bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Steam Generated Anticorrosive Oxide Films on Aluminium Alloys
Authors: Din Rameez Ud , Jellesen Morten Stendahl , Ambat Rajan
Published: February 2020

Aluminium and its alloys are widely used in structural and transportation industry owing to their high strength to weight ratio. The surface of aluminium under normal conditions has a thin oxide film (2.5-10 nm) responsible for its inherent corrosion resistance. This oxide film can further be converted or transformed into functional conversion coatings in order to enhance corrosion resistance and adhesion to paint systems. Chromium based conversion coatings have been extensively used on aluminium alloys to improve adhesion of subsequent paint layers and corrosion resistance. However, the use of hexavalent chromium is strictly regulated due to its toxic nature and suspected carcinogenicity. So, it is highly imperative to develop other alternatives for chrome conversion coatings. Treatment of aluminium with natural water at elevated temperatures results in the formation of different forms of aluminium oxide (γ-AlO(OH) , Al(OH)3) depending on the preparation parameters/conditions. Moreover, with the knowledge of factors controlling film growth, composition and morphology, such oxide layers carry huge potential for practical applications.

Pure aluminium (AA1090, 99.94 wt. %) and other aluminium alloy surfaces were exposed to high pressure steam produced by an autoclave at a temperature of 107 – 121 °C and pressure of 15 -17 psi for 10 minutes to produce a thin coating of aluminium oxide. The aim of this study is to understand the effect of high pressure steam with and without different chemical additives on surface morphology and growth of oxide film on aluminium alloys and the effect of microstructure. Performance of the grown oxide film was evaluated by electrochemical testing and corrosion testing such as salt spray and filiform testing. Surface morphology was observed by using FEG-SEM, EDX and FIB-SEM. Metal oxide surface characterization and compositional depth profiling were investigated by using XRD, XPS and GD-OES respectively.
Corrosion Studies of Austenitic and Ferritic Stainless Steels in Solution Containing Chloride Ions
Authors: Ribeiro Josimar , de Andrade Adalgisa Rodrigues , Soares Thiago Freitas , Moreira Roberta Rossi
Published: February 2020

The corrosion behavior of stainless steel AISI 304 and AISI 430 was investigated in NaCl 3.0% in the presence and absence of the pyridine and benzimidazole inhibitors. The electrochemical study was performed using the technique of polarization, the surface morphology of the electrodes was characterized by using the techniques of X-rays Diffraction, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) and the composition was investigated by EDX (Energy Dispersive X-rays). Figure 1 shows the X-ray diffraction pattern of stainless steels investigated in this paper. As can be seen in this Figure, the AISI 304 steel has diffraction peaks at the following 2θ angles: 44.59 °, 50.79 °, 74.71 ° and 90.62 ° that have been associated of nickel-iron (FeNi) phase composed (PDF [3-1209]). Beyond this phase was also observed phase of chromium (Cr) peaks (at 44.56 ° and 84.84 °) associated with the X-ray diffraction pattern PDF-data [1-1261]. It is perceived that there is a separation between two different cubic phases, but the chromium phase has a space group Im3m while the iron-nickel phase has not been identify the spatial group. The results obtained by the potentiodynamic polarization curves showed that the AISI 304 steel is more resistant AISI 430. The efficiency of the inhibitor was tested at six different concentrations (2 ppm, 25 ppm, 50 ppm, 100 ppm, 500 ppm and 1000 ppm) for each, and all concentrations was observed an increase in potential, so raising corrosion resistance. All analyzes obtained show that higher corrosion resistance with 50 ppm of pyridine for steel AISI 304 and 50 ppm of benzimidazole to AISI 430.

Figure 1. XRD pattern of the AISI 304.

Table 1. Results obtained from Tafel studies for the alloys in different concentration of the pyridine inhibitor.

AISI 304
AISI 430

Solution (NaCl 3%)
Ecorr (mV)
Rp
(kΩ cm2)
I (%)
Ecorr (mV)
Rp
(kΩ cm2)
I (%)

Absence of inhibitor
-283
31.05
-
-426
1.94
-

5 ppm
-200
79.00
61.0
-415
2.19
11.4

25 ppm
-193
94.65
67.9
-403
3.83
49.3

50 ppm
-186
105.80
70.7
-385
4.42
56.1

100 ppm
-203
83.48
62.8
-327
8.87
78.1

500 ppm
-213
62.54
50.4
-300
18.44
89.5

1000 ppm
-221
49.27
37.0
-314
5.09
61.9

This paper was supported by the funding agencies: FAPES, CAPES and CNPq.
Corrosion in Construction Materials
Authors: Marquez Andres
Published: February 2020

Corrosion in construction materials continues to be a significant factor in the degradation, weakening and loosening of key properties of the different components or structures they are part of. I-beams, angle bars, reinforcing bars (rebars), stainless steel, among others, are subject to conditions (in some cases extreme) that in a way or the other affect the performance of the structure. This works aims at being an explorative evaluation of the corrosion of such construction materials under different conditions, such as acids, Temperature, gas bubbling, among others. Several experiments are performed, and the findings are analyzed, discussed and interpreted, as to identify mainly the most corrosion resistant combination and at the same time the most corrosive combination.
Effect of Surface Morphology on the Corrosion of Electroless Nickel/Immersion Gold Films
Authors: Lee Dong-Jun , Ha Jun-Seok , Chu Hyun-Soo , Lee Hyo-Jong
Published: February 2020

