bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determining Microwire Morphology and Current Transient Trends from Single Microwire Electrodeposition
Authors: Zhang Tim , Fahrenkrug Eli , Maldonado Stephen 
Published: February 2020

This presentation describes work on understanding and controlling the electrochemical liquid-liquid-solid (ec-LLS) process for the preparation of crystalline semiconductor materials. In this work, data are presented to test the hypothesis that the current-time transient collected during a potentiostatic ec-LLS deposition of Ge microwires contains useful details about the crystal growth. A photoresist pattern with a single hole was fabricated on top of a conductive support to make an ultramicroelectrode (UME) with a defined diameter ranging between 10 and 35 microns. These single-hole UMEs were filled with a liquid metal which acted as the electrode and crystal solvent in ec-LLS. Individual germanium microwires were then electrodeposited onto the liquid metal by chronoamperometry from an aqueous solution using a variety of different potential, temperature, and liquid metal conditions. Current transients will be discussed in relation to their correlation with morphological and crystallographic features of as-prepared Ge microwires. The prospects for real-time adjustment of microwire growth during an ec-LLS process will be presented.
Understanding of Rate-Limiting Behavior and of Diffusion in Commercial LiCoO2 Electrodes Via Electrochemical Impedance Spectroscopy
Authors: Ahmed Kazi Rakib , Ozkan Mihri , Ozkan Cengiz 
Published: February 2020

Electrochemical impedance spectroscopy has been used to investigate rate-limiting conditions in commercial LiCoO2 cathodes. The insights gained may be extended to most lithium-ion battery systems. In general, two possible rate-limiting conditions may exist in a lithium-ion battery - i) diffusion limited, and ii) electron exchange-rate limited. In the former case, rate of diffusion (of ions) is slower than that of redox reactions occurring at active material surface - leading to a negative concentration gradient (of ions) toward the electrode surface for cathodic reactions. In the latter case, a positive concentration gradient persists toward the electrode surface for cathodic reactions. Insights into electrical equivalent circuits derived via electrochemical impedance spectroscopy have led to novel ways of recognizing the rate-limiting behavior in LiCoO2 half-cell.
Rotational Waves in an Oscillatory Electrochemical System
Authors: Sebek Michael L , Kiss Istvan Z 
Published: February 2020

The existence of waves in distributed systems has been observed in chemical systems mainly through reaction-diffusion methods and such waves can be rotational when performed on a ring-shaped surface. In such ring systems, phase model analysis predicts several waves may co-rotate in an even distribution over the ring.
In this contribution, an experimental setup composed of twenty nickel electrodes undergoing electrodissolution is constructed to investigate rotational waves. The electrodes are positioned into the ring topology by coupling. Only complete synchrony is attained when coupled. In order to arrive at a rotational state, the temporary application of topology alterations and global feedback is required.
Four rotational solutions are found, distinguished by the rotational velocity and the number of waves in each rotation. The rotational velocity is defined as ν0/m where ν0 is a base velocity of all rotations and m is the integer winding number which is equal to the number of waves in the rotation. The non-rotational solution, m=0, is characterized by complete synchronization while the rotational solutions are winding numbers m=1,2,3,4 where a specific winding number is achieved by the application of appropriate topological tuning. Any further increase in winding number is shown to not be stable without external assistance. The results indicate rotational waves, predicted by phase model approximations, can be realized by the application of the experimental method.
In-Situ x-Ray Diffraction Study of Pt(111) Oxidation during Oxygen Reduction Reaction (ORR)
Authors: Drnec Jakub , Ruge Martin , Reikowski Finn , Rahn Bjorn , Carlà Francesco , Felici Roberto , Stettner Jochim , Magnussen Olaf M. , Harrington David A. 
Published: February 2020

