experimental data.In this paper, we extend these previous ideas on the importance of considering electrocrystallization as a fundamental step in the scale formation process. There exist several models of the potentiostatic current time transient in the electrocrystallization literature [15,16]. Taking the potentiostatic data from Hassan et al [14], we fit the current time transient to some models from literature [15,16]. This fitting provides rich information about the kinetics of nucleation. We speculate on some differences from the models in Luo et al [15] by current transient fitting. We also provide expressions for surface coverage of siderite under different applied potentials with the Avrami equation to account for the scale protection factor more rigorously. Improved estimates of the protection factor by our methods can lead to reduced overestimation of corrosion rates thereby improving pipeline integrity assessments in existing software packages. References Kermani, A. Morshed, Corrosion 59 (2003) 659–683.Nyborg, NACE 02233, Corrosion 2002, OnePetro 2002.Nyborg, NACE 10371, Corrosion 2010, OnePetro 2010.Nešić, M. Nordsveen, R. Nyborg, A. Stangeland, Corrosion 59 (2003) 489–497.Nordsveen, S. Nešić, R. Nyborg, A. Stangeland, Corrosion 59 (2003) 443–456.Nesic, K.-L.J. Lee, V. Ruzic, NACE 02237, Corrosion (2002).Sun, S. Nešić, Corrosion 64 (2008) 334-346.L. Johnson, M.B. Tomson, Paper No. 268, CORROSION/91, NACE International, 1991.Van Hunnik, Pots,Hendriksen NACE 96006, Corrosion(1996).Ingham, M. Ko, G. Kear, P. Kappen, N. Laycock, J. A. Kimpton, D. E. Williams, Corrosion Science, 52, 3052-3061 (2010).Ingham, M. Ko, N. Laycock, J. Burnell, P. Kappen, J. A. Kimpton,D. E. Williams, Corrosion Science, 56, 96-104 (2012).Ko, B. Ingham, N. Laycock,D.E. Williams, Corrosion Science, 90, 192-201 (2015).Ingham, M. Ko, N. Laycock, N. Kirby and D.E. Williams, Faraday Discussions, 180, 171-190 (2015).Hassan Sk, A.M. Abdullah, M. Ko, B. Ingham, N. Laycock, D.E. Williams, Corrosion Sci., 126, 26–36 (2017).Gong Luo, Yuan Yuan, De-Yu Li, Ning Li, Guo-Hui Yuan, Coatings 2022, 12(8), 1195.Bewick, H.R. Thirsk, M. Fleischmann, Trans. Faraday Soc. 58 (1962) (2200- &). Figure 1