Electroless nickel with immersion gold (ENIG) process has been widely used as a surface finishing for PCB (Printed Circuit Board). The ENIG process provides a uniform coating on Cu layer without any complex patterning process, and so it has wide and diverse electronic industrial applications; fine pitch surface mount, ball grid array(BGA), flip chip BGA packages and so on. However, there is a reliability issue in the ENIG process. Many researchers have pointed out that severe corrosion of electroless Ni surface is the one of the major factors to reliability failure. In the extreme case, it is known as the black pad which caused a failure of solder joint. A content of phosphorous higher than Ni-P deposits was detected on the failed pad surface, and galvanic cell formation resulted into the corrosion due to the difference of P concentration. The Ni surface has a mud-cracked appearance and the phosphorous content is abnormally higher (exceeding 10 wt%). Another similar issue related to ENIG process is pad discoloration due to Ni oxidation on the top of ENIG pad. Such discoloration pad is regarded as a failure due to cosmetic reason and a lack of clear standards. Sometimes, it actually leads to high contact resistance due to Ni oxides on the top of ENIG layer. Excessive oxidation of Ni layer may result in the non-wetting of solder to the ENIG layer during the reflow process for solder ball attachment because it is difficult for the flux to remove such excessive oxides. The Ni oxidation may be owing to Ni cation diffusion passing through Au immersion during wet process such as rinsing steps in the downstream process after ENIG treatment, which is an electrochemical phenomenon as well. Here, the pad discoloration of Ni corrosion during Electroless nickel with immersion gold (ENIG) treatment was investigated by SEM, XPS and cross-sectional EDS analysis. The Ni corrosion happened at the nodule boundary for relatively thinner layer whereas the corrosion pits were generated in the thick Ni deposits. The electroless Ni was amorphous structure, which meant that the domain boundary energy between two Ni nodules did not change during Ni growth. However, the cusp stress at the surface intersection of two nodules gradually decreased during Ni growth, and hence the corrosion mode changed from nodule boundary corrosion to pit corrosion. It can be surmised that the nodule boundary corrosion can be suppressed by increasing Ni nucleation as well as Ni thickness.
Analysis of Water Quality for Pitting Corrosion Risk of Copper Used in Heat Exchanger of Air Conditioner
Authors: Hoshi Yoshinao , Ochi Kentaro , Shitanda Isao , Itagaki Masayuki
Published: February 2020

The leakage accident of the water supply pipe and the pipe heat exchanger was the major problem [1, 2], which is attributed to the pitting corrosion of copper. The mechanism of the pitting corrosion of copper has been investigated widely [1-5]. Campbell [1, 3, 4] discussed the occurrence of the pitting corrosion of copper under flowing hard and soft water in the water pipes, indicating that the dissolution of copper was influenced by the water quality significantly.

In the present study, the pitting corrosion risk of copper used in the heat exchanger of air conditioner was investigated by the parameters of the water quality sampled by the copper heat exchanger of the air conditioner of all over the country in Japan. The parameters (pH, acid consumption, total hardness) and the concentrations of Cl- and SO4
2- of the sampled water were analyzed to construct two-dimensional phase diagrams. The polarization curve measurement was performed by three-electrode system. The working electrode (0.20 cm2) was the copper plate and the counter electrode was the platinum wire. The KCl-saturated silver/silver chloride electrode (SSE) was used as the reference electrode. The measurement was started from the rest potential to 1.0 V vs. SSE at 100 mV/min. All the potentials in this paper were referred to SSE. The compositions of test solution were determined by the results of the analysis for the sampled water from the copper heat exchanger of the air conditioner of all over the country in Japan. All measurements were made at 25 oC. The results of the two-dimensional phase diagrams and the electrochemical measurement were discussed in this paper.

Reference

[1] H. S. Campbell, Journal of Applied Chemistry, 4, 633 (1954).

[2] V. F. Lucey, British Corrosion Journal, 2, 175 (1967).

[3] H. S. Campbell, Water Treatment and Examination, 20, 11(1971).

[4] H. S. Campbell, Journal Institute of Metals, 77, 345 (1950).

[5] R. May, Journal Institute of Metals, 82, 65 (1953).
Effects of Hydrogen Sulfide on the Corrosion Behavior of High Strength Steel in Alkaline Solutions
Authors: Beck Justin , Feng Ruishu , Lvov Serguei N. , Ziomek-Moroz Margaret
Published: February 2020

The effects of hydrogen sulfide (H2S) on the corrosion of high strength carbon steel have been studied due to their relevance to the oil and natural gas industries. Since H2S behaves as an acid in aqueous solutions, the presence of dissolved H2S results in a decrease in pH through dissociation into H+(aq) and HS-(aq) ions. It is known that the effects of sulfide on iron oxidation dependent on the solution pH. For example, at very low pH the metal surface is free of corrosion products and resulting in high rates of active corrosion. In a pH region from 3 to 5, the addition of H2S can result in an initial increase in corrosion rate that decreases over time as a protective iron sulfide layer forms and passivates the metal. Our goal was address the corrosion processes on high strength carbon steel due to H2S at high pH values.

In-situ electrochemical corrosion measurements were performed for high strength low alloy steel in 5 %wt. NaCl solution at 85 °C. The solution pH was tested from 7 and 12 to simulate conditions that may be present for drill pipes operating in deep-well environments. Exposure for each sample was at least 60 hours to allow for the observation of steady-state behavior. It was found that the calculated corrosion rate dramatically increased from around 3 mm y-1 or less to over 10 mm y-1 as the solution pH fell below 9, which is an event that could occur if pH control is temporarily lost during gas or oil extraction operations.

