bluuebunny/crossref_metadata_2025 huggingface dataset:
Palladium Nanodendrites for Electrocatalytic Applications
Authors: Chetty Raghuram , Maniam Kranthi Kumar , Muthukumar Volga
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFC) are attractive energy conversion devices for portable applications and electric vehicles owing to their high efficiency, high power density and low operating temperature. However, the high price and the limited resources of platinum catalysts are among the main challenges hindering their further commercialization. As palladium (Pd) possesses a similar valence electronic configuration to platinum and also has high methanol-tolerant ability, researchers have devoted to develop palladium-based catalysts as a promising alternative to platinum. A number of wet-chemical routes have been developed to produce Pd nanostructures to improve the catalytic activity and selectivity. However, they have been limited due to the use of organic surfactants, polymeric stabilizers at elevated temperature or template techniques relying on the use of nanometer-sized pores as structure-directing agents, which are technically complicated, due to the requirements for template removal to obtain pure products.

In this work, Pd dendrites were prepared by electrochemical deposition directly on carbon-based substrates, which are widely used as support material in fuel cells. Electrodeposition of Pd was carried out on an electrochemically activated carbon black substrate using potentiostatic and cyclic voltammetric techniques. Comparison was also made with Pt dendritesprepared by the electrochemical deposition. The effects of electrochemical activation, deposition potential, time, precursor concentration and carbon loading were studied in relation to the morphology and development of the nanostructures. The results indicated that controlled insertion of defects on the carbon black during electrochemical activation favored a good metal-support interaction and improved the hydrophilicity of the surface, resulting in a dendritic morphology with enhanced catalytic activity towards oxidation and reduction reactions in fuel cells.
Modeling ORR/Oxide Formation and Pt Dissolution - from Liquid Electrolyte to Polymer Electrolyte Systems: Issues and Approaches
Authors: Jayasankar Barathram , Karan Kunal , Harvey David
Published: February 2020

Recently, we presented an extension of Wang’s multi-step oxygen reduction reaction (ORR) kinetic model [1] to account for sub-surface oxide formation. Our model adequately captures three distinct oxygen electrochemistry on Pt features: ORR kinetics, oxide formation and reduction during cyclic voltammetry, and logarithmic oxide growth – and was extended to Pt dissolution [2]. Experimental data on oxygen electrochemistry on Pt and Pt dissolution are largely available for liquid electrolyte systems. Extension of the aforementioned model to fuel cell electrodes offers some challenges. The kinetic model depends on proton and water concentrations. In a liquid electrolyte system, similar to the ex-situ systems that comprise of dilute acid electrolytes to study ORR and cyclic voltammetry, the respective concentrations can be calculated in a straightforward manner. However in an actual fuel cell catalyst layer, where the liquid water is present is not clear. The concentration of liquid water can be treated to be that of the pure water but for Pt dissolution modeling, one needs to know the volume of the water pool surrounding the Pt crystal. The pH or proton concentration poses another challenge. The proton conductivity of ionomer is known to be RH dependent. However, the local proton concentration is not known and is expected to be function of local liquid water content. This is turn is expected to be a function of material composition, catalyst layer structure, RH, and operating current. This is illustrated by the trends shown in Figure 2 that highlight the effect of RH on cyclic voltammetry [3]. Furthermore these issues have a bearing on the ability to calculate platinum ion concentration within the catalyst layer in degradation studies.

This presentation will discuss these important issues and some of the approaches we are taking to address the challenges.

References

[1] J.X. Wang, J. Zhang and R.R. Adzic J. Phys. Chem.A, 2007, 111 (49), 12702–12710.

[2} Jayasankar, Barathram, Kunal Karan, and David Harvey. "Platinum degradation model in the presence of oxygen." Meeting Abstracts. No. 15. The Electrochemical Society, 2013.

