bluuebunny/crossref_metadata_2025_split huggingface dataset:
Model for Formation of Self-Ordered Anodic Oxide Nanomaterials
Authors: Mishra Pratyush , Hebert Kurt 
Published: February 2020

Porous anodic films are self-organized porous oxides nanomaterials formed by electrochemical oxidation. Pores in porous alumina and nanotubes in TiO2nanotube layers initiate after an initial stage of barrier oxide growth. The porous film eventually evolves into a hexagonally-ordered array of parallel cylindrical pores or nanotubes of order 10-100 nm diameter with a characteristic spacing that scales directly with the cell voltage.
We explore the roles of mechanical stress and oxide flow in self-ordering, through a modeling analysis of stress-driven viscous flow of oxide (1-3). The model is based on coupled viscous flow of oxide and stress- and electric field-driven migration of metal and oxygen ions (1). Stress at the film interfaces is generated by ion-transfer processes and relaxed by viscous flow, resulting in layers with elevated compressive or tensile stress within a few nm of the interfaces (2,3). Experimental evidence for these layers has been found from in situ stress measurements (2-4). We present linear stability analysis incorporating the surface stress boundary conditions in the coupled oxide flow-electrical migration model of Houser and Hebert (1). The calculations reveal self-organized pattern formation with steady-state pore spacing-voltage scaling ratios that compare favorably to those found experimentally, for both porous alumina and TiO2nanotube layers. The scaling ratios are independent of oxide viscosity or uncertainties in the values of any other model parameters. In the case of Al anodization, oxide flow resulting in pore patterns is driven by elevated stress near the oxide-solution interface, through a mechanism that has common features with the Marangoni instability in thin liquid films. Stress near the oxide surface is produced because strong electrolyte anion adsorption suppresses oxide growth on the surface. Such near-surface stress is not present in TiO2nanotube layers (5). Instead, compressive stress driving flow arises at the metal-oxide interface from the volume change upon conversion of metal to oxide.
REFERENCES

J. E. Houser and K. R. Hebert, Nature Mater., 8, 415 (2009).

K. R. Hebert, P. Mishra, J. Electrochem. Soc., 165, E737 (2018).

K. R. Hebert, P. Mishra, J. Electrochem. Soc., 165, E744 (2018).

Ö. Ö. Çapraz, P. Shrotriya, P. Skeldon, G. E. Thompson, K. R. Hebert, Electrochim. Acta, 167, 404 (2015).

Q. Dou, P. Shrotriya, W. F. Li, K. R. Hebert, Electrochim. Acta, 295, 418 (2019).
Electrochemical Preparation of TiOx-Electrodes: Effect of the Counter Electrode on the Charge Transfer Properties
Authors: Brüninghoff Robert , Paradelo Rodriguez Ainoa , Mul Guido , Mei Bastian Timo 
Published: February 2020

Sub-stoichiometric titanium dioxide (TiOx) is known for its corrosion resistance and electrical conductivity.1 Thus, it is recognized as promising material for (photo-)electrochemical applications and used as protective layer in PEC water splitting or electrode material for water treatment.1,2 In general, its properties strongly depend on the synthesis and the conductivity of TiOx can be tuned by its Ti/O ratio.1,3 TiOx is commonly prepared by hydrogenation;3 however, the requirements for high pressure, high temperature and hydrogen atmosphere are cumbersome imposing a potential safety risk. Over the past years, electrochemical preparation of TiOx via cathodic polarization of TiO2 substrates became an interesting alternative.4

Pt is widely used in electrochemistry as counter electrode5 and frequently applied for TiOx preparation;4 however, the suitability of Pt as (anodic) counter electrode (CE) is questionable since the stability of Pt is often overestimated.5 As Pt contamination can severely influence the electrocatalytic properties this study focuses on the preparation of TiOx using three different CE (Pt, Iridium mixed metal oxide, Boron doped diamond) and the influence of the CE will be discussed in detail.
It will be shown using state of the art techniques such as SEM, XPS and highly surface sensitive low energy ion scattering (LEIS) spectroscopy that indeed Pt contamination dominates the properties of TiOx (Figure 1a). In contrast, for Iridium mixed metal oxide and Boron doped diamond CEs no related contaminations were observed allowing to determine the intrinsic properties of TiOx electrodes. Using Fe2
+/3+ redox couple experiments and electrochemical impedance spectroscopy we determined the charge transfer properties of the TiOx electrodes prepared with BDD and IrMMO (Figure 1b). Although both BDD and IrMMO appear to be suited for the preparation of TiOx differences in the doping are observed that will be discussed in detail in this contribution.
References:

