bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transient Potential Induced Dissolution of Metal Biporlar Plates Used in Proton Exchange Membrane Fuel Cell
Authors: Hong Yuan-Yuan , Wang Xian-Zong , Muneshwar Triratna , Cadien Ken , Luo Jing-Li 
Published: May 2020

Corrosion of metallic bipolar plates (BPPs) under the aggressive working conditions is the major issue that impedes its application in proton exchange membrane fuel cells (PEMFCs). Transient potential is generated during the different operating conditions of PEMFCs such as start-up/shut-down(SU/SD), and dynamic loading stages. Transient potential-induced corrosion is a serious problem encountered by BPPs. To investigate the influence of transient potentials on corrosion of BPPs, potential pulses with different amplitudes are applied to specimens. Also, a novel zirconium oxynitride coating is prepared via atomic layer deposition to improve the stability of BPPs.
Results show that transient potentials generated at passive and transpassive potential regions are both detrimental to the stability of BPPs. For the uncoated samples, a larger potential fluctuation in the passive region could induce a much higher frequency of passive film breakdown than that generated by a smaller potential fluctuation during the cyclic pulse tests. In the transpassive region, upon increasing transient potentials, the passive film formed on surface enters the potential dependent dissolution region, leading to severe intergranular corrosion after a certain cycles of pulse tests.
The zirconium oxynitride coated samples present improved performance in both normal potentiostatic polarization and transient potential conditions. The enhanced corrosion resistance of coated samples is attributed to the continuous formation of protective oxide layer which has a wider band gap than passive films formed on uncoated samples. Therefore, the coated sample enters the transpassive potential region at a more positive potential and thus exhibits much lower dissolution rate. Moreover, the Mott-Schottky plots suggests that the defect density of the coated samples is much lower than the uncoated counterpart, and the deterioration of uncoated sample performance under different transient potentials is related to the passive film disorder degree.
From our study, transient potentials would accelerate the degradation of BPPs, and the development of bipolar plates coated with dense protective surface films could help mitigate the dissolution induced by the transient potentials, thus improving stability and durability of BPPs. Specially, a layer of coating with a wider band gap between Fermi level and valance band is beneficial to reduce the dissolution in the transpassive potential region.
A Phase-Field Model Study of Microstructural Effects on the Corrosion of Mg Alloys
Authors: Montiel David , DeWitt Stephen , Chadwick Alexander F. , Thornton Katsuyo 
Published: May 2020

Understanding how alloy composition and thermal history determine the corrosion behavior is crucial to designing alloys with lower corrosion rates. We employ a model that combines the phase-field and smoothed boundary methods [1] to investigate the effect of second phases and particles on the corrosion behavior of Mg alloys. In this model, the dissolution rate at the metal/electrolyte interface is determined by the coupling of mass transport within the electrolyte and the Butler-Volmer electrochemical kinetics at the interface. The model is implemented in the PRISMS-PF framework [2,3], an open-source framework for phase-field modeling that employs a matrix-free finite element method. Simulations of corrosion are conducted with varying microstructure and compositions with associated corrosion parameters representative of Mg alloys. Specifically, we show how our approach can describe the experimentally observed microgalvanic effects due to the presence of impurities and second phases. Finally, we show the results of a parametric study of the dependence of the rate for various combination of the corrosion parameters for each phase.
This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering as part of the Center for PRedictive Integrated Structural Materials Science (PRISMS Center) at University of Michigan.
[1] A.F. Chadwick, J.A. Stewart, R.A. Enrique, S. Du, K. Thornton, Numerical Modeling of Localized Corrosion Using Phase-Field and Smoothed Boundary Methods, J. Electrochem. Soc. 165 (2018) C633–C646.
[2] S. DeWitt, S. Rudraraju, D. Montiel, W. B. Andrews, K. Thornton, PRISMS-PF: A General Framework for Phase-Field Modeling with a Matrix-Free Finite Element Method. Submitted to npj Comput. Mater.
[3] http://prisms-center.github.io/phaseField/
Synergism in Tribocorrosion: From Theoretical Approach to Lab Test Outcome on Hard Chromium Replacement
Authors: Georgiou Emmanuel , Celis Jean-Pierre 
Published: May 2020

