bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatially-Resolved Electrochemical Methods for the Nanoscale Investigation of Reactivity and Transport in Materials for Energy Conversion and Storage
Authors: Rodríguez-López Joaquín , Shen Mei , Simpson Burton H , Barton Zachary J , Burgess Mark
Published: February 2020

Electrochemistry plays a central role in developing technologies for energy storage and conversion such as batteries, fuel cells and photoelectrochemical systems. The analysis, quantification, and unraveling of several fundamental properties of these systems, many of which lack adequate in situ analytical methods, would impact positively our ability to understand, manipulate, and design better technologies. I will describe how reactive imaging techniques such as those based on Scanning ElectroChemical Microscopy (SECM) provide a unique approach to research in catalysis, batteries and novel materials such as graphene. Here, micro- and nano-electrode probes can be used to detect adsorbed species and to image their reactivity with spatial and temporal resolution on electrodes. SECM can use selective species that interrogate surface-bound molecules and reaction intermediates in electrocatalytic reactions, thus allowing us to obtain information about their surface dynamics. These studies follow those obtained in model electrode surfaces such as graphene, where the differential reactivity of chemically-formed species or selectively adsorbed redox-active complexes can be used to describe the impact of processing steps on this material and possibly to design new strategies in Electrocatalysis. Likewise, current efforts in our laboratory have explored the quantification and imaging at the Nanoscale of photoelectrogenerated species at strontium titanate anodes and their correlation to powerful in situ X-ray structural results from our collaborators. Another front in our laboratory, consists in using ion-sensitive and selective strategies to provide a distinctive method of analysis for lithium-ion batteries, ion-selective membranes and ionic conductors. These methods allow assessing and tuning the impact of different chemical and electrochemical conditions on the ability of these materials to transfer ions. Efforts towards the imaging of these dynamic processes will be described.
Electrochemical Impedance Spectroscopy of Geobacter Sulfurreducens Biofilms on Rotating Disk Electrodes
Authors: Babauta Jerome T , Beyenal Haluk
Published: February 2020

Electrochemical impedance spectroscopy (EIS) has received significant attention recently as a method to measure electrochemical parameters of Geobacter sulfurreducens biofilms. Here, we grew G. sulfurreducens biofilms on rotating disk electrodes to determine the effect of mass transfer processes on the biofilm impedance. We controlled the rotation rate of the electrode up to 530 rpm to control the microscale gradients forming inside G. sulfurreducens biofilms respiring on the electrode. A 24% increase above a baseline of 82 µA was achieved with a rotation rate of 530 rpm. We compared the effect of rotation on the biofilm to a mass transfer-controlled soluble redox mediator, ferrocyanide, to make the distinction between infinite Warburg and pseudocapacitive responses. We observed a 340% increase above baseline using ferrocyanide at 530 rpm, indicating that the primary limitation of electron transfer rates in G. sulfurreducens biofilms was not mass transfer.

Control of mass transfer processes was also used to quantify the change in biofilm impedance during the transition from turnover to non-turnover conditions. An equivalent electrical circuit model was used to estimate the electrochemical parameters of the biofilm. We found that only one element of the biofilm impedance, the interfacial resistance, changed significantly from 900 to 4,200 Ω under turnover and non-turnover conditions, respectively. We ascribed this change to the electron transfer resistance overcome by the biofilm metabolism and estimate this value as 3,300 Ω. Additionally, under non-turnover, the biofilm impedance developed pseudocapacitive behavior indicative of bound redox mediators. Pseudocapacitance of the biofilm was estimated at 740 µF and was unresponsive to rotation of the electrode. Overall, we tested the hypothesis that the rotating disk electrode can be used as an electrochemical tool that controls mass transfer processes when studying electrochemically active biofilms and facilitates our understanding of EIS in microbially-driven electrochemical systems. The increase in electron transfer resistance and pseudocapacitive behavior under non-turnover could be used as indicators of acetate limitations inside G. sulfurreducens biofilms.
Electrochemical Characterization of Various Self-Assembled Nanocomposite Electrodes in E.coli-Catalyzed Mediatorless Microbial Fuel Cell
Authors: Nahm KeeSuk , KIM Pil
Published: February 2020

Microbial fuel cells (MFCs) is one of the promising green energy sources to produce electricity from organic wastes with the help of bacteria as catalyst. It converts the chemical energy in organic wastes into electricity by bioelectrochemical reactions. In spite of the promise of MFCs, their applications are limited by low power generation efficiency. Power limitations can be addressed by the use of better suited anodes, and to modify the electrode surface with nanostructures is one of the ways to improve the efficiency of the anode. In this study, We have demonstrated MFCs performance based on Escherichia coli (E.coli) by optimizing the electrode surface structure using various nanomaterials like reduced grapheme oxide(rGO), graphite nanofiber(GNF) and carbon nanotube(CNT). Each of the nanomaterials is doped with iron particles of 3~10nm size, and were formed into a nanocomposite. The synthesized nanocomposites was assembled on the anode electrode surface by directly applying a magnetic field. This conductive multilayer of nanocomposites coated on anode enhances the electron transfer between the bacteria and the anode. The electrochemical activities with each catalysts of such as Fe/rGO, Fe/GNF and Fe/CNT are investigated by cyclic voltammetry, Impedance spectra and polarization curve measurements.
Glucose Oxidase Affects Laccase and Bilirubin Oxidase Direct Bioelectrocatalytic Cathodes
Authors: Milton Ross D , Giroud Fabien , Thumser Alfred E , Minteer Shelley D. , Slade Robert CT
Published: February 2020