[3] Ruichun Jiang, H. Russell Kunz, James M. Fenton. “Investigation of membrane property and fuel cell behavior with sulfonated poly (ether ether ketone) electrolyte: Temperature and relative humidity effects”. Journal of power sources 150 (2005) 120-128
Validation of Various Oxidation and Reduction Models for SOFC Electrodes
Authors: Yang Tao , Celik Ismail Bektas , Pakalapati Suryanarayana Raju , Finklea Harry O. , Gerdes Kirk
Published: February 2020

Oxidation and reduction models for SOFC electrodes are essential for accurate predictions of performance. In our study, the optimal models for oxidation and reduction in electrodes are determined by comparing results from various models with experimental results. For oxidation in anode, the models we apply include Bessler’s hydrogen oxidation model (2005, 2010) and Butler-Volmer type rate equations. The models used for reduction and transportation of oxygen in cathode included Butler-Volmer model and a micro scale model with parallel 2PB and 3PB pathways. Other reaction kinetics models are also considered. The optimal models are then used in our simulations for full cell study. Parametric studies are performed for better prediction of SOFC electrodes. Different porosity distributions, cell dimensions and concentrations are applied in the simulation, and their effects on the performance are analyzed through quantitative studies involving polarization curves and impedance behavior.
The Role of Mixed Conduction in W-WO3 Redox Kinetics
Authors: Milshtein Jarrod David , Pal Uday Bhanu , Gergel Diana , Basu Soumendra Nath , Gopalan Srikanth
Published: February 2020

The tungsten - tungsten trioxide (W-WO3) materials system has recently shown excellent promise as a medium for grid level energy storage and for solar energy conversion. In both these applications the thermal energy transfer is accompanied by a redox reaction in the W-WO3 couple. For viability of this system as an energy storage medium, it is important to have facile redox kinetics that allows us to rapidly store and release energy. Facile kinetics are also required in the utilization of this system in solar syngas production. In this paper we show that the addition of an ionic conducting phase, namely yttria stabilized zirconia (YSZ) greatly enhances the redox kinetics of the W-WO3 couple. Specifically, the reduction kinetics of the WO3-W reaction are facilitiated by the addition of YSZ. As a control experiment, a redox experiment with a filler material that is not an ionic conductor did not show such an enhancement in the kinetics. Chemical reaction rates were determined by transient thermogravimetry, and the data were analyzed using relevant kinetic and transport theory.
INVITED TALK - Chemical Durability of SOFCs
Authors: Sasaki Kazunari , Hanasaki Masahiro , Nishimura Takashi , Hosoi Takami , Daio Takeshi , Tachikawa Yuya , Shiratori Yusuke , Taniguchi Shunsuke
Published: February 2020

Introduction

Solid oxide fuel cell (SOFC) is the promising type of fuel cells with e.g. high electric efficiency and fuel flexibility. Durability and reliability are the most important technological issues on such an early commercialization stage. In our research group, we are focusing on the chemical degradation of SOFCs, determining the lifetime of SOFCs operating at high temperatures using various kinds of practical fuels. In this paper, various extrinsic and intrinsic degradation phenomena are systematically classified and their degradation mechanisms are discussed [1-3].

Extrinsic chemical degradation phenomena

While the advantage of SOFCs is their fuel flexibility, impurity species can often flow into the SOFC system, causing degradation phenomena. Due to their high operational temperatures, species with a high vapor pressure can also evaporate and flow into the SOFC stacks from system components. In addition, the use of low-purity raw materials could cause impurity poisoning by the contaminants in such raw materials. Possible extrinsic degradation phenomena are summarized in Fig. 1, including mechanisms associated with surface adsorption/desorption in the case of sulfur at a relatively low concentration, but associated with accumulation and reaction product formation for other impurities.

Intrinsic chemical degradation phenomena

External impurities can be, in principle, removed by using a getter as a desulfurization reactor or by using fuels with better purity. However, chemical degradation associated with diffusion from neighboring components may become important in long-term operation. As compiled in Fig. 2, various intrinsic degradation phenomena have been revealed by evaluating SOFC samples after long-term tests beyond one thousand or several thousand hours. Future perspectives are also presented including the importance of long-term / cycle testing followed by detailed microstructural analysis.

Acknowledgements: We thank for the financial support by METI to establish Next-Generation Fuel Cell Research Center. Financial supported by the NEDO SOFC project is gratefully acknowledged.

References

[1] K. Sasaki et al., J. Power Sources, 196[22], 9130 (2011).

[2] K. Sasaki et al., J. Electrochem. Soc., 153 [11], A2023 (2006).

