bluuebunny/crossref_metadata_2025_split huggingface dataset:
In Situ STEM Observation of Pt Nanoparticles on Carbon Surface in the Air Condition
Authors: Hayashi Akari , Zhao Xiaojing , Sasaki Kazunari 
Published: February 2020

Electrocataysts for PEFCs are most commonly composed of Pt nanoparticles on carbon supports. Even though such electrocatalysts are highly active, their durability is still a problem. Especially, carbon corrosion at high potential followed by Pt agglomeration is a major issue to be overcome. Against the carbon corrosion, graphitization of carbon surface is one of possible solutions. In our studies, so far, the surface of carbon black, such as Vulcan and Ketjen black, was graphitized though the simple heat treatment, and then further Pt nanoparticles were deposited on such heat-treated carbon. As a result, durability of such electrocatalysts was successfully increased. On the other hand, we have found that degradation mechanism cannot be explained only by agglomeration and growth of Pt particles, according to the TEM observation before and after the electrochemically accelerated durability tests. Therefore, in this study, an accelerated durability test is newly introduced by using in-situSTEM observation in the air condition to understand the degradation mechanism.
For our study, Hitachi 300 kV Cold-FE TEM (HF-3000) was used. Continuous SEM/STEM observation for 30 minutes was performed at 200 oC in the air condition. A standard catalyst, Pt on Vulcan carbon was first investigated, and still images of SEM made out of the movie are shown in Figure 1. As seen, Pt particles, whose size was about 2 nm, were initially well dispersed on carbon particles. They did not move around very much and were rather embedded into the carbon surface owing to carbon corrosion. Interestingly, in this case, TEM images themselves cannot give us information on degradation mechanism since the particle size is not much changed. Now, we have found that decreased PEFC performance is rather derived from the fact that embedded Pt particles lose their active sites.
On the other hand, Pt particles on graphitized carbon were more agglomerated, but not much embedded into the carbon surface. Since the durability of PEFC performance is higher with graphitized carbon, we believe embedded Pt is a major reason for degradation. Details of comparison with electrochemically accelerated test are also discussed.
Study of through Plane Cation Contamination in Polymer Electrolyte Fuel Cell
Authors: Uddin Md. Aman , Qi Jing , Wang Xiaofeng , Ozdemir M. Ozan , Khajeh Hosseini Dalasm Navvab , Bonville Leonard J. , Pasaogullari Ugur , Molter Trent 
Published: February 2020

The effect of through plane cation contamination on PEFC was investigated using a multilayered membrane cell. The MEA, similar to Watanabe et al. (1, 2), was prepared using five layers of Nafion® 211 (~1 mil=25.4 μm thickness) membrane, and four Pt wires (electrodes) were placed between the membranes (Figure 1). Pt electrodes were used to monitor the through-plane potential that results from the permeation of hydrogen and oxygen from anode and cathode, respectively. 1.14 mM CaSO4 solution was injected into the air stream through a nebulizer at a rate of 65 μL/min, corresponding to a 5 ppm of CaSO4based on dry air. Both the anode and the cathode flow fields were made of aluminum alloy, T6061 and were gold-plated to prevent corrosion.
As shown in Figure 2, the electrode closest to the cathode showed the same potential to the cell voltage and all the other electrodes showed zero potential. At the electrode closest to cathode, the potential was dominated by oxygen permeated from cathode, and in the other electrodes, oxygen permeated from cathode was negligibly smaller than hydrogen permeation, and the electrode potential was dominated by hydrogen oxidation reaction. After 32 hours with pure air, there was enough oxygen permeation from the cathode to other layers of membrane to symbolize the membrane degradation.
Posttest analyses showed that in spite of the gold plating, the aluminum flow fields were corroded. Aluminum corrosion byproducts degraded the cell performance from the beginning of the test. When CaSO4 was injected with air, the cell performance degraded rapidly (Figure 2). Aluminum was deposited as Al2O3 or Al(OH)3on the flow field and GDE surfaces causing mass transport losses. No calcium/sulfur was detected in the deposit from EDX analysis. It might happen that the presence of calcium/sulfur in the deposit was below the detection limit of EDX.
HFR was increased due to contamination. In the membrane layer close to the cathode, the HFR increase was more than 50% (Figure 3).

Acknowledgements

The authors gratefully acknowledge financial support from NSF (CBET-0748063), DOE-EERE through University of Hawaii-Hawaii Natural Energy Institute (DE-EE0000467).