Glucose oxidase (GOx) is commonly incorporated into glucose-oxidising/oxygen-reducing enzymatic biological fuel cells (EBFCs), as the anodic biocatalyst. The flavin adenine dinucleotide (FAD) cofactor of GOx is tightly bound, and possesses an associated favourable low redox potential allowing the use of a wide range of electron mediators, which in turn increases the theoretical maximum open-circuit potential (OCP) of EBFCs. Furthermore, GOx is highly specific to glucose and offers high catalytic activity, making it a good choice for futuristic implantable EBFCs. GOx-based anodes do, however, exhibit a major significant drawback; electron transfer to the electrode following the enzymatic oxidation of glucose competes with the natural electron acceptor of GOx: oxygen. The reduction of oxygen by GOx can dramatically lower the dissolved oxygen concentration of a solution, whilst simultaneously producing hydrogen peroxide.

Laccase and bilirubin oxidase (BOd) can undergo the enzymatic 4-electron reduction of dissolved oxygen to water, and efficient direct electron transfer (DET) has been established for both enzymes. The inhibition of laccase and BOd by halides (primarily fluoride and chloride ions) is well documented; it is reported that BOd exhibits greater resistance to halide inhibition. Nevertheless, DET can also instil a degree of resistance to chloride inhibition. Lastly, BOd can efficiently reduce oxygen to water at near-neutral and physiological pH, making it a favourable choice of biocatalyst in implantable devices.

The research presented within this paper investigates the effect of the parasitic reduction of oxygen to hydrogen peroxide by GOx, on laccase and BOd direct bioelectrocatalytic cathodes. We report that GOx can produce significant quantities of hydrogen peroxide and thereby significantly affect laccase and BOd cathodes (albeit by different mechanisms), even when DET is established (a mode previously used to remediate chloride inhibition). Furthermore, we compare and contrast the performance of laccase and BOd when GOx is replaced with “oxygen-insensitive” FAD-dependent glucose dehydrogenase (FAD-GDH).

This research has implications for the future design of EBFCs.

This research is funded by the UK SuperGen Biological Fuel Cells Consortium (Contract: EP/H019480/1), National Science Foundation Grant #105797 and the Air Force Office of Scientific Research (AFOSR).
Proton Conduction in Metal-Organic Frameworks: Insights from Molecular Dynamics Simulations
Authors: Paesani Francesco
Published: February 2020

Metal-organic frameworks have recently been proposed as promising proton conducting materials for potential applications in fuel-cell technologies. Compared to other porous materials (e.g., zeolites), MOFs are highly tunable, which allows not only the size and shape but also the physicochemical properties of the frameworks to be rationally designed for specific applications. Here, I describe the results of molecular dynamics simulations that are used to develop a microscopic picture of the mechanisms associated with water-mediated proton conduction in MOFs as a function of temperature, water loading, and pore size/shape. Particular emphasis is put on the correlation between proton conduction and both structural and chemical properties of the frameworks as well as on the dynamical behavior of the water molecules adsorbed in the MOF pores.
A Sers Characterization of the Stability of Thiosulfate and Related Electrolytes at the Gold-Electrolyte Interface
Authors: Lipkowski Jacek , Smith Scott , Mirza Jeff , Baron Janet , Choi Yeonuk
Published: February 2020

Recent studies of the Au leaching process have employed thiosulfate as the alternative complexing ligand to cyanide for gold extraction from ores containing carbonaceous components which preferentially absorbs gold and gold-cyanide complexes ( the so called preg-robbing). Thiosulfate, in the presence of an appropriate oxidant such as dissolved oxygen, is well known to complex Au(I) ions and form a soluble [Au(S2O3)2]3- complex. However, the kinetics of this process are inhibited by the formation of a passivating layer of species on the Au surface that block the lixiviant reagents from reaching the underlying Au atoms, thereby preventing full recovery of Au from the ore. To determine the composition of this passive layer, the interfacial behaviour of tetrathionate, trithionate, the [Au(S2O3)2]3- complex and thiosulfate upon immersion of a Au nanorods electrode into each of the electrolyte solutions was investigated using surface enhanced Raman spectroscopy (SERS). Raman bands indicative of adsorbed tetrathionate, trithionate, and [Au(S2O3)2]3- were identified at early immersion times. However, bands assigned to decomposition products such as elemental sulfur, were observed in all SERS spectra at longer immersion times. The SERS spectra for tetrathionate, trithionate, the [Au(S2O3)2]3- complex were compared to SERS spectra collected in a thiosulfate electrolyte in an attempt to better identify the passivating species that accumulate on the Au surface in typical gold leaching conditions. In thiosulfate solution, Au surface passivation by elemental sulfur did not occur to the same extent relative as in the three other electrolytes in the time period studied. This behavior indicates that complexation of the oxidized Au atoms by thiosulfate and its subsequent mass transportation into the bulk electrolyte is the predominantly favoured pathway at early immersion times. However, the disappearance of the Raman bands characteristic of the [Au(S2O3)2]3- complex and the appearance of bands indicative of elemental sulfur on the Au surface at longer immersion times confirms the growth of a passivating film of elemental sulfur on the gold surface in the thiosulfate electrolyte, albeit at much longer immersion times.
The Carbon/Iodide Interface in Protic Ionic Liquid Medium for Application in Supercapacitors
Authors: Béguin François , Skowron Piotr , Anouti Mérièm , Frackowiak Elzbieta
Published: February 2020

Among various energy storage systems, great interest is focused on electrochemical capacitors (ECs) because of their high power and long cycle life. The most typical devices operate through the charge/discharge of the electrical double-layer at the electrode/electrolyte interface in aqueous or organic medium and as well as in ionic liquid. The capacitance can be significantly enhanced by quick redox reactions originating from the electrolyte species at the electrode/electrolyte interface, for example by using iodide salt aqueous solutions [1]. However, in the later case, the voltage of the system is limited to 1 V due do the low thermodynamic window of water. Therefore, we propose to investigate a possible extension of this window by using solutions of iodide salt in ionic liquids (ILs).