The change in corrosion rate corresponded to an observed change in the electrochemical impedance spectroscopy (EIS) behavior, with a shift from two well-defined time constants at more alkaline conditions to what appeared to be a single low-frequency time constant at more neutral pH. Varying the rate of stirring in the test vessel did not appear to change the corrosion behavior across the pH range tested, suggesting that the corrosion process was not diffusion limited.

The results were correlated to previous work that found the mechanical failure mechanism to shift from stress corrosion cracking at alkaline conditions to hydrogen induced cracking over a similar pH range. This would suggest that changing the pH alters the nature of the corrosion process, possibly by changing the mechanism or the nature of the corrosion product film. Thermodynamic modeling has been performed to investigate the stable corrosion products and aqueous species at each condition. Pourbaix diagrams suggest that corrosion products shift from iron sulfides to iron oxides as the solution pH is increased.
Exploring Different Avenues of Microbattery Fabrication through Electrodeposition
Authors: Rehnlund David , Asfaw Habtom Desta , Sun Bing , Böhme Solveig , Valvo Mario , Wei Wei , Oltean Gabriel , Brandell Daniel , Edström Kristina , Nyholm Leif
Published: February 2020

Microbattery research sparked from the rapid expansion and miniaturization of micromelectromechanical systems (MEMS) has recently produced a wide variety of different cell designs and electrode geometries. Three-dimensional (3D) electrodes are currently the most promising approach addressing the requirement of high energy and power density on a limited surface area. Expansion in the third dimension offers an increased surface area thereby enabling high energy density without substituting rate performance [1]. Dense packing of all microbattery components offers short diffusion length for charge carriers, e.g. Li-ions and electrons, while contributing to the decrease of the overall cell volume [2].

Of all the techniques studied so far, template-assisted fabrication is the most common route to achieve nanostructured electrodes. By such means, electrodeposition has been used to grow nanopillar [3] and aperiodic ‘sponge’ electrodes.

This work presents results from our studies on electrochemical fabrication of nanostructured electrodes based on nanopillar and aperiodic design as well as integration of a polymer electrolyte coating. Both nanostructured anodes and cathodes will be presented based on the core current collector of carbon, aluminium and copper.

Acknowledgements

This work has been supported by the STandUP for Energy project, the Swedish Energy Agency (STEM), and the Swedish Research Council (VR).

References

1. K. Edström, D.B., T. Gustafsson, L. Nyholm, Electrodeposition as a Tool for 3D Microbattery Fabrication. The Electrochemical Society Interface, 2011. 20: p. 41-46.

2. R.W. Hart, H.S. White., B. Dunn, D.R. Rolison, 3-D Microbatteries. Electrochemistry Communications, 2003. 5: p. 120-123.

3. M. Valvo, M. Roberts., G. Oltean, B. Sun, D. Rehnlund, D. Brandell, L. Nyholm, T. Gustafsson, K. Edström, Electrochemical elaboration of electrodes and electrolytes for 3D structured batteries. Journal of Materials Chemistry A, 2013. 1: p. 9281-9293.
Electrodeposition Based Synthesis of Metal-Air Battery Cathodes
Authors: Marschilok Amy C , Takeuchi Esther S , Takeuchi Kenneth J
Published: February 2020

Metal air batteries offer the opportunity for unprecedented energy density improvements relative to existing battery technologies. Air cathodes are usually comprised of a catalyst, conductive additives, binder, and current collector. The current collector provides support and conductivity, the binder provides physical adhesion, and the catalyst facilitates the oxygen reduction process at the cathode. Thus, each component plays an important role in the function of the overall electrode. Additionally, access of the catalyst particle to oxygen is critical, so the cathode porosity must be appropriately tuned. Electrodes are often fabricated using physical mixing methods, where issues can include poor interparticle contact and limited access of the interior catalyst particles to oxygen.

An electrodeposition based strategy for fabrication of a composite air cathode will be discussed. The first layer consists of a current collector substrate, which can be two dimensional (planar) or three dimensional in design. The second layer consists of a conformal conductive polymer coating. The third layer consists of catalyst particles. The second and third layers are each prepared using stepwise deposition processes.

Advantages of the electrodeposition fabrication method will be described. Three-dimensionally structured composites can be easily generated via use of three dimensional substrates. All of the catalyst nanoparticles are positioned on the outer surface of the composite electrode, allowing facile access of oxygen gas molecules to the catalyst particle surfaces. Finally, the conductive polymer provides added conductivity and improved stability to the composite. Resulting impact on conductivity and oxygen reduction activity of the composite electrode will be discussed.

References

1. S.H. Lee; S. Zhu; C.C. Milleville; C.-Y. Lee; P. Chen; K.J. Takeuchi; E.S. Takeuchi; A.C. Marschilok. Electrochem. Solid-State Lett.
2010,
13(11), A162-A164.

2. A.C. Marschilok; S. Zhu; C.C. Milleville; S.H. Lee; E.S. Takeuchi; K.J. Takeuchi. J. Electrochem. Soc.
2011,
158(3), A223-A226.

