bluuebunny/crossref_metadata_2025_split huggingface dataset:
Approaches to Understanding AEM Degradation Using Model Compounds
Authors: Foister Shane , Roy Asa Logan , Servedio Luke , Goenaga Gabriel A. , Papandrew Alex , Zawodzinski Thomas A. 
Published: February 2020

The development of anion exchange membranes (AEMs) with sufficient conductivity and durability for use in alkaline fuel cells has become an increasingly active area of research. And while a number of polymer scaffolds bearing a variety of different cationic groups have been examined as AEMs, no clear solution has been found. The degradation of cationic groups, the polymer backbones, or both components of candidate AEMs upon prolonged exposure to alkaline media presents the greatest challenge and hence greatest opportunity in the field of AEM discovery.
Several studies have examined the degradation of intact AEMs using techniques suited to the characterization of polymeric materials including infrared spectroscopy, Raman spectroscopy, and NMR spectroscopy.1,2 This approach to unraveling AEM degradation allows simultaneous, parallel investigation of conductivity, water uptake, ion exchange capacities, as well as experiments in fuel cells. Recent work in this area has even implicated cation degradation as a trigger for further decomposition of polymer backbones leading to membrane failure.3

Some groups have begun to approach AEM degradation using small model compounds that mimic the structure of the cationic component. These small organic models and their degradation products are amenable to study by techniques not readily suited to polymeric systems. For example, NMR experiments on model quaternary ammonium and azolium species have provided baseline data on the mechanisms of decomposition operative under alkaline conditions.
Our work seeks to expand the use of model compounds for understanding the mechanism(s) of AEM degradation. Our approach includes small molecule mimics for different cationic groups, polymer backbones, and hybrid models wherein cationic groups are attached to polymer resins like chloromethylated polystyrene. The aim of our approach is to increase the throughput of techniques that can be used to evaluate the stability of different cation-polymer combinations while providing chemical insights into their mechanisms of degradation. By attaching cationic models to robust resins like cross-linked chloromethylpolystyrene, the decomposition products can be isolated by filtration and analyzed by mass spectrometry (MS). The sensitivity and amenability of MS to high throughput formats compliments NMR-based experiments on model compunds or dissolved membranes.

References

1. C. G. Arges and V. Ramani, JECS, 160, F1006 (2013).
2. S. A. Nunez and M. A. Hickner, ACS Macro Lett.,
2, 49 (2013).
3. C. G. Arges and V. Ramani, PNAS, 110, 2490 (2013).
Reductive Ring-Expansion of 1-Bromoalkyl-2-Oxocycloalkanecarboxylates at Silver Cathodes
Authors: Wappes Ethan , Mubarak Muhammad , Peters Dennis G. 
Published: February 2020

