bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulation of Surface pH-Effects and Near-Surface Ion Distributions during Reactions at the Solid/Liquid Interface
Authors: Auinger Michael 
Published: February 2020

Many processes such as the corrosion of metals, the charging of a battery or reactions in electrocatalysis are prone to local activity changes of reactive species. In such complex systems, these changes often define the macroscopic behavior. However, a clear experimental deduction of individual reactions on the overall current signal appears to be very difficult in many cases. Whereas the influence of the local ion activities near the surface, exemplified for the Hydrogen Oxidation Reaction (HOR) / Hydrogen Evolution Reaction (HER) on Pt in H2-saturated solutions has been discussed previously [1], it could be shown that for fast reactions, thermodynamic modeling predictions agree well with measured cyclic voltammograms [1, 2]. Further it was demonstrated that even in a weakly buffered solution (up to 10 mM total buffer concentration), the analytical equation not only reflects the experimental current-voltage characteristics but is also capable to deliver the local distribution of all contributing ions in the diffusion zone.
This work critically reviews the original modeling approach [1], illustrates its limitations and presents recent developments towards a more general model by including the local enrichment of buffer species and (slow) reaction kinetics, depending on the actual conditions at the electrode surface and in the bulk solution. Obtained results will be compared to recent progress in the field [3, 4], showing that the influence of local activity changes near the surface are likely to affect the behavior of the macroscopic system. This becomes particularly relevant for local electrochemical processes such as either atmospheric corrosion, the dissolution of a cathodic protection layer (e.g. Zn coated steel) or other reactions that consume/produce a large amount of protons.
While the modeling approach presented in this work cannot be directly used to derive the properties of a complex electrochemical system with a large multitude of reactive species and reaction steps, it remains helpful to deduce the influence of individual components on the macroscopic system.

References

[1] M. Auinger, I. Katsounaros, J. C. Meier, S. O. Klemm, P. U. Biedermann, A. A. Topalov, M. Rohwerder, K. J. J. Mayrhofer, Phys. Chem. Chem. Phys. 13 (2011) 16384-16394.
[2] I. Katsounaros, J. C. Meier, S. O. Klemm, A. A. Topalov, P. U. Biedermann, M. Auinger, K. J. J. Mayrhofer, Electrochem. Commun. 13 (2011) 634.
[3] D. Strmcnik, M. Uchimura, C. Wang, R. Subbaraman, N. Danilovic, V. van der Vliet, A. P. Paulikas, V. R. Stamenkovic, N. M. Markovic, Nat. Chem. 5 (2013) 300.
[4] M. D. Arce, H. L. Bonazza, J. L. Fernandez, Electrochim. Acta 107 (2013) 248.
(Invited) Numerical Simulations of Mass Transport Using Separation of Variables: an Old Method Rejuvenated with Symbolic Algebra Software
Authors: Holm Thomas , Sunde Svein , Seland Frode , Harrington David A. 
Published: February 2020

Separation of variables is a classic method of solving partial differential equations, such as the convective diffusion equations that are ubiquitous in electrochemistry. It leads to infinite series solutions, which are exact analytical solutions. However, various parameters involved in the series have to be numerically evaluated, and the series converge rather slowly, which has meant that this method has not been used for practical numerical calculations of concentration profiles for electrochemical problems. We show here that these difficulties can be overcome, and demonstrate the use of the symbolic algebra program Maple in a practical implementation of this for steady-state convective diffusion past electrodes in a 2-D channel [1].
The key to successful implementation has been the use of asymptotic formulas to reliably locate the eigenvalues, so that the numerical solver does not miss any.
The method has the following advantages:
1. It is a mesh-free method, so a separate step of validating the mesh or grid is not necessary.
2. The global error can be estimated by evaluating the series to more terms.
3. Each segment (above an electrode or insulating section) is solved at once, so changing the length of an electrode does not change the difficulty of the calculation.
4. Workup of the concentrations to derived quantities such as currents or collection efficiencies can be done without any degradation of accuracy.
The present implementation assumes diffusivities of reactant and product are equal, which allows the generation of both concentration profiles in a single calculation by using a recently developed transformation method [2]. It also neglects axial diffusion. Future work will seek to remove these limitations, and extend the results to 3-D and time-dependent systems.
References:
[1] T. Holm, S. Sunde, F. Seland and D.A. Harrington, A Semianalytical Method for Simulating Mass Transport at Channel Electrodes, J. Electroanal. Chem.,745 (2015) 72-79.
[2] D.A. Harrington, Rules to Transform Concentrations and Currents for Irreversible Reactions to those of Quasireversible Reactions, Electrochim. Acta., 152 (2015) 308-314.
Figure 1. Concentration Profile for a Collection Efficiency Calculation at Electrodes in a Channel. X = distance along channel, Y = distance across channel (dimensionless variables). Electrode between X = 0 and X = 1 producing species at the limiting current, Electrode between X = 2 and X = 3 consuming species at the limiting current.

