bluuebunny/crossref_metadata_2025 huggingface dataset:
Liquid-Water Distribution in Compressed Gas-Diffusion Layers Using X-Ray Computed Tomography
Authors: Zenyuk Iryna V , Parkinson Dilworth Y. , Weber Adam Z
Published: February 2020

Effective liquid-water management is essential for commercializing polymer-electrolyte fuel cells (PEFCs). At lower operating temperatures, there is a need to remove liquid water from the cathode electrode to ensure optimal reactant transport1. To achieve maximum water permeation, it is necessary to optimize the gas-diffusion layers (GDLs). Currently, there is a lack of understanding of water transport, especially under in-situ conditions wherein the GDLs are selectively compressed under lands to provide good electrical conductivity but remain uncompressed under the gas flow channels. In this study, we use synchrotron X-ray micro computed tomography (CT) to study the water distribution in commercially available GDL materials under various levels of compression. We correlate the GDL’s morphological properties such as local spatially-resolved porosity and void-size distribution to local liquid-water distribution and water-transport capability.

Water imbibition through the GDL driven by a static water column was imaged in a sample holder with a grooved stomp. Controlled levels of GDL compression were achieved by tuning an ultra-fine pitch threaded bolt on top of the stomp. Liquid-water profiles were resolved as local averages in in-plane and through-plane directions. Figure 1 shows local liquid-water distributions for three GDLs under different levels of compression as local averages through the GDL depth. Narrowing of the liquid front was observed with increasing compression (decreasing thickness), where most of the liquid is transported under the channel. It appears that at lower compressions the advance of the liquid front is uniform; this is due to uniform porosity and due to availability of void space at the GDL|injection plate interface that allows liquid-water redistribution. At high compressions, porosity and liquid saturation are directly correlated, something that was not observed for the uncompressed sample. This finding is relevant for the design of GDL architectures with modulated porosity, where liquid-water removal can be directed through controlled porosity levels.

Figure 1 Average YZ liquid saturation as a function of X position for three compressions at capillary pressure of 1.4 kPa Acknowledgement

This work was funded by Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231. This work made use of facilities at the Advanced Light Source (ALS), supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy.

References

A. Steinbach, “High Performance, Durable, Low Cost Membrane Electrode Assemblies for Transportation Applications”, DOE
Annual Merit Review (2014).

Figure 1
Insights into the Oxygen Reduction Reaction Activity of Pt/C and PtCu/C Catalysts
Authors: Coleman Eric J , Co Anne C.
Published: February 2020

A mechanistic electrochemical study of the oxygen reduction reaction (ORR) on a carbon-supported PtCu core-shell catalyst is presented.  The catalyst was prepared by galvanic displacement of nanoporous copper with Pt.  The electrochemistry of the catalyst was explored at pH 1 and pH 13.  Hydrogen peroxide reduction and rotating ring-disk electrode (RRDE) studies showed that the PtCu/C catalyst facilitates a 4e- direct or series reduction to water in alkaline electrolyte.  Tafel data suggests that the ORR rate limiting step for PtCu/C does not change when the catalyst is subject to pH extremes.  The ORR activity of the PtCu/C catalyst was found to be 2 to 3 times higher than the ORR activity of commercially available Pt/C (Johnson Matthey).  Adsorption of OH- was quantified for PtCu/C and Pt/C, and PtCu/C was observed to have a reduced affinity towards OHads in both acid and alkaline electrolyte, which was found to promote the rate of the ORR relative to Pt/C.  Based on this study, we propose that:  1) Pt-based catalyst has a unique rate of change of OHads coverage which is correlated to their ORR activity and 2) All Pt-based catalysts have the same rate of change of OHads coverage during irreversible oxide formation.

Figure 1
Gas Permeation Study in Thin and Ultra-Thin Ionomer Films
Authors: Tesfaye Meron , McCloskey Bryan D , Weber Adam Z
Published: February 2020

Commercially available perfluorinated sulfonic-acid (PFSA) ionomers like Nafion and 3M-ionomer are widely used both as electrolyte membranes and as conductive binders in electrode structures in polymer-electrolyte fuel cells (PEFCs). However, these ionomers are also major contributors to unexplained large mass-transfer overpotentials at high current densities in PEFCs[1]. Bulk ionomer films (> 1 µm thickness) in electrolyte membranes provide charge separation, ion transport, and prevent reactant/product gas crossover. For increased performance in PEFCs, bulk ionomers of high conductivity, high selectivity, and low gas permeability are desired. In electrode structures, thin (< 1 µm) and ultra-thin (< 0.025 µm) films serve as ionic charge carriers to catalytic sites. Here, low resistance to gas transport for increased supply of reactants to catalytic sites is required. These conflicting properties required for two separate functions of ionomers in bulk and thin film make optimizing mass-transport very difficult. Complicating ionomer and transport optimization even more, conditions such as temperature, humidity, casting method, annealing, and confinement result in thin-film properties that deviate from those of bulk. Therefore, thorough understanding of mass transport resistances in both bulk and thin film ionomers is key in increasing efficiency in PEFCs.

Significant amount of work has been done to study gas transport and permeation in bulk ionomer films [2,3]. However, much remains to be explored in thin and ultra-thin ionomer films. In this talk, we present data for gas permeation in thin and ultra-thin PFSA films. Thin ionomer films are supported on well studied, highly permeable rubbery poly(dimethylsiloxane) (PDMS). Dry O2, N2, H2 and CO2 permeability of the ionomer film is measured using a constant-volume, variable-pressure permeation system. Experimental results and variations of permeability of thin films from bulk films as a function of temperature and thickness will be presented. In addition, to tackle the complex and not fully understood effect of water in gas transport, an experimental set-up and approach for measuring effects of humidity on gas permeability of thin films will also be presented.