[3] K. Sasaki et al., ECS Trans., 57 [1], 315 (2013).
New Electrode of La0.75Sr0.25Mn0.5Cr0.5-XCuxO3-δ (x=0, 0.05, 0.10, 0.20) for Symmetric Solid Oxide Fuel Cell
Authors: Lu Jun , Yin Jiewei , Sun Lin , Lv Weiming , Yin Yimei , Ma Zi-Feng
Published: February 2020

Abstract:

New perovskite oxides La0.75Sr0.25Mn0.5Cr0.5-x
Cu
x
O3-δ (LSMCr0.5-x
Cu
x
,
x=0, 0.05, 0.10, 0.20) have been developed as both cathode and anode for symmetric single solid oxide fuel cells (SOFCs). The as-prepared LSMCr0.5-x
Cu
x
powders are rhombohedral perovskite phase, and their properties are remarkably affected by Cu content (x). For example, the particle sizes and electrical conductivities of LSMCr0.5-x
Cu
x
increase with x both in air and in 5% H2-Ar atmosphere. Their p-type conductivity shows lower values under 5% H2-Ar reducing atmosphere than in air due to the decrease of the ratio of Mn4+/Mn3+ cation pairs through the reduction of Mn4+. Among of the oxides, LSMCr0.45Cu0.05 shows the best anodic and cathodic performance in symmetrical half cells. The maximum power density of a LSMCr0.45Cu0.05 / ScSZ / LSMCr0.45Cu0.05 symmetric single SOFC reaches as high as 451.2 mW·cm-2 in wet H2 as fuel at 900 oC.

Keywords

: solid oxide fuel cell; symmetric cell; LSCM; Cu substitution

Acknowledgements:

This research was financially supported by the Natural Science Foundation of China (21173147), 973 Program of China (2014CB239700). Thanks were also given to the support of National Key Laboratory of Metallic Matrix Composite Material.

*Corresponding author. Tel.: +86 21 34206255; Fax: +86 21 54741297.

E-mail address: yimei@sjtu.edu.cn (Y.-M. Yin).
Carbon Ceramic Electrodes Modified with Alpha-Nickel Hydroxide Applied to the Electro-Oxidation of Methanol in Alkaline Medium
Authors: Módolo Márcio Luiz , Danczuk Marins , Anaissi Fauze Jacó , Araki Koiti , Fujiwara Sergio Toshio
Published: February 2020

Direct methanol fuel cells (DMFCs) are attractive power sources for portable electronic devices owing to their advantages of low operating temperature, easy transportation and fuel storage, high-energy efficiency, low exhaustion and fast start-up. The alkalines DMFCs have drawn particular attention in this area for the advantage of high alcohol oxidation kinetics and of the potential use of cheaper non-Pt catalysts. Nickel hydroxide has been extensively studies as electro-catalysts for methanol oxidation. In this present work alpha nickel hydroxide was synthesized and incorporated into carbon ceramic electrodes. The nickel hydroxide was obtained by mixing nickel acetate and glycerin with heating at 50 ° C under constant agitation. The obtained solution was mixed with a solution of NaOH dissolved in butanol, the mixture obtained was stirred for 6 hours and then allowed to stand for 15 days. Carbon ceramic (CC) was obtained by the Sol-Gel process, methyltrimethoxysilane (MTMS) was mixed with ethanol and the catalyst used was NaOH after partial hydrolysis of MTMS graphite was added to the mixture, the material obtained was allowed to stand for 48 h. The ceramic-carbon (CC) was mixed with nickel hydroxide in the proportion of 5, 10, 30, 50 and 70% (w/w) Ni(OH)2/CC. The mixture was homogenized and packaged in glass tubes of 0.03 cm2 and 1 cm in height, and nickel-chromium wire was inserted as electrical contact. The material obtained was designated as ECC/α-Ni(OH)2 and was used as an electrode for electro-oxidation of methanol in alkaline medium. The x-ray diffraction confirmed the presence of lamellar graphite. The images of SEM/EDS confirmed the presence of nickel hydroxide dispersed irregularly in the sample. Initial studies indicated that the electrodes with the higher concentrations of nickel hydroxide produce higher current intensities at higher anode potential. In studies of the electro - oxidation of methanol was chosen electrode produced with 10 % of Ni(OH)2, because it has the lowest potential anodic peak. The ECC has no catalytic activity for the electro-oxidation of methanol, but the ECC/α-Ni(OH)2 promotes the electro-oxidation of methanol potential of 0.53 V vs. Ag/AgCl, yielding a current density of about 100 mA/cm2. The highest oxidation current was obtained with 1.90 mol/L of methanol. The ECC has no signs of poisoning, because there is no decrease in the intensity of the anodic current after 1000 cycles. The electrode showed promising thermal behavior, with no loss of electrochemical activity until the temperature of 200oC. All results indicate that the ECC/α-Ni(OH)2 is a promising material for electro-oxidation of methanol in alkaline medium, to obtain high current densities.
New Approach of Data Mining from the Complex Impedance Plane: Parameters You Have Always Wanted to Have
Authors: Macak Jan M. , Patil Deepak , Fraenkl Max , Zima Vitezslav , Shimakawa Koichi , Wagner Tomas
Published: February 2020

