bluuebunny/crossref_metadata_2025 huggingface dataset:
Grain Boundary Engineering to Improve Ionic Conduction in Thin Films for Micro-SOFCs
Authors: Tarancón Albert , Morata Alex , Pla Dolors , Saranya Aruppukottai M. , Chiabrera Francesco , Garbayo Inigo , Cavallaro Andrea , Canales-Vázquez Jesús , Kilner John A. , Burriel Mónica
Published: February 2020

New emerging disciplines are specifically devoted to study trivial and non-trivial effects resulting from working in the nanoscale, however, the implementation of these nanostructures in real devices is still a major challenge. Thin film deposition and silicon microtechnology is probably the most promising and straightforward combination for the reliable integration of nanomaterials in real devices. In particular, the implementation of pure ionic and mixed ionic/electronic conductors (MIECs) in thin film form allows the miniaturization of multiple solid state devices. A simple combination of three oxides properly integrated in silicon enables anode/electrolyte/cathode structures for the fabrication of solid oxide fuel cells (SOFCs). These micro-SOFCs represent a new family of micro-power generators that will drive a revolution in portable power generation [1].

In this lecture, we will talk about the implementation of novel nanoionics concepts in micro-SOFCs by using micro and nanofabrication technologies. We will put special attention on the contribution of grain boundaries to the mass transport properties in interface-dominated materials such as thin films. Grain boundary engineering will be presented as a powerful tool for reducing the resistance associated to electrolytes [2] and even control the intrinsic transport nature and performance of MIEC materials [3].  

References:

[1] I. Garbayo, D. Pla, A. Morata, L. Fonseca, N. Sabaté and A. Tarancón, Full ceramic micro solid oxide fuel cells: towards more reliable MEMS power generators operating at high temperatures, Energy Environ. Sci. 7 (2014) 3617

[2] A. Chroneos, B. Yildiz, A. Tarancón, D. Parfitt, J. A. Kilner, Oxygen diffusion in solid oxide fuel cell cathode and electrolyte materials: mechanistic insights from atomistic simulations,Energy Environ. Sci. 4(2011) 2774

[3] A. M. Saranya, D. Pla, A. Morata, A. Cavallaro, J. Canales-Vázquez, J. A. Kilner, M. Burriel and A. Tarancón, Engineering mixed ionic electronic conduction in La0.8Sr0.2MnO3+

δ

nanostructures through fast grain boundary oxygen diffusivity, Adv. Energy. Mat (2015) 1500377
Multi-Layered Thin Film Y:BaZrO3 Electrolytes for Anode-Supported Protonic Ceramic Fuel Cells
Authors: Bae Kiho , Jang Dong Young , Noh Ho-Sung , Kim Hyun Joong , Hong Jongsup , Kim Byung-Kook , Yoon Kyung Joong , Son Ji-Won , Shim Joon Hyung
Published: February 2020

Acceptor-doped barium zirconate electrolytes, represented as yttrium-doped barium zirconate (Y:BaZrO3 or BZY), are expected to allow ceramic fuel cells to be operated at intermediate temperatures in the range below 600 °C. This is because BZY conducts protons and exhibits a relatively high ionic conductivity with relatively small activation energy, especially compared to ceramics that conduct oxide ions, including yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC). The bulk conductivity of BZY is greater than that of YSZ by about one order at 600 °C and by two orders at 400 °C and, unlike cerate-based materials, BZY was found to exhibit good phase stability (1). Thus, there have been numerous efforts to develop BZY-based protonic ceramic fuel cells (BZY-PCFCs). Although several studies have reported BZY-PCFCs to perform well, with outputs of 140 mW/cm2 and 180 mW/cm2 in the intermediate temperature regime at 400 °C (2) and 450 °C (3), respectively, both of these were achieved in the form of freestanding nanoscale membranes. For practical production and use, however, fabrication of the BZY electrolyte in anode-supported stacks would be more desirable. Yet, the performance of anode-supported BZY-PCFCs is not yet as good as that of solid-oxide fuel cells. To our knowledge, 170 W/cm2 is the greatest power output achieved with BZY-based fuel cells at 600 °C (4). An attempt to adopt a thin BZY electrolyte (4μm thickness) in anode-supported PCFCs has produced a power output of merely 110 W/cm2 at 600 °C (5), attributed to the prevalence of a relatively large ohmic resistance, which implies the presence of structural defects such as poor grain adhesion (5). After performing a series of experiments, we realized that the adoption of multiple anode support layers with multi-step sintering promotes the structural and mechanical stability of thin film BZY electrolytes. As a result, the power output has exceeded 700 mW/cm2 at 600 °C with an open circuit voltage over 1 V. At this presentation, we will share our recent experimental results and discuss the cell performance in relation with structural characteristics and composition.

