bluuebunny/crossref_metadata_2025 huggingface dataset:
Cyclic Voltammetry of Ge and Te in Basic Conditions: An Investigation of Surface Coverages.
Authors: Sisk Peter W , Stickney John Lewellen
Published: February 2020

Cyclic Voltammetry of Ge and Te precursors in basic solution can lead to a better understanding of the surface limited reactions taking place at the substrate-solution interface. GeTe is a phase-change chalcogenide material with excellent stability for the crystalline and amorphous phases. The stoichiometry of the film is very important as the 1:1 compound is shown to have the highest switching rates.1 Controlling the stoichiometry has proven to be difficult using conventional methods, so in this study, deposition conditions for stoichiometric GeTe are sought using Electrochemical Atomic Layer Depostion (E-ALD). EALD is a process developed by this author’s lab which makes use of underpotential deposition (UPD) to put down fractions of a monolayer of the desired material. This process can then be repeated for as many cycles as are needed to grow films of the desired thickness. Before a deposition sequence can be made, the interactions of the individual elements must be investigated, both on the substrate, and on each other. This is achieved through the use of cyclic voltammetry, which measures the current generated as each element is either deposited or stripped from the surface as a function of electrochemical potential. By quantifying the current, the number of deposited or stripped atoms can be calculated, giving an estimate of the surface coverage. Investigations have identified the surface limited and bulk potentials for each element on the substrate as well as their substrate coverage. The next step will be to develop a sequence using these potentials to develop high quality, epitaxial films.

References:

Physical Review B. 2006, 73, 045210.
(Invited) Simulation of CdSe Based Quantum Dot Hybrid Light Emitting Diodes Using Tcad Continuous Models
Authors: Grassi Roberto , Arroyo Iker , Iniguez Benjamin , Drevon Tark , Plews Andrew , Chourou Slim , Townsend Mark , Nejim Ahmed
Published: February 2020

Organic-inorganic hybrid quantum dot (QD) based light emitting diodes (LEDs) have been investigated. Stacked hybrid QD LED structures, based on cadmium selenide QD with cadmium sulfide barrier shells, have been fabricated at the Universtiat Rovira i Virgili using spin coating techniques. These have been modelled, with Technology Computer Aided Design (TCAD) software, using two different carrier conduction models.

Two quantum confinements models are used to predict the electronic transport through these stacks. A 1D simulation of a stack with a single QD mono-layer, using the Silvaco Radiant tool based on the Atlas engine, is reported. This approach allows device designers to optimise the current density and spectral response as a function of QD radius (as shown in the figure) and transport layer thicknesses. Furthermore, a second approach using a 3D QD simulation in which the user can investigate the effect of the QD radius and barrier layer thickness on the carrier confinement in the structures is shown.

This work demonstrates the capability of 1D simulations, using the Radiant software tool, to model the behavior of single QD mono-layer structures. The user friendly input graphical user interface, as well as the speed of the simulation, helps to iterate the design quickly to optimise QD size and transport layer thicknesses for maximum intensity at the desired spectral output.

Figure 1
(Invited) Roll Coated Organic Dye-Based Photovoltaics for Indoor Energy Harvesting Applications
Authors: Welch Gregory Charles
Published: February 2020

Organic photovoltaics (OPV) remain one of the hottest topics in energy science today owing to the potential to convert the energy of light into electricity in an affordable and versatile manner. Researchers around the world continue to develop new materials, optimize devices, and understand operation resulting in ever increasing power conversion efficiencies. As chemists, developing new photoactive organic materials is of interest. A recent goal has been to move away from fullerene base systems. In the pursuit of new materials to replace fullerenes, our research group has gravitated towards using classic dyes. This presentation will cover the design and practical synthesis of some new organic conjugated molecules based upon ‘dye stuffs’, their use as non-fullerene acceptors in both greener solvent processed OPV cells, translation to large area slot-die coating methods, and operation under indoor lighting environments.
Lateral GaN Jfet Devices on Large Area Engineered Substrates for Robust Power Switching
Authors: Anderson Travis J. , Gallagher James C , Foster Geoffrey M , Koehler Andrew D , Tadjer Marko J , Hobart Karl D. , Aktas Ozgur , Odnoblyudov Vladimir , Basceri Cem , Kub Fritz J
Published: February 2020