Conventional analysis of data recorded using the Electrochemical Impedance Spectroscopy (EIS) is a relatively simple procedure from the mathematical point of view. It involves an elucidation of electrode processes to derive their characteristic parameters. Another advantage is that it represents a quick visualization tool being still a very sensitive technique [1,2]. However, it has a number of disadvantages too. Often, the interpretation of EIS data using equivalent circuits is quite difficult due to a tedious search for a good fitting correlation. Moreover, results do not give information about number of moving ions (cations or anions), hopping time etc. Knowledge and consideration of these parameters would be very helpful in many electrochemistry-related fields, such as for instance in the development of solid state batteries and in the semiconductor field.

Being unhappy with these drawbacks and limitations of the conventional data analysis method, we recently developed a new approach [4] in which the Z
1 - Z
2 complex impedance plane (where Z
1 and Z
2are the real and imaginary parts of the impedance of materials) has been analyzed, based on Dyre’s random-walk theory. Through this approach we have obtained from EIS data (that are measured anyway), a new set of physical parameters, yet unseen and unmined:

i) the diffusion coefficient D and

ii) the number of moving ions N
ions,

both parameters further distinguishable in the bulk region of the sample as well as at the interface.

The presentation will explain in detail our recently developed approach that has the potential to find a widespread use in various electrochemical fields, such as in batteries, solar cells, fuel cells and semiconductor industry in general. The presentation will show, how helpful this approach can be to understand the electrode polarization as well as the ionic transport mechanism in various conductors. In particular, we will discuss in detail recent results achieved on various materials, including selected ionic conductors [3-5], silicons and titanium dioxides [6].

Literature:

D. D. Macdonald, Transient Techniques in Electrochemistry, Springer US, 1977.

E. Barsoukov, J. R. Macdonald, Impedance Spectroscopy Theory, Experiment, and Application, Second Ed., John Wiley and Sons, New Jersey, 2005

S. Stehlik, J. Orava, T. Kohoutek, T. Wagner, M. Frumar, V. Zima, T. Hara, Y. Matsui, K. Ueda, M. Pumera, J. of Solid State Chem. 183 (2010) 144.

S. Stehlik, K. Shimakawa, T. Wagner and M. Frumar, J. Phys. D: Appl. Phys. 45(2012) 205304.

D.S. Patik, K. Shimakawa, V. Zima, J. Macak, and T. Wagner, J. Appl. Phys. 113 (2013) 143705.

T.Wagner et al., Ms in preparation.
Degradation Behavior of PTB7/PC71bm and P3HT/PC71bm Organic Solar Cells with a TiOx Interlayer
Authors: Abdel-Fattah Tarek M , Younes Enas m , Namkoong Gon , El-Maghraby Mohamed , Elsayed Adly , Abo Elazm A. H.
Published: February 2020

Recently, the performance of organic solar cells has dramatically improved by incorporating a functional interfacial layer between active layer and metal electrode, forming bulk heterojunction (BHJ). Many interfacial materials, such as metal oxides, self-assembled monolayers (SAMs) and conjugated polyelectrolytes (CPEs), have successfully enhanced energy conversion efficiency of solar cells [4]. Among these interlayers, titanium oxide (TiOx) was used for an optical spacer as well as a hole blocking layer which led to an increase in the power conversion efficiency (PCE). In addition TiOx is known to improve the stability of the organic solar cell devices [5].