1. K. D. Kreuer, Annu. Rev. Mater. Res., 33, 333 (2003).

2. J. H. Shim, J. S. Park, J. An, S. Kang, T. M. Gür, and F. B. Prinz, Chem. Mater., 21(14), 3290 (2009).

3. Y. B. Kim, T. M. Gür, S. Kang, H-J. Jung, R. Sinclair, and F. B. Prinz, Electrochem. Commun., 13(5), 403 (2011).

4. L. Bi , E. Fabbri , Z. Sun, and E. Traversa, Energy Environ. Sci., 4, 409 (2011).

5. D. Pergolesi, E. Fabbri, and E. Traversa, Electrochem
.
Commun., 12, 977 (2010).
Effect of Catalyst Layer and Fuel Utilization on the Durability of Direct Methane SOFC
Authors: Georges Samuel , Nóbrega Shayenne D. , Cheah Seng Kian , Steil M. C. , Bultel Yann , Rieu Mathilde , Viricelle Jean-Paul , Gelin Patrick
Published: February 2020

Among energy conversion systems, high temperature Fuel Cells are considered of great interest for delocalized, renewable and clean electricity and heat power production. The high operating temperature (500°C - 800°C) is likely to allow the use of various types of hydrocarbons instead of hydrogen as the fuel with high efficiency and flexibility. Theoretically, the fuel can be catalytically converted into hydrogen directly at the anodic side. Practically, the most important drawback is the formation of carbon deposits on the anode, poisoning the electrocatalytic activity of the electrode. Hence, one of the main current challenges remains the increase of the life-time of these systems (especially avoiding carbon deposition and anode pollution), and long term reliable operation with fuel flexibility. Such performances have not been achieved yet.

We recently demonstrated the fundamental importance of the fuel utilization on the carbon deposition limits. The quantity of steam released by the anode is directly proportional to the current density, and then to the fuel utilization UF. Below a given value of UF, the system does not produce enough steam to ensure the internal catalytic conversion of the hydrocarbon flux, resulting in irreversible degradation of the cell by carbon methane cracking. This observation and the deep understanding of the anode operation in methane allowed us to achieve long term operation with pure hydrocarbons without carbon deposition at the surface of conventional Ni-YSZ anodes. The thermodynamical limits of carbon deposition as a function of fuel utilization were also investigated.

Current developments and technological simplifications based on new principles of operation and original architectures designed in this finality will be presented. In particular the presentation will emphasize on the Gradual Internal Reforming and Electro-catalytic separation principles applied to the design of original anodic systems, and on the demonstration of the reliability of the systems in different pure hydrocarbons or carbon-based fuels (no H2O, CO2, O2 or carrier gas addition) [1-4]. The effect of the fuel utilization on the limits of carbon deposition will be discussed and the long term durability in pure dry methane will be demonstrated. The perspectives of direct operation of SOFC on waste fuels in order to decrease the amount of CO2 rejects in delocalized energy production systems will be discussed.

