bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemical Characterisitcs of Thin Carbon Coatings for Metal Bipolar Plates - Evaluation of the Relative Porosity Using EIS
Authors: Bramfeldt Hanna , Jansson Anna , Rannou Gilles , Thierry Dominique 
Published: February 2020

The anticipation of a rapidly growing market demand for PEM fuel cell components, places the focus on the establishment of advanced, high-throughput processes to satisfy the material requests of the industry. Sandvik Materials Technology AB uses a roll-to-roll PVD process to produce carbon-coated steel for PEMFC bipolar plates that meet both technical requirements of corrosion resistance and electrical conductivity, as well as economic requirements. The main advantages of using pre-coated steel for bipolar plate production are increased productivity and decreased risks associated with parts handling. Furthermore, a consistently high material performance is achieved as the result of a very stable coating process combined with large batch sizes (several tons).
For improved corrosion resistance, low porosity coatings are generally desired. A method for electrochemical impedance spectroscopy (EIS) has been developed in which the relative porosity has been evaluated for carbon coated steel. The carbon coating is deposited on top of an intermediate metallic layer, which serves to enhance adhesion and corrosion resistance. Using this method, we have been able to verify that increasing the coating thickness and the number of coating layers resulted in a decrease in the porosity index. More interestingly, however, we have been able to show that the relative porosity index can be related to interfacial contact resistance measured for coated samples subjected to potentiostatic testing (100 h at 0.7 V vs. AgCl). The interfacial contact resistance of studied samples varied between 3-13 mΩcm2 at a pressure of 140 N/cm2.

Together these results indicate that the evaluation of relative porosity by means of EIS can be used as a relevant tool for assessing the corrosion resistance of coated metal intended for use as PEM bipolar plates.
Aluminum Bipolar Plates for PEM Fuel Cells
Authors: Swider-Lyons Karen , Natishan Paul M. , Sassin Megan B. , Moran James , Policastro Steven , Wang Conghua , Gould Benjamin D. 
Published: February 2020

Aluminum is an attractive material for fuel cell bipolar plates because it is lightweight, and relatively easy to form with features for flow channels and to weld. The challenge is that it is highly susceptive to corrosion in fuel cell operation environment. For instance if the aluminum contacts the highly cathodic carbon in the gas diffusion layers, it can be come a sacrificial anode. Al will also oxidize at the low pH of PEM fuel cells, as it is only stable between pH 6-8. Any aluminum oxide formation on the surface will increase its interfacial contact resistance and result in resistive losses in the stack. Our approach is to develop a robust coating/protection system for the aluminum, with the final coating consisting of a passivation layer embedded with Au microdots. The passivation layer prevents the aluminum corrosion while the Au maintains conductivity. The corrosion of the aluminum is monitored with electrochemical impedance spectroscopy and scanning electron microscopy. The results are compared to corrosion of titanium and stainless steel bipolar plates with a similar TiO2/Au coating.
Characterization of Low EW Ionomers in Fuel Cells
Authors: Kusoglu Ahmet , Weber Adam Z 
Published: February 2020