Electrodeposition of Cu Nanocubes in the Presence of Cl- and Br-

Electrodeposition is one of the simple methods for fabricating metal and alloy thin films. Electrodeposition is performed by applying external electrical energy to conductive substrates immersing in electrolytes containing metal precursors. Metal ions or complexes are reduced on a substrate surface and form metal films. The properties of metal thin films and surface morphology of the electrodeposit can be modulated by the parameters of electrodeposition, the composition of electrolytes, i.e., the concentrations of metal precursors and additives. Furthermore, the atomic composition of alloy films can also be easily controlled by electrochemical parameters in the electrodeposition process.1 As explained, the electrodeposition process has various advantages in producing metal thin films with desired properties. However, creating nanostructures with precisely controlling their shapes in the nm scale is relatively difficult. In colloidal syntheses, various nanocrystals, including nanowires, nanospheres, octahedrons, nanocubes, and nanoplates, can be obtained by introducing shape-directing agents.2-4 In the case of electrodeposition, the template-assisted electrodeposition method is the most common to form nanostructures,5,6 and relatively few examples of shape controlling by additives have been reported. Although the formation of metal nanowires in the presence of 3,5-diamino-1,2,4-triazole (DAT) has been recently reported,7 shape control of metal deposits by additives during the electrodeposition process is still limited to few nanostructures. Electrodeposition induces metal growth relatively faster than colloidal synthesis, and a precise nucleation step is not involved in the electrodeposition, which is critical in colloidal syntheses. In this study, we have adopted pulse-reverse electrodeposition to modulate metal nucleation at the initial stage of electrodeposition and also maximize the effects of additives. Pulse-reverse electrodeposition has been researched for controlling the properties of metal thin films and changing the adsorption of additives.8,9 Therefore, pulse-reverse electrodeposition can catch up with the shape control in colloidal syntheses. This presentation will introduce how the parameters in pulse-reverse electrodeposition and additives (halide ions) affect the shape of Cu nanocrystals. References 1) T. P. Moffat, J. J. Mallett, and S. M. Hwang, “Oxygen Reduction Kinetics on Electrodeposited Pt, Pt100− x Nix , and Pt100−xCox” J. Electrochem. Soc. 156, B238 (2009)2) Y. Xia, Y. Xiong, B. Lim, and S. E. Skrabalak, “Shape-Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?” Angew. Chem. Int. Ed. 48, 60 (2009)3) K. A. Fichthorn, Z. Chen, Z. Chen, R. M. Rioux, M. J. Kim, and B. J. Wiley, “Understanding the Solution-Phase Growth of Cu and Ag Nanowires and Nanocubes from First Principles” Langmuir 37, 4419 (2021)4) D. Huo, M. J. Kim, Z. Lyu, Y. Shi, B. J. Wiley, and Y. Xia, “One-Dimensional Metal Nanostructures: From Colloidal Syntheses to Applications” Chem. Rev. 119, 8972 (2019)5) K. R. Yeo, J. Y. Eo, M. J. Kim and S.-K. Kim, “Shape Control of Metal Nanostructures by Electrodeposition and their Applications in Electrocatalysis” J. Electrochem. Soc. 169, 112502 (2022)6) C. Liu, Z. Li, P. Yu, H. W. Wong, and Z. Gu, “Vertically Aligned and Surface Roughed Pt Nanostructured Wire Array as High Performance Electrocatalysts for Methanol Oxidation” ACS Appl. Energy Mater. 1, 3973 (2018)7) T. T. H. Hoang, S. Ma, J. I. Gold, P. J. A. Kenis, and A. A. Gewirth “Nanoporous Copper Films by Additive-Controlled Electrodeposition: CO2 Reduction Catalysis” ACS Catal. 7, 3313 (2017)8) M. J. Kim, T. Lim, K. J. Park, S. K. Cho, S.-K. Kim, and J. J. Kim “Characteristics of Pulse-Reverse Electrodeposited Cu Thin Films: I. Effects of the Anodic Step in the Absence of an Organic Additive” J. Electrochem. Soc. 159, D538 (2012)9) M. J. Kim, T. Lim, K. J. Park, O. J. Kwon, S.-K. Kim, and J. J. Kim “Characteristics of Pulse-Reverse Electrodeposited Cu Thin Film: II. Effects of Organic Additives” J. Electrochem. Soc. 159, D544 (2012) Figure 1

Impedimetric transduction from a single-step thin film nanoporous aluminum oxide as a DNA sensing electrode

A two-step anodization process has been widely used to grow a perfectly arranged Anodic Aluminum Oxide (AAO) nanoporous with high regularity and circularity. However, this method requires more time and electricity cost since the second step anodization will be conducted more than a couple of hours up to 24 h to obtain a perfect hexagonally arranged AAO. Besides, the usage of toxic chromic acid to remove the rough surface after the first anodization is not recommended. To solve this issue, a single-step of anodization method to grow AAO at 15 °C in 0.3 M of oxalic acid at 40 V for 1 h has been proposed. In this study, the growth AAO thin film will be tested as a DNA biosensor electrode. Prior to that, instead of using toxic chemicals, couple of drops of phosphoric acid solutions were used to treat the rough, uneven surfaces by promoting hydroxyl groups while at the same time widening and revealed the underneath pores. The AAO thin film is ready for the next step of surface modification without a second anodization step. Surface chemical functionalization using 3-aminopropyl-triethoxysilane (APTES) and glutaraldehyde is performed to immobilize the aminated-ssDNA probe on the surface. The electrochemical impedance technique is employed to monitor the changes in each layer of surface modifications. The charged transfer resistance (Rct) values are linearly increased with each new additional layer on the AAO surfaces during each step of surface modification and with the increase in ssDNA complementary target concentrations (10 fM-10 μM). From the performance test, the single-step AAO thin film electrode has shown great results in functioning as a DNA biosensor through a selectivity test. It has the capability to differentiate the complementary sequences from the single mismatched target with 3-fold.