References

1. S. Takaichi, H. Uchida and M. Watanabe, Electrochemistry communications,9, 8 (2007).
2. S. Takaichi, H. Uchida and M. Watanabe, J. Electrochem. Soc.,154, 12 (2007).
Development of Novel High Efficiency Single-Layer Gas Diffusion Layers for Proton Exchange Membrane Fuel Cell
Authors: Lee Hung-Fan , Chen-Yang Yui Whei 
Published: February 2020

Abstract

In this study, a series of single-layer gas diffusion layers(SL-GDL-Gx, x=1-3) for application in proton exchange membrane fuel cell (PEMFC) were successfully prepared by addition of various amount of graphene in a home-made composite-based single-layer gas diffusion layer (SL-GDL) prepared with a simple and inexpensive process. The surface morphologies of the as-prepared SL-GDL-Gx were characterized by scanning electron microscopy (SEM) and found that all the SL-GDLs had micro-porous layer (MPL)-like structures, in which the carbon black and VGCF powders were well-dispersed and covered on surface of the added graphene layers. The characteristics of the as-prepared SL-GDL-Gx, including electronic resistance, gas permeability, mechanical property, and hydrophobicity, were investigated. The fabrication of the SL-GDL-Gx–based membrane electrode assembly (MEA) for PEMFC was carried out by hot-pressing the assembly of NRE212 and the Pt catalyst coated SL-GDE-Gx electrodes. It was found that the best performance of the PEMFCs fabricated with SL-GDL-Gx measured at 80°C under the humidified H2/O2system was obtained from the one with SL-GDL-G3, which contained 5.0% of graphene, and was approximately 77.8% higher than that of the one fabricated with SL-GDL, and as efficient as that of the one fabricated with SGL 35BC, a commercial dual-layer GDL.

Acknowledgement

The authors gratefully acknowledge National Science Council, Taiwan, R.O.C and Chung Yuan Christian University for supporting the research work.
Table1.

SL-GDL-Gx(x=1-3)
Graphene amount (wt%)

SL-GDL-G1
0.0

SL-GDL-G2
2.5

SL-GDL-G3
5.0
Atomistic Simulation Studies of TiO2 Nanosheets
Authors: Ngoepe Phuti Esrom , Matshaba Malili Gideon , Sayle Dean C 
Published: February 2020

Studies on TiO2 nanosheets for energy storage and conversion, including anode in lithium ion batteries (LIB) and electrodes in dye solar cells respectively, are not as abundant as those of nanoparticle and nanoporous structures [1]. Such nanosheets are ideal owing to exposure of highly reactive surfaces, such as the anatase {001}facets, which can now be stabilised [2]. Electrochemical investigations reveal that the exposed (001) high-energy facets of the nanosheet result in enhanced rate capability which originates from both the shortened diffusion path and lowered insertion energy barriers on the active surface for Li+ ions [3]. Furthermore, the electrolyte/electrode contact is enhanced via hollow structures; and such features collectively allow for more efficient lithium diffusion in anodes of LIB. In addition to the anatase polymorph [4], TiO2–B [5] nanosheets have also been observed.
Generally, studies of nanostructures with the brookite structure are scarce since this polymorph is difficult to grow. Aggregations of nanoparticles with the brookite structure have been reported [6]. However, TiO2 nanosheets with the brookite and rutile components have been recently observed [7]. In order to understand such nano-architecture better, we present results of TiO2 simulated nanosheets, which were generated by amorphisation recrystallisation method [8]. Simulated X-ray diffractions of such structures allude to the presence of the brookite and rutile polymorphs. In addition analysis of their microstructures clearly show zigzag patterns associated with the brookite and straight tunnels related to twinned rutile polymorphs. The lithiated nanosheets of TiO2 were also investigated, and lithium ions were located well within the observed tunnels. The suitability of this TiO2polymorph and nano-architecture for lithium ion batteries electrodes, as compared to the bulk form, will be discussed.