Tribocorrosion is defined as the study of chemical, electrochemical and mechanical factors on the material degradation in mechanical systems undergoing a relative displacement of the mechanical contacts. The combination of knowledge about corrosion processes and tribological processes does not provide yet sufficiently knowledge on the tribocorrosion mechanisms that can be used industrially. By using various electrochemical methods like open-circuit potential measurements, polarization curves, and EIS measurements, important information are nowadays obtained,on the kinetics of reactions taking place in sliding contacts, as well as on the depassivation/repassivation of protective surface films, and on the interactions between electrochemical reactions and friction.
In this presentation, at first a brief review of the existing modelling of the coupling of tribology and corrosion will be presented, as well as the development of a standard test for the determination of synergism under tribocorrosion.
Then the outcome of following R&D-work initiated as a result of the EU legislation to replace hard chromium, will be presented:
• establishing a methodology to evaluate tribological properties of Ni-P coatings under tribo-corrosive conditions,
• correlating structural characteristics of coatings (grain size, phase distribution, intermetallic formation, particle strengthening) with tribo-corrosive behaviour,
• comparing Ni-P coatings with benchmarks and hard chrome coatings under tribo-corrosive conditions.
In the discussion, a major focus will be given on the aspect of synergism linked to the galvanic coupling generated along sliding tracks immersed in electrolytes.
Pushing the Boundaries of Conversion Coatings with an Unconventional Approach
Authors: Kumar Kuldeep , Bezer Silvia 
Published: May 2020

In the 20th century, the use of steel as the primary construction material for applications such as vehicles, bridges, and buildings led to the development of surface protection by phosphate based conversion coatings. The discovery of anti-corrosion property of phosphatized surfaces can be dated back to 1906 when iron and steel were phosphatized using a phosphoric acid solution. Over time, numerous technical enhancements were achieved in the performance of phosphate coatings such as reduction in process time and temperature and the use of oxidizing agents such as nitrates for accelerated kinetics. However, zinc phosphate is not a universally suitable system; with the current market growth of aluminum alloys and their suitability for lightweight applications, automotive industries are utilizing aluminum alloys (e.g. AA6022) to reduce the vehicle weight to improve fuel efficiency. Interestingly, running aluminum alloys in zinc phosphate baths leads to excessive sludge formation and faster depletion of pretreatment bath. The frequent bath replenishments, increased sludge disposal costs, and new environmental constraints on the usage of phosphorous, nitrates, and nickel compounds in the pretreatment solution, drive the investigation of new technologies based on titanium and zirconium compounds. Zirconium and titanium based coatings offer several advantages over conventional zinc phosphate coatings, e.g. a very thin film thickness (~100 nm), a simpler process, and an environmentally friendly pretreatment solution.
During the formation of conversion coatings, the very top surface of metal alloys undergoes an oxidation reaction (e.g. M → Mn+ + ne‒). This reaction is coupled with the reduction of hydrogen ion in the pretreatment bath (e.g. H+ + e‒ → ½ H2) which leads to a slightly higher pH in the vicinity of metal substrate. If adjusted to suitable conditions, the passivating species are hydrolyzed on the substrate and determines the corrosion and adhesion properties of the alloy surface. The research at PPG Industries focuses on tuning the chemistry of pretreatment solutions, chemical modifications of subsequent layers, and engineering processing conditions which can favor the thermodynamic stability and kinetic growth of coating systems. Besides that, the utility of several analytical tools such as SEM, XPS, XRF and various modes of corrosion testing – cabinet tests, electrochemical tests, and immersion tests – are instrumental in the ongoing research. This presentation will focus on the historical development of conversion coatings, shortcomings in the phosphatized surfaces, processing and mechanism of thin film coatings, and ongoing research at PPG Industries.
Bandgap Engineering of Ge Nanocrystals by Size Controlled Deposition and Doping
Authors: Honeit Florian , Beyer Jan , Heitmann Johannes 
Published: May 2020

