bluuebunny/crossref_metadata_2025 huggingface dataset:
(Battery Division Student Research Award sponsored by Mercedes-Benz Research & Development) Revisiting the Electrochemical Stability Window of Solid Electrolytes
Authors: Han Fudong
Published: February 2020

The development of next-generation batteries has raised higher requirements on safety and energy density, both of which can be potentially improved by developing solid-state batteries (SSBs). Significant advances have been made in achieving superionic solid electrolytes (SEs) with a wide electrochemical stability window (ESW) from 0 to 5 V. The ESW of solid electrolytes was usually measured from cyclic voltammetry of Li/SE/inert metal semi-blocking electrode. Because of the wide ESW, solid electrolytes hold great promise for high energy density batteries with high columbic efficiency and long cycle life.

In this presentation, we challenge the claimed ESW of solid electrolytes. The conventional method to measure ESW provides an overestimated value because the kinetics of the electrochemical decomposition reaction is limited in the semi-blocking electrode. A novel experimental method using Li/SE/SE+carbon cell is proposed to approach the intrinsic stability window of solid electrolytes. The ESWs of Li10GeP2S12 (LGPS) and Li7La3Zr2O12 (LLZO), the most promising SE for sulfide and oxide electrolytes respectively, are examined using the novel experimental method. The results suggest that both SEs have much narrower electrochemical stability window than claimed (Figure 1). The cathodic and anodic decomposition products for both electrolytes are also characterized. The measured stability window and the decomposition products agree well with the calculated results from first principles. The reversible decompositions of LGPS at both high and low voltages enable the realization of a battery made from a single material.

The electrochemical decompositions of the SEs in SSBs can lead to large interfacial resistances between electrode and electrolyte, depending on the properties of the decomposition products. The interfacial resistances arising from the decomposition of SEs have rarely been considered in previous research because the batteries are cycled within the “claimed” stable window of SEs. Suppressing the (electro)chemical reactions between LiCoO2 cathode and LLZO electrolyte by engineering their interphase enables a high performance all-ceramic lithium battery. By taking advantage of the electrochemical decomposition of SEs, an effective approach to suppress Li dendrite formation in sulfide electrolyte is also demonstrated.

References

[1] F. Han, Y. Zhu, X. He, Y. Mo, C. Wang,
Adv. Energy Mater., 6 (2016) 1501590.

[2] F. Han, T. Gao, Y. Zhu, K. J. Gaskell, C. Wang,
Adv. Mater., 27 (2015) 3473.

[3] F. Han, J. Yue, C. Chen, N. Zhao, X. Fan, Z. Ma, T. Gao, F. Wang, X. Guo, C. Wang,
Joule, 2 (2018) 497.

[4] F. Han, J. Yue, X. Zhu, C. Wang,
Adv. Energy Mater., (2018) 1703644.
Atomic Layer Deposition of ORR Catalysts for Rechargeable Zinc-Air Batteries
Authors: Clark Michael Patrick , Cadien Ken , Ivey Douglas G
Published: February 2020

The move towards cleaner and renewal energy production, such as solar and wind power, necessitates the development of efficient, safe and cost effective energy storage methods. Zinc-air batteries (ZABs) are prime candidates to meet these requirements and store large amounts of electricity. They use oxygen in the atmosphere as the cathode reactant in the discharge process. Oxygen diffuses into the cell and is reduced to hydroxyl ions in the presence of a catalyst at the air electrode (oxygen reduction reaction or ORR). At the same time, the zinc electrode is oxidized and dissolves in the electrolyte, producing zincate ions. During recharging, zinc metal is reduced from zincate ions and plated at the zinc electrode. Oxygen evolution (OER) occurs at the air electrode. There are challenges in implementing zinc-air batteries for large scale energy storage. The ORR and OER processes at the air electrode are sluggish and electrode stability can be poor because of catalyst delamination and/or substrate corrosion during battery cycling. Effective electrodes for ZABs require a catalyst that is efficient, stable and electrochemically active.

Atomic layer deposition (ALD) is a gas phase deposition technique capable of fabricating thin films from a wide variety of materials. ALD utilizes alternating pulses of reactants that each undergo self-limiting reactions on the sample surface, producing uniform and conformal films, with good composition control and sub-nanometer thickness control. These features of ALD are particularly attractive for fabricating ORR catalysts in zinc-air battery electrodes, as they can lead to increased surface areas and three-phase boundary areas, both of which should lead to better performance and cyclability. In this study, ALD is used to produce air electrodes with Mn oxide as the ORR catalyst. The process is optimized and deposits are characterized using microstructural characterization (e.g., electron microscopy, X-ray diffraction, surface science techniques and Raman spectroscopy) and electrochemical characterization (e.g., linear sweep voltammetry, electrochemical impedance spectroscopy and galvanostatic cycling) methods. Successful materials are tested in two different battery configurations, i.e., a two electrode set-up and a three-electrode set-up where the ORR and OER reactions are decoupled. The three-electrode configuration limits the potential window to which each electrode is subjected, greatly improving stability and cyclability.
Fast Charging Strategy Based on Electrochemical Model and Dynamic Programming for a Lithium-Ion Battery Cell
Authors: Xu Meng , Wang Xia
Published: February 2020

Fast charging technology of lithium-ion batteries is critical to commercial application of electrical vehicles (EV). Typically, recharging lithium-ion batteries using standard charging methods takes more than one hour which is considerably longer than refueling of the internal-combustion-engine (ICE) car, roughly 8-10 min. To reduce the charging time, fast charging increases the total current which can adversely affect the cycle life, performance and safety of the battery, such as lithium plating, increased battery temperature, higher heat generation rate, and thermal runaway. The charging energy efficiency can be reduced because of the increased heat generation during fast charging. Therefore, controlling the temperature rise and improving the charging energy efficiency using well-designed fast charging strategies are indispensable for its application in electric vehicles.