Development of nano structures for solar driven desalination

Now-a-days there is shortage of pure water in several areas. So, the emerging technology solar driven desalination is one of the core practices that employ solar energy for fresh water making in sunny areas with lacking quality of water resources. In this work, the nano structure was developed using two step anodization procedure. Anodization was performed on pure aluminum foil (99.99 % purity) in 0.3 M of oxalic acid at constant voltage and effect of temperature on the morphology of formed porous anodic aluminum oxide (AAO) film was investigated. The temperature is varied between −5 to 25 °C. The characterization of the material is done using Scanning Electron Microscopy (SEM), Energy dispersive X-ray (EDAX), Ultraviolet-Differential reflectance spectroscopy (UVDRS). It is observed that, at −5 °C, micro indentations are formed on surface. At 5 °C, pores are randomly formed on the surface. At 15 °C, nano balls are formed on the surface. Whereas, at 25 °C, complete nano porous structure is formed. Hence, the formed nano structures were applied in solar driven desalination. In comparison to all other temperatures, we have observed that, the nano porous structure developed at 25 °C has 27 % of higher evaporation than the conventional.

Fabrication of near superhydrophobic Pt-TiO2 hybrid nanoflake composite as food sensor in food processing industry.

The current finding reports on the development of highly ordered closely packed TiO2 nanotube arrays on Ti substrate via two-step anodization process. The nanotubes developed by second anodization step (TNT2) were encapsulated with Pt nanoflakes using electro-deposition followed by hydrothermal treatment process. The FE-SEM, FTIR, XRD and contact angle measurement, respectively were done to find out the morphological, functional group, phase structural and wettability of the samples. The tube diameter and length were found to be 110-120 and 50-100 nm and 437 and 682, respectively for first (TNT1) and second anodization. The structural order of the TNT has enhanced in the second anodization process. Chronoamperometric results showed that the Pt-TNT2 exhibited enhanced and steady state electro-catalytic activity than Pt-TNT1. Pt-TNT2 nanoflake composite showed near SHP behaviour than the TNT without Pt. The food processing machinery developed using near SHP Pt-TNT2 could be cleaned easily due to its high non-wettability. Hence, Pt-TNT2 can be used for making food processing equipment.

Novel photoanodes based on (Mo-Cr) co-doped titania nanotube for highly efficient photocathodic protection performance of stainless steel

Mo-doped, Cr-doped, and Mo-Cr co-doped titania nanotube arrays were synthesized through the single step anodization of titanium. Mo-Cr co-doped titania nanotubes prepared showed great improvement on photocatalytic activity in the protection of stainless steel (403SS) under visible light irradiation compared with Mo and Cr mono-doped titania. The open-circuit potential (OCP) of 403SS (in 3.5 wt% aqueous NaCl) coupled with the best co-doped sample (Cr50:Mo50-TNT) was reduced from −240 to −690 mV, while the electrode potential was maintained at −320 mV even upon turning the light off. This study also identified the effect of the addition of sulfur compounds as hole scavengers on the photoelectrochemical (PEC) properties and photoelectrochemical cathodic protection (PCP) by the best Mo-Cr co-doped titania nanotube. Sodium sulfate and sulfite, sodium thiosulfate, sodium sulfide, potassium metabisulfite and thiourea have been used as hole scavengers. The order of photocurrent is as follows: Na2S > K2S2O5 > CS(NH2)2 > Na2S2O3 > no hole scavengers > Na2SO4 > Na2SO3. Mo-Cr co-doped titania nanotube show much more favorable PCP impact on 403SS than the pure titania sample, according to the results of the changes in the potentials and current densities. Furthermore, the results finally proved that sodium sulfide is the most appropriate hole scavenger.