Free-radical ring-expansion reactions are useful for the synthesis of a variety of organic compounds; these reactions are especially attractive for the preparation of large rings in natural products.1 One such ring expansion, outlined by Dowd and Choi,2 employs tri-n-butyltin hydride in the presence of 2,2′-azobis(2-methylpropionitrile), commonly referred to as AIBN, to cleave a carbon–halogen bond and to induce ring expansion. These reagents are efficient, but are also environmentally dangerous. To remove the need for these harmful chemicals, our laboratory (which has a long-standing interest in the reductive cleavage of organic halides) has previously utilized glassy carbon cathodes to initiate reductive ring expansion and has obtained modest yields—up to 26%—of the ring-expanded product.3 More recently, it has been discovered that silver cathodes have a catalytic ability to cleave carbon–halogen bonds.4 In the present work, we have explored the use of silver cathodes for reductive ring-expansion reactions of the subject compounds, and we have been able to achieve higher yields of ring-expanded products at less negative potentials than previously found through the use of glassy carbon electrodes.
Figure 1 shows a cyclic voltammogram for the reduction of methyl 1-(bromomethyl)-2-oxocyclopentanecarboxylate (1) at a silver cathode in dimethylformamide (DMF) containing tetramethylammonium tetrafluoroborate (TMABF4). We attribute the first cathodic peak at approximately –0.4 V to reductive cleavage of the carbon–bromine bond, whereas the second cathodic peak at –1.4 V is due to reduction of the cyclopentanone moiety. Interestingly, the first cathodic peak appears at a potential that is nearly 1 V more positive than that found with a glassy carbon electrode. Two other substrates—methyl 1-(bromopropyl)-2-oxocyclopentanecarboxylate (2) and ethyl 1-(bromomethyl)-2-oxocyclohexanecarboxylate (3)—that have been studied exhibit similar electrochemical behavior (Figure 2).
Controlled-potential electrolyses have revealed that the electrochemically induced ring-expansion reaction occurs in a fashion similar to that of the original chemical reaction. We have observed a one-electron reduction of 1that affords the desired ring-expanded product in high yield—up to 95%. In addition to the ring-expanded product, side products (found by means of gas chromatography–mass-spectrometry) include a dehalogenated product and an unexpected side product that are shown in Figure 3. Yields of the various products obtained from the three substrates mentioned in the preceding paragraph depend on the length of the haloalkane side-chain and on the size of the ring.
References
1. Hierold, J.; Lupton, D. W. Org. Lett.
2012, 14, 3412–3415.
2. Dowd, P.; Choi, S. C. Tetrahedron
1989, 45, 77–90.
3. Mubarak, M. S.; Barker, W. E., IV, Peters, D. G. J. Electrochem. Soc.
2007, 154, F205–F210.
4. Isse, A. A.; Berzi, G.; Falciola, L.; Rossi, M.; Mussini, P. R.; Gennaro, A. Appl. Electrochem.
2009, 39, 2217–
2225.
Optimizing Electron Transfer Mediators Based on Arylimidazoles by Ring Fusion: Synthesis, Electrochemistry and Computational Analysis of [9,10-D]Phenantroimidazoles
Authors: Francke Robert , Little R. Daniel 
Published: February 2020

One approach to increase the efficiency of electroorganic synthesis is to use electron transfer catalysts in an indirect electrolysis (1). Since the electron transfer step is shifted from a heterogeneous to a homogeneous process, the kinetic inhibition associated with the electron transfer from electrode to substrate can be eliminated (2). Typically, higher and/or totally different selectivity is achieved. The electron transfer can occur even against a potential gradient if one or more of the subsequent steps is an irreversible chemical reaction (1,2). In many cases, a mediator can help to suppress undesired side reactions and electrode passivation.
A new class of metal-free, easy to synthesize redox catalysts based on the triarylimidazole framework 1 was developed in our laboratory (see Figure, left) (3). Since the electronic character of the substituents strongly affects the oxidation potential, the redox properties of the mediators can be tuned within a wide range and tailored to catalyze specific redox reactions (4). The successful conversion of several model compounds using catalytic amounts of 1 demonstrates that triarylimidazoles can be useful mediators for the activation of benzylic C-H bonds under mild conditions.
With a simple structural modification of 1 a significant improvement of the redox properties can be achieved (5). By connection of the ortho-carbons of the aromatics positioned at C-4 and C-5, fused framework 2 is generated (see Figure, right). The distortion from planarity is thereby strongly decreased and the influence of the substituents on the redox properties is enhanced. This modification not only opens up a much broader range of available redox potentials for the resulting [9,10-d]phenantroimidazoles (2), but also leads to improved stability of the corresponding radical cation. These concepts were verified with eight new [9,10-d]phenantroimidazole derivatives, using cyclic voltammetry and DFT calculations. An excellent linear correlation of the calculated effective ionization potentials with the experimental oxidation potentials was obtained, allowing for an accurate prediction of oxidation potentials of derivatives yet to be synthesized. Moreover, high catalytic activity was found for electrooxidative C-H activation reactions.
References:
1. J.-M. Savéant, Chem. Rev.
108, 2348 (2008).
2. E. Steckhan, Angew. Chem. Int. Ed. Engl.
25, 683 (1986).
3. C.-C. Zeng, N.-T. Zhang, C. M. Lam and R. D. Little, Org. Lett.
14, 1314 (2012).
4. N.-T. Zhang, C.-C. Zeng, C. M. Lam, R. K. Gbur and R. D. Little, Org. Chem.
78, 2104 (2013).
5. R. Francke and R. D. Little, manuscript submitted (2013).
Reaction Integration Using Electrochemically Generated Cationic Reactive Intermediates
Authors: Hayashi Ryutaro , Ashikari Yosuke , Shimizu Akihiro , Nokami Toshiki , Yoshida Jun-ichi 
Published: February 2020

