bluuebunny/crossref_metadata_2025 huggingface dataset:
Local Electrochemistry on Thin Foils to Investigate Intergranular Corrosion in AA2024
Authors: Oltra Roland , Bonzom Remy
Published: February 2020

Intergranular corrosion (IGC) on Al-Cu alloys, is controlled by the preferential anodic dissolution of the Cu depleted zone induced by the structural hardening treatments [1].The main dissolution process affects the active anodic head at the tip of the grain boundary and for a minor part the faces of the surface of the grain « crevice » behind the active anodic head [2]. Therefore it could be assumed that the measure of the anodic part of the total current during potentiostatic experiments would be useful to establish charge and mass balance to evaluate the IGC propagation rate. Actually electrochemical analysis is not largely spread in IGC studies of aluminum alloys and physical based methods like the foil penetration technique were preferred to define IGC propagation rate [3,4].

In a recent work [5], we combined local electrochemical probe and thin foil penetration techniques to select only one grain boundary propagating on the longitudinal direction (rolling induces long grains, up to 700µm length, leading to a columnar microstructure). In this presentation, the combination of the specially designed microelectrochemical cell controlled by a SECM stage with a direct optical interrogation of the backside of a 50µm thick foil AA2024 will be described. This local and “in volume” approach allowed us to analyze the current transient resulting from the full penetration of a well-selected intergranular path. By linking the 2D spatially resolved electrochemistry to optical observation on the backside of the foil (1D), it was possible to relate the total current to the successive steps involved during the “in volume” attack (3D) of a well-defined grain boundary trace.

It will be discussed how this approach could be applied to deduce the IGC propagation rate from mass balance using the Faraday law and could support more robust assumptions on the effect of microstructure on IGC propagation rate because it would be easier to manage a spatial control of the location of the IG attack.

Acknowledgements

This work is supported by French ANR-14-CE07-0027-01 – M-SCOT: Multi Scale COrrosion Testing.

References

[1]

J. R. Galvele, S. M. De Micheli, Mechanism of intergranular corrosion of Al-Cu alloys, Corros. Sci. 10 (1970) 795–807.

[2] S.P. Knight, M. Salagaras, A.R. Trueman, The study of intergranular corrosion in aircraft aluminium alloys using X-ray tomography,
Corros. Sci.
53 (2011) 727-734.

[3] W. Zhang, G.S. Frankel, Localized corrosion growth kinetics in AA2024 alloys,
J. Electrochem. Soc
149 (2002) B510-B519.

[4] A. Rota, H. Böhni, Contribution to the growth kinetics of the intergranular corrosion of age-hardened Al-Cu alloys – Part I : Results of the foil penetration technique,
Mater. Corros.
40 (1989) 219-228.

[5] R.Bonzom, R.Oltra, Droplet cell investigation of intergranular corrosion on AA2024, Electrochem. Commun. 81 (2017) 84–87

Figure 1
Nondestructive Degradation Evaluation for Organic Coated Steels By Surface Potential Measurement
Authors: Katayama Hideki , Itou Sayaka , Akashi Takaya
Published: February 2020

Organic coatings have been widely used for most steel structures as a cost-effective way for corrosion protection and ornamental design. Various methods have been suggested in order to check a degree of corrosion of organic coated metals. For example, visual observation and gloss measurement are well known as typical evaluation methods for organic coated metals.In this study, the corrosion performance of organic coated steels exposed to corrosive environment was estimated by surface potential measurement. In this study, the corrosion behavior of organic coated steels exposed to corrosive environment was monitored by surface potential measurement. In addition, the change in surface potential distribution was compared with the result of electrochemical impedance measurement in 0.5 M NaCl solution after measuring the surface potential.

Carbon steel of the size of 3cm x 5cm was used as a substrate, and the organic coated steel samples were prepared by spraying a clear acrylic lacquer coating. Wet-dry cyclic corrosion test was conducted by alternating the condition of adding 20μl droplet of 0.5M NaCl solution and drying at 293K and 40%RH.

After several cycles, a part of the surface exposed to corrosive environment showed lower potential than the other area. As the corrosion proceed, the change area grew up and the surface potential further declined. The electrochemical impedance characteristics also changed with an increase of wet and dry cycle number. The change in surface potential corresponds to that in the impedance characteristics, indicating that the deterioration process of the coated steel can be monitored by the surface potential measurement from the stage of the coating film deterioration.
(Invited) A Data Science Approach for Quantitative Analysis of Total Differential Capacity Plots
Authors: Thompson Nicole L. , Alamdari Sarah , Cohen Theodore A. , Masse Robert , Cao Guozhong , Holmberg Vincent C. , Pfaendtner Jim , Beck David A.C.
Published: February 2020

In order to characterize battery performance, electrodes are typically cycled for weeks or months at a time, resulting in an extremely large dataset of charge-discharge curves, a subset of which are often analyzed individually in the form of total differential capacity plots. Due to the difficulty in analyzing these datasets in their entirety, qualitative interpretations based on a subset of cycling data prevail in the literature. Here, we present software that quantitatively analyzes cycling datasets in their entirety by extracting peak characteristics from every cycle through a pseudo-Voight distribution fit. Initial results demonstrate that our system can differentiate between cycling data for two different battery chemistries, and we have implemented a database backend, allowing users to perform analyses and return to their data at a later point. We hope that this will lay the framework for an open source database, fostering collaboration and advancement within the electrochemistry community.
Electronic Structure of Tantalum Oxide with Oxygen Vacancy and Polyvacancy, Oxygen Interstitial, Tantalum Interstitial and Tantalum Substituting Oxygen
Authors: Perevalov Timofey V. , Islamov Damir R.
Published: February 2020