The ILs selected were triethylammonium bis(tetrafluoromethylsulfonyl)imide [Et3NH]-[TFSI] and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide [Emim]-[FSI]. Two iodides, triethylammonium iodide [Et3NH]-[I] or tetraethylammonium iodide [Et4N]-[I], were introduced in the ionic liquid at a concentration of 0.25 mol L-1. The electrochemical experiments as cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy were conducted using a two-electrode cell construction. In some experiments, a silver wire was added as pseudo-reference to monitor the potential of individual electrodes. Activated carbon (AC) with high microporosity coated on aluminum foil from Batscap (France) was used as working and counter electrode. Glass microfiber paper (Whatman) was utilized as separator. Galvanostatic (0.2 A·g-1) cycling up to 1.8 V in two-electrode cell (Figure 1B) demonstrates a remarkable increase of capacitance when [Et3NH]-[I] is added to [Et3NH]-[TFSI], from 78 to 157 F·g-1. The voltammogram of figure 1A shows clearly that the increase of capacitance is caused by the positive electrode where faradaic processes occur.

Acknowledgements:The Foundation for Polish Science is acknowledged for supporting the ECOLCAP Project realized within the WELCOME Program, co-financed from European Union Regional Development Fund.

[1] G. Lota, E. Frąckowiak, Electrochemistry Communication, 11 (2009) 87-90
Probes Based on Silica Sol-Gels for Voltammetry in the Absence of Electrolyte in the Sample Phase
Authors: Cox James A. , Miecznikowski Krzysztof , Steinecker William H. , Pacey Gilbert E.
Published: February 2020

Silica sol-gels that are processed at room temperature contain residual solute. By selection of salts that have the properties of a humidistat in the sol, the resulting gel will contain a controlled amount of water, thereby making the resistance of the sol-gel independent of humidity of a contacting gas phase. Further, when the processing conditions result in a mesoporous sol-gel, diffusion coefficients of electroactive species that are encapsulated therein are in the 10-6 cm2s-1 range. The latter is illustrated by the cyclic voltammetry of hexacyanoferrate when a solid-state cell is fabricated to incorporate three electrodes in the silica matrix. This design is extended to the voltammetry of gas-phase species by extending the working electrode beyond the sol-gel so that a three-phase boundary is formed. In this manner the detection of carbon monoxide, hydrazine, and hydrogen peroxide by amperometry is achieved.

This cell design was evaluated as an amperometric detector for gas chromatography. Initial experiments were in the flow injection mode with He flowed at 0.63 mL min-1 as the carrier gas and100- µL injections of H2 comprised the sample. Wirh a Pt working electrode at 0.5 V vs. a Pt quasi-reference electrode, linear response to concentration over range 1.7 x 10-6 g to 7.6 x 10-6 g was observed. Extensions to 1,2-ethandithiol, phenol, p-cresol, and thioanisole yielded detection limits of 4, 1, 3, and 70 ppmv (k = 3 criterion), respectively, when operating the working electrode at 800 mV. Application to aqueous samples in the absence of supporting electrolyte also were achieved; however, a problem is that leaching of the electrolyte from the sol-gel cell was a limitation. To address this problem, the sol-gel matrix is being modified to contain a macromolar cation (anion) of a size that is greater than the ca. 0.5 nm pore size of the silica. An example is to immobilize 3,4- ethyelenedioxythiophene (EDOT) in the sol-gel and oxidize it to the polymeric form, PEDOT. Results on the polymerization process will be shown, and the efficacy of the resulting composite as a matrix for a probe to determine various species in water in the absence of supporting electrolyte will be presented.
High Pressure NMR Investigation of 3M Fuel Cell Ionomers
Authors: Pilar Kartik , Farrington Jaime , Rua Armando , Cuffari David , Ostrovskiy Eugene , Suarez Sophia , Stallworth PE , Greenbaum Steve
Published: February 2020

Nuclear Magnetic Resonance (NMR) measurements were obtained for polymer electrolyte membranes (PEM) provided by 3M Corp. through the courtesy of Dr. Steve Hamrock. These membranes have potential for use within PEM Fuel Cells (PEMFCs) and can operate at somewhat lower relative humidity than NAFION. NMR spin-lattice relaxation (T1) and static gradient self-diffusion measurements were obtained as a function of applied hydrostatic pressure for three different equivalent weight (EW) membranes at several values of water content. T1 measurements allow us to study the rotational molecular motion of water within the membranes, whereas diffusion directly probes translational motion (1). By measuring both T1 and self-diffusion, possible relationships between rotational and translational motion within the membranes can be observed and effects due to water content or EW can be found.