References

[1] Su X., Wu Q-L., Zhan X., Wu J., Wei S. and Guo Z. (2012) J. Mater Sci. 47,2519.
[2] Yang H. G., Sun C. H., Qiao S. Z., Liu J. Z. Smith S. C. Cheng H. M. and Lu G. Q. (2008) Nature 453, 638.
[3] Knauth P. and Tuller H. L. (1999) J. Appl. Phys. 85, 897.
[4] Wei X., Liu J., Chua Y. Song J. and Liu X. (2011) Energy Environ. Sci. 4,2054.
[5] Liu S.,Jia H., Han L., Wang J., Gao P., Yang J. and Che S. (2012) Adv. Mater. 24,3201.
[6] Reddy M. A., Pralong V., Varadaraju U. V. and Raveau B. (2008), Electrochem. Solid-State Lett. 11, A132 – A134.
[7] Sussman M., Clouteau, Yasin A., Guo F., and Demopoulos G.P. (2013) Abstract #881, 224th ECS Meeting, © 2013 The Electrochemical Society.
[8] P.E.Ngoepe, R.R. Maphanga and D.C. Sayle, (2013), “Towards the Nanoscale”, Chapter 9 in Computational Approaches to Energy Materials, pp 261-290, edited by C.R.A. Catlow, A. Sokol and A. Welsch, John Wiley and Sons Ltd.
Comparative Iinvestigation of the High Temperature Corrosion Resistant Model and Commercial Fe-Cr-Al-RE Alloys with Different Chromium Content
Authors: Tsurtsumia Olga , Kutelia Elguja 
Published: February 2020

The alloys of Fe-Cr-Al-RE system are the high temperature oxidation resistant materials and they are normally are intended to apply at the temperatures up to 1200OC. Usually the composition of the mentioned system is varied by the main elements values as well as RE’s and other alloying elements amount and the variety of the latter. The high temperature behavior of the Fe-Cr-Al-RE bulk alloys and the coatings with the chromium content of up to 25wt% and the Al that of up to 5wt% is investigated widely, whereas higher chromium content alloys of the mentioned system are barely studied.
The oxidation peculiarities of high (>40wt%) chromium content Fe-Cr-Al-RE model alloy with some minor additives were compared to that of the two commercial (Aluchrom YHf and PM2000) alloys of the same system. According to the experimental results the new material investigated exhibited the slowest oxidation rate (as it is shown in the Fig.1a) and the thinnest oxide scale formation comparatively to the other two alloys which makes it a quite promising high temperature oxidation resistant material [1-3].
The processes taking place on the surface of model alloy exposed to high temperatures are discussed and compared to those of the two commercial alloys. The attempt to disclose the ways differentiating the oxide scale formation on the investigated low and high chromium containing alloys of Fe-Cr-Al-RE system was made and the factors influencing the slower oxide development process for the model alloy were suggested.
The obtained kinetic data after the high temperature cyclic oxidation (120/15 minutes of heating up/cooling down cycling) in laboratory air at 1100OC during 2000 hours is compared for all the investigated tree alloys having either polished or rough surface conditions before the exposures at the elevated temperatures. Thus, the initial surface condition on the protective oxide scale growth kinetics was studied. Besides, the oxide scale growth rate dependence on the specimen thickness was studied as well for the alloys exposed at the same elevated temperatures during 1000 hours, where new model alloy has showed the outstanding priority comparing to the other two commercial alloys investigated (Fig. 1b). SEM analysis was applied for the evaluation of the oxidized specimens’ surfaces as well as their cross-sections. References

Tsurtsumia O., Kutelia E., Bulia B., Mikadze O., Materials Science Forum Vols. 595-598, 2008, (Trans Tech Publications) pp. 833-840

Tsurtsumia O., Kutelia E., Bakhtiyarov S., Proceed. Of 17th Int. Corrosion Congr. USA, Las Vegas, Nevada, October, 2008

Kutelia E., Tsurtsumia O., Eristavi B., Adanir H., Bakhtiyarov S., Journal on Engineering and Technology, 2006, Vol. 1, No. 4, pp. 61-71
Effect of Dopant and Impurity Segregation on the Ionic Conductivity of Doped Ceria Electrolytes
Authors: Sulekar Soumitra S. , Peacock Bruce T. , Nino Juan C. 
Published: February 2020

