bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of the Performance of the Hydrodynamics in the Diluted Compartment of an Electrodeionization Reactor
Authors: Enciso-Pérez Rubi , Rodríguez-Torres Israel
Published: February 2020

The hydrodynamic behavior of the electrodeionization reactor allows the improvement of the performance of the process as a whole. The challenge lies on the adequate modelling of the packed bed compartment, due to the particle size of the ion exchange resins.

The present study focusses on the improvement of the hydrodynamic behavior of the diluted compartment to achieve a plug flow in the diluted compartment of the reactor by adjustments in the geometry design via CAD.

The reactor, with 32cm2 ion exchange membranes, has two concentrated and one diluted packed bed compartment where the solution to be treated is introduced to the reactor and deionized while being in contact with the ion exchange resin.

Using CFD software, the existing geometry for the reactor was simulated and then subsequent variations were made to achieve a plug flow in the diluted compartment, minimizing the stagnant and channeling zones.

The results, allow the study of the velocity profiles in the compartment for the different geometries modeled and the selection of the configuration that allow the removal of the maximum quantity of ions from the inlet solution.
Beyond Chevrel Phase Mo6S8 : High Energy Density Mg Battery Cathodes
Authors: Mizuno Fuminori , Arthur Timothy S. , Zhang Ruigang , Ling Chen
Published: February 2020

Rechargeable magnesium batteries have recently gained more and more attention for a possible candidate of post lithium-ion batteries, because of i) potentially high energy density ((3.0V x 2e- for Mg) / (4.0V x 1e- for Li) = 1.5), ii) low cost (high clarke number; Mg (1.93) vs. Li(0.006)) and iii) intrinsic safety (no dendrite growth for Mg, while needle-like dendrite for Li). In 2000, a great success of Mg battery was achieved by Prof. Aurbach in the system comprising Mg metal anode, Chevrel phase Mo6S8cathode and Grignard based electrolyte [1]. The prototype Mg battery can work very well over >2000 cycles. Guided by this discovery, intensive researches on anode, cathode and electrolyte materials have accelerated all over the world, to maximize the advantages of the Mg battery system.

Although there have many hurdles to be overcome in the Mg batteries, the biggest hurdle is that the cathode energy density stays much lower than expected. The Chevrel phase Mo6S8 is the only reported cathode material with good cyclability, but due to low operation voltage (1.2 V vs. Mg) and low capacity (122 mAh/g), it is theoretically difficult to realize the Mg battery which is competitive with lithium-ion batteries in term of energy density. Therefore, cathode materials having high operation voltage and high capacity are strongly desired. Previously, we worked on MnO2 cathodes and tried to understand its reaction mechanisms. Although MnO2 cathodes show higher average voltage (1.5 V vs. Mg) and high initial capacity (280 mAh/g) [2], they faced certain restrictions (i.e. structural deformation, thermodynamically preferred conversion reaction and resistive shell formation (Figure 1)) during magnesium ion intercalation into the host structure, resulting in a severe capacity fading during cycling [3,4]. Based on this knowledge, we have been currently researching solutions to such issues while continuously trying to find new cathode candidates. For example, CaFe2O4 phase MgMn2O4 [5], carbon cluster fullerene (C60) [6], amorphous vanadium oxide [7], and so on.

In this presentation, we will discuss about key challenges in improving the cathode performances of these materials and in further enhancing the energy density of Mg batteries.

References [1] D. Aurbach et al., Nature, 407 (2000) 724. [2] R. Zhang et al., Electrochem. Commun., 23 (2012) 110. [3] C. Ling et al., submitted for publication (2014). [4] T. Arthur et al., submitted for publication (2014). [5] C. Ling et al., Chem. Mater., 25 (2013) 3062. [6] R. Zhang et al., submitted for publication (2014). [7] T. Arthur et al., submitted for publication (2014).
Pd-Co/CNF Composite Material as Electro-Catalysts for Lithium-Oxygen Batteries
Authors: Cho Sung Man , Hwang Sunwoo , Koo Bon Seok , Yoon Woo Young
Published: February 2020

Lithium-Oxygen (Li-O2) batteries have attracted much attention owing to their high energy densities compared to conventional lithium ion batteries, and are one of the promising lithium secondary batteries for electric vehicles (EVs) and hybrid electric vehicles (HEVs). The theoretical specific energy density of the Li-O2 battery with the discharge reaction of 2Li++O2+2e-→Li2O2 is 3505 Wh kg-1. However, the low energy efficiency, poor rate capability, and limited cycle life of these batteries cause problems for their commercialization. The sluggish oxygen redox reaction results in low power and high overpotentials. Also, the pores of oxygen cathode can easily be blocked by insoluble discharge products, which cause incomplete discharge, inhibiting the flow of oxygen to the reaction sites. Therefore, the design of cathodes having oxygen diffusion pathway and uniform distribution of catalysts is the key role which can enhance the performances of Li-O2 batteries. This work focuses on the electrochemical effects of palladium-cobalt (Pd-Co)/carbon nanofiber (CNF) composite catalyst for a cathode. The nanosized Pd-Co catalysts are embedded evenly into CNFs. The high catalytic activity of Pd-Co catalysts reduce the overpotentials, which can improve the energy efficiency. Furthermore, the interconnected pore network structure creates effective gas diffusion channels, thus improving specific capacity and cycle life for Li-O2 cell. PdCo/CNF composite catalysts are synthesized by using polyol method and electrospinning method. Cells were tested at the current densities of 100 mA g-1 and 200 mA g-1with limited voltage of 2.0 to 4.5V. The morphology of the samples was observed on a field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The structure of the samples was characterized by X-ray diffraction (XRD) spectroscopy and Inductively coupled plasma atomic emission spectrometry (ICP-AES). The result was analyzed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV).

