bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of the Transmission Line EIS Model to Fuel Cell Catalyst Layer Durability
Authors: Easton E. Bradley , Saleh Farhana Sultana , Reid O'Rian O.
Published: February 2020

Typical catalyst layers (CL) employed in PEM fuel cells are composed of a carbon supported Pt catalyst bound together with an ionomer, most often Nafion. Both the carbon support and ionomer play a crucial role in optimizing the catalyst utilization by proving electronic and ionic conductive pathways, respectively, without hindering gas transport. Upon fuel cell operation, the catalyst layer can degrade by one of 3 primary pathways:

Loss of Pt surfaces area through Pt dissolution/Ostwald ripening

Corrosion of the carbon support

Degradation of the ionomer network

The contribution of each of these pathways depends upon CL compositions as well as the cell operating conditions.

The extent of degradation is normally monitored in situby cyclic voltammetry (CV) by measuring changes in the electrochemically active surface area (ECSA) of Pt. However, CV is limited in that it can only conclusively confirm the presence of the first pathway. Contributions from the other 2 pathways are typically confirmed by post mortem analysis of the CL.

We have recently reported that the addition of periodic electrochemical impedance spectroscopy (EIS) measurements to an accelerated degradation testing protocol (ADTP) allows one to clearly diagnose the presence of the other 2 degradation pathways. By performing EIS under conditions where the transmission line model is valid, the presence of carbon corrosion can be clearly detected by a characteristic shift in the EIS response over time [1], as shown in Figure 1. Likewise, the loss of ionic conductivity can also be observed through a unique change in a typical capacitance plot [2].

Our methodology has since been extended and further validated by studying the stability of numerous commercial and in-house prepared catalysts using with different carbon supports. In this presentation, we will describe how EIS can be incorporated into almost any ADTP protocol and how changes in the EIS response can be used for in situdiagnosis of degradation pathways that can be attributed to CL components. In particular we will describe how the presence and absence of both Pt and C impacts the degradation processes and subsequently the EIS response [3]. Furthermore, we will also demonstrate how by carefully selecting the DC bias potential one can quantitatively monitor ECSA degradation (pathway 1) with EIS (instead of CV) by using monitoring the pseudo-capacitance associated with H-adsorption (Figure 2) [4].

References

F. S. Saleh and E. B. Easton, J. Electrochem. Soc., 159, B546 (2012).

J. I. Eastcott and E. B. Easton, J. Power Sources, 245, 487 (2014).

F. S. Saleh and E. B. Easton, J. Power Sources, 246, 392 (2014).

O. Reid, F. S. Saleh, and E. B. Easton, Electrochim. Acta, 114, 278 (2013)
Understanding the Reactivity of Enol Ether Radical Cation: Investigation of Electrochemical [2 + 2] Cycloaddition Reactions
Authors: Yamaguchi Yusuke , Okada Yohei , Chiba Kazuhiro
Published: February 2020

Electrochemical process has proven to be powerful tool to form carbon-carbon bond and has widely used to construct various carbon skeletons. Especially, the electrochemical carbon-carbon bond forming reactions have demonstrated to afford complicated ring systems effectively, including naturally occurring compounds. For example, enol ether radical cations are readily produced in anodic oxidations of enol ethers and provide versatile reactive intermediates. This reaction is synthetically intriguing due to the umpolung process that polarity of nucleophilic enol ethers is reversed to give enol ether radical cations which function as electrophilic species.

We have developed the electrochemical reactions in lithium perchlorate/nitromethane (LPC/NM) electrolyte solution, which exhibits a remarkable accelerating property as a Lewis acid catalyst and stabilize carbocation intermediates. The feature of LPC/NM allows facile synthesis of biologically relevant compounds, such as dihydrobenzofuran derivatives1 and azanucleoside derivatives.2 In LPC/NM, unactivated olefins can serve as efficient nucleophiles to trap anodically generated cationic species. In this context, we also have developed electrochemical [2 + 2] cycloaddition reactions between enol ethers and unactivated olefins, affording cyclobutane products(Scheme 1).3 The reaction was initiated by anodic oxidation of enol ether (1) and thus generated enol ether radical cation (2) was trapped by unactivated olefin nucleophile to give transient cyclobutyl radical cation (3). In order for successful cyclobutane formation, electron rich aromatic ring was required as an electron donor to form relatively long lived aromatic ring radical cation (4), which was finally reduced by cathode or starting enol ether, affording neutral cycloadduct (5) (Scheme 2).

Although our previous work have focused on the use of enol ether (1) for electrochemical [2 + 2] cycloaddition reactions, the reactivity of enol ether radical cation (2) still remains unclear. To investigate the reactivity of such enol ether radical cations, we designed and synthesized several types of new substrates and then subjected them to the electrochemical [2 + 2] cycloaddition reactions(Scheme 3). Synthetic and mechanistic details would be discussed in the presentation.

Reference

(1) Kim, S.; Hirose, K.; Uematsu, J.; Mikami, Y.; Chiba,K. Chem.
–
Eur.
J.
2012, 18, 6284–6288.

(2) Kim, S.; Shoji, T.; Kitano, Y.; Chiba, K. Chem. Commun.
2013, 49, 6525–6527.