Figure 1
(Invited) Nanoelectrochemical Modeling: Elucidation of the Reaction Mechanism
Authors: Mirkin Michael V. , Yu Yun , Zhou Min , Oleinick Alexander , Svir Irina , Amatore Christian Andre 
Published: February 2020

We recently introduced new methodology for detecting charged reactive intermediates of heterogeneous processes and used it to investigate the oxygen reduction reaction at polycrystalline Pt. A nanometer-sized pipette filled with organic solvent immiscible with the external aqueous solution was used as a tip in the scanning electrochemical microscope (SECM) to detect and identify a short-lived superoxide intermediate and determine the rate of its generation at the catalytic Pt substrate. The interpretation of that experimental data was based on a simplified model that left a number of open questions about superoxide desorption and its lifetime in neutral aqueous solution. Here we report the results of finite element simulations based on a more exact model and aimed at the detailed mechanistic analysis of this system.
(Invited) Advanced Control of Two-Phase Flow in Gdl for PEM Fuel Cells
Authors: Wang Yun 
Published: February 2020

Water management is a central issue in the development of polymer electrolyte fuel cells (PEFCs): liquid water could considerably increase the oxygen transport resistance and hence the transport polarization whereas dryness dehydrates the electrolyte membrane, raising the Ohmic voltage loss. PEFCs produce water during operation and the electro osmosis enlarges the water imbalance between the anode and cathode sides, making water management a complex operation that requires a careful treatment. Issues such as diffusion media dewetting, anode rehydration, and internal humidification have received much attention in recent years. Modeling, numerical simulation, and advanced imaging techniques are capable of revealing details of transport phenomena, and are a powerful tool for elucidating water management.
In this talk, I will cover the below subjects which are the major contributions of UC Irvine to water management: 1.) nonisothermal two-phase flow modeling; 2.) transient dewetting of gas diffusion layer (GDL); 3.) theoretical approach of defining control parameters to characterize two-phase flows; and 4.) experimental evaluation of two-phase flow in PEFCs using neutron radiography. In 1.), a nonisothermal two-phase model, accounting for vapor-phase diffusion and heat pipe effect, was developed and implemented to investigate liquid water distribution. The model was validated in detail against liquid water distribution across GDLs. In 2.), a transient model was developed to capture the phase change and interface movement in PEFCs. A case study will be presented to show the timescale of material dewetting at different regions of GDLs. In 3.), A dimensionless parameter Da0 will defined to characterize the in-plane two-phase region. When Da0 is over 1, part of the GDL region is free of water due to waste heat production and evaporation. A liquid-free GDL region is defined and related to Da0. Impacts of operating temperatures, GDL thermal conductivities, and current densities on the region will be discussed. In 4.), I will present an in-situ study to examine the water content in PEFCs using neutron radiography. Various conditions such as different PTFE loadings in the GDL including the micro-porous layer (MPL), different flow fields (single-channel and quad-serpentine channels), and co-/counter-flow configurations are investigated.
Cell Reversal Phenomenon during Start-up of Alkaline Fuel Cell Stacks
Authors: Akhtar Naveed 
Published: February 2020