The membranes studied had EWs of 700, 825, and 1000, and each was prepared with both 10% and 20% water content (wt. %). Measurements were conducted at several temperatures. For T1 measurements, we used deuteron NMR in membranes equilibrated with D2O because of the high sensitivity of nuclear quadrupole relaxation to rotational motions (2). In order to measure diffusion (using proton NMR on samples equilibrated with H2O) in samples contained within a high pressure Cu/Be cell, it was necessary to use a spin-echo pulse sequence in the static gradient in the fringe field of a 7.3 T superconducting magnet. Figure 1 displays isothermal variable pressure T1 results obtained for the 700 EW membrane with 20 wt. % D2O. It can be seen that T1 values increase with temperature and decrease with pressure.

The results for different membranes also suggest that values for T1 increase with higher membrane EW and with higher D2O content. It is found that there is an increase in activation volume, Δv, with lower water content and lower temperatures, which was calculated using

Δv = -kT[lnT1/P]T [1]

Table 1 displays the activation volume of each membrane at various temperatures with 20 wt. % D2O.

Measurements of water self-diffusion as a function of pressure for each sample at different water content are underway. Diffusion activation volumes will thus be obtained and compared with those for deuteron spin-lattice relaxation. Such comparison will shed light on the relationship between water translational and rotational motion inside the ionomer, and hopefully lead to insight into the proton transport mechanism.

REFERENCES

1. Jayakody, JRP, Stallworth, PE, Mananga, ES, Farrington-Zapata, J, and Greenbaum, SG. J. Phys. Chem. B
108, 4260 (2004).

2. Fontanella, JJ, Wintersgill, MC, Chen, RS, Wu, Y, and Greenbaum, SG. Electrochimica Acta
40, 2321 (1995).

This work was supported by the Office of Naval Research.
Electrocatalysts for Electrochemical Energy Storage and Conversion Studied By Advanced Characterization Methods
Authors: Strasser Peter
Published: February 2020

New functional nanocatalyst materials are key to the realization of future sustainable energy storage and conversion technologies. Their successful development and optimization requires insight into the relation between atomic scale structure and macroscopic catalytic activity using ex-situ and in-situ scattering, spectroscopy and microscopy. In this talk, we will highlight some of our recent work focused on the preparation, characterization and understanding of electrocatalytic nanomaterials for energy technologies. Particular focus will be placed on the use of and insights from advanced spectroscopic, real-space, and reciprocal-space methods including STEM-EELS microscopy, Photoelectron and absorption spectroscopy as well as ex-situ and in-situ scattering techniques. Our discussions will include materials for hydrogen and liquid fuel cells, water splitting cells, and fuel production electrolyzers.
Invited Presentation: Mathematical Modeling of Diffusion-Induced Stress and Other Coupled Physics in Li-Ion Batteries
Authors: Christensen Jake
Published: February 2020

The pursuit of high-energy-density, low-cost electrochemical energy storage systems for electric vehicles inevitably requires careful examination of the coupling between mechanics, electrochemistry, thermodynamics, and mass transport in batteries. High-capacity Li battery materials such as Li alloys and Li metal undergo large volume changes during battery cycling, and the stress induced by these volume changes must be accommodated at the material, composite, or device level in order to reduce the rate of battery degradation. Here we review some early work in the modeling of diffusion-induced stress in Li-ion insertion materials,[1,2] showcase other examples of multiscale, multidomain battery models,[3,4] and discuss future research directions in the field of battery modeling.

1. J. Christensen and J. Newman, "Stress generation and fracture in lithium insertion materials,"
Journal of Solid State Electrochemistry, 2006. 10(5): p. 293-319.

2. J. Christensen and J. Newman, "A Mathematical Model of Stress Generation and Fracture in Lithium Manganese Oxide," Journal of the Electrochemical Society, 2006. 153(6): p. A1019-A1030.

3. J. Christensen, D. Cook, and P. Albertus, "An Efficient Parallelizable 3D Thermoelectrochemical Model of a Li-Ion Cell," Journal of The Electrochemical Society, 2013. 160(11): p. A2258-A2267.

4. S. Patnaik, An Electrical Network Model for Computing Current Distribution in a Spirally Wound Lithium Ion Cell, MS Thesis, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology: Cambridge, MA (2012).
Understanding and Predicting Li Dendrite Formation in Li-Ion Batteries: Phase Field Model
Authors: Zhang Hao-Wei , Liu Zhe , Liang Linyun , Chen Long-Qing , Qi Yue , Harris Stephen J , Lu Peng
Published: February 2020

Lithium dendrite formation can lead the degradation and failure of Lithium ion battery, either because dendrite pieces lose electrical contract with the rest of the Li electrode (typically during Li stripping on discharge) or because growing dendrite can penetrate the separator and lead to internal short-circuiting. In this presentation, we will discuss a nonlinear phase-field model for the Li electrochemical deposition process to predict the conditions for dendrite formation along with their morphology. The model incorporates microstructure and evolution of the anode, the SEI (solid-electrolyte interphase layer) and the Li metal phase as functions of temperature, current density and history. It also describes the effect of electrode geometry on the nucleation and growth of Li-deposits. The simulation will suggest the optimum electrode geometry to prevent the Lithium dendrite formation. The 2D morphological evolution during Li deposition under different electrochemical conditions specified by charging current density, the ionic concentrations, reaction rate and applied potentials at the electrodes will be discussed.
Characterization of Mechanical Degradation in Lithium Ion Battery Electrodes
Authors: Barai Pallab , Mukherjee Partha P.
Published: February 2020

Active particles inside Lithium Ion Battery electrodes are responsible for hosting Li ions during operation. Li ions intercalate and deintercalate in the host material through diffusion process. This induces significant amount of diffusion induced stress, which may lead to mechanical degradation in terms of formation of microcracks in the active particles [1]. Nucleation of these microcracks results in formation of spanning cracks which eventually leads to catastrophic failure of the material.