Acknowledgement

We would like to thank Norman Su for providing assistance in permeation system assembly and operation. This work made use of facilities at the Biomolecular Nanotechnology Center at University of California, Berkeley and the Molecular Foundry at Lawrence Berkeley National Laboratory. This work was funded in part by the University of California Chancellor's Graduate Fellowship and the Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231.

References

[1]Nonoyama, N. et al (2011). Journal of Electrochemical Society. 158(4)

[2] Buchi FN, Wakizoe M, Srinivasan S. J Electrochem Soc 1996;143:927–32.

[3] Ogumi Z, Takehara Z, Yoshizawa S. J Electrochem Soc 1984;131:769–73
Multiple Advance Diagnostics to Probe the Effect of Balance of Plant Materials on Fuel Cell Performance
Authors: Staub Charles B , Christ Jason M , Bender Guido , Macomber Clay S. , Wang Heli , Dinh Huyen N
Published: February 2020

Extensive research on fuel cell stack materials has led to advances in lower cost, high performing materials. With the decrease in the cost of stack materials, lowering the cost of the balance of plant (BOP) components has increased in importance. In order to decrease the overall cost of the automotive and stationary fuel cell systems and make them as competitive as possible, low-cost system component materials that provide similar function, performance and durability are needed. However, intelligently selecting low cost materials for application in polymer electrolyte membrane fuel cell (PEMFC) systems requires understanding the potential adverse effects that system contaminants may have on the fuel cell performance and durability. Limited work in this area has been conducted to-date.

There are many prospective BOP materials that can be used in fuel cell systems. Our material selection was based on the material’s physical properties (i.e., whether it will be stable in fuel cell operating conditions), commercial availability, cost and input from OEMs and fuel cell system manufacturer. Families of material chosen for the study include structural materials, elastomers for seals and (sub)gaskets, and assembly aids (adhesives, lubricants).

Two types of low cost structural plastic materials – a polythlalamide and a polyamide – were studied. Leachates obtained from these plastics were a mixture of organics, inorganics, and ions and were introduced to a working fuel cell to determine their effect on the fuel cells performance. Organics that were identified in the leachate solutions via gas chromatography mass spectrometry (GCMS) include 1,8 Diazacyclotetradecane-2,7-dione (DCTDD), aniline, and caprolactam. These plastic materials also released anions: chloride, phosphate, nitrates, and sulfates. In-situmeasurements such as infusion, cyclic voltammetry, impedance spectroscopy, and I-V curves were carried out to better characterize the contaminants effects of the mixtures of compounds in the extracts. The effect of the individual organic model compound (caprolactam), anion (sulfate) and mixtures of the two species were also studied to better understand the contamination mechanisms of specific species and their interaction with one another.

This presentation will also briefly describe the ex-situ electrochemical quartz crystal microbalance (EQCMB) technique used to study the adsorption effect of organic compounds, derived from system contaminants, on Pt surface. EQCMB was used to measure the change in mass of the electrode as a function of potential.

The authors would like to acknowledge funding from the U.S. Department of Energy EERE Fuel Cell Technologies Office, under Contract No. AC36-08GO28308 with the National Renewable Energy Laboratory and collaborations with colleagues at GM and 3M. Structural plastic materials were provided by GM and membrane degradation products for this study were provided by 3M.
Pt/Metal Oxide Micro-Nanostructures for Chemical-Electrical Signal Transduction
Authors: Ray Nathan J , Karpov Eduard G
Published: February 2020

Investigation of heterogeneous catalysis using bifunctional systems of nanodispersed Pt on porous oxide structures is important for a broad range of applications including photocatalysis, fuel cells, solid state chemical sensors, and others. Active transducers exhibit great potential through their ability to convert surface-released chemical energy into electrical signal. We report on a class of nanocomposite mesoporous systems that generate this electrical signal when subjected to catalytic oxyhydrogen reactions of their surface; these systems include, but are not limited to, mesoporous TiO2 decorated with electrically continuous arrays (meshes) of Pt nanoparticles. It has been proposed that the proton spillover hypothesis of the electromotive force in the mesoporous chemical-electrical transducer nanostructure leads to a multi-modal nature of the “chemicurrent” - non-thermal electrical signals related to hot electron and e-h pair generation.  Structural and surface morphology play a pivotal role in the generation, transport, and recombination of electrical charge in these bifunctional catalytic systems. In this presentation, we discuss plasma electrolytic oxidation procedures that allow for the further optimization of mesoporous nanocomposite structures by controlling parameters such as pore density within the samples.
Cationic Polymerization Initiated By Electrochemically Generated Dendritic Cations
Authors: Yoshida Jun-ichi , Takumi Masahiro , Nagaki Aiichiro
Published: February 2020

Dendritic diarylcarbenium ions, which were generated by the electrochemical oxidation of dendritic diarylmethylsilane, were found to initiate the cationic polymerization of vinyl ethers in flow microreactor systems. Extremely fast micromixing and high-resolution residence time control are responsible for narrow molecular weight distribution of the resulting linear-dendritic hybrid polymers. The end-functionalization was also successfully achieved.
Electrochemical Reduction of 2,2′,6,6′-Tetrabromobisphenol A at Silver Cathodes in Dimethylformamide
Authors: Gerroll Benjamin , Peters Dennis G
Published: February 2020