The objective of this work is to optimize the charging current profile based on electrochemical thermal model and dynamic programming for a 26650 cylindrical lithium iron phosphate (LFP) battery. The proposed model is implemented on a multi-stage constant current (MSCC) fast charging strategy for charging from 0 % to 80 % of its rated capacity within 30 minutes. The goal of the optimization is to maximize the charging energy efficiency or/and minimize the temperature rise and charging voltage. The control variable of various charging current protocols using the C-rate level ranging from 0.6 C-rate and 2.6 C-rate are applied to the MSCC fast charging. The constraints of the optimization include temperature and cell voltage, which are applied to prevent thermal runway and reduce the capacity fade. The optimized charging current profile based on various initial temperatures, ambient temperatures, and heat transfer coefficients will be compared. In addition, the effect of constraints on optimization results will be discussed.

To study the effect of fast charging based on the battery dynamics, the electrochemical model first proposed by Newman et al. has been addressed. Even though the electrochemical model is not suitable for online application, the results can serve as a benchmark to evaluate and improve an existing online algorithm for battery fast charging optimization. However, few of those works using electrochemical models discussed the effect of fast charging strategies on battery electrochemical and thermal behavior, as well as charging energy efficiency under various charging current patterns.

Based on dynamic programming and electrochemical thermal model, this research proposes a new method to optimize charging current profile under various constraints and different optimization goals, which are useful for fast charging application of lithium-ion batteries on electric vehicles.
Piezoelectrochemical Energy Harvesting in Commercial Lithium Ion Batteries
Authors: Preimesberger Juliane Irine , Kang SeungYeon , Arnold Craig B.
Published: February 2020

As technology becomes smaller and smaller, the need for micro-energy sources becomes increasingly imperative. One promising technology to address this need is piezoelectrochemical harvesting, a recently identified mechanism to directly convert mechanical energy to electrochemical potential[1-4]. In piezoelectrochemical (PEC) materials, the chemical potential of ions is affected by an applied stress, and under such circumstances these materials can be used in a thermodynamic cycle to harvest energy, at a relatively slow rate commensurate with the kinetic transport in electrochemical systems. Previous work[1] has demonstrated that commercial lithium cobalt oxide (LCO) batteries exhibit the PEC effect, as both the lithium cobalt oxide cathode and lithium-intercalated graphite anode are PEC materials. The coupling factor between the change in equilibrium potential and applied mechanical stress has been found to be linear.

In this presentation, we will discuss our research to use piezoelectrochemical energy harvesting to increase the voltage generated from commercial lithium ion batteries. We measured the differential expansion and differential voltage of a lithium ion battery, and used this data to estimate the coupling factor as a function of state-of-charge (SOC). We analyzed the coupling factor for commercial LCO batteries, and found the SOC where the coupling factor was maximized. At this SOC, batteries were placed under a mechanical load to harvest energy. The voltage generated was quantified by measuring the voltage drop across a resistor. To understand how the PEC effect operates in multiple batteries, we wired cells in series and parallel, and performed similar mechanical load experiments. As expected, the PEC voltage can be increased by compressing batteries in series. Increasing the PEC voltage generated would allow the effect to be used in practical applications such as micro-energy devices.

References:

[1] J. Cannarella and C. B. Arnold, “Toward Low-Frequency Mechanical Energy Harvesting Using Energy-Dense Piezoelectrochemical Materials," Advanced Materials, 27, 7440 (2015).

[2] S. Kim, S. J. Choi, K. Zhao, H. Yang, G. Gobbi, S. Zhang, and J. Li, “Electrochemically driven mechanical energy harvesting," Nature Communications, 7, 10146 (2016).

[3] N. Muralidharan, M. Li, R. E. Carter, N. Galioto, and C. L. Pint, “Ultralow Frequency Electrochemical−Mechanical Strain Energy Harvester Using 2D Black Phosphorus Nanosheets,”

ACS Energy Lett., 2, 1797 (2017).

[4] E. Jacques, G. Lindbergh, D. Zenkert, S. Leijonmarck, and M. H. Kjell, “Piezo-Electrochemical Energy Harvesting with Lithium-Intercalating Carbon Fibers,” ACS Appl. Mater. Interfaces,
7, 13898 (2015).
Use of Lithium Iron Phosphate (LFP) Batteries As Piezoelectrochemical Materials to Increase Low-Frequency Mechanical Energy Harvesting
Authors: Kang SeungYeon , Preimesberger Juliane Irine , Arnold Craig B.
Published: February 2020

Efficient energy harvesting from nonconventional sources is increasingly important these days where energy usage is continuously rising and providing power to newly developed electronic systems require nontraditional power sources. Piezoelectrochemical (PEC) materials undergo a volume change as a result of an electrochemical reaction and can be expected to produce orders of magnitude more energy per volume than conventional piezoelectrics due to the high energy density associated with Faradaic reactions. Through maximizing PEC effect, one may be able to achieve great advancement in the energy harvesting research field. In this work, we utilize off-the-shelf lithium iron phosphate (LFP) battery pouch cells to study and maximize the conversion of mechanical energy to electrochemical energy.