Successful start-up of any fuel cell is one of the basic and mandatory requirements before a useful power can be drawn out of it. In a liquid electrolyte alkaline fuel cell, the start-up dynamics are slightly more complicated as compared to the solid electrolyte type of fuel cells. The reason being that besides reactant gases, liquid electrolyte has to be present. This is to ensure that it acts as a barrier between the reactant gases to allow a useful cell potential to be obtained. During start-up, the competition between each of the fluid’s dynamics dictates the voltage of the cell. The cases, in which the cells are either facing a lag in air supply or a lag in fuel supply, would be temporarily starved of reactants and will not be able to establish a useful open circuit potential. The experiments show that during such events, the underlying cells may reverse in polarity and locally damage the electrodes. This damage can be prevented if the local reactant supply is restored as early as possible; therefore, the cells are able to generate useful driving potentials. The analysis suggests that the presence of air/fuel mixture in a single compartment is the likely reason for cell reversal.
Theoretical Calculations of Ammonia Oxidation Kinetics on Platinum, Iridium and Their Bimetallic Clusters
Authors: Estejab Ali , Botte Gerardine G 
Published: February 2020

Introduction

Population increase and technology growth are the main reasons for increasing demand of energy sources and fossil fuels consumption as the main energy source consequently increases. However, these fuels emit large amounts of greenhouse gases to the atmosphere. Moreover, they are not renewable resources. Hydrogen as an energy carrier is attractive because the only product of its combustion is water. However, production and storage of hydrogen raises concerns about costs and safety. Ammonia (NH3) can be used as a hydrogen source and it requires about 5% of the thermodynamic cell voltage (0.06 V) needed to produce hydrogen from water [1-4].
2NH3(aq)+6OH- → N2(g)+6H2O+6e- E°=-0.77V vs. SHE (1)
6H2O+6e- → 3H2(g)+6OH- E°=-0.83V vs. SHE (2)
2NH3(aq) → N2(g)+3H2(g) E°=0.06V (3)

Objectives

In order to decrease the cost of hydrogen production through ammonia electrolysis, the kinetics of the process should be known. While experimental techniques are the primary procedure for elucidating the kinetics especially on monometallic surfaces, theoretical calculation can be fascinating in terms of investigation of intermediates produced during the surface reaction. These intermediates can not be recognized with traditional experimental methods on monometallic, bimetallic or polymetallic surfaces. In this work, density functional theory calculations are performed on four platinum-iridium clusters, Pt3-xIrx (x=0-3) to examine ammonia oxidation in alkaline media. The adsorption of NH3-x(x=0-3) on these clusters and the effect of cluster composition on the adsorption are investigated. The hybrid B3LYP level of theory is used in Gaussian 09 along with the LANL2DZ and 6-311++g basis sets.

Results

Our Preliminary results for the HOMO-LUMO gap of adsorbed species on clusters, combined with activation and dissociation energy calculations of sequential dehydrogenation reactions of NH3→NH2→NH→N showed that Ir3 is more active than Pt3for ammonia oxidation. Additionally, the combination of iridium and platinum makes a more favorable pathway for the ammonia oxidation reaction. However, experimental analyses indicate improved reactivity on platinum in comparison to iridium in ammonia oxidation. This suggests the possibility of two different mechanisms for ammonia oxidation on platinum and iridium.

References

[1] F. Vitse, M. Cooper, and G. G. Botte, "On the use of ammonia electrolysis for hydrogen production," Journal of Power Sources, vol. 142, pp. 18-26, 2005.
[2] G. G. Botte, "Electrochemical method for providing hydrogen using ammonia and ethanol," U.S. Patent No. 8,221,610 2012.
[3] G. G. Botte, M. Cooper, and F. Vitse, "Electro-catalysts for the oxidation of ammonia in alkaline media," U.S. Patent No. 7,485,211 2009.
[4] B. K. Boggs and G. G. Botte, "Optimization of Pt-Ir on carbon fiber paper for the electro-oxidation of ammonia in alkaline media," Electrochimica Acta, vol. 55, pp. 5287-5293, 2010.
Investigation of Graphene Oxide Coating for Protection against Seawater Corrosion
Authors: Kolathodi Muhamed Shareef , Voigt Victoria , Singh Gurpreet 
Published: February 2020