2,2′,6,6′-Tetrabromobisphenol A (TBBPA) is a brominated flame retardant that is bonded chemically to epoxy resins in circuit boards and that is added to high-impact polystyrenes.  TBBPA is found ubiquitously throughout the environment in sewage runoffs and in water and soil samples, as well as in living organisms.  There have been many documented methods for the degradation of TBBPA, including both chemical and physical methods.  In this study we have focused on the electrochemical degradation of TBBPA at silver electrodes in dimethylformamide (DMF) containing 0.10 M tetramethylammonium tetrafluoroborate (TMABF4).  Initially, cyclic voltammograms were recorded to characterize the electrochemical behavior of TBBPA at both glassy carbon and silver cathodes, as shown in the accompanying figure.  At glassy carbon, only two irreversible cathodic peaks are observed.  On the other hand, reduction of TBBPA at a silver cathode gives rise to three cathodic peaks, which appear at potentials significantly more positive than for glassy carbon.  To investigate the possible debromination of TBBPA, controlled-potential (bulk) electrolyses have been performed with a silver gauze electrode in a DMF–0.10 M TMABF4.  Using GC–MS for the separation, identification, and quantitation of products arising from bulk electrolyses, we have determined that mixtures of mono-, di-, and tribrominated species are produced.

Figure 1
Effects of Electrolyte, Current Density and Electricity Consumption on the Anodic Oxidation of Cyclic Amides
Authors: Becker James Y. , Golub Tatiana
Published: February 2020

Anodic oxidation of N-alkylamides in the presence of nucleophiles such as water, alcohol or carboxylic acid, affords the respective alpha- hydroxy, -alkoxy or -carboxy derivatives as final products (Eq. 1).

The electrochemical properties of three cyclic amides of the type N-acylazacycloalkanes (I - III) (Scheme 1) have been investigated in acetonitrile by cyclic voltammetry. Each one of them exhibits one irreversible anodic wave (at ~2 V) and one irreversible cathodic wave (at around -1.3 V).

Preparative anodic oxidation of I - III in methanol at C anodes under various electrochemical conditions (current density, electricity consumption and supporting electrolytes) led to four major products by all three substrates: alpha-methoxy- and alpha,alpha'-dimethoxy cyclic amides, and two cyclic eneamide derivatives. Their relative ratio was found to be highly dependent on the nature of the electrolyte and current density.

References

[1] E. Steckhan in Organic Electrochemistry (H. Lund, M.M. Baizer, Eds.), 3rd Ed., Chap. 15, pp. 601-607, Marcel Dekker, New York, 1990.

[2] T. Golub and J. Y. Becker, J. Electrochem. Soc., 2013, 160 (7), G1-G5.

Figure 1
Electrochemical Behavior of Nitrobenzene in Aqueous CTAB
Authors: Haque Inam-ul
Published: February 2020

A mechanistic study of the electroreduction of nitrobenzene was undertaken following previously reported voltammetric investigations of nitrobenzene reduction on bare and dioctadecyldimethylammonium chloride (DODAC) covered platinum electrode [1]. The electrochemical reduction of nitrobenzene in aqueous micellar solution of cetyltrimethylammonium bromide (CTAB) at platinum electrode using cyclic voltammetry revealed two distinct cathodic and anodic peaks with interpeak separation of about 60-65 mV indicating a reversible/quasi-reversible charge transfer reaction pertaining to one electron couple of ArNO2/ArNO2

.-
as reported in literature [2-6]. Additional interpretation of experimental cyclic voltammogram was done by using digital simulation. Diffusion co-efficient values of nitrobenzene calculated using Randle-Sevcik equation were found close to the reported values [5-6].

References

(1)  Haque, I. U.; Tariq, M. J. Chem. Soc. Pak.
2011, 33, 529-534.

(2)  Sripriya, R.; Chandrasekaran, M.; Noel, M. Colloid Polym Sci.
2006, 285, 39-48.

(3)  Ernst, S.; Ward, K. R; Norman, S. E.; Hardacre, C.; Compton, R. G.  Phys. Chem. Chem. Phys. 2013, 15, 6382-6389.

(4)  Jara-Ulloa, P.; Nunez-Vergara, L. J.; Squella, J. A. Electroanal. 2007, 19, 1490-1495.

(5)  Smith, W. H.; Bard, A. J. J. Am. Chem. Soc. 1975, 97, 5203-5210.

(6)  Kaifer, A. E.; Bard, A. J. J. Phys. Chem., 1985, 89, 4876-4880.
Low Cost Aqueous Redox Flow Batteries Employing Sustainable Organic Anolytes
Authors: Liu Tianbiao , Wang Wei , Wei Xiaoliang , Nie Zimin , Vijayakumar Murugesan , Sprenkle Vincent
Published: February 2020

Redox flow battery (RFB) represents one of the most promising technologies for large-scale stationary energy storage up to MW (power) or MWh (energy) and has attracted increasingly popularity among academic and industrial research groups. There are many attractive technic advantages of RFB including decoupling of energy storage and power output, exceptional design flexibility, excellent scalability and modularity, long service life, high efficiency, etc. These technic merits make RFB a well-suitable choice to stabilize the power grid and overcome the intermittency of renewable energy sources (e.g. solar, wind, and hydroelectricity). We have recently identified a class of sustainable and low cost redox active organic anolytes for aquesous RFBs. In this presentation, we will report our progress on the electrochemical studies of the novel organic anolytes and their flow cell performance in combination with low cost catholytes, e.g. FeCl2. ARFBs employing low cost anolytes and catholytes hold promise in replacement of traditional vanadium aqueous RFB (VRFB), which is limited for wide implementation by the low abundance and high cost of vanadium precursors.