Germanium nanocrystals (nc) offer promising properties for different applications in electronics and photonics, like non-volatile memories [1] or photodiodes for the visible or infrared wavelength region [2, 3]. For those applications, a spatially and size controlled synthesis is necessary to enable for example electrical isolation between the nanocrystals or the proper adjustment of the optical bandgap.
Recent work has shown that the material systems Ge/TaZrOx, Ge/SiO2 and Ge/TaZrOx/SiO2 fulfil these requirements. To form size controlled nc, a Ge rich oxide layer like SiO2 or TaZrOx and pure oxide layer are deposited alternatingly via co-sputtering. Subsequent rapid thermal annealing forms the Ge nc by phase separation and crystallization. During the annealing process the pure TaZrOx interlayers act as a diffusion barrier for Ge, so these nc are confined to the thickness of the deposited mixed layer. The addition of a pure SiO2 interlayer leads to enlarged nc size by growth of the nc into the SiO2 layer. The use of an additional SiO2 layer has the further advantage of improved lateral nc separation in comparison to structures without the SiO2 interlayers. This leads to an improved electrical isolation of each nc. Still the bandgap of these nc can be adjusted easily by their size due to the quantum confinement effect.
Another advantage of Ge is the full compatibility to Si based processes. However, both Si and Ge has an indirect band gap, so the efficiency of e.g. light emitting diodes is low. The fabrication of Sn containing Ge can lead to a direct bandgap [4]. In our work we show the formation of Sn doped Ge nc in TaZrOx and SiO2, to create nc of controlled size. Our focus is the crystallization process of the nc, to avoid formation of pure Sn crystals, but still achieve a complete separation of the Ge-Sn alloy from the oxides. Samples with different Sn concentrations are annealed in a range of 500 °C to 800 °C and checked by Raman scattering and TEM. Furthermore, the influence of the used oxide on the nc crystallization temperature is investigated.
[1] Tiwari, S. Appl. Phys. Lett. 1996, 69, 1232
[2] Haas, S. J. Appl. Phys. 2013, 113, 44303
[3] Lehninger et al. Phys
.
Stat. Sol. (a), 2018, 155, 1701028
[4] Slav, A. et al. ACS Appl.NanoMater. 2019, 2, 3626−3635
Single Nanocrystals Studies of Upconverting Nanoparticles
Authors: Krajnik Bartosz , Holodnik Katarzyna , Noculak Agnieszka , Golacki Lukasz , Kostiv Uliana , Horak Daniel , Podhorodecki Artur 
Published: May 2020

Upconverting nanocrystals (UCNC) such as NaYF4:Er3+, Yb3+ have been recently a subject of intensive investigation due to their unique optical properties and high potential in applications in biology and medicine as multifunctional diagnostic probes. Despite the level of attention paid to this material, their very low emission quantum yield is still an important problem excluding them from clinical applications. Thus, understanding of UCNC emission intensity limitation together with a development in growth protocols are crucial challenges to bring these materials to clinical practice. One of the main obstacles, which slowdown the progress in this field, is the complicity of the emission quantum yield measurements. Moreover, even the relative emission intensity measurements (from sample to sample), became a very challenging experiment in case of UCNC. These two difficulties make the optimization of growth process and understanding of experimental data very challenging tasks.
In this paper, we will discuss the influence of relative ions concentration, size and the shape of UCNC on their optical properties. We will also show our results obtained for a single UCNC, measured however in the wide field mode giving also the possibility of statistical analysis of UCNC properties. These results will include both the optical imaging as well spectroscopic data. With these results we will show, that this type of experiment enables to measure the relative UCNC emission intensity from sample to sample, what allows for optimization of nanocrystals growth as well as enables to understand the physical limitation of UCNC emission intensity. In particular, we will investigate the effects of Yb3+ ions clustering and its impact on NaYF4:Yb3+, Er3+ UCNC emission intensity. We will also support our conclusions with numerical data.
Based on our results we will explain the influence of Yb3+ concentration on optical properties of UCNC in details. Moreover, based on obtained experimental and numerical results we will explain the existence of optimal Yb3+ concentration in UCNC often reported in the literature.
Thermally Stimulated Evolution of Optical and Structural Properties of Germanium-Doped Alumina Films
Authors: Khomenkova Larysa , Makasheva Kremena , Petrik Peter , Bonafos Caroline , Ratel-Ramond Nicolas , Melnichuk Oleksandr , Melnichuk Lyudmyla , Balberg I. , Gourbilleau Fabrice , Korsunska N. 
Published: May 2020