[1] Y.C. Lu, B.M. Gallant, D.G. Kwabi, J.R. Harding, R.R. Mitchell, M.S. Whittingham, Y. Shao-Horn, Energy Environ. Sci., 6, 750 (2013).

[2] L.J. Hardwick, P.G. Bruce, Curr. Opin. Solide. St. M., 16, 178 (2012).

[3] M.A. Rahman, X. Wang, C. Wen, J. Appl Electrochem, 44, 5 (2014)

[4] W. Wang, D. Zheng, C. Du, Z. Zou, X. Zhang, B. Xia, H. Yang, D.L. Akins, J. Power Sources, 167, 243 (2007)

[5] B.W. Huang, X.Z. Liao, H. Wang, C.N. Wang, W.S. He, Z.F. Ma, J. Electrochem. Soc. 160, A1112 (2013)
Dynamics of Polysulfide Dissolution for Various Electrolytes in Working Li-S Battery By in-Operando Technology
Authors: Lin Chia-Nan , Chang Chih-Ching , Li Chun-Lung , Wu Nae-Lih , Tsai Li-Duan , Fang Jason
Published: February 2020

The lithium-sulfur (Li-S) battery is a promising electrochemical system as a high-energy storage device. However, the performance of Li-S battery is strongly limited by the S insulation, dissolution of lithium polysulfide (PS) and high self-discharge rate. These problems can lead to short cycle life and poor efficiency for application. Therefore, the LiNO3 mixed in the electrolyte or used high lithium salt concentration electrolyte was studied, the results showed that coulombic efficiency was enhanced substantially when this additive was used, indicating that the PS/lithium reaction and PS shuttling were decreased.

In this study, we examined the interplay between PS diffusion and cycle processes. Moreover, we was designed to test PS migration in electrolytes featuring distinct salt concentrations, and in-operando TXM (Transmission X-Ray Microscopy) analysis (Fig. 1) was used to study the dynamics of PS dissolution. These findings demonstrated that using the lithium salt at a high concentration in the electrolyte enhanced the electrochemical performance of the battery. The S particle did not dissolve completely until the middle of the 2nd plateau of the lithiation process at high lithium salt concentration, indicating that the dissolution that occurs during lithiation was delayed.

The results presented here demonstrate that using electrolytes containing a lithium salt at a high concentration can not only inhibit the dissolution of lithium PS but also effectively retard the migration of the lithium PS in the electrolyte, which substantially enhances the electrochemical performance of the battery. We believed that the strategy of developing a hybrid electrolyte by incorporating lithium salt and liquid PS is a very promising electrolyte for long cycling Li-S battery.
Solid Electrolytes Based on Fast Fluorine Ion Motions — 19F T1ρ NMR Relaxation vs Conductivity Measurements of Mechanosynthesized Nanocrystalline Ba0.6La0.4F2.4
Authors: Preishuber-Pflügl Florian , Wilkening Martin
Published: February 2020

The use of mechanosynthesis for the preparation of ion conductors provides access to new compounds whose properties are governed by chemical metastability, defects introduced and size effects present. The benefits of this valuable synthesis method manifest in enhanced ion transport properties of the prepared nanocrystalline ceramics. Such materials are useful candidates to act as solid electrolytes, e.g., in fluorine ion batteries [1]. Here, the introduction of large amounts of La3+ into the cubic structure of BaF2 was carried out by using high-energy ball-milling. The replacement of Ba2+ with a trivalent cation leads to the formation of an increased number fraction of point defects in the metastable crystal structure, which resulted in an increase of the dc-conductivity when compared to pure, nano-sized BaF2 [2]. Until now, only little is known about activation energies and jump rates of the elementary hopping processes of such materials. In the present study, we used broadband impedance spectroscopy and 19F NMR relaxometry to get to the bottom of ion jump diffusion proceeding on short-range and long-range length scales in Ba0.6La0.4F2.4. The dielectric measurements revealed an activation energy of 0.57 eV for macroscopic ion transport, whilst NMR, which is sensitive to both long-range motion and localized jumps, gave much smaller activation energies [3]. This was confirmed by high-frequency impedance measurements carried out at frequencies as high as 3 GHz that enabled us to compare the results from complementary methods applied in the same time window.

[1] C. Rongeat, M. A. Reddy, R. Witter, and M. Fichtner, J. Phys. Chem. C, 117, 4943 (2013).

[2] A. Düvel, J. Bednarcik, V. Šepelák, and P. Heitjans, J. Phys. Chem. C, in press (2014), DOI: 10.1021/jp410018t.