Acknowledgment

We acknowledge financial support from the U.S. Department of Energy’s (DOE’s) Office of Electricity Delivery and Energy Reliability (OE) (under Contract No. 57558). Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.
Limits of Li-Ion Batteries for Public Transportation
Authors: Patey Timothy John
Published: February 2020

Accelerating a 50-ton rather than a 1-ton electric vehicle presents new scientific and engineering challenges. In view of this, our work discusses the power limits of Li-ion batteries as on-board energy storage devices in traction systems used in public transportation. This is based on a thermal analysis of a high power Li-ion battery and an aging/thermal model of it. Included within this process are the following details:

1) General analysis of required heat transfer coefficients.

2) Estimation of internal thermal conductivity along and parallel to electrodes.

3) Use of a thermal network model to calculate internal temperature.

Based on this approach, routes to develop higher power Li-ion batteries are discussed based on our current understanding of the electrochemical and heat transfer limitations. A proposal on future electrochemical devices, designed especially for public transportation, is also discussed in detail.

Figure 1
The Deep Sea Water and Heat Energy of Thermoelectric Generation Study
Authors: Chen Meng Chu
Published: February 2020

This study is a preliminary evaluation of the potential for using deep sea water and solar energy (or hot-spring water) source to economic benefits of thermoelectric power in Taiwan. we investigated that solar energy and high temperature spring water was replaced to the surface sea water to increase the temperature difference (70~85oC). Use of innovative, green, renewable energy resource  enables the  City (Town) to reduce its demand for electricity by approximately 0.5 million kilowatt hours annually (reduction  of up to 65 per cent compared to conventional power system, reduced electricity demand and consequently lower emissions of air pollutants and greenhouse gases.)  We propose an energy-balanced mathematical model considering thermal sources and heat effects to precisely evaluate the capacity of thermoelectric power systems.

The research is low temperature of the use the deep ocean water establishes  thermoelectric power system, applies the building already some power system in the substitution, not can only enrich DSW the multi-dimensional use, can gain the energy conservation to reduce the carbon essence benefit.
Modulating Electron Transfer Dynamics Via Graphene Interactions in Donor-Acceptor Systems
Authors: D'Souza Francis , Lim Gary N. , KC Chandra
Published: February 2020

Sequential electron transfer or electron transfer/hole transfer between energetically well-positioned entities of photosynthetic reaction center donor-acceptor models is one of the commonly employed mechanisms to generate long-lived charge separated states.  Wealth of information, applicable towards light energy harvesting and building optoelectronic devices, has been acquired from such studies.  In the present study, we report charge stabilization in multi-modular donor-acceptor pentads comprised of phenothiazine, subphthalocyanine and fullerene as molecular components.1  In these pentads, the subphthalocyanine and fullerene serve as primary electron donor and acceptor, while the phenothiazine entities act as secondary hole transferring agents. The newly synthesized compounds were characterized by optical absorption and emission, computational and electrochemical methods.  The redox potentials measured using differential pulse voltammetry were used to estimate free-energy changes for charge separation, hole migration, and charge recombination processes.  Using femto- and nanosecond transient absorption techniques, evidence for charge separation, and kinetics of charge separation and recombination were obtained in polar benzonitrile and nonpolar toluene solvents.  The kinetic data obtained by analyzing the time profiles of the radical ions revealed occurrence of ultrafast charge separation and relatively slow charge recombination processes as a result of electron transfer-hole shift mechanism in these pentads.  The measured rate of charge separation, k
CS were in the range of  1.2 - 4.4 x 1010 s-1 while the rate of charge recombination, k
CR were in the range of 1.3 - 5.4 x 106 s-1, depending upon the design and solvent polarity, revealing charge stabilization in the pentads.  Further, by the interaction of phenothiazine entities of the triad with graphene, modulation of electron transfer events has been accomplished.  Details of these investigations will be presented.

1KC, C. B.; Lim, G. N.; Zandler, M. E.; D’Souza, F., Org. Letts. 2013, 15, 4612-4615.
First Observation of the Pore Dynamics in Ordered Mesoporous Electrode Materials By in Operando Small Angle X-Ray Scattering
Authors: Park Gwi Ok , Yoon Jeongbae , Park Eunjun , Kim Yunok , Kim Hyunchul , Kim Hansu , Yoon Won-Sub , Kim JI Man
Published: February 2020

To monitor dynamic volume changes of electrode materials during electrochemical lithium storage and removal process is of utmost importance for developing high performance lithium storage materials. We herein report an in operando probing of mesoscopic structural changes in ordered mesoporous electrode materials during cycling with synchrotron-based small angle X-ray scattering (SAXS) technique. In operando SAXS studies combined with electrochemical and other physical characterizations straightforwardly show how porous electrode materials underwent volume changes during the whole process of charge and discharge, with respect to their own reaction mechanism with lithium. This comprehensive information on the pore dynamics as well as volume changes of the electrode materials will not only be critical in further understanding of lithium ion storage reaction mechanism of materials, but also enable the innovative design of high performance nanostructured materials for next generation batteries.
Pre-Coated Ce/Co-Coated Steel: Mitigating Cr Vaporization, Increasing Corrosion Resistance at Competitive Cost
Authors: Falk Windisch Hannes , Mertzidis Ioannis , Svensson Jan-Erik , Froitzheim Jan
Published: February 2020