From functional materials to biologically active compounds, the role of organic synthesis has been expanding continuously. Accordingly, the power and speed of organic synthesis should be enhanced to meet future demands for synthesis of various organic molecules. In this context, conventional step-by-step synthesis is being supplemented with integrated synthesis that combines multiple reactions in a single operation in one pot or in a flow system without isolating the intermediates.
In this presentation we report on time integration of electrochemical oxidation and chemical oxidation based on the “cation pool” method. For example, electrochemically generated carbocations are reacted with dimethylsulfoxide to give the corresponding alkoxysulfonium ions, which are well-known as key intermediates of Swern—Moffatt oxidation. The subsequent treatment with triethylamine gives the corresponding carbonyl compounds. Moreover, the reactions of halogenuim and arylchalcogenium cation pools stabilized by dimethoxysulfoxide with alkenes followed by treatment with triethylamine give a-halo and arylchalcogen-substituted carbonyl compounds, respectively.
“Brick-and-Mortar” Self-Assembly Synthesis of Electrode Architectures
Authors: Guo Bingkun , Fulvio Pasquale , Sun Xiao-Guang , Dai Sheng 
Published: February 2020

Carbonaceous materials usually have a better electronic conductivity than metal oxides for meeting requirements in high-rate capability applications. However, both carbonaceous and metal-oxide materials suffer slow lithium diffusion rates within the corresponding electrode materials. This deficiency limits the high-rate capability for a number of electrode materials. Herein, we report an one-step “brick-and-mortar” self-assembly synthesis of carbon and oxide composites as anode materials for lithium ion batteries. The objective of this work is to demonstrate that mesoporous carbons and oxides derived from soft-template synthesis not only entail a high storage capacity but also, most importantly, can be made through a “brick and mortar” self-assembly synthesis to have a significantly enhanced electronic conductivity. This enhanced electronic conductivity in 3D architectures is the key to providing high rate capability.
The main part of this work was supported by the U.S. Department of Energy’s Office of Basic Energy Science, Division of Materials Sciences and Engineering, under contract with UT-Battelle, LLC.
In Situ Spectroscopic Studies of the Electrochemistry of Dioxygen in Non-Aqueous Li-Air Battery Electrolytes
Authors: Hardwick Laurence J , Aldous Iain , Padmanbhan Vivek , Nichols Richard 
Published: February 2020

The non-aqueous lithium-oxygen battery is one of a host of emerging opportunities available for enhanced energy storage [1]. Unlike a conventional battery where the reagents are contained within the cell, the lithium-oxygen cell uses dioxygen from the atmosphere to electrochemically form the discharge product lithium peroxide. Degrees of reversible oxidation and formation of lithium peroxide has been demonstrated in a number of non-aqueous electrolyte classes, mostly notably in dimethysulfoxide based electrolytes [2], thus making the lithium-oxygen cell a potential energy storage device. A schematic representation of the rechargeable non-aqueous Li-O2 cell is shown in the Figure. On discharge, lithium ions formed at the lithium metal anode are transported across the electrolyte and into the pores of the air-cathode. O2 from the atmosphere enters the cathode, and dissolves into the electrolyte within the pores. It is then reduced at the porous carbon electrode surface by electrons from the external circuit and combines with Li+ from the electrolyte, leading to the formation of solid Li2O2 as the final discharge product. Surprisingly, the reaction in some electrolytes is fairly reversible, Li2O2 can be oxidised, releasing oxygen gas. The challenge for the Li-O2 cell is the progress of development of the air-cathode that allows highly reversible formation of Li2O2 in a stable electrolyte within its pores [3-6].
This talk will present our groups recent results of the electrochemistry of dioxygen in non-aqueous electrolytes on planar and single crystal electrodes, of which particular electrolytes could have practical application within a lithium-oxygen cell. Discussion will touch upon how the electrochemistry can be related to electrode substrate and will be presented with in situ spectroscopic studies that identify intermediate and surface species during the oxygen reduction reaction.