Group IV semiconductor nanoclusters/nanocrystals attract a great interest because of substantial transformation of their optical, electrical and luminescent properties due to quantum confinement effects. During last decades significant attention was paid to the Si nanocrystals (ncs) embedded in Si oxide or nitride, and later, to the Ge-ncs embedded in these matrices. The mechanism of these 'ncs' formation was investigated in details.
Recently we have reported on the Si-ncs formation in hafnia and alumina thin films. This work will present the results obtained for the Ge-rich Al2O3 films. The effect of Ge content and annealing conditions on the evolution of optical and structural properties of these materials and formation of Ge-ncs will be addressed.
The films with different Ge content were grown on quarts substrates by magnetron co-sputtering of Ge and Al2O3 targets in argon plasma. After deposition, they were annealed in nitrogen atmosphere and analyzed by means of spectroscopic ellipsometry, FTIR, Raman scattering, XRD and photoluminescence methods. It is observed that suitable thermal treatment leads to the decomposition of nonstoichiometric films and results in the Ge-ncs formation. The formation of Ge-ncs via phase separantion requires lower temperatures (600-700°C) than that for Si-ncs production in alumina host (1050-1100ºC). An annealing at 800-950ºC results in the Ge out-diffusion from the films via formation of volatile GeO. This process results in the significant depletion of the near-surface regions in germanium that was confirmed by an appearance of gradient in the refractive index via film volume.
Decomposition process stimulates also an appearance of visible and near-infrared photoluminescence. The shape of luminescent spectrum depends significantly on both Ge content and the excitation wavelength. It is observed that exciton recombination inside nanocrystals dominates at longer wavelength excitation, whereas the UV-blue excitation results in the radiative recombination via interface or host defects in the materials. This result was found to be caused by the competition of different radiative channels in the films. The evolution of optical and luminescent properties will be discussed in details.
Extreme Fast Charging: The Current State of Understanding
Authors: Tanim Tanvir R , Dufek Eric J. , Kim Sangwook , Evans Michael C , Dickerson Charles C 
Published: May 2020

Enabling fast charging between 10 to 15 minutes has been identified as one of the key challenges to facilitate rapid penetration of battery electric vehicles in the mass market. 1,2 Fast charging in 10 to 15-minute, however, could create multiple performance and safety consequences for the conventional graphite-based lithium ion batteries. Our earlier studies have identified the key bottlenecks of enabling extreme fast charging for a low loading (⁓2 mAhcm-2) cell (high power design).3–5