In this study, the organic photovoltaic with bulk heterojunction (BHJ), thieno(3,4-b)-thiophene/ benzodithiophene copolymer and (6,6)-phenyl C71 butyric acid methyl ester (PTB7/PC71BM) treated with titanium oxide (TiOx) interlayer was fabricated and compared with the stability of organic solar cells based on poly (3- hexylthiophene) and [6,6]-phenylC71 butyric acid methyl ester (P3HT/PC71BM) with TiOx interlayer. TiOx was prepared by sol-gel chemistry method. The crystalline structure of TiOx was described by X-ray diffraction (XRD) while the absorption spectrum, and surface morphology of the BHJ were studied by UV-Vis spectroscopy and atomic force microscopy (AFM) respectively.

Organic solar cells were fabricated by spin-coating PEDOT:PSS layer on the top of ITO glass substrate. After annealing, the substrates were then transferred into a nitrogen filled glove box for spin-casting photoactive layers. Then TiOx layer was spin coated in air. Subsequently, aluminum (Al) electrode was deposited, producing the devices active area of ~ 10 mm2. Finally after Al deposition, the P3HT/PC71BM device was subjected to annealing treatment in glove box.

The electrical properties of the resultant devices were investigated by measuring the current density–voltage (J–V). Also the normalized efficiency of both devices as a function of time has been measured and stability was analyzed in terms of optical, structural and morphological degradation.

References

[1]K.-D. Kim, D. C. Lim, H. O. Seo, J. Y. Lee, B. Y. Seo, D. J. Lee, Y. Song, S. Cho, J.-H. Lim, Y. D. Kim, Applied Surface Science, 279, 2013, 380– 383.

[2] W. Zhang, B. Zhao, Z. He, X. Zhao, H. Wang, S. Yang, H. Wu and Y. Cao, Energy Environ. Sci., 6, 2013, 1956–1964.

[3] Y.-M. Chang and C.-Y. Leu, J. Mater. Chem. A, 1, 2013, 6446–6451.

[4] H. Zhou, Y. Zhang, J. Seifter , S. D. Collins, C. Luo, G. C. Bazan, T.-Q. Nguyen , and A. J. Heeger, Adv. Mater, 25, 2013, 1646–1652.

[5] S. H. Park, A. Roy, S. Beaupre, S. Cho, N. Coates, J. S. Moon, D. Moses, M. Leclerc, K. Lee and A. J. Heeger, Nature Photonics, 3, 2009, 297-303.
Visible Light Driven Decomposition of Organic Compounds By Two Different Cocatalysts
Authors: Jeevagan Arockiam John , Tsuda Takashi , Saravanan Govindachetty , Gunji Takao , Hashimoto Masanari , Kaneko Shingo , Miyauchi Masahiro , Matsumoto Futoshi
Published: February 2020

1.
Introduction

Photocatalytic decomposition of organic pollutants is one of the promising method for environmental purification. Most of the researchers focused on efficient decomposition of environmental organic contaminants under visible light irradiation or indoor fluorescent light.1 Oxide-supported metal catalysts are widely acknowledged as important catalysts that are related to versatile key in photochromism, chemical sensing and photocatalytic activity. Tungsten trioxide (WO3) acts as a ideal visible light photocatalyst owing to its small band gap energy (2.4-2.8 eV) and high oxidation power of vanlence band holes. But, WO3 exhibits low photocatalytic activity due its high recombination rate of photoexcited electrons and holes. In order to suppress the recombination of photoexcited carriers and significantly increase the photocatalytic efficiency, most research has focused to prepare WO3 doping constituent or WO3 composites.2,3 In the present study, we have synthesized PtPb/WO3 and PtAu/WO3 alloy catalysts, demonstrated to exhibit the efficiency for the decompostion of organic pollutants under visible light irradiation.

2.
Experimental

A simple one-pot synthesis approach to obtain WO3 supported PtAu catalyst is as follows. In the synthesis, 0.5 g of WO3was suspended in 15 mL of anhyrous methanol for 15 min in a two neck round bottom flask. Pt (0.0075 g) and Au (0.0045 g) precursors were dissolved in 15 mL anhydrous methanol in the shielded vial uder Ar atmosphere and transferred to the suspensions. Then, the solution was stirred for 30 min to yield homogeneous color soluion. Required amount of NaBH4 in mehtanol was injected into the suspensions. The product were washed and centrifuged with anhydrous methanol for three times and dried under vacuum. Similar procedure was followed to synthesis the PtPb/WO3 catalyst.