The electronic properties of Ta2O5 are limited by its defects. The defects are problem if Ta2O5 is used in DRAM or as a blocking layer in a flash charge trapping memory (CTM), because it leads to a high conductivity via the traps and the threshold voltage instability. On the contrary, the high defects concentration opens the possibility of using Ta2O5 as a storage medium in the CTM [1] and resistive random-access memory (ReRAM) [2]. The aim of the study is the investigation of the electronic structure of O vacancy (VO), O polyvacancy, interstitial O and Ta atoms, O-to-Ta substitution in Ta2O5 to clarify the trap nature responsible for the charge localization and transport. The simulations carried out for the λ-Ta2O5 [3] 168-atom supercell in terms of the DFT in Quantum-ESPRESSO code. The calculated bandgap of λ-Ta2O5 is 4.2 eV. All types of native defects, except for the O interstitial, form defect states into the λ-Ta2O5 bandgap. The value of trap thermal ionization energy 0.5 eV are comparable to the experimental ones 0.7-0.8 eV [4], and optical trap energy 0.9 eV for the VO indicate that the VO in Ta2O5 can act as the charge trap, and participate in charge transport. The width of density of states defect peaks indicate the charge localization in space. The electron localization on the VO in Ta2O5 is due to the polaronic effect. The negative charge distributed between the nearest Ta atoms and it reflects the bonding character of the Ta orbitals charge density. Its allows us to conclude that the chains of closely located oxygen vacancies in TaOx can act as a conductive shunt and participate in the resistive switching. Each subsequent O vacancy forms near the already existing one, and no more than 2 removed O atoms, related to Ta atom. The O polyvacancy forms a filled defective band in Ta2O5 bandgap.

The work is supported by the Russian Science Foundation grant #17-72-10103.

[1] K. Hota, F.H. Alshammari, K. N. Salama et. al, Acs. Appl. Mater. Inter. 9, 21856 (2017).

[2] M. Kim, S.R. Lee, S. Kim, M. Chang et. al, Adv. Funct. Mater. 25, 1527 (2015).

[3] H. Lee, J. Kim, S.J. Kim et. al, Phys. Rev. Lett. 110, 235502 (2013).

[4] V. Egorov, D.S. Kuzmichev, P.S. Chizhov et. al, Acs. Appl. Mater. Inter. 9, 13286 (2017).

Figure 1
(Invited) Apprehension of Large Coercive Field in Ferroelectric HfO2 Thin Films
Authors: Migita Shinji
Published: February 2020

A special feature of ferroelectric HfO2 films is that they have large coercive fields (EC), as large as 1 MV/cm and more. A merit of the large coercive field is that a sufficient memory window is attainable even in ultrathin films. For example, a 2-V-memory window is available by 10-nm-thick Hf-Zr-O ferroelectric film. Compared with the conventional ferroelectric oxide capacitors using Pb(Zr, Ti)O3 and SrBi2Ta2O9 that applies around 100-nm-thick films, the ferroelectric HfO2 films contribute to the scaling of film thickness about one order. It is attractive for the development of high-density non-volatile memories integrated on LSI. On the other hand, the large coercive fields of ferroelectric HfO2 films bring serious concerns such as breakdown and endurance in capacitors. In this work, we studied the influence of large coercive fields on the endurance properties of Hf-Zr-O capacitors.

Metal-ferroelectric-metal (MFM) capacitors that consist of TaN/Hf-Zr-O/TaN were prepared on heavily doped Si substrates. TaN electrode films were deposited by DC sputtering, using Ta target and mixture gas of Ar and N2. Hf-Zr-O films were prepared by RF sputtering, using HfO2 and ZrO2 targets and Ar gas. The metal composition was adjusted to Hf : Zr=50 : 50, and the thickness is 10 nm. After deposition of the top TaN film, crystallization anneal was processed in a vacuum condition at 700 degree Celsius. Finally, top electrodes were patterned by photolithography and dry etching.

Ferroelectric properties of 10-nm-thick Hf-Zr-O capacitors were investigated by the polarization-voltage measurements. The ECvalue of this capacitor was evaluated to be 1 MV/cm. The electrical breakdown by the DC mode was measured to be about 4 MV/cm. Remnant polarization (Pr) and endurance properties of the capacitors are summarized in the figure. The Pr is faint when the applied electric field is less than the EC. The Pr value increases drastically when the electric fields are set between EC and 2xEC, and then gradually saturates over 2xEc. Thus a larger electric field is favorable for the achievement of large and stable polarization. In contrast, the endurance characteristics show a negative trend with the electric field. The endurance cycle as large as 108 was observed when the electric field is 2xEC, but it decreases drastically with the increment of electric field over 2xEC. It indicates that the capacitors are damaged even when the electric field is much lower than the breakdown field. Although a better endurance is expected at electric field lower than 2xEC, it makes a sacrifice of the Pr value and the stability. This trade-off relationship is considered to be a critical hurdle for the application of ferroelectric HfO2 capacitors.

This work was supported by JST CREST Grant Number JPMJCR14F2, Japan.

Figure 1
Nanomechanical Properties of ALD Hafnium Oxide (HfO2) on Silicon-on-Insulator (SOI) and Strained Silicon-on-Insulator (sSOI) Films
Authors: Mohammed Yousuf , Zhang Kai , Baumgart Helmut , Elmustafa A A
Published: February 2020

Hafnium oxide is used as replacement for silicon oxide as a gate insulator in field-effect transistors [1]. HfO2 is used as a high-κ dielectric in DRAM capacitors and in advanced metal-oxide-semiconductor FET devices and in optical coatings [2].