This presentation will discuss the effects of extreme fast charging on moderate loading cells (⁓3 mAhcm-2). The key cell limitations during such high rate charging will be revisited for moderately loaded graphite/NMC532 single layer pouch cells. The long-term performance and aging issues for 4C to 6C charging rates will be shown with experimental data. The identified dominating aging mechanisms will also be presented for the two different fast charging rates.
The benefits of using different charging protocols, e.g., constant current- constant voltage and several multistep charging protocols will also be shown. Lastly, the opportunities and challenges of Li plating detection via electrochemical means will also be discussed.
References
1. Howell et al., D. Enabling Extreme Fast Charging: A Technology Gap Assessment.
2. Ahmed, S. et al. Enabling fast charging – A battery technology gap assessment. J. Power Sources
367, 250–262 (2017).
3. Tanim, T. R. Extreme Fast Charging of Lithium-Ion Battery: Understanding Bottlenecks and Safety Issues. (2019).
4. Tanim, T. et al. Extreme Fast Charge Challenges for Lthium-Ion Battery: Variability and Positive Electrode Issues. J. Electrochem. Soc.
166, A1926–A1938 (2019).
5. Colclasure, A. et al. Electrode scale and eletrolyte effects on extreme fast charging of lithium-ion cells. J. Electrochem. Soc.
submitted, (2019).
(Invited) Operando Optical Monitoring of Nanoparticle Electrodeposition
Authors: Lemineur Jean-François , Noël Jean-Marc , Combellas Catherine , Kanoufi Frederic 
Published: May 2020

Electrodes, made of nanoparticles (NPs), are key components in electrochemistry to store and convert energy. The nanometer scale allows exalting surface properties and revealing, in addition to the composition, the importance of size, shape and NP organization on the kinetic and thermodynamic performance of devices. Therefore, the use of ultra-small objects and the study of their formation and reactivity appear as one of the best ways to meet the current energy challenges.
Herein, electrodeposition, one of the most popular electrochemical methods for producing nanostructured electrodes, is coupled to an ultra-sensitive interferometric microscopy technique to probe operando the heterogeneity of electrochemical processes at the single NP level. The strategy is illustrated through the monitoring of the electrochemical growth of individual silver NPs, whose sizes can be tracked dynamically down to 10 nm in diameter. Optical images are further used to quantify the presence of metal nanoclusters at the early stages of the electrodeposition and to highlight galvanic reactions occurring between NPs with distinct surface free energies.
As interferometric microscopy relies on refractive index changes, the technique can be applied to many kinds of nanomaterials and electrochemical experiments. For example, the optical coupling has proved to be useful for studying NP transformation.
Figure. Schematic representation of the coupling and same location microscopy experiment with a scanning electron microscope.
J.-F. Lemineur, J.-M. Noël, C. Combellas, D. Ausserré, F. Kanoufi. Angew. Chem. Int. Ed., 2018, 57,11998-12002.
J.-F. Lemineur, J.-M. Noël, C. Combellas, D. Ausserré, F. Kanoufi. Faraday. Discuss., 2018, 210, 381-395.

Figure 1
(Invited) Molecular Models for Electrodeposition Inhibitors, Suppressors, and Anti-Suppressors
Authors: Gewirth Andrew A. , Schmitt Kevin Gary , Rooney Ryan , Schmidt Ralf , Bandas-Rivera Christopher 
Published: May 2020

We evaluate the effect of chain length for a series of alkyl sulfonic acid additives on Cu electrodeposition by using a combination of electrochemical and Raman spectroscopic methods. The combination of these methods suggests that effective Cu electrodeposition acceleration processes require: 1) direct tethering of mercaptoalkylsulfonate species to the electrode, 2) partial desolvation of Cu2+ by the sulfonate group to minimize its solvent reorganization energy, and 3) stabilization of Cu+ adjacent to the electrode surface by addition of halide. Finally, we use the cis-trans ratio idea developed for SPS to examine the effect of inhibitors on SPS activity.
We also investigate the behavior of Cu plating bath suppressor additives poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) using normal Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS), and electrochemical quartz crystal microbalance (QCM) measurements. Raman and SERS show a clear spectroscopic trend of increased intensity in higher wavenumber modes in the CH stretching region as the environment is changed from pure material to solution to surface for both PEG and PPG. The spectral changes associated with PEG are larger than those associated with PPG, suggesting that the relatively more hydrophilic PEG undergoes more conformational changes upon surface association relative to the more hydrophobic PPG. In the presence of Cl-, PPG forms a denser surface layer compared to PEG on a Cu underpotential deposition (UPD) layer on Au. These differences are consistent with the increased hydrophobicity of PPG relative to PEG.