Perfluorosulfonic-acid (PFSA) ionomers play a key role in the polymer-electrolyte fuel-cell (PEFC), in which they are primarily used as the proton-exchange membrane (PEM) with their remarkable transport properties and chemical/mechanical stability, but they also function as the nanometer thick "thin" electrolyte film in the catalyst layers binding the catalytic sites and providing proton transport pathways. In the thin-film regime, an ionomer exhibits vast deviations in its properties which are controlled by its interfaces with the air and the catalytic particles, i.e., carbon and platinum. While bulk membrane is responsible mainly for the ohmic resistances, in the catalyst layers, transport resistance in the ionomer film resulting from its interfacial interactions has direct implication on the mass-transport limitations in the PEFC, especially at higher current densities. Thus, it is imperative to understand the origins of ionomer-related transport resistances in fuel-cell catalysts, and how they changes with ionomer's chemistry and equivalent weight (EW).
In this talk, we present our findings on the impact of EW and hygrothermal environmental stressors the structure and properties of ionomers across the lengthscales, i.e., from bulk membrane (PEM) to catalyst ionomer film in CLs. It will be shown through X-Ray scattering studies how hygrothermal ageing induces morphological changes in the catalyst ionomer films, and subsequently alters their swelling and sorption behavior as investigated by ellipsometry and quartz crystal microbalance (QCM). From the collected data, structure-swelling-uptake correlations are generated for PFSA ionomers of various EWs, both as bulk membrane and thin films. From the grazing-incidence X-ray scattering (GIXS), changes in the size and orientation of water domains in the ionomer film are determined in response to humidity, heat-treatments and hygrothermal ageing, which result in substantial changes in these morphological features. Nanostructrual anisotropy, phase-separation and sorption kinetics are all found to be related and affected by the substrates the ionomer film is interacting with. The investigation on the impact of equivalent weights (EWs) and PFSA side-chain chemistries on ionomer’s response demonstrated a key role EW plays in controlling the structure/transport relationship of the ionomer, especially in the catalyst layers. Impact of ageing and heat-treatments on ionomer’s structure and properties are similar for both bulk and thin films, but found to be more pronounced for the latter. Our results provide new insights into the environmental and operational stressors controlling ionomer's functionalities, especially as thin-films in fuel-cell catalysts.
Local Structure and Proton Transport in HT-PEFCs Measured with Neutron Scattering
Authors: Holderer Olaf , Ivanova Oxana , Khaneft Marina , Hopfenmüller Bernhard , Lüke Wiebke , Majerus Anne , Appavou Marie-Sousai , Szekely Noemi , Krutyeva Margarita , Kentzinger Emmanuel , Zorn Reiner , Lehnert Werner 
Published: February 2020

The conception, design and optimization of fuel cells in general requires a good knowledge of the underlying physical processes on all length scales. In this contribution we focus on High Temperature Polymer Electrolyte Fuel Cells (HT-PEFCs) based on a proton conducting membrane such as poly2,2’-m-(phenylene)-5,5’-bibenzimidazole (PBI) doped with phosphoric acid (PA) and show how microscopic techniques can be related to macroscopic properties of the fuel cell. A major part of our studies uses different neutron scattering techniques, a tool which is well suited for studying thick objects due to the large penetration depth. Contrast variation by using different isotopes and the sensitivity to light elements are the major advantages of neutron scattering. The self-correlation function of protons is deduced from incoherent scattering, which gives access to the relevant transport processes in fuel cells.
Small angle neutron scattering (SANS) provides insight into the fractal structure of the PA doped membrane on length scales of ~10-500 nm. We present results on the variation of the microscopic structure between different lots of the same material. Small angle X-ray scattering (SAXS) provided insight into the Pt distribution and structure of the electrode layers, a multicomponent system consisting of carbon support, PTFE and the Pt catalyst itself.
With quasielastic neutron scattering (QENS), proton diffusion can be measured on local length scales of about 0.1-10 nm (1). The length scale dependent energy transfer measured with QENS gives insight into local proton transport processes in the PBI membrane and in the adjacent electrode layers and allows to relate microscopic proton mobilities with macroscopic measurements, e.g. of the proton conductivity of the membrane (2).
Complementary techniques such as X-ray scattering, TEM or PFG-NMR round up the picture on a broad range of length scales. With this approach, the proton conducting membrane and the electrode layers of a HT-PEFC is studied and the results then linked to macroscopic properties of the membranes.

O. Holderer, O. Ivanova, B. Hopfenmüller, M. Zamponi, W. Maier, A. Majerus, W. Lehnert, M. Monkenbusch, R. Zorn, Int. J. Hydrogen Energy
39 (2014) 21657 – 21662

A. Majerus, F. Conti, C. Korte, W. Lehnert, D. Stolten, ECS Transactions
50 (2) (2012) 1155-1165

Figure 1
PEM Water Electrolysis - New Approaches Towards Catalyst Separation, Recovery, and Recycling
Authors: Carmo Marcelo , Holtz Daniel , Lüke Wiebke , Stolten Detlef 
Published: February 2020