Thin films of hafnium oxide (HfO2) were deposited by atomic layer deposition (ALD) on silicon-on-insulator (SOI) and benchmarked against strained-silicon-on-insulator (sSOI). Both types of films have been tested for surface morphology, crystal structure and nanomechanical properties. The nanomechanical properties have been tested using a nanoindenter from Keysight equipped with a three sided Berkovich diamond tip. The crystalline structure has been verified using X-ray diffraction. The surface morphology has been examined using atomic force microscopy (AFM) and the film thickness was verified using field emission scanning electron microscopy (FE-SEM) as indicated by the cross-sectional FE-SEM image as shown in Figure 1.

We will discuss the structural and mechanical properties of the films citing the superiority of the ALD technique that is particularly used in the fabrication of the films that are presented in this study.

References

Intel (11 November 2007). "Intel's Fundamental Advance in Transistor Design Extends Moore's Law, Computing Performance".

Zhu, C. Tang, L. R. C. Fonseca, and R. Ramprasad 47, 7399 (2012).

Figure 1
KPFM and XPS Metrology of Self-Assembled Monolayer Barrier for Copper Metallization
Authors: Ofek Almog Rakefet , Sverdlov Yelena , Kadan Kian , Burstein Larisa , Dagan Ronen , Shacham-Diamand Yosi
Published: February 2020

Silane based Self assembled monolayer (SAM) has been demonstrated as a diffusion barrier layer on lowK dielectrics for sub 10 nm Cu interconnects for Integrated Circuit (IC) applications. A key problem in developing barrier layer is its monitoring capability, especially its thickness, uniformity, its coverage and defect density.

The aim of this work is to develop surface analysis methods for characterizing those variables providing in line monitoring techniques that can predict barrier quality and reliability. The approach presented in this paper was to examine the defect density and coverage properties of the SAM on LowK dielectric using physical methods for the characterization of monolayer thick films, i.e. Variable Angle X-Ray Photoelectron Spectroscopy (VA -XPS) and Kelvin Probe scanning Force Microscopy (KPFM).

The SAMs were deposited on three different substrates: bare-Si wafers, thermal oxide/Si and Low-k dielectrics on silicon wafers. The silanization was performed by chemical deposition from various solvents, both polar and non-polar, containing 1-2% silane in ethanol as a solvent at temperature range between 60oC to 120oC.

The deposited films where characterized as follows: Variable Angle XPS measurement of High Resolution Multiplex . Next, the XPS data was analyzed as follows: a plot of ln [𝑵𝒔𝒖𝒃 𝝀𝒔𝒖𝒃 𝑰𝒐)/(𝑵𝒐 𝝀𝒐 𝑰𝒔𝒖𝒃+1] Versus 1/sin(α) was drawn , where Nsub is the atomic number density for the substrate , No is the atomic number density for the overlayer, 𝝀𝒔𝒖𝒃 is the substrate Inelastic Mean free Path, 𝝀o is the overlayer Inelastic Mean free Path, Isub is the signal intensity of electrons coming from the substrate, Io is the signal intensity of electrons coming from the overlayer and α is the take of angle from the sample surface. The Thickness of the overlayer was calculated from the slope of the graph. Using that data thickness of the SAM was obtained. The method and results will be shown and compared to other methods such as TEM. The XPS data yielded average values on large areal spots (> 10-4 cm2).

To achieve high resolution analysis a Kelvin probe force microscopy (KPFM) were performed on SAM. KPFM gives a good image of SAM on low K material. We can learn a lot about Homogeneity and Coverage properties. A study of the nucleation and growth of the SAM, dependent on temperature and time was conducted. It seems that after 60 minutes, the SAM had the best homogeneity and surface coverage. (Figure 1).

After mastering the use of the two methods for SAM, the results are compared in order to find the most suitable method for SAM metrology and monitoring that can be employed by the Semiconductor industry.

Figure 1
Adhesion Force Degradation in Degraded Single Junction Amorphous Silicon Module By Scanning Probe Microscopy
Authors: Osayemwenre Gilbert Omorodion
Published: February 2020

The adhesion force between two interface layers in amorphous silicon solar (a-Si:H) module plays a crucial role in its carrier transport across the various interfaces. The quality of each interface layer depends on its mechanical properties. In other words, its mechanical property influences the performance of a-Si:H module. In this study, two mechanical properties of a PV module, which include interfacial adhesion and deformation across layers, were studied. The binding force between interfaces is susceptible to defects as a PV module begins to degrade. Therefore, the changes that occur in the adhesion force of a degraded a-Si:H is a proper tool for degradation analysis. Thus, this paper deals with the microstructure, defects, and mechanical properties of a-Si:H module. The aim of the study was to cross-examine which region of the degraded module was more prone to mechanical degradation. The degradation of adhesive strength results to mechanical defects, which can be observed as microstructural defects when mapped with Scanning Probe Microscope (SPM). The dearth of information on the correlation between these microstructural defects, and adhesive degradation is the motivations for this study. SPM was used to measure the adhesion force between interface layers, at a rate of 0.701Hz. In order to achieve uniformity in the results, each scanning was 512 lines for a retraced direction and the mapping was captured in an upward direction. The study shows that adhesion force exhibits a higher decay in the intrinsic layer interface p/i than in other regions. In addition, the sample from the affected region demonstrated a higher decrease in its adhesion force at the sample time has a higher deformation. Mechanical degradation at nanoscale level enhances interfacial delamination, which can potentially result to premature failure. Thus, an in-depth comprehension of adhesive degradation is essential in degradation analysis.
Impact of Contact in Molecular Junctions: When Physics Dictates the Chemical Properties
Authors: Van Dyck Colin Jean-Louis , Bergren Adam Johan
Published: February 2020

Molecular junctions are nanomaterials made of one molecule, or a thin organic layer, sandwiched between two metallic electrodes.[1] These systems are now widely and intensively studied due to a high potential for nanoelectronic applications. If these devices can now be reliably made and characterized, this field of research is facing a clear issue: the modification of the molecular structure offers a poor control over the device characteristics.