GaN-based power switching devices are of significant interest for high efficiency power conversion circuits in medium voltage applications. However, there are still significant challenges preventing mass production and widespread adoption. In particular, lateral HEMT devices lack avalanche capability for rugged power switching, vertical device technology is not mature, the manufacturing cost associated with small diameter substrates is relatively high, and CTE mismatch issues create limitations on epi thickness as well as bow issues for GaN-on-Si. As a scalable substrate solution, Qromis, Inc. has developed commercial substrates designated QST™ which are engineered to be thermally matched to GaN, enabling thick epitaxial layers capable of >1kV devices on 200 mm diameter wafers suitable for fabrication in a CMOS fabrication facility. Taking advantage of this platform, we present a GaN-based lateral junction gate field effect transistor (JFET) device structure for robust power switching. The p-GaN gate functions to collect secondary holes while a second buried p-GaN blocking layer is implemented to pull the electric field below the surface as in a Reduced Surface Field (RESURF) structure. Unlike a HEMT process, the LJFET epi design and process sequence requires appropriate design of the doping in the buffer, gate, and channel layers for charge balancing, and additional process modules for N+ doping for source/drain contact (via ion implantation), low-damage p+ etching to define the gate, and N implantation to partially compensate the p- layer for field management. These steps have been independently optimized. Device testing indicated high current capability (>1A) in large gate width devices and high current density (~200 mA/mm) in smaller devices. The discrepancy is attributed to a processing issue creating spreading resistance in the ohmic contacts indicating a need for thick metallization. Gate continuity was tested by electroluminescence from the forward biased p-n junction, and breakdown tests indicated >1kV blocking capability with low leakage current. In summary, a conceptual prototype for a lateral GaN JFET device was demonstrated experimentally with promising current density and breakdown performance.
Stability and Electronic Properties of Silicon-Rich Silicon Carbide Structures
Authors: Alkhaldi Noura Dawas , Barman Sajib Kumar , Huda Muhammad N
Published: February 2020

The high stability of silicon carbide make it an attractive materials to be used in different applications such as solar cells. Silicon-rich silicon carbide (Si-rich SiC) materials are necessary to tune the band gap for efficient solar light absorptions. Si-rich SiC materials which are thermodynamically stable can be used in solar cell applications without requiring the expensive pure grade silicon or pure grade silicon carbide. Density functional theory (DFT) calculations were used in order to examine different phases of Si-rich SiC to predict stable structures. Since the configurations play a significant role in getting stable results, different configurations of silicon and carbon atoms in Si-rich SiC were considered. The electronic structures were studied, and the total energies were calculated as well as the formation energies. We will present that higher-order hexagonal-phases are more favorable structures than other Si-rich SiC structures due to their more covalent nature of bonding compared to the cubic counterpart.
(Invited) optically Controlled Nanowired Biointerfaces
Authors: Tian Bozhi
Published: February 2020

Biological systems have complex chemical, physical and genetic networks, which cover multiple length and time scales. Many of these interactions and synergies are made possible through biological nanowire structures, such as bacterial pilli. Synthetic analogs of the biological nanowires could mimic the structure and function of naturally occurring ones, and have yielded innovations in biointerfaces. Among the synthetic nanowires, those of semiconductors display many important electrical and optical properties and can be controllably synthesized and fabricated into a broad range of electronic and photonic devices, allowing for the formation of functional interfaces from biomolecular to whole organ levels. In this talk, I will first review the fundamentals in semiconductor-based biointerfaces, and highlight specialized material and device designs for multiscale biointerfaces. Then, I will present a few cases on optical control of nanowired neural, cardiac and microbial systems. Finally, I will propose several areas where significant impact could be made in the future for nanowired biological systems.
Electrochemical Quantification of Sulfatase Activity for Point-of-Care Diagnosis
Authors: Dang Brandon , Pham Patricia , Yue Xinping , Wang Zhe
Published: February 2020

Sulf 1&2, as the 6-O endosulfatase of heparan sulfate proteoglycans (HSPGs), has been reported in many previous works that it plays the critical role in the pathogenesis of a variety of human cancers, especially lung and breast cancer. However, there are very few reports about point-of-care detection of Sulf 1&2 currently. In this work, an electrochemical method using HSPGs as an anchor was employed to quantify the activity of Sulf 1&2. HSPGs, a glycoprotein with the common characteristic of containing one or more covalently attached heparan sulfate (HS) chains and is also a type of glycosaminoglycan, can mediate the activation of a variety of cell growth factor signal pathways to promote the progression of cancers. Here, electrochemical impedance spectroscopy (EIS) was used to monitor the changes of electrical properties of HSPGs with Sulf 1&2 variation. Through analyzing and calculating the electrical parameters obtained by EIS, such as charge, capacity and degree of phase, we established the calibration curve of sulf 1&2 concentration, which could be further used to evaluate the sulf 1&2 activity within human blood samples. This work offers a new method for sulf 1&2 detection and has great potential in the early detection of cancers.
Rheological Study of Micro Porous Layer and Its Effect on Transport Properties in a PEMFC
Authors: Mehrazi Shirin , Chuang Po-Ya Abel
Published: February 2020

