One-step electrodeposition of superhydrophobic coating on 316L stainless steel

Superhydrophobic coatings were fabricated through a one-step electrochemical process onto the surface of 316L stainless steel samples. The presence of hierarchical structures at micro/ nanoscale and manganese stearate into the coatings gave superhydrophobicity to the coating, with contact angle of ~160◦, and self-cleaning ability. Corrosion resistance of 316L samples was also assessed also after the electrodeposition process through Electrochemical Impedance Spectra recorded in an aqueous solution mimicking seawater condition

Enhancing corrosion resistance of anodized AA7075 alloys by electrodeposition of superhydrophobic coatings

Electrodeposition of superhydrophobic coatings was carried out on anodized AA7075 alloy to further enhance its corrosion resistance. Several compositions of electrodeposition bath were studied to find the most suitable one to obtain superhydrophobic coating. Scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy proved the deposition of coatings with different characteristics depending on electrodeposition bath composition. Highest contact angle value (∼ 160°) and highest corrosion resistance were obtained for the Mn-containing coating, proving also high stability after 21 days of immersion in an aqueous solution mimicking seawater. Experiments on flat pellet samples were carried out to split the effect due to the material composition with respect to that due to the coating morphological features, estimating the vacuum fraction of the superhydrophobic coatings according to the Cassie Baxter model

Band Gap Modeling of Different Ternary and Quaternary Alumina Garnet Phases Y3(AlXGa1-X)5O12 (YAGG) and Lu3(AlXGa1-X)5O12 (LuAGG). A Semiempirical Approach

A further generalization to quaternary oxide systems of the modeling equation of optical band gap values, based on the semiempirical correlation between the differences in the electronegativity of oxygen and the average cationic electronegativity, proposed some years ago, has been carried out by expanding the approach recently employed for ternary mixed oxides. The choice of oxide polymorphs and their influence on the fitting procedure of an experimental data set is evidenced by a detailed discussion of the fitting process of the literature's experimental band gap data pertaining two quaternary oxide systems of the garnet family, namely, Y3(AlxGa1-x)5O12 (YAGG) and Lu3(AlxGa1-x)5O12 (LuAGG), playing an important role in several engineering applications. The two investigated systems, moreover, span a quite large range of band gap energy values (from similar to 5.5 to similar to 7.5 eV), as a function of the Al/Ga ratio, allowing a rigorous test of the proposed modeling equation. Based on the wide existing literature on the presence of excitonic effects in the investigated systems some empirical correlations between an optical gap and a band gap in the presence of excitonic effects are suggested, too, which could provide some rationale to overcome the discrepancies frequently encountered in comparing band gap values reported in the literature for the same materials. The results of this work confirm the ability of this semiempirical approach in providing good agreement between experimental and theoretical band gap values also for very complex systems, where more sophisticated density functional theory-based methods face some difficulties in predicting the correct values

A Generalized Semiempirical Approach to the Modeling of the Optical Band Gap of Ternary Al-(Ga, Nb, Ta, W) Oxides Containing Different Alumina Polymorphs

A generalization of the modeling equation of optical band gap values for ternary oxides, as a function of cationic ratio composition, is carried out based on the semiempirical correlation between the differences in the electronegativity of oxygen and the average cationic electronegativity proposed some years ago. In this work, a novel approach is suggested to account for the differences in the band gap values of the different polymorphs of binary oxides as well as for ternary oxides existing in different crystalline structures. A preliminary test on the validity of the proposed modeling equations has been carried out by using the numerous experimental data pertaining to alumina and gallia polymorphs as well as the crystalline ternary Ga(1-x)AlxO3 polymorphs (α-Ga(1-x)AlxO3 and β-Ga(1-x)AlxO3) covering a large range of optical band gap values (4.50-8.50 eV). To make a more rigorous test of the modeling equation, we extended our investigation to amorphous ternary oxides anodically formed on Al-d-metal alloys (Al-Nb, Al-Ta, and Al-W) covering a large range of d-metal composition (xd-metal ≥ 0.2). In the last case, the novel approach allows one to overcome some difficulties experienced in fitting the optical band gap dependence from the Al-d-metal mixed anodic oxide composition as well as to provide a rationale for the departure, at the lowest d-metal content (xd-metal < 0.2), from the behavior observed for anodic films containing higher d-metal content

Ionic shortcut currents via manifolds in reverse electrodialysis stacks

Reverse electrodialysis (RED) is a blue energy technology for clean and sustainable electricity harvesting from the mixing entropy of salinity gradients. Recently, many efforts have been devoted to improving the performance of RED units by developing new ion-exchange membranes and by reducing the detrimental phenomena affecting the process. Among these sources of “irreversibility”, the shortcut currents (or parasitic currents) flowing through alternative pathways may affect the process efficiency. Although such phenomena occur in several electrochemical processes (e.g. fuel cells, bipolar plate cells and vanadium redox flow batteries), they have received a poor attention in RED units. In this work, a process simulator with distributed parameters was developed and experimentally validated to characterize the shortcut currents and to assess their impact in RED stack performance under different designs and operating conditions. Results showed that shortcut currents can play a crucial role in stacks with a large number of cell pairs when the electrical resistance of the parasitic pathways is relatively low, e.g. configurations with concentrated brines, high resistance membranes, short channels or large manifolds. Future designs of efficient industrial-scale units cannot ignore these aspects. Finally, the model can be easily adapted for the simulation of electrodialysis and other electromembrane processes

Highly Active and Stable NiCuMo Electrocatalyst Supported on 304 Stainless Steel Porous Transport Layer for Hydrogen Evolution in Alkaline Water Electrolyzer