The basic idea of the design in Molecular Electronics is that the molecular level landscape in the junction will affect the electron transport, offering control over the current/voltage characteristics.[1-3] Driven by chemical intuition, the usual design of molecular junctions relies on electron donating or accepting building blocks. In this presentation, we show and explain that this approach which focuses on the isolated molecule properties provides a very limited or even erroneous picture as the contact of a molecule to two metal electrodes leads to a completely different entity.

Using first principle DFT calculations, we demonstrate that the contact of an asymmetric organic layer to metal electrodes comes with the creation of spontaneous and very intense electric fields in the junction.[4] The origin of this field are the permanent dipole moments in the junction. The built-in field completely modifies the energy landscape in the junction. We argue that only a design that takes into account such large contact renormalization effects could finally lead to the control of the electronic structure of molecular junctions and then move the molecular electronics effort in the intelligent design era.

[1] Aviram and Ratner, Chemical Physics Letters, “Molecular rectifiers”, 1974

[2] Van Dyck and Ratner, Nano Letters, 10.1021/nl504091v, 2015

[3] Van Dyck and Ratner, J. Phys. Chem. C, 10.1021/acs.jpcc.6b07855, 2017

[4] Van Dyck and Bergren, Accepted in Advanced Electronic Materials, “Large Built-in Fields Control the Electronic Properties of Nanoscale Molecular Devices with Dipolar Structures”, 2018

Figure 1
Atomic Scale Growth Processes of Thin Films As Revealed By Fast Surface X-Ray Diffraction
Authors: Shirasawa Tetsuroh , Voelgeli Wolfgang , Arakawa Etsuo , Takahashi Toshio , Matsushita Tadashi
Published: February 2020

X-ray crystal truncation rod (CTR) scattering and reciprocal space mapping (RSM) are widely used to characterize the structure of thin films. The methods can provide the structural information, such as the atomic structure, shape and size of crystalline domain, and strain distribution, in any ambient conditions without destructing the specimen. The use of the methods is often limited in the static structure analysis, because the acquisitions of CTR scattering profile and RSM dataset are often time consuming (mins to hrs).

Our group has developed a method that can measure a wide range of CTR profile and RSM in a single acquisition by using an energy-dispersive converging X-rays [1]. The technique allows the in-operando observation of atomic scale processes of photo-induced surface phenomenon [2] and electrochemical processes at the solid-liquid interface [2] with a time resolution of 1 s. The time frame is also reasonable to study the thin film growth processes.

In this contribution talk, we show the atomic scale growth processes of ultra thin films, Bi and Bi2Se3, as reveled by the energy-dispersive surface X-ray diffraction. In the growth of Bi film, we observed: the formation of wetting atomic layer at the interface, the growth of black phosphorous phase, which does not exists in bulk, below the thickness of ~2 nm, and the growth of bulk Bi structure in the upper layer. In the growth of Bi2Se3 film, we observed a strained Bi2Se3 structure in the first a few Bi2Se3 layers. The relationships between the growth behaviors and the electronic properties, namely, the quantum confinement effect in Bi and the topological phase transition of Bi2Se3, are discussed.

[1] T. Matsushita, T. Takahashi, T. Shirasawa, E. Arakawa, H. Toyokawa, and H. Tajiri, J. Appl. Phys. 110, 102209 (2011).

[2] T. Shirasawa, W. Voegeli, E. Arakawa, T. Takahashi, and T. Matsushita, J. Phys. Chem. C 120, 29107 (2016).

[3] T. Shirasawa, T. Masuda, W. Voegeli, E. Arakawa, C. Kamezawa, T. Takahashi, K. Uosaki, and T. Matsushita, J. Phys. Chem. C 121, 24726 (2017).
Anion Radical Mediated High Capacity Redox Flow Battery
Authors: Nanda Jagjit , Self Ethan Craig , Ruther Rose E. , Delnick Frank M.
Published: February 2020

The energy density of conventional redox flow batteries (RFBs) is dictated by their capacity (which is directly related to the solubility of the redox species in the electrolyte) and operating potential. RFBs have low operating potentials ca. 1.5 V, resulting in poor energy densities (25 – 30 Wh/kg for an all vanadium RFB), whereas systems containing organic electrolytes with wider electrochemical windows can potentially have moderately higher energy densities. A new approach to improve the performance of nonaqueous redox flow batteries (RFBs) through electrochemically-mediated reactions is demonstrated. Soluble anion radical species (biphenyl and pyrene) mediate reversible sodium storage in a red phosphorus anode located in an external plug flow reactor in the absence of binders or conductive additives. Because the anion radical species can be recycled several times throughout the cell stack during a single charge/discharge cycle, a mediated RFB effectively decouples the battery’s energy density from the redox species’ solubility in the electrolyte. Furthermore, this technology offers inherently safe operation and is unaffected by the large volume changes of red P (>300%) due to the use of an external plug flow reactor. This presentation will describe the mechanism of a mediated RFB and discuss important design considerations (e.g., selection of appropriate electrolyte, mediators, active materials, etc.). Results showing electrochemically mediated sodiation and desodiation of a phosphorus anode in a redox flow configuration will be presented