ORR is one of the most studied electrochemical reactions due to it’s tremendous fundamental and practical importance. Oxygen is common, readily accessible oxidizing agent and therefore Pt ORR cathode is part of many energy conversion devices, e.g., fuel cells. Unfortunately, slow kinetics of ORR negatively affects the performance and it is currently one of the main bottleneck in large scale fuel cells commercialization. It is partly caused by the presence of surface Pt oxides, which slow the reaction rate and trap reaction intermediates on the surface. The oxide formation and dissolution is also known to cause dissolution of Pt catalyst, which further degrades the performance.
Even though the electrochemical formation of surface oxides on platinum surface has been extensively studied in the past, there are still many questions unanswered. Mainly about the detailed structure of the oxide and its growth mechanism [1 and references there-in]. Most of the studies were performed in the absence of O2, the fuel cell oxidant, and therefore they are less relevant to the fuel cell operation as gaseous O2 can modify the oxidation potentials and mechanism. Given the above, further fundamental understanding of Pt oxidation mechanism measured in-situ is clearly needed in order to determine the role of surface oxides in ORR and its effect on the fuel cell performance. Here we show the results of in-situ study of electrochemical oxide formation on Pt(111) and how it is influenced by presence of O2 during ORR.
We find that oxide growth, and Pt-O site switching, is present as soon as 700 mV vs. Ag|AgCl reference electrode in 0.1M HClO4 and causes slow, irreversible roughening of the surface. When the potential is increased, the roughening is more severe and after several tens of cycles from -125 mV to 900 mV, the surface loses it’s order. This is seemingly in contradiction with widely accepted notion that cycling the Pt(111) up to 900 mV does not affect significantly surface structure. We show that the roughening is dependent on the initial state of the sample and it is an autocatalytic process.
Adding oxygen into the electrolyte does not have any notable effect on the oxidation potentials or kinetics and it is in disagreement with previous results where negative shift of the oxidation onset was observed in O2 containing electrolyte [2]. This results points to the fact that OH- is dominated species during Pt electrooxidation and oxygen has only a side role. However, depending on the history of the sample, it is likely that PtO species are present on the surface and should be taken into the account in theoretical investigations.
[1] Kongkanand and Ziegelbauer, Journal of Physical Chemistry C, 116 (2012) 3684-3693; [2] Matsumoto, Miyazaki, Imai, Phys. Chem. C, 115 (2011) 11163−11169.
Exceptionally Fast Hydrogen Absorption and Desorption through Platinum Overlayers
Authors: Polczynski Piotr , Jurczakowski Rafal Robert 
Published: February 2020

Palladium alloys are widely used in heterogeneous catalysis, in this group Pd–Pt systems are of particular catalytic interest. They are active components for anodes in low temperature fuel cells and hydrogenation of aromatic compounds in fuels. Platinum monolayers deposited on palladium have been recognized for their unique catalytic properties towards oxygen reduction reaction. However, the hydrogen absorption has never been studied on platinized palladium. In this work we have demonstrated for the first time that platinum overlayers deposited on palladium surface are not only permeable to hydrogen but also enhance the kinetics of the hydrogen absorption/desorption by several orders of magnitude. In this study palladium-hydrogen was chosen as a model system forming nonstoichiometric hydrides.
The hydrogen electrosorption in thin palladium films (50-1000nm) has been investigated at electrodes covered with platinum overlayers. The highest absorption kinetics have been observed for Pd electrodes fully covered with 1 – 3 platinum monolayers. By means of electrochemical impedance spectroscopy (EIS) we have shown that the process is diffusion limited at platinized samples. Diffusion coefficient, D
H, determined in EIS, is two orders of magnitude higher than that previously reported for thin palladium films and approaches D
Hfor bulk palladium. The approach provides insight into the mechanism of hydrogen absorption and the process of hydrogen transport in metals-hydrogen systems.
Surprisingly high stability of the platinized palladium enable its use in heterogeneous catalysis, hydrogenation reactions, or hydrogen purification. It should be stressed that palladium has already been proven to serve as an efficient catalyst to facilitate hydrogen insertion into other metal hydrides. Therefore, another set of potential applications is related to hydrogen storage or sensing systems, where fast and selective reaction in the presence of hydrogen is required.
New Method to Determine Eley-Rideal Barriers for 2e- and 4e- Oxygen Reduction Reactions in Fuel Cells
Authors: Yu Ted H. , Tsai Ho-cheng , Ravishankar Sundararaman , Goddard William A 
Published: February 2020

We use atomic level simulations with density functional theory (DFT) to calculate barriers on Pt and Pd catalysts for Eley-Rideal (ER) reactions during the oxygen reduction reaction (ORR) in fuel cells. In our new method, we simulate the hydrogen coming into the reaction from H+ in the solution. Our method of calculating potential dependent ER barriers in fuel cells does not use external potential or nonzero charged calculations. The barriers are determined using a single nudged elastic band (NEB) calculation. A new scheme determines simultaneous zero-capacitance anode/cathode barriers. An accurate solvation method is used to include the effect of water solvation1