F. C. Walsh and R. G. A. Wills, Electrochim. Acta, 55, 6342–6351 (2010), doi: 10.1039/c6ra14507h

B. Xu, H. Y. Sohn, Y. Mohassab, and Y. Lan, RSC Adv., 6, 79706–79722 (2016), doi: 10.1039/c6ra14507h.

X. Yan, L. Tian, X. Tan, M Zhou, L. Liu and X. Chen, MRS Commun., 6, 192–203 (2016), doi: 10.1557/mrc.2016.33.

J. Swaminathan, R. Subbiah, and V. Singaram, ACS Catal., 6, 2222–2229 (2016), doi: 10.1021/acscatal.5b02614.

J. G. Chen, C. W. Jones, S. Linic, and V. R. Stamenkovic, ACS Catal., 7, 6392–6393 (2017), doi: 10.1021/acscatal.7b02839.

Figure 1
Formation Mechanisms of Anodic Oxide Nanotubular/Nanoporous Structures
Authors: Raja Krishnan S. 
Published: February 2020

Formation of ordered arrays of nanoporous or nanotubular oxides of Al, Ti, and other valve metals during anodization has been reported extensively. These nanostructured oxides could find applications in solar energy conversion, energy storage, photocatalysts for environmental remediation, sensors, templates for nanowire growth, and supports for various catalysts because of their unique geometry and resultant physical properties. Various theories on the formation mechanism of the ordered nanostructures have been proposed in the literature including the field assisted dissolution mechanism[1], localized dielectric breakdown model[2], comparison of the Gibb's free energies of the compact oxide formation and chemical dissolution[3], and morphological instability of the oxide due to ion migration and oxide dissolution[4].
In this presentation, formation of ordered nanoporous anodic oxides of different substrate materials such as pure Ti, Ti-Mn alloy, Zr-W alloy, and bismuth will be analyzed based on the I-t plots and surface perturbation model proposed by Asaro and Tiller[5]. Compressive stresses are developed due to thickening of oxide layer and electrostriction. This compressive stress undulates the barrier film which leads to the surface perturbation. The perturbation releases strain energy of the oxide layer which is balanced by the increase in the surface area. These surface undulations affect the local chemical potentials because of the curvature effect. The presence of surface active species in the anodization electrolyte such as [MeF6]2- helps enhance the surface perturbation. The formation of ordered nanostructure could be explained based on the interaction between electrostatic strain energy and surface energy during anodization in specific environments.
[1] Z. Su and W. Zhou, Adv. Mater., 2008, 20, 3663–3667.
[2] Z. Su, W. Zhou, F. Jiang and M. Hong, J. Mater. Chem., 2011, 22, 535–544.
[3] M. Wang, Y. Liu and H. Yang, Electrochim. Acta, 2012, 62, 424–432
[4] K. R. Hebert, S. P. Albu, I. Paramasivam and P. Schmuki, Nat. Mater., 2012, 11, 162–166.
[5] R. J. Asaro and W. A. Tiller, Metall. Trans., 1972, 3, 1789 – 1796.
In-Situ optical Microscopy Corrosion Experiments for Correlating Microstructure to Corrosion Susceptibility in Aluminum Alloy
Authors: Desai Choundraj Jahnavi 
Published: February 2020