1. J-M. Klein et al., Journal of Power Sources 193, (2009) 331

2. S. D. Nobrega et al., Journal of Power Sources (2012) 156-159

4. S. Georges et al., ECS Transactions 57(1) (2013) 3023-3030

4. S.D. Nobrega et al., Journal of the Electrochemical Society, 161(3) (2014) F354-F359

5. J. Puig et al., Fuel Cells 14 (6) (2014) 1014-1021

6. K. Girona et al., Canadian Journal of Chemical Engineering 93 (2) (2015) 285-296
Development of Ceria-Based Microtubular Solid Oxide Fuel Cells
Authors: Sumi Hirofumi , Yamaguchi Toshiaki , Shimada Hiroyuki , Hamamoto Koichi , Suzuki Toshio
Published: February 2020

Gadolinia-doped ceria (GDC) has higher oxide-ion conductivity than a conventional yttria-stabilized zirconica (YSZ).  GDC is one of the most desirable materials as an electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs) operated below 600 °C.  A nickel-GDC cermet anode has high catalytic and electrochemical activities against fuel oxidation in SOFCs.  For example, direct butane utilization was successfully demonstrated for Ni-GDC anode-supported microtubular SOFCs.  Furthermore, an La0.6Sr0.4Co0.2Fe0.8O3(LSCF)-GDC composite cathode shows high performance at intermediate temperature.  We applied GDC materials to electrolyte, anode and cathode for microtubular SOFCs.
Three-Dimensional Microstructure of PEFC Electrodes: Activity and Durability
Authors: Workman Michael J , Artyushkova Kateryna , Halevi Barr , Serov Alexey , Atanassov Plamen
Published: February 2020

Large-scale deployment of PEMFCs based on catalysts synthesized using non-precious metals (non-PGM) is facing a major challenge: the need for increased lifetime. One way to improve durability is to maintain the chemical makeup and integrity of the pore structure, thereby increasing the effectiveness of the catalyst layer over the lifetime of the fuel cell. The durability of non-PGM catalyst layers is directly related to the interaction of catalyst with ionomer and ionomer dispersion. Composition of the catalyst from both chemical speciation and morphology (porosity, roughness, texture), will determine the interaction between the catalyst and ionomer. Additionally, the pore structure is critical to the transport of oxygen to active sites and removal of water. The change in pore-structure induced by the chemical changes introduced during fuel cell operation has to be understood in order to design non-PGM electrocatalysts with longest possible lifetime. In this work, we will employ focused ion beam/scanning electron microscopy (FIB-SEM) sectioning to obtain a visual 3D representation of catalyst layer morphology. These 3D reconstructions will be used to generate detailed estimates of the evolution of structural parameters such as: specific surface area, total porosity, connectivity of pores, and others as a result of degradation studies. These analyses will be supported by the chemical post-mortem analysis obtained with high-resolution X-ray Photoelectron Spectroscopy. Structural metrics obtained from different components of MEA and chemical metrics obtained from XPS will be linked directly to the properties of the catalyst itself facilitating the design of highly durable fuel cells.

Figure 1
Development of Platinum-Niobium as a CO Tolerant Catalyst for PEFC Operating with CO Contaminated Hydrogen
Authors: Rocha Thairo A. , Colmati Flavio , Ciapina Eduardo Gonçalves , Linares José J , Gonzalez Ernesto Rafael
Published: February 2020

Traditional Polymer Electrolyte Fuel Cells (PEFC) are fed with hydrogen in the anode and oxygen in the cathode. This type of fuel cell is especially attractive because of the high efficiency at low temperature. However, the use of reformate hydrogen compromise cell performance due to the presence of traces of carbon monoxide (CO). This contaminant is adsorbed on the surface of Pt, blocking the sites necessary for the hydrogen oxidation reaction. In this context, to improve the CO tolerance of fuel cell anodes, several bimetallic Pt-based catalysts have been proposed. [1] Some studies reported in the literature have suggested the use of niobium (Nb) as the second element in bimetallic catalysts. [2] Thus, this study aims at analyzing the effect of the addition of Nb to Pt in order to develop a CO tolerant catalyst. Pt3Nb/C catalyst was prepared using a modified impregnation method, [1] physically and morphologically characterized and tested electrochemically in a single fuel cell operating on the traditional Nafion® membranes at 85 oC.