Previously we proposed that stress and voltage are linearly related by a PEC coupling factor, k , which is defined as the change in equilibrium potential Uo of an electrochemical reaction with respect to change in applied stress σ. This factor, k can also be expressed in terms of the mechanical strain ε produced from an electrochemical reaction involving volumetric charge qv which shows that the coupling between stress and voltage is a consequence of the work of mechanical expansion due to the electrochemical motion of charged species. As a result, larger harvested energy density can be associated with high k values and high volumetric capacities and this physically corresponds to materials that exhibit high expansion with flat discharge voltage curves. We choose LFP batteries that have flat voltage curves to experimentally demonstrate the concept of mechanical energy harvesting through the piezoelectrochemical coupling. We show that the expansion mostly originating from the graphite anode combined with the flat voltage characteristics of the LFP cathode result in a higher energy yield.
Failure Analysis of the Rechargeable Porous Zinc Electrode in Alkaline Electrolyte
Authors: D'Ambrose Michael , Yadav Gautam Ganapati , Turney Damon , Gallaway Joshua W , Nyce Michael , Messinger Robert J. , Banerjee Sanjoy
Published: February 2020

Metallic zinc (Zn) is an attractive negative electrode material for rechargeable batteries because it is a non-toxic, earth abundant metal. It has a low equilibrium potential of -1.35 V vs. mercury-mercuric oxide (Hg/HgO) in concentrated alkaline electrolyte and a high gravimetric discharge capacity of 820 mAh/g. During discharge, Zn oxidizes and forms a dissolved complex known as the zincate ion, Zn(OH)4
2-, from which zinc oxide (ZnO) precipitates as a solid. On charge, Zn(OH)4
2- is reduced to metallic Zn. Motivation to study the Zn electrode in rechargeable batteries is driven by a target overall battery energy density of 200 Wh/L that is sustainable for 500 or more charge-discharge cycles. This corresponds to a Zn electrode discharge density in the range of 650 mAh/mL.

The cycle life of the porous Zn electrode in concentrated alkaline electrolyte is observed to decrease with increasing percentage of discharge capacity of Zn accessed. The percentage of discharge capacity of Zn accessed is known as the depth of discharge (DOD). Zn electrodes were cycled in the range of 1% to 15% Zn DOD in zinc-manganese dioxide (Zn-MnO2) batteries and in the range of 15% to 30% Zn DOD for zinc-nickel (Zn-Ni) batteries. Additives were incorporated into the zinc electrodes for the tests done on Zn-Ni batteries. Additives used were surfactant cetyltrimethylammonium bromide (CTAB), bismuth oxide (Bi2O3), synthetic layered silicate Laponite, and calcium hydroxide (Ca(OH)2). The potential values of the Zn electrodes vs. Hg/HgO reference electrodes were recorded.

During healthy galvanostatic discharge, Zn electrodes displayed a nearly constant potential vs. Hg/HgO at approximately -1.35 V. Tests that failed due to Zn exhibited a shift from this equilibrium potential that corresponded to a loss of cell voltage. This shift may be attributed to concentration overpotential as ZnO is precipitated, thereby inhibiting the hydroxide ions from reaching the reacting metal interface. The shift may also be due to formation of a passivated layer on the electrode which effectively blocks the remaining active material. There are generally two regimes observed in the potential curves of the Zn electrode vs. Hg/HgO prior to cell failure. Beyond the healthy plateau at -1.35 V, the first regime consists of a sloping potential while the second regime is an additional plateau. The second plateau shifts with increasing cycle number and corresponds to cell death. See the attached figure for discharge curves of a Zn electrode cycled at 5% Zn DOD. The second plateau is believed to be due to passivation of the Zn electrode. The additives were observed to modify the discharge potential curve of the Zn electrode vs. Hg/HgO.

Figure 1
Improved Photovoltaic Performances of Quasi-Solid Photoelectrochemical Solar Cells By Mitigating Charge Recombination Rate at Electrolyte and Photoanode Interface
Authors: Kim So-Eun , Kang Bo-Sung , Lee Ji-Eun , Song Hyeon-Bee , Kang Moon-Sung
Published: February 2020

There has been much attention towards dye-sensitized solar cells (DSSCs) for the past decades due to their attractive features such as high energy conversion efficiency and low production cost etc. Recently, cobalt complexes have been suggested as one of the most promising candidates for replacing conventional iodine redox couples owing to their high voltage characteristics. Even though respectable energy efficiency exceeding 12% was reported by employing liquid electrolyte that consists of cobalt complex redox mediator and volatile solvent, the use of volatile liquid solvent cannot ensure the long-term stability of DSSCs. In this work, therefore, novel polymer gel electrolytes (PGEs) including cobalt complexes as redox couples have been prepared for efficient and long-term stable DSSCs. In addition, several ways to mitigate the charge recombination rate at the interface between PGE and photoanode have been systematically investigated. The electron transport properties in mesoporous TiO2 electrodes (i.e. electron lifetime and diffusion coefficients) have been evaluated through IMPS and IMVS analyses. In addition, the photovoltaic performances of DSSCs employing prepared PGEs have been evaluated via the J-V curve measurements and various electrochemical characterizations.

