bluuebunny/crossref_metadata_2025 huggingface dataset:
Screen Printed Porous La0.20Sr0.25Ca0.45TiO3 Fuel Electrode Scaffold Microstructures: Optimisation of Interaction with Impregnated Catalysts for More Durable Performance
Authors: Price Robert , Cassidy Mark , Schuler J. Andreas , Mai Andreas , Irvine John T. S.
Published: February 2020

Solid Oxide Fuel Cells (SOFC) offer an efficient method of electricity and heat production through electrochemical conversion of hydrocarbon fuels (e.g. methane) rather than direct combustion in conventional boiler units. The current industrial standard SOFC anode material is the Ni-based cermet. Although it shows high electrocatalytic activity for H2 and CO oxidation, it suffers from redox instability, Ni-grain agglomeration, gas feed sulfur intolerance and severe coking in the presence of hydrocarbon fuels. This deactivates the catalyst over time, hence a suitable replacement anode material is highly desired. La0.20Sr0.25Ca0.45TiO3 (LSCTA-) is a promising candidate for this role, acting as a ‘backbone’ structure into which electrocatalytic particles (NiO and CeO2) may be impregnated. This material has previously been used as an anode material in short-stack and full-scale testing at Hexis AG. Short-stack (5 cells) tests showed initial good performance (running at 200 mA cm-2) at 900 °C, however degradation was observed between 50 – 100 hours of operation. 1 Whilst in 1kW (nominal) Hexis Galileo 1000 N micro combined heat and power unit tests, an initial power output of ~700 W was obtained, decreasing to 250 W after 600 hours. 1 Post-test analysis revealed that non-optimal anode backbone microstructures and a small layer thickness led to poor current distribution and the generation of localised temperature ‘hotspots’ within the cells, leading to degradation of stack performance over time 1 (despite the initial comparability to the Ni-CGO standard at Hexis). Current research is focussing on the optimisation of the interaction between the backbone microstructure and impregnated electrocatalytic particles in order to improve electrochemical performance whilst minimising degradation. This paper will discuss initial research into optimisation of screen printed anode structures and the interaction with impregnated particles, including: NiO, CuO, CeO2 and lanthanum strontium chromium manganite (LSCrM).

Reference:

1.           Verbraeken, M. C. et al. Short stack and full system test using a ceramic A-site deficient strontium titanate anode in 11th European SOFC and SOE Forum, 1–13, (2014).
Microstructure-Based Damage Modelling of Plasma Sprayed Ceramic Coatings in SOFC-Layer Systems
Authors: Guski Vinzenz , Krebs Axel , Weber Ulrich , Schmauder Siegfried
Published: February 2020

Solid oxide fuel cells (SOFC) have developed to promising energy conversion devices for many applications. However, operation conditions under elevated temperatures, especially high temperature regimes and repeated temperature changes imply extreme demands for the used materials, questioning durability and reliability of such devices.

The scrutinized SOFC isolation layer system as shown in Figure 1 consists of a staple of ceramic layers sprayed on a steel substrate (interconnector). The main focus in this project is investigating application induced failure mechanisms under service conditions.

A newly developed ceramic of Mg-spinel type offers self-healing capabilities (Fig. 2). The self-healing effects provide fracture annihilating potential and promising mechanical capabilities. The manufacturing process of these ceramics causes a complex microstructure with structural defects such as pores or debonded splats. Splats are rapidly solidified molten ceramic particles on a substrate. Residual stresses, caused by quenching stresses during manufacturing as well as thermo-mechanical mismatch stresses due to temperature change may lead to crack initiation in the ceramic and subsequent mechanical weakening effects, respectively.

We present a microstructure-based approach to simulate the influence of thermal cycling on the ceramic coating stress evolution. This stress evolution and, thus, the damage behaviour is affected by the above mentioned influences. The numerical model represents a SOFC system which consists of a ceramic layer on a steel substrate and a thermally grown oxide (TGO) interlayer (Fig. 3). Assuming fracture mode I, the load case normal to the crack plane, the focus is set on the evolution of principal stresses in the ceramic microstructure.

The results of micromechanical simulations show how stress localisations due to structural defects such as pores or microcracks heavily influence this stress evolution and, therefore, the crack initiation in the ceramic layer.

We found the directions of the principle stresses in the microstructure facilitate delamination of the layer. Parameter studies show how residual stresses, TGO and interface roughness affect the stress evolution in the ceramic layer. A comparison of the new self-healing ceramic with a standard reference material point out the promising properties of this newly developed material. Detailed microstructure analyses and insights provide an understanding of the main failure mechanisms of the ceramic layer in depth and deliver clear optimization potentials for sprayed ceramic layer systems of SOFCs.

Figure 1
Three-Dimensional Computational Fluid Dynamics Modelling for a Planar Solid Oxide Fuel Cell of a New Design
Authors: Pianko-Oprych Paulina , Zinko Tomasz , Jaworski Zdzislaw
Published: February 2020

The aim of the work is to investigate the electrochemical processes of a planar Solid Oxide Fuel Cell (SOFC) and to estimate the performance of a novel SOFC design. The design involves cross-flow bipolar plates. Flow channels were designed to connect pairs of four orifices at the corners of the SOFC plates. Each of the bipolar plates has an air channel system on one side and a fuel channel system on the other side. One pair of channels in adjacent plates is used for the air flow along the cathode electrode, the other for the fuel flow along the anode of each cell. A schematic of the design proposed by Bossel [1] is shown in Fig. 1.

