bluuebunny/crossref_metadata_2025 huggingface dataset:
Update on Nexceris' SOFC Stack Technology
Authors: Arkenberg Gene , Swartz Scott , Sellers Chad
Published: February 2020

Over the past several years, Nexceris has been developing solid oxide fuel cell (SOFC) stacks based on its patented FlexCell planar cell design. The FlexCell is an electrolyte-supported planar SOFC cell design based on a thin electrolyte membrane layer that is mechanically supported by a mesh of electrolyte material, this design enables high performance at targeted operating temperature range of 750 to 850°C. The dense cell periphery provides an optimum sealing surface, and thin anode layers in the FlexCell enable high single-pass fuel utilization without sacrificing performance. Nexceris has demonstrated that SOFC stacks built with this technology are capable of providing targeted power outputs with high single-pass fuel utilization (up to 80 percent), and achieving high efficiencies (45 to 50 percent, LHV basis) when operating on reformed hydrocarbon fuels. More recently Nexceris has leveraged these attributes to establish a stack design which also enables exceptionally high gravimetric power density. Another key capability of Nexceris’ stacks is unprecedented performance and stability with sulfur containing fuels, an enabling attribute for SOFC systems operating on military logistic fuels (such as JP-8). Nexceris’ stacks exhibit stable operation with reformate fuels having as much as 50 ppm H2S, with test durations of 500 hours.

Ongoing work is aimed at designing high efficiency SOFC systems based on Nexceris’ high power density and sulfur tolerant stack attributes. This work is supported by utilizing an in-house built process model which can accurately predict stack and system performance over a wide array of operating conditions (starting fuel, reforming conditions, fuel flow rate and utilization, cell area, number of cells, etc.). Nexceris currently is demonstrating its SOFC technology at 1-5 kW scale via in-furnace stack testing, ex-furnace hot box testing, and breadboard system testing. This presentation will provide a status update on Nexceris’ SOFC technology.
Microstructural and Electrochemical Characterisation of Degradation in Nickel Impregnated Scandia-Stabilised Zirconia Electrode during Isothermal Annealing
Authors: Chen Jingyi , Ruiz-Trejo Enrique , Atkinson Alan , Brandon Nigel P.
Published: February 2020

The impregnation of nickel into porous ceramic scaffolds has been introduced as a promising alternative fabrication technique for solid oxide fuel cell (SOFC) anode as compared to conventional powder mixing [1]. Nevertheless, the stability of impregnated electrodes has not been extensively studied and understood [2]. SOFCs operate at a temperature range from 500 oC to 1000 oC and are expected to have a life time of 40,000 hours [3]. In this study, we examine the degradation of impregnated electrodes in a wet hydrogen atmosphere at a working temperature of SOFCs.

Nickel was impregnated into a porous scandia-stabilised zirconia scaffold through 12 impregnation cycles. The impregnated electrodes contained approximately 40 wt% of nickel. Continuous van der Pauw measurement was carried out when the electrode was aged at 650 oC, 800 oC and 950 oC in an atmosphere with 5 vol% hydrogen and 95 vol% nitrogen, at open circuit. A fall in sheet conductivity was found in the electrode during ageing within 1000 min. The conductivity fall was attributed to nickel microstructural evolution during ageing. Electrochemical impedance spectra were collected at a constant time intervals during isothermal annealing at 650 oC, 800 oC and 950 oC for the impregnated electrode. Four resistance contributions were decoupled by equivalent circuit fitting, i.e. the ohmic resistance, the oxygen transfer resistance and the anodic reaction resistance, and the gas diffusion resistance. The increase in both the ohmic resistance and the polarisation resistances with time revealed the isothermal degradation brought about a diminishing active anode area. A more pronounced decrease in anodic polarisation resistance suggested a reduction in triple phase boundary (TPB) density. Secondary electron images of electrodes before and after ageing showed an increase in nickel particle size and a decrease in the number of particles, providing microstructural evidence of nickel coarsening. Nickel coarsening was identified as the main mechanism of degradation for the electrode in wet hydrogen as it caused a reduction in both TPB sites and percolating nickel paths. Combining time-dependent electrochemical performance with post-mortem electrode microstructure clarifies the physical processes behind the degradation quantified by increasing area specific resistances.