3. A.C Marschilok; S.H. Lee; C.C Milleville; P. Chen; E.S Takeuchi; K.J Takeuchi. J. Composite Materials.
2012,
47(1), 33–40.
Fabrication and Characterization of Thin-Film Nickel Hydroxide Electrodes for Micro-Power Applications
Authors: Falahati Hamid , Kim Edward , Barz Dominik P.J.
Published: February 2020

INTRODUCTION

Micro power sources are very attractive for nano- and micro-scale devices, such as Point-of-Care medical diagnostics and Micro Electro Mechanical Systems, where only low power densities and capacities are required. In the present work, we report on the micro-fabrication of patterned α-Ni(OH)2 films which are suitable for rechargeable nickel metal hydride (Ni-MH) and nickel-zinc (Ni-Zn) micro-batteries as well as for micro-capacitors. The main objective of the current research is to investigate the influence of three-dimensional (3D) patterned structures on the mechanical stability as well as on the electrochemical performance of the electrode.

ELECTRODE FABRICATION

The patterned electrode is fabricated through multi-layered films which are deposited by employing e-beam evaporation, UV photolithography (using a negative KMPR photoresist), and electro-deposition techniques. In detail, thin films of chromium and nickel with a thickness of 40nm are deposited on glass and used as adhesion (seed) and current collector layers, respectively. NiOx/Ni(OH)2 is electro-deposited from NiCl2 solution followed by electro-precipitation of Ni(OH)2 films from Ni(NO3)2.6H2O aqueous solution to form a grid-like patterned layer. Figure 1 schematically depicts the fabrication process.

MATERIALS & ELECTROCHEMICAL CHARACTERIZATION

The chemical composition of the micro fabricated electrodes is characterized by employing X-Ray diffraction (XRD) and X-Ray photoelectron spectroscopy (XPS). The feature size of the grid-like pattern is determined to be roughly 20 microns in height by using a mechanical profilometry technique. Figure 2 illustrates the XPS spectrum of the Ni(OH)2 electrode material based on the Ni2p3/2 spectrum. The electrochemical characteristics are studied using cyclic voltammetry (CV) in a 1M KOH electrolyte. Measurements are performed for unpatterned as well as patterned electrodes to investigate the influence of the 3D structure as shown in Figure 3.

CONCLUSIONS

We observe that electrode patterning considerably improves the adhesion of the α-Ni(OH)2 film to the nickel current collector layer. It is also found that the micro fabricated α-Ni(OH)2 electrode is reversible and diffusion limited according to the Randles-Sevcik linearity. Furthermore, the electrolyte concentration dependency is studied via CV which shows minimum concentration of around 0.2M required for good electrode REDOX reactions.
Comparison of Aqueous and Non-Aqueous Deposition of Cobalt Via Electroplating Method
Authors: Abdel-Fattah Tarek M , Huff Clay , Dushatinski Thomas
Published: February 2020

The purpose of this study is to compare the deposition of cobalt onto a copper substrate from aqueous and non-aqueous cobalt chloride solutions. The aqueous solution had a pH of 2 and had an equal concentration of cobalt as the non-aqueous. The non-aqueous solution consisted of a 2:1 molar ratio ethylene glycol to choline chloride solution.

Deposition was performed for 10, 15 and 30 minute intervals with both solutions at 3 volts potential difference between the copper plate and reference. The suitable electroplating temperatures were found to be 70° C for the non-aqueous solution and 22° C for the the aqueous. The aqueous was initially run at 70° C to keep the temperature variable constant, but was found incapable of producing consistent films and was run at a lower temperature of 22° C. The coating deposited by the non-aqueous solution was black of color and had controllable thickness based on time. The aqueous coating was shiny silver, and was measured to be thinner than that of the non-aqueous films, but still had controllable thickness.

The black cobalt thin films could have applications in optical systems to reduce parasitic light. Also the non-aqueous has applications in thermal active solar cells as they are conductive and absorb a wide range of the electromagnetic spectrum emitted by the sun, converting it to applicable thermal energy. The metallic looking cobalt thin films could be applied as mirrors in x-ray optics systems after polishing, as they may have different angles of diffraction.

Referencies:

1Florea, A.; Anicai, L.; Costovici, S.; Golgovici, F.; Visan, T. 2010, Surf. Interface Anal, 42, 1271-1275

2Abdel-Fattah, T.M.; Crooks, R. SurfaceCharacterization of High Purity Niobium Electropolished with an Ionic Liquid. 2010, ECS Trans, 33, 571

3Abdel-Fattah, T.M.; Loftis, J.D. Surface Characterization of High Purity Metals of Silver and Nickel Electropolished with an Ionic Liquid. 2010, ECS Trans, 25, 57

4Ionic Liquid Electropolishing of Metal Alloys for Biomedical Applications. Abdel-Fattah, T.M.; Loftis, J.D.; Mahapatro, A. 2010, ECS Trans, 25, 57

5Abdel-Fattah, T.M.; Loftis, J.D. Comparison of the Electrochemical Polishing of Copper and Aluminum in Acid and Acid-free Media. 2009, ECS Trans. 25, 327

6Damiano, B.; Wixtrom, A.; Abdel-Fattah, T. Electrochemical Deposition of Cobalt onto the Surface of Copper Using a Choline Chloride-Based Ionic Liquid. 2012,
ECS Trans. 50(11) 277-281
Thermal Analysis of High-Power Prismatic LiFePO4 batteries: Modeling and Experiment
Authors: Yazdanpour Maryam , Taheri Peyman , Bahrami Majid
Published: February 2020

A 90Ah prismatic LiFePO4/graphite battery (Sinopoly Battery Ltd., China) is used for the experiments and thermal modeling [cf. Fig. 1].

In the experimental study, a power processing system is employed to cycle the experimental battery. Constant-current discharge tests at 1C-rate (90A), 2C-rate (180A), and 3C (270A) are performed to measure the battery voltage and surface temperatures.