[3] F. Preishuber-Pflügl, and M. Wilkening, Phys. Chem. Chem. Phys., in press (2014), DOI: 10.1039/C4CP00422A.
Invited: the Aprotic Li-O2 Battery: O2 Reduction Mechanisms
Authors: Johnson Lee , Li C , Liu Zheng , Chen Yuhui , Freunberger Stefan A , Bruce Peter G.
Published: February 2020

While O2 reduction in aqueous environments has been studied extensively for many decades, O2 reduction in aprotic solvents has received much less attention. One spin-off of the recent interest in rechargeable Li-O2 batteries, Fig. 1,1,2 based on aprotic electrolytes is that it has highlighted the importance of understanding the fundamental mechanisms of O2 reduction in such a medium.3-10 Indeed understanding the mechanisms of O2 reduction are essential if progress is to be made towards realizing the potential of the rechargeable aprotic lithium-O2 battery.1,2

A number of authors have made important contributions to understanding O2 reduction in non-aqueous electrolytes.3-5,7
We have combined a range of electrochemical, spectroscopic and microscopy methods to investigate the mechanism of electrochemical O2 reduction in aprotic electrolytes. The results of these studies will be presented, along with the implications of the results for the future of rechargeable Li-O2 batteries.

References

(1) Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J.-M. Nat Materials
2012, 11, 19.

(2) Li, F.; Zhang, T.; Zhou, H. Energy & Environmental Science
2013, 6, 1125.

(3) Adams, B. D.; Radtke, C.; Black, R.; Trudeau, M. L.; Zaghib, K.; Nazar, L. F. Energy & Environmental Science
2013, 6, 1772.

(4) Horstmann, B.; Gallant, B.; Mitchell, R.; Bessler, W. G.; Shao-Horn, Y.; Bazant, M. Z. The Journal of Physical Chemistry Letters
2013, 4, 4217.

(5) McCloskey, B. D.; Scheffler, R.; Speidel, A.; Girishkumar, G.; Luntz, A. C. The Journal of Physical Chemistry C
2012, 116, 23897.

(6) Mitchell, R. R.; Gallant, B. M.; Shao-Horn, Y.; Thompson, C. V. The Journal of Physical Chemistry Letters
2013, 4, 1060.

(7) Trahan, M. J.; Mukerjee, S.; Plichta, E. J.; Hendrickson, M. A.; Abraham, K. M. Journal of The Electrochemical Society
2013, 160, A259.

(8) Peng, Z.; Freunberger, S. A.; Hardwick, L. J.; Chen, Y.; Giordani, V.; Barde, F.; Novak, P.; Graham, D.; Tarascon, J. M.; Bruce, P. G. Angewandte Chemie International Edition
2011, 50, 6351.

(9) Sharon, D.; Etacheri, V.; Garsuch, A.; Afri, M.; Frimer, A. A.; Aurbach, D. The Journal of Physical Chemistry Letters
2012, 4, 127.

(10) Zhai, D.; Wang, H.-H.; Yang, J.; Lau, K. C.; Li, K.; Curtiss, L. A.; Amine, K. Journal of the American Chemical Society
2013.
Future Electrochemical Energy Harvesting Developments Initiated by Different Energy Storage and Supply Scenarios
Authors: Winkler Wolfgang , Williams Mark C. , Miyamoto Akira , Suzuki Ai
Published: February 2020

Future electrochemical developments, such as energy harvesting, will be influenced by different energy supply scenarios. These scenarios are long term, midterm and short term. Long term would be mainly fluctuating regenerative electricity (wind and solar) with energy harvesting as a main primary energy supply. A midterm scenario with natural gas from fracking to be used (in trigeneration systems) with a growing energy harvesting for primary energy supply . In the short term energy harvesting involves mainly waste thermal energy. In all times energy storage would enable and enhance all scenarios.
Enhancement of La0.6Sr0.4Co0.2Fe0.8O3
-δ Activity by Ion Implantation for Low-Temperature SOFC Cathodes
Authors: Huang Yi-Lin , Pellegrinelli Christopher , Lee Kang Taek , Perel Alexander , Wachsman Eric D.
Published: February 2020

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) has been demonstrated to be one of the best performing mixed ionic-electronic conductors (MIEC) for SOFC cathode materials. Surface exchange on LSCF, however, limits the oxygen transport and the performance. In this study, we investigated a composite cathode with surface modification of LSCF for enhanced oxygen dissociation on the surface, while utilizing LSCFs ability to transport oxygen through the bulk. Manganese ions were ion implanted into LSCF bar samples. Various implantation energies and ion concentrations were used to create samples with different Mn-ion depth profiles. The oxygen transport properties were characterized by electrical conductivity relaxation (ECR), using DC four-point probe measurements during the oxygen re-equilibration processes. The oxygen transport properties, chemical diffusion coefficient (Dchem) and chemical surface reaction coefficient (kchem) were obtained by fitting ECR data using the diffusion equations. kchem changes with different Mn doping levels and doping energies of manganese ions. The Mn ion implanted LSCF samples showed an enhanced kchem, improving the overall oxygen reduction reaction (ORR) for LSCF cathodes.
Towards the Microstructural Optimization of SOFC Electrodes Using Nano Particle Infiltration
Authors: Kishimoto Masashi , Lomberg Marina , Ruiz-Trejo Enrique , Brandon Nigel P.
Published: February 2020

Solid oxide fuel cells (SOFCs) are receiving increasing attention because of their ability to convert the chemical energy of fuels into electrical energy in an efficient and clean manner. It is generally accepted that electrode microstructure plays an important role in determining the performance and durability of SOFC electrodes because it has a significant influence on various transport phenomena and electrochemical reactions within the electrodes. In order to satisfy the growing demand for their performance and reliability, it is strongly required to understand the microstructure-performance relationships, and to optimize the microstructure.