[1] M. Lomberg, E. Ruiz-Trejo, G. Offer, and N. P. Brandon, “Characterization of Ni-infiltrated GDC electrodes for solid oxide cell applications,” J. Electrochem. Soc., vol. 161, no. 9, pp. F899–F905, 2014.

[2] S. P. Jiang, “Nanoscale and nano-structured electrodes of solid oxide fuel cells by infiltration: Advances and challenges,” Int. J. Hydrogen Energy, vol. 37, no. 1, pp. 449–470, Jan. 2012.

[3] H. Tu and U. Stimming, “Advances, aging mechanisms and lifetime in solid-oxide fuel cells,” J. Power Sources, vol. 127, no. 1–2, pp. 284–293, Mar. 2004.
Coke Resistant and Sulfur Tolerant Ni-based Cermet Anodes for Solid Oxide Fuel Cells
Authors: Li Meng , Hua Bin , Jiang San Ping , Li Jian
Published: February 2020

Conventional Ni-based cermet anodes of solid oxide fuel cells (SOFCs) are highly susceptible to deactivation from carbon deposition and sulfur poisoning in sulfur-containing hydrocarbon fuels. Here we propose a viable approach to substantially enhance the carbon deposition resistance and sulfur tolerance of the Ni-gadolinia doped ceria (Ni-GDC) anode. Perovskite BaCe0.9Yb0.1O3-
δ (BCYb) is adopted to modify Ni-GDC anode via wet impregnation. Since BCYb nanoparticles could selectively deposit on Ni surfaces in a Ni-GDC anode backbone, a slight amount of infiltrates could lead to the excellent modification of the Ni grains without blocking the gas diffusion channels. The deposited BCYb nanoparticles decrease the exposed surfaces of Ni grains, showing promise to inhibit carbon deposition and sulfur species adsorption. BCYb has high oxygen ion conductivity, beneficial to the transportation of oxygen ions to remove the adsorbed carbon and sulfur (Fig. 1). Therefore, the stability of conventional Ni-GDC anode in wet methane fuel (3% H2O in CH4) is remarkably improved with modification of BCYb nanoparticles. The voltage of a full cell with conventional Ni-GDC anode decreases rapidly from 0.58 to 0.15 V within 6 h at 200 mA cm-2 and 750 °C. While in the case of a cell with BCYb modified Ni-GDC anode, designated as B+Ni-GDC, the cell voltage is essentially constant at around 0.65 V over a period of 48 h tested under identical conditions. Furthermore, the impregnation of BCYb nanoparticles can also improve sulfur poisoning resistance of Ni-GDC anode. The enhanced stability is observed in 500 ppm of H2S/H2 at 650 °C. The B+Ni-GDC anode manages to retain its microstructure in CH4 and H2S-containing H2 fuels, resulting in stable performance output. In addition, the electrochemical performance of Ni-GDC anode is also improved with BCYb modification in both wet H2 and CH4 fuels. The BCYb impregnation approach shows promising potential in the development of highly active and stable Ni-GDC based anodes for direct hydrocarbon SOFCs.

Figure 1. Schematic diagram showing carbon and sulfur removal processes on BCYb modified Ni-GDC anode.

Figure 1
Automated SOFC Design Exploration
Authors: Lueth Christopher A , Walchshofer Christian F
Published: February 2020

Fuel cells are a clean alternative to internal combustion engines and many experts consider them to be the future of ground-transportation. Solid oxide fuel cells are already heavily used in Japan for clean energy grid storage applications. Unlike combustion of hydrogen and oxygen that only generates heat, electrochemical reactions of hydrogen and oxygen may be separated to harness ion and electron transport for high efficiency energy conversion.

We present computer automated engineering of fuel cell stack design to maximize power production and minimize energy losses. Validated cell models are applied to 3-D stack simulations, where optimization algorithms obtain better designs, faster. Each simulation conserves flow, energy, species, and charge transport using efficient sparse segregated solvers. Automated workflows and state-of-the-art search algorithms allow for fast design space exploration of fuel cell material properties, dimensions, and boundary conditions. Bibliography

[1]
O. R. J. G. a. J. M. V. Costa-Nunes, "Comparison of the performance of Cu–CeO 2–YSZ and Ni–YSZ composite SOFC anodes with H 2, CO, and syngas," Journal of power sources, vol. 141, no. 2, pp. 241-249, 2005.