(3) (a) Yamaguchi, Y.; Okada, Y.; Chiba, K. J. Org. Chem., 2013, 78, 2626–2638. (b) Yamaguchi, Y.; Okada, Y.; Chiba, K. Electrochemistry
2013, 81, 331–333 and references therein.
Electrochemical Synthesis of Azanucleoside Derivatives Using a Lithium Perchlorate-Nitromethane System
Authors: Shoji Takao , Kim Shokaku , Kitano Yoshikazu , Chiba Kazuhiro
Published: February 2020

Nucleoside analogues have played an important role in the viral decease and cancer therapy. To date, various nucleosides analogous have been investigated to improve their therapeutic effects and toxic properties. The modification of the sugar moiety has produced new active analogous. Especially, the design of furanose rings that include various heteroatoms has been one of the most useful approaches in the search for new nucleoside analogues with beneficial biological activity.

Azanucleosides, in which the furanose oxygen atom is replaced by a nitrogen atom, have attracted interest because of possibility of their further modification through the nitrogen atom and structural similarity to the franose ring system. Considerable efforts have been dedicated to develop the efficient method for the synthesis of azanucleoside derivatives. Most of the synthetic strategies have been designed in order that N-glycosyl bond has been formed through an iminium ion intermediate. This process is necessary to incorporate a leaving group into the pyrrolidinyl precursor to generate the key reactive intermediate. However, access to such precursors requires a multi-step synthetic sequence, which includes cumbersome operations and harsh reaction condition. Indeed, this process often removes the opportunity of providing diverse azanucleosides based on further modification of the nitrogen atom.

To address this challenge, we reasoned that direct and selective insertion of a nucleobase to the N-a position of prolinol moiety would avoid the redundant multi-step synthetic operation. We proposed that an electro-organic method might provide such an approach to overcome the challenge of direct introduction of a nucleobase into an unactivated pyrrolidine moiety. Previously, we have demonstrated the direct modification of pyrrolidine derivatives using LiClO4-CH3NO2 electrochemical oxidation system. This reaction system can accumulate desired iminium ion intermediates, anodically derived from N-protected pyrrolidine derivatives by C-H bound activation, enabling coupling with a variety of nucleophiles in one-pot reaction. In this conference, we report the electrochemical azanucleoside synthesis by coupling an unactivated prolinol derivative with a nucleobase through anodic oxidation using LiClO4-CH3NO2 solution system, and demonstrate the utility of this transformation by addition of various nucleophiles to readily available prolinol derivatives in a regioselective manner.
Functionalized Poly(phenylene) Efficiency and Stability in Vanadium Redox Flow Batteries
Authors: Largier Timothy Damian , Cornelius Chris J
Published: February 2020

Perflourinated polymers have long been considered for applications that take advantage of their high mechanical strength and innate thermochemical stability. Recently, a phenylated polyelectrolyte has been synthesized that shows great potential in applications such as in proton exchange membrane fuel cells, alkali fuel cells, and vanadium redox flow batteries (VRB’s). Typical membranes in VRB’s suffer from high vanadium ion permeability and membrane degradation. Poly(phenylene)s show promise in this area. Synthesis typically involves Diels Alder polymerization (scheme 1), followed by post-sulfonation. For the purely aromatic parent polymer, molecular weights were obtained in the range of 80-110 000 g/mol, with an average density of 1.058 g/cm3. IR reveals significant sulfonic group stretching frequencies at 1180, 1126 and 1035cm-1. The materials show glass transition temperatures around 398 degrees Celsius. Thermal gravimetric analysis reveals that the functionalized polymers thermal stability is predominantly limited by the sulfonic functional group. It appears to have superior thermal stability over commercial Nafion 117, only showing minor degradation below 400oC. Sulfonated poly(phenylene)’s with a targeted sulfonation stoichiometry of 4:1 displays a proton conductivity of roughly 96 mS/cm2 at 35oC, with water uptake of 79.7%. Work is being done to test these materials for VRB’s, most notably vanadium ion permeation and membrane degradation. These properties are tested as a function of molecular weight, polymer structure, and ion exchange capacity.
Development of Lithium Sulfur Batteries with Improved Cycle Life and High-Power Properties
Authors: Yan Jianhua , Liu Xingbo , Li Bingyun
Published: February 2020

Tremendous eﬀort has been applied to developing viable lithium sulfur batteries and significant progress has been reported. However, lithium sulfur batteries still exhibit signiﬁcant capacity decay over cycling, probably due to the detachment or dissolution of LixS from the carbon surface during the discharge process. Here, we report the development of a new type of lithium sulfur batteries using functionalized multiwall carbon nanotube (MWCNT). We assembled an electrode consisting of densely packed MWCNT composites, which enabled strong interactions between the nonpolar carbon and the polar LixS clusters. We characterized the electrodes using Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared spectroscopy (FTIR). We found that the electrodes had high cycling performance with speciﬁc capacities of 1250 mAh/g and 990 mAh/g at the C/5 and C/2 current rates, respectively. Up to 80% capacity was retained over 300 cycles at C/5 and 200 cycles at C/2. The developed battery may be promising for applications in hybrid vehicles and renewable energy.
Porous Fe2O3 Doped Cathodes for Lithium-Sulfur Batteries
Authors: Shen Cai , Zhao Chong Chong , Han Weiqiang
Published: February 2020

Lithium-sulfur (Li/S) battery is a promising electrochemical system that has the possibility to achieve high-energy (theoretical capacity of 1675 mAh/g). However, the system suffers from several drawbacks including dissolution of intermediate polysulphide reaction species into electrolyte. In response to this challenge, novel advances in materials design such as new electrolytes1
,
2 polymer coated sulfur nanosphere core/cell structure3 and conductive mesoporous/nano carbon framework for constraining sulfur have been proposed4
,
5. These techniques significantly improve the cycling performance of Li/S batteries but falls short of completely controlling polysulphide dissolution. Recently, a new concept of embedding small fraction of porous silica particles (SBA-15) within carbon-sulfur nanocomposites and acted as an internal polysulfide reservoir has been proposed by Nazar et al. to stabilize the system6. In line with this concept, here we report the use of porous Fe2O3 doped sulfur cathode to improve the performance of Li/S batteries. A doping of 5% Fe2O3shows improved cycling performance with highly stable reversible discharge capacity of ca. 574 mAh/g after 50 cycles.