Aluminum-Magnesium alloys (5xxx series) are widely used in marine applications, structural components in transportation, and military due to their high corrosion resistance, low density, and good mechanical properties. However, at moderate and high temperatures (>50oC) these alloys are vulnerable to sensitization, or precipitation of β phase (Al3Mg2) preferentially on grain boundaries, resulting in susceptibility to intergranular corrosion and environmentally induced stress corrosion cracking. The primary research theme of this talk is to understand how microstructure variations dictate local corrosion susceptibility of aluminum 5456 in corrosive environments.
To explore microstructure effects, we corroded sensitized aluminum 5456 in a dilute nitric acid solution. Prior to corrosion, electron backscatter diffraction (EBSD) was used to characterize the microstructure and deformation state of the alloy in terms of the grain structure, geometrically necessary dislocation density, constituent particles, and grain boundary character. In situ optical microscopy corrosion experiments were then used to directly observe corrosion initiation and propagation behavior, with fiducial markers used to correlate the observed corrosion behavior with the characterized microstructure. Image recognition algorithms facilitated the quantification of corrosion sites and corrosion propagation rates as a function of time and grain boundary path. Obtaining this information is crucial as the microstructural features that govern corrosion initiation may be different from the features that dictate propagation pathways. My talk will focus on the microstructure characteristics that dictate corrosion susceptibility to initiation as well as propagation and the relevance of these data for developing corrosion- and sensitization-resistant microstructures.
Investigation of Localized Corrosion Phenomena in Selective Laser Melted 316L Stainless Steel
Authors: Macatangay Duane Armell , Chmielinski Alex Piotr , Kelly Robert G. 
Published: February 2020

Selective laser melting (SLM) refers to the additive manufacturing of bulk material from powder on a layer by layer basis through melting via laser and rapid solidification. In recent years, additively manufactured metallic alloys produced by SLM have garnered attention due to opportunities in waste reduction, time and cost efficiency, and fabrication of geometrically complex structures. However, limited work has been performed to investigate the corrosion properties of these alloys. Understanding these mechanisms is crucial in assessing the attendant risks associated with the use of AM alloys in engineering design.
Stainless steels such as 316L produced by SLM have presented advantages due to the corrosion resistant properties of these alloys. However, the non-equilibrium microstructure in these SLM materials, significantly different from that of the wrought counterpart, result in heterogeneities that may lead to localized corrosion such as melt pool boundary attack. A point of concern in stainless steels is intergranular corrosion due to the formation of secondary phases such as chromium carbides that deplete chromium from grain boundaries when the material is exposed to temperature ranges of 450 – 800 °C. While low-carbon steels such as 316L have great resistance to deleterious chromium carbide precipitation, this phenomenon has not been investigated in great detail in the case of selective laser melted 316L. However, it has been shown that precipitation of secondary phases is accelerated in SLM alloy systems such as Inconel 625 with respect to the wrought counterpart. Intergranular corrosion can ultimately lead to intergranular stress corrosion cracking, a form of brittle failure.
This study investigates localized corrosion phenomena such as melt-pool boundary attack and intergranular corrosion and the associated microstructure-based mechanisms in the corrosion of these SLM 316L alloys. Galvanostatic etching, potentiodynamic scans through the double-loop potentiokinetic reactivation method, and mass-loss testing of wrought and SLM 316L are utilized to reveal the electrochemical behavior of these alloys. Additionally, focused ion beam and transmission electron microscopy are utilized to understand the microstructural origins of the observed corrosion phenomena.
A Model Framework for Linking Changing Electrolyte Properties to Galvanic Corrosion Simulations
Authors: Policastro Steven A , Hangarter Carlos M , Anderson Rachel M 
Published: February 2020

Electrolytes that form from atmospheric processes can differ widely in composition and thickness and the concentrations of dissolved gases, such as oxygen, in these thin electrolytes vary due to temperature and salinity changes. These changes within the electrolyte can substantially vary the oxidative properties of the electrolyte, which in turn alters the corrosion kinetics of the substrate. In this report, we present an approach for linking measurements of atmospheric properties, such as temperature, pressure, and relative humidity to changes in electrolyte properties, such as dissolved oxygen concentration, film thickness, and salinity. Using Butler-Volmer reaction kinetics, with parameters obtained from fits to polarization data obtained under actual electrolyte thin films equilibrated at different relative humidity values, and bulk polarization measurements, to simulate the electrochemical reactions, we model galvanic corrosion between aluminum and stainless steel alloys, such as UNS A902024 and UNS S13800, in response to changing environmental conditions.
This work was sponsored by the U.S. Naval Research Laboratory under its core research program. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Office of Naval Research, the U.S. Navy or the U.S. government.
Metallic Foams Prepared By Electrolytic Plasma Deposition
Authors: Durut Frédéric , Botrel Ronan , Pinot Julien , Rocher Sandrine , Chicanne Cédric , Theobald Marc , Vignal Vincent 
Published: February 2020