Doped ceria is a good electrolyte candidate for intermediate temperature solid oxide fuel cells (IT-SOFC) because of its enhanced ionic conductivity. Segregation of dopants and impurities at grain boundaries may degrade the performance of these materials. This grain boundary segregation can be mitigated through manipulation of processing conditions. Recent studies have shown that, at 550°C, Sm0.75Nd0.75CeO2-δ made by co-precipitation from nitrates followed by microwave sintering exhibits enhanced ionic conductivity (2.8 × 10-3 S·cm-1) as compared to the ball milled and conventionally sintered (1.9 × 10-3 S·cm-1) samples (1). Here we focus on the effects that the composition and processing have on the bulk and grain boundary contributions to ionic conductivity and gain a systematic understanding of the underlying processes. Scanning electron microscopy (SEM), electron energy dispersive spectroscopy (EDS) and electron backscattered diffraction (EBSD) studies indicate that the co-precipitated and microwave sintered samples exhibit smaller grain size, lower impurity content and less segregation at grain boundaries and triple point junctions as compared to conventional solid state processing route. These results are correlated with ionic conductivity data obtained from electrochemical impedance spectroscopy (EIS).
REFERENCES:

S. Omar, “Enhanced Ionic Conductivity of Ceria-Based Compounds for the Electrolyte Application in SOFCs”, Ph.D. Dissertation, University of Florida (2008).
On the Utility of Constant Phase Elements to Characterize Heterogeneous Ceramic Grain Boundaries
Authors: McNealy Benjamin E. , Hertz Joshua L. 
Published: February 2020

Electrochemical impedance spectroscopy (EIS) is frequently used in conjunction with simple equivalent circuit models to quantify grain, grain boundary, and electrode properties in electrochemical cells involving ionic or mixed conducting ceramics. Constant phase elements (CPEs) are often used in the equivalent circuit to obtain a better fit of experimental data. However, the CPE is a mathematical abstraction with no clearly defined physical meaning, and its use remains poorly justified. Depression of the grain boundary impedance arc was previously shown to occur in samples with heterogeneous grain boundary conductivity [1]. Here, we use numerical modeling to investigate the utility of CPE-based equivalent circuit fitting in quantifying heterogeneous grain boundary conductivity and/or permittivity.
A 2D electrical model of a polycrystalline ceramic conductor with individually defined grain boundary properties was developed, allowing impedance spectra to be generated for arbitrary distributions of grain boundary conductivity and/or permittivity. For the present study, the relevant properties of each grain boundary were assigned randomly according to a specified distribution. Heterogeneous conductivity values followed a log-normal distribution, while heterogeneous permittivity values followed an exponential distribution with a maximum equal to the bulk grain permittivity. Simulated impedance spectra (Fig. 1) were produced by solving Poisson’s equation and fitted to an equivalent circuit consisting of two parallel R-CPE elements in series. Grain boundary conductivity and permittivity values were calculated from the circuit parameters Rgb
, Qgb
, and ngb
.
As expected, increasingly heterogeneous grain boundary properties correlated to increasingly depressed impedance arcs and reduced CPE exponent. When only the conductivity or the permittivity was heterogeneous, the spread of parameter values could be estimated from the CPE exponent. However, this was no longer possible when both parameters were heterogeneous. As one might hope, in all cases, the grain boundary conductivity determined from the CPE-based equivalent circuit was within ±30% of the actual mean grain boundary conductivity. Conversely, simple use of the CPE’s Qparameter as a capacitance results in severe error in calculating the mean grain boundary permittivity. A commonly used equivalent capacitance expression given by Brug [2] still caused the calculated permittivity to deviate by up to 60% from the actual mean value. However, a new empirical equation [3] allowed a more accurate estimate that differed from the mean by no more than 35% (Fig. 2). Recent extensions of this work to quantification of the impedance of the electrode–solid electrolyte interface will also be presented.
[1] J. Fleig, Solid State Ionics 131 (2000) 117–127.
[2] G.J. Brug et al., J. Electroanal. Chem. Interfacial Electrochem. 176 (1984) 275–295.
[3] B.E. McNealy and J.L. Hertz (under review).
On the Role Played By Catalytic Metallic Additives on TiO2 for the Photoreduction of CO2
Authors: Andreu Teresa , Manzanares Marta , Fàbrega Cristian , Morante Joan Ramon 
Published: February 2020