Technical challenges related to catalyst flooding in a polymer exchange membrane fuel cell (PEMFC) have led to various studies to improve water management through evolutionary gas diffusion layer (GDL) design[1] [2].It has been well established that a GDL consisting of a macro-porous substrate coated with a hydrophobic microporous layer (MPL) has an indispensable role in gas and water transport [3]. However, a fundamental understanding of the MPL role and its optimal composition and structure are still lacking. Currently, the most widely used MPL in a PEMFC is made from ink dispersion that consists of carbon, PTFE, and solvent. Before MPL optimization is possible, the desired properties of the MPL ink dispersion and its interaction with the macro-porous substrate needs to be studied. In this study, we used rheological measurements as an evaluation tool to study a baseline MPL ink with Acetylene Black (AB) and PTFE. Specifically, we performed intensive rheological experiments to study the following three properties of the MPL ink: 1) flow properties, like viscosity, through continuous ramp rate, 2) viscoelastic properties through cyclical sweeping method, and 3) transient properties through recovery and relaxation measurement. Our preliminary results show that the ink stability, size of the primary agglomerate, viscosity, viscoelastic property, and creep recovery are strongly influenced by carbon to PTFE ratio and the weight percentage of the solid content. Built on the foundation of our previous work, we expand our study to include two types of carbon materials, AB and Carbon Nano Tube, three PTFE/Carbon ratios (20%, 30%, and 40%), and two solvent ratios (IPA rich and water rich) in this study. Standard Toray-H-060 substrate with 20% PTFE is used as the baseline macro-porous substrate and the MPL ink is applied directly onto the substrate by rod coating. The GDL is then dried and sintered accordingly. Both ex-situ evaluations, such as surface roughness, hydrophobicity, coating quality, and MPL penetration, and in-situ fuel cell testing are performed to study the effect of MPL on transport and performance under both wet and dry conditions. Our results provide new insights to enhance transport properties in a PEMFC by optimizing the design of MPL ink. Detail experimental results will be presented at the conference.

References

[1] H. K. Atiyeh, K. Karan, B. Peppley, A. Phoenix, E. Halliop, and J. Pharoah, “Experimental investigation of the role of a microporous layer on the water transport and performance of a PEM fuel cell,” J. Power Sources, vol. 170, no. 1, pp. 111–121, 2007.

[2] J. H. Nam, K. J. Lee, G. S. Hwang, C. J. Kim, and M. Kaviany, “Microporous layer for water morphology control in PEMFC,” Int. J. Heat Mass Transf., vol. 52, no. 11–12, pp. 2779–2791, 2009.

[3] Z. Qi and A. Kaufman, “Improvement of water management by a microporous sublayer for PEM fuel cells,” J. Power Sources, vol. 109, no. 1, pp. 38–46, 2002.
Failure Mechanism of PEM Fuel Cell after a Durability Testing of 1000 h Under High Back Pressures
Authors: Cai Chao , Rao Yan , Li Shang , Pan Mu
Published: February 2020

Proton exchange membrane fuel cells (PEMFCs) are expected to service under relative higher back pressures due to the target of higher outpower. In this condition, the durability of fuel cells will be a huge challenge for commercialization. In our study, we performed a 1000-hour durability experiment on a PEMFC in order to investigate the durability under high back pressures. A semi-empirical fuel cell polarization curve model was used to separate the activation losses and concentration losses and study their changes with testing time at different current densities. In addition, we investigated the charge transfer resistance (Rct) related to the oxygen reduction reaction (ORR) in the catalyst layer, and the mass transfer resistance (Zd) though Electrochemical Impedance Spectroscopy (EIS). Moreover, the contact angle and Energy-Dispersive X-Ray spectrum (EDX) of carbon paper surface were characterized. The result indicated that the rise of mass transfer resistance was the biggest contribution to the loss of cell voltage with testing time. The decrease of the contact angle of carbon paper surface implied that the weakening of hydrophobicity contributed to the increase of mass transfer resistance, which comes from the PTFE loss observed from EDX. This may result from the aggravating corrosion of PTFE or physical erosion induced by the flooding in fuel cell under high back-pressure. More stable GDL should be developed to meet the needs of PEM fuel cells with high performance and long lifetime.

Figure 1
Optimization of a Conductive Hydrogel Nanocomposite for Use in Responsive Wound Management Technology
Authors: Linhart Abigail N. , Lange Heather R. , Chura William E. , Keleher Jason J.
Published: February 2020

Hydrogel nanocomposites have been commonly researched in the biomedical field due to their swelling properties, tensile strength, and ability to act as a scaffold for cell growth. These nanocomposites can be further modified with active components, such as conductive polymers and nanoparticles (NPs), to enhance wound management properties and elicit a response upon changes in the surrounding environment. This research focuses on the synthesis and characterization of a multi-layered nanocomposite comprised of a NP crosslinked hydrogel and a bulk conductive layer. The integration of the conductive NPs increases the surface interactions between the hydrogel and conductive polymer to enhance electron transport between the layers. Therefore, as wounds secrete, ions diffuse through the hydrogel into the bulk conductive layer to further increase the electron transfer in the nanocomposite via p-doping. This results in an increase in lux efficiency of an LED which can be correlated directly to the degree of swell of the hydrogel to indicate when the gel has reached maximum swell capacity. Various conductive polymers such as polyaniline (PANI), polypyrrole (PPy), and polythiophene (PTh) have been investigated to determine the impact structural differences have on the conductivity of the nanocomposite. Initial results suggest that due to the higher doping degree of PANI by Cl- ions, electrons transfer more readily therefore increasing the conductivity of the nanocomposite compared to that of the other bulk polymers.
Electrochemical Precipitation of Struvite in Acidic Environment
Authors: Teymouri Ali , Kékedy-Nagy László , Greenlee Lauren F. , Herring Andrew M.
Published: February 2020