Here we focus on electrodes fabricated with nano-particle infiltration technique, where ceramics structure constructs a framework structure called scaffold, to which nickel particles are introduced in the form of nano particles. 3D microstructural analysis using the focused ion beam scanning electron microscopy (FIB-SEM) (e.g. Figure) revealed that the infiltration technique has a greater potential, compared with the conventional powder mixing and sintering approach, to control the electrode microstructure, which is significantly useful to satisfy the requirements for the electrode microstructure, such as transport properties and electrochemical activities. Numerical simulations for the electrochemical and mechanical analyses are also conducted using the acquired 3D microstructures, delivering a guideline to optimize the electrode microstructure.

Figure. 3D reconstructed microstructure of an SOFC anode prepared using infiltration technique. A ceria scaffold (grey), infiltrated nickel particles (green) and extracted triple-phase boundary lines (red).
Benchmarking ORR Activity of Pt-Alloy/C Electrocatalysts Utilizing Improved TF-Rde Methods
Authors: Shinozaki Kazuma , Zack Jason , Pylypenko Svitlana , Pivovar Bryan S , Kocha Shyam S
Published: February 2020

Thin-film rotating disk electrode (TF-RDE) measurements have been performed to screen the Oxygen Reduction Reaction (ORR) activity of electrocatalysts for PEMFC applications. Through progressive refinement of the technique by several researchers, a number of factors that play a critical role -on measured ORR activity -have been recently reported. Some of the factors include catalyst loading (electrode thickness), film uniformity (spin coating), Nafion cap thickness, ink dispersion/formulation, corrections for iR and background currents, etc. However, for most of these studies, Nafion was typically employed either to improve the catalyst ink dispersion or to glue catalysts on a glassy carbon substrate.

In our previous study, we verified the effect of Nafion on the ORR activity as a function of I/C ratio. The measured activity enhancement was reported ~1.8 times for a Pt/HSC catalyst when Nafion was completely eliminated. Further studies demonstrated that the activity could be further enhanced (~2.7 times compared to a Nafion-based catalyst layer) for extremely thin, uniform films that were Nafion-free. The thin films of low Pt loading were prepared either by incorporation of a surfactant in the dispersion or by drying of the electrodes under controlled conditions.

While relative standard deviation (RSD; based on ~30 samples for each method) for Nafion based catalyst films ranged ~9–15%, RSD for Nafion-free thin, uniform films was ~6%. This clearly demonstrates high reproducibility of measured ORR activity with the Nafion-free thin, uniform films. Although the reason of the increase has not been elucidated yet, O2 transport and proton transport resistances within the catalyst layer are the most probable causes. Comparison of Tafel plots for Nafion-free and Nafion-based films to a polycrystalline Pt electrode provides some insight into the mechanism. Definitive anion adsorption features of Nafion ionomer were not observable for the Pt/C catalysts in our studies. Although further study is necessary to identify the cause of the large increase, the use of thin films without Nafion seems justified to reduce O2 transport and proton transport resistance within the catalyst layer.

In this work, we have studied the ORR activity for various commercially available Pt based alloy catalysts to provide improved baselines using our new techniques. Figure 1 is a plot comparing the ORR activity of baseline Pt/C to PtCo/C catalysts films deposited by conventional Nafion incorporation method (thick coffee ring structured film) and the Nafion-free method (thin-uniform film).

The measured specific activity (Figure 1) for Nafion-free, thin-uniform Pt/C films compared to that for a similar Nafion-based film increased by a factor of ~2.7 and is very similar to the enhancements observed for PtCo/C films. Additionally, the specific activity enhancements due to alloying with Co are similar for Nafion-based and Nafion-free films.
Invited: Development of Highly Phosphonated Polymers for Fuel Cell Membranes
Authors: Jannasch Patric
Published: February 2020

Phosphonated polymers may show high intrinsic proton conductivities at low water contents provided that the local concentration of phosphonic acid groups is very high [1,2]. Moreover, the lower acidity of aryl- and alkylphosphonic acids in relation to sulfonic acids requires higher acid contents to reach high conductivities also at higher water contents. In this context, poly(vinylphosphonic acid) (PVPA) has emerged as an interesting component for fuel cell membranes because of its extremely high concentration of phosphonic acid, corresponding to 9.25 mmol –PO3H2 per g dry material. However, the high ionic content leads to complete water solubility as well as poor mechanical properties in the solid state. Consequently, it is necessary to develop synthetic strategies to efficiently immobilize the PVPA in the membranes before practical use.

We have previously immobilized PVPA by preparing various block and graft copolymers with PVPA segments [3]. These copolymers where found to self-assemble and form robust membranes with nanostructured morphologies and high proton conductivities. Very recently we have pursued a number of novel synthetic strategies towards different highly phosphonated membranes. These approaches include phosphonated norbornene copolymers prepared via ring opening metathesis polymerization (ROMP) [4], multiblock copolymers selectively grafted with PVPA via anionic polymerization [5], as well as block and graft copolymers containing the more acidic poly(tetrafluorostyrenephosphonic acid) via atom transfer radical polymerization (ATRP) [6]. Challenges and selected results on the synthesis and properties of these copolymers and membranes will be presented and discussed along with future prospects.

Acknowledgement

We gratefully acknowledge the financial support from the Danish Council for Strategic Research through contract no.09-065198, as well as the funding from the European Community’s Seventh Framework Programme (FP7/2010–2013) under the call ENERGY-2010-10.2-1: Future Emerging Technologies for Energy Applications (FET) under contract 256821 QuasiDry.