[2]
F. Scholz, "Thermodynamics of electrochemical reactions," Electroanalytical Methods. Springer Berlin Heidelberg, pp. 11-31, 2010.

[3]
A. D. S. B. B. a. J. G. P. Le, "Validation of a Solid Oxide Fuel Cell Model on the International Energy Agency Benchmark Case with Hydrogen Fuel," Fuel Cells, vol. 15, no. 1, pp. 27-41, 2015.

[4]
S. G. Bratsch, "Standard electrode potentials and temperature coefficients in water at 298.15 K," Journal of Physical and Chemical Reference Data , vol. 18, no. 1, pp. 1-21, 1989.

Figure 1: In solid oxide fuel cells, hydrogen fuel diffusing through the porous anode (left) reacts with oxygen ions traveling across the electrolyte membrane separator (middle) and produce electrons conducting through the solid porous cathode (right). Power is generated by flow of electrons from anode through an external circuit to the cathode (top), where they recombine with oxygen, in the air feed diffusing through the porous cathode, to repopulate membrane oxygen ions.

Figure 1
Computational Analysis of Dynamic Tubular SOFC with a Built-in Chemical Iron Bed
Authors: Jin Xinfang , Guo Meng , White Ralph E. , Huang Kevin
Published: February 2020

Solid oxide fuel cells (SOFCs) with enhanced fast ramping power capability and overload tolerance can find important applications in grid frequency regulation and data center overload protection. Recently, we have demonstrated a new SOFC configuration featuring a built-in chemical Fe-bed in the anode chamber of a tubular SOFC and exceptional fast power ramping and overload tolerance. In this presentation, we showed our theoretical understanding of the enhanced dynamic performance through a two-dimensional axial symmetrical numerical model. The model couples the charge and mass transport in the tubular SOFC with chemical reaction kinetics in the Fe-bed, producing axial distributions of Nernst potential, H2O/H2 molar ratio, local current density and fuel utilization under different operating conditions. The crucial role of Fe-bed in providing instant fuel to support fast ramping and overload currents has been explicitly explained by this computational model.
Multi-Physics Simulation of SOFC Button Cell with Multi-Step Charge Transfer Model in Composite LSM/YSZ Cathode
Authors: Yang Tao , Liu Jian , Finklea Harry O. , Abernathy Harry , Hackett Gregory A
Published: February 2020

In the present study, numerical simulation of a solid oxide fuel cell (SOFC) button cell with a multi-step oxygen reduction reaction (ORR) mechanism in a composite cathode was developed for better understanding of processes within the SOFC. The ORR mechanism involves both surface charge transfer through triple phase boundary (3PB) and bulk charge transfer via a two phase boundary (2PB) pathway. The developed multi-physics simulation considered the charge conservation and species transportation through porous media. The developed simulation was first applied to a dense thin film study only involving surface adsorption and the 2PB pathway. By calibrating the simulation with measurements of dense thin film cathodes, the kinetic rates of rate-determining steps in ORR model were decided. Finally, the simulations of full SOFC button cell were calibrated with measured cell performance (polarization curves and impedance behavior) at three different air/fuel utilization conditions. It was found that it is beneficial to determine the kinetic rates of rate-determining steps in a multi-step charge transfer model before calibrating the simulations for full cell system. With the determined rates, the various performance of different cells can be attributed to the microstructure versus material variations. Therefore, the present study not only helps better understand the details of processes in SOFC but also provides guidance for electrode design and manufacturing.
Determination of Temperature and Fuel Utilization Distributions in SOFC Stacks with EIS
Authors: Tallgren Johan , Boigues Muñoz Carlos , Mikkola Jyrki , Himanen Olli , Kiviaho Jari
Published: February 2020

Efficient operation of solid oxide fuel cell (SOFC) stacks requires uniform temperature and fuel utilization distributions in the stack. Especially high fuel utilizations (FU) necessitate uniform fuel flow distributions to avoid anode redox of the cell with the highest local FU. A uniform temperature distribution helps to prolong the life-time of the stack. Knowledge about such distributions would aid in both stack design and in monitoring the “state-of-health” of stacks. This work presents a method to determine the fuel utilization and temperature distribution in SOFC stacks with electrochemical impedance spectroscopy (EIS). EIS is a powerful and non-destructive technique that enables an in-depth analysis of the stack in-operando. The equations for relating the measured impedance and fuel utilization and temperature are derived from common equations describing the SOFC stack. Thus, the relations are anchored in physical processes. The method is demonstrated with an ElringKlinger AG 10-cell stack at nominal operation conditions. The difference in fuel flow, i.e. fuel distribution, and temperature between individual cells was determined. The temperature distribution exhibits a stack effect, where the top and bottom-most cells are the coldest, and is in line with the cell voltages. The paper evaluates the method and its usability in SOFC research.