In the modelling study, a three-dimensional transient model has been developed to predict the thermal behaviour of the battery during galvanostatic processes. A transient heat conduction equation is sufficient to describe the thermal phenomenon of domain (1); while the heat transfer mechanism in domain (2) is modelled by the natural convection. A convective-radiation boundary condition is considered at the boundaries of the domain.

The above-mentioned models are performed in a finite element solver (COMSOL Multiphysics, Version 4.4), and the accuracy of the model is validated through comparison with the experimental data.

Some Results

The rate of heat generation which is the main parameter calculation in the thermal model, is approximated from [1],

g=I/ν[(V-V
oc
)+T
dV
oc/dT] (1)

where I and V denote the battery operational voltage and current, respectively, ν represents the battery volume, V
oc
is the open circuit voltage of the battery and T
is

temperature. The heat generation terms can be determined by using experimental tests or electrochemical models, which the first approach is applied in this study. A constant value of -0.4337 mV/K adapted from Ref. [2], is considered for term dV
oc/dT. The rate of heat generation caused by the polarization losses, V-Voc
, is defined from the measured electrical performance of the battery.

The heat generation rates inside the battery (domain (1)) during three different galvanostatic discharge processes (90 A, 180 A, and 270 A) are calculated based on Eq. (1) and the battery electrical performance, and then the obtained expressions are implemented into the thermal model.

In Fig. 2, the modeling results for average surface temperature of the battery (shown by solid lines) are compared to the corresponding experimental data (symbols), during constant-current discharge processes with 90 A, 180 A, and 270 A. The comparison shows an excellent agreement between the predicted results and the data from the experiments.

In future, an electrical model will be coupled to the presented model to describe the ohmic heating in the electrodes as a result of the electrical constriction resistance.

[1] D. Bernardi, J. Electrochem. Soc., Vol. 132, pp. 5-12, (1985).

[2] A. Samba et al. , J. Electrochimica Acta, Vol. 117, pp. 246–254, (2014).

[3] P. Taheri et al., J. Electrochem. Soc., Vol. 160, pp. A1731–A1740, (2013).
Influence of Surface Treatments on the Electrochemical Reactivity of VO2+/VO2
+ Redox Couple Using Carbon Fiber Ultramicroelectrodes
Authors: Miller Mallory Arlene , Savinell Robert F. , Wainright Jesse S.
Published: February 2020

Several surface treatments for flow battery electrodes have been reported in the literature to enhance performance of the all-vanadium redox flow battery (RFB). An increase in carbon-oxygen functional groups has been correlated with an increase in rate of electron transfer for the VO2+/VO2
+ redox reaction and thus, enhanced performance of the all-vanadium RFB. It is proposed that surface oxide groups act as electron transfer mediators by providing reaction or adsorption sites. Thus far, treatments reported in the literature are difficult to compare, as the evaluation of each treatment varies. The use of carbon fiber ultramicroelectrodes, prepared from treated felts, can be used as a definitive basis for comparing treatments and investigating the true effect of surface alterations. Reaction kinetics of the VO2+/VO2
+ reaction can then be calculated and compared across treatments.

First, fabrication and sample mounting methods for the carbon fibers were verified by comparison to platinum ultramicroelectrodes. Then the role of the surface structure of carbon felts for the aqueous all-vanadium redox flow battery (RFB) was investigated. The graphite felt had undergone thermal, chemical, or electrochemical treatments in order to alter surface structure. The structure and composition of the felts was analyzed using x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Electrochemical performance was evaluated using cyclic voltammetry (CV), pulse voltammetry (PV), and electrochemical impedance spectroscopy (EIS). Thermally treated felts (300oC for 30hrs in air) exhibited a loss of surface functional groups, but an increase in double layer capacitance attributed to an increase in the active surface area (9.9 times that of untreated). This suggests that available surface area plays a larger role than the specific functional groups on the surface of the carbon electrodes in increasing the electrokinetics of the VO2+/VO2
+ redox reaction.
A Generalized 3D Multiphysics Model for Li-Ion Intercalation Batteries
Authors: Allu Srikanth , Pannala Sreekanth , Nanda Jagjit , Simunovic Srdjan , Turner John A
Published: February 2020

We present the computational implementation and results of a unified formulation across the electrode-electrolyte-electrode system. This formulation utilizes a rigorous volume averaging approach typical of multiphase formulation1, 2 and recently extended to supercapacitors3. Unlike previously used methods for Lithium ion batteries based on a segregated formulation4, 5 with intermediate boundaries, by having a unified, single-domain approach, complex geometries are naturally incorporated with the numerical algorithms guaranteeing stability and convergence. The same formulation also applies to 1D, 2D and 3D geometries irrespective of the complexities associated with dimensionality as well as with electrode/electrolyte spatial arrangements. In addition, the formulation accounts for any spatio-temporal variation of the different properties such as electrode/void volume fractions and anisotropic conductivities. This generality will aid in upscaling of local material properties directly into the system-level model. The resulting governing equations are solved using finite element techniques. The modeling results are validated for standard Li-ion cells and compared against the cell level performance (see Fig. 1 for sample results). Furthermore, we conduct an investigation of the effect of spatial variability of the void volume fraction and anisotropy on the performance of multidimensional cell configurations. We analyze the cell level performance and relate it to the detailed spatio-temporal variations of charge and discharge behavior in the electrodes. Finally, we present the coupling of the electrochemical, electrical, thermal, and mechanical processes inherent to cell performance.