Acknowledgments:

This work was supported by a grant (No.2017000140002/ RE201702218) from the Environmental Industry Advancement Technology Development Project of Korea Environmental Industry & Technology (KEITI) funded by Korea Ministry of Environment (MOE).
Control of Interfacial Properties between Polymer Gel Electrolytes and Counter Electrodes for Efficient Quasi-Solid Photoelectrochemical Solar Cells
Authors: Kim So-Eun , Kang Bo-Sung , Lee Ji-Eun , Song Hyeon-Bee , Kang Moon-Sung
Published: February 2020

There has been much attention towards dye-sensitized solar cells (DSSCs) for the past decades due to their attractive features such as reasonable energy conversion efficiency and low energy production cost. Recently, cobalt complexes have been suggested as one of the most promising candidates for replacing conventional iodine redox shuttles owing to their high voltage characteristics. Although high energy efficiency exceeding 12% was reported by employing liquid electrolyte that consists of cobalt complex redox mediator and volatile solvent, the use of volatile liquid solvent cannot ensure the long-term stability of DSSCs. In this work, therefore, novel polymer gel electrolytes (PGEs) including cobalt complexes as redox couples have been developed for efficient and long-term stable DSSCs. The physicochemical properties of PGEs were adjusted by selecting proper solvent and functional additives (for improving cobalt complex solubility and cation transference number etc.). Polyethers with polar groups (e.g. PEO and PMO) and polymers without polar groups (e.g. PVdF-HFP) were used as the polymer additives for the gelation of the liquid electrolytes with various blending ratios. Especially, various organic solvents with relatively high boiling points were tested to prepare long-term stable polymer gel electrolytes containing cobalt complex redox shuttles. Solvents with high donor number induced significant dissolution of dyes attached on TiO2 and therefore the low volatile solvents with moderate donor number and dielectric constant were utilized in this work. DSSCs employing PGEs with cobalt redox couples also showed better long-term stability compared with those of DSSCs filled with liquid electrolytes at 50 oC for 700 h. In addition, several types of conjugated polymer based counter electrodes have been prepared and used for the fabrication of DSSCs to decrease the high charge transport resistance occurred between the PGE and counter electrode. The photovoltaic and electrochemical performances of the DSSCs have been systematically analyzed via the J-V curve measurement and various electrochemical characterizations such as EIS and CV analyses.

Acknowledgments:

This work was supported by a grant (No.2017000140002/ RE201702218) from the Environmental Industry Advancement Technology Development Project of Korea Environmental Industry & Technology (KEITI) funded by Korea Ministry of Environment (MOE).
La, Rb and Ba Additions on the Effect of Oxygen Reduction in Molten Alkali Carbonates
Authors: Lee Choong-Gon , Koomson Samuel
Published: February 2020

The effects of La, Rb and Ba additions to (Li+Na)2CO3 electrolyte were investigated using a half-cell and a coin-type MCFC. The effect of La and Rb on oxygen reduction on a gold electrode in a (Li+Na)2CO3 melt at 650oC were examined using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CD
0.5 values determined from CV and EIS were not comparable. The addition of 0.5 mol% of La2O3 to (Li + Na)2CO3 showed a remarkable increase in CD
0.5 values determined by both EIS and CV analyses. The effect of La and Rb on cell performance of coin cells using (Li+Na)2CO3 as electrolyte and operated at 650oC were examined using I-V curve. The total voltage loss was decreased by 13% when 0.5 mol% of La2O3 was added to (Li + Na)2CO3 electrolyte but was decreased by 9% when 3 mol% of Rb2CO3 was added to (Li + Na)2CO3.
Fabrication and Performance of Supercapacitor Devices Using Binder-Free CNT Electrodes
Authors: Brahim Sean , Zhang Sanliang , Maat Stefan
Published: February 2020

Electric double layer capacitors (EDLCs) are a category of supercapacitors that generally compliment the performance of batteries through delivery of high power with significantly longer cycle life. The conventional active electrode material utilized in these EDLCs is activated carbon (AC) possessing high surface area through templated porosity. However, one of the primary limitations with AC-based supercapacitors using organic electrolytes is the operational voltage maximum around 2.75 V. Operation at higher voltages that push the 2.75 V barrier is the next essential developmental breakthrough to enable significant boosts to both energy and power densities of supercapacitors. Research into alternative active electrode materials is equally critical to enable and support high voltage operation of supercapacitors. This work demonstrates the fabrication of carbon nanotube (CNT) electrodes from organic-based dispersions without the inclusion of surfactant or binder, and subsequent assembly into supercapacitor devices. The performance of pouch cells assembled from the CNT electrodes and using conventional organic electrolytes at operating voltages ≥ 2.7 V is discussed. A significant and linear voltage dependence of capacitance (~ 3 times higher than AC) was observed for cells with CNT electrodes up to operational voltages ~ 3.5 V, which are currently not achievable using AC-based cells. Repeatable charge-discharge operation of the CNT-based EDLCs was demonstrated at 3.5 V and 70°C, with consequential increase to capacitance by ~ 25 - 30 % compared to 2.7 V operation. Power and energy densities were increased by 1.5 and 2 times respectively at 3.5 V compared to operation at 2.7 V. The performance characteristics from such CNT-based pouch cells were benchmarked against commercial-grade AC supercapacitor devices using organic electrolytes and rated at 2.75 V (single cell). Long-term performance advantages were observed for the CNT-based monocells at 3.5 V and 70°C, which passed 100k cycling tests at full discharge. Under the same test conditions, commercial AC-based cells failed early during the 100k cycling. Response times approaching 2 ms (at -45° phase angle) were also demonstrated with EDLC devices using thin CNT electrodes with 1 mF capacitance. Such EDLC devices may potentially rival aluminum electrolytic capacitors (AECs) for alternating current line-filtering applications, offering significant space savings compared to the bulky AEC components. Finally, the scalable fabrication of binder-free CNT electrodes from surfactant-free dispersion of the material was demonstrated by roll-to-roll, slot-die coating onto an Al foil current collector. The processing of these conformal CNT coatings, assembly into 18650 cylindrical cells, and the resulting EDLC performance characteristics are discussed. The CNT-based 18650 cells had an average capacitance of 7 F at 2.7 V, with low average ESR of 7 mΩ at 1 kHz, and average response time of 120 ms at -45° phase angle.