Phosphorus is a key element of fertilizers required for the food production chain worldwide. However, its global supply is limited to phosphate rocks, which is a non-renewable resource expected to last 50 to 300 years. Nutrients recovery from phosphorus-rich wastewater streams is a promising solution to conserve this valuable resource. It will also contribute to the sustainability of the commercial fertilizers’ production globally, by reducing the overall demand for new phosphorus sources. In this study, phosphorus from synthetic wastewater has been recovered electrochemically in the form of slow-release fertilizer known as struvite, magnesium ammonium phosphate hexahydrate (MgNH4PO4 .6H2O). The effect of two different types of sacrificial anodes (pure magnesium vs. AZ31 alloy) as the magnesium source on the electrochemical production of struvite were compared. Precipitates on the surface of the anode, cathode and the bulk solution were fully characterized in terms of elemental composition, structure, crystallinity, and morphology of the particles. The effect of temperature on open circuit potential was investigated with detailed characterization of anode surface. In addition, the ratio of faradaic vs non-faradaic precipitation of struvite was evaluated at different temperatures. The preliminary data on a single-compartment reactor containing 0.077 M dihydrogen ammonium phosphate resulted in a phosphorus and nitrogen removal of 38.8 ± 6.8 wt% and 16.0 ± 5.8 wt% respectively, for the experiments conducted with pure magnesium anode compared to that of 31.6 ±0.5 wt% and 7.7 ± 0.9 wt% in the case of AZ31 alloy. This study is the first of its kind to compare the production of struvite in an acidic environment without any pH adjustments.
(Invited) From Precursors to Devices: Using Neutron Scattering to Study Synthesis, Processing, and Material Properties
Authors: Sacci Robert L
Published: February 2020

In this talk, I will report the use of neutron scattering to probe the synthesis of the lithium ion conductor Li7La2Zr2O14 (LLZO) from different precursors and how phonons affect the ion transport in situ. Only a few solid state systems have been studied systematically in terms of synthesis and processing mechanisms. These types of studies and the facilitating in situ techniques are essential to not only solid-state chemistry but chemistry in general. In relation to energy storage devices, we need materials that allow for increased energy density, power performance, lifetime and safety. Solid state batteries are a promising solution in improving a number of these areas over traditional Li-ion batteries; however, efficient synthesis and processing of materials for solid-state batteries are needed to overcome cost concerns [cite]. As such, we need to understand how these materials are formed in order to improve functionality, robustness, and lower processing cost.

Neutron scattering has advantages over x-ray scattering and optical spectroscopies; for example, neutrons have high penetration power and are sensitive to isotope labeling. The combination of these two facts allow for precursor-to-property investigations. In the first part we will raise the question does the initial state of precursors affect reaction mechanism? Specifically, we probe the difference in the reaction the mechanism of LLZO synthesis from a dehydration of eutectic mixture and freeze drying of aerosolized solution. We will show that the reaction rate and chemical structure is strongly affected by how the precursors were mixed.

Moving from synthesis to material property I will report on the simultaneous use of impedance spectroscopy and inelastic neutron scattering (INS) to probe ion transport/phonon correlations. INS is analogous to infrared and raman spectroscopy in that it probes molecular vibrations and phonons of materials. However, unlike optical spectroscopies, INS has no selection rules, as they interact directly with nuclei and not the electrons in the system. Appling an AC signal whose frequency is in resonance with ion transport shows structural or chemical effects in the INS spectra. These effects seem to correlate with phonons that are are associated with Li ion transport.
The Impact of Coal Mineral Matter (alumina and silica) on Carbon Electrooxidation in the Direct Carbon Fuel Cell
Authors: Moradmand Simin , Allen Jessica A , Donne Scott W
Published: February 2020

Direct carbon fuel cell (DCFC) as an electrochemical device has been considered to generate electricity from coal with higher efficiency and lower air pollution issues than the traditional coal-fired power plant. The coal char as one the main carbonaceous fuel source has been successfully used in DCFC and showed good performance in different cell configurations.

Despite the advantages of DCFC, the development of this technology still has some challenges which must be addressed before becoming commercially viable. The carbon part of coal char consumed during electrochemical reaction to produce the electricity while the mineral part of it will stay unchanged after the reaction and accumulate in the system by the time. Some of these mineral matters act as the inhibitors for carbon electrooxidation and some of them play as the catalysis.