            Figure 1. A schematic of the proposed planar SOFC design:

(a) cathode side view, (b) anode side view [1]

A three-dimensional Computational Fluid Dynamics (CFD) model for an anode-supported planar SOFC with complex bipolar plates has been developed using the ANSYS Fluent code with additional Fuel Cell Tools module. The conservation equations of mass, momentum, energy and species as well as electrochemical models were solved for the fuel cell. The distributions of temperature and gas flow through the gas channels and PEN (positive electrode/electrolyte/negative electrode) structure were studied. The results identified the most susceptible areas for significant increase of the temperature at high current density, which can lead to hot spots formation and destruction of the electrodes. Knowledge of such parameters as the flow fields, pressure losses or temperature variation over the fuel cell area allowed to validate the effectiveness of the new SOFC design and is useful in further design modification.

Acknowledgments

The research programme leading to these results received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement no [325323]. Acknowledgments are due to the partners of SAFARI project. The work was also financed from the Polish research funds awarded for the project No. 3043/7.PR/2014/2 of international cooperation within SAFARI in years 2014-2016.

[1] U. Bossel, Rapid startup SOFC modules, Energy Procedia, 28, 2012, 48-56. DOI: 10.1016/j.egypro.2012.08.039.

Figure 1
A High Resolution Multi-Physics Numerical Model for Planar SOFC Stack
Authors: Li Ang , Fang Xiurong , Lin Zijing
Published: February 2020

An SOFC stack is the basic functioning unit of SOFC as an electrical power generation device. The physical condition of an operating SOFC stack is vastly different from that of a laboratory button cell. The ability to analyze the performance characteristics of SOFC stacks is immensely helpful for advancing the SOFC technology for large scale commercial applications. Here we report a successful development of a high space resolution multi-physics mathematical model for full scale planar SOFC stacks which is, to the best of our knowledge, the first of its kind.

This 3D stack model takes into account the coupled physical processes of mass, charge and heat transport, chemical and electrochemical reactions, applicable for both methane and hydrogen based fuels. The computational domain contains all components of the stack, including fuel and air channels, internal manifolds, cathode-electrolyte-anode assemblies, interconnects, seals and frames. The computational model is constructed using the commercial CFD software, FLUENT®, supplemented with in-house developed external subroutines to ensure all governing equations and physical properties are correctly coupled and solved successfully. Boundary conditions for the stack and that between material components are all properly incorporated into the computational model.

To illustrate, Figure 1 shows a geometric model for a 30-cell stack with a counter- or co-flow design. The size of the stack is 136mm  143mm  133mm. The manifold consists of two/three gas inlet-outlet channels for each air or fuel flow. Every fuel cell consists of 30 channel-rib pitches, i.e., there are 900 repeating units for the electrochemically active area of the 30-cell stack. To properly resolve all the stack components involved, the computational model consists of a total of about 27 million grids.

Multi-physics numerical simulations of this truly high resolution computational model of 30-cell stack have been successfully performed in a 2-CPU/16-core PC. Detailed information about the distributions of physical quantities is revealed, e.g., concentrations of chemical species, temperature profile, current density and electrical potential distributions, chemical and electrochemical reaction rates, etc.

To summarize, the goal of performing detailed multi-physics simulations for realistic planar SOFC stacks has been achieved. Performance simulation with this high resolution, high computing efficiency numerical model can do much to advance the SOFC technology by improving the stack design and optimizing the operating parameters.

Figure 1
High Efficient Combined Heat and Power SOFC System for Residential Power Applications: Lifetime-Efficiency-Simulations Using AspenPlusTM
Authors: Spieker Carsten , Spitta Christian , Noponen Matti , Hallanoro Paul , Ruetten Thomas
Published: February 2020

High temperature Solid Oxide Fuel Cells (SOFC) systems are high efficient energy conversion systems with low emissions e.g. for residential power applications. The objective of this work is to provide a flexible model of a SOFC system that is capable of predicting system performance in a wide range of operating conditions as well as predicting system lifetime performance based on experimentally determined SOFC performance and endurance curves. The system model is developed using AspenPlusTM unit operation blocks and the SOFC electrochemical model is implemented using the embedded AspenPlusTM Microsoft Excel Workbook. Validation of the model is performed by comparison to experimental results.

The adaption of this model to different SOFC system simulation approaches will be discussed. Furthermore for a SOFC based mCHP system development simulation results predicting an electrical efficiency higher than 50 % and an overall system efficiency higher than 85 % for the whole lifetime will be presented.
Effects of Lamination Conditions on the Performance of Anode-Supported Solid Oxide Fuel Cells
Authors: Timurkutluk Bora , Timurkutluk Cigdem , Ciflik Yelda , Korkmaz Hatice , Kaplan Yuksel
Published: February 2020