2D materials such as graphene oxide, and Boron nitride-Carbon nanotube composite were prepared by chemical oxidation technique and coated on metallic substrates (copper foil) by slurry coating followed vacuum drying method. The anticorrosion and chemical resistivity of the coated substrates was studied quantitatively and qualitatively in 0.1 M NaCl solution using electrochemical and microscopic techniques. In general, all the coatings prevent corrosion while graphene oxide layer reduces the corrosion rate ~1/20 times of the bare copper. The mechanism of the corrosion inhibition also discussed in detail.
(Invited) Impacts of Environmental Stress Factors on Li-Ion Battery Safety Margins
Authors: Barrera Thomas Paul , Brown Glen M 
Published: February 2020

Since the mid-1990’s, many commercial, automotive, and aerospace platforms have transitioned from heritage aqueous electrolyte nickel-based energy storage batteries to lithium-ion battery (LIB) based electrical power subsystems. For space applications, the transition from nickel-hydrogen (Ni-H2) batteries to LIB’s was accelerated by growing concerns with Ni-H2 raw materials obsolescence issues. Although significant research efforts were undertaken to mitigate the risk of Ni-H2 raw materials obsolescence, the recurring cost of maintaining multiple Ni-H2 battery technology supply sources was prohibitive versus the longer-term benefits of supporting a deliberate transition to LIB technologies. Other transitional market forces such as consumer demands to reduce system mass, volume and cost continue to drive the commercial electronics and automotive industries. While it is widely recognized that the mass market for LIB’s in consumer electronics is reaching maturity, the automotive and aerospace marketplace continues to experience new technology growth opportunities. These emerging markets are highly leveraged against economic incentives to pursue safe and reliable LIB design solutions to meet demanding customer requirements.
Traditionally, implementing safe and reliable LIB design solutions into aerospace platforms included considerations of simplistic first-order interactions between thermal, mechanical, and electrical environmental stress factors. However, industry experience indicates that the effect of certain synergistic stress factors on LIB performance characteristics in their service environments is a complex multi-dimensional problem. For example, induced and natural environmental stress factors such as thermal cycling, vibration, and radiation have been shown to impact LIB battery performance and in some cases, safety margins. Specifically, certain high-performance LIB aerospace and automotive power systems have recently been challenged to understand the principles governing lithium-ion cell thermal runaway in far greater detail than previously accepted.
The severity of lithium-ion cell thermal runaway has created a need for identifying LIB design modifications which reduce degree of severity. The consequences of thermal runaway have the potential to make lithium-ion chemistry an at-risk technology for some applications. To mitigate these risks, investigators from academia, government, and industry have shifted research efforts toward identifying key factors which contribute to the severity of thermal runaway. This work focuses on identifying gaps and opportunities in achieving new paradigms for mitigating LIB safety hazards. Challenges with current technologies to increase LIB safety margins and steps required to reach the readiness level required for successful insertion in an industrial application will also be presented.
Safety Testing in Lithium Ion Cells Comparing Thermally Stable Nanofiber-Based Separators to Traditional Polyolefin Separators
Authors: Morin Brian , Kaschmitter James , Khokhlov Pavel , Hu Carl 
Published: February 2020

2.7 Ah Pouch cells of LiFePo4 and graphite were made with four different separators:

25 micron polypropylene dry process (PP)

25 micron ceramic coated polyethylene wet process (PE)

Dreamweaver Silver 25 micron

Dreamweaver Gold 25 micron.

Starting electrical performance was nearly identical between the cells before testing:

Hard Short: The cells were shorted between their tabs. The cells all performed the same, with the anode tab (4 mm tab) getting red hot, and the cells slowly heating and internally gassing until the seal broke.

Overcharge: The cells were charged at 2C from 30% SOC. All uncoated cells failed at 5.55 V by outgassing, while the ceramic coated PE failed at 5.9 V. There were no flames, and the temperature rise was uniform between cells.

Hot Box: Cells made with PP and PE/ceramic separators both had fast temperature rise and they also both experienced a catastrophic short after around 20 minutes. DWI Silver and Gold cells maintained operational voltage for 1 hour and survived without shorting. The short for the PE/ceramic cell occurred with onset at around 140 C, and for the PP cell at around 145 C. Both of the DWI cells rose to 170C, the oven temperature, without experiencing a short.