In this study, the impact of two main mineral matters exist in the coal char, alumina and silica, have been investigated in carbon electrooxidation in the half-cell setup. These mineral mixed with ternary (Li2CO3 , Na2CO3 ,
K2CO3 ) with the different mass ratio to obtain the optimum condition for carbon electrooxidation. In addition, the influence of silica and alumina on the melting temperature of electrolyte have been studied with TGA/DTA method to observe any changes in melting temperature or activation energy of melting.
(Battery Division Postdoctoral Associate Research Award Sponsored by MTI Corporation and the Jiang Family Foundation) Synchrotron Characterization to Inform Design for Cathode Materials in Li/Na Batteries
Authors: Mu Linqin , Lin Feng
Published: February 2020

The ever-increasing demand for renewable energy storage and electrifying transportation calls for developing high energy density electrode materials for rechargeable alkali metal ion batteries. Cathode materials such as layered oxides play a crucial role in determining the energy density and safety of batteries. Major efforts have been invested to push the cathode capacity approaching its theoretical limit while reducing the cost of raw materials (e.g., Co-free cathode pathways). However, the technical challenges are amplified under aggressive operating conditions, particularly at elevated temperatures or high charging voltages. Understanding the fading mechanisms under these aggressive conditions (e.g., chemomechanical breakdown, interfacial degradation, metal dissolution, charge heterogeneity) will inform the material design principles. With advanced synchrotron X-ray, electron, and electrochemical diagnostics, we will present our recent progress in probing the fading mechanisms in Li ion and Na ion batteries. Our study has treated batteries as ecosystems and thoroughly considered the cathode-anode crosstalk. Finally, we will explain how we have made use of the gained knowledge to guide our syntheses of Co-free Li cathodes, water-processable Na cathodes, and hierarchically doped electrode materials.
Fabrication and Characterization of High Performance Intermediate Temperature Micro-Tubular Solid Oxide Fuel Cells
Authors: Ren Chunlei , Gan Yun , Lee Myongjin , Yang Chunyang , Green Robert , Xue Xingjian
Published: February 2020

A phase inversion-based dual-layer co-extrusion approach was advanced to fabricate micro-channel array structured micro-tubular solid oxide fuel cells (MT-SOFCs). The inner graphite layer was used as a sacrificial layer to eliminate the middle sponge-like layer and inner surface dense skin layer, which were normally formed using the single layer extrusion method. As a result, the micro-channel array generated in the outer layer was a more open structure and facile fuel/gas diffusion was obtained. The fuel/gas permeability of such an anode substrate Ni-Ce0.8Sm0.2O1.9 (Ni-SDC) was ∼9 times that of an anode substrate fabricated using the phase inversion-based single layer extrusion method. The open circuit voltages (OCVs) of the corresponding cell Ni-SDC/SDC/PrBaCo2O5+δ were 0.89 V–0.85 V at 500–600°C, much higher than those of other SDC electrolyte based MT-SOFCs. The peak power density of the cell was ∼1484 mW cm−2 at 600°C, approximately 1.5 times that of a similar cell with an anode substrate fabricated from the single layer extrusion method. This is also the highest performance among the SOFCs with the same material system in open literature. The fuel utilization rate was also significantly improved in different degrees depending on the supplied inlet fuel flow rates.
New Insights on the Surface and Stress Behavior of Manganese-Oxide As Oxygen Reduction Reaction Catalyst in Alkaline Electrolyte
Authors: Keisar Or , Ein-Eli Yair , Cohen Yair
Published: February 2020

The electro-catalysts for oxygen reduction reaction (ORR) on air-cathode have a decisive impact on metal-air batteries and fuel cells. Much effort has been invested in finding a cost effective electro-catalyst, enabling a decrease in the ORR over-potential and enhancing the power source device discharge performance.[1-2]

Manganese-oxides (MnOx) are particularly interesting as non-precious ORR electro-catalysts candidates due to their rich oxidation states, chemical compositions and their variety of crystal structures[1-3]. In order to broaden our understanding on the catalytic mechanism of Manganese-Oxide and its surface chemistry during ORR, we performed unique in-situ electrochemical surface stress (ESS) measurements[4].

The in-situ ESS response was measured on an Au/MnOx electrode in both Ar and O2 saturated environments. A complex stress response was measured during the electrochemical scan caused by various crystal structure transitions[5]. The presence of oxygen resulted in a less compressive stress response during the ORR; suggesting that part of the activated sites on the surface are reduced and re-oxidized (Mn4+↔Mn3+) during the ORR. These observations evidently support the proposed ORR catalytic mechanism[3,5].

In addition, an overall tensile trend was recorded during multiple cycling, pouring some light on the poor mechanical stability of the MnOx film. This insight has major implications on the applicability of MnOx as a catalyst on practical carbon based electrodes.

References:

R. Mainar, L.C. Colmenares , O. Leonet , F. Alcaide , J.J. Iruin , S. Weinberger , V. Hacker , E. Iruin , I. Urdanpilleta , J.A. Blazquez., Manganese oxide catalysts for secondary zinc air batteries: from electrocatalytic activity to bifunctional air electrode performance, Electrochimica Acta 217 (2016) 80–91.

Li, M. Gong, Y. Liang, J. Feng, J.-E. Kim, H. Wang, G. Hong, B. Zhang, and H. Dai., Advanced zinc-air batteries based on high-performance hybrid electrocatalysts, Nature Commun., 4 , (2013), 1805-1811.

A. Stoerzinger, M. Risch, B. Han and Y. Shao-Horn, Recent insights into manganese oxides in catalyzing oxygen reduction kinetics, ACS Catal., 5, (2015), 6021-6031.