This work is supported by Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy and The Office of Electricity Delivery and Reliability, U. S. Department of Energy.
Semi-Solid Hypervalency Based Li-S Battery Electrolytes
Authors: Navarro-Suárez Adriana M. , Johansson Patrik
Published: February 2020

The urge for electrochemical energy storage devices with high gravimetric and volumetric energy density is imminent and the lithium−sulfur (Li-S) battery has been poised as a major next generation battery concept candidate. While it has a (very) high theoretical energy density, low cost and non-toxicity of starting materials,[1] its practical application has been hampered by several obstacles; the active material(s) elemental sulfur (S8) and lithium sulfide (Li2S) are both electronic insulators, polysulfides dissolve into the electrolyte and diffuse between the cathode and anode – generating an active material loss, there are dendrites formed at the lithium metal anode, etc.[2,3]

To address (some of) these problems, the solubility properties of the electrolyte are of utmost importance [4] and here we use semi-solid electrolytes – materials without flow but malleable – to hinder the dissolution of sulfur and possibly also mitigate the creation of lithium dendrites. These electrolytes are composed of matrices of hypervalent molecules i.e. with large internal dipole moments, heavily doped with Li-salts to generate Li+ conduction paths via percolation networks.[5] We report on initially assessed physico-chemical properties, basic electrochemical properties such as ion conductivity (Figure 1), before progressing to feasibility tests in Li-S battery cells.

This work was funded by “Batterifondsprogrammet” of the Swedish Energy Agency.

Figure 1. Arrhenius plots of two different hypervalency based electrolytes and the matrix used.

Reference
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[1] Q. Pang, X. Liang, C.Y. Kwok, L.F. Nazar, Nat. Energy 1 (2016) 16132.

[2] X. Judez et al., J. Electrochem. Soc. 165 (2018) A6008–A6016.

[3] J. Scheers, S. Fantini, P. Johansson, J. Power Sources 255 (2014) 204–218.

[4] S. Drvarič Talian, S. Jeschke, A. Vizintin, K. Pirnat, I. Arčon, G. Aquilanti, P. Johansson, R. Dominko, Chem. Mater. 29 (2017) 10037–10044.

[5] T. Mizumo, R. Fujita, H. Ohno, J. Ohshita, Chem. Lett. 40 (2011) 798–800.

Figure 1
Co-Deposition of Catalytic Pt-Rh Thin Films in the Self-Terminated Regime
Authors: Ambrozik Stephen , Dimitrov Nikolay , Moffat Thomas P.
Published: February 2020

The drive to adopt alternative energy technologies for a more sustainable energy future has been inhibited by insufficient activity, poor durability and high cost of fuel cell catalysts. To overcome these drawbacks there has been significant interest in the exploration of core-shell nanoparticles, related overlayer thin films and alloy architectures. These bimetallic systems offer significant tunability based on ligand effects associated with nearest neighbor bonding 1, strain effects associated with lattice mismatch between the constituent metals , and geometric effects dictated by the local atomic distribution of elements. In order to realize such effects significant effort is underway to develop inexpensive, easy fabrication methods for forming these alloy and over-layer architectures 2-7.

Recently, self-terminated electrodeposition reactions have been discovered and adopted for the fabrication of ultra-thin metal films with monolayer level control 8-11. For the electrodeposition of Pt and/or Ir on Au and Ni12 the deposition of growing metal at high overpotentials is quenched at the onset of hydronium reduction by hydrogen adsorption. In this work, the electrodeposition of Pt-Rh alloys at potentials coincident with hydronium reduction will be discussed. In contrast to Pt, the electrodeposition of Rh is not terminated by hydrogen adsorption. The introduction of minimal quantities of [RhCl6]3- into the NaCl-[PtCl4]2- electrolyte disrupt the quenching of the Pt partial deposition reaction. The impact of Rh concentration on deposition rate, film morphology and composition was examined with voltammetry, SEM, XPS, and ISS. Finally, the tunability of as deposited films of varied thickness and composition toward the ethanol oxidation reaction will be discussed.

(1) Bligaard, T.; Norskov, J. K. Electrochimica Acta
2007, 52, 5512.

(2) Nutariya, J.; Fayette, M.; Dimitrov, N.; Vasiljevic, N. Electrochimica Acta
2013.

(3) Viyannalage, L. T.; Vasilic, R.; Dimitrov, N. Journal of Physical Chemistry C
2007, 111, 4036.

(4) Brankovic, S. R.; Dimitrov, N.; Sieradzki, K. Electrochemical and Solid- State Letters
1999, 2, 443.

(5) Brankovic, S. R.; Wang, J. X.; Adzic, R. R. Surface Science
2001, 474, L173.

(6) Ambrozik, S.; Dimitrov, N. Electrochimica Acta
2015, 169, 248.

(7) Adzic, R. R.; Zhang, J.; Sasaki, K.; Vukmirovic, M. B.; Shao, M.; Wang, J. X.; Nilekar, A. U.; Mavrikakis, M.; Valerio, J. A.; Uribe, F. Top Catal
2007, 46, 249.

(8) Ahn, S. H.; Tan, H.; Haensch, M.; Liu, Y.; Bendersky, L. A.; Moffat, T. P. Energy Environ. Sci.
2015, 8, 3557.

(9) Liu, Y.; Gokcen, D.; Bertocci, U.; Moffat, T. P. Science
2012, 338, 1327.

(10) Ritzert, N. L.; Moffat, T. P. J. Phys. Chem. C
2016, 120, 27478.