Cr vaporization and oxide scale growth are probably the two most detrimental degradation mechanisms associated to Cr2O3-forming alloys as interconnect material in SOFC. Different type of perovskite or spinel coatings are commonly used to mitigate Cr vaporization. Furthermore a number of studies have suggested that reactive element coatings (Ce, La, Hf) can reduce the oxidation rate of Cr2O3-forming alloys. However, the use of coatings increases cost due to addition processing and handling costs.

The present study investigates the effectiveness of thin Ce and Co Physical Vapor Deposited (PVD) coatings with respect to Cr vaporization, corrosion resistance and Area Specific Resistance (ASR). The coatings were applied in a continuous roll-to-roll process which allows for high volumes.

The use of pre-coated interconnects is thus more economic than a batch process. However, a consequence of the pre-coated concept is that the coating is subject to deformation when the pre-coated steel is pressed into the interconnect shape.

Therefore this study also investigates the effect of deformation on the coating. Coated steel strips were bi- and uniaxially deformed. Furthermore a commercially used  interconnect shape is investigated and the effects on Cr evaporation and corrosion are studied: Cr vaporization was measured in an air-3% H2O environment at 850 °C for 336 h. The results revealed that when the pre-coated steel was deformed, large cracks were formed. However, upon exposure those cracks did heal forming a continuous surface oxide rich in Co and Mn. As an effect of the rapid healing, no increase in Cr vaporization was measured for the pre-coated material.
In Situ Tailored Nickel Nano-Catalyst Layer for Internal Reforming Hydrocarbon Fueled SOFCs
Authors: Myung Jaeha , Neagu Dragos , Tham Mark , Irvine John T. S.
Published: February 2020

Solid oxide fuel cells (SOFCs) have been strongly attracted as the next energy technology due to their high efficiency and eco-friendly energy convertor. SOFCs do not only directly convert to electricity from hydrogen, also from various hydrocarbon fuels such as methane, propane, and so on. However, the conventional Ni cermet anode suffers carbon deposition when directly used with hydrocarbon fuels because of pyrolysis and Boudouard reactions.  

In this work, non-stoichiometry perovskite (La0.8Ce0.1Ni0.4Ti0.6O3) as reforming layer can lead to Ni nano particle exsolution with homogenous distribution and high population in reduction atmosphere. This catalyst layer was applied on Ni-GDC anode supported single cell to prevent carbon deposition through reforming hydrocarbon fuel at outer surface.  

The catalyst layer showed excellent attachment with Ni-GDC anode and resistance of carbon deposition. The performance of Ni–GDC anode-supported single cells with catalyst layer was about 1 W/cm2 in hydrogen fuel as similar as without catalyst layer. We are also analyzing of cell performance in dry methane and partial oxidation of methane to clarify the presence of nano nickel particles in the catalyst layer and its effect on the electrode-catalytic activity and polarization resistance.
Advanced 3D Imaging and Analysis of SOFC Electrodes
Authors: Tariq Farid , Kishimoto Masashi , Cui Guansen , Yufit Vladimir , Lomberg Marina , Ruiz-Trejo Enrique , Chen Zhangwei , Brandon Nigel P.
Published: February 2020

Meeting increasing energy demands, storage demands and energy portability in a clean efficient manner will be expedited through an ability to directly image and analyse solid oxide fuel cell (SOFC) materials and components. In particular, the performance of SOFC electrodes is dependent on their nano/micro-structure as electrochemical reactions and transport phenomena are strongly affected by their complex porous microstructure. Furthermore, during processing or operation, microstructural evolution may degrade electrochemical performance.

Tomographic techniques allow the 3D imaging and characterisation of complex microstructures at length scales down towards tens of nanometers; which are inadequately described in 2D. While performance is acknowledged to be dependent on reactions at electrode surfaces and interfaces, the detailed nature of these in technological electrodes is still not fully understood.

Here we use tomographic techniques to probe the 3D SOFC electrode structure at nanometer to micrometer length scales. For the first time characterisation of specific necks and interfaces within SOFC electrodes is derived. Micro/nano structural changes are followed to facilitate understanding the differences which occur with shape, structures and morphology at high resolution. These are correlated with measured experimental values to provide insight into microstructure-property relationships. In doing so, the engineering of tailored electrodes during 3D printing is afforded.

When coupled with electrochemical and thermo-mechanical computational models, the results show that nano/microstructural and compositional variations can significantly affect performance of SOFC electrodes. This coupled approach provides important insights for electrode design and understanding the sources of performance degradation.

Figure 1
­­Additive Manufacturing for Solid Oxide Cell Electrode Fabrication
Authors: Lomberg Marina , Boldrin Paul , Tariq Farid , Offer Greg , Wu Billy , Brandon Nigel P.
Published: February 2020

Electrode microstructure plays a critical role in determining the electrochemical performance and durability of Solid Oxide Cells. Additive manufacturing can potentially offer a highly-defined electrode microstructure, as well as fast and reproducible electrode fabrication. Selective laser sintering (SLS) is an additive manufacturing technique in which the three-dimensional structures are created by bonding subsequent layers of powder using laser power.