In photocatalytic processes, it is not only need to generate an electron-hole pair, but the electronic transfer must be efficient in the reaction process, involving multi-electronic redox reactions, occurring at the near vicinity at the surface of the semiconductor. All these factors need the surface engineering of the semiconductor to increase the overall efficiency of the process. The surface properties of TiO2 can be modified by the addition of some elements which give rise to a local lattice modification, introduce new potential catalysts issues and alter or vary the composition and bond ending of the last two nanometers layer being it essential and outstanding for the final photocatalytic properties.
In this contribution, we will present a comparative analysis among different potential additives such as magnesium, indium. More detailed surface analysis techniques have revealed significant changes at the outer part of the TiO2 material. XPS spectra, especially at the energy zone of oxygen and titanium, and corresponding to the last two nanometers, show significant evolution of the different detected bonds as the concentration of the additives is increased.
All these data have been correlated with the photocatalytic behavior for CO2 reduction as a function of the additive concentration below the limit of their solubility for avoiding segregation effects. A correlation between Ti+3 and adsorbed molecular oxygen concentration found in these outer layers will be discussed as well as their correlation with the total productivity rate, considering all the effective photogenerated electrons for the reduction of CO2 from the GC analysis of the products obtained, including CO, CH4 and C2 hydrocarbons. These findings confirm that the benefit introduced by the catalytic additive is mostly related to the “surface quality” and how it is lost as the concentration of additive is increased. Likewise, it is determined that the overall productivity is kinetically limited by a four-hole chemistry of the water oxidation reaction, like in the photoactivated water splitting process. Nevertheless, in spite of these limitative issues, significant increases, a factor of 3 o 4, can be achieved in the productivity of reduced CO2 if the concentration do not overcome some limits whereas the selectivity of the products becomes determined by the nature of the additive.
Regioselective Electrochemical Fluorination of Open-Chain Dithioacetal Derivatives Bearing Electron-Withdrawing Substituents at the α-Position: Product Selectivity Depending on Supporting Fluoride Salts
Authors: Fuchigami Toshio , Yin Bin , Inagi Shinsuke 
Published: February 2020

Selective fluorination of organic molecules is of much importance to develope new pharmaceuticals and agrochemicals. We have systematically studied electrochemical fluorination of various heteroatom compounds including heterocycles.1-3)

In this study, we have investigated fluorinated product selectivity depending on ionic liquid fluoride salts.Anodic fluorination of dithioacetals bearing various electron-withdrawing substituents was achieved with high regioselectivity in the presence of Et3N-3HF to give α-fluorinated products in good to excellent yields. On the other hand,Et3N-5HF and Et4NF-5HF containing high HF content was used as a fluorinating reagent, fluorodesulfurization of dithioacetals such as ethyl α,α-bis(phenylthio)acetate and α,α-bis(phenylthio)acetone was promoted markedly; however, α-fluorination of α,α-bis(phenylthio)acetonitrile proceeded without desulfurization exclusively to provide the corresponding α-monofluorinated product in excellent yield regardless of fluoride salts.

References:

1) Fuchigami, T.;Inagi, S. Chem. Commun. (Feature Article)
2011, 47, 10211.
2) Sawamura, T.; Takahashi, K.; Inagi, S.; Fuchigami, T. Angew. Chem. Int. Ed. 2012, 51,4413.
3) Takahashi, K.; Inagi, S.; Fuchigami, T. J. Electrochem. Soc. 2013, 160, G3046.
Synthesis and Characterization of Imidazolium Chiral Ionic Liquids Prepared from Low-Cost Chiral Amines for Its Use in Asymmetric Organic Electrosynthesis
Authors: Frontana-Uribe Bernardo A. , Rodríguez-Cárdenas Esdrey 
Published: February 2020

Room temperature ionic liquids (RTIL’s) are organic salts with low melting points (less than 0°C) and are in the focus of green chemists as alternative solvents, due to their attractive properties such as chemical electrochemical and thermal stability, non-flammability, low vapor pressure, high ionic conductivity and designable structure.[1],[2] These solvents are constituted of organic cations and inorganic or organic anions. So there is a great possibility to design and tune their properties for various applications just by careful selection of the cation or anion to obtain the desired properties.[3],[4] In the last few years, researchers have turned their interest to synthesis of chiral ionic liquids (CILs). Many CILs have been designed, synthesized and used in organic reactions.[5] Nevertheless, the use of RTIL’s in organic electrosynthesis is well known,[6] the use of the CILs has been overlooked. Chiral imidazolium ionic liquids derived from both enantiomers of a-phenylethylamine using a simple and low cost methodology were synthesized. In this communication it is reported their physicochemical properties, thermal behavior, water content and hydrophilicity, density and electrochemical behaviour. The first studies of the application of these chiral solvents in organic electrosynthesis will be discussed, using the classical pinacolic coupling and CO2activation looking for asymmetric electrochemical reactions.

The authors thank the financial support of PAPIIT-UNAM project IN202011.

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