3. Results and Discussion

Figure 1 shows the TEM images of (a) Pt/WO3 (b) PtPb/WO3 and (c) PtAu/WO3 photocatalysts. Pt and PtPb and PtAu NPs are showed monodispersity and homogeneity on the WO3 supports. The average particle size of the three catalysts can be ranked as PtPb/WO3~PtAu/WO3 > Pt/WO3. The TEM results show that the addition of Pb and Au increases the size of NPs. Figure 2 depicts that the CO2 formation profile over different photocatalysts under visible light irradiation time. PtPb/WO3 photocatalyst (1 wt %) shows the higher rate of CO2formation over other photocatalysts. The details about the characterization and photocatalytic activity of catalysts would be discussed in the presentation.

4. References

1. M.R. Hoffmann, S.T. Martin, W. Choi and D.W. Bahnemann, Chem. Rev., 95, 69, (1995).

2. R. Abe, H. Takami, N. Murakami and B. Otani, J. Am. Chem. Soc., 130, 7780, (2008).

3. M. Miyauchi, Phys. Chem. Chem. Phys., 10, 6258, (2008).
Low Temperature PEM Degradation: Failure Modes & Mitigation Strategies
Authors: Gittleman Craig S , Coms Frank D. , Lai Yeh-Hung
Published: February 2020

There are three critical membrane degradation mechanisms that can lead to failure of polymer electrolyte fuel cell systems: chemical degradation, mechanical degradation, and membrane shorting. This talk will focus on the individual failure modes; with attention dedicated to describing the fundamental model-based mechanistic understandings, appropriate accelerated stress tests that enable rapid screening and relevant in-situ diagnostics to track membrane health during fuel cell operation, as well as discussions of effective mitigation strategies to prevent or minimize the risk of failure caused by the specific modes of membrane degradation. The effect of simultaneous chemical and mechanical degradation will also be discussed.

Both chemical and mechanical degradation of perfluorosulfonic acid (PFSA) membranes have been extensively studied, and effective mitigation strategies have been developed that can significantly extend PFSA proton exchange membrane (PEM) lifetimes. Accelerated stress tests (ASTs) have been developed that can be used to screen various membrane types and mitigation strategies, and effective in-situ diagnostics have been developed to track degradation of PFSA membranes during fuel cell operation. The failures observed in these accelerated tests as seen by postmortem analysis mimic the failures of PFSA membranes in field tests. Durability of PFSA membranes will be discussed and an overview of the degradation of alternate PEM chemistries, such as hydrocarbon membranes, will also be provided. Insight into the degradation of these materials is limited because there is hardly any field data which can be used to determine the root causes of failure and validate that the ASTs are accelerating the relevant stressors and, also, because appropriate diagnostics, such as those used for PFSA membrane systems, have not been developed.

This talk will also address shorting of PEMs in fuel cell systems. Shorting is a two step process during which soft shorts are created by penetration of conductive materials though the thickness of the membrane. Soft shorts become hard shorts when there is a voltage excursion that leads to high local temperatures and subsequent thermal decay of the PEM. These hard shorts are the severe events that lead to fuel cell stack failure. Results and analysis suggest that the PEM type is not the limiting factor in preventing membrane shorting, and that mitigation is best achieved by a combination of design and operating strategies.
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).
ECS Organic & Biological Electrochemistry Division Manuel M. Baizer Award C-H Amination of Aromatic Compounds Based on Electrochemical Oxidation
Authors: Morofuji Tatuya , Shimizu Akihiro , Yoshida Jun-ichi
Published: February 2020

We have developed a new method for synthesizing aromatic primary amines from aromatic compounds based on electrochemical oxidation of aromatic compounds in the presence of pyridine followed by the reaction of the resulting N-arylpyridinium ions with an alkylamine. This transformation serves as a powerful method for C−H amination of aromatic compounds without using metal catalysts and harsh chemical reagents. Synthetic utility of the method is demonstrated by C−H amination of aromatic compounds bearing a nitro group to give a key intermediate for the synthesis of bioactive compounds such as a VLA-4 antagonist.
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
Micro-Battery Development for Fish Tracking System Applications
Authors: Liu Bo , Cartmell Samuel , Lozano Terence , Wang Qiang , Li Huidong , Deng Daniel , Xiao Jie
Published: February 2020