We have demonstrated a random lattice spring based methodology to characterize the development of microscopic damage and their subsequent nucleation to form crack fronts [2]. According to the lattice spring method, breaking of each bond is simulated by solving the equilibrium equation. Initially, evolution of fracture happens in a diffused manner (see Fig. 1(a)). Once the stress concentration at a microcrack tip starts to dominate over the disorder term, the material fails to sustain any more loads and a spanning crack develops (see Fig. 1(b)). In lattice spring model, when a bond breaks, the strain energy associated with that spring gets released (see Fig. 1(a)).

In acoustic emission experiments, released energy waves associated with cracking of materials are detected [3]. Figure 1(c) shows the formation of microscopic damage and cracks inside an active particle during the discharge process. Figure 1(d) shows that the amount of mechanical degradation saturates after 4 – 5 discharge/charge cycles. The goal of this research is to develop a computational scheme to capture the experimentally observed energy release during Li intercalation inside active particles.

References

[1] S. Kalnaus, K. Rhodes, and C. Daniel, J Power Sources,
196(19), 8116-8124 (2011).

[2] P. Barai and P. P. Mukherjee, J Electrochem Soc,
160(6), A955-A967 (2013).

[3] K. Rhodes, M. Kirkham, R. Meisner, C. M. Parish, N. Dudney, and C. Daniel, Rev Sci Instrum,
82 (7), (2011)
Multifunctional Surface Coating As Artificial Solid Electrolyte Interphase for Lithium Ion Batteries
Authors: Xiao Xingcheng
Published: February 2020

Surface modification on electrode has been reported to be an effective way to mitigate the mechanical degradation, improve the cycling stability, coulombic efficiency, and abuse tolerance. However, less work has been done to fundamentally understand its role on the formation of solid electrolyte interphase (SEI) and lithium transport. In this talk, we reported some important findings on the effect of surface coating on SEI formation. We found that the oxide coating can suppress electrolyte decomposition, therefore significantly reduced the SEI thickness (from around 20 nm thick without coating down to 1nm). Al2O3 coating also went through the structural changes which better facilitate charge transfer. We have demonstrated that the self-modified coating served as an artificial SEI layer which not only stabilized the interface between electrolyte and electrode, but also mitigated the mechanical degradation of electrode and improved the cycling stability. We will give a few examples to show how surface coating can help improve the battery performance from different aspects.
Invited Presentation: Elastic Anomalies and Electromechanical Effects in Gd-Doped Ceria
Authors: Korobko Roman , Lubomirsky Igor , Frenkel Anatoly
Published: February 2020

We have recently reported that at room temperature thin films of Gd-doped ceria exhibits a very large electrostriction effect. Our measurements with glass(150 µm)\Cr(100 nm)\Ce1-xGdxO2-x/2(500 nm)\Cr(100 nm) cantilevers demonstrate that the magnitude of the electromechanical effect strongly depends on the value of the in-plane compressive strain. Under a 60 kV/cm field at room temperature, strain-free films may generate stress in the range of 30-150 MPa, whereas the films with compressive strain of a few tenth of a % can generate stress in excess of 500 MPa. The electromechanical response persists till the frequency of at least 6 kHz, which excludes a possibility of macroscopic material transfer. Modulated in-situ EXAFS and XANES measurements indicate that the microscopic origin of the electromechanical response is related to rearrangement of the local environment of cerium rather than gadolinium ions. Electric field affects the equilibrium between locally distorted and undistorted CeCe-VO complexes, which is similar to the mechanism responsible for a number of previously described inelastic anomalies. The magnitude of the electrostriction effect exhibits a complicated dependence on the Gd-content and suggests that cerium-vacancy interaction facilitate the mechanical response whereas vacancy-vacancy interactions weaken it. Our findings confirm that the presence of CeCe-VO complexes is essential for electromechanical activity and elastic anomalies. Tailoring the electrostriction effect in doped or oxygen-deficient ceria may therefore be possible by a proper choice of dopant chemistry and concentration.
Invited Presentation: Chemo-Mechanical Stress and Its Impact on the Stability and Reliability of Solid Oxide Fuel Cells
Authors: Kawada Tatsuya
Published: February 2020

As a device of ceramic multilayers, solid oxide fuel cell has a risk of having mechanical failures when material selection is not appropriate. It may cause a fatal damage of a cell and the whole stack. Thermo-mechanical properties, i.e. thermal expansion mismatch between the materials or temperature gradient inside a cell is the primary cause of a mechanical failure. In addition, chemical strain can also lead to a serious problem if a nonstoichiometric compound is used as a major component of the cell stack, which is the case of most SOFCs under development. The chemical strain is a function of local temperature and oxygen potential which is determined by mass, charge, and heat transport in the materials and at the interfaces. Thus, the chemo-mechanical or electro-chemo-mechanical aspects of the materials should be carefully taken into consideration in designing and operating the cells.