In order to study laser-matter interactions on the Megajoule Laser facility, CEA needs to synthesize metallic foams with specific characteristics. The goal is to realize in a millimetric scale, metallic foam samples with a density lower than 10% of the bulk material and structured with a micrometric porosity (< 5 µm). To obtain these specific materials, CEA has developed an innovative process using the Contact Glow Discharge Electrolysis technique (CGDE) to grow metallic foam at a cathode surface. Under specific conditions and when a critical potential is applied, an uniform and stable gaseous envelop is formed around the immersed cathode in the ionic solution. Due to the high electrical field at the electrode surface, channels plasma are formed with the propagation of streamers between the cathode and the liquid surface. When the electrical arcs meet the liquid, metallic cations are reduced to form metallic strands with a bush-like shape. In these conditions, several metallic foams can be obtained (Au, Cu, Pt, Ag, alloys …) with a relative density of 0.5%. All strands of the foam are about 100 nm in diameter and are interconnected together to form porosity about 1 µm. This very fast process allows synthesizing 1 mm thick of foam in less than 10 seconds. This presentation explains the patented process offering a versatile technological way to synthesize microporous and ultra-light metal foams. A new phenomenomenological process is proposed to describe the different steps that take place from plasma formation to nano-foam growth.
The structure (see picture below) of the foams (several m²/g, and ultra-low density ~ 0.5% relative density) could be used for many applications such as battery, fuel cells, hydrogen trapping, catalysis...

Figure 1
Electrodeposition of Porous Fe-Ni-Co Nanowires Using Hydrogen Gas Bubbles
Authors: Li Deyang , Podlaha Elizabeth J. 
Published: February 2020

The use of hydrogen gas bubbles as a dynamic template accompanied with metal species reduction has recently been used to create porous metal thin films, where the metal deposits within spaces between bubbles. Creating porous nanowires within a nanoporous template is a greater challenge, as the gas bubbles can block the pores of the template, preventing deposition. Thus, the competition between the rate of metal deposition and hydrogen evolution reaction needs to be balanced. While this talk will focus on the electrodeposition process in creating porous metal nanowires, the selected Fe-Ni-Co material serves as a model oxygen electrocatalyst.
Conditions making it possible to potentiostatically electrodeposit porous Fe-Ni-Co nanowires using a polycarbonate (PC) nanotemplate are presented. Results show that the pH plays an important role not only in defining the rate of hydrogen evolution, but also the type of metal ion species that are reduced, leading to a change of composition. The porous structure, obtained from the solution having a pH less than 1.0, was confirmed by SEM and TEM. Such an observation is contradictory to the results from anodic alumina oxide (AAO) templates, where no nanowires or very short nanowires were found at the same conditions due to bubble coalescence. The changes in the ionic strength gradient at the electrode surface towards the bulk electrolyte, and the absorbed metal ion intermediates, are suggested to play an important role in deterring bubble coalescence making it possible to create porous nanowires.
(Invited) Electrodeposition of Au/Cu2o Core-Shell Nanowire Arrays As Photocathode Model Systems for Solar Hydrogen Production
Authors: Yang Florent , Ulrich Nils , Leber Angela , Trautmann Christina , Toimil-Molares Maria Eugenia 
Published: February 2020

In the past decades, research on the synthesis and characterization of semiconductor nanowires has considerably progressed, especially for applications in the field of energy conversion, such as photoelectrochemical water splitting for hydrogen production. The dimensions, geometry, and areal density of nanowires significantly influence physical processes such as light absorption, electron-hole generation and scattering, as well as recombination of the charge carriers. Among the available fabrication methods, electrodeposition in etched ion-track membranes enables the controlled synthesis of three-dimensional assemblies of functional nanostructures with tailored composition, size and density.
We present here the fabrication and characterization of Au/Cu2O core-shell nanowire arrays consisting of a metallic core acting as nanostructured electrical contact, and a well-defined semiconductor shell responsible for light absorption and charge carrier generation and transport. The metallic Au core wires are first fabricated by electrodeposition in etched ion-track membranes. Diameter, length, and number density of the nanowires are adjusted by the membrane parameters. After dissolving the polymer membrane, the Au nanowire arrays are conformally coated by a Cu2O layer by electrodeposition. The thickness of the semiconductor layer is controlled by the deposition time. To increase their chemical stability in aqueous solutions the photoelectrodes are additionally coated with a thin TiO2 film by atomic layer deposition. The photoelectrochemical performance of these Au/Cu2O/TiO2 nanowire-based photoelectrodes will be presented, in particular, as a function of nanowire length, diameter, and areal density. The influence of the nanowire geometry and the core-shell arrangement on the generated photocurrent will be discussed in detail and compared with the photocurrents generated by planar Cu2O/TiO2 films.
Stability Investigations of [Emim]AlCl4 Ionic Liquid
Authors: Shi Meng , Zhao Haiyan , Jiang Junhua 
Published: February 2020