References:

(1) Ryu, H. S.; Ahn, H. J.; Kim, K. W.; Ahn, J. H.; Cho, K. K.; Nam, T. H.; Kim, J. U.; Cho, G. B. J Power Sources
2006, 163, 201.

(2) Wang, J.; Chew, S. Y.; Zhao, Z. W.; Ashraf, S.; Wexler, D.; Chen, J.; Ng, S. H.; Chou, S. L.; Liu, H. K. Carbon
2008, 46, 229.

(3) Li, W. Y.; Zheng, G. Y.; Yang, Y.; Seh, Z. W.; Liu, N.; Cui, Y. P Natl Acad Sci USA
2013, 110, 7148.

(4) Ji, X. L.; Lee, K. T.; Nazar, L. F. Nat Mater
2009, 8, 500.

(5) Xin, S.; Gu, L.; Zhao, N. H.; Yin, Y. X.; Zhou, L. J.; Guo, Y. G.; Wan, L. J. J Am Chem Soc
2012, 134, 18510.

(6) Ji, X. L.; Evers, S.; Black, R.; Nazar, L. F. Nat Commun
2011, 2.
Electrolyte Additive Performance in Lithium Ion Batteries: From Coin Cells to 400-Mah Pouch Cells
Authors: Polzin Bryant J , Trask Steve E , Zhu Ye , Li Yan , Bettge Martin , Abraham Daniel P , Jansen Andrew N.
Published: February 2020

Electrolyte additives have been widely reported to improve Lithium-Ion battery performance. Even small quantities of various additives have been shown to create stable SEIs on both the anode and cathode, improve safety, and stabilize electrolytes. Our work has focused on SEI forming additives that work on both the anode and cathode electrodes. Promising bi-functional additives that we have chosen to study in coin cells and larger format pouch cells are lithium bis(oxalate)borate (LiBOB) and lithium difloro(oxalate)borate (LiDFOB).

As part of DOE’s Applied Battery Research for Transportation (ABR) Program, a high voltage and high capacity cathode was paired with a high capacity graphite anode for this study. This electrode couple has the potential for applications in plug-in hybrid (PHEV) and battery electric vehicles (EV). The cathode selected was from the LMR-NMC class of materials; Toda HE5050 ( Li1.2Ni0.15Mn0.55Co0.1O2) and the anode was A12 graphite from Phillips 66. Coin cells were assembled with these materials and tested with a number of different electrolyte and additive combinations. Several compositions have shown an improvement in the coin cell performance, shown in Figure 1.

Based upon promising coin cell results from electrolyte and additive combinations, they were tested in 400-mAh pouch cells. The improved performance that was present in the coin cells was not observed in the pouch cells. Figure 2 shows the 400-mAh pouch cell performance of these additive combinations.

This presentation examines the differences in coin cells and pouch cells relative to additive performance. Examples of these differences are: formation conditions, electrolyte quantity, additive concentrations, etc. By studying these conditions, we will be able to simulate and vary pouch cell conditions via coin cell analysis. The coin cell conditions and performance will be verified against 400-mAh pouch cell performance data to ensure that the conditions and performances are scalable. By following this process less battery materials will be required and will speed up the optimization process in pouch cells.

Lastly, knowing the challenges that electrolyte additives present in scaling up cell size, we will provide some recommendations for coin cell testing that should be considered in the evaluation of research materials.
Study of Diffusion Kinetics and Microstructure for FeF3-CF (Carbon-Fiber) 3D Composite Electrodes
Authors: Zhou Hui , Martha Surendra K , Li Juchuan , Pannala Sreekanth , Dudney Nancy J , Nanda Jagjit , Wang Junjie , Braun Paul V
Published: February 2020

Recently, we investigated the role of electrode architecture on the capacity retention and hysteresis of iron (II and III) fluoride conversion compound.1 The unique electrode architecture consists of nanometer sized iron fluoride particles (~ 25-50nm) coated with multilayer graphitic platelets and bound to an electronic backbone comprising of an interconnected network of carbon fibers (5-9 µm diameter). The carbon coated fluoride particles are bound to the carbon fiber through a carbonaceous binder derived from petroleum pitch.2 This unique combination of reduced particle size and electrode architecture significantly improves the local electronic conductivity enhancing the electrochemical performance such as better capacity retention and C-rate performance. Further, we observe a significant reduction of voltage hysteresis to ~ 0.9V compared to 1.5 V for normal FeF3 slurry electrodes3. Electrochemical cycling at elevated temperature (60oC), improves the reaction transport kinetics yielding almost theoretical specific capacity (700 mAhg-1) with reasonably good cycle life with a small concomitant reduction in the hysteresis (Figure 1). The estimated overall energy density based on the active mass of FeF3 in the electrode is about 1650 Wh kg-1covering both the intercalation and conversion window (1.5–4.5 V). The overall performance of this 3D-structured cathode is impressive, and may provide a new cathode/electrode concept for next generation high energy density batteries.