Impact of the chemical strain on the reliability is highest when electrolyte itself shows oxygen nonstoichiometry, and is used in an electrolyte-support type configuration. Doped ceria is an example as pointed out by several researchers. Transition metal doped lanthanum gallate also shows significant chemical stress when used as an electrolyte. The valence state of cobalt changes from 4+ to 2+ depending the local oxygen potential, the oxygen vacancy concentration changes significantly. The stress distribution was calculated under open circuit, operation, and short-circuited conditions for the flat- constrained and partially constrained situations. Large tensile stress is anticipated on the cathode side. Temperature distribution also enhances the development of the stress. Similarly as the electrolyte material, oxide interconnects such as lanthanum chromite based materials can also causes chemical stress in the cell. On the other hand, electrode material such as lanthanum cobaltite or cobalt ferrite has less effect of chemical expansion under normal operation conditions even though chemical strain is large when oxygen partial pressure decreases. Although overpotential at the electrode locally reduces the cathode material, the thickness of the electrochemically active layer is around or less than 10 micrometer in air. Together with the high porosity of the electrode, those materials are safely used in actual cell stacks. However, under accidental conditions such as stoppage of air flow, the large chemical expansion of the mixed conductor cathode causes fatal failure in a cell.

In contrast to the significance of chemical to mechanical coupling in SOFC materials, effects of mechanical stress on the chemical properties are not well understood, and expected to be negligible in a practical SOFCs. Direct effect of stress on the oxygen nonstoichiometry was found negligible by using electromotive force measurements.
Temperature Dependence and Desorption Kinetics of Porphyrins at the Solid-Solution Interface
Authors: Hipps K W , Mazur Ursula , Chilukuri Bhaskar , Bhattarai Ashish
Published: February 2020

The energetics and kinetics of metal porphyrin adsorption on conducting surfaces from solution are of great importance for the formation of self assembled structures for applications. In this study variable temperature solid-solution interfacial scanning tunneling microscopy (STM) imaging is used to probe the self assembly of porphyrin adlayers. It will be shown that the adsorption of cobalt octaethylporphyrin (CoOEP) and NiOEP from phenyloctane onto Au(111) is kinetically controlled and essentially irreversible below about 100°C. Above 100°C slow desorption and re-adsorption processes cause exchange of porphyrin species on the surface. Analysis of the results from studies conducted with varying concentration and temperature result in the relative free energies and enthalpies of activation for the desorption process. DFT calculated values of adsorption energy will be compared to the experimental results.
Synthesis and Photophysical Studies of Hydrophilic Zinc Phthalocyanine Dendrimers
Authors: Setaro Francesca , Torres Tomas , de la Escosura Andres , Hahn Uwe , Nonell Santiago , Ruiz Gonzalez Ruben
Published: February 2020

Phthalocyanines (Pc) and their metalloderivatives (MPc) are two-dimensional 18 π-electron aromatic porphyrin synthetic analogues1. Due to their excellent photochemical and photophysical properties, together with their chemical versatility, Pcs are perfectly suited for their application as photosensitizers (PS) in photodynamic therapy (PDT).

Pcs exhibit a strong absorption band in the visible region of the UV/vis spectrum from 630 to 750 nm and, in the presence of an appropriate central atom, they yield long-lived triplet excited states and high singlet oxygen photo-production2. Yet, although several Pcs disclose their capability to act as photosensitizing agents3, not many of them are soluble in aqueous media4.

In this communication, we report the synthesis, photochemical and photophysical characterization of a series of new metallodendrimers built around a zinc phthalocyanine core. Within the last step of the synthetic route, the terminal esters were hydrolyzed, giving rise to a dramatic change in polarity upon formation of multiply charged species that are very soluble in aqueous media.

Through photochemical and photophysical studies, we corroborated the capacity of these water-soluble species to produce singlet oxygen in air-saturated solution. Moreover, along with increasing dendritic shell, a significant increase in the generation of singlet oxygen was observed. These highly hydrophilic Pc dendrimers may thus be advantageous for the purpose of producing 1O2 in biological media by photosensitization.

References

[1] a) G. de la Torre, C.G. Claessens, T. Torres Chem. Commun 2000 (2010); b) G. de la Torre, G. Bottari, U. Hahn, T. Torres Struct. Bond
1, 135 (2010).

[2] a) C.G. Claessens, U. Hahn, T. Torres, Chem. Rec.
8, 75 (2008); b) L.M. Moreira, F.V. dos Santos, J.P. Lyon, M. Maftoum-Costa, C. Pacheco-Soares, N.S. da Silva, Aust. J. Chem. 61, 741 (2008); c) Handbook of Porphyrin Science, K.M. Kadish, K.M. Smith, R. Guilard (Eds.) vol. 4. World Scientific: Singapore, 2010.

[3] a) J.W. Hofman, F. van Zeeland, S. Turker, H. Talsma, S. A. G. Lambrechts, D. V. Sakharov, W. E. Hennink, C. F. van Nostrum, J. Med. Chem.
50, 1485 (2007); b) X.J. Jiang, S. L. Yeung, P. C. Lo,W.P. Fong, D. K. P. Ng, J. Med. Chem.
54, 320 (2011); c) J.T.F. Lau, X.J. Jiang, D.K.P. Ng, P.C. Lo, Chem. Commun. 49, 4274 (2013).