Although selective laser sintering can be applied to a wide range of materials, including metals and ceramics, the scientific and technical aspects of the manufacturing parameters and their impact on microstructural evolution during the process are not well understood.  

In the present study this novel approach for electrode fabrication was evaluated by conducting a proof of concept study. A Ni-patterned fuel electrode was laser sintered on a YSZ substrate. The optimization process of laser parameters (laser sintering rate and laser power) and the electrochemical results of a full cell with laser sintered electrode are presented. The challenges and prospects of using selective laser sintering for SOC fabrication (for example, to create electrodes with unique 3D hierarchical porous structures) are discussed.

Figure 1
Detailed H2 and CO Electrochemistry for a MEA Model Fueled by Syngas
Authors: Lee Won Yong , Ong Katherine M , Ghoniem Ahmed F
Published: February 2020

SOFCs are capable of directly oxidizing CO in addition to H2, which allows them to be coupled to a gasifier that converts coal, biomass or other carbonaceous fuels to synthesis gas.   Most membrane-electrode-assembly (MEA) models neglect CO electrochemistry because H2 oxidizes more readily and most CO presumably shifts to H2 by the water-gas-shift reaction in the presence of H2O.  In this paper we examine this assumption, especially at conditions of high current density and high CO-content syngas.  The comprehensive 1D-MEA model presented here incorporates detailed mechanisms for both H2 and CO oxidation.  The rate parameters and rate-limiting steps for the H2 mechanism are selected by fitting the model to experimental porous anode data for H2/H2O mixtures.  The kinetic parameters of the CO mechanism were determined by matching the data to EIS measurements. The anode’s physical parameters, triple-phase-boundary length and nickel pattern width, are then determined by fitting the CO mechanism to porous anode data for CO/CO2 mixtures.  The resulting H2 and CO mechanisms are then combined, along with surface reforming kinetics, into a single model that iterates through anode activation overpotential to resolve the individual current contributions of each fuel.  We find that the model under-predicts experimental data for H2/CO mixtures when CO electrochemistry is neglected, but fits the data well at high current densities when CO oxidation is included.  Furthermore, the combined model fits H2/CO data best when a single charge-transfer step in the H2 mechanism is assumed to be rate-limiting over the full range of current densities.  This single rate-limiting step assumption for H2/CO mixtures differs from a previous finding that the H2 adsorption step becomes rate-limiting at high current densities for H2/H2O mixtures.  This implies that adding CO to the fuel stream can fundamentally alter the H2 oxidation process.  The individual H2 and CO current contributions for CO-rich syngas confirm that the addition of CO oxidation can delay H2 current saturation at high anode activation overpotentials, hence improving cell performance.  These results indicate that CO oxidation cannot be neglected in MEA models running on CO-rich synthesis gas, and further studies are needed on the combined CO and H2 mechanism on Ni-YSZ.
Coking-Resistance and Sulfur-Tolerance Study of La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ Anode
Authors: Han Minfang , Xu Na , Yang Zhibin , Zhu Tenglong
Published: February 2020

Solid oxide fuel cell (SOFC) has experienced a growing interest in the last few decades because of generating energy more efficiently than the conventional combustion of fossil fuels. By using the same material as anode and cathode of symmetric solid oxide fuel cell (SSOFC), the production of reliable and repeatable cells would be simpler. In this work, La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) has been investigated firstly as potential cathode material for SOFC. The cathode polarization resistances are only 0.1 Ω cm2 at 800 oC. The stability of phase structure, electrode microstructure and polarization resistances for the LSCFN in the atmosphere of air have been studied. Then, LSCFN have been investigated as potential anode material for SOFC. The results show that LSCFN have high catalytic activity in methane catalytic combustion reaction, the total conversion temperature of 1% CH4 using LSCFN as catalyst was as low as 650 oC. The performance of carbon-resistance and sulfur-tolerance in SOFC were studied using LSCFN ceramic anode with La0.8Sr0.2Ga0.83Mg0.17O3-δ (LSGM) electrolyte. Long-term operation of such single cell under methane lasted for 120 hours without degradation. The output power density fueled with H2-50 ppm H2S was stable enough in 120 hours’ operation which indicated a good sulfur-tolerant performance. Finally, the maximum power densities generated by the SSOFC cell with LSCFN electrode are 650 mW cm-2 in H2, and the cell maximum power output has demonstrated to be not affected by the redox cycling of the anode during a total of 21 cyclic testing, indicating that the LSCFN has excellent redox stability. All of these results indicate that LSCFN can potentially be a promising candidate for the electrode material of SSOFC.
High Performance Air Electrode for Solid Oxide Regenerative Fuel Cells Fabricated by Infiltration of Nano-Catalysts
Authors: Yoon Kyung Joong , Hong Jongsup , Kim Hyoungchul , Son Ji-Won , Lee Jong-Ho , Kim Byung-Kook
Published: February 2020