Figure 1
Effects of Electrode Wettability on Discharge Capacity Li-O2 Batteries
Authors: Wang Fangzhou , Li Xianglin
Published: February 2020

Three kinds of customized electrodes with various wettability are fabricated in this study. Results show that electrodes containing polyvinylidene fluoride (PVDF) binder are lyophilic while the binder of polytetrafluoroethylene (PTFE) results in the lyophobicity of electrodes. The electrode with mixed wettability is composed of two lyophobic carbon coatings on top and bottom and one lyophilic carbon coating in the middle. The intermittent current (1.0 – 0 mA/cm2) strategy indicates resting Li-O2 batteries (for 10 min) between each discharge (for 5 min) to improve the oxygen transfer within the porous electrode. The lyophilic electrode has the highest increase rate of discharge capacity after applying intermittent current while the electrode with mixed wettability achieves the highest specific discharge capacity. The specific discharge capacity of the PVDF 15% electrode is 1664.8 ± 259.6 mAh/g at intermittent current but it is only 807.6 ± 137.6 mAh/g at continuous 1.0 mA/cm2. The discharge capacity is improved by 106.2%. The specific discharge capacity of Li-O2 battery with mixed binders increases from 1645.9 ± 98.3 mAh/g to 2256.7 ± 225.8 mAh/g when the operation changes from continuous discharge current to intermittent discharge current. The intermittent discharge strategy is optimized based on the mixed wettability electrode and results show that discharging at 1.0 mA/cm2 for 5 min and resting for 5 min periodically achieves highest discharge capacity. This study emphasizes that the lyophobicity of electrode and intermittent discharge strategy can both enhance the O2 diffusion and thus increase the discharge capacity of Li-O2 batteries.
Study of Portland Cement Based Materials with Addiction from Cactus Opuntia Ficus-indica
Authors: Díaz Blanco Yohandry , Uruchurtu Jorge , Menchaca Carmina
Published: February 2020

Reinforcing Steel bars corrosion is one of the most common causes of reinforced concrete structures deterioration. Steel rebars are protected against corrosion by both chemical and physical mechanisms. The chemical protection is provided by the concrete high pH (12–13), which promotes the formation of a passive film on the steel surface. On the other hand, concrete acts as a physical barrier, hindering the access of aggressive agents. With the main aim of extending useful life of the structures and reducing the corrosive process in concrete, currently many investigations focus on the use of organic materials to analyze the electrochemical and mechanical behavior of concrete. For centuries, the use of cactus (Nopal) and its properties had special relevance in the economic, social and religious life of ancient civilizations. Currently, the mixture of cactus mucilage and lime is used as a layer to protect or repair historic buildings in Mexico.The main aim of this work is to analyze the electrochemical and mechanical behavior of Portland cement mixtures with cactus mucilage as a substitute for water. Three concentrations of cactus mucilage, 1:1, 1:2 and 1:3 ratios in cactus-water by weight were obtained. Concrete mixture was designed with a characteristic strength of f'c = 250 kg/cm2, Portland cement CPC 30R, coarse aggregate with a maximum size of 20 mm and river sand as fine aggregate. The proportions of mixtures were designed for a mucilage/cement ratio of 0.45. Each specimen contained three corrugated steel bars grade 42 of 3/8 inch. Samples were placed in a 3% sodium chloride solution after 28 days simulating an aggressive environment such as seawater and there were evaluated for 245 days through different electrochemical techniques. Half-cell potential is one of the most used techniques to analyze corrosion in concrete. Noble potential values were obtained for all samples with cactus mucilage compared to the control sample; calomel saturated electrode (CSE) was used. The electrochemical noise (EN) technique was performed using three nominally identical steel electrodes; noise resistance values and localization index for each sample were obtained. Linear polarization resistance (LPR) is a non-destructive technique, which provides information about the kinetics of corrosion in concrete. The samples with cactus mucilage after 245 days maintained values of corrosion rate close to 0.1 μA/cm2, remaining in the negligible corrosion rate interval while the control sample reached a value of 0.5 μA/cm2 close to the high corrosion rate interval. The compression strength technique was performed after 28 days of concrete curing. The samples with 1:3 concentration of cactus mucilage reached a resistance of 97.6% with respect to the control sample.
Correlating the Microstructure and Surface Morphology of Additively Manufactured 304L Series Stainless Steel to Its Corrosion Response
Authors: Melia Michael Anthony , Schaller Rebecca Filardo , Nguyen Hai-Duy , Taylor Jason Mark , Rodelas Jeffrey , Schindelholz Eric John
Published: February 2020