[4] a) N. Nishiyama, Y. Morimoto, W.D. Jang, K. Kataoka, Adv. Drug Deliver. Rev.
61, 327 (2009); b) U. Hahn, F. Setaro, X. Ragàs, S. Nonell, A. Gray-Weale, T. Torres, Phys. Chem. Chem. Phys.
13, 3385 (2011); c) M. Nishida, H. Horiuchi, A. Momotake, Y. Nishimura, H. Hiratsuka, T. Arai, J. Porphyrins Phthalocyanines
15, 47 (2011); d) T.L. Doane, C.H. Chuang, A. Chomas, C. Burda, ChemPhysChem
14, 32 (2013).
Cobalt Corrole Catalyzed Hydrogen Evolution Reaction: Surprising Electronic Effects and Characterization of Key Reaction Intermediates
Authors: Mahammed Atif , Mondal Biswajit , Rana Atanu , Dey Abhishek , Gross Zeev
Published: February 2020

A surprising effect of halide substituents on reduction potentials and catalytic activity of beta-pyrrole halogenated cobalt corroles has been deduced by experimental and computational methods. The proton-activating cobalt(I), as well as the cobalt(II) corrole that is formed in the step during which hydrogen is formed, were characterized by NMR spectroscopy.
Controlling Molecular Alignment on Highly Ordered Pyrolitic Graphite of Porphyrin-Tb(III) Double-Decker Single Molecular Magnets
Authors: Inose Tomoko , Tanaka Daisuke , Tanaka Horfumi , Ivasenko Oleksandr , Nagata Toshi , De Feyter Steven , Ishikawa Naoto , Ogawa Takuji
Published: February 2020

Single molecular magnets (SMMs) that show slow magnetic relaxation properties at low temperatures have great potential for use as nanoscale memory devices or quantum computers. In our study, we focused on porphyrin-Tb(III) double-decker complexes and their magnetic properties.1,2 Our goal was to control the molecular alignment of SMMs on highly ordered pyrolitic graphite (HOPG) by a self-assembling process. We synthesized protonated, anionic, and radical forms of octaethylporphyrin (OEP)-Tb(III) double-decker complexes and observed the molecular alignment of each molecule on HOPG using scanning tunneling microscopy (STM). The STM observations demonstrated that all OEP-Tb(III) double-decker complexes had similar pseudo-hexagonal packing structure stability on HOPG, regardless of differences in the electronic structure (Figure 1). In particular, the lattice parameters of protonated form 1 (a = 1.41 ± 0.03 nm, b = 1.46 ± 0.05 nm) showed almost the same values as anionic form 2 (a = 1.34 ± 0.01 nm, b = 1.42 ± 0.01 nm) and radical form 3 (a = 1.39 ± 0.04 nm, b= 1.45 ± 0.06 nm).

We also prepared and observed the molecular alignment of a protonated 5,15-bisdodecylporphyrin (BDP)-Tb(III) double-decker complex. This complex showed a lamellar packing structure on HOPG (Figure 2). Herein, we succeeded in isolating stable 2D supramolecular structures of all the OEP-Tb(III) double-decker complexes on HOPG. Control of molecular alignment was also realized by changing the substituents.

References:

1) A. Candini et al., Nano Lett.
2011, 11(7), 2634.

2) D. Tanaka, T. Inose, T. Ogawa et al., Chem. Commun.
2012, 48, 7796.
Wafer Scale Cu Plating Process Optimization for Defectivity Improvement
Authors: Ahmed Shafaat , Huang Qiang , Cheng Tien , Findeis Paul , Gruszecki Craig R , Simon Andrew H , Mclaughlin Paul S , Lustig Naftali , Engbrecht Edward , Lakritz Mark N , Wang Pei I , Montgomery Christa L , Mittal Surbhi , Baumann Frieder H , Truong Connie-Nga , Baker-O'neal Brett C. , Grunow Sarah L , Chudzik Michael P , Grunow Stephan
Published: February 2020

Defect-free copper damascene plating becomes more and more challenging as the BEOL interconnects continues to scale. In addition to the challenge from the small critical dimension, the thin liner/seed required for the overall resistance imposes even more challenges to the plating. The coverage of the Cu seed at the thickness used can be poor on the sidewalls of trenches and vias. The discontinuous Cu seed and the exposed or oxidized Ta liner are generally associated with the slit voids, cluster voids defects from plating. Furthermore, a non-optimized PVD etch back and re-sputtering process or its bias power could also cause a much localized variation of Cu-seed thickness along the side walls. When a trench side wall locally misses Cu seed void can easily form due to the lack of Cu nucleation during the entry and pulse step of plating, which is observed as slit hollow metal defect as being exposed after CMP. However, when the lack of Cu-seed occurs on both sidewalls of a trench a single line open hollow metal (shown below) defect is often observed, which we called HMS1 defects.

A typical PLY wafer map of HMS1 defect and its corresponding typical SEM review image (inset) is shown in Fig.1. Although this particular wafer shows the HMS1 defect signature spreading from 6:00-3:00 O’clock along the edge of the wafer, this defect signature can rotate 360 degree from wafer to wafer and/or lot to lot as shown by stacked map in Fig.1b. The stacked map also indicates that the density of HMS1 defects is high along the edge of the wafers at 6:00-3:00 O’clock position. Fig.2a-b shows a typical top down SEM images of HMS1 defect and its corresponding longitudinal cross-section TEM image respectively. Although the top surface shows the absence of the copper plating across the width of the line, its cross-sectional image confirms that copper was plated from the bottom of the trenches but stopped after the trench was partially filled. In this paper we will explain the mechanism of HMS1 defects formation and its modulation by co-optimization of Cu-seed process and plating entry condition. Detail failure analysis will also be presented to correlate the post plating defect with the localized absence of Cu-seed along the trench side wall where Cu did not nucleate during plating. The methodology in achieving a low defectivity on a wafer scale will be discussed.