References:

1. A. Prosperetti, in Computational Methods for Multiphase Flow, edited by A. Prosperetti and G. Tryggvason (Cambridge University Press, Cambridge, 2007).

2. C. Y. Wang, W. B. Gu and B. Y. Liaw, J. Electrochem. Soc. 145 (10), 3407-3417 (1998).

3. S. Allu, B. Velamur Asokan, W. A. Shelton, B. Philip and S. Pannala, Journal of Power Sources 256 (0), 369-382 (2014).

4. P. Arora, M. Doyle and R. E. White, J. Electrochem. Soc. 146 (10), 3543-3553 (1999).

5. M. Doyle, T. F. Fuller and J. Newman, J. Electrochem. Soc. 140 (6), 1526-1533 (1993).
Atomic Layer Deposited Platinum Electrocatalysts on Chemically Functionalized Graphene
Authors: An Jihwan , Diankov Georgi , Park Joonsuk , Ercius Peter , Goldhaber-Gordon David , Prinz Fritz B.
Published: February 2020

Electrocatalysts play important roles in the performance of electrochemical energy conversion devices such as fuel cells and photoelectrochemical cells. Graphene is a promising candidate for the backbone structure for electrocatalysts due to its large surface area (theoretical value of 2630 m2/g) and good electrical conductivity. Catalyst particles, e.g., Pt nanoparticles, can be integrated with graphene via wet-process route, physical vapor deposition, or chemical vapor deposition. Catalyst-graphene composite materials synthesized via these routes, however, often suffer from low chemical/mechanical stabilities, low particle density, or non-uniform coverage [1,2].

Atomic layer deposition (ALD), which is a modified chemical vapor deposition (CVD) method, is capable of decorating dense nanoparticles chemically bonded to 3-dimensional substrates in a uniform manner. In ALD, the substrate is exposed to the alternate pulses of precursor molecules, and coated with nanoparticles or conformal thin film depending on the cycle numbers. Nevertheless, the integration of graphene with ALD catalyst particles, e.g. Pt, has been challenging because the basal plane of the pristine graphene is chemically inert due to strongly sp2-bonded carbon atoms where the nucleation cannot readily occur [3].

To this end, we present a chemical functionalization method of graphenes for the subsequent ALD platinum nucleation. We show that the low-power hydrogen plasma treatment hydrogenates the basal plane of graphene and significantly increases the chemical reactivity of the basal plane, facilitating the nucleation of the Pt nanoparticles by ALD. We systematically study the dependence of the particle density and the areal coverage on the graphene thickness and on the hydrogenation duration. While the areal coverage of Pt nanoparticles on the basal plane of the pristine graphene is negligible after 100 cycles of ALD Pt (<5 %), that of the few layer graphene hydrogenated for 2 mins hugely increases to > 80 %.

We also investigate the individual particle shape, facets, and the interface between the particle and the graphene in atomic scale using probe-corrected scanning TEM (TEAM1). We show that the ALD Pt particle has epitaxially grown on the graphene with a large density of high-index facets, which makes it a promising candidate for mechanically and chemically stable electrocatalyst with high catalytic activity.

Acknowledgment

We thank Precourt Institute of Energy at Stanford university for financial support.

References

[1] E. J. Yoo, et al., Nano Lett. 9(6), pp. 2255-2259 (2009)

[2] B. Seger and P. V. Kamat, J. Phys. Chem. C 113(19), pp. 7990-7995 (2009)

[3] S. Sun, et al., Sci. Rep. 3, p. 1775 (2013)
Mechanistic and Structural Investigation of LixMnO2 Cathodes during Cycling in Li-Ion Batteries
Authors: Donne Scott W , Dose Wesley M , Sharma Neeraj
Published: February 2020

Increasingly there is demand for clean energy sources and suitable batteries to store this energy. Manganese dioxide and lithiated variants are a promising alternative to conventional Li-ion cathodes due to their cost, abundance, safety and electrochemical performance. Cathodes which operate by a single-phase lithium insertion/extraction process can offer some intrinsic advantages over those with two-phase processes. In this work, in-situ and ex-situ synchrotron X-ray diffraction (XRD) is used to investigate the structural evolution and lithium insertion/extraction mechanism of various LixMnO2 cathodes. Li0.30MnO2 is found to cycle solely with a single-phase mechanism, in contrast to previous literature reports, with only subtle changes in the crystal structure. However, a better cycling discharge capacity is realised through a two-step lithiation synthesis, thermally lithiated Li0.08MnO2 which is then electrochemically lithiated to Li0.33MnO2. After an irreversible two-phase reaction early in the first discharge, this material cycles by a single-phase reaction with good structural reversibility and a stable unoptimised cycling capacity of 120 mAh/g. Comparing cathodes using a combination of in-situ and ex-situ synchrotron XRD data allows us to rationalise cathodic performance with structure and thereby directing research into promising candidates.
A Study on DNA Loop Formation Dynamics Using Surface Plasmon Resonance (SPR)
Authors: Arugula Mary , Yang Fuling , Somasundaram Subramaniam , Easley Christopher J , Shannon Curtis , Simonian Aleksandr
Published: February 2020