Figure 1 shows the ionic currents signal m/z = 44 obtained by on-line differential electrochemical mass spectrometry (DEMS) experiments, corresponding to CO2 formation. Lower CO oxidation overpotential is observed for the material with Nb, which is a consequence of the facilitated CO oxidation on Pt3Nb/C catalyst. Figures 2 and 3 show the results corresponding to performance of a single fuel cell operating on H2 or H2 + 100 ppm CO. As it can be seen, the Pt3Nb/C catalyst outperforms Pt/C 20%. The high CO tolerance of this material is usually explained by two distinct mechanisms: the bifunctional and electronic mechanisms. In the first, the Nb act as a source of oxygenated species, required for the electro-oxidation of CO to CO2 at overpotentials lower than that for pure Pt. The electronic effect can be discussed in terms of the changes of the position of the Pt 5d-band center induced by the presence of the second metal that modifies the CO adsorption energy, reducing the CO coverage on Pt, and leaving more free Pt sites available for H2 electro-oxidation. These effects will be discussed using on-line DEMS measurements and in situ X-ray absorption spectroscopy (XAS) analyses.

ACKNOWLEDGEMENTS

Authors thank FAPESP, CNPq and CAPES, Brazil, for the financial support.

REFERENCES

[1] Pereira, L. G. S., Paganin, V. A., Ticianelli, E. A. Electrochimica Acta, 54, 192 (2009).  

[2] Rocha, T. A., Ibanhi, F., Colmati, F., Linares, J. J., Paganin, V. A., Gonzalez, E. R. Journal of Applied Electrochemistry, 43, 817 (2013).

Figure 1
Development of Alkaline Membranes and Alkaline Membrane Fuel Cells
Authors: Zhuang Lin
Published: February 2020

In this invited keynote lecture, I will talk about the recent research progress on alkaline membranes and alkaline membrane fuel cells. The following topics will include:

High performance alkaline membranes and ionomers

Hydrogen oxidation reaction (HOR) catalysts in alkaline media

Nonprecious metal catalysts for oxygen oxidation reaction (ORR) in akaline media

Performance and challenge of alkaline membrane fuel cells.

References

Wang, Y., Wang, G., Li, G., Huang, B., Pan, J., Liu, Q., Han, J., Xiao, L., Lu, J. & Zhuang, L., Pt-Ru Catalyzed Hydrogen Oxidation in Alkaline Media: Oxophilic Effect or Electronic Effect? Energy Environ. Sci.
8, 177-181 (2015).

Pan, J., Chen, C.,  Li, Y., Wang, L., Tan, L., Li, G., Tang, X., Xiao, L., Lu, J. & Zhuang, L. Constructing Ionic Highway in Alkaline Polymer Electrolytes. Energy Environ. Sci.
7, 354-360 (2014).

Pan, J.,  Li, Y., Han, J., Li, G., Tan, L., Chen, C., Lu, J. & Zhuang, L. A Strategy for Disentangling the Conductivity-Stability Dilemma in Alkaline Polymer Electrolytes. Energy Environ. Sci.
6, 2912-2915 (2013).

Pan, J., Chen, C., Zhuang, L. & Lu, J. Designing advanced alkaline polymer electrolytes for fuel cell applications. Acc. Chem. Res.
45, 473-481 (2012).
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
Novel Approach to Measure Key Structural Parameters of PEM Fuel Cell Catalyst and Gas Diffusion Layer Based on Archimedes Principle
Authors: Zahiri Beniamin , McCague Claire , Bahrami Majid , Stumper Jürgen , Mérida Walter
Published: February 2020