The NELLHI (grant agreement no. 621227) and INNO-Sofc (grant agreement no. 671403) projects, which have received funding from the European Union’s Fuel Cells and Hydrogen Joint Technology Initiative, are acknowledged. Additionally, the STEP project, funded by the Finnish Funding Agency for Innovation TEKES and Projekträger Jülich (Germany), is acknowledged.
Short Stack Kit for the Open Flange™ Set-up Using Soft Mica Seals
Authors: Coquoz Pierre , Coton Noelia , Cottier Florian , Pappas André , Middleton Hugh , Ihringer Raphaël
Published: February 2020

Fiaxell has been active since 2008 in the Solid Oxide Fuel Cells (SOFC) industry and has been developing components and products for SOFC research.

Fiaxell is the inventor of the “2R-Cell”, an anode supported cell able to withstand full re-oxidation and thermal cycles. The 2R-Cell is robust and has demonstrated high fuel utilization (85-90%) and electrical efficiency up to 50% with pure hydrogen on button cells.

Fiaxell has developed the Open Flange™ Set-Up in order to test SOFC and SOEC cells. The Set-Up allows researchers to do various experiments, such as current-voltage characteristics, polarization, impedance spectroscopy measurements, electrolysis, co-electrolysis and in situgas processing (POX, SR) thanks to its integrated steam generator.

Fiaxell is now offering a complete short stack kit that can be directly mounted onto the Open Flange™ Set-Up platform.

This kit allows researchers to perform a range of experiments and to study stack parameters such as flow distribution, electrical contact resistance, and to investigate protective coatings to avoid chromium evaporation, in situfuel processing and sealing gas tightness. Each parameter can be independently characterized and optimized by combining ideal and real stack conditions on both sides of the cell, for instance Crofer steel on the anode and gold mesh on the cathode.

Fiaxell is proposing Crofer 22H interconnects with different flow pattern designs for 50 X 50 mm and 80 X 60 mm cells. Alternatively, customers can propose their own customized design which can then be chemically grooved and laser cut by Fiaxell. The short stack kit comes with soft mica sealing but can also be made gas tight with any glass paste or other sealants. The soft mica seals have been designs to be easily removed and replaced, contrary to the use of glass based sealants that require mechanical grinding to remove.

Mechanical simulations and calculations have been made to ensure that the design of the end Flange™ is adequate to compress the entire stack without any distortion or stress concentration points, especially on the interconnect plates.

In order to see the gas distribution in the interconnect pattern, Fiaxell has developed an alternative, and complementary method to simulation, which consists of direct visualization and image analysis of the real flow motion. Screen captures will be included and discussed.

In this paper, we present the experimental results of the short stack tests using two different interconnect patterns and also discuss the effectiveness of the soft mica gasket seals.

Image caption: Exploded view of
two
cells short stack showing the three bipolar plates (interconnect) and soft mica gaskets (in beige). The short stack has been designed as a kit to be integrated directly on the Open Flange™ Set-Up platform.

Figure 1
Sulfur Poisoning of Ni/CGO Anodes: A Long-Term Degradation Study
Authors: Riegraf Matthias , Costa Rémi , Schiller Guenter , Friedrich K. Andreas
Published: February 2020

Although continuous progress is achieved with respect to lifetime and performance improvements, solid oxide fuel cells (SOFC) continue to struggle with commercialization. One important factor to possibly reduce overall costs of SOFC systems would be the omission of desulfurization units during the fuel processing. However, sulfur-containing impurities in the most common fuels such as natural gas and biogas lead to significant performance drops upon exposure to Ni-based anodes. In this regard, it has been shown that Ni/gadolinium-doped ceria (CGO) anodes display lower performance drops upon short-time sulfur exposure than Ni/YSZ. However, their long-term resistivity towards sulfur exposure has not been investigated so far, although this is likely to be the most vital factor determining SOFC lifetime.