(11) Wang, R.; Bertocci, U.; Tan, H.; Bendersky, L. A.; Moffat, T. P. J. Phys. Chem. C
2016, 120, 16228

(12) Liu, Y.; Hangarter, C. M.; Garcia, D.; Moffat, T. P. Surface Science
2015, 631, 141.
(Invited) Photoelectrochemical Water Splitting Devices By Electrochemical Processing
Authors: Xu Yin , Ahmed Rasin , Zangari Giovanni
Published: February 2020

Photoelectrochemical (PEC) solar energy conversion utilizes sunlight to produce high purity hydrogen fuel via water splitting, thus providing clean energy on demand. In a PEC device at least one electrode (here the anode) is semiconducting in order to absorb radiation and generate electron/hole (e/h) pairs; holes are injected from the anode to the electrolyte, carrying out water oxidation, while electrons travel to the cathode, performing hydrogen reduction. In this talk we will discuss two distinct semiconductor photoanodes for solar water oxidation.

TiO2 nanotube arrays (NTs) made by electrochemical anodization are stable in operation and feature low cost, but the wide bandgap (3.2 eV) limits the photocurrent, and the low mean free path of the charge carriers increases recombination. In order to improve performance we carried out various modifications to the pristine material, including (i) Li intercalation to limit e/h pairs recombination[1], (ii) addition of electrocatalysts to amplify the water oxidation rate[2], (iii) formation of sub-stoichiometric TiO2-x by H2 annealing to enhance oxygen vacancies as active sites, or annealing in gaseous ammonia to implement nitrogen doping, resulting in visible absorption. All these modifications result in a significant increase in the PEC response, showing a sizeable cathodic shift of the photocurrent onset (~ 100 mV) and up to a 5-fold photoresponse increase at 1.23VRHE.

Gallium Arsenide (GaAs) on the other hand exhibits a direct bandgap of 1.43eV, resulting in efficient photon-to-electron conversion and excellent PEC performance. GaAs however suffers from fast photocorrosion in aqueous media, leading to semiconductor dissolution or oxidation. Electrodeposition of a thin Ni layer on GaAs using a chemistry that leads to self-terminating growth and affords continuous coverage at few nm thickness[3] provides a passivating layer through which electrons/holes may tunnel. The effect of Ni films of up to 4.4 nm on n-doped GaAs was studied; the dependence of thickness on the deposition time at 10 s and 60 s was observed via X-ray reflectometry, confirming growth inhibition during deposition. Ni-coated GaAs showed enhanced photocorrosion resistance compared to a bare GaAs substrate, while self-limiting Ni films on GaAs retains a high value of photocurrent (8.5mA cm-2 at 1.23V vs. RHE) compared to non-self-limited deposited sample (6.5 mA cm-2 at 1.23V vs. RHE), owed to a full coverage of the Ni layer and high photo-transmissivity due to a low coalescence thickness (~3.5nm).

References

[1] Tsui, L. K., Saito, M., Homma, T., & Zangari, G. (2015). Journal of Materials Chemistry A, 3(1), 360-367.

[2] Tsui, L. K., Xu, Y., Dawidowski, D., Cafiso, D., & Zangari, G. (2016). Journal of Materials Chemistry A, 4(48), 19070-19077.

[3] Vanpaemel, J. et al., (2015) Langmuir, 30, 2047–2053.
In-Situ SERS Analysis of SEI Formation at Graphite Electrode in Li Ion Battery Using Manipulated Plasmonic Sensor Element
Authors: Kunimoto Masahiro , Yanagisawa Masahiro , Homma Takayuki
Published: February 2020

In order to improve the performance of Li ion rechargeable batteries, solid-liquid interfacial phenomena taking place at the electrode during the operation should be well understood. For example, detailed analysis of solid electrolyte interphase (SEI) thin films formed at the electrode surface, which plays the key role to determine the battery’s properties, is a crucial issue. We have developed precise spectroscopy technique using surface enhanced Raman scattering (SERS), to realize highly selective interfacial analyses [1,2]. Here, transparent micro lens, partially covered with nano particles of plasmonic metals, such as Ag, Au, etc., is an essential component, which is called as “plasmonic sensor”. The sensor situated onto a particular sample enhances Raman signals from its surface, allowing us to get information only about the chemical state of the surface.

To employ this technique for in-situ analysis of SEI film formation on the electrode surface in Li ion rechargeable battery, this study optimizes the equipment and employs it for the analyses of solvent species dependence of SEI properties. The organic solvents employed here were the mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with 1:1 (volume), and that of propylene carbonate (PC) and EMC with 1:1. The graphite and LiCoO2 films were used for anode and cathode, respectively. 1.0 mol/L of LiPF6 was contained in each solvent. The design of plasmonic sensor implemented in the measurement cell was optimized so as to be movable by magnetic manipulation, which can avoid obstruction by the sensor to the diffusion of species during the reaction, realizing highly selective interfacial analyses. This setup was shown to serve also in effective Raman signal enhancement; the greater magnetic force to properly press down the sensor provides more significant signal enhancement. The SERS measurement results suggested that SEI formation depended on the solvent species employed: Li2O3 product was detected only in the case of PC-EMC. The time-dependent behavior of SEI formation was also obtained, indicating the mechanism of SEI formation.

Acknowledgements

This research was partially supported by the “Development of Systems and Technology for Advanced Measurement and Analysis”, and the “Research & Development Initiative for Scientific Innovation of New Generation Batteries (RISING 2)” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

References:

[1] M. Yanagisawa, M. Saito, M. Kunimoto, T. Homma, Appl. Phys. Express, 9, 122002 (2016) .