Figure 1. (a). Voltage vs. capacity profiles of a Li/FeF3 cell (on carbon fiber) cycled between 1.5 V and 4.5 V (C/50 rate) at 60oC. (b) Capacity plotted as a function of cycle number for the Li/FeF3 cell. Capacity is evaluated based only on FeF3 active material.

Although initial cycle life looks promising, we notice capacity fade after 50 cycles clearly suggesting that further investigation are needed to understand the diffusion kinetics and/or structural stability of various intermediate conversion phases. We will present detailed investigation of various reaction phases and the kinetics of FeF3 and FeF2 electrodes at room temperature, 45 and 60 °C based on potentiostatic intermittent titration (PITT), electrochemical impedance spectroscopy (EIS), electron microscopy (S/TEM) and X-ray diffraction (XRD).

Acknowledgement

This research is sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.

References:

S. K. Martha, J. Nanda, H. Zhou, J. C. Idrobo, N. J. Dudney, S. Pannala, S. Dai, J. Wang, and P. V. Braun, RSC Advances. (Accepted 2013).

S. K. Martha, N. J. Dudney, J. O. Kiggans and J. Nanda, J. Electrochem. Soc., 159, A1652-A1658 (2012).

P. G. Bruce, B. Scrosati, and J-M. Tarascon, Angew. Chem. Int. Ed., 47, 2930-2946 (2008).
Glass-Ceramic Solid Electrolytes for Lithium and Sodium Ion Batteries
Authors: Rost Axel , Schilm Jochen , Langklotz Ulrike , Schneider Michael , Kramer Dörte , Michaelis Alexander
Published: February 2020

Common Lithium and Sodium Batteries have crucial drawbacks in operation caused by the type of separators and electrolytes. Polymeric separators used in Li-batteries show an insufficient stability against rising temperatures and the growth of dendrites. So hot spots, internal shortcuts, and even fire can result. The used solid electrolytes for Na Batteries made of β/β’’-Al2O3 work at temperatures around 300 °C what leads to low efficacies by energy consumption for heating of the battery system. Cracks in Al2O3 separators can cause severe failure by leakage of molten sodium. For both types of batteries solid glass-ceramic electrolytes can contribute to a higher level in security and safe operation of battery systems by several superior material properties. By high mechanical strength, a precise distance between the electrodes is defined. Due to high thermal stability, thermal runaways are impeded. Glass-ceramic and ion conducting materials can be used as particles or porous solids in combination with liquid electrolytes for common batteries but gastight solid electrolytes even enable new battery concepts like lithium-air batteries. Thin and mechanical stable Na-Ion conducting electrolytes show high conductivities even at ambient temperatures and enable room temperature sodium batteries. Dense galss-ceramic solid electrolytes also enable the use of two different types of liquid electrolytes for anode and cathode compartment.

In the study glasses are molten, quenched and crystallized to obtain ion conductive solid state glass-ceramic electrolytes. The material systems therefore are Li1+xAlxTi2-x(PO4)3 for Li-Ion Batteries and Na3+3x-yRE1-xPySi3-yO9 (RE: rare earth) for Na-Ion Batteries respective both are analogues of the NaSiCON-Structure. Glasses with varying ratios of Al/Ti and RE/P/Si are molten and after crystallization by different thermal treatments widely characterized (HTM; DTA; XRD; REM). Impedance spectroscopy measurements are carried out to determine the conductivity with respect to the chemical composition, thermal treatment and microstructure. Room temperature conductivities up to 10-4 S/cm will be presented and discussed. Promising compositions are processed as slurry for tape casting to gain thin and dense glass-ceramic solid electrolyte tapes for the application in room temperature Batteries.
Atomic Friction at Electrodes: Anisotropy Effects at Regularly Stepped Gold Electrodes
Authors: Baltruschat Helmut , Podgaynyy Nikolay , Iqbal Shahid
Published: February 2020

Friction under ambient conditions often involves wet surfaces, and thus electrochemical interfaces. Yet measurements of friction at an atomic scale under electrochemical conditions are scarce though accessible by combination of AFM with an electrochemical cell. For HOPG, a change of friction forces at steps edges was observed with a change of potential.[1] Our interest has been in the influence of potential, Cu UPD on Au(111) and organic adsorption on atomic-scale friction.[2]

We will present friction measurements performed on Au(111) single crystal electrodes and the effect of adsorbates on atomic stick-slip resolution. The range of normal force necessary to observe stick-slip resolution depends on the type of ionic adsorbates. At the small normal load of 15 nN transition to atomic stick-slip resolution is observed, when sulfate is adsorbed on the surface. The reason for that transition could be a penetration of the tip in to the double layer. At the pzc on clean gold stick-slip behaviour not shows any transition or penetration effects. The adhesion on the force-distance curve disappear with a copper adsorption.

However, with a monolayer of Cu on Au(111) a transition to stick-slip behavior is present, but without atomic resolution. We found 3 different types of stick-slip pattern on copper monolayer in diapason of normal loads between 0 and 100 nN; slip length is equal 4,6; 9,2; and 13,8 Å. The slope of stick combines the stiffness of tip and sample. That stiffness is independent from adsorbat or normal load and always have the same value at about 12 nN/nm, which is much smaller than torsion spring constant of cantilever 190 nN/nm.