Ha, J.L. Oberst, Z. Zeng, T. T.H. Hoang, Y. Cohen, D.J. Wetzel, R.G. Nuzzo, J. Greeley and A.A. Gewirth, In Situ Surface Stress Measurement and Computational Analysis Examining the Oxygen Reduction Reaction on Pt and Pd., Electrochimica Acta, 260, (2018), 400-406.

Gorlin, B. Lassalle-Kaiser, J. D. Benck, S. Gul, S. M. Webb, V. K. Yachandra, J. Yano and T. F. Jaramillo, In situ X-ray absorption spectroscopy investigation of a bifunctional manganese oxide catalyst with high activity for electrochemical water oxidation and oxygen reduction, J. Am. Chem. Soc., 135, (2013), 8525-8534.
Developing New Chemistries for Redox Flow Batteries
Authors: Liu T. Leo
Published: February 2020

Aqueous organic redox flow batteries (AORFBs) have emerged as an attractive alternative RFB technology because redox active organic molecule materials are synthetically tunable, sustainable, and potentially low cost. The presentation will cover our recent research efforts in developing viologen anolyte materials for both anion and cation exchange pH neutral AORFBs with a variety of catholyte materials including ferrocene, TEMPO, ferrocyanide and halides. The viologen AORFBs demonstrated outstanding battery performance including an energy density of up to 30.4 Wh/L, a power density up to 220 mW/cm2, energy efficiency up to 72% at 60 mA/cm2, and capacity retention up to 99.999% per cycle up to 1000 cycles, representing the most stable organic RFB reported to date. In addition, this presentation will discuss mechanistic understandings of investigated redox active molecules using a variety of spectroscopic tools. Particularly, the presentation emphasizes that fundamental understandings of redox active electrolytes at molecular level are crucial to develop new generations of redox flow batteries for large scale and dispatchable renewable energy storage.

References: (1) Luo, J.; Hu, B.; DeBruler C.; Yuan, B.; Zhao, Y.; Hu, M.; Wu, W.; Liu, T. L.*Joule, 2019, 3, 1-15. (2) Luo, J.; DeBruler C.; Hu, B.; Hu, M.; Wu, W.; Liu, T. L.*,J. Mater. Chem. A, 2019,7, 9130-9136. (3) DeBruler C.; Hu, B.; Moss, J.; Luo, J.; Liu, T. L.*,ACS Energy Letters 2018, 3, 663-668. (4) Luo, J.; Hu, B.; DeBruler C.; Liu, T. L.*,Angew. Chem. Int. Ed. 2018, 57, 231-235. (5) Hu, B.; Tang, Y.; Luo, J.; Grove, G.; Guo, Y.; Liu, T. L.*,Chem. Commun. 2018, 54, 6871-6874. (6) Hu, B.; Liu, T. L.* J. Energy Chem. 2018, in press. (7) DeBruler C.; Hu, B.; Moss, J.; Liu, X. Luo, J.; Sun, Y; Liu, T. L.*, Chem, 2017, 3, 961-978. (8) Luo, J.; Sam, A.; Hu, B.; DeBruler C. Liu, T. L.* Nano Enegry, 2017, 42, 215-221. (9) Hu, B.; Seefeldt, C., DeBruler C.; Liu, T. L.*, J. Mater. Chem. A 2017, 5, 22137-22145. (10) Hu, B.; DeBruler C., Rhodes, Z.; Liu, T. L.*, J. Amer. Chem. Soc., 2017, 129, 1207-1214. (11) Liu, T.;* Wei, X.; Nie, Z.; Vince, S.; Wang, W.* Adv. Energy Mat. 2016, 6, 1501449.(12) Filed US Patents covering applications of water soluble viologen, ferrocene derivatives, and TEMPO for RFBs. (13) Group website: www.tianbiaoliu.org.
Effects of Native Solid Electrolyte Interphase Layer Formation of Cu Electrode on Lithium Electrodeposition/Dissolution Processes
Authors: Kondo Toshihiro , Uchino Yukina , Smaran Kumar Sai , Ohama Ayano , Niida Asako , Nishihara Kaho
Published: February 2020

Lithium has been extensively expected as one of the most ideal anode materials of the next generation lithium-based batteries such as a lithium-air battery (LAB), because of its higher theoretical specific capacity (3860 mA h g-1) and its most negative redox potential (-3.04 V vs. SHE). During charging, however, it is well known that the dendrite, which further leads to poor performance and short circuit, forms on the lithium anode surface. In addition, solid electrolyte interphase (SEI), which is generated by decomposition of electrolytes and/or solvents, also accumulates on the anode surface during the anode reaction. An ideal SEI layer is expected to be higher and lower conductive for lithium ion and electron, respectively, and it is flexible and has a relatively uniform flat surface with an appropriate thickness, in order to avoid dendrite formation [1]. Thus, we have been trying to construct the “ideal SEI” on the electrode surface [2].