Several functionalized porous transport layers with Pt-free electrocatalysts for hydrogen evolution reaction in alkaline conditions, based on Ni, Cu, and Mo, are prepared through electrodeposition onto a 304 stainless steel mesh. Morphological characterization confirms the fabrication of electrodes with high electrochemical surface active area due to the formation of hierarchical nanostructures. Mo presence into the electrocatalysts increases the activity toward the hydrogen evolution reaction. The optimization of electrodeposition process leads to the preparation of highly active NiCuMo electrocatalyst that exhibits near zero onset overpotential and overpotentials of 15 and 113 mV at 10 and 100 mA cm(-2), respectively, in 1 m KOH electrolyte. Moreover, this electrocatalyst shows superior stability with respect to other Pt-free electrocatalysts, reaching 100 h of durability with low overpotentials value demonstrating the successful preparation of very promising functionalized porous transport layers for future-generation alkaline electrolyzers

Effect of TiO2 and Al2O3 Addition on the Performance of Chitosan/Phosphotungstic Composite Membranes for Direct Methanol Fuel Cells

Composite chitosan/phosphotungstic acid (CS/PTA) with the addition of TiO2 and Al2O3 particles were synthesized to be used as proton exchange membranes in direct methanol fuel cells (DMFCs). The influence of fillers was assessed through X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, liquid uptake, ion exchange capacity and methanol permeability measurements. The addition of TiO2 particles into proton exchange membranes led to an increase in crystallinity and a decrease in liquid uptake and methanol permeability with respect to pristine CS/PTA membranes, whilst the effect of the introduction of Al2O3 particles on the characteristics of membranes is almost the opposite. Membranes were successfully tested as proton conductors in a single module DMFC of 1 cm(2) as active area, operating at 50 degrees C fed with 2 M methanol aqueous solution at the anode and oxygen at the cathode. Highest performance was reached by using a membrane with TiO2 (5 wt.%) particles, i.e., a power density of 40 mW cm(-2), almost doubling the performance reached by using pristine CS/PTA membrane (i.e., 24 mW cm(-2))

A Computational Tool for the Microstructure Optimization of a Polymeric Heart Valve Prosthesis.

Styrene-based block copolymers are promising materials for the development of a polymeric heart valve prosthesis (PHV), and the mechanical properties of these polymers can be tuned via the manufacturing process, orienting the cylindrical domains to achieve material anisotropy. The aim of this work is the development of a computational tool for the optimization of the material microstructure in a new PHV intended for aortic valve replacement to enhance the mechanical performance of the device. An iterative procedure was implemented to orient the cylinders along the maximum principal stress direction of the leaflet. A numerical model of the leaflet was developed, and the polymer mechanical behavior was described by a hyperelastic anisotropic constitutive law. A custom routine was implemented to align the cylinders with the maximum principal stress direction in the leaflet for each iteration. The study was focused on valve closure, since during this phase the fibrous structure of the leaflets must bear the greatest load. The optimal microstructure obtained by our procedure is characterized by mainly circumferential orientation of the cylinders within the valve leaflet. An increase in the radial strain and a decrease in the circumferential strain due to the microstructure optimization were observed. Also, a decrease in the maximum value of the strain energy density was found in the case of optimized orientation; since the strain energy density is a widely used criterion to predict elastomer's lifetime, this result suggests a possible increase of the device durability if the polymer microstructure is optimized. The present method represents a valuable tool for the design of a new anisotropic PHV, allowing the investigation of different designs, materials, and loading conditions.The authors thank the British Heart Foundation for financial support for this work under Grant NH/11/4/29059 and SP/15/5/31548

Performance of H2-fed fuel cell with chitosan/silicotungstic acid membrane as proton conductor

Composite organic\u2013inorganic proton exchange membranes for H2\u2013O2 fuel cells were fabricated by ionotropic gelation process combining a biopolymer (chitosan) with a heteropolyacid (silicotungstic acid). According to scanning electron microscopy analysis, compact, homogeneous and free-standing thin layers were synthesized. X-ray diffraction proved the crystallinity of the fabricated membranes and showed the presence of Chitosan Form I polymorph soon after the reticulation step and of the Form II polymorph after the functionalization step. Fourier-transform infrared spectroscopy demonstrated that the Keggin structure of the heteropolyacid is maintained inside the membrane even after the fabrication process. These membranes worked properly as proton conductors in a low-temperature (25 \ub0C) fuel cell apparatus using hydrogen as fuel recording a promising power density peak of 268 mW cm 122 with a Pt loading of 0.5 mg cm 122

On the modelling of an Acid/Base Flow Battery: An innovative electrical energy storage device based on pH and salinity gradients

Electrical energy storage can enhance the efficiency in the use of fluctuating renewable sources, e.g. solar and wind energy. The Acid/Base Flow Battery is an innovative and sustainable process to store electrical energy in the form of pH and salinity gradients via electrodialytic reversible techniques. Two electromembrane processes are involved: Bipolar Membrane Electrodialysis during the charge phase and its opposite, Bipolar Membrane Reverse Electrodialysis, during the discharge phase. For the first time, the present work aims at predicting the performance of this energy storage device via the development of a dynamic mathematical model based on a multi-scale approach with distributed parameters. Four models, each one at a different scale, are fully integrated in a comprehensive process simulator. The model was preliminary validated by a comparison with experimental data and a good agreement was found. A sensitivity analysis was performed to identify the most detrimental phenomena. Results indicate a loss of 25–35% of Round Trip Efficiency caused by parasitic currents in the manifolds. Therefore, they may represent the main limit to the present technology performance in scaled-up stacks converting more power. Suitable geometries and operating conditions should be adopted to tackle this issue (e.g. isolated blocks), thus enhancing the battery Round Trip Efficiency