Friction is increased at step edges due to the the Schwoebel barrier. This effect is reduced when steps are decorated by Pd on Au. Due to this effect of steps on friction, vicinally stepped surfaces show a large anisotropy for friction, although atomic resolution is obtained even when scanning perpendicular to the steps.

[1] E. Weilandt, A. Menck, O. Marti, Surface and Interface Analysis
1995, 23, 428; B. Schnyder, D. Alliata, R. Kötz, H. Siegenthaler, Applied Surface Science
2001, 173, 221.

[2] M. Nielinger, H. Baltruschat, Physical Chemistry Chemical Physics
2007, 9, 3965.; F. Hausen, M. Nielinger, S. Ernst, H. Baltruschat, Electrochimica Acta
2008, 53, 6058.
Advances in the Use of Carbon Anodes for Pyrochemical Electroreduction of Used Nuclear Fuel
Authors: Motsegood Perry , Willit James L. , Williamson Mark A.
Published: February 2020

Pyrochemical processing of used nuclear fuel is a molten salt process performed at elevated temperatures and is part of a series of processes resulting in the separation of actinides from fission products. Used metal oxide fuel (MOX) is reduced electrochemically to generate metals prior to electrorefining, typically performed at 650oC in LiCl-Li2O. The reduction of kilogram lab scale quantities of UO2 have been successfully performed as surrogates to actual fuel using platinum anodes1-2, but progression toward engineering or pilot scale-up presents different requirements for anode materials.

Carbon (graphite) is commonly used in commercial molten salt processes within the ore refining industry. It is cost effective, readily available, and a logical choice for scale-up needs. However, different chemistries result from this change in anode materials in both the salt and off gas streams. Instead of forming oxygen at a platinum anode, CO/CO2 becomes the byproduct gas. Although initially insoluble, CO/CO2 residence time within the LiCl-Li2O salt is thought to be problematic because of the formation of reactive carbon species, with respect to the metal, that are soluble and could lead to undesirable side reactions in the system.

This report will discuss an advanced test cell for evaluating the use of carbon as an anode material for the electroreduction of UO2 to uranium metal in molten LiCl-Li2O. We will present design challenges and report on the implementation of advances for the accommodation of process changes with respect the new anode material. Finally, preliminary results on the efficiency and chemical effects of carbon anodes will be discussed.

References

Laszlo Redey and Karthick Gourishankar, “Direct Electrochemical Reduction of Metal-Oxides” US Patent US6540902 B1, Granted April 1, 2003

S. D. Herrmann, S. X. Li, M. F. Simpson and S. Phongikaroon, Separation Science and Technology
2006, 41, 1965-1983.
Study of Magnetic Effects on Lanthanide Electrochemistry
Authors: Knoche Krysti L. , Leddy Johna
Published: February 2020

Lanthanide isotopes are produced during fission of 235U, most of which decay to stable nonradioactive lanthanide elements in a relatively short amount of time1. The lanthanide elements can be difficult to separate from each other in solution because they have extremely similar properties, including masses, ionic radii, oxidation states, and standard potentials2. Present lanthanide detection and separation methods are tedious and time-consuming.

Lanthanides do have different numbers of unpaired 4f electrons, resulting in distinct magnetic properties. Here, Boron-doped diamond (BDD) electrodes are magnetically modified to exploit this difference. Recent data suggests that modification of electrodes with chemically inert magnetic particles enhances current for electrochemical reactions3. The effect scales with the magnetic moment of the redox species and the number of unpaired electrons.

Electrochemically, lanthanide analysis is limited by their standard potentials (in the range of -1.99 and -3.90 V vs NHE4). These potentials fall outside of the potential window of common electrolyte solutions. For example, in aqueous solutions at platinum, the potential window is limited between +1.3 and -0.7 V vs NHE by solvent electrolysis5. Previously, researchers have resorted to mercury drop electrodes or chemically modified carbon paste electrodes to look at lanthanide compounds2. BDD electrodes offer a safer, simpler alternative; the overpotentials for hydrogen and oxygen occur at very extreme potentials on BDD compared to other materials such as glassy carbon, platinum, and gold. This allows for a wider potential window for investigation of lanthanide compounds. Here, nonaqueous lanthanide solutions are investigated at a BDD electrode6.

1. Binnemans, K., Chem Rev
2007, 107 (6), 2592-2614.

2. Schumacher, P. D.; Doyle, J. L.; Schenk, J. O.; Clark, S. B., Rev Anal Chem
2013, 32 (2), 159-171.

3. Lee, G. G. W.; Leddy, J.; Minteer, S. D. Chem Commun
2012, 48 (98), 11972-11974.

4. Cotton, S., Lanthanide and actinide chemistry. Wiley: 2007; Vol. 27.

5. Bard, A. J.; Faulkner, L. R., Electrochemical Methods, Fundamentals, and Applications. 2 ed.; John Wiley & Sons, Inc: New York, 2001.

6. Martin, H. B.; Argoitia, A.; Landau, U.; Anderson, A. B.; Angus, J. C. J Electrochem Soc
1996, 143 (6), L133-L136.
Dissolved Hydrogen Voltammetric Probe and Its Application for Photosynthetic Bacterial Hydrogen Production Rate Evaluation
Authors: Zlatev Roumen , Stoytcheva Margarita , Medina Pablo Alberto Romero , Reyes Ana Luisa , Magnin Jean-Pierre
Published: February 2020

As known, the dissolved hydrogen undergoes electrochemical oxidation, the mechanism of which depends on the electrolyte pH. In alkaline solutions the OH- participates in the hydrogen oxidation according to the reaction: H+ OH-= H2O+2e-, while in acid solutions the electrochemical oxidation is direct: H2=2H++2e-. In both cases electrolyte acidifying occurs because of the OH- consumption or H+generation, making suitable the application of very acid electrolytes to avoid the sensor characteristics changes caused by a great pH changes over time.