Commercialization of fuel cells and demand for large scale manufacturing of their components necessitates the design of novel characterization methods which produce consistent results in a timely and cost efficient manner. In this work, we report a simple approach to measure the porosity, pore volume and thickness of catalyst and gas diffusion layers based on the principle of buoyancy in different fluids. Moreover, the method allows for obtaining the ionomer content of the catalyst layer. By applying this method on a porous PTFE substrate with known pore surface area and varying ionomer content, we are able to measure the density of the ionomer film vs. thickness at high (nm) resolution. Water sorption measurements on these model samples yield the maximum water content as a function of ionomer thickness. Water sorption measurements made on individual components of the catalyst layer (Pt/C and bulk ionomer) were also compared against those made on a catalyst layer. We observed a discrepancy between water uptake of individual constituents and catalyst layer. We utilized such difference in measured and expected water uptake to estimate the thickness of ionomer in the catalyst layer. This is the first attempt to estimate the thickness of ionomer in catalyst layer using a bulk scale ex-situ method. Overall, we show that this method is a lower cost and faster technique for measuring key characteristics of porous layers when compared with alternative methods such as electron microscopy and spectroscopy techniques. Furthermore, it can be easily adopted by industry and large manufacturing divisions.
Determining the Electrochemically Active Area of IrOx Powder Catalysts in an Operating Proton Exchange Membrane Electrolyzer
Authors: Zhao Shuai , Yu Haoran , Maric Radenka , Danilovic Nemanja , Capuano Chris , Ayers Katherine E , Mustain William E
Published: February 2020

Iridium oxide is one of the most common anode catalysts in commercial PEM electrolyzers because of its strong mix of high activity and stability under oxygen evolution reaction (OER) conditions. Unfortunately, benchmarking iridium oxide OER catalysts has proven difficult since it does not have the ability to underpotential adsorb protons like platinum and other transition metal eletrocatalysts, making it difficult to estimate the electrochemically active surface area (ECSA), as well as OER specific and mass activity. In this work, we determined an ECSA-CV pseudocapacitive charge correlation for IrOx (cm2/C) that was used to determine the in-situ electrochemically active surface area of iridium oxide in an operating PEM electrolyzer. The ECSA-charge correlation will be reported along with the in-situ catalyst utilization and both the specific and mass activity of IrOx for the OER.
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.
Luminescent Materials Informatics Based on Confirmatory Factor Analysis
Authors: Sohn Kee-Sun , Singh Satendra , Park Woon Bae , Kim Minseuk
Published: February 2020

The theoretical understanding of phosphor luminescence is far from complete. To accomplish a full understanding of phosphor luminescence, the data mining of existing experimental data should receive equal consideration along with theoretical approaches. We mined the crystallographic and luminescence data of 75 reported Eu2+-doped phosphors with a single Wyckoff site for Eu2+ activator accommodation, and 32 descriptors were extracted. A confirmatory factor analysis (CFA) based on a structural equation model (SEM) was employed since it has been helpful in understanding complex problems in social sciences and in bioinformatics. This first attempt at applying CFA to the data mining of engineering materials provided a better understanding of the structural and luminescent-property relationships for LED phosphors than what we have learnt so far from the conventional theoretical approaches.
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.
Engineering of Rare-Earth-Metal Oxysulfate (RE2O2SO4) Hollow Nanospheres for Upconversion
Authors: Chen Gen , Yan Litao , Luo Hongmei
Published: February 2020

Bulk glass and crystalline materials are usually used for upconversion, but bulk materials are often not suitable for certain applications such as biological imaging or biolabelling. Upconversion materials on nanometer scales are desirable. However, synthesis of small nanocrystals that exhibit high monodispersibility and excellent upconversion properties remains a challenge.

In this work, nanoscale monodisperse rare-earth-metal-doped oxysulfate RE2O2SO4 (RE = Y, Gd) hollow spheres were prepared for upconversion via a biomolecule-assisted hydrothermal method followed by calcination. The size and crystallinity of nanospheres, as well as the upconversion properties could be tuned by changing the experimental conditions such as surfactants, hydrothermal/annealing temperature, and chemical compositions. Upconversion properties revealed that the energy transfer between the sensitizer and the activator was strongly depended on the concentration of activator, the ratio of sensitizer to activator, chemical compositions and crystallinity of the hollow spheres.
Improvement of Luminescence Properties and Particle Growth of AlN Phosphors By Si-Doping
Authors: Cho Yujin , Dierre Benjamin , Fukata Naoki , Hirosaki Naoto , Takahashi Kohsei , Takeda Takashi , Sekiguchi Takashi
Published: February 2020