Solid oxide fuel cells (SOFCs) operate at high temperatures and produces electricity and heat energy from fuels in an electrochemical way. Membrane electrode assembly (MEA) composed of a dense electrolyte coated with two porous electrodes on each side is generally constructed on the electrolyte. However, high operation temperatures are required to obtain acceptable performance values due to high electrolyte resistance as a result of the use of thick electrolyte layer as a mechanical support for MEA. Alternatively, the cells can be fabricated as anode-supported where the anode is responsible for supporting the cell mechanically. By doing so, the operation temperature can be lowered due to reduced electrolyte thickness. In this study, the effects of isostatic pressing parameters i.e. temperature and pressure for NiO/YSZ anode support on the anode-supported cell performance and the microstructure of the anode support are investigated. The experimental results reveal that the cell performance is strongly influenced by the pressing parameters. In this aspect, the optimum pressing temperature and pressure are found to be 50 °C and 40MPa, respectively.
Effect of Cathode Contacting on Anode Supported Cell Performances and Degradation
Authors: Spotorno Roberto , Piccardo Paolo , Schiller Guenter
Published: February 2020

Stacking Solid Oxide Fuel Cells implies the use of contacting layers, especially in the cathode compartments where ohmic losses are introduced at the interface between the electrode and the interconnect  due to the high interfacial resistance and the lowered contact area caused by geometrical and porosity issues. Such losses compromise the current distribution over the electrodes strongly influencing the system performances in terms of power outputs. The contacting issues are weakly dependent on the operating conditions compared to other dissipative contributions related to the cells. This implies the need to solve them at the structural level in order to ensure high system performances. A dedicated testing setup has been used to test anode-supported cells with different contacting solutions. The contact geometry effect has been evaluated comparing the use of platinum meshes and stamped metallic bipolar plates (Crofer 22 APU) as current collectors. Additionally, the application of a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) paste between the cathode and the interconnect allowed to estimate the beneficial effect of the contacting layer enhancing the current distribution at the cathode side of the cell. The system performances have been investigated by means of current-voltage curves. Electrochemical impedance spectroscopy measurements were carried out to distinguish the loss contributions within the system and study the degradation phenomena. Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction techniques were adopted as post-experiment characterization to investigate microstructural changes and elements migration in order to confirm the observed changes in performances.
Water Splitting on Model-Composite La0.6Sr0.4FeO3-δ (LSF) Electrodes in H2/H2O Atmosphere
Authors: Opitz Alexander Karl , Nenning Andreas , Kogler Sandra , Rameshan Christoph , Rameshan Raffael , Blume Raoul , Haevecker Michael , Knop-Gericke Axel , Rupprechter Guenther , Kloetzer Bernhard , Fleig Juergen
Published: February 2020

Solid Oxide Fuel Cells (SOFCs) attract substantial commercial interest owing to their high efficiency in generating electrical power from fuels such as methane or hydrogen. In recent years, also the research on the inverse process – the conversion of excess electrical energy in chemical energy via Solid Oxide Electrolysis Cells (SOECs) – is gaining more and more attention. As electrode on the reducing side of both SOFCs and SOECs commonly Ni/yttria stabilized zirconia (YSZ) electrodes are used but they are known to suffer from several problems, like sulfur poisoning (in SOFC operation), sintering of Ni particles, poor redox cycling stability, and coking. In contrast, mixed conducting oxide anodes are expected to exhibit improved properties.

In the present contribution the electrode kinetics of the perovskite-type mixed conductor La0.6Sr0.4FeO3-δ (LSF) is investigated in H2/H2O atmosphere by means of impedance spectroscopy and the results are compared to the polarization resistance of LSF in O2 atmosphere. To compensate for the relatively low electronic conductivity of LSF under reducing conditions a sputter deposited Pt thin film grid was used as a current collector. Interestingly, the surface resistances of these model-composite electrodes in H2/H2O and O2 at 600 °C were virtually the same indicating a high electrochemical activity of the LSF surface when operated as SOFC anode.

Moreover, synchrotron-based near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and impedance spectroscopy experiments were conducted simultaneously on electrochemically polarized LSF electrodes. Of special interest was the effect of electrochemical polarization on the composition and valence states of near surface cations of the LSF electrodes. Under cathodic polarization the formation of near-surface metallic iron was observed, accompanied by a strong improvement of the electrode’s water splitting activity [1]. This correlation of metal exsolution and electrochemical performance suggests a fundamentally different water splitting mechanism in presence of the metallic iron species and may provide new directions in the quest for novel mixed conducting SOEC cathodes for high-temperature electrochemical water splitting.

[1]          A. K. Opitz et al., Angewandte Chemie International Edition 54 (2015) p. 2628-2632.

Figure 1
Fabrication of Thin-Film Yttria-Stabilized Zirconia Electrolyte by Aerosol-Assisted Chemical Vapor Deposition
Authors: Jang Dong Young , Kim Manjin , Kim Hyun Joong , Bae Kiho , Kim Jun Woo , Shim Joon Hyung
Published: February 2020