The following new ER calculated barriers supplement our previous calculations of Langmuir-Hershelwood (LH) barriers2.
OOHad + H+ + e- -> HOOHad

OHad + H+ + e- -> HOHad

OOad + H+ + e- -> OOHad

OOHad + H+ + e- -> HOOHad

OOHad + H+ + e- -> 2OHad

Using the combined ER and LH barriers, we determine the rate determining step for ORR for Pt and Pd at different potentials. The ER barriers calculated agree well with previous methods3. They also can predict whether a catalyst favors the 2e- or 4e-ORR.
Figure 1: The barriers differ significantly for 2e- and 4e- ORR on Pt and Pd. For Pd, HOOH formation is favored by 0.06 eV at 0.8 V. On the other hand for Pt, water formation is favored by 0.33 eV at 0.8 V. The Pt water formation barrier also agrees with previous methods3.
References:
1. R. Sundararaman, K. Letchworth-Weaver and T. A. Arias, J Chem Phys 137(4), 044107 (2012).
2. T. H. Yu, T. Hofmann, Y. Sha, B. Merinov, D. J. Myers, C. Heske and W. A. Goddard, J Phys Chem C (117), 26598-26607 (2013).
3. V. Tripkovic, E. Skulason, S. Siahrostami, J. K. Norskov and J. Rossmeisl, Electrochim Acta 55, 7975-7981 (2010).

Figure 1
Molecular Simulation and Performance Prediction of High-Temperature Molten-Salt Batteries
Authors: Li Hao-Yu , Chen Chung-Fu , Cheng Yi-Chia , Hong Che-Wun 
Published: February 2020

This research aims to enhance the discharging rate and to improve the overall performance of a high-temperature molten salt battery. We use molecular dynamics (MD) simulation techniques to develop some novel ternary and quaternary molten electrolytes to replace conventional binary LiCl–KCl ones [1]. These novel electrolytes are listed in Table I and their molecular structures are shown in Figure 1. These molecular structure configurations are based on their minimal total energies and we use Hamiltonian dynamics to predict their trajectories and subsequent properties.
Our simulation results are consistent with the results of previous experimental studies regarding the LiCl-LiBr-based ternary (LiCl–LiBr–NaCl & LiCl–LiBr–NaBr) and quaternary (LiCl–LiBr–NaCl–KCl & LiCl–LiBr–NaBr–KBr) electrolytes. The simulation results with greater ionic conductivity and higher melting points are consistent with experimental results reported by previous literatures [2, 3]. The tendency is shown in Figure 2. In addition, the MD results have found that the lithium ion mole fraction in the molten-salt electrolytes affects the ionic conductivity significantly as shown in Figure 3.
This paper demonstrates that MD simulation technique is a useful tool to screen various design ideas on the multi-component electrolytes in a more efficient way. The molecular composition of each component of the molten-salt electrolytes can be optimized using this simulation technique instead of trial-and-error experiments. The target region shown in Figure 4 is easy to easy to achieve through this computational technique.

REFERENCES

P. Masset, and R. A. Guidotti, J. Power Sources, 164, 397 (2007).

S. Fujiwara, M. Inaba, and A. Tasaka, J. Power Sources, 196, 4012 (2011).

S. Fujiwara, U. S. Patent, US008221912B2 (2012).

Figure 1
Modelling of Transport Processes inside Rechargeable Oxide Battery
Authors: Erfurt Viktoria , Braun Waldemar , Singheiser Lorenz , Berger Cornelius M. 
Published: February 2020