During the electrochemical reaction, on the other hand, electrochemical quartz crystal microbalance (EQCM) technique gives us information not only of mass change on the electrode surface but also resonance resistance change, which shows surface area change of the electrode [3,4] and/or density and viscosity change at the electrode/electrolyte solution interface [5,6]. Moreover, this technique provides us the viscoelasticity of the formed layers on the electrode by the admittance analysis. Using this technique, we found that the native-SEI, which is prepared by the pre-electrochemical treatment of Cu EQCM electrode, strongly effects on the lithium electrodeposition/dissolution processes.

Acknowledgements: This work was totally supported by the Advanced Low Carbon Technology Research and Development Program (ALCA), specially promoted research for innovative next generation batteries (SPRING) from the Japan Science and Technology (JST).

References:

[1] X.-B. Cheng, R. Zhang, C.-Z. Zhao, F. Wei, J.-G. Zhang, Adv. Sci.3 (2016) 1500213.

[2] K. S. Smaran, S. Shibata, A. Omachi, A. Ohama, E. Tomizawa, J. Phys. Chem. Lett.8 (2017) 5203.

[3] K. Kanamura, S. Shiraishi, Z. Takehara,J. Electrochem. Soc.147 (2000) 2070.

[4] D. Aurbach, M. Moshkovich, Y. Cohen, A. Schechter, Langmuir15 (1999) 2947.

[5] K. Naoi, M. Mori, Y. Naruoka, W. M. Lamanna, R. Atanasoski, J. Electrochem. Soc.146 (1999) 462.

[6] N. Serizawa, S. Seki, K. Takei, H. Miyamoto, K. Yoshida, K. Ueno, N. Tachikawa, K. Dokko, Y. Katayama, M. Watanabe, T. Miura, J. Electrochem. Soc.160 (2013) A1529.
Model for Formation of Self-Ordered Anodic Oxide Nanomaterials
Authors: Mishra Pratyush , Hebert Kurt
Published: February 2020

Porous anodic films are self-organized porous oxides nanomaterials formed by electrochemical oxidation. Pores in porous alumina and nanotubes in TiO2nanotube layers initiate after an initial stage of barrier oxide growth. The porous film eventually evolves into a hexagonally-ordered array of parallel cylindrical pores or nanotubes of order 10-100 nm diameter with a characteristic spacing that scales directly with the cell voltage.

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

REFERENCES

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

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

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

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

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

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

Pt is widely used in electrochemistry as counter electrode5 and frequently applied for TiOx preparation;4 however, the suitability of Pt as (anodic) counter electrode (CE) is questionable since the stability of Pt is often overestimated.5 As Pt contamination can severely influence the electrocatalytic properties this study focuses on the preparation of TiOx using three different CE (Pt, Iridium mixed metal oxide, Boron doped diamond) and the influence of the CE will be discussed in detail.

It will be shown using state of the art techniques such as SEM, XPS and highly surface sensitive low energy ion scattering (LEIS) spectroscopy that indeed Pt contamination dominates the properties of TiOx (Figure 1a). In contrast, for Iridium mixed metal oxide and Boron doped diamond CEs no related contaminations were observed allowing to determine the intrinsic properties of TiOx electrodes. Using Fe2
+/3+ redox couple experiments and electrochemical impedance spectroscopy we determined the charge transfer properties of the TiOx electrodes prepared with BDD and IrMMO (Figure 1b). Although both BDD and IrMMO appear to be suited for the preparation of TiOx differences in the doping are observed that will be discussed in detail in this contribution.

References:

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

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

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

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

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

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

Formation of ordered arrays of nanoporous or nanotubular oxides of Al, Ti, and other valve metals during anodization has been reported extensively. These nanostructured oxides could find applications in solar energy conversion, energy storage, photocatalysts for environmental remediation, sensors, templates for nanowire growth, and supports for various catalysts because of their unique geometry and resultant physical properties. Various theories on the formation mechanism of the ordered nanostructures have been proposed in the literature including the field assisted dissolution mechanism[1], localized dielectric breakdown model[2], comparison of the Gibb's free energies of the compact oxide formation and chemical dissolution[3], and morphological instability of the oxide due to ion migration and oxide dissolution[4].

In this presentation, formation of ordered nanoporous anodic oxides of different substrate materials such as pure Ti, Ti-Mn alloy, Zr-W alloy, and bismuth will be analyzed based on the I-t plots and surface perturbation model proposed by Asaro and Tiller[5]. Compressive stresses are developed due to thickening of oxide layer and electrostriction. This compressive stress undulates the barrier film which leads to the surface perturbation. The perturbation releases strain energy of the oxide layer which is balanced by the increase in the surface area. These surface undulations affect the local chemical potentials because of the curvature effect. The presence of surface active species in the anodization electrolyte such as [MeF6]2- helps enhance the surface perturbation. The formation of ordered nanostructure could be explained based on the interaction between electrostatic strain energy and surface energy during anodization in specific environments.

[1] Z. Su and W. Zhou, Adv. Mater., 2008, 20, 3663–3667.

[2] Z. Su, W. Zhou, F. Jiang and M. Hong, J. Mater. Chem., 2011, 22, 535–544.

[3] M. Wang, Y. Liu and H. Yang, Electrochim. Acta, 2012, 62, 424–432

[4] K. R. Hebert, S. P. Albu, I. Paramasivam and P. Schmuki, Nat. Mater., 2012, 11, 162–166.