References

[1] Steininger, H. Schuster, M., Kreuer, K. D., Kaltbeitzel, A., Bingol, B., Meyer, W. H., Schauff, S.,Brunklaus, G., Maier, J.,Spiess, H. W., Phys.
Chem. Phys., 2007, 9, 1764.

[2] Bingöl, B., Jannasch, P., Proton Conducting Phosphonated Polymers and Membranes for Fuel Cells, in Phosphorus-Based Polymers - From Synthesis to Applications, ed. S. Monge and G. David, 2014, Royal Society of Chemistry, in press.

[3] a) Perrin, R., Elomaa, M., Jannasch, P., Macromolecules, 2009, 42, 5146, b) Parvole, J., Jannasch, P. Macromolecules
2008, 41, 3893, c) Ingratta, M., Elomaa, M., Jannasch, P. Polym. Chem.,
2010, 1, 739.

[4] Bingol, B., Kroeger, A., Jannasch, P., Polymer, 2013, 54, 6676.

[5] Sannigrahi, A., Takamuku, S., Jannasch, P., Polym. Chem.,
2013, 4, 4207.

[6] Dimitrov, I., Takamuku, S., Jankova, K., Jannasch, P., Hvilsted, S., J. Membr. Sci.,
2014, 450, 362.
Kinetic Modeling of Chemical Degradation Phenomena in Fuel Cell Ionomers
Authors: Ghelichi Mahdi , Melchy Pierre-Éric Alix , Eikerling Michael
Published: February 2020

A kinetic model has been developed to describe the chemical degradation of Nafion-type polymer electrolyte membranes. The model accounts for pathways of radical formation and consumption along with mechanisms of ionomer degradation through radical attack. Systematic simplifications on the set of model equations lead to analytical expressions for concentration of aggressive hydroxyl radical as a function of initial iron content and hydrogen peroxide concentration. The ionomer degradation model employs a coarse-grained structure of Nafion ionomer. . It distinguishes units corresponding to head groups and trunk segments of sidechains. The backbone segment between two sidechains is the third unit considered in the degradation model. A set of differential equations is formulated to describe the consumption of these units and determine the associated rate of fluorine loss and the change in the ion exchange capacity (IEC). A parametric study was performed to study the impact of different degradation mechanisms, degradation conditions, and chemistries of the PFSA on fluorine loss and IEC change. The rate constants of degradation processes are found through comparison with the experimental degradation data. Results will be discussed in view a structural stabilization of PEMs and the mitigation of chemical degradation.
Effect of Oxygen Concentration on Current Density Distribution in the Land-Channel Direction
Authors: Shrivastava Udit N , Tajiri Kazuya
Published: February 2020

Fundamental study of reactants and products distribution in a proton exchange membrane fuel cell (PEMFC) has always been focus of research. Baker at. el. applied limiting current density as a tool to predict the overall oxygen diffusion resistance from the channel to the catalyst layer. Their results showed that at high current densities operation (relatively wet condition) the oxygen diffusion resistance is much higher than the low current densities operation (relatively dry condition) [1]. However, this method is unable to determine the effect of land-channel geometry on the oxygen diffusion resistance.

In our previous studies, we have measured the current density distribution in the land-channel geometry at 340 µm resolution and found that in a wet condition, current densities are higher in channel areas than in land areas [2-3].

In this work, we are going to present current density distribution as a function of oxygen concentration in the land-channel direction. This method can be used to obtain local polarization curves at 35 degree C and 100% RH (see attached Figure) under the land and channel. Subsequently, it will be used to measure local limiting currents and can be used to resolve oxygen diffusion resistance distribution in the land-channel direction. Similarly, using hydrogen pumping, in low hydrogen concentration effect of land-channel geometry on the current density distribution can be analyzed.

References

D.R. Baker, D. Caulk, K.C. Neyerlin, M.W. Murphy. J. Electrochem. Soc., 156, B991 (2009).

U.N. Shrivastava, K. Tajiri. ECS Trans., 58, 1643 (2013)..

U.N. Shrivastava, K. Tajiri. Electrochemistry letters. Submitted.
Optimization of Component Material Properties and Flow Channel Geometric Parameters in a PEM Fuel Cell Cathode
Authors: Lange Kyle , Lueth Christopher , Godfrey Aaron , Hartridge Steve
Published: February 2020

PEM fuel cells are generally composed of components which have spatially uniform material properties. In other words, the material properties in one location in a fuel cell component are the same as those in a different location in the same component. Such components are cost-effective and easy to manufacture and model. However, recent advances in additive manufacturing at the micro- and nano-scale level have enabled the creation of parts and components whose material properties are spatially non-uniform. Components with spatially non-uniform material properties could potentially improve the performance of a PEM fuel cell.

To further illustrate the potential benefit of fuel cell components with spatially non-uniform material properties, consider the cathode side of a fuel cell with a serpentine flow channel. At the inlet, the oxygen concentration is highest, while at the outlet, the oxygen is depleted due to electrochemical reactions. However, the material properties of the typical gas diffusion layer are the same near the inlet as they are near the outlet. Due to the non-uniformity of the reactant concentration profile, it stands to reason that the performance of the fuel cell could be impacted by a gas diffusion layer which has a spatially variable effective diffusivity.