This work presents the first in-depth analysis of long-term degradation due to sulfur poisoning of Ni/CGO10-based SOFC. A parameter study of the sulfur-induced long-term degradation of commercial, high-performance single cells was conducted with an accumulated cell testing time of more than one year. The long-term degradation behavior is investigated at 900 °C for different H2S concentrations and varying H2/H2O/N2 fuel gas atmospheres. The sulfur poisoning periods of the different cells varied from 100 up to 1500 h. The progress of the degradation during the experiments was monitored by means of electrochemical impedance spectroscopy.

It is shown that Ni/CGO anodes can be exposed to 10 ppm H2S and operated without significant irreversible degradation at a current density of 0.5 A·cm–2 for 1500 h for certain fuel gas mixtures, demonstrating their promising long-term stability. However, for reduced hydrogen partial pressures in the fuel gas, the same H2S concentration leads to a considerable voltage decrease that is reflected by an increase in anode charge transfer and ohmic resistance. Furthermore, the microstructural evolution of the Ni/CGO is examined ex-situ by means of SEM and correlated to the anode performance degradation. The existence of a stable operating regime for Ni/CGO anodes under sulfur exposure is clearly shown and the critical operating parameters are outlined. The presented results give important insights into the degradation processes occurring during long-term operation of Ni/CGO anodes as well as strategies for stable SOFC operation. Moreover, the results encourage to further optimize the performance and sulfur tolerance of Ni/CGO anodes.
Electrochemical Performance of Solid Oxide Electrolysis Cells with LSCF6428-SDC/SDC Electrode for H2O/CO2 High Temperature Co-Electrolysis
Authors: Yoo Young-Sung , Jeon Sang-Yun , Park Min-Ah , Lee Jungmin , Lee Younghee
Published: February 2020

High temperature co-electrolysis of H2O/CO2on solid oxide electrolysis cell (SOEC) is one technology to produce syngas using carbon dioxide. In this study, Ni-8YSZ/8YSZ/LSCF6428-SDC button cells were fabricated and the effect of different heat treatment temperatures on the performance of SOEC was investigated. The SOEC with LSCF6428-SDC air electrode, SDC buffer layer, and YSZ-(LSCF- SDC) adhesion layer gave better performance in overall results and the voltage obtained for this SOEC at current density of 0.8 A.cm-1 was from ~ 1.2 V to ~ 1.8 V. Co-electrolysis and the electrochemical performance of the cells were dependent on heat-treatment temperature of the electrode and the buffer layers. To identify the electrochemical processes occurring at the electrodes of SOEC, analysis of the electrochemical impedance (EIS) data was carried out.
The Exploration of Working Reactions for Electrolysers Using Statistical Mechanics
Authors: Williams Mark C , Richards George , Gemmen Randall
Published: February 2020

This brief thermodynamic analysis theoretically explores the performance of an electrolyser for various working reactions (WR). The electrolyser cell (EC) system is composed of an electrolyser and heat engines. The lowest electrical requirement for working reactions for electrolysis will have the highest possible Carnot temperature, Tc , and ∆T∆rS(T) values needed to minimize ΔG and maximize the amount of thermal that could be converted to chemical energy in an electrolyser. In addition, reactions with multiple products and few reactants create additional entropy, that is, many high entropy products coming from a few low entropy reactants, are optimal. A procedure using statistical mechanics was developed and employed to locate optimal WR’s focused on the values of ΔrSo, Tc, and the number of products and reactants. The research and development direction for electrolyser WR’s is discussed.
Long Term Tests of Ni-YSZ|YSZ|GDC|Pr0.6Sr0.4CoO3-δ in SOFC and SOEC Regimes
Authors: Nurk Gunnar , Kukk Freddy , Kanarbik Rait , Möller Priit , Lust Enn
Published: February 2020

Stability of electrochemical performance in time is one of the most important properties of SOFC/SOEC materials looking from the commercialization point of view. Long term characterization is resource consuming and therefore only commercially more interesting compositions are tested in time range of several thousand hours [1]. However, for better understanding of reasons and mechanisms of degradation processes alternative materials should also be tested in addition for the more attractive ones.