Solid oxide fuel cells (SOFCs) are one of the most promising fuel cells because of their cost-effective materials, high efficiency, and fuel flexibility. However, the high operating temperature of SOFCs (>800°C) hinders their practical use. Performance enhancement by reducing the electrolyte thickness using thin-film deposition techniques may solve this drawback, because the large ohmic resistance of ion transport through the solid electrolyte lattice is the main factor increasing SOFCs’ operating temperature; this can be dramatically decreased with a thin electrolyte. Aerosol-assisted chemical vapor deposition (AACVD) uses aerosol droplets to transport high-mass precursors with reactive carrier gases. AACVD provides the opportunity to produce multicomponent materials at higher deposition rates with a cost-effective system compared to other thin-film deposition techniques. In this work, fully dense thin yttria-stabilized zirconia (YSZ) electrolyte films less than 1 μm thick were successfully fabricated by AACVD on the anode-supported SOFCs. For the AACVD, Zr(acac)4 (acac=acetylacetonate) and Y(acac)3 precursors were used as a solution in ethanol. High-purity N2 was used as the carrier gas, and the substrates were heated to 450°C during the deposition. As a result, good fuel cell performance with a maximum power of 80‒590 mW/cm2 was obtained at 450‒600°C. The details of the microstructures of our films and cells, together with the electrochemical performance evaluated from SOFCs with these AACVD YSZ electrolytes, will be presented at the session.
Single Cubic Phase Scandia-Stabilized Zirconia: Stabilization and Aging at 600oC
Authors: Santos Emanuelle Zangerolame , Muccillo R.
Published: February 2020

Zirconia stabilized with 8-12 mol% scandia shows the highest value of oxide ion conductivity among zirconia-stabilized oxides. However, the cubic-rhombohedral phase transition at approximately 600°C prevents its use as high temperature solid electrolyte. To circumvent this problem, several additives have been proposed. In this work, ZrO2:10 mol% Sc2O3 was mixed to MnO2 to evaluate its effect on cubic phase stabilization, oxide ion conductivity and aging at 600oC. Pressed ceramic pellets of zirconia stabilized with 10 mol% scandia with addition of 1.0, 1.5, 2.0 and 2.5 mol% MnO2 were sintered at 1500 °C/2 h. X-ray fluorescence analysis was carried out to evaluate the manganese content. In situ high temperature X-ray diffraction data were collected to follow the rhombohedral-to-cubic transition. All specimens were analyzed by X-ray diffraction for structural phase evaluation and dilatometry for monitoring shrinkage. Polished and thermally etched surfaces of the sintered pellets were observed in scanning electron and scanning probe microscopes. Impedance spectroscopy measurements were carried out in the frequency range 5 Hz-13 MHz in the 300-500 °C temperature range. The single cubic structure is achieved for the specimen with 1 mol% MnO2 nominal addition, with no traces of the rhombohedral phase present in the ScSZ sintered pellets. The oxide ion conductivity of the YSZ + 1 mol%MnO2 specimen was monitored at 600 oC for 100 days by impedance spectroscopy measurements. After an initial decay, the ionic conductivity value of the solid electrolyte remained constant, suggesting its use as solid electrolyte in SOFCs operating at that temperature.
Standalone Portable SOFC Power Generator for Autonomous Operation
Authors: Reissig Michael , Mathé Jörg , Planitzer Stefan , Vötter René , Rechberger Juergen
Published: February 2020

Since 2002 AVL is working on fuel cells with the focus on mobile and stationary SOFC systems. In 2014 the first completely standalone mobile SOFC power generator fueled with diesel was demonstrated. The system is equipped with all required additional components for autonomous operation like a battery pack and power electronics. During startup, the internal auxiliaries (e.g. the air blower), are consuming energy from the battery pack to heat the stack up to operating temperature. At a certain point the SOFC system starts to produce electricity which is used to recharge the batteries. An external consumer can draw a power of up to 5kW from the system. Short term power peaks (positive or negative) are buffered by a super cap. The operation is automatically controlled by the control unit implementing an energy management system. This enables a very user-friendly operation where the control system takes care of an always sufficient state-of-charge level of the battery pack. The presentation will also give a general status report and outlook of the AVL APU power generator development program.
Evaluation of Gadolinium Doped Barium Zirconate Electrolyte for Solid Oxide Fuel Cell
Authors: de Florio Daniel Zanetti
Published: February 2020

High proton conductivity perovskites can be utilized in many important applications. In this work gadolinium doped barium zirconate ([gadolinium oxide] = 0, 5, 10, 15 and 20% mol) was prepared by Pechini method from nitrates precursors. The powders were studied by simultaneous thermal analysis, X-ray diffraction, and scanning electron microscopy. These powders were then uniaxially pressed at 1 ton/cm2 in cylindrical discs (diameter = 10 mm and thickness ~ 1 mm) and theirs geometrical densities were determined. These pellets were sintered at temperatures of 1773 K/1 h and 1523 K/1 h with and without amounts of boric acid as sintering aid respectively, follow by geometrical and Archimedes density measurements. Phase analysis was carried out by X-ray diffraction, and fracture and polished samples surfaces were observed in scanning electron microscopy. The parallel faces of each sample was painted with platinum paste and electrical characterized by impedance spectroscopy in the frequency range from 32 MHz to 1 Hz, under static air and standard mixture (3% hydrogen/97% nitrogen) flow, in the RT up to 1273 K. The main results indicate that dense (>96 % of theoretical density) barium zirconate perovskite phase was obtained for samples liquid phase sintered with high electrical conductivity.
The Uk's First Commercially Funded SOFC Micro CHP Progarmme: Experience to Date
Authors: Cape Jon
Published: February 2020

Over a three year period iPower has developed and now launched the UK’s first commercially funded fuel cell micro CHP programme. This utilises the SOFC based BlueGEN product. From current information this is also a world first in providing FC CHP free of charge to the user on a commercial basis.

This is not an academic paper. It is a practical paper sett9ng out experience to date with this live commercialisation process.