In this work, we use STAR-CCM+ to simulate heat transfer/production, flow, species transport, electrodynamics, and electrochemical reactions in the cathode side of a fuel cell with a serpentine flow channel. We use Optimate+, a STAR-CCM+ embedded optimization package, which uses a proprietary hybrid-adaptive algorithm named SHERPA, to maximize the total current generated in the cathode side of the fuel cell by changing the porosity profiles in the gas diffusion layer and catalyst layer, the platinum loading profile in the catalyst layer and the geometric parameters of the flow channel design. We will present results from our simulations and optimization study in addition to discussing the limitations of our physical model and future topics for research.
2D Platinum Network ORR Catalyst on Carbon and Niobium Oxide Hybrid Support
Authors: Xu Chunchuan , Yang Jun , Pence Benjamin , Gath Kerrie , Pietrasz Patrick , Sulek Mark , Sun Kai , Sohm Evan , Meng Guangnan
Published: February 2020

2D platinum network catalyst on graphitic carbon and amorphous NbOx hybrid support has been synthesized by Arc Plasma Deposition (APD) method. The 2D platinum structure on the conductive, corrosion resistant amorphous metal oxide significantly increases the catalyst stability under RDE accelerated stress tests. RDE and 5cm2MEA single cell test results showed that the catalyst has higher specific and mass activities than those of conventionally prepared platinum on graphitic carbon (Pt/C) catalyst. The microstructures of the catalyst were characterized by transmission electron microscopy (TEM).

Amorphous NbOx conductive metal oxide was deposited from either Nb2O5 in Ar or Nb in a gas mixture of 30 vol.% of O2 in Ar onto carbon particles by using Arc Plasma Deposition (APD) system (Ulvac-Riko, Inc). The obtained NbOx on carbon particle are isolated amorphous islands, with the value of x between 1 and 2.5. When Pt was deposited onto the formed NbOx islands, a platinum 2D nano-network was obtained, as schematically shown in Figure 1. The platinum particles with about 5 nm size can be uniformly deposited on the support NbOx and carbon. Figure 2 shows the percentage change of ECSA and mass activity under AST using square wave 1.0V~1.5V for carbon corrosion (a) and 0.1V~1.0V for Pt (b). The specific (SA) and mass activities (MA) are about 400 m A/cm2
Pt and 350A/gPt, respectively. The accelerated stress tests show that the durability of the catalyst is about 3~5 times higher than those of synthesized Pt on carbon catalyst through wet chemical methods under the same carbon corrosion and platinum stress conditions. The polarization curve and EIS data of Pt/C and Pt/NbOx/C on a 5 cm2 single cell are shown in Figure 3. Pt/NbOx/C cell with 0.07mg/cm2 Pt loading and Pt/C cells with 0.19mg/cm2 Pt loading have a similar polarization curve.
Invited: Comparative Study of the Electrocatalytic Oxidation of Glycerol on Pd-Au/CMO and Pd-Au/MWCNT Nanocatalysts Prepared by the Polyol Method in Alkaline Media
Authors: Arenas-Carmona Rosita , Morales-Acosta Diana , Martinez-Luevanos Antonia , Rodriguez-Varela F.J.
Published: February 2020

Studies on fuel cells are currently increasing because of their great potential for portable, transport and stationary power supply applications. Recently, the use of alkaline electrolytes has called the attention of several groups worldwide because the electrochemical kinetics occurring at fuel cell electrodes is enhanced, and platinum-free catalysts that otherwise show low activity in acid media can be used. In alkaline DAFCs, the use of polyols as fuels is an interesting alternative. Particularly, glycerol is less toxic than methanol and has a relatively high theoretical energy density (5.0 kWh kg-1) compared to methanol (6.1 kWh kg-1). Pd has been known to exhibit superior activity for the glycerol electro-oxidation in alkaline solution. Beside this, the combination of Pd and Au has exhibited a synergetic effect increasing the catalytic activity for selective oxidation of polyols. In this work, the influence of two carbon supports on the electrocatalytic performance of Pd-Au materials for the glycerol oxidation reaction in KOH electrolyte is investigated. Pd-Au/OMC and Pd-Au/MWCNT have been synthesized by the polyol reduction method. The catalysts have been characterized by XRD, EDS, TEM and electrochemical techniques. The results show the influence of the carbon support on the catalytic activity of the Pd-Au anodes. Such effect could be attributed to the fact that the relatively large pores in the OMC support facilitate the mass transfer process, promoting a high concentration of exposed active sites to participate in the reaction.
Self-Supported PdSnx Catalysts for the Electrooxidation of Alcohols
Authors: Coutanceau Christophe , Zalineeva Anna , Padilla Monica , Serov Alexey , Baranton Stève , Atanassov Plamen
Published: February 2020

Palladium-based nanocatalysts possess high activity and stability towards alcohol oxidation reactions in alkaline media, and can then be considered as possible economical substitutes of Pt for alcohol oxidation. There is indeed an increasing number of published works devoted to the development of Pt-free anode catalysts for direct alcohol fuel cells1-3.

In addition, Sn is known to an excellent co-catalyst for the electrooxidation of alcohol, particularly ethanol, in acidic as well as in alkaline media.4,5

In the present communication, we present the synthesis by the sacrificial support method (SSM), which was developed by the research group of Prof. Atanassov6,7
, of a series of self-supported PdSnx catalysts with different atomic ratios and their physicochemical characterization by different methods, such as BET, SEM, TEM, EDX, XPS, and electrochemical method.