In the following years, polymer electrolyte membrane (PEM) water electrolysis may well be reaching the gigawatt magnitude of hydrogen production, in order to attend the energy storage demand of intermittent power sources such as wind and solar[1]. At its end-of-life, each electrolysis system will have a redundant stack, expecting tough recycling and re-use requirements for this efficient but rather expensive energy storage system. Practical application of PEM electrolysis already strongly depends on the resolution of these issues.
The optimum strategy will require stack dismantling and separation of the major components. Steel, aluminum, and titanium components shall be processed using the general recycling stream, but the membrane electrode assembly (MEA) and bipolar plates will require a specialized recycling process. The most common approach is to shred the used MEA, dissolve and recover the membrane, burn off the carbon and organic additives, and recycle platinum group metals (PGMs) catalysts using solvent extraction.
Platinum and iridium can be in principle infinitely recycled. In practice, however, recycling of precious electrocatalysts used in PEM water electrolysis is often inefficient or essentially nonexistent because of limits imposed by component design, unavailable recycling technologies, low yield, and the thermodynamics of separation. In any case, the recycling of these precious metals can be promoted if beneficial actions are demonstrated.
In this study, we have developed a novel recycling approach in order to obtain high collection rates of the expensive catalyst material, improve the design for the recycling of the different components including the Nafion electrolyte, and demonstrate the deployment of a modern and efficient recycling methodology for PEM water electrolysis. Our goal was to proof the concept of a closed-loop material system. We have found that recycled catalysts and membranes can be used to fabricate new MEAs without significantly affecting the performance. There is still room for much improvement, but limitations of many kinds - not all of them technological – shall not impede in the long term the complete closure of the materials cycle.
[1] M. Carmo, D. Fritz, J. Mergel and D. Stolten, International Journal of Hydrogen Energy, 38, 4901-4934 (2013)
Investigation of Wet/Dry Cycling of Polymer Electrolyte Membrane By Full-Cell Scale Numerical Simulation with Transient Load Profiles
Authors: Takayama Tsutomu , Yoshimura Hideto , Motegi Haruki , Takayama Ryo , Kariya Natsuki , Yoneda Masakazu 
Published: February 2020

Overview

Wet/dry cycling in membrane of a PEFC is simulated under time-dependent load profiles which imitate actual driving conditions. Wet/dry cycling is an important issue to extend durability of PEFCs, since mechanical degradation is more likely to take place where gradation of water content distribution in membrane is large and wet/dry cycling is frequent. Performances of a 30cm times 10cm full cell is simulated, calculating transport of gas species and liquid water coupled with electrochemical reactions and current balances. Load profile is given by time-dependent total current conditions. Based on simulated results, dependence of wet/dry cycling on channel configurations and operating conditions are discussed.

Numerical Modeling and Results

Simulation is performed by our own simulation software for PEFCs, which is capable of simulating full-stack fuel cell system for fuel cell vehicles (up to 400 cells) under transient operating conditions. An important feature of this software is that macroscopic models are applied for microscopic phenomena in the MEA such as electrochemical reactions and proton/water transport. Heat transfer and fluid of liquid-gas two phase fluid with phase changing are also taken into account. These models are coupled with multi-dimensional heat and mass transport equations, including effective parameters for gas diffusivity and permeability in the GDL and equivalent hydraulic diameter in the flow channel. This software can also simulate cathodic degradation by carbon corrosion reactions.
Performance of cell is simulated under assumed load profiles, modeled by transient output current boundary conditions. Typical time-scale and range of supposed current conditions is 1[sec] and0.1-1.0[A/cm2], respectively, which imitates actual driving conditions on urban streets. Stoichiometric ratio and humidity of reactant gas are also changed simultaneously with the load profile.
Simulated results show transient behavior of wet/dry cycling. For example, soon after the output current is increased, large difference in reaction current density can be created, depending on the distribution of reactant gas flow. This results in large gradient of water content in membrane, where mechanical degradation is expected depending on flow distributions and operating conditions. In the same way, water content distribution between stacked cells can be simulated. In addition, effect of different time-scales of load profiles and response of water distribution can be discussed. These results can be useful information to consider the possibility of mechanical degradation.
Unconventional Water Splitting Platforms
Authors: Hashemi Mohammad H. , Modestino Miguel A. , Psaltis Demetri 
Published: February 2020