In recent years a desire to rapidly prototype complex metallic parts has driven the advancement of metal additive manufacturing (AM). Powder bed selective laser melting (SLM) and laser engineered net shape (LENS) have emerged as prevalent techniques for producing a wide range of complex metal components. That said, the non-equilibrium processes associated with SLM and LENS techniques lead to microstructural heterogeneity and irregular surface structures throughout components, which can be cause for corrosion behavior considerably different from conventionally processed materials. This presentation will investigate and compare the corrosion behavior of 304L stainless steel produced by the SLM and LENS processes. An emphasis will be on how the heterogeneous microstructures of the AM components influence breakdown of passivity and repassivation in aqueous solutions. The impact of surface treatments, such as laser surface modification, have on AM component roughness and subsequently the corrosion response will be explored.
Electrochemical Behavior of Inconel 800 and Waspaloy with Application in Aeronautical Industry
Authors: Rocha Reséndez Rodolfo , Cabral José Angel , Samaniego Gamez Oliver P. , Diaz Joel , Estupiñan-Lopez Francisco , Tiburcio Citlalli Gaona , Almeraya Facundo
Published: February 2020

Superalloys are highly used materials in the aeronautical industry because they have excellent mechanical strength, creep resistance at high temperatures, good surface stability, corrosion resistance and oxidation. In the present work, the corrosion resistance in superalloys, such as INCONEL 800 and Waspaloy, are investigated, which are Fe and Ni base alloys respectively. The electrochemical tests were polarization linear resistance (PLR) and electrochemical noise (EN), in order to determine the corrosion rate and the corrosion mechanism. Samples of 1 cm2 of area were taken per material, being evaluated in three different media: water (H2O), sodium chloride (NaCl) and sulfuric acid (H2SO4) at two different temperatures of 25 and 60 ° C. The results show that superalloys are susceptible to higher corrosion rates as the temperature of the test increases.
Luminescence Properties of Porous Silicon Influenced By Magnetic Metal Filling
Authors: Granitzer Petra , Rumpf Klemens , Poelt Peter , Reissner Michael
Published: February 2020

In this work the influence of magnetic metal filling on the photoluminescence of luminescent porous silicon is presented. The metal deposits affect the optical properties but also give rise to specific magnetic behavior. Due to the metal filling of the porous silicon the photoluminescence is blue-shifted and furthermore an increase of the intensity is observed. The influence of the magnetic metal filling on the optical properties (photoluminescence, decay time) is discussed and the magnetic characterization of the nanocomposits is presented.

First the optical properties of the luminescent PSi are investigated, second Ni is deposited within the porous silicon samples and subsequently the nanocomposite specimens are characterized optically again and also magnetically. The samples are structurally characterized by SEM, EDX and TEM.

The optical properties are investigated with respect to the shift of the photoluminescence and their decay times due to the metal filling. Photoluminescence spectra of bare PSi show a maximum around 620 nm whereas in the case of Ni filled samples the peak is blue-shifted to around 580 nm and the luminescence intensity is increased.

Concerning the magnetic properties of the nanocomposite the embedded Ni structures can be superparamagnetic from the size of the pore diameters but due to the branched morphology the achieved deposits tend to be interconnected and thus do not offer necessarily a superparamagnetic behavior. Also temperature dependent magnetization measurements give no hint for superparamagnetism. Field dependent magnetization measurements performed with the magnetic field applied perpendicular and parallel to the sample surface show a high magnetic anisotropy. It can be clearly seen that the samples offer a film-like behavior due to the interconnected Ni structures which is represented by the easy axis parallel to the surface. In the frame of this work the optical characterization of luminescent PSi with respect to its photoluminescence compared with Ni filled samples is discussed in detail as well as the corresponding magnetic properties of the nanocomposites. Furthermore the influence of an external magnetic field on the optical properties is elucidated. The presented systems are promising candidates for applications in optoelectronics and also for magneto optical integrated devices.
Influence of Li+ on the Compact and Porous Anodizing of Ti: Achieving Porous Anodizing Conditions Just By the Addition of Li+ Ion
Authors: Dick Luís Frederico Pinheiro , Allongue Philippe , Knörnschild Gerhard , Maltez Rogerio Luis , Valente Renato Castro , Peñafiel-Castro Jhon Alexander , Meneses Carolina Remedi
Published: February 2020

The incorporation of foreign atoms in trace amounts modifies electronic properties and spectral response by the so-called band gap engineering
1. Among different dopants, the incorporation of Li+ cations into TiO2 is important for expanding the oxide’s technological applications. Li+ and H+ doping of TiO2 was carried out using electrochemical processes or salt impregnation, which improved solar to electricity efficiency of Dye Sensitized Solar cells and Perovskite solar cells (where a TiO2 layer is used as electronic transporting layer), as well as photocatalytic performance 2-3. Thermochemical treatments, N and V doping by standard ion implantation or Ag doping by metal plasma ion implantation was also reported 4-6.