Change of electricity supply infrastructure based on renewables (photovoltaic, wind, biomass, etc.) requires large storage capacities to ensure continuous electricity supply if photovoltaics or wind turbines are not in operation due to weather conditions. At high temperatures of around 800 °C modified planar solid oxide fuel/electrolyzer cells (SOFC/SOEC) can be used as storage devices (Fig. 1). The concept of SOFC/SOEC can be transferred to a so-called rechargeable oxide battery (ROB). Instead of directly fueling the cell with mixtures of hydrogen and steam in the now sealed-off fuel compartment a metallic component is integrated which will be converted to metal oxide during discharging (Fig. 2) and back to metal during charging by reducing the metal oxide (Fig. 3).
An interesting metal / metal oxide system is iron/iron oxide which results in a reasonable open circuit voltage of approximately 1.02 V per cell at 800 °C due to the dissociation pressure of e.g. iron oxide (FeO) in the range of pO2≈10-18bar.
Oxidation and reduction rates strongly depend on the exact atmospheric compositions, the surface area, the porosity, and the diffusion velocities in the storage component. Latter will change due to the chemical expansion (change of pore sizes) during charging and discharging of the battery. Also the formation of oxide or metallic layers on top of the storage components can massively influence the reaction kinetics.
Therefore, in this study a 1D and a 2D model are developed to simulate the gas diffusion in the prevailing H2O/H2 atmosphere from the cell to the storage component (and back) as well as the gas-solid reaction in the porous iron/iron oxide. The model is implemented using the Navier-Stokes equations and the method of finite elements in Matlab.
The redox process which takes place within the microscopic pores of the metallic storage material can be described by the following equations:
Me + H2O ⇌ MeO + H2

2Me + 3H2O ⇌ Me2O3 + 3H2

3Me + 4H2O ⇌ Me3O4 +4H2

In addition, the formation of volatile oxides or hydroxides has to be considered which may cause long-term degradation of the storage components:
Me + 2H2O ⇌ Me(OH)2 + H2

MeO + H2O ⇌ Me(OH)2

Me3O4 + 2H2O + H2 ⇌ 3Me(OH)2

The degradation process reduces the performance of the battery along with its recyclability and lifetime. Therefore the degradation should be held as low as possible. Thus, the model contributes to identifying the critical processes in the battery and will allow for optimizing both the battery design and the operation conditions.

Figure 1
Self-Assembly, Transport, and Thermodynamics in Nafion Membranes: Insight from Dissipative Particle Dynamics Simulation
Authors: Vishnyakov Aleksey , Lee Ming-Tsung , Neimark Alexander V. 
Published: February 2020

Composed of perfluorinated backbone with sulfonate sidechains, Nafion self-assembles upon hydration and segregates into interpenetrating hydrophilic and hydrophobic subphases. This segregated morphology determines the transport properties of Nafion membranes that are widely used as compartment separators in fuel cells and other electro-chemical devices, as well as permselective diffusion barriers in protective fabrics. We introduce a coarse-grained model of Nafion, which accounts explicitly for polymer rigidity and electrostatic interactions between anionic sidechains and hydrated metal cations. By means of dissipative particle dynamics (DPD) and Monte Carlo (MC) simulations, we explore geometrical, transport, and sorption properties of hydrated Nafion-type polyelectrolyte membranes. Novel methodology will be presented for calculating water adsorption isotherms and transport coefficients as a function of the degree of hydration.
Electrooxidation of Ethanol and Formic Acid on Core-Shell Nanoparticles with Different Platinum Shell Thickness
Authors: Gorzkowski Maciej T. , Polczynski Piotr , Jurczakowski Rafal Robert , Lewera Adam 
Published: February 2020

Core-shell nanoparticles with platinum as the shell and less expensive metal as a core allow for important reduction of the amount of expensive and rare platinum used while maintaining similar platinum active surface area.
More efficient use of platinum is not the only benefit of core-shell nanoparticles. Platinum monolayer deposited on the core made from another metal exhibits modified catalytic and electronic properties. Partially responsible for this behavior are: i) charge transfer from the core metal and ii) changes induced by modified lattice parameter. The monolayer shell forms a so called “pseudomorphic monolayer” with lattice parameter equal to that of metal forming the core, resulting in altered conduction band width and center of d-band energy in relation to Fermi edge. In the case of platinum shell on a palladium core, contracted Pt lattice leads to broadening of the conduction band and shifting d-band center closer to the Fermi edge.
Core-shell nanoparticles with platinum shell have been widely investigated as the catalyst in the process of oxygen reduction, but data available on their properties as the catalysts for oxidation of small organic molecules is scarce. Experimental investigation of such properties of core-shell nanoparticles with different platinum coverage and different platinum shell lattice parameter due to changes in shell thickness is an important step in determination of relation between electronic properties of the material used and reaction mechanism. Understanding this relation is crucial in constructing more effective direct ethanol fuel cell anode catalysts.
On the Effects of Halides on the Hydrogen Peroxide Reduction Reaction in Aqueous Electrolytes
Authors: Jebaraj Adriel J.J. , Georgescu Nicholas , Scherson Daniel 
Published: February 2020