P.G. Bruce, S. Freunberger, L.J. Hardwick, J.-M. Tarascon, Nature Mater. (2012) 11 19

Z. Peng, S.A. Freunberger, Y. Chen, P.G. Bruce, Science, (2012) 337 563

S. Freunberger, Y. Chen, N. Drewett, L.J. Hardwick, F. Bardé, P.G. Bruce, Angew. Chem. Int. Ed. (2011) 50 8609

S. Freunberger, Y. Chen, Z. Peng, J. Griffin, L.J. Hardwick, F. Bardé, P. Novák, P.G. Bruce, J. Amer. Chem. Soc. (2011) 133 8040

Z. Peng, S. Freunberger, L.J. Hardwick, Y. Chen, V. Giordani, F. Bardé, P. Novák, J.-M. Tarascon, D. Graham, P.G. Bruce, Angew. Chem. Int. Ed. (2011) 50 63514

M. Leskes, N Drewett, L.J. Hardwick, P.G. Bruce, G.R. Goward, C.P. Grey, Angew. Chem. Int. Ed. (2012) 51 8560
High Lithium Ionic Mobility in Mo6S8 Chevrel Phase Cathodes
Authors: Kim Soo , Aykol Muratahan , Wolverton Chris , Cho Jaehyun , Cho Byung-Won 
Published: February 2020

Rechargeable magnesium batteries have been recognized as an alternative solution to lithium ion batteries because of their advantages of excellent safety and cost [1]. Chevrel phase compounds, MxMo6S8(M = metal), are promising cathode materials in Mg batteries, because they display exceptionally fast cation transport for multi-valent ions compared to any other host materials. However, depending upon the composition and synthesized temperature of the Chevrel phase, the kinetics of Mg diffusion is highly affected at both room temperature and elevated temperature.
In addition, there are many on-going efforts to discover improved electrolytes for Mg batteries. It has been recently demonstrated that using an electrolyte with a concentrated lithium salt could benetit the thermodynamic and kinetic in a lithium-sulfur cell [2]. Here, we report the experimental and computational calculation results to explain unusually high ionic mobility of lithium in Mo6S8 chevrel phase cathode materials. When a concentrated lithium salt of 0.5M LiCl is added to the conventional APC electrolytes, almost full theoretical capacity can be achieved at room temperature in Mo6S8 Chevrel phase cathode materials at very high C-rates up to 20, 30C.

References

[1] D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, and E. Levi, Nature, 407, 724 (2000).
[2] E. S. Shin, K. Kim, S. H. Oh, W. I. Cho, Chem. Comm., 49, 2004 (2013).
A Comparative Study of O3 and P2 Phases in Some Oxides for Na Batteries
Authors: Liu Lei , Ceder Gerbrand 
Published: February 2020

Na-ion batteries have attracted growing attention due to the high abundance and low cost of Na compared with Li.
As a promising category of cathode materials for Na-ion batteries, layered oxides have been widely studied. Among the rich diversity of structure, emphasis has been mainly focused on O3 and P2-phases (in Delmas’ denotion1. ) Several layered oxides have been studied recently, NaMnO2
2, NaNiO2
3, NaxCoO2
4, Na2/3Mn1/2Fe1/2O2
5, etc. For most O3-type oxides, the reversible capacity is limited to 120 mAh/g, corresponding to 0.5 Na per formula unit, while for most P2-type oxides, the reversible capacity is about 160 mAh/g which is equivalent to ≈ 0.67Na extracted and intercalated during cycling.
We synthesized a series of O3- and P2-type compounds with the same transition metal components via solid-state reaction and carried out a comparative study between the O3 and P2 structure. Besides performance, we evaluated the structure/valence transition and Na+ mobility.
The structural transitions during Na+ intercalation/deintercalation are similar for most reported O3-type oxides with an O3-P3 transition, while the P2 phases usually experience more reversible phase transitions, accompanied by stacking faults. We carried out in-situ XRD observation to study the structure evolution of our new O3- and P2-type materials.
The valence evolution of the transition metals in O3- and P2-type materials was evaluated. A good understanding of the valence evolution of transition metals in layered oxides will benefit the design and tailoring of this category of materials.
In-Situ Electrochemical Microscopy of PEM Fuel Cell Materials
Authors: More Karren L. , Unocic Raymond R , Cullen David A 
Published: February 2020