The presentation will set out key challenges, success factors and learning points from deployment to date under the programme and prospects for future development. It will include independent third party data and case study material.
Utilisation of Coal in Direct Carbon Fuel Cells
Authors: Irvine John , Fuentes Cuesta Aida , Mottram Andrew , Jiang Cairong , Savaniu Cristian , Jain Sneh
Published: February 2020

Hybrid Direct Carbon Fuel Cells merge Solid Oxide Fuel Cell (SOFC) and MCFC technologies, using a solid oxide electrolyte to separate the cathode and anode compartments, while a molten carbonate electrolyte is utilised to extend the anode/electrolyte region. Oxygen is reduced to O2- ions at the cathode and transported across the solid electrolyte membrane to the anode compartment, where carbon is oxidised to CO2. Molten carbonate could enhance the carbon oxidation in two ways as a fuel carrier or as an electrochemical mediator.  The maximum energy density can be achieved by fully oxidising carbon to CO2 offering very high efficiencies. This concept has been demonstrated using a wide range of carbons and carbon-rich fuels such as coal, plastics, carbon colloids, activated carbons and charcoals.  In a short stack of 3 cells delivered a maximum power output at 650oC of 5.4 W, at over 100mWcm-2.

The underlying chemical processes in DCFCs are complex involving a series of catalytic and electrochemical reactions of a complex fuel.  Coal and biochars are quite far from pure carbon comprising of high hydrogen content and often significant oxygen, sulphur and nitrogen contents as well as inorganic, ash components.  Here we report on the pyrolysis and oxidation reactions and processes that occur in situ and in DCFC relevant conditions.  Of key importance is interplay between carbon and its oxides as direct oxidation of carbon to carbon dioxide delivers the ultimate efficiency.  There is a change in process above 750oC where the reverse Boudouard reaction becomes dominant and our focus is on understanding the lower temperature electrochemical processes.
Direct Coal Oxidation in Modified Solid Oxide Fuel Cells
Authors: Deleebeeck Lisa , Gil Vanesa , Ippolito Davide , Campana Roberto , Hansen Kent Kammer , Holtappels Peter
Published: February 2020

Solid oxide fuel cells are fuel flexible in the sense that they can convert a variety of fuels into electricity because of the use of an oxygen ion conducting electrolyte. Traditional solid oxide fuel cells utilize gaseous reactants, such as hydrogen and carbon monoxide, derived from hydrocarbon based fuels, but also ammonia has been reported. A challenge is still the application of this type of cell for the conversion of solid, carbon containing fuels such as coal or biomass derived carbon in terms of pyrolized wood , e.g. charcoal (direct carbon fuel cell (DCFC)). However, several high power densities based on carbon as fuel have been reported for so called hybrid solid oxide fuel cells.

Hybrid direct carbon fuel cells may employ a classical solid oxide fuel cell e.g. using Ni-cermet anodes together with carbon dispersed in a carbonate melt on the anode side. In a European project, the utilization of various coals has been investigated with and without addition of an oxidation catalyst to the carbon-carbonate slurry or anode layer.

The nature of the coal and the catalyst composition affect both open circuit voltage and power output. Highest open circuit potentials and power densities were observed for bituminous coal and by adding manganese oxide or praseodymium-doped ceria to the carbon/carbonate mixture. Comparing the performance of an anode supported (315 micron thick anodes) and cathode supported cells (15 micron thick cathode) indicates a superior performance of the latter cell type when using carbon black as carbon source. Using biomass derived carbon (charcoal) as fuel without an additional catalyst resulted in an open circuit voltage of 984 mV and a maximum power density of 121 mW/cm2, similar to the power output of bituminous coal and using ceria or manganese based catalysts.

Further outlook on the kinetics of the carbon oxidation processes occurring in the vicinity of the anode of these cells will be provided.
Development of a Direct Ammonia Fueled Hydrogen Membrane Fuel Cell
Authors: Aoki Yoshitaka , Kobayashi Syohei , Tsuji Etsushi , Habazaki Hiroki
Published: February 2020

Recently, ammonia has attracted a considerable interest as a prospective carbon-free fuel source for fuel cells due to the low cost, ease in liquefaction and transportation at ambient temperatures, and high volumetric energy density. As for SOFCs, some promising performance has been obtained with the use of ammonia. However, only the hydrogen generated from the thermal decomposition of ammonia serves as the fuel. As a result, the anode material is required to be active for the ammonia decomposition as well as the electro-oxidation of hydrogen. Hydrogen membrane fuel cell (HMFC), which was firstly proposed by Ito et al.,1 consists of an ultrathin proton conducting ceramic electrolyte supported on a dense hydrogen permeable metal anode. The cell facilitates efficient power generation, giving 900 mW cm-2 at 500°C,1 since reduced electrolyte thickness can significantly decreases the ohmic loss at lower temperatures. Hence, HMFC is attractive as a direct ammonia fuel cell system at intermediate temperature range, if the ammonia can be electro-oxidized at the surface of hydrogen membrane anodes. In this study, we studied the ammonia-fueled HMFC based on Pd dense anode supports and BaCe0.8Y0.2O3 (BCY) electrolyte thin films. BCY electrolyte thin films of 1.0 mm thickness were deposited on a Pd foil by RF magnetron sputtering. La0.5Sr0.5Fe0.8Co0.2O3 (LSCF) cathode was screen-printed on BCY and thus, HMFC was obtained. The direct ammonia-fuelced HMFC clearly gives a stable open circuit voltage (OCV) of about 0.9 V and a maximum peak power density of about 100 mW cm-2 at 600˚C.
Preliminary Results on a 5W Portable Butane MT-SOFC Stack As a Battery Charger
Authors: Jung Han Kyu , Hong Jong-Eun , Dhir Aman , Majewski Artur Jacek , Hari Bostjan , Steinberger-Wilckens Robert , Chung Yong Sik , Sung Jae Gi , Chung Jong Shik , Sammes Nigel Mark
Published: February 2020