[5] R. J. Asaro and W. A. Tiller, Metall. Trans., 1972, 3, 1789 – 1796.
In-Situ optical Microscopy Corrosion Experiments for Correlating Microstructure to Corrosion Susceptibility in Aluminum Alloy
Authors: Desai Choundraj Jahnavi
Published: February 2020

Aluminum-Magnesium alloys (5xxx series) are widely used in marine applications, structural components in transportation, and military due to their high corrosion resistance, low density, and good mechanical properties. However, at moderate and high temperatures (>50oC) these alloys are vulnerable to sensitization, or precipitation of β phase (Al3Mg2) preferentially on grain boundaries, resulting in susceptibility to intergranular corrosion and environmentally induced stress corrosion cracking. The primary research theme of this talk is to understand how microstructure variations dictate local corrosion susceptibility of aluminum 5456 in corrosive environments.

To explore microstructure effects, we corroded sensitized aluminum 5456 in a dilute nitric acid solution. Prior to corrosion, electron backscatter diffraction (EBSD) was used to characterize the microstructure and deformation state of the alloy in terms of the grain structure, geometrically necessary dislocation density, constituent particles, and grain boundary character. In situ optical microscopy corrosion experiments were then used to directly observe corrosion initiation and propagation behavior, with fiducial markers used to correlate the observed corrosion behavior with the characterized microstructure. Image recognition algorithms facilitated the quantification of corrosion sites and corrosion propagation rates as a function of time and grain boundary path. Obtaining this information is crucial as the microstructural features that govern corrosion initiation may be different from the features that dictate propagation pathways. My talk will focus on the microstructure characteristics that dictate corrosion susceptibility to initiation as well as propagation and the relevance of these data for developing corrosion- and sensitization-resistant microstructures.
Investigation of Localized Corrosion Phenomena in Selective Laser Melted 316L Stainless Steel
Authors: Macatangay Duane Armell , Chmielinski Alex Piotr , Kelly Robert G.
Published: February 2020

Selective laser melting (SLM) refers to the additive manufacturing of bulk material from powder on a layer by layer basis through melting via laser and rapid solidification. In recent years, additively manufactured metallic alloys produced by SLM have garnered attention due to opportunities in waste reduction, time and cost efficiency, and fabrication of geometrically complex structures. However, limited work has been performed to investigate the corrosion properties of these alloys. Understanding these mechanisms is crucial in assessing the attendant risks associated with the use of AM alloys in engineering design.

Stainless steels such as 316L produced by SLM have presented advantages due to the corrosion resistant properties of these alloys. However, the non-equilibrium microstructure in these SLM materials, significantly different from that of the wrought counterpart, result in heterogeneities that may lead to localized corrosion such as melt pool boundary attack. A point of concern in stainless steels is intergranular corrosion due to the formation of secondary phases such as chromium carbides that deplete chromium from grain boundaries when the material is exposed to temperature ranges of 450 – 800 °C. While low-carbon steels such as 316L have great resistance to deleterious chromium carbide precipitation, this phenomenon has not been investigated in great detail in the case of selective laser melted 316L. However, it has been shown that precipitation of secondary phases is accelerated in SLM alloy systems such as Inconel 625 with respect to the wrought counterpart. Intergranular corrosion can ultimately lead to intergranular stress corrosion cracking, a form of brittle failure.

This study investigates localized corrosion phenomena such as melt-pool boundary attack and intergranular corrosion and the associated microstructure-based mechanisms in the corrosion of these SLM 316L alloys. Galvanostatic etching, potentiodynamic scans through the double-loop potentiokinetic reactivation method, and mass-loss testing of wrought and SLM 316L are utilized to reveal the electrochemical behavior of these alloys. Additionally, focused ion beam and transmission electron microscopy are utilized to understand the microstructural origins of the observed corrosion phenomena.
A Model Framework for Linking Changing Electrolyte Properties to Galvanic Corrosion Simulations
Authors: Policastro Steven A , Hangarter Carlos M , Anderson Rachel M
Published: February 2020

Electrolytes that form from atmospheric processes can differ widely in composition and thickness and the concentrations of dissolved gases, such as oxygen, in these thin electrolytes vary due to temperature and salinity changes. These changes within the electrolyte can substantially vary the oxidative properties of the electrolyte, which in turn alters the corrosion kinetics of the substrate. In this report, we present an approach for linking measurements of atmospheric properties, such as temperature, pressure, and relative humidity to changes in electrolyte properties, such as dissolved oxygen concentration, film thickness, and salinity. Using Butler-Volmer reaction kinetics, with parameters obtained from fits to polarization data obtained under actual electrolyte thin films equilibrated at different relative humidity values, and bulk polarization measurements, to simulate the electrochemical reactions, we model galvanic corrosion between aluminum and stainless steel alloys, such as UNS A902024 and UNS S13800, in response to changing environmental conditions.

This work was sponsored by the U.S. Naval Research Laboratory under its core research program. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Office of Naval Research, the U.S. Navy or the U.S. government.