High-resolution imaging of the structural changes to Pt-based catalyst nanoparticles supported on carbon blacks using in-situ electrochemical liquid cell transmission electron microscopy (TEM) are being correlated with the behavior of similar materials incorporated in membrane electrode assemblies (MEAs) subjected to accelerated stress tests (ASTs), to elucidate catalyst and catalyst-support degradation phenomena contributing to fuel cell performance loss. Specialized in-situ holders for the TEM have been developed that incorporate patterned electrodes within a closed liquid flow cell that enable the interactions between catalyst particles and their supports to be imaged during potential cycling in relevant liquid electrolytes, such that the critical stages of materials corrosion during fuel cell operation can be imaged in real time at nm-scale resolution. The direct TEM observations of the changes to the catalyst (Pt dissolution and particle growth/coalescence) and carbon supports (mechanisms of progressive support corrosion) during in-situ electrochemistry, combined with the post-mortem evaluation of cathode layers comprised of similar Pt/C materials after AST of MEAs, provide an unprecedented means by which to “capture” catalyst and catalyst-support degradation mechanisms such that materials optimization strategies can be implemented to enhance fuel cell durability.
Research sponsored by (1) the Office of Fuel Cells Technologies, Office of Energy Efficiency and Renewable Energy, the U.S. Department of Energy and (2) ORNL’s Center for Nanophase Materials Sciences, Scientific User Facilities Division, Office of Basic Energy Sciences, the U.S. Department of Energy.
Electrochemical Impedance Spectroscopy of Geobacter Sulfurreducens Biofilms on Rotating Disk Electrodes
Authors: Babauta Jerome T , Beyenal Haluk 
Published: February 2020

Electrochemical impedance spectroscopy (EIS) has received significant attention recently as a method to measure electrochemical parameters of Geobacter sulfurreducens biofilms. Here, we grew G. sulfurreducens biofilms on rotating disk electrodes to determine the effect of mass transfer processes on the biofilm impedance. We controlled the rotation rate of the electrode up to 530 rpm to control the microscale gradients forming inside G. sulfurreducens biofilms respiring on the electrode. A 24% increase above a baseline of 82 µA was achieved with a rotation rate of 530 rpm. We compared the effect of rotation on the biofilm to a mass transfer-controlled soluble redox mediator, ferrocyanide, to make the distinction between infinite Warburg and pseudocapacitive responses. We observed a 340% increase above baseline using ferrocyanide at 530 rpm, indicating that the primary limitation of electron transfer rates in G. sulfurreducens biofilms was not mass transfer.
Control of mass transfer processes was also used to quantify the change in biofilm impedance during the transition from turnover to non-turnover conditions. An equivalent electrical circuit model was used to estimate the electrochemical parameters of the biofilm. We found that only one element of the biofilm impedance, the interfacial resistance, changed significantly from 900 to 4,200 Ω under turnover and non-turnover conditions, respectively. We ascribed this change to the electron transfer resistance overcome by the biofilm metabolism and estimate this value as 3,300 Ω. Additionally, under non-turnover, the biofilm impedance developed pseudocapacitive behavior indicative of bound redox mediators. Pseudocapacitance of the biofilm was estimated at 740 µF and was unresponsive to rotation of the electrode. Overall, we tested the hypothesis that the rotating disk electrode can be used as an electrochemical tool that controls mass transfer processes when studying electrochemically active biofilms and facilitates our understanding of EIS in microbially-driven electrochemical systems. The increase in electron transfer resistance and pseudocapacitive behavior under non-turnover could be used as indicators of acetate limitations inside G. sulfurreducens biofilms.