1-Ethyl-3-methylimidazolium tetrachloroaluminate, abbreviated as [EMIm]AlCl4, is a widely-investigated ionic-liquid electrolyte for electrochemical processes and energy storage applications due to its wide electrochemical window, low melting point, low vapor pressure, and high conductivity. Thermal and chemical stability of [EMIm]AlCl4 at room temperature and moderately elevated temperatures is an important factor of affecting its promising applications. The focus of this work is to systematically study the stability of [EMIm]AlCl4 at elevated temperatures.
Electrochemical studies of [EMIm]AlCl4 were first performed by measuring its open circuit potentials and cyclic voltammograms at varying temperatures and holding time. The voltammograms shown in Figure 1(a) exhibit that [EMIm]AlCl4 has a wide electrochemical window ranging from -1.6 to 1.2 V vs an Al reference electrode. The anodic and cathodic currents outside the window may correspond to the surface oxidation of the working electrode and decomposition of impurities present in the electrolyte. After the [EMIm]AlCl4 electrolyte was heated at 110 oC for 48 hours, a white suspension layer was observed at the top layer of the electrolyte, which is attributed to the formation of alumina oxides. Considerable changes of the voltammograms for the heated [EMIm]AlCl4 were shown in Figure 1(b), characteristic of the appearance of anodic and cathodic peaks in the electrochemical window and significantly increased currents. These voltammetric characters indicate the formation of electrochemical active species in the electrolyte through the decomposition of [EMIm]AlCl4.
In this presentation, we will introduce our electrochemical and analytical results regarding thermal and electrochemical stability of the [EMIm]AlCl4 electrolyte, and discuss the origins of chemical changes occurring during the thermal degradation of [EMIm]AlCl4.

Figure 1
Electrodeposition of Aluminium–Nickel Films in 1-Butyl-1-Methylpyrrolidinium-Bis(trifluoromethylsulfonyl) Amide
Authors: Ispas Adriana , Schlag Leslie , Eggert Lara , Böttcher René , Bund Andreas , Jacobs Heiko O. 
Published: February 2020

The aluminum-nickel system is well characterized as multilayer thin films, as well as in mechanical alloying. Normally, one obtains the multilayers by chemical vapor or physical vapor deposition. Mechanical alloying is based on ball milling of the individual metal powders, for different time and in different molar ratios. An equimolar mixture of Ni and Al powder yields a material, which can be ignited via a self-sustaining exothermic reaction, similar to self-propagating high temperature synthesis reactions. Al-Ni powders obtained by ball milling are therefore classified as high energy powders.
An elegant and easy route to obtain Al-Ni multilayers or composites is electrodeposition. The standard electrode potential of Al(III)/Al(0) lies around -1.68 V vs. SHE (standard hydrogen electrode), while that of Ni(II)/Ni(0) is only of -0.26 V vs. SHE. Therefore, any attempt to obtain multilayers by electrodeposition is challenging, and would involve complexing chemistry. On the other hand, one can relatively easy co-deposit Al and Ni in ionic liquids, ILs, e.g., Al films with dispersed Ni particles, or Ni films with dispersed Al particles.
In this study, Al and Ni particles were prepared from the gas phase directly in ILs. The experiments were performed in 1-butyl-1-methylpyrrolidinium-bis(trifluoromethylsulfonyl)amide under bubbling with nitrogen gas and inside a glove box (moisture and oxygen contents below 0.5 ppm).
The co-deposition experiments were performed by cyclic voltammetry and potentiostatic depositions, in a temperature range from room temperature to 120°C. The morphology and composition of the layers were analyzed by SEM/EDX and optical microscopy and will be further discussed in this contribution.