We recently reported 7 that Li+ is incorporated in the bulk of compact TiO2 layers during the anodization of Ti in lithium perchlorate (LiClO4), moving in the opposite direction expected for a cation under the applied electric field. Using Elastic Recoil Detection Analysis (ERDA) we observed that Li+ is accumulated in the form of more or less flat concentration profile along the thickness of compact layer (Fig. 1). Moreover, cell voltage profiles are strongly affected when Li+ is added to the electrolyte independent of anion of the salt. When the Li+ concentration is increased from 0.1 M to 0.5 M by addition of perchlorate or nitrate, the cell voltage transient changes from a curve typical for a compact anodizing with sparking to that of porous anodizing (Fig. 2). This transient change and the fact that the potential plateau during anodizing decreases as [Li+] is increased indicates that Li+ incorporation into the oxide greatly increases ionic conductivity and Ti oxide dissolution. Preliminary results show that a thick irregular tubular oxide structure is formed. The direct incorporation of Li+ into tubular TiO2 during its formation opens new possibilities for techniques of tubular oxide preparation. A mechanism for Li incorporation against the electric field is presented, as well as for the enhanced oxide dissolution.

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7. J. A. Penafiel-Castro, B. Hahn, R. L. Maltez, G. Knornschild, P. Allongue, and L. F. P. Dick, Chemical Communications , 2018, 54, 3251-3254.

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Turning Nano Porous Aluminium Black: An in Situ High-Energy X-Ray Diffraction and X-Ray Fluorescence Study
Authors: Vinogradov Nikolay , Linpe Weronica , Harlow Gary Steven , Evertsson Jonas , Drnec Jakub , Lundgren Edvin
Published: February 2020

Anodized aluminum, commonly used everyday applications, is effectively coloured by electro chemical deposition of materials into the nano-porous anodized aluminum oxide (NP-AAO). The colouring process is sensitive to the details of the nano-porous structure, and increased knowledge is essential to increase the effectiveness of the process to prevent cost, time and environmental losses.

To study the electro deposition of material into nano-scale objects and coloring as it happens in a harsh electrolyte is notoriously difficult. As a consequence, knowledge about the coloring process has been obtained from time consuming ex-situ studies, in which the composition of the sample may change upon exposure to ambient environments.

We have recently performed in situ studies of the formation of ordered NP-AAO using Grazing Transmission Small Angle X-ray Scattering (GTSAXS) [1].

The small x-ray beams produced by modern synchrotron radiation facilities provides the means for non-intrusive X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) on a micron and sub-micron scale, allowing for high temporal and spatial resolution as the coloring process is occurring. In the present study, we have used micro XRD and XRF to study the electro deposition of Sn into the NP-AAO. An X-ray beam of 5 microns and an energy of 70 keV was used to penetrate the electrolyte and focused on the 20 micron thick layer of NP-AAO. Prior to deposition, the anodized alumina was pre-treated electrochemically in situ using a selected number of chemical procedures. The Sn deposition, which colours the aluminum black, was followed by XRF and initiates at the pore bottom and crystalizes as Sn metal nanowires along the pore height according to XRD.

References:

[1] N. A. Vinogradov, G. S. Harlow , F. Carlà, J. Evertsson, L. Rullik, W. Linpé, R. Felici and E. Lundgren, ACS Appl. Nano Mater. In Press. DOI: 10.1021/acsanm.7b00303

Figure 1
Mechanism of Tarnishing of Silver Alloys Under Sulphide
Authors: Ortiz-Corona Janette , Larios-Duran Erika Roxana , Rodriguez-Gomez Francisco Javier
Published: February 2020

Silver and silver alloys is subject of corrosion in environments that contain sulphide (H2S). Thus, become tarnished and a blackish thin film is formed on the metallic surface. This problem is very important in the field of corrosion and conservation. Currently, there is growing attention in the study about tarnishing process in silver alloys, which allows supporting decision-making in the conservation of silver artefacts. However, previous works focused on the corrosion mechanisms and surface treatments of pure silver, more than on silver alloys.

This work investigates the corrosion mechanism on the tarnishing of silver alloys in a 0.07% v/v ammonium sulphide solution as an accelerator of the tarnishing process for 48 h. The Electrochemical Impedance Spectroscopy (EIS) and Scanning Electron Microscopy (SEM) are used as analysis techniques. The impedance measurements reveal that the copper content at the alloy modifies the kinetic of silver tarnishing. On the basis of experimental results, a reaction model for the tarnishing process of silver alloys in sulphide media is proposed. The reaction mechanism is depicted as that of silver modified by the copper content.
Influence of Uniaxial Deformation on Surface Morphology and Corrosion Performance of Trivalent Chromium Based Coatings for Packaging Steels
Authors: Whiteside Jordan William James , McMurray Hamilton Neil , de Vooys Arnoud C.A.
Published: February 2020

The packaging steel industry has many products for the consumer market which are deformed to a required shape. Products produced in this way undergo different types of deformation, including uniaxial, biaxial and plane strain. In a situation where the steel is coated and then deformed, the coating must still offer a substantial level of protection for inhibiting corrosion.

An In Situ scanning kelvin probe (SKP) experiment was used to investigate the kinetics of organic coating disbondment on uniaxially deformed trivalent chromium coated steel. The studied material was a model trivalent chromium coated steel prototype, designed for over coatings with a lacquer or polymer laminate. The samples were uniaxially deformed to 5%, 10%, 20%, 25% strain using a Hounsfield/Tinius Olsen tensile tester prior to any further experimentation. The strain percentages selected corresponded to the yield point elongation zone, strain-hardening zone and early and late necking zones respectably. A model Poly(vinyl) butyral (PVB) coating was applied to the uniaxially deformed samples. A defect was created in the PVB coating and the sample exposed to aqueous sodium chloride electrolyte in 95% relative humidity. The disbondment kinetics of the polymer overcoat were measured every hour using the SKP, for up to 120 hours.