Nail Penetration: Cells made with both PP and PE separators dropped immediately to a persistent 0V along with faster and higher temperature rise (up to 115 C) than the cells made with Gold (40 C) and Silver (60 C). The Dreamweaver cells, on the contrary, experienced only a small voltage drop of approximately 100 mV, with a slow rise thereafter as the cell discharged. The DWI cells continued to function throughout the test and retained 2/3 of their charge and capacity after completion of the test.

Shutdown Function: In no test was a shutdown function observed to improve the performance in any of the cells.

Figure 1
The Effects of High G Impacts on Li-Ion Batteries
Authors: Shahed Khah Nasrin , Offer Gregory James , Patel Yatish , Bhagat Rohit , Dashwood Richard 
Published: February 2020

Increasing electrification of vehicles has led to a growing demand for Li-ion batteries in automotive applications. Automotive vehicles experience cyclic mechanical loads during operation, which may include; acceleration, deceleration, shock, vibration and collision. Most of these events are not severe and do not have an instantaneous effect on the battery, however it is unclear if there is a cumulative effect over time. This cumulative effect may have a significant impact on performance and safety of the battery. The collective effect of these types of mechanical events is not well characterised and there exists a gap in knowledge. This is due to the difficulty in replicating real world conditions in the laboratory.
This project focusses on the study of Li-ion batteries during static testing (3-point bend) and dynamic testing (acceleration/deceleration pulses). Several 3 point bend tests were carried out where the cell was bent to up to 30 mm and the relaxation behaviour was captured by monitoring the reduction in load over time. The electrochemical impedance of the cells was also monitored during the relaxation period and then cycled between 2.7 and 4.2 V. After each cycle, EIS was performed in order to detect impedance variation. The gradual separation of the internal structure of the cells was also captured using X-ray tomography as demonstared in fig.1. This image reveals clear separation of the internal layers at the point of contact with the side rollers and this significant separation will directly impact the performance of the cell in long term. High precision coulometry was also used as another technique to predict the cycle life of the cells besides identifying any degradation mechanism due to the severe bending. For dynamic testing cells were exposed to up to 1000 g pulses, using a drop tower (10 kJ maximum energy input). Impedance, differential capacity, and capacity of the cells were analysed before the drop, after the drop and then periodically during storage at 35oC.
Results from the high g impact tests showed that there was damage caused to the cells, but this could not be observed using EIS until after electrochemical cycling, which then manifested as an increase in the impedance of the cell. This suggests that the mechanisms are more complicated than simple damage caused by the impact, but that the impact causes damage which cannot be detected. These damages are then exacerbated by charging/discharging which then can be identified. We expect this to have significant implications for safety particularly that it may not be possible to detect damage caused by impacts without working the cells, hence this has an inherent risk. The long term effects of these incidents with regards to failure threshold are yet to be investigated.
Figure.1: CT image demonstrating clear separation of the internal layers of a pouch cell under 3 point bend loading.

Figure 1
In-Situ Scanning Electron Microscopy Observation of Lithium Dendrite Growth on Carbon Electrodes
Authors: Tang Ching-Yen , Dillon Shen J. 
Published: February 2020

The formation of lithium dendrites at the anode during charging can result in capacity fade and potentially lead to internal short circuits. Adopting high capacity next-generation technologies, such as Li-air or Li-S, exacerbates this problem. Although this phenomenon has been known to be a primary safety concern and source of failure for decades, limited remedies exist to suppress dendrites growth. This partially stems from our limited understanding of the mechanism(s) governing Li dendrite nucleation and growth during cycling. While several models have been proposed, a general agreement has yet to be reached, which motivates our current work.
In this work, in-situ scanning electron microscopy was used to investigate the growth of lithium dendrites. The cell was composed of lithium cobalt oxide as the cathode, carbon film as the anode, and a Li imide salt dissolved in P13TFSI ionic liquid as the electrolyte. We were able to observe operando growth of lithium dendrites on the carbon film. The experimental configuration differs from typical Li-ion systems, since the dendrites do not grow along the field gradient, suggesting that this is not the primary source of dendrite growth. The morphologies and growth rates of lithium dendrites were characterized as a function of time and applied voltage. Additionally, the focused ion beam was utilized to cross section the lithium dendrites in-situ in order to characterize the internal morphology. The results provide new insights into the roles of surficial reactions and stresses in driving the formation of dendrites.