The influence of the Pd:Sn atomic ratio on the electrocatalytic behavior towards alcohol oxidation is investigated in alkaline medium, with particular interest to glycerol which is a renewable raw material produced from the biofuel industry. In addition to the promotional effect of tin towards the catalytic activity, the effect on the mechanism of glycerol electrooxidation is also determined using in situ infrared spectroscopy measurements.

At last, the promotional effect of tin is also confirmed for other primary and secondary monoalcohols, and polyols.

1- A. Serov, C. Kwak, Appl. Catal. B: Environmental 90, 313(2009).

2- C. Bianchini and P. K. Shen, Chem. Rev. 109, 4183(2009).

3- M. Simoes, S. Baranton and C. Coutanceau, Appl. Catal. B: Environmental 93, 354 (2010).

4- C. Lamy, S. Rousseau, E. M. Belgsir, C. Coutanceau, J. -M. Léger, Electrochim. Acta 49, 3901 (2004).

5- R. M. Modibedi, T. Masombuka, M. K. Mathe, International Journal of Hydrogen Energy 36, 4664 (2011).

6- A. Serov, U. Martinez, P. Atanassov Electrochem. Comm. 34, 185 (2013).

7- A. Serov, U. Martinez, A. Falase, P. Atanassov Electrochem. Comm. 22, 193 (2012).

Acknowledgment: Anna Zalineeva thanks the Center for Emerging Energy Technologies, Farris Engineering Center (UNM) for assistance and technical support, and the county council of Poitou- Charentes (France) for financial support. UNM portion of this work was funded in part by DOE-BES EPSCoR Implementation Award: “Materials for Energy Conversion”.
The Application of Ultrasound to the Coating of Platinum Catalyst on Membrane for Proton Exchange Membrane Fuel Cell
Authors: Kim Youngkwang , Kim Kanghoon , Choi Insoo , Kim Jae Jeong , Kwon Oh Joong
Published: February 2020

MEA (Membrane Electrode Assembly) consisting of the electrodes coated with a catalyst and the membrane is the most important in fuel cell. In fabricating MEA, there are two ways to coat catalyst depending on a coating substrate, i.e. CCM (Catalyst Coated Membrane, coating on membrane), and CCS (Catalyst Coated Substrate, coating on carbon paper). Generally, CCM is known as a better way than CCS, and spray coating has been widely used for CCM method. In this study, CCM method was also adopted to make MEA, however, catalyst was coated sonochemically to introduce a new catalyst coating method in making MEA.

The most convincing and famous mechanism known for a sonochemical metal ion reduction is a reduction of metal precursor by radicals generated by hot spot during ultrasound irradiation1. Thus we introduced ultrasound irradiation for synthesizing and coating of platinum on membrane simultaneously. In applying ultrasound irradiation, we changed experimental conditions such as time of radiation and the intensity of radiation. The amount of platinum loaded on membrane was proportion to the time and the power of ultrasound irradiation as shown in Fig. 1. The solution used for platinum electrode formation includes not only platinum precursor but also a reducing agent and a surfactant to help precursor reduction. After Pt catalyst coating, remaining impurities like a reducing agent and a surfactant were removed by using stirring in pure water.

In order to check whether platinum was successfully loaded on membrane, FE-SEM (Field Emission Scanning Electron Microscope) and EDS (Energy Dispersive x-ray Spectroscopy) analyses were carried out as shown in Fig. 2, and it proved the effectiveness of ultrasound irradiation in making platinum electrode on membrane. Furthermore, we looked into the electrochemical characteristics of the MEA using CV (Cyclic Voltammertry) and EIS (Electrochemical Impedance Spectroscopy), and then the result was compared with that of a conventional MEA. MEAs, both new and conventional, were made into single cells for a performance test and a comparison. In making a single cell with the MEA made by ultrasound irradiation, ionomer effect was thoroughly studied to take advantage of thin thickness of platinum catalyst layer. It is known that the mass transfer through thin film catalyst layer is fast without ionomer2.

In thus presentation, all the results investigated in the study will be presented with in-depth discussion.

References:

1. J. H. Bang and K. S. Suslick, Adv. Mater., 22, 1039 (2010).

2. A. K. Schmoeckel, G. D. Vernstrom, R. Atanasoski, and M. K. Debe, J. Power Sources, 161, 1002 (2006).
Methanol and Ethanol Electro-Oxidation on the Platinum-Cobalt Catalyst Deposited on the Titanium Surface
Authors: Stankevičienė Ina , Cinciene Zana , Balciunaite Aldona , Zabielaite Ausrine , Vaiciuniene Jurate , Verbickas Rolandas , Selskis Algirdas , Tamasauskaite-Tamasiunaite Loreta , Norkus Eugenijus
Published: February 2020

This work is focused on the preparation of platinum-cobalt catalysts deposited on the titanium surface (denoted as Pt(Co)/Ti) using simple chemical methods as electrocatalyts towards the electro-oxidation of methanol and ethanol in an alkaline medium. The Pt-Co catalysts were deposited on the titanium surface by a two-step process which involves electroless cobalt deposition followed by a spontaneous Pt displacement from platinum-containing solution.

The morphology, structure and composition of the prepared catalysts were examined by Field Emission Scanning Electron Microscopy, Energy Dispersive X-ray Analysis and Inductively Coupled Plasma Optical Emission Spectroscopy. The electrochemical behavior of the prepared catalysts towards the oxidation of methanol and ethanol was investigated by means of cyclic voltammetry, chronoamperometry and chronopotentiometry.