[2] M. Kunimoto, Y. Sun, M. Yanagisawa, T. Homma, ECS Meeting Abstracts, MA2017-02, 131 (2017).
(Invited) (More) Uniform Control of Oxidative Dissolution, Complexation, and Electrodeposition Using 3D Wiring of Aperiodic Zinc Sponge Anodes in Rechargeable Alkaline Batteries
Authors: Long Jeffrey W. , Ko Jesse S. , Geltmacher Andrew B. , Parker Joseph F. , Rolison Debra R.
Published: February 2020

Our team at the U.S. Naval Research Laboratory has solved the chronic impediment of cell-shorting dendritic growth that has thwarted development of rechargeable zinc alkaline batteries—particularly to depths of zinc utilization that can challenge lithium-ion energy density. We do so using architectural design in which zinc particles are fused into a porous, highly conductive, and 3D-wired “sponge” monolith, as verified by X-ray tomography. This architectural configuration controls the behavior of the zinc anode during cycling such that an inner core of metallic zinc persists—even when discharging >90% of the zinc present—thus permitting recovery of >95% of that deeply discharged metal upon electroplating recharge. An additional key to our ability to oxidize and then re-plate the zinc lies in retaining at the inner and outer surfaces of the sponge the secondary discharge product, namely the zinc oxide that precipitates out of solution when zincate ions (the primary discharge product) dehydrate upon reaching supersaturation concentrations. The more uniform reactivity of zinc sponge anodes will be demonstrated for rechargeable Ni–Zn, Ag–Zn, and Zn–air cells.
(Invited) Electrochemical Micromachining Based on Confined Etching
Authors: Zhan Dong-Ping , Han Lianhuan , Tian Zhong-Qun , Tian Zhao-Wu
Published: February 2020

Micromachining is becoming the cutting-edge of high-tech manufacturing because of the increasing industrial demand for supersmooth surfaces and functional three-dimensional micro/nano-structures in microelectromechanical systems, ultra-large scale integrated circuits, miniaturized total analysis systems, precision optics and so on. Taking advantage of no tool wear, no surface stress, environmental friendliness, simple operation, and low cost, electrochemical micromachining (ECM) has an irreplaceable role in micromachining.

We present here our perseverant research in the last two decades on how to “confine” the ECM processes to occur at micrometer or even nanometer scale, that is, to ensure ECM with nanoscale accuracy. We have been developing the confined etchant layer technique (CELT) to fabricate three-dimensional micro- and nanostructures (3D-MNS) on different metals and semiconductor materials since 1992. In general, there are three procedures in CELT: (1) generating the etchant on the surface of the tool electrode by electrochemical or photoelectrochemical reactions; (2) confining the etchant in a depleted layer with a thickness of micro- or nanometer scale; (3) feeding the tool electrode to etch the workpiece. Scavengers, which can react with the etchant, are usually adopted to form a confined etchant layer. Through the subsequent homogeneous reaction between the scavenger and the photo or electrogenerated etchant in the electrolyte solution, the diffusion distance of the etchant is confined to micro- or nanometer scale, which ensures the nanoscale accuracy of electrochemical machining.

However, because the thickness of the electrolyte solution between the tool electrode and the workpiece are usually at micro/nano-meter scale, it is a challenge to solve the problems of potential distribution and mass transfer in the ultra-thin layer electrolyte cell. In this presentation, we will introduce our recent work on the external physical field induced electrochemical reactions in which there is no need of 2-electrode or 3-electrode system in the conventional electrochemical system.
Electrochemical Advanced Oxidation Processes Enabled By Novel Electrode Materials
Authors: Chaplin Brian P.
Published: February 2020

Electrochemical advanced oxidation processes (EAOPs) have emerged as promising water treatment technologies for the elimination of a broad-range of organic contaminants and inactivation of pathogens. Progress has been facilitated by the development of stable, novel electrode materials that efficiently generate high yields of hydroxyl radicals. However, key challenges still remain, including toxic byproduct formation, low electro-active surface area, and costly electrode materials. In this talk I will discuss our ongoing research efforts aimed at advancing EAOPs, which includes the synthesis of selective electrodes for the minimization of byproduct formation and development of inexpensive, high surface area, porous electrodes for enhanced electrochemical activity. A combination of electrochemical reactivity experiments, electrochemical characterization, and density functional theory modeling was used to develop a mechanistic understanding of the interactions of contaminants with these novel electrode materials. Results from this work are being used to develop more efficient and compact treatment technologies, including ‘self cleaning’ membranes and multi-functional point-of-use water treatment devices.
Electrochemical Stripping to Recover Nitrogen from Wastewater
Authors: Tarpeh William Abraham
Published: February 2020

Electrochemical water treatment replaces chemical inputs with electricity, allowing for fine-tuning of unit processes through control of applied current and potential. These modular systems are flexible to varying degrees of centralization and robust to handle intermittent flows and shock loadings. Recovering nitrogen from separately collected urine can potentially reduce costs and energy of wastewater nitrogen removal and fertilizer production. Through benchtop experiments, we demonstrate the recovery of nitrogen from urine as ammonium sulfate using electrochemical stripping, a combination of electrodialysis and membrane stripping. Nitrogen was selectively recovered with 93% efficiency in batch experiments with real urine and required 30.6 MJ kg N–1 in continuous-flow experiments (slightly less than conventional ammonia stripping). The effects of solution chemistry on nitrogen flux, electrolytic reactions, and reactions with electro-generated oxidants were evaluated using synthetic urine solutions. Fates of urine-relevant trace organic contaminants, including electrochemical oxidation and reaction with electro-generated chlorine, were investigated with a suite of common pharmaceuticals. Trace organics (<0.1 mg L–1) and elements (<30 mg L–1) were not detected at appreciable levels in the ammonium sulfate fertilizer product. This novel approach holds promise for selective recovery of nitrogen from concentrated liquid waste streams such as source-separated urine, anaerobic digester effluent, and nitrogen-rich food waste.
Electrochemical Oxidation and Advanced Oxidation Processes Using 3D Hexagonal Co3O4 Arrays Anode for 4-Nitrophenol Decomposition Coupled with Simultaneous CO2 Conversion to Liquid Fuels Via Flower-like CuO Cathode
Authors: Jian-Ping Zou
Published: February 2020