Aluminum Nitride (AlN) has been regarded as a promising material for ceramic phosphors. Recently, we have developed a high efficiency blue AlN phosphor by co-doping with Si and Eu [1-2]. It has been proven that particle have grown rapidly with the highest luminescent intensity on the proper Si doping. Now, it is important to understand the role of Si on AlN particle growth and luminescence enhancement.

For this purpose, AlN powders doped with Si from 0 to 4 at. % were prepared using gas-pressure sintering (GPS) furnace at 1950°C in N2 atmosphere. Firstly, particle size, phases and luminescence spectra of Si-doped AlN powder were investigated using SEM, XRD and CL. Secondly, the defect were evaluated by EPR to identify the defects transitions. Finally, the particle growth mechanism was clarified by cross-sectional CL-EDS.

From 0.4 to 2.0 % Si, particle growth of AlN powders as well as ultraviolet emissions at 290 and 350 nm are enhanced. The 350 nm emission may be attributed to native AlN defects such as vacancy-oxygen complexes. The shoulder at 290 nm and 450 nm can be ascribed to the different states of Si related defects in AlN by EPR analysis. Cross sectional CL images show that the 1.6 % Si-doped AlN yields 280 nm emission at the surfaces of AlN particles (Fig. 1). Many particles are connected to each other with these bright surfaces. It suggests that the Si-rich surface may act as the binder of AlN particles and enhance the Ostwald growth.

References:

[1] T. Takeda et al., J. Mater. Chem., 20, 9948 (2010).

[2] B. Dierre et al., ECS J. Solid State Sci. Technol., 2, R126 (2013).

Figure:

Cross sectional SE (a), CL images taken at 280 nm (b), 350 nm (c) for 1.6% Si-doped AlN powders and schematics explanning the growth mechanism (d))

Figure 1
Inverse Nephelauxetic Effect in the Pressure Dependence of R-Line Energy of Ruby
Authors: Ogasawara Kazuyoshi , Novita Mega
Published: February 2020

Recently Mn4+-doped materials are drawing attention as candidates for novel red phosphors for white LED. Therefore, understanding the factors which determine the multiplet energies of d3 ions such as Mn4+ and Cr3+ in crystals is quite important. Experimentally the R-line (2E) energy of ruby (Cr3+:α-Al2O3) shows a redshift under pressure. However, this seems to be inconsistent with the interpretation based on the ordinary “Nephelauxetic effect.”  When the applied pressure increases, the molecular orbitals mainly consisting of Cr 3d should contract. Therefore, the Coulomb repulsion among d electrons increases and the energy of 2E, which belongs to (t2g)3configuration, should increase.

In order to clarify the origin of this discrepancy, we have performed first-principles calculations of multiplet energies of ruby under various pressures. The structural optimization around the impurity Cr3+ ion in α-Al2O3 under pressure was performed using the CASTEP code. The model clusters consisting of 63 atoms were constructed based on the optimized structure and multiplet calculations were performed using the DVME code. The underestimation of electron correlation effects were corrected by the configuration dependent correction (CDC) and the correlation correction (CC). In order to clarify the factors which determine the behavior of 2E energy, the effect of covalency and the effect of correlation correction were investigated quantitatively based on the Coulomb integrals.

The results show that the pressure dependence of 2E energy was well reproduced by the first-principles calculations. The detailed analysis indicated that the Coulomb integral of t2g orbital increases for higher pressure as expected from the contraction of the molecular orbitals. However, due to the strong electron correlation effect, the effective Coulomb integral of t2g orbital significantly decreases, resulting in the decrease of 2E energy. This behavior is opposite to the prediction from the ordinary Nephelauxetic effect and can be called an “Inverse Nephelauxetic effect.”