A microtubular design for a solid oxide fuel cell (MT-SOFC) is studied for use in stacks for high strength and portability. Adapting readily available butane as the fuel source and intermediate temperature operation, MT-SOFC can replace batteries for various portable applications. This work studies the fabrication and preliminary performance results of a 5W MT-SOFC stack using butane as the fuel. The tubes were produced using a standard die extruder into a Ni-ceria-10mol% scandia stabilized zirconia (ScSZ) anode support. A ScSZ electrolyte and a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode were added on top of the tube, respectively, via a dip-coating method. The outer and inner diameters of the unit cell were 3mm and 2mm, respectively. The fabrication process was optimized and the electrochemical properties of a unit cell operated at intermediate (600~700oC) temperature are described. Unit cells were then stacked for an output of 5 watts.

Fig. 1. (a) Pre-sintered anode support MT-SOFC; (b) Fabricated anode support MT-SOFCs; (b) Schematic of 5W MT-SOFC stack.

Acknowledgement

This work was sponsored by KETEP No. 4.0010459.01.

Figure 1
Characterization of Terbium and Samarium Co-Doped Ceria Films as SOFC Electrolyte Prepared by Using Ultrasonic Spray Pyrolysis Method
Authors: Vestli Mihkel , Nurk Gunnar
Published: February 2020

Because of the high ionic conductivity at intermediate temperatures (500–700 °C), doped ceria oxides are of special interest as the promising electrolyte materials for the intermediate temperature solid oxide fuel cells (IT-SOFC). However, main drawback of the ceria based solid electrolytes is the partial electronic conductivity at reducing conditions resulting in an internal partial short-circuiting of the cell and decreased total efficiency for SOFC. Tb, considered an electron trap, was found to suppress the partial electronic conductivity for microcrystalline ceria electrolyte. The aim of this work is to study the influence of Tb and Sm dopant concentration ratio on the microstructural and electrical properties of Ce0.9Sm0.1-xTbxO2-δ films.

Tb and Sm cations binary co-doped ceria films were deposited using the ultrasonic atomizing spray pyrolysis method. The crack-free homogenous films with different dopant concentration were deposited and thereafter annealed at fixed temperatures 900, 1200 and 1300 °C, respectively. It was demonstrated that several microstructural parameters of oxide films are controlled by the sintering temperature. The Ce0.9Sm0.1-xTbxO2-δ films formed were analyzed using X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, atomic force microscopy and four probe dc technique at different pO2 and T values.

Based on the SEM analysis the average thickness of Ce0.9Sm0.1-xTbxO2-δ films were 700 nm. The XRD patterns for the Ce0.9Sm0.1-xTbxO2-δ films annealed at 1200 °C indicated the high degree of crystallinity. Tb dopant ions influence the microstructural properties like median diameter of grain, microstrain, lattice parameter and electrical properties like activation energies of ionic and electronic conductivity of the Ce0.9Sm0.1-xTbxO2-δ film. Significantly higher microstrain value for smallest Tb dopant concentration and strong dependence of electrical properties on that was observed. The activation energy of ionic conductivity was lowered in that case, while the activation energy of electronic conductivity was increased. The lower bound of electrolytic domain for Ce0.9Sm0.09Tb0.01O2-δ film was lowered by one order of magnitude toward lower oxygen partial pressures. Further increase of Tb amount increased the activation energy of ionic conductivity, shifting the lower bound of electrolytic domain toward higher oxygen partial pressures.
Influence of Sintering Additive on the Electrical Conductivity, Chemical Stability and Sinterability of BaCe0.55Zr0.3Y0.15O3-δ
Authors: An Hyegsoon , Shin Dongwook , Choi Sung-Min , Hong Jongsup , Yoon Kyung Joong , Son Ji-Won , Kim Byung-Kook , Lee Jong-Ho
Published: February 2020