The Pt(Co)/Ti catalysts with low Pt loading demonstrated their significantly higher electrocatalytic activity towards methanol and ethanol oxidation as compared to that of bare Pt and Co/Ti electrodes and seem to be a promising anode materials for direct methanol and ethanol fuel cells.
Application of Carbon Coated Stainless Steel for Bipolar Plate in Proton Exchange Membrane Fuel Cell
Authors: Hsieh HoYen , Wang Wen-Lin , Lan ChaoHo
Published: February 2020

Stainless steel bipolar plates for the polymer electrolyte membrane (PEM) fuel cell offer many advantages over conventional machined graphite. Austenitic stainless steel 316L is a traditional candidate for metal bipolar plates.During a long operation time, metal oxide formation leads to contact resistance, and metal dissolution can cause contamination of the membrane electrode assembly (MEA). A pure Carbon was coated on the surface of Stainless steel and provided a good anticorrosion layer. The carbon film has a low area specific resistance compared to the composite coating because it has a high surface conductivity. In addition, The ICR between the carbon-coated SS316 and the carbon paper is 225–1247 mΩ-cm2 under compaction forces between 20 and 280 N cm−2. The carbon-coated SS316L shows good corrosion resistance in the simulated PEMFC environment. After testing the single cell for 4000hr, the power density was decay less than 1%. Therefore, the carbon-coated SS316L has an excellent durability property.

Key words : fuel cell, carbon and bipolar plate
Study on Condition of Low-Cost Carbon-Based Surface Treatment for Application of Metallic Bipolar Plates in PEMFC
Authors: Kim Myong-Hwan , Goo Youngmo , Yoo Seung-Eul
Published: February 2020

Metallic bipolar plates coated with low-cost carbon-based surface treatment were developed for polymer electrolyte membrane fuel cells(PEMFC) and were evaluated by properties(corrosion, contact resistance) and performance(I-V curve). The carbon-based coating by dry surface treatment exhibited a good mechanical strength and corrosion resistance. But these could not be applied as bipolar plates because of a high electrical resistance by non-conductive structure(sp3↑, sp2↓). In this study, we developed the metallic bipolar plates with conductive structure((sp3↓, sp2↑) by change of coating temperature and thickness.

The coating thickness(A type, B type) and temperature(A-1~4, B-1~4) were used as parameters for conductive bipolar plates. The B type sample was more thicker than A type and A-4 sample was treated with heat more higher than A-1. These samples were evaluated by properties and performance of unit cell.

The surface treatment temperature of A-3 sample exhibited low contact resistance and corrosion current density. This trend showed in B type sample. Therefore, the condition of A-3 or B-3 revealed the optimum temperature in this experiment. However, the increase of coating thickness was for nothing in properties. The fuel cell assembled from metallic bipolar plates coated with carbon-based surface treatment exhibited the same performance as compared with graphite.
Invited: Study of Fundamental Aspects of Ionomer Structure in Different States
Authors: Ohira Akihiro , Kuroda Seiichi , Yamaguchi Makoto , Oshima Tatsuya , Matsuura Toyoaki , Ogu Kenichi , Rikukawa Masahiro
Published: February 2020

In PEFC system, the ionomer is used as a binder and an electrolyte membrane. The characteristics of low gas permeability and high proton conductivity are required for the electrolyte membrane, while, if the ionomer is used as a binder, conductivity should be high as well as electrolyte membrane, but in this case, high gas permeability should be better which is opposed to the case of membrane characteristic. Nafion® is used for binder and electrolyte membrane, but there still has been unclear factor about structural difference in both binder and membrane states, especially we do not know about the effect of structure and physical properties of ionomer in a catalyst layer on cell performance.

In this study, we prepared model ionomer materials and electrodes, and conducted the structural analysis in order to understand the effect on the cell performance systematically.

Perfluorinated sulfonic acid ionomer Nafion® and di-block copoly(p-phenylene) ionomer having sequentially controlled hydrophilic and hydrophobic parts were targeted as the model ionomer1 (Scheme 1). As the model electrode, we also used Pt-dispersed carbon electrodes in which several nanometers Pt particles dispersed2. We performed microscopic observation and scattering analysis in order to understand the structures in solution and thin film solid states.

Here Nafion® thin film was prepared on platinum nano-particle dispersed carbone electrode as a model for the ionomer film within a catalyst layer. We found that aggregated structure of ionomer changed with carbon surface area, the size of aggregated structure became large, and proton conductive domain also enlarged with the increase in carbon surface area. These results imply that the morphology and the property of ionomer covering catalyst support could be dominated by balance of interaction between carbon and platinum. In the case of hydrocarbon ionomer, it has been found that di-block copolymer forms higher order structure over a range of several hundred nm by means of AFM observation. Furthermore, the gas permeability of di-block copolymer film was comparable to that of Nafion®. Details will be discussed at presentation.

Acknowledgement

Ministry of Economy, Trade and Industry (METI), Japan and New Energy and Industrial technology Development Organization (NEDO) are acknowledged for granting the work.

References

1. K. Umezawa, T. Oshima, M. Yoshizawa-Fujita, Y. Takeoka, and M. Rikukawa, ACS Macro Lett.
2012, 1, 969−972.

2. T. You, O. Niwa, M. Tomita, and S. Hirono, Anal. Chem.
2003, 75, 2080-2085.