A 3-electrode probe similar to the Clark type oxygen probe construction was proposed, elaborated, and characterized as a dissolved hydrogen sensor. Its analytical characteristics such as LOD, sensitivity, response time, and linear response concentration range were determined as a function of the temperature, membranes materials, the electrolytes composition, and pH. Coulometric controlled electrochemical hydrogen generator was applied for standard solution preparation.

The sensor characterization results are presented and discussed together with the results obtained from its application for the real time determination of the rate of hydrogen production by the varieties B10 and IR3 of the photosynthetic strain Phodobacter Capsulatus.

Acknowledgement. This work was supported by CONACyT Mexico: Research grant No. 152961, CONACYT-SENER “Sustentabilidad Energética” 2010-01.
Pt Based Alloy Nanoparticles for Oxygen Reduction Prepared By a Solvothermal Method
Authors: Gumeci Cenk , Marathe Archis , Behrens Rachel Lynn , Chaudhuri Jharna , Korzeniewski Carol
Published: February 2020

In this study, platinum based alloy (PtNi, PtCo, PtNiCo) nanocatalysts with well controlled sizes and shapes have been synthesized using a one pot, facile and surfactant free solvothermal approach for application to the oxygen reduction reaction (ORR). Focus is on the fine-tuning of PtNi and PtNiCo nanostructure with the aim of achieving a defined particle geometry that can withstand treatment leading to a Pt-skin like structure and long electrochemical durability cycles. Effects of synthesis variables that include temperature, heating rate and the nature and ratio of metal precursor salts will be discussed. The samples were characterized using X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), high-resolution scanning transmission electron microscopy (HR-STEM), energy-dispersive x-ray spectroscopy (EDS) and thermogravimetric analysis (TGA). EDS mapping and line scans coupled with HR-STEM imaging was utilized to study the elemental distribution within individual Pt alloy nanoparticles, for as prepared samples, electrochemically activated samples and samples after electrochemical durability cycling. The as-prepared samples were subjected to an electrochemical treatment (activation) in deaerated 0.1 M HClO4 to form a Pt-skin like structure. Activated samples exhibited ~ 3-10 fold greater enhancement in ORR activity than commercially available Pt-C in terms of both specific activity and mass activity. Furthermore, most Pt alloy particles retained their activity after the course of the electrochemical durability cycling.
Enhanced Transport and Electrocatalysis in External Magnetic Field
Authors: Nowicka Anna Maria , Kowalczyk Agata , Donten Mikolaj , Stojek Zbigniew Jan
Published: February 2020

Recently we have turned to a new material for modification of glassy carbon electrodes: carbon nanocapsules with iron core (C-Fe). The carbon coating plays an important role; it separates the magnetic nanoparticle from the medium, protects it against oxidation and dissolution and adsorbs strongly on GC surface. C-Fe nanocapsules appeared to be a useful surface modifier. We have found that the adsorption of the nanocapsules on the GC electrode surface led to a shift of the reduction voltammetric peak/wave of oxygen by more than 200 mV toward less negative potentials. After applying an external magnetic field in the cell a substantial increase in the reduction current was observed. Similar increase of current was noted for ferroceneacetate anion, a paramagnetic molecule.

The C-Fe nanocapsule layer appeared also to be a good matrix for immobilization of laccase. The presence of laccase on the electrode surface modified with carbon nanocapsules caused an additional significant shift, compared to the C-Fe layer, of the position of the oxygen reduction signal toward positive potentials. The application of an external magnetic field led again to a strong increase in the reduction current. We have characterized the effect in function of the magnetic field intensity, the angle between the electrode surface and the magnetic field direction and the concentration of the substrate.

The application of magnetic field apparently helped to get appropriate orientation of the immobilized laccase at the surface. The high efficiency of electroreduction of oxygen was maintained after removal of the magnets.

The significant enhancement of dioxygen reduction current was compared with the simulations. For this purpose the profile of the magnetic field in the neighborhood of the electrode surface was constructed and the force of interactions of paramagnetic oxygen molecules with magnetic nanoparticles was calculated.
Electrocatalysts for Fuel Cells: From the Nanoscale to the Macroscale
Authors: Sung Yung-Eun
Published: February 2020

Due to being highly efficient and environmentally friendly, fuel cells are one of the most promising energy conversion devices to power the energy demands of the future. However, commercialization of fuel cells is hindered by the sluggish kinetics of the oxygen reduction reaction. Therefore methods to improve the specific activity of catalysts that facilitate the oxygen reduction reaction have been and continue to be a popular area of research. Accomplishments that have been achieved due to tailoring the activity of catalyst by alloying and core-shell at the nanoscale level will be discussed. Briefly, alloying Pt with another transition metal results in electrical and structural modifications as well as bifunctional behaviour at the alloy surface. These modifications lead to higher catalytic activity relative to pure Pt in fuel cells. Also, since electrocatalytic reactions are strongly dependent on the surface structure of metal catalysts, the atom-level design of the surface structure plays a significant role in a high catalytic activity and the utilization of electrocatalysts. Furthermore, I will present studies regarding the tuning of the electronic and geometric structures of Pt via adsorption of molecules and atomic arrangement. Finally, our recently developed three-dimensional ordered electrode structure for fuel cells will be presented in the symposium
Electrochemical Characterization Reveals Multiple Distinct Electron Transport Pathways in Anode Biofilms of Geobacter Sulfurreducens
Authors: Popat Sudeep , Yoho Rachel , Ajulo Oluyomi , Torres César
Published: February 2020

Geobacter sulfurreducens has become a model microorganism for anode respiration in the field of microbial electrochemistry. Our group has studied the sigmoidal behavior of the current/potential response of G. sulfurreducens, modeled through the Nernst-Monod relationship. In its current form (Fig. 1), the Nernst-Monod relationship assumes that there is a single limiting redox process, which governs the energy that is gained by G. sulfurreducens from anode respiration.