Ceramic proton conductors have regarded as an electrolyte materials for the next-generation intermediate-temperature solid oxide fuel cell (IT-SOFC) due to their lower activation energy than oxygen ion conductor in its operating condition. Among those candidates, Ba based perovskite-structured materials such as Yttrium doped BaCeO3 and BaZrO3 are frequently used because of their high proton conductivity. In addition, a discovery of BaCeO3-BaZrO3 solid solution (BCZYs) providing an acceptable compromise between chemical stability and proton conductivity consolidates its recognition as a promising electrolyte material. However, due to the refractory nature of BCZYs, a detrimental in electrical conductivity caused by an inevitable barium deficiency from the high temperature sintering, prohibits its practical utilization, and thus, many of studies were devoted to reduce sintering temperature of BCZYs. Recently it was reported that, even though the exact mechanism was not understood yet, the addition of some transition metal oxide such as nickel oxide, zinc oxide and copper oxide gives a tremendous enhancement in sintering of BCZYs. Moreover, sintering aid-assisted sintered BCZYs have some similarity in resulting feature such as reduced bulk electrical conductivity and enhanced chemical stability which has been expected due to barium deficiency in BCZYs. Recently, solid state reactive sintering (SSRS) in which synthesis and sintering of BCZYs occurs at the same time by employing nickel oxide as a sintering aid, was reported. According to their study, barium deficiency was induced by the formation of barium-transition metal compound (BaY2NiO5) consequently acting as a sintering aid during sintering. Therefore, addition of extra sintering aid with a form of BaY2NiO5 on BCZYs is supposed to be more efficient to prevent barium deficiency. Hence, in order to compare the effect of different form of sintering additives, we investigate the electrical conductivity, chemical stability and sinterability of BaCe0.55Zr0.3Y0.15O3-δ with various types of nickel oxide additives (simple oxide form, NiO and compound form, BaY2NiO5) via dilatometery, DC 4-probe, EIS, XRD and TG/DSC analysis. In this presentation, in addition to the experimental results, possibility and limitation of compound form of sintering aid will be also discussed.
Systematic Parameter Study on the Influence of Humidification and Current Density on SOEC Degradation
Authors: Hoerlein Michael P. , Schiller Guenter , Tietz Frank , Friedrich K. Andreas
Published: February 2020

A special measurement setup with the ability to measure four cells simultaneously in reversible SOEC/SOFC mode was implemented. As preliminary experiment extensive characterization of anode supported Ni-YSZ|YSZ|CGO|LSCF cells provided by Forschungszentrum Jülich was conducted including polarization curves and impedance measurements in the range from 750 °C to 850 °C and fuel gas humidifications from 40 mol% H2O to 80 mol% H2O in SOFC and SOEC mode.

Core of this work is the systematic investigation of the influence of the operating parameters temperature, fuel gas humidification and current density on SOEC long-term degradation and its underlying individual processes. In order to obtain this information a series of five 1000 h experiments with an operating temperature between 750 °C to 850 °C and fuel gas humidification between 40 mol% H2O to 80 mol% H2O was devised. During each measurement over 1000 h four cells are measured simultaneously under identical conditions with the exception of current density where each cell runs galvanostatically with a fixed value between 0 A/cm2 and 1.5 A/cm2.  The progress of degradation was monitored in-situ approximately every 150 h by impedance spectroscopy. It was possible to isolate fuel electrode processes R1+2, an oxygen electrode process R3, a mass transport limitation on the fuel electrode R4 and the electrolyte resistance R0. It could be shown that the processes R0 and R1+2 show a strong correlation between current density and degradation; however the processes R3 and R4 exhibit degradation behavior completely independent of the applied current. Furthermore it could be shown that the oxygen electrode process R3 demonstrates rapid degradation during the first approximately 500 h dominating the overall cell degradation, however slowing down to be negligible after 1000 h.

Post-mortem investigations are being conducted in order to localize and identify the rate limiting processes R0 to R4. In this way we will be able to explain the observed degradation for each process and also validate the observed dependencies ex-situ. Additionally, the remaining long-term experiments are being conducted in order to complete this study and clarify the correlation between degradation processes and fuel gas humidity as well as operating temperature.
Characterization of the Contact Resistance of Cathodic SOFC Contacting
Authors: Udomsilp David , Roehrens Daniel , Menzler Norbert H. , Conradt Reinhard , Guillon Olivier
Published: February 2020

DC conductivity experiments were carried out in order to characterize the area specific resistances (ASR) of various multi-layer-structures that represent the contacting interface between cathode and interconnect of state-of-the-art planar anode-supported SOFCs. The investigation focused on quantifying the influence of various chromium evaporation protection layer materials (MnOx, MnCo1.9Fe0.1O4 (MCF)), perovskitic cathode contact layers (LCC10, LCC12, LSCF), operational parameters during stack joining and the effect of pre-annealing of multi-layer samples on the overall ASR of the model system. The results demonstrated the influence of different material combinations as well as the duration of heat treatment during the joining process on the cell resistance, whereas we did not observe an obvious effect from pre-annealing. During the microstructural post-test analysis we found a coarsened and inhomogeneous microstructure of the MnOx barrier layer, which indicates a strong interaction with the adjacent materials. In addition, the adhesion of those MnOx layers deposited by wet powder spraying is lower when compared to MCF layers deposited by atmospheric plasma spraying, which contributed to long term behavior of the resistances obtained. With these results it is possible to give a recommendation for the choice of contacting and chromium evaporation layer system and the operational parameters during the first heat up of an SOFC stack.
Ceres Power Steel Cell Technology: Rapid Progress Towards a Truly Commercially Viable SOFC
Authors: Leah Robert Timothy , Bone Adam , Lankin Mike , Selcuk Ahmet , Rahman Mahfujur , Clare Andrew , Rees Lee , Phillip Stephen , Mukerjee Subhasish , Selby Mark
Published: February 2020

Ceres Power is continuing to make excellent progress in the development of its low-temperature metal supported SOFC design (the ‘Steel Cell’) based predominantly around the use of ceria. This unique design architecture allows for a robust, low cost, subsidy free fuel cell product, whilst retaining the advantages of fuel flexibility, high efficiency and low degradation.