Fig.1 (a) shows a HMS1 PLY defect map on a single wafer and (b) shows stacked map of this defect from 20 lots

Fig.2. (a) shows a typical top down HMS1 defect and (b) shows its corresponding x-section TEM image
Advances in H2-Br2 Fuel Cell Research
Authors: Nguyen Trung Van , Yarlagadda Venkata , Konwar Dhrubajit , Masud Jahangir , Lin Guangyu
Published: February 2020

Development of new electrode materials for the bromine reactions and stable and active catalysts for the hydrogen reactions in HBr/Br2 solutions and the discharge/charge performance of an acid-based H2-Br2 fuel cell with these materials will be discussed. New development and performance results on an alkaline-based H2-Br2fuel cell system will also be presented.

Acknowledgements

This work was funded by NSF through grant number EFRI-1038234 and DOE/ARPA-E under award number DE-AR0000262.
Degradation of Electrode Materials in Vanadium Redox Flow Batteries
Authors: Pezeshki Alan , Sun Che-Nan , Zawodzinski Thomas A. , Mench Matthew M.
Published: February 2020

Recent works in vanadium redox flow batteries (VRFBs) have been successful in improving the energy density by increasing vanadium solubility in the electrolyte1 and achieving high power density through electrode modification, membrane selection, and superior cell design 2,3. These accomplishments lead to significant reduction of the system cost and therefore enhance the economic attractiveness of VRFB technology.

To achieve market implementation, the large-scale energy storage system requires a balance between performance, cost, and durability. While power and energy densities have been recently improved, the investigation of component durability, which is equally important, has yet to be reported in significant detail.

In this work, we demonstrate an approach to study the electrode degradation in single-cell VRFBs.

Ex-situ electrolyte soaking experiments were used to determine conditions under which the electrodes degrade, and the extent of the degradation. Several techniques were adopted to characterize property changes in the degraded materials. Various carbon materials were investigated to determine viable candidates and characteristics required for long-term use in VRFB systems.

Additionally, in-situ cycling tests of various carbon materials have been carried out to illustrate the relationship between material degradation and cell performance decay. Declines in performance (Fig. 1) are monitored and correlated to changes in the material properties. Modification of the cycling parameters reveals operating conditions leading to the most severe decay in the carbon material, so that accelerated degradation protocols can be developed for evaluation of additional materials.

References

1. L. Li, S. Kim, W. Wang, M. Vijayakumar, Z. Nie, B. Chen, J. Zhang, G. Xia, J. Hu, G. Graff, J. Liu, Z. Yang, Adv. Energy Mater., 1, 394, (2011).

2. Q. H. Liu, G. M. Grim, A. B. Papandrew, A. Turhan, T. A. Zawodzinski, M. M. Mench, J. Electrochem. Soc.,
159, A1246, (2012).

3. D.S. Aaron, Q. Liu, Z. Tang, G.M. Grim, A.B. Papandrew, A. Turhan, T.A. Zawodzinski, M.M. Mench, J. Power Sources, 206, 450, (2012).

4. M. Zhang, M. Moore, J.S. Watzon, T.A. Zawodzinski, R.M. Counce, J. Electrochem. Soc., 159, A1183, (2012).
Laser-Perforated Carbon Paper Electrodes for High-Power Vanadium Redox Flow Batteries
Authors: Mayrhuber Immanuel , Dennison Christopher R , Kalra Vibha , Kumbur Emin Caglan
Published: February 2020

Recently, there has been considerable effort to increase the power density and lower the cost of vanadium flow battery (VRFB) systems via new system architectures and optimized electrode materials. To date, research on electrodes has primarily focused on improving the surface area, surface chemistry, pore size distribution and resistivity of the material to improve the reaction kinetics, mass transport ability and the areal series resistance (ASR).While carbon felt materials have been conventionally used, the recent push for higher power densities has required the application of new electrode materials.

Carbon paper was proposed by Aaron et al. as high-performance VRFB electrode material [1]. This material has a reduced thickness and high active surface area, as compared to carbon felt, which reduces the ASR and overpotential, and significantly improves the current- and power density. In their study, the authors demonstrated a VRFB with a peak power of 557 mW cm-2 . Liu et al. further improved the performance of a VRFB with no-gap architecture by thermal pre-treatment of carbon paper electrodes in air [2]. The thermal treatment showed a 16% improvement in power density compared to the raw material.

Although carbon paper electrodes exhibit significantly higher power density than carbon felt electrodes, they have a significantly lower porosity and reduced pore size. As a result, mass transport is expected to be problematic in these materials. To address these limitations, we utilized a procedure similar to Manahan et al. [3] by introducing laser perforations to facilitate the transport of reactants within this type of electrodes. A CO2 laser was employed to cut different hole patterns in SGL 10AA carbon paper. Specifically, the hole diameter and hole density (number of holes per electrode) were varied in order to better understand the tradeoffs between improved mass transport and reduced surface area in these materials. It was found that a 30% improvement in power density (as compared to non-perforated electrode) was achieved through optimization of the perforation pattern. Interestingly, this condition corresponds to a loss of 15% of the original surface area due to laser perforation. The results of this study highlight the fact that by proper tailoring the transport pathways in the electrode structure, it is possible to achieve significantly higher power density with a low surface area electrode material.

References:

[1] D.S. Aaron, Q. Liu, Z. Tang, G.M. Grim, A.B. Papandrew, A. Turhan, T.A. Zawodzinski, M. M. Mench, Journal of Power Sources 206 (2012) 450-453.

[2] Q.H. Liu, G.M. Grim, A.B. Papandrew, A. Turhan, T.A. Zawodzinski, M.M. Mench, Journal of The Electrochemical Society 159 (2012) A1246-A1252.

[3] M.P. Manahan, M.C. Hatzell, E.C. Kumbur, M.M. Mench, Journal of Power Sources 196 (2011) 5573-5582.