The Spontaneous Repassivation of Cr Containing Steels and Multi-Principal Element Alloys

The corrosion resistance of an alloy in most environments will depend on its ability to spontaneously passivate at the corrosion potential. This is especially true for localized forms of corrosion such as occur in acidic, occluded environments during pitting and crevice corrosion. In the laboratory however, the kinetics of passivation are mainly investigated using electrochemical methods that require polarization of the material via an external power source. Spontaneous passivation cannot directly be observed by this approach. It is therefore of interest to investigate the repassivation phenomena as it occurs at open circuit, driven by the oxidizing agents present in the electrolyte.To this end, we have recently developed a methodology to determine the kinetics of spontaneous passivation using element-resolved electrochemistry (atomic spectroelechemistry, or ASEC) [1-3]. Passivation may be measured by first disrupting the original passive film using an electrochemical perturbation and then monitoring the corrosion rate as a function of time on an element-by-element basis. As the passive film reforms, the corrosion rate decreases allowing a real time monitoring of film formation. The perturbation may be either a cathodic pulse to reduce the passive film as in a conventional polarization curve experiment, or it may be an anodic pulse into the transpassive domain.In addition, the contribution of the individual alloying elements to dissolution and to passive film formation may be quantitatively accessed thereby yielding insight into one of the fundamental questions for engineering new alloys - what is the specific role of the different alloying elements? For example, it is widely recognized that for the Cr containing alloys, Cr is the primary constituent of the passive film, at least when Cr is above about 12%. However, the presence of other elements may affect the efficiency of Cr-oxide film formation, some like Mo in a beneficial way [2], others like Mn in a negative way [3]. Via a simple mass balance, the elemental dissolution rate profiles may be transformed into a time resolved elemental surface enrichment profile. This allows a direct look into the role of the alloying elements.The Figure gives an example of this approach based on the results from Ref. 3. The system under investigation was the high entropy Cantor alloy containing alloyed nitrogen in a sulfuric acid solution. The left-hand side gives the open dissolution rate for an experimental sequence of (a) open circuit, (b) cathodic activation (300 s at -0.8 V vs. SCE), (c) repassivation at open circuit (300 s). Repassivation is indicated by the initially large corrosion rate (active state) followed by the decrease of the corrosion rate as the passive film reforms. The contribution of the individual alloying elements is shown all of which dissolved congruently with the exception of Cr which was below the congruent level (black line) indicative of Cr surface enrichment. The right hand side gives the quantity of Cr enriched on the surface during the sequence calculated by mass balance. Cr dissolves during the cathodic activation but reforms as soon as the potential is released. Also shown is the Cr enrichment during an anodic step to 0.4 V which leads to a more rapid and significant build-up of surface Cr.This presentation will review the methodology of spontaneous passivation measurements for both austenitic stainless steel (304L) and for the high entropy Cantor alloy (equimolar NiFeCrCoMn) with variable Mn content. In particular, we will focus on the differences between repassivation following cathodic activation and transpassive activation. The mechanisms of spontaneous repassivation will be discussed with an emphasis on how the alloying elements influence repassivation under these two conditions.1) K Ogle “Atomic emission spectroelectrochemistry: real-time rate measurements of dissolution, corrosion, and passivation”, Corrosion 75 (2019)1398-1419. Open access. 2) X Li, J D Henderson, F P Filice, D Zagidulin, M C Biesinger, F Sun, B Qian, D W Shoesmith, J J Noël, K Ogle, “The contribution of Cr and Mo to the passivation of Ni22Cr and Ni22Cr10Mo alloys in sulfuric acid”, Corrosion Science 176, (2020) 109015.3) X Li, P Zhou, H Feng, Z Jiang, H Li, K Ogle, “Spontaneous passivation of the CoCrFeMnNi high entropy alloy in sulfuric acid solution: The effects of alloyed nitrogen and dissolved oxygen”, Corrosion Science 196(2022)110016. Figure 1

Fabrication of Pyramid-Like Structured Cu Coatings by Pulse-Reverse Current Electrodeposition