Specifically designed micro-batteries have been developed for injectable fish tags. Through appropriate lamination and fabrication process, cylindrical CFx-based micro-batteries have been prepared in the lab readily for mass production. High pulse current and required service life have both been achieved as well as doubling the gravimetric energy density of the battery. The newly designed micro-batteries have intrinsically low impedance, leading to significantly improved electrochemical performances at low temperatures. Successful field trial by using the micro-battery powered transmitters injected into fish has been demonstrated, providing an exemplary model of transferring fundamental research into practical devices with controlled qualities.
Study of Average and Local Structures of Variedly Ordered LiNi0.5Mn1.5O4 By Neutron Diffraction
Authors: Chen Yan , An Ke , Liang Chengdu
Published: February 2020

The spinel-type LiNi0.5Mn1.5O4 cathode materials exhibit varied Ni/Mn cation ordering by the synthesis process and subsequent thermal treatment, resulting in differential electrochemical behaviors in Li-ion batteries. In order to achieve a well-defined ordering structure and its influence to the electrochemical properties, a series of LiNi0.5Mn1.5O4 samples are prepared with systematically controlled Ni/Mn ordering by the variant of annealing time at 700 C. The average crystal structures and local structures are characterized by measuring the neutron diffraction patterns and the pair distribution functions (PDF), respectively. With the advantage of neutron's high sensitivity to Ni and Mn, the two cations are definitely differentiated. The crystal structures as well as the occupancies of Mn and Ni are determined using Rietveld refinement, so that the ordering degree tuning up by annealing time is verified. However, the PDF reveals that the disordered model with Fd-3m space group does not fit the local structure. The M-O bonds (M = Mn or Ni) has dependence only on the type of cation but not on the ordering degree. In the view of the local structure of LiNi0.5Mn1.5O4, the environment of LiO4 tetrahedral and MO6 octahedral are redrawn. The electrochemical properties and cycling behaviors of the LiNi0.5Mn1.5O4 cathodes with various ordering degrees will be discussed and linked with the local structures.
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).
Ceramic Li Ion Electrolytes for Next Generation Solid-State Li Ion Batteries
Authors: Thangadurai Venkataraman , Narayanan Sumaletha
Published: February 2020

At present, there is a growing interest in the development of safe and low-cost all-solid-state Li ion batteries for transport applications due to their higher practical volumetric and gravimetric energy densities compared to other known secondary batteries. The commercial Li ion battery utilizes LiPF6 dissolved organic polymer as an electrolyte, graphite anode and LiCoO2 electrode that exhibit several issues including safety, low energy density and inadequate chemical stability and durability. To this end, numerous solid-state Li ion electrolytes such as two-dimensional layered structures Li-beta alumina and Li3N, and three-dimensional structured Li4SiO4, Li2+2xZn1-xGeO4, Li1+xTi2−xAlxP3O12, (Li,Ln)TiO3 and Li5La3M2O12 (M = Nb, Ta) have been studied for all-solid-state Li ion batteries. Among these materials, garnet-like oxides have recently gained much attention because of their high Li ion conductivity, low electronic conductivity at high Li activity, and high electrochemical stability window, up to 6 V/Li. The lithium stuffing in the parent garnet-type Li5La3M2O12 increases Li ion conduction. For example, x = 0.75 members of Li5+2xLa3M2-xYxO12
show the highest Li ion conductivity of 10-4 Scm-1 at room temperature. In this talk, role of crystal chemistry on Li ion conductivity of the garnet-type solid Li ion electrolytes will be presented.
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.
Vibrational Spectroscopic Investigations of Commercial Nafion 112 and Related Fluorinated Ionomer Materials
Authors: Behrens Rachel Lynn , Karaoglan Gulten , Zheng Shu , Holtz Mark , Korzeniewski Carol
Published: February 2020

Fourier transform infrared (FTIR) and ultraviolet (UV) Raman spectroscopy methods were applied to analyze commercial Nafion and structurally related fluorinated ionomer membranes. Nafion, a commercial perfluorosulfonic acid material, has been the focus of extensive study, as it is utilized in a wide range of areas, including energy production and chemical sensing. However, issues with water management and temperature stability have motivated the search for other types of ionomer. As such, structurally related fluorinated membranes have been developed in attempts to optimize essential properties, such as water transport and proton conductivity. Structural differences in these materials were examined by vibrational spectroscopy. Raman studies were performed using an UV source to allow the enhancement of the Raman signal and reduce fluorescence versus a visible source. Characteristics derived from the spectra will be discussed, and comparisons will be made between the two vibrational methods.