Surface plasmon resonance (SPR) is a well-established optical technique for studying DNA-DNA binding (hybridization) in the fields of molecular biology and biomedical sensing. With the emergence of high performance protein-to-DNA switches as electrochemical biosensors, the importance of understanding DNA binding dynamics at gold surfaces has significantly increased. One such method, the electrochemical proximity assay (ECPA), has been shown capable of direct protein quantitation as low as 20 fM. We report here the SPR study of a DNA loop model of ECPA that mimics probe/target binding with a DNA loop. In the assay, the loop-like structure holds methylene blue (MB) in close proximity with the gold surface when target is present, ensuring efﬁcient electron transfer. Investigations on hybridization dynamics were carried out by immobilizing thiolated capture DNA onto the gold surface of the SPR sensor chip to form self-assembled monolayer. DNA loop oligonucleotides and MB-DNA sequences were alternately hybridized to the complementary strands to form a loop-like structure. Sensogram results showed increase in refractive angle (RA) in real time (flow-mode) analysis of binding sequence of the DNA complementarities. In order to verify this binding recognition event, one of the counterpart DNA probe sequences (DNA loop or SH-DNA) were eliminated which showed no discernable RA signal, suggesting loss in loop structure. Further investigations on analysis of time required for thiolated DNA to self-assemble onto the gold surface and optimization of concentrations under stopped-flow (batch mode) conditions were carried out. With this proof-of-concept dynamics of the DNA loop model system, we anticipate that this study can significantly improve the speed and sensitivity of ECPA-based biomarker recognition.
Trace Detection of 2, 4, 6-Trinitrotoluene Using Electrochemical Gas Sensors
Authors: Sekhar Praveen K. , Zhou Jie , Hamblin E. R. , Brosha Eric L.
Published: February 2020

In this article, selective and sensitive detection of trace amounts of 2, 4, 6-trinitrotoluene (TNT) is demonstrated. The screening system is based on a sampling/concentrator front end and electrochemical potentiometric gas sensors as the detector. Preferential hydrocarbon and nitrogen oxide(s) mixed potential sensors with integrated heaters were used to capture the signature of the explosive. Quantitative measurements based on hydrocarbon and nitrogen oxide sensor responses indicated that the detector sensitivity scaled proportionally with the mass of the explosives (down to 250 ng). The sensitivity was found to depend on the flow rate and sensor orientation. The sensitivity was found to increase with increasing flow rate. This detection technique has the potential to become an orthogonal technique to the existing explosive screening technologies for reducing the number of false positives/false negatives in a cost-effective manner.
Rational Design of Amperometric Gas Sensors with Ionic Liquid Electrolytes
Authors: Carter Michael T , Stetter Joseph R , Findlay Melvin W , Patel Vinay
Published: February 2020

KWJ Engineering has invested several years of research and development into producing a new, next generation amperometric gas sensing technology for a variety of toxic gases and gases of environmental interest. This approach is based on adaptation of the conventional ideas of amperometric gas sensing into a new, printed package that is very small and ultralow power for modern applications. In the course of this development, we have also been interested in whether room temperature ionic liquids (RTILs) could be used as electrolytes in the amperometric sensor, replacing the conventional aqueous sulfuric acid electrolyte that is usually used. Furthermore, we are interested in whether RTILs can impart advantages in amperometric gas sensing that have not been possible with conventional electrolytes. The availability of diverse RTILs with interesting and sometimes unique chemical properties suggests that selection of the proper RTIL could, for example, significantly improve sensitivity or selectivity to a particular analyte, enabling detection with unprecedented advantages over conventional approaches. This paper will address these issues relative to the design of amperometric gas sensors with RTILs components. We are interested in finding whether an RTIL can impart a distinct advantage over current practice, and furthermore what the critical criteria are for successful selection of RTIL electrolytes in the printed sensor format. We will address these questions as we review recent results from several programs on gas sensor development for toxic and environmental gases.
Pattern Recognition of Dopamine, Epinephrine, Norepinephrine, Serotonin, Acethylcholine, GABA, and Glutamate in Biological Samples Using Stochastic Sensing
Authors: Stefan-van Staden Raluca Ioana , Moldoveanu Iuliana , VAN Staden Jacobus Frederick
Published: February 2020

Pattern recognition is essential in chemical analysis of biological fluids. Reliable and sensitive methods for neurotransmitters analysis are needed.

Therefore, we developed for pattern recognition of neurotransmitters dopamine, epinephrine, norepinephrine, serotonin, acethylcholine, GABA, and glutamate a method based on stochastic sensing. Microsensors based on diamond paste modified with 5,10,15,20-tetraphenyl-21H,23H-porphyrine, hemin and protoporphyrin IX in stochastic were designed and characterized.

The proposed method can perform pattern recognition of the seven neurotransmitters on biological fluids at a lower determination level than chromatographic methods. The pattern recognition showed high reliability (RSD<1% for more than 6 months) for the simultaneous determination of the seven neurotransmitters in whole blood, cerebrospinal liquid, urine, zebra fish and snails.

Accordingly with the statistic evaluation of the results at 99.00% confidence level, the proposed sensors can be used for pattern recognition and quantification of neurotransmitters with high reliability. The best stochastic microsensor was the one based on diamond paste modified with protoporphyrin IX.

Acknowledgements The present work was supported by the European Commission through the DENAMIC project (Contract-No. 282957) and by UEFISCDI, Romania Contract-no. 186/23.10.2012.
Post-CMOS Integration of MEMS Inertial Sensors Using Oxidized Porous Silicon Technique
Authors: Ge Daohan , Ren Naifei
Published: February 2020

At present, MEMS inertial sensor technology has an exhaustive range of applications in the field of mass-produced commercial products, such as smart phones, PDAs, automobiles, and pedometers, which cause a strong demand for small, robust, low-cost and CMOS- integrated inertial sensors. DRIE process has been widely used in the post-CMOS approach to create high aspect ratio structures [1], but the high expense and long consuming time are usually unacceptable for the mass manufacturing. In addition, during the ion beam bombardment, CMOS structures inevitably suffers from a certain amount of damages which might reduce the device performance [2].