Fig. 1 shows the Nernst-Monod equation. Here, j is the current produced at the anode potential E, jmax
is the maximum current, n is the number of electrons transferred, F is the Faraday constant, R is the gas constant, T is the temperature, and EKA
is the anode potential that results in j as half of jmax
.

Our previous studies have used the Nernst-Monod relationship to model slow-scan cyclic voltammograms (CV) of G. sulfurreducens grown at -0.4 V vs. Ag/AgCl with n=1, and an EKA
= -0.42 V vs. Ag/AgCl. Our ability to fit the data further corroborated the assumption of a single redox processes controlling the metabolic response of G. sulfurreducens. However, several published studies and our own recent work also suggested that the Nernst-Monod relationship did not always fit the CV data. Thus, we used electrochemical impedance spectroscopy (EIS) as a function of anode potential in a G. sulfurreducens biofilm, with the aim of getting further insight on the electron transport processes for anode respiration. EIS can theoretically allow separating the contribution of various processes governing electron transfer rates, as long as they are separated in their characteristic frequency (i.e. have different time constants).

We have performed EIS analyses, at various anode potentials, on G. sulfurreducens biofilms grown at -0.3 V vs. Ag/AgCl. These have shown the existence of more than one charge transfer process governing its electron transport, each with a different EKA
. This suggests that there are multiple governing redox cofactors in G. sulfurreducens that are used in combination to perform anode respiration. Through chronoamperometry experiments we have also further shown that G. sulfurreducens has the ability to change which cofactors are used depending on the poised anode potential.

We hypothesize that the distinct redox cofactors possibly help G. sulfurreducens respire different forms of iron, whose oxide forms present in nature have different redox potentials. Our results also suggests that the Nernst-Monod relationship needs to be expanded to include the presence of multiple redox cofactors with different EKA
, and these may differ for different anode-respiring bacteria.
Oxygen Reducing Enzymes Encapsulated in Silica Matrix By Chemical Vapor Deposition
Authors: Perry Albert Thomas , Babanova Sofia , Atanassov Plamen
Published: February 2020

Silica encapsulation is becoming a promising technique used to preserve the activity and prolong the stability of different bacteria, enzymes, and organelles. This allows continued functionality, while ceasing colonial growth in bacteria, and decreasing the catalytic decay in enymes1. This approach was extensively studied and explored in the development of enzymatic and bacterial electrodes for biofuel cell application2,3.

University of New Mexico developed a technique for silica encapsulation - chemical vapor deposition (CVD). This technique relies on the extremely high volatility of the silica precursor (tetramethyl orthosilicate or TMOS), which interacts with water containing solution, carries out a hydrolysis and condensation creating silica gel (Fig. 1). This silica gel matrix is permeable to the electrolyte keeping the biological species hydrated.

In this study, the influence of silica encapsulation on the performance, activity, and stability of three different oxygen reducing enzymes (bilirubin oxidase, laccase and ascorbate oxidase) were evaluated. Ink composites consisting of carbon nanotubes, tetrabutylammonium bromide (TBAB) modified Nafion, 1-pyrenebutanoic acid succinimidyl ester (PBSE) and the enzymes were prepared. The inks were deposited on Rotating Disk Electrode (RDE)4. These electrodes were exposed to TMOS vapors to perform the encapsulation. The time of exposure was varied as a way to control the thickness of the created silica layer. Increased time of exposure leads to increased silica gel thickness and density. This was confirmed by the decrease of the generated current with the increased encapsulation time (Fig. 2). A thicker silicon layer introduces diffusional barrier that causes diffusional losses leading to decreased current production. Therefore the time of TMOS exposure is an important parameter that has to be carefully controlled.

Although a linear dependence of the current recorded during the RDE measurements and the square root of the rotation rate (Fig. 3) was observed we cannot use the Koutecky-Levich equation to determine the number of electrons exchanged during the oxygen reduction reaction. An alternative approach was applied.

References:

1. Bergogne, L., S. Fennouh, S. Guyon, J. Livage, C. Roux, Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A. Mol. Cryst. Liq. Cryst.
2000, 354, 79–89.