The influence of adsorbed species on the kinetics and mechanism of a number of redox reactions has been recognized for decades1. In particular, the adsorption of both chloride and bromide on Pt electrodes in acidic electrolytes, is known to promote the two-electron reduction of oxygen to peroxide instead of the desired four-electron reduction to water 2,3. This contribution seeks to gain insights into the reduction of H2O2 on a polycrystalline Pt electrode in 0.1 M HClO4 solutions containing a few ppm of either Cl- or Br-. The strategy employed makes use of a chronoamperometric method recently developed in our laboratories to determine independently, the effects of potential, E, and coverage of the adsorbate, q, on the peroxide reduction reaction on a Pt rotating disk electrode, RDE

EXPERIMENTAL

All measurements were performed in an all-glass, three-compartment cell in a 1 mM H2O2 in 0.1 M HClO4 solution either neat or containing 10 µM NaCl or 10 µM KBr. Experiments were performed with a rotating Pt ring-Pt disk electrode, Pt|Pt RRDE, (Pine Instruments, (A = 0.164 cm2) using a bipotentiostat (Pine Instruments). A Pt foil and a reversible hydrogenelectrode in the same solution (RHE) were used as counter and reference electrodes, respectively.

RESULTS AND DISCUSSION

Shown in Fig.1 are polarization curves recorded at a scan rate, ν = 10 mV/s for a Pt disk electrode in 0.1 M HClO4 containing 1 mM H2O2in the absence (black curve) and in the presence of either 10 mM NaCl or 10 μM KBr (red curve). In contrast to the rather subtle effects of chloride, the presence of bromide gives rise to a substantial, ca. 0.3 V, shift in the onset for peroxide reduction.
Chronoamperometric curves, i.e. disk current, idisk vs time, obtained in upon stepping the potential from a value Eo, at which its coverage q is negligible 0, to a value Eads at which q attains a finite value are displayed in Fig. 2. The results of these experiments make it possible to correlate the disk current, i, as a function of Eads at fixed q, or as a function of q for a fixed Eadsas illustrated in Panels A and B in Fig. 3, respectively. Implications of these results on the effects of these impurities on the oxygen reduction reaction (ORR) will be discussed.

ACKNOWLEDGEMENTS

This work was supported by a grant from NSF (CHE-0911621).

REFERENCES

Marković, N. M.; Ross Jr, P. N., Surf. Sci. Reports
2002, 45, 117-229.

Stamenkovic, V.; M. Markovic, N.; Ross Jr, P. N., J. Electroanal. Chem.
2001, 500, 44-51.

Schmidt, T. J.; Paulus, U. A.; Gasteiger, H. A.; Behm, R. J., J. Electroanal. Chem.
2001, 508, 41-47.

Figure 1
Laboratory Experiments and Undergraduate Research Projects Incorporating Electroanalytical Techniques at Benedictine University
Authors: Ronkainen Niina Johanna 
Published: February 2020

Freshman level undergraduate students often receive a superficial introduction to electrochemistry through topics such as redox reactions, oxidation states, electrolytes, and galvanic cells. Given this level of exposure to electrochemistry, it is often difficult to appreciate the relevance of electroanalytical chemistry to modern society. Unlike analytical chemistry techniques involving spectroscopy and chromatography, electroanalytical chemistry, specifically modern electrochemical techniques such as voltammetry and amperometry, are underrepresented in most undergraduate chemistry laboratory course curricula. With the increasing popularity of chemical sensors, biosensors and nanotechnology, electroanalytical detection methods are becoming more commonplace in research laboratories and chemical industry. In addition to the sensitivity the techniques mentioned offer, voltammetry is often used in characterization of nanomaterials, other redox active species and transducers. Moreover, electroanalytical methods offer an attractive alternative compared to other analytical methods due to portability, low cost and ease of use of the equipment. This talk will address the teaching of modern electroanalytical methods and their common applications at the sophomore and senior-level lecture and laboratory courses at a PUI, specifically Benedictine University. Several of the laboratory experiments and some undergraduate research projects which utilize cyclic voltammetry, linear sweep voltammetry, and amperometry will also be discussed.