A novel electrocatalytic system was developed to realize one-pot conversion of organic pollutants into liquid fuels, such as methanol (CH3OH) and ethanol (C2H5OH). The process combines the catalytic oxidation of organic pollutants with electrocatalytic reduction of CO2. We first coupled the electrocatalytic process with SO4
•− based advanced oxidation processes (AOPs) for the degradation of 4-Nitrophenol (4-NP) using a 3D-hexagonal Co3O4 anode. In this step, 4-NP was mineralized to CO2 and then the CO2 was converted into CH3OH and C2H5OH by electrocatalytic reduction using a flower-like CuO cathode. Experimental results show the destruction of 4-NP (60 mL, 10 mg/L) can be as high as 99 %. And the yield of CH3OH and C2H5OH was 98.29 μmol L−
1 and 40.95 μmol L−
1, respectively, which represents a conversion of 41.8 % of 4-NP into liquid fuels and the electron efficiency was 73.1%. In addition, we found that 3D-hexagonal arrays of Co3O4 with different morphologies can be obtained by adding different amounts of urea. Also, we investigated the formation mechanism of the novel 3D-hexagonal Co3O4 arrays for the first time. A mechanism was proposed to explain the electrocatalytic steps involved in the conversion of 4-NP to CH3OH and C2H5OH and the synergetic effects between AOPs and electrocatalysis.

Figure 1
Mathematical Modelling of the Electrochemical Degradation of Dyeing Wastewaters in Presence of Chloride Ion in a FM01-LC Reactor with Expanded Meshes Anodes (DSA)
Authors: Cruz-Díaz Martin Rogelio , Rodríguez Francisca Alicia , Rivero Eligio Pastor , González Ignacio
Published: February 2020

In the present work a mathematical model to describe the indirect electrochemical oxidation of dyeing wastewaters in presence of chloride ion in a FM01-LC reactor in undivided mode coupled to Continuous Stirring Tank (CST) was implemented. The FM01-LC reactor was modeled with the Nernst-Planck equations in order to takes into account the dispersion, migration, and convection terms; the Poisson equations (through flow mode) for describe the potential distribution in solution, and the electro-oxidation (pseudo first order kinetic) of chloride ions in the anode side (CCl
-), the electrochemical reduction of chlorine oxidizing species (Cox) under mass transport control (mass transfer coefficient) in cathode side; while in the CST the chemical oxidation reactions between active chlorine species and organic matter through homogeneous second order kinetics were considered, which were evaluated through consumption of the chemical oxygen demand (CCOD) and the color decay (Ccol). The reactor operated as a batch recirculation system under galvanostatic conditions, the electrolyses were carried out at two current densities, 132 and 200 A m-2, with 1.0 mM of indigo carmine dye and 0.05 M of NaCl; four liquid flow rates: 0.9, 1.8, 2.7, and 3.6 L min-1 were used. As anode five titanium expanded meshes coated with IrO2-SnO2 doped with Sb2O5 and five stainless steel expanded meshes as cathode were used [1].

Figure 1(a) shows the simulation of the (a) chlorine oxidizing species (Cox) without the presence of dye, and the experimental and mathematical prediction: (b) the chloride ion, CCl
-, consumption; (c) the color, Ccol, removal, and (d) the chemical oxygen demand, CCOD, decay at four liquid flow rates: 0.9, 1.8, 2.7, 3.6 L min-1 and a current density of 132 A m-2 (i=5.0 A).

It can be observed that the proposed mathematical model describe adequately the experimental evolution of different chemical species (Cox, CCl
-, CCOD, and Ccol).

Figure 1
Numerical Analysis of Hydrodynamics, Potential and Current Distribution, and Mass Transfer of Aluminum Ions in an Electrocoagulation Reactor Using CFD By Euler-Lagrange Approach
Authors: Villalobos Lara Alan Daniel , Pérez-Segura Tzayam , Uribe Agustin , Fuentes Ramirez Rosalba
Published: February 2020

The reactor design for tannery wastewater treatment using computational fluid dynamics (CFD) techniques was carried out. The effluent contains different types of pollutants such as organic matter, salts, heavy metals, and dyes difficult to degrade. Due to the complexity of the effluent, a treatment based on an electrocoagulation process is proposed. In most of the references is mentioned that the characterization and design of this type of process is carried out empirically or semi-empirically, so in this work the influence of hydrodynamics, mass transfer of aluminum ions and secondary current distribution was studied. An electrochemical rotating cylinder electrode (RCE) reactor was used, with 6 working electrodes and an aluminum RCE as counter electrode. Besides, a decanter was incorporated in the reactor design. Current distribution and fluid velocity profiles as well as particle tracking animations were obtained. The most suitable geometry was designed from the theoretical results of the sedimentation process and aluminum ions generation. Finally, some operating parameters such as velocity inflow and velocity of the RCE were evaluated.