Pr0.6Sr0.4CoO3-δ (PSC) is an alternative material for widely used La0.6Sr0.4CoO3-δ
with excellent activity as medium temperature SOFC cathode. However, so far there is lack of long-term test results for PSC. This study concentrates on the long term electrochemical characterization and microstructural post-test analysis of Ni-YSZ|YSZ|GDC|Pr0.6Sr0.4CoO3-δ
5 × 5 cm single cell, where YSZ is the yttria stabilized zirconia and GDC is the gadolinia doped ceria. Performance test conducted in SOFC mode at 650 °C and at cell potential 0.85 V was 17820 h long. Initial degradation of electrochemical performance was 2.6 % per 1000h. During second half of experiment degradation was only 1% per 1000h. Total power loss during test was 34.6 %. Moderate increase of total activation energy Etot at 0.8 V cell potential takes place (ΔEtot = 0.38 eV) and it increases from 0.57 eV to 0.95 eV. At 1V cell potential ΔEtot = 0.22eV, from 0.34 to 0.56 eV. Post mortem HR-SEM and TOF-SIMS analysis of tested cell has been performed and collected data show that minor structural changes caused by nickel coarsening in porous anode have been taken place. TOF-SIMS mappings of 5 × 5 cm electrode visualize the mobility of Sr from cathode into the electrolyte interface during electrode preparation. Some mobility of Si from gas-sealing glas to electrode as well as Cr deposition from Crofer 22APU current collector into electrode surface has been established.

[1] L. Blum, U. Packbier, I. C. Vinke, L.G. J. de Haart, Fuel Cells,
13 (4) 646-653
Performance Characterization of Glass-Ceramic Sealants in Dual Atmosphere Environment for Reversible Solid Oxide Cell (R-SOC) Applications
Authors: Ferrero Domenico , Sabato Antonio Gianfranco , Javed Hassan , Lanzini Andrea , Herbrig Kai , Walter Christian , Santarelli Massimo , Smeacetto Federico
Published: February 2020

Reversible Solid Oxide Cells (RSOCs) are a promising technology for electrical energy storage through hydrogen – a flexible multi-purpose energy carrier. A key component of planar stacks of cells is the sealant joining the cell to the interconnect, which must be chemically and physically stable and ensure gas tightness between oxidizing (air) and reducing atmospheres (H2).

Novel glass-ceramics compositions for a working temperature of 850 °C were designed and characterized in terms of sintering capability, thermal and thermomechanical properties. Crystalline phases and different amounts of residual glassy phase were tailored in order to assure a good thermomechanical compatibility with a Crofer22APU interconnect. The gas tightness of the glass-ceramic sealant has been tested in a dual atmosphere environment at 800 °C and nearly atmospheric pressure. Samples comprising of two plates of interconnect material (Crofer22APU) have been joined together by the sealant and have been exposed to air on one side and H2/steam on the other side to investigate the gas leakage rate through the sealant. The leakage rate has been evaluated by measuring the volumetric gas flow rate at the outlet of each chamber. The gas tightness of the sealant has been tested in relevant RSOC conditions at different pressure gradients between the two atmospheres (from 5 mbar to 50 mbar), flow rates and H2/H2O ratios.

The compatibility between the glass-ceramic sealants and the Crofer stainless steel (bare and pre-oxidised) is reviewed and discussed by means of SEM and EDS analysis before and after the dual atmosphere tests.
A Reactive Force Field (ReaxFF) for Molecular Dynamics Simulations of NiO Reduction in H2 Environments
Authors: Oberhoffer Simon , Iskandarov Albert M , Umeno Yoshitaka
Published: February 2020