Over the last year, extensive development and verification of the technology has been undertaken on the latest generation of Steel Cell technology, which offers further enhancements in technology readiness level and manufacturability.  Over the same period, third parties have deepened their testing and development engagements with Ceres Power for a broadening range of market applications at cell, stack, fuel cell module and product levels. This paper provides an update on Ceres’ development, verification approach and latest results.
Effects of Doping on O Ion Migration in Pr2NiO4-Based Oxides
Authors: Aspera Susan Meñez , Sakaue Mamoru , Alaydrus Musa , Linh Nguyen Hoang , Kasai Hideaki
Published: February 2020

Recent studies related to SOFC technology involve materials design on the electrodes and electrolyte layes in search of candidate materials with high O ion conductivity even at lower operating temperatures. This involves understanding the detailed mechanisms of O ion diffusivity at materials which are known to be good O ion conductors at low temperatures. From the many candidate materials, a group of perovskite materials in the K2NiF4 structure has been eyed as promising materials for these purpose, specifically Pr2NiO4-based materials. Interest in the study of Pr2NiO4 and Pr2NiO4-based materials rooted from its potential application as a mixed ionic and electronic conductor (MIEC) as a cathode material for SOFC.

In this study, first principles calculation based on density functional theory (DFT) was used to analyze the structural and electronic properties of Pr2NiO4 and doped Pr2NiO4 systems (Pr2-yRyNi1-x-y-zExTzO4 (R=La, and E=Cu and T=Ga)). With the aim of determining possible Pr2NiO4-based candidate materials for the electrolyte layer, the effects of doping on the migration of O-2 on an assumed promising system was analyzed.

Two types of cation dopant sites were assumed in this study: (1) a large cation dopant substituting Pr, and (2) a smaller cation dopant substituting Ni. For the first case, the effect of La dopants, with different concentrations, on the change in the structural and electronic properties of the host bulk structure was analyzed. It was observed that La dopants have a dominant effects on the change in the lattice parameter along the the c direction due to the difference in ionic radius. This is assumed to be a factor affecting the O ion conductivity within the material. For the second case, co-doping of Cu and Ga (Pr2Ni0.5Cu0.25Ga0.25O4), and doping of Ga (Pr2Ni0.5Ga0.5O4) with different structures were analyzed. For the co-doped system, it was observed that due to nearly similar atomic radii of Cu and Ga, no cation-O atoms elongation were observed. Cu dopants are considered to increase the electronic conductivity of the system. On the other hand, Ga doping shortens the Ga-Oap distance while elongating the Ni-Oap distance, which affects O ion migration through interstisialcy. Furthermore, electronic property analysis also shows that there is a minimal state for the Ga orbitals along the Fermi level as compared with the host Ni atom. And that higher oxidation state of Ga than Ni will tend to cause increased concentration of interstitial O atoms. These results show favorable characteristics for an electrolyte material.
In Situ TEM Temperature Study of Solid State Reaction of Lanthanum Oxide and Chromia
Authors: Karlsson Lisa S , Olsson Claes-Olof A , Lundberg Mats W , Berger Robert , Westlinder Jörgen
Published: February 2020

Rare earth elements like La and Ce are known to improve the corrosion resistance of coated ferritic steels [1, 2]. The solid state reaction between La-rich oxide and Cr2O3 has been studied by x-ray diffraction (XRD) and in situ heating TEM with electron diffraction. The La-rich oxide powder was found to be porous and polycrystalline and would start by healing the pores and forming a transition phase of orthorhombic CrLaO3 [3] before migration of La is found at the interfaces (Figure 1). After full reaction pure La2O3 has been observed by HRTEM in a region initially starting as porous La-rich oxide (Figure 2).

1.            S. Canovic, et al., Oxidation of Co- and Ce-nanocoated FeCr steels: A microstructural investigation. Surface & Coatings Technology, 2012.

2.            M.W. Lundberg, et al., Precoated AISI441 for SOFC interconnectors studied by TEM methods. ECS Transactions, 2013. 57(1): p. 2321-2329.

3.            C.P. Khattak and D.E. Cox, Structural Studies of the (La,Sr)CrO3 System. Materials Research Bulletine, 1977. 12: p. 463-472.

Figure 1
Issues and Challenges of Ni-Rich Layered Lithium Transitional Metal Oxide for High Energy Lithium-Ion
Authors: Cho Jaephil
Published: February 2020

High energy density lithium ion batteries are extremely demanded for portable electronic devices and electrical vehicles. Since the energy density of the batteries rely heavily on the cathode material used, a major effect has been in progress to develop alternative cathode materials with a higher degree of lithium utilization and specific energy density. In particular, layered Ni-rich lithium transitional metal oxides can deliver higher capacity with lower cost compared to the conventional LiCoO2, regarding as the most promising candidates. However, these Ni-rich compounds still have several challenges associated with their intrinsic properties, such as cycle life, thermal stability, and safety issues. There have been numerous breakthroughs to deal with these problems by extensive scientific efforts. In this review, the performance enhancement of Ni-rich cathode materials through structure tuning or interface engineering will be discussed. The underneath mechanisms and remaining challenges will also be discussed for further development to bring these cathode materials from laboratory interest into large scale application.