Renewable hydrogen has the potential to reshape our fossil fuel based energy infrastructure as it would allow the integration of a larger share of clean energy sources. Electrolysis of water is one of the most promising pathways toward clean hydrogen production. Although high efficiency electrolyzers are commercially available, their high cost has been a major obstacle for their large scale deployment.
Design simplifications of these devices are necessary in order for clean hydrogen fuel to be deployed. Here, we demonstrate two proof-of-concept devices for water splitting which differ significantly from their conventional counterparts. The first one is a membrane-less electrolyzer which by balancing fluid mechanic forces manages to keep the produced oxygen and hydrogen gas streams separated as shown in Figure 1. This allows the system to operate without commonly required ion conductive membranes, and in this way could reduce the electrolyzer’s cost and enhance its efficiency.
The second device absorbs water from humid ambient air streams in a Nafion thin-film as demonstrated in Figure 2. The absorbed water molecules split into hydrogen and oxygen streams which are later collected at independent collection ports. The design simplicity of this system makes it appropriate for solar powered hydrogen production since integration of photoactive components can be easily implemented.
Currently, integration of photoelectrodes into these devices is underway. Large scale implementation of the membrane-less device is another ongoing effort.

References

[1] Hashemi, S. Mohammad H., Miguel A. Modestino, and Demetri Psaltis. "A membrane-less electrolyzer for hydrogen production across the pH scale." Energy & Environmental Science (2015).
[2] Modestino, Miguel Antonio, et al. "Vapor-fed microfluidic hydrogen generator." Lab on a Chip (2015).

Figure 1
Advancements in Anion Exchange Membrane Cations
Authors: Sturgeon Matthew R , Long Hai , Park A M , Pivovar Bryan S 
Published: February 2020

Anion-exchange membrane fuel cells (AME-FCs) are of increasingly popular interest as they enable the use of non-Pt fuel cell catalysts, the primary cost limitation of proton exchange membrane fuel cells. Benzyltrimethyl ammonium (BTMA) is the standard cation that has historically been utilized as the hydroxide conductor in AEMs. Herein we approach AEMs from two directions. First and foremost we study the stability of several different cations in a hydroxide solution at elevated temperatures. We specifically targeted BTMA and methoxy and nitro substituted BTMA. We've also studied the effects of adding an akyl spacer units between the ammonium cation and the phenyl group. In the second approach we use computational studies to predict stable ammonium cations, which are then synthesized and tested for stability. Our unique method to study cation stability in caustic conditions at elevated temperatures utilizes Teflon Parr reactors suitable for use under various temperatures and cation concentrations. NMR analysis was used to determine remaining cation concentrations at specific time points with GCMS analysis verifying product distribution. We then compare the experimental results with calculated modeling stabilities. Our studies show that the electron donating methoxy groups slightly increase stability (compared to that of BTMA), while the electron withdrawing nitro groups greatly decrease stability in base. These results give insight into possible linking strategies to be employed when tethering a BTMA like ammonium cation to a polymeric backbone; thus synthesizing an anion exchange membrane.
Utilizing various strategies, several different cations were tethered to perfluoro polymers to produce membranes. These membranes are then ion exchanged to obtain hydroxide conductivities. In addition to conductivities, membrane stability lifetimes were also measured using a similar technique to cation stabilities.