Ni/YSZ cermet is a widely used SOFC anode material, particularly due to its combination of good electric conductivity, high catalytic activity and low cost. Nonetheless, Ni/YSZ cermet anodes are facing unique challenges such as nickel agglomeration and reoxidation, eventually resulting in anode degradation. A solution to these problems might be obtained via a better comprehension of the underlying manufacturing processes, particularly the final H2-induced reduction reaction of NiO to Ni. Experimental approaches have contributed immensely toward a better understanding of these phenomena, yet are generally limited in terms of spatial and temporal resolution, thus motivating us to investigate the problem from a multiscale simulation viewpoint. In this study, we developed a reactive force field (ReaxFF) for nickel/oxygen interactions, which was specifically tailored toward molecular dynamics (MD) simulations of NiO reduction in H2 environments. The force field parameters were derived by fitting the ReaxFF energies and forces of various nickel/oxygen structures to the respective values of first-principles calculations. The structures considered here include bulk NiO, Ni2O3 and Ni3O4 at various densities, NiO under shear, the NiO(100) surface, oxygen vacancies in bulk and surface NiO as well as oxygen adsorbed onto the NiO(100) surface. The developed force field was subsequently used to predict the reduction kinetics of nano-scale NiO crystals in a H2 atmosphere at different temperatures and hydrogen partial pressures. Here, we observed a significantly improved structural stability of bulk NiO at temperatures over 700 K, compared to our previous ReaxFF nickel/oxygen description [1] and similar ReaxFF parameter sets published by other authors [2]. Besides quantifying the reduction rate, further core phenomena such as the induction period before the onset of a steady state reduction process, the pore formation in NiO at lower temperatures, as well as the importance of oxygen vacancies during the reduction are discussed and compared with experimental results.

Fig. 1 NiO nanocrystal after 0.2 ns of MD reduction simulation at a global temperature of 850 K and hydrogen partial pressure of 10 bars, using our previous ReaxFF parameter set (left) and the parameter set introduced in this publication (right).

References

[1] Oberhoffer, S., Iskandarov, A., Umeno, Y., "Reduction of NiO in a H2 Environment: A ReaxFF Molecular Dynamics Study",2016 Asian SOFC Symposium (2016.09.04-07), The University of Tokyo, Japan.

[2] Zou, C., Shin, Y. K., van Duin, A. C., Fang, H., Liu, Z. K. "Molecular dynamics simulations of the effects of vacancies on nickel self-diffusion, oxygen diffusion and oxidation initiation in nickel, using the ReaxFF reactive force field.", Acta Materialia 83 (2015): 102-112.

Figure 1
Engineering FEA Sintering Model Development for Metal Supported SOFC
Authors: Chatzimichail Rallou , Dawson Richard , Green Sarah , Sullivan Daniel , 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.

Predicting the thermal stress and deformation evolution during processing is important in the design and manufacture of metal supported SOFC. This leads to reduced waste during manufacturing and feeds into cell and stack designs to produce low stress and mechanically robust modules for high performance and excellent durability.

In a collaboration between Ceres Power and Lancaster University, funded by Innovate UK, an engineering FEA model is being developed to understand the manufacturing processes, such as the densification of the ceria based electrolyte. In such models material properties, such as the Thermal Expansion Coefficient, Young’s Modulus, layer densification rates and creep, are very important. These properties, when interacting with the applied thermal processes, give rise to stresses within the layers resulting in permanent deformation and residual stresses at the end of the process step at room temperature.

We will present results using the developed modelling techniques in example metal supported SOFCs to demonstrate the importance of the above mentioned properties. Sensitivity study results will be also presented to show the impact of variability of the material properties.
Pore-Scale Analysis of Diffusion Transport Parameters in Digitally Reconstructed SOFC Anodes with Gradient Porosity in the Main Flow Direction
Authors: Espinoza Mayken , Sundén Bengt , Andersson Martin
Published: February 2020

One of the promising devices to obtain electrical and thermal energy with considerable high efficiency is the solid oxide fuel cell (SOFC). The electrical energy is the result of the electrochemical reactions that occur inside the fuel cell (FC) when the reactant gases gases reach the so-called three-phase boundary (TPB). The non-homogeneous and anisotropic characteristics of the layer between the gas channel and the TPB region requires a pore-scale analysis to understand the effect of microstructural configurations. The purpose of this paper is to understand the behavior of the fluid flow through the digitally reconstructed SOFC anodes, with gradient porosity in the main flow direction, using the lattice Boltzmann method (LBM). The impact of the porosity distribution over the fluid behavior is determined for different digitally created SOFC anodes. The SOFC anodes are analyzed keeping the total porosity constant, but varying the local porosity in the flow direction. The impact of a gradient porosity over the gas-phase tortuosity and the normalized effective diffusion coefficient are presented.
An Efficient Ge and Sm Co-Doped Ceria Nanocomposite Electrolyte for Low Temperature Solid Oxide Fuel Cells
Authors: Raza Rizwan , Arshad Sarfraz
Published: February 2020