The disbondment kinetics have been quantified as a plot of distance (µm) vs time (tdel− ti), see Figure 1. The linear plots suggest as the strain percentage is increased the distance of delamination over a 24 hour period increases. Scanning electron microscope (SEM) images, shown in Figure 2, display cracking of the trivalent chromium coating. The availability of the underlying iron is estimated by studying the surface controlled hydrogen evolution curves. Increasing the uniaxial strain produced higher values for hydrogen evolution.

It is proposed that the increase in hydrogen evolution levels can be related to an increase in the exposure of iron caused by the cracking formations found on the surface. The cracking shown on the surface of the trivalent chromium coated steel (Figure 2) is also suggested to cause the increase in cathodic disbondment rates found during the SKP investigations. Cracking of the surface and exposure of iron is suggested to allow for a continuous cathodic front, causing an ingress of electrolyte underneath the PVB model coating. This investigation displays a link between surface cracking, caused by deformation, and the delamination rates of organic coatings on trivalent chromium coated steels.

Figure 1
Electrochemical Evaluation of Steel-Concrete Interaction after Application of Curing with SiO2-Based Nanoparticles
Authors: Esquivel Aldrhyn Miguel , Fajardo Gerardo , Acosta Andres
Published: February 2020

The present work shows the progress of an ongoing research where, the influence of SiO2 –based nanoparticles (Nbs) ingress into hardened concrete specimens through the curing on the electrochemical behaviour of concrete-steel system was evaluated. For this, prismatic specimens of reinforced concrete were fabricated with two w/b ratios: 0.3 and 0.7. A suspension of 0.1 and 0.3% (by weight) of Nbs in water was applied during curing of specimens in periods of 1, 3 or 7 days.

Then, samples were separated in two different environments for at least 28 days: immersion in tap water and in laboratory conditions. Subsequently, specimens were exposed to penetration of chlorides using wetting and drying cycles as a simulation of conditions in a marine environment. The main techniques to evaluate the behaviour of embedded steel in specimens in this period were electrical resistivity, corrosion potential and linear polarization resistance. Also, chloride content and pH values of matrix concrete were assessed several times.

It was found, that the introduction of Nbs in hardened concrete can react with the cement matrix reducing its permeability, therefore, this phenomenon could get a great influence on initiation and propagation corrosion time.
The Role of Nitrate Ions in Repassivation of Crevice Corrosion on Type 316L Stainless Steel
Authors: Aoyama Takahito , Sugawara Yu , Muto Izumi , Hara Nobuyoshi
Published: February 2020

In our previous studies, suppression of crevice corrosion for Type 316L stainless steel was confirmed to occur when the solution outside of the crevice was changed from 1 M NaCl to 1 M NaCl-1 M NaNO3
1. The repassivation inside crevice was thought to be caused by the active to passive transition produced by the increase in pH. The inhibition effect of NO3
- ions was expected to be attributed to increase in pH inside the crevice induced by reduction reaction of NO3
- ions. In this reduction process, there is possibility of the generation of NO2
- and/or NH4
+ ions inside the crevice. In this study, the role of NO3
- ions in the repassivation process for Type 316L was investigated.

A commercial Type 316L stainless steel was used as specimens. The specimens were heat-treated at 1373 K for 3.6 ks and then water-quenched. The specimens were polished down to 1 µm with a diamond paste. After that, ultrasonic cleaning was conducted in ethanol. Anodic polarization measurements were conducted in deaerated acidic 1 M NaCl, 1 M NaCl-0.01 M NaNO2 or 1 M NaCl-0.01 M NH4Cl at 298 K. The pH of the solutions was adjusted to 0.2 with HCl to simulate the solution inside the crevice. The surfaces of the specimen were coated with an epoxy resin, with the exception of the electrode area (ca. 10 × 10 mm). The potential scan rate was 3.8 × 10-4 V s-1 (23 mV min-1). The reference electrode was an Ag/AgCl (3.33 M KCl) electrode. All the potentials cited in this work refer to the Ag/AgCl (3.33 M KCl) electrode.

Figure 1 shows the anodic polarization curves measured in deaerated acidic 1 M NaCl, 1 M NaCl-0.01 M NaNO2 or 1 M NaCl-0.01 M NH4Cl at 298 K. In all the solutions, active and passive regions were observed. In this work, the potential range of which current density indicated over 1.0 A m-2 was defined as an active region. In 1 M NaCl, the active region was from -0.28 to -0.12 V, and the peak current density of the active region was 6.6 A m-2. In 1 M NaCl-0.01 M NaNO2 and 1 M NaCl-0.01 M NH4Cl, the active regions were from -0.26 to -0.20 V and -0.24 to -0.17 V, respectively. These results suggest the active region was narrowed by NO2
- or NH4
+ ions. The negative loop of current in 1 M NaCl-0.01 M NaNO2 was assumed to originate from narrowing the active region. In addition, the anodic peak current densities in 1 M NaCl-0.01 M NaNO2 (1.7 A m-2) and 1 M NaCl-0.01 M NH4Cl (1.3 A m-2) were lower than that in 1 M NaCl.

In addition to above results, in situ observations inside the crevice were performed, and the role of NO3
- ions in the repassivation process for Type 316L was determined.

Reference;

1. T. Aoyama, I. Muto, Y. Sugawara, and N. Hara, ECS Trans., 80(10), 519-526 (2017).

Figure 1