A high performance air electrode fabricated by infiltration of highly active nano-catalysts into a porous scaffold is demonstrated for high-temperature solid oxide regenerative fuel cells (SORFCs). The nitrate precursor solution for Sm0.5Sr0.5CoO3 (SSC) catalyst is impregnated into a porous La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) – gadolinia-doped ceria (GDC) composite backbone, and extremely fine SSC nano-particles are uniformly synthesized by in-situ crystallization at the initial stage of SORFC operation via homogeneous nucleation induced by urea decomposition. The SSC nano-catalysts are in the size range of 40-80 nm and stable against coarsening upon the SORFC operation at 750oC. The electrochemical performance is significantly improved by incorporation of SSC nano-catalysts in both power generation and hydrogen production modes. Systematic analysis on the impedance spectra reveals that the surface modification of the air electrode with nano-catalysts remarkably accelerates the chemical surface exchange reactions for both O2 reduction and O2- oxidation, which are the major limiting processes for SORFC performance.
Fuel Flexible and Efficient Semionics Single Layer Fuel Cell
Authors: Raza Rizwan
Published: February 2020

Fuel cells are traditionally based on a three-layer configuration - anode, electrolyte and cathode –leading to a complex structure, not least since the three layers have to be chemically stable and mutually compatible. Our new electrolyte-free, single layer fuel cell represents a radically new approach to fuel cell research and design.

An advanced fuel flexible single layer/electrolyte free fuel cell with a functional nanocomposite was developed. Several different types of fuel, for example, gaseous (hydrogen and biogas) and liquid fuels (bio-ethanol and bio-methanol), were used in the experiments. Maximum power densities of 800, 300, 500, 400 mW cm-2 were achieved using hydrogen, bio-gas, bio-methanol, and bio-ethanol, respectively. These results show that single layer/electrolyte free fuel cell systems with functional nanocomposite offer significant advantages in reducing the operational and capital costs for the production of power and heat with a multi-fuel flexibility.

This system might be the one of the promising solutions for sustainable energy development. This study is based on nanocomposites for advanced fuel cell technology (NANOCOFC) to develop functional nanocomposite materials for next generation marketable products.

 

References

 

B.Zhu, Rizwan Raza, Q.Liu, H.Qin, L.Fan, “Fuel cells based on the electrolyte and non-electrolyte separator”
Energy and Environmental Sciences
, 2011, 4 (8), 2986 - 2992.
Tubular SOFC with Hollow Fiber Ceramic Support and Inner Coating
Authors: Yang Zhibin , Zhu Tenglong , Han Minfang
Published: February 2020

In this work, zirconia supported segmented-in-series type single cell with inner side coating was studied. The support tube was fabricated through phase-inversion method using 3%mol Y2O3 doped ZrO2 (TZP). Then the NiO-8%mol Y2O3 stabilized ZrO2 (YSZ) anode layer, YSZ electrolyte layer and (La0.8Sr0.2)0.95Mn3O3-
δ (LSM)-YSZ cathode layer and LSM layer was applied by screen printing and high-temperature sintering in proper orders. Finally, La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) - Gd0.1Ce0.9O1.95 (GDC) composite layer was coated on the inner side of the support tube. Cell performance characterization was conducted using room-temperature humidified hydrogen and methane at a gas flow rate of 40mL/min inside the tube and ambient air at cathode side. Results show that, the open circuit voltage at 850 oC under H2 and CH4 was 1.04V and 1.08V separately, while the corresponding maximum power density was 96 and 106 mW/cm2 respectively. No obvious degradations were observed in the stability test under humidified H2 for 50h and CH4 for 250h.
Production and Performance of Copper-based Anode-supported SOFCs
Authors: Azzolini Andrea , Sglavo Vincenzo Maria , Downs J A
Published: February 2020

The production of tubular SOFCs supported by a cermet anode formulated with copper was successfully achieved. The optimization and the experience developed in the process of extrusion allowed to produce the composite anodes quickly and with good reliability. The low melting temperature of copper and its two oxides imposed a limit on the maximum temperature reachable during co-sintering of the cell. The study of the effect of different sintering aids on the densification of the GDC10 permitted to select Li2O as the most effective, being able to enhance the sinterability of the material and to decrease of more than 600°C its sintering temperature. Although its effect was remarkable, the densification of the thin electrolytic layer when bonded to the supporting anode could not be accomplished without analyzing and solving the issues related to its constrained sintering. A complete cell with a 10 um perfectly dense and crack free Li2O-GDC10 electrolyte, Li2O-GDC10:Cu2O 75:25 vol% anode and GDC10:LSF20 50:50 vol% cathode was obtained after one step sintering for 3h at 1020°C in argon atmosphere. The co-sintering permitted perfect adhesion of the three layers and no sign of debonding. One of the main fabrication problems related to the employment of Cu2O in the cermet anode was its low coefficient of thermal expansion that caused the onset of tensile stress in the electrolyte during cooling and the opening of brittle fractures on its surface. When the Cu2O was increased to 35vol% to insure the electrical conductivity of the anode, the sintering temperature had to be decreased to 995°C to minimize the cracks formation, although this affected the densification of the electrolyte layer. Cells formulated with Cu2O suffered from incomplete densification, cracks and oxidation of the cuprite during reduction. These issues made impossible to perform electrochemical tests.

Employment of CuO was less problematic, thanks to its resistance to oxidation and its higher CET. SOFCs were fabricated with Li2O-GDC10 electrolyte, Li2O-GDC10:CuO 60:40 vol% anode and GDC10:LSF20 50:50 vol% cathode. Sintering at 1020°C resulted in a fully dense electrolyte with a fine grain structure, although some cracks due to differential shrinkage could not be completely avoided. Despite this, the cell had a maximum OCV of 0.54 V and the highest measured power density was 8.98 mW cm-2 with a peak power density projected to be 27.5 mW cm-2 when tested at 600°C in dry H2. More test at lower temperatures are currently in progress.