Copper (Cu) coatings with a high surface area have attracted significant attention for functional devices due to their high thermal and electrical properties. Pulse-reverse current (PRC) electrodeposition has been introduced to fabricate Cu coatings for a long history, but compared to the individual anodic step, little attention has been paid to the synergistic effects of anodic and cathodic steps. The new parameter “artificial exchange current density” (j A) has been demonstrated to quantify the effects of anodic and cathodic currents on the morphology in our previous work. Herein, a key metric−the relative current amplitude−that is positively correlated with j A, is used to further clarify the role of j A in the electrodeposition process. We fabricate Cu coatings with well-dispersed pyramid-like structures and find the relative current amplitude dominates the formation of a larger raised structure at the initial nucleation stage. Moreover, it is speculated that the anodic current can dissolve high-energy planes and achieve a highly (111)-oriented texture. Afterward, screw dislocation drives the spiral growth of grains, resulting in pyramid-like structures. This study not only enriches our understanding of the artificial exchange current density in PRC electrodeposition but also guides us to achieve Cu coatings with high surface area.

Nanoporous WO3 grown on a 3D tungsten mesh by electrochemical anodization for enhanced photoelectrocatalytic degradation of tetracycline in a continuous flow reactor

• A nanoporous WO 3 /W electrode was obtained via mild anodization of W mesh. • Photo-electrocatalytic (PEC) degradation of tetracycline in continuous flow reactor. • PEC was 3x times more efficient than photocatalysis alone. • Continuous flow reactor design is scalable and highly efficient. The efficient removal of organic micropollutants remains a major challenge for conventional water treatment technology. Photocatalysis, while effective, has not been widely adopted due to cost and implementation challenges. Here, an effective alternative is proposed through the integration of photocatalytic and electrochemical degradation of tetracycline (TC) in a continuous flow reactor using a WO 3 /W mesh as photo-electrode. WO 3 nanoporous structures were grown on a tungsten (W) metal mesh via one step anodization in aqueous oxalic acid electrolyte (0.05 mol/L). The prepared materials were then used as 3D array photoanode in a continuous flow photo-electrocatalytic reactor. The combined influence of anodization time and post-treatment annealing temperature on the photo-electrochemical activity of the WO 3 /W mesh was examined through morphological and structural analysis. W mesh anodized for 4 h, and subsequently annealed at 450 °C have a homogenous nanoporous structure uniformly distributed and well adhering onto the W mesh, with average pore diameter of ∼ 80 nm and pore wall thickness of ∼ 250 nm. These materials are transparent, have high conductivity and WO 3 monoclinic phase. Under optimal conditions of recirculating flow rate of 230 mL min −1 and bias potential of + 1.0 V vs Ag/AgCl/KCl (3 mol/L), the photo-electrocatalytic degradation led to a TC removal of up to 90 % after 60 min of treatment, almost 3 times higher than photocatalysis only. The excellent results by integration of photocatalysis and electrochemical degradation in a flow reactor, combined with a scalable WO 3 /W mesh, offers a useful information for upscaling and designing for practical issues in water treatment (such as costs and efficiency).

Nanostructured Superhydrophobic Titanium-Based Materials: A Novel Preparation Pathway to Attain Superhydrophobicity on TC4 Alloy.

This study develops the nanostructured superhydrophobic titanium-based materials using a combined preparation method of laser marking step and the subsequent anodizing step. The structural properties were determined using an X-ray diffractometer (XRD) and scanning electron microscope (SEM), while the performance was explored by wear and corrosion tests. The laser marking caused a rough surface with paralleled grooves and protrusions, revealing surface superhydrophobicity after organic modification. The anodizing process further created a titanium oxide (TiO2) nanotube film. Both phase constituent characterization and surface elemental analysis prove the uniform nanofilm. The inert nanosized oxide film offers improved stability and superhydrophobicity. Compared to those samples only with the laser marking process, the TiO2 nanotube film enhances the corrosion resistance and mechanical stability of surface superhydrophobicity. The proposed preparation pathway serves as a novel surface engineering technique to attain a nanostructured superhydrophobic surface with other desirable performance on titanium alloys, contributing to their scale-up applications in diverse fields.