2. Luckarift, H. R., S. R. Sizemore, J. Roy, C. Lau, G. Gupta, P. Atanassov, G. R. Johnson Chem. Commun., 2010, 46, 6048–6050

3. Ivnitski, D., K. Artyuskova, R. A. Rincón, P. Atanassov, H. R. Luckarift, G. R. Johnson .Small
2008, 4 (3), 357–364.

4. Brocato, S., Lau, C., and Atanassov, P. (2012) Mechanistic study of direct electron transfer in bilirubin oxidase, Electrochim. Acta, Elsevier Ltd 61, 44–49.
Thyalkoid-Based Bio-Solar Cells
Authors: Minteer Shelley D. , Rasmussen Michelle
Published: February 2020

Thylakoid bio-solar cells have been developed previously which are capable of direct solar energy conversion through photosynthesis. However, the current output of these cells is quite small compared to mediated systems. Several methods have been implemented to improve the performance. Incorporation of fluorescent carbon quantum dots leads to an increase in photocurrent generation. The conductive quantum dots allow for greater transfer of electrons. Additionally, the quantum dots absorb at wavelengths not necessary for photosynthesis but emit light at wavelengths at which the photosystems of the thylakoids absorb. This makes it possible for the electrodes to use more of the light spectrum. A second method involved the intercalation of conjugated oligoelectrolytes into the thylakoid membrane. These molecules allow for greater electron transfer through the membrane which decreases the resistance in the thylakoid bio-solar cell. Additionally, the photocurrent produced by the thylakoid electrodes increased as well. A third method involves separating thylakoids into stacked regions (grana) and non-stacked regions (stroma) which have very different composition of photosynthetic components. Electrodes modified with stroma thylakoids give much larger currents, up to three times larger than full thylakoid membranes.
Rational Design of Redox Mediators for Application to Enzymatic Fuel Cells
Authors: Kavanagh Paul
Published: February 2020

Enzymatic fuel cells (EFCs) based on mediated electron transfer involve the ‘wiring’ of enzymes at the anode and cathode using redox mediators. The potential difference between the redox mediators used at the anode and cathode can influence the cell voltage and, consequently, the power output of the EFC.1,2
In addition, the potential difference between the redox mediator and the enzyme binding site can influence the rate of electron transfer (as predicted by Marcus theory) and hence, the catalytic turnover at each electrode. Ideally, for maximum power output, the catalytic reactions at each electrode should occur at low overpotentials (to ensure a large cell voltage) with a high catalytic turnover of substrates. Therefore, judicious choice of enzyme and redox mediator combination at the anode and cathode is essential. For example, it has been proposed that, at the anode, the redox potential of an electron mediator should have a value of about 50 mV downhill of the enzyme active site to generate current with minimal loss in cell voltage.3Although, under physiological conditions, the redox potential of the binding site of a wild type enzyme is, for the most part, fixed there is scope to manipulate the electronic character of the redox mediator. Here, we present an approach for the rational design of metal complexes which possess desirable electrochemical characteristics to act as redox mediators for specific enzymes, such as glucose oxidase, in an effort to maximise EFC power output.

1. S. C. Barton, J. Gallaway and P. Atanassov, Chem. Rev., 2004, 104, 4867–4886.

2. P. Kavanagh, D. Leech, Phys.Chem. Chem. Phys., 2013, 15, 4859-4869

2. A. Heller, AIChE J., 2005, 51, 1054–1066.
Microelectrode Analysis of Cell Plasma Membrane Cholesterol
Authors: Burgess Jim , Yu Xiaochun , Moreno Monica
Published: February 2020

Cholesterol efflux from the cell plasma membrane is known to be increased in cell-line and mouse models of cystic fibrosis. A noninvasive means of characterizing plasma membrane cholesterol efflux at affected tissues is needed to extend the trends found in models of cystic fibrosis to humans suffering from the disease. Microelectrode induced cholesterol efflux from the plasma membrane surface of tissue is proposed as a strategy to demonstrate increased cholesterol efflux for cystic fibrosis in human subjects. Data demonstrating detection of cholesterol efflux from the human buccel mucosa is reported as proof-of-concept for the in vivo diagnostic assay. Cholesterol oxidase modified Pt microelectrodes positioned in contact with the mucosa show increased signal relative to control electrodes indicating observation of cholesterol efflux from mucosa surface cells. Electrochemical detection of cholesterol involves accumulation of enzymatically produced hydrogen peroxide at the electrode surface and periodic oxidative depletion of peroxide in a series of potential step experiments. A nano-electrode array strategy is proposed as a means of increasing signal-to-background of these measurements. Electrodeposition of platinum particles on a carbon microelectrode will be described as an approach to electrode array formation. This work was supported by NIH 1R01EB009481.
Photo-Induced Charge Transfer and Spectroscopy Across a Series of Pbttt Model Compounds
Authors: Callahan Rebecca , Springer Michael , Walba David , Rumbles Garry
Published: February 2020

Organic-based excitonic photovoltaics are a promising low-cost renewable energy source. New solution-processable polymer and small molecule electron donor materials often utilize solubilizing alkyl tails. Herein we study the effects of alkyl tails on charge transfer between a fullerene and a model compound of the highly-conducting PBTTT polymer with varied alkyl tail lengths, ranging from one to thirteen carbons.

First, we photophysically characterize the model compounds. Solution-phase spectroscopy and electrochemistry demonstrate similar energetics across the compounds series. Intermolecular aggregation in films leads to two distinct film absorption and photoluminescence features, which interestingly does not appear to follow tail length or odd-even trends. Second, we utilize the electrodeless time-resolved microwave conductivity technique to study photo-induced charge transfer and carrier dynamics. Specifically we create a donor-acceptor heterojunction with the soluble fullerene PCBM. Last, we create an electron acceptor “dilute regime” to study the tail-length effects on charge transfer. Our transient microwave absorption experiments show that the charge generation yield is intimately tied to tail length across the model compound series. Alkyl tails, which are often incorporated to enable solubility, can in fact act as a charge transfer barrier in bulk heterojunctions.