These results do show that SOFCs can be produced with a copper cermet anode using similar methods used with NiO-based anodes by a one-step firing procedure at relatively low temperatures, thus having cost and high energy savings. The use of copper can allow for the use of light hydrocarbons in the cell without external reforming equipment or need of high steam to carbon ratio, and without the risk of carbon deposition in the cell
Performance of SOFC Power Unit Assisted by Paper-Structured Catalyst
Authors: Shiratori Yusuke , Sakamoto Mio , Tran Quang Tuyen , Uchiyama Yasuyuki , Uchiyama Naoki
Published: February 2020

This study aims at the performance enhancement of direct internal reforming (DIR)-SOFC. Paper-structured catalyst (PSC) is a flexible catalyst material composed of inorganic fiber network loaded with metal catalyst which can be applied into cell stack to assist hydrocarbon reforming. Catalytic performance of PSC was considerably improved by the dispersion of Mg/Al hydrotalcite (HDT) in the inorganic fiber network to have higher tolerance to fuel impurity (sulfur) poisoning because of the formation of fine Ni particles and suppression of Ni loading on the inorganic fiber (SiO2-Al2O3) to cause coking.

High temperature SOFCs can convert chemical energy of a fuel directly to electricity even in the feed of low calorie gas. The use of engine-exhaust, which is most accessible lean gas, as a fuel for SOFC is promising idea. Recently, a compact SOFC unit operated by the direct feed of engine-exhaust was developed by Atsumitec Co., Ltd. However, performance of the DIR-SOFC unit can easily deteriorate, unless fuel is homogeneously supplied into the unit in which several numbers of stacks were arrayed. This study demonstrated that insertion of the HDT-dispersed PSC into the real SOFC stack between the cells led to 36 % increase in the performance because PSCs can boost up the output power of stacks placed at the positions where fuel is not well supplied.
Development of Medium-Temperature Solid Oxide Fuel Cells and CO2 and H2O Co-Electrolysis Cells in Estonia
Authors: Lust Enn , Tamm Kadi , Nurk Gunnar , Möller P , Kivi Indrek , Kanarbik Rait , Heinsaar Alar
Published: February 2020

Various micro/mesoporous activated complex oxides as cathodes or andodes, bilayered Ce0.9Gd0.1O2-d|Zr0.92Y0.08O2-d electrolyte and various Ni-cermet and Ni-free anodes or cathodes have been designed and tested for high power density solid oxide fuel cells (1.5...1.6 W/cm2 (1073 K) and solid oxide electrolyzers. FIB-TOF-SIMS, FIB-SEM-EDX, HTXRD, BET, AFM and electrochemical impedance methods have been applied for analysis of the materials and completed single cells. Influence of porosity distribution (BET and 3D FIB-SEM data), cell potential and fuel composition on power density and fuel conversion efficiency has been demonstrated.
Recent Progress of SOFC Combined Cycle System with Segmented-in-Series Tubular Type Cell Stack at MHPS
Authors: Miyamoto Koji , Mihara Masahiro , Oozawa Hiroyuki , Hiwatashi Kenichi , Tomida Kazuo , Nishiura Masanori , Kishizawa Hiroshi , Mori Ryutaro , Kobayashi Yoshinori
Published: February 2020

Mitsubishi Hitachi Power Systems, Ltd. (MHPS) is one of the first companies to focus on the potential of the Solid Oxide Fuel Cells (SOFC) as a component of large-scale power plant and has promoted segmented-in-series tubular type cell, the module and the system development since the 1980s. We are developing for commercialization of an SOFC-micro gas turbine (MGT) system from several hundred to several MW class. Recently prototype of a 250 kw class SOFC-MGT hybrid system was operated at Tokyo Gas Senju Techno Station. This system was very stable without voltage degradation at the rated for 4,100 hours. At the same time, we have started the development of fundamental technologies for realization of SOFC-Gas Turbine (GT)-Steam Turbine (ST) triple combined cycle system that aims to achieve more than 70% of power generation efficiency. We report the recent progress of the SOFC-micro gas turbine (MGT) hybrid system and development of triple combined cycle system.
Material Characteristics and Electrochemical Performance of YxBa2-XCo2O5+δ Cathode for Solid Oxide Fuel Cell
Authors: Hung I-Ming , Wang Jeng-An , Kuo Jen-Yuan , Lin Tai-Nan
Published: February 2020

A new YxBa2-xCo2O5+δ cathodes were successfully prepared by solid-state reaction method. The structure, microstructure, conductivity, coefficient of thermal expansion and electrochemical properties of these YxBa2-xCo2O5+δ cathodes were conducted by XRD, SEM, 4 DC four-terminal method, thermomechanical analysis and AC impedance, respectively. The YBaCo2O5+δ is a single phase with double perovskite structure. The second phases of YBa2Co3O9-δ and Y2O3 were observed as the x>1 and x<1, respectively. The conductivity of all YxBa2-xCo2O5+δ amples increased as temperature increased, and show a p-type conductor characterization. The YBaCo2O5+δ exhibited a maximum conductivity of 256 S/cm at 300 oC. The coefficient of thermal expansion is 13.8*10-6, which is close to that of Samaria-doped Ceria (SDC) electrolyte. The YBaCo2O5+δdid not react with SDC electrolyte below 1050 oC. The YBaCo2O5+δ is a potential cathode material for intermediate temperature solid oxide fuel cell.