Figure 1
Fabrication and Performance of Membrane Electrode Assembly Using a Hydrophilic Pt/[TaOPO4/VC] Electrocatalyst
Authors: Garsany Yannick , Sassin Megan B. , Gould Benjamin D. , Swider-Lyons Karen 
Published: February 2020

Oxide- and phosphate-supported catalysts promote the oxygen reduction reaction (ORR) in acid and alkaline electrolyte. We previously reported a high mass- and area-specific ORR activity for an electrocatalyst with 18 wt% loading of 2.4 nm Pt nanoparticles supported on a 3 wt% tantalum oxyphosphate-treated VC (Pt/[TaOPO4/VC]). The electrocatalyst was heat treated at 660◦C in a reducing atmosphere and characterized using thin-film rotating disc electrode (RDE) in an acidic electrolyte and alkaline electrolyte. However preliminary experiments show that the performance of the Pt-TaOPO4 catalysts as measured by RDE is not representative of its performance in a proton exchange membrane fuel cell (PEMFC), possibly because of the hydrophilicity of the oxyphosphate. We reconcile the difference between RDE and PEMFC performance by developing a range of catalyst layers (CLs) fabricated by decal method and by direct deposition of the Pt/[TaOPO4/VC] electrocatalyst onto the Nafion® membranes using an in-house built ultrasonic spray coating system. Nitrogen adsorption, mercury porosimetry, and scanning electron microscopy (SEM) are used to investigate the effects of ionomer/carbon ratio (I/C) on the surface area, pore structure and morphology of the CLs; cyclic voltammetry and polarization curves are used to determine the electrochemically active area (ECSA) and PEMFC performance.
The Pursuit of Novel Phosphor Hosts for the Next Generation of Solid State Lighting
Authors: Brgoch Jakoah 
Published: February 2020

The development of novel rare-earth phosphor hosts necessary for the next generation of solid-state lighting requires a unique approach to materials discovery. Researchers often rely on chemical substitution of known compounds or searching phase-space to identify new materials; however, the result is often the formation of known structure-types and incremental advances in phosphor technology. Recently, our work showed a hybrid approach of computation and experiment is an ideal alternative for novel phosphor design. By calculating the Debye temperature and band-gap of potential host compounds using Density Functional Theory, high-efficiency materials can be screened a priori ensuring the only best materials are experimentally explored. Following this methodology, our research has developed a number of materials ranging from borates to nitrides with high efficiency and thermal stability at elevated temperatures. Moreover, the complementary use of computation and synthesis provides the fundamental understanding of the composition, structure, and property relationship necessary for the continued advanced optical materials.
Synthesis of Phosphor Materials By New Low-Temperature Solid-State Reaction Method Showing Abnormally High Diffusion
Authors: Toda Kenji , Hasegawa Takuya , Kaneko Tatsuro , Toda Ayano , Kim Sun Woog , Uematsu Kazuyoshi , Ishigaki Tadashi , Koide Junko , Toda Masako , Kudo Yoshiaki , Sato Mineo 
Published: February 2020

A solid-state reaction method has been usually used as a basis synthesis processing technique to obtain the ceramic materials, including phosphor materials, because of its very simple and easy. However, ceramic materials are generally synthesized at high temperature when the solid state reaction method used as synthesis method. Because ionic-diffusion in ionic crystal is very slow at room temperature, high temperature is essential for solid state reaction. The high temperature synthesis leads to increase in the processing cost and irregular particle morphology of the obtained powder. On the other hand, we recently proposed the novel low-temperature synthesis methods, such as water assisted room temperature solid state reaction (WASSR) method and solid hydratethermal reaction (SHR) method, to synthesize the ceramic materials in a single phase form at low temperature,1-3 and we successfully synthesized the functional ceramic materials including phosphors. Furthermore, we demonstrated that the reaction mechanism of novel low temperature synthesis methods is different from the conventional solid state reaction and solution reaction. In this study, we present the practicability of our original novel solid state reaction methods on an industrial application in the ceramic oxide materials synthesis processing.
References

K. Toda, M. Sato, K. Uematsu, and T. Ishigaki, Japanese Unexamined Patent Application Publication No. 2011-16670 (2009).

S.W. Kim, T. Kaneko, K. Toda, K. Uematsu, M. Sato, J. Koide, M. Toda, and Y. Kudo, IDW'2014, PH1-3 (2014).

T. Kaneko, S.W. Kim, A. Toda, K. Uematsu, T. Ishigaki, K. Toda, M. Sato, J. Koide, M. Toda, Y. Kudo, T. Masaki, and D.H. Yoon, Sci. Adv. Mater., (2015) in press. doi:10.1166/sam.2015.2364.