Here we demonstrate a low-cost and CMOS compatible production method to fabricate CMOS-MEMS inetial sensors. A thick oxidized prous silicon (OPS) layer is selectively grown on the silicon substate before the standard CMOS processes for dielectric isolation and thermal isolation. The OPS techique has a substantial cost advantage over DRIE techniqe and can produce very thick layers without severe stress problems.

Lowly-doped p-type wafers (20-40 Ωcm, 500 μm-thick, [100] -oriented and polished) were used in our experiments. The whole process includes three main steps: formation of OPS layers, CMOS sturctures fabrication, and the MEMS structures fabrication.

To create thick porous silicon layer, ohmic contact was achieved by sputtering an 800 nm-thick Al film on the backside of samples. The electrolytes used for anodization contained 48 wt.% aqueous HF and DMF. Galvanostatic current densities of 500 mAcm-2 were applied from an Agilent power source with a tolerance up to 60 V. Macropore arrays with depth of about 48 μm were obtained, followed by an optimized oxidation process to form OPS layers. After that, standard CMOS process steps were used to produce electronic components. Finally, the MEMS structures are completely built on top of the finished CMOS substrate by partely removing the OPS layers, leaving the CMOS layers unthouched.

Figure 1 show SEM pictures of the cantilever beam-mass structure (Figure 1a) and comb structure (Figure 1b) released by removing the OPS layer. Figure 1c shows the MEMS inertial stuctures and CMOS electronic components obtained on the same chip. This represents an effective method to integrate MEMS sensors with electronic circuits.

References

[1] E. H. Roderick, R. H. Williams, Metal-Semiconductor Contacts, 2nded., Oxford Science, New York (1987).

[2] J.Chae, H. Kulah, K. Najafi, J. Micromech. Microeng., 15 (2005) 336.
Effect of Sulfide-Containing Solutions on the Corrosion of Cu-Ni Alloys; Electrochemical and Surface Studies
Authors: Al-Kharafi Faizah M , Abdel Nazeer Ahmed , Abdullah Ragab M , Galal Ahmed
Published: February 2020

The copper-nickel alloy (CuNi 90/10) is extensively used in different oil industries and marine structures. Some of the main usage of this class of alloys is piping in seawater and heat exchangers. In several occasions, the alloy is exposed to sulfide-containing solutions of chloride and sulfate. There is limited information available on the effect of sulfide on the corrosion rate of Cu-Ni alloy and the interrelation between the surface structure of the films formed and the concentration of metal ions dissolved in the electrolyte side. A systematic study is required to understand the role of sulfide both in promoting film formation and dissolution of the alloy in presence of sodium chloride, sodium sulfate and sulfuric acid. We found that the presence of sulfide ions with a concentration of 20 ppm resulted in a relative increase in the rate of corrosion compared to sulfide-free electrolytes. The rates of corrosion are 3.98, 3.13, 5.30, 9.30, 13.1 mm year-1 in 0.1 M H2SO4, 0.1 M Na2SO4, 0.58 M NaCl, 0.1 M H2SO4 + 0.58 M NaCl, and 0.58 M NaCl + 0.1 M Na2SO4, respectively [1]. The corresponding rates of corrosion in the same electrolytes containing 20 ppm sulfide ions are: 6.22, 14.52, 20.36, 15.35, and 23.75 mm year-1, respectively. The rate of corrosion of the alloy is highest in case of 0.58 M NaCl, and 0.58 M NaCl + 0.1 M Na2SO4 containing 20 ppm sulfide. Electrochemical impedance spectroscopy (EIS) measurements indicate that relatively thicker passive films are formed over the alloy surface in these electrolytes as indicated in Figure 1. Moreover, the film thickening increases with time of exposure of the electrode in these electrolytes. This finding is ascertained from the systematic experiments and data obtained from FE-SEM images (Figure 2), XPS analyses of the films morphologies and structures, and electrolyte composition determined from ICP-MS measurements. The alloy was exposed to different time intervals (namely 30 s, 30 min and 60 min, respectively) of anodizing potential of +0.15 V vs. Ag/AgCl in different electrolytes. The concentration of Cu and Ni ions in the electrolyte side progressively increases with time of exposure in all electrolytes studied. The relative concentration is lowest in Na2SO4 solution containing sulfide, and is highest in Na2SO4 + NaCl. The composition of the passive film reflects that beside oxides/hydroxides, metallic sulfides are also formed. The protective layer is formed mainly of Cu2O and NiO2with ratios that differ according to the type of electrolyte. A possible mechanism for the corrosion of Cu-Ni alloy in presence of sulfide is as follows [2]:

O2 + 2H2O + 4e- = 4OH-

S2- + H2O = HS- + OH-

Cu + HS- = Cu(HS-)ads

Cu(HS-) = Cu(HS) + e-

Cu(HS) = Cu+ + HS-

2Cu+ + HS- + OH- = Cu2S + H2O

[1] F.M. Al-Kharafi, A. Abdel Nazeer, R.M. Abdullah, A. Galal, ECS Transactions, 58 (xx) 2013.

[2] K. Rahmouni, M. Keddam, A. Srhiri, H. Takenouti, Corros. Sci., 47, 3249-3266, 2005.