Electrochemical studies of Fuel cell with different composite electrolyte

In this paper, three composite electrolytes (Ce0.8Sm0.2O1.9/Na2CO3) SDC, (Ce0.8Gd0.2O1.9/Na2CO3) GDC and (La0.8Sr0.2Ga0.8Mg0.2O3−δ/Na2CO3)LSGM nanocomposite electrolytes have been studied, also see the effect of Na2CO3, present as second phase, and effect of Ni support, sintering and pressure for dry pressing for fuel cell performance. The electrolytes were prepared through co-precipitation method. Different techniques were used to characterize the prepared electrolytes. The crystal structures were determined using x-ray diffraction (XRD) and structural morphologies were analyzed through scanning electron microscopy (SEM). The four probe dc conductivity and two probe AC impedance analysis were carried out in open air. The fuel cell performance was determined with and without Nickel support on anode side which resulted in a considerable difference in obtained peak power densities. It is suggested that prepared electrolytes can find potential applications in low temperatures Solid Oxide Fuel Cells (LT-SOFCs).

Key words: nanocomposite, LTSOFCs, Crystal structure, SDC, Sintering
Reducing the Gadolinium Dopant Content by Partial Substitution with Yttrium in a Ce0.9Gd0.1O1.95-based Oxide-Ion Conductor
Authors: Mori Masashi , Sumi Hirofumi , Suda Eisaku
Published: February 2020

Because of its high oxide-ion conduction and the chemical inactivity, Ce1-xGdxO2-δ fluorites are used as a reaction protection layer between the electrode and the ZrO2 electrolyte and addition materials to electrode elements for intermediate-temperature SOFCs. The rare-earth ores have 17 kinds of rare-earth elements including Sc and Y. However, Gd exists a low mineral content in the ores. Gadolinium element is used as magnetic devices, magnetooptic disk device, and control rod of the nuclear reactor. Under the present conditions, demand for Gd increases.

The conductivity and sintering characteristics are very important as SOFC components and it is well known that two typical compositions, Ce0.9Gd0.1O1.95 and Ce0.8Gd0.2O1.9, have be commercially available. Although many papers for the properties have been reported, the appropriate compositions of Gd are unclear. The reason for this is that the properties are strongly affected by synthesis methods and sintering conditions.

In the present study, the appropriate compositions of Gd-doped cerias with a Gd content of 0 ≤ x ≤ 0.2, which were prepared using the conventional co-precipitation method, have been discussed from the viewpoint of sintering characteristics, electrical conductivity and its long term stability. Sintering characteristics of the doped ceria samples have a tendency to decrease with increasing Gd content. The maximum conductivity of 2.56×10-2 S/cm at 600ºC was observed for the sample with 10 mol% Gd dopant. During the annealing process at 600ºC, the conductivity decreased with annealing time due to the grain-boundary resistance. The synchrotron X-ray diffraction analysis showed to be Gd2O3 phase in the fluorite and the decrease of lattice parameter. These results suggest that the decrease of the conductivity should be related to the segregation of Gd element at the grain-boundary of the Ce0.9Gd0.1O1.95 fluorite.
Low Temperature Synthesis and Properties of Gadolinium-Doped Cerium Oxide Nanoparticles
Authors: Machado Marina F. S. , Moraes Leticia P. R. , Monteiro Natalia K , Esposito Vincenzo , de Florio Daniel Zanetti , Marani Debora , Fonseca Fabio C.
Published: February 2020

Gadolinium-doped cerium oxide (GDC) is an attractive ceramic material for solid oxide fuel cells (SOFCs) both as the electrolyte or in composite electrodes. The Ni/GDC cermet can be tuned as a catalytic layer, added to the conventional Ni/yttria-stabilized zirconia (YSZ), for the internal steam reforming of different fuels. Such an anode allows the SOFC to operate with hydrocarbon fuels by internal reforming. GDC exhibits high oxygen ion conductivity at a wide range of temperatures and displays a high resistance to carbon deposition. However, an inconvenience of ceria-based oxides is the high sintering temperature needed to obtain a fully dense ceramic body, which can result in undesired reactions with YSZ. In this study, a green chemistry route for the synthesis of 10 mol% GDC nanoparticles is proposed. Such a low temperature synthesis provides control over particle size and sinterability of the material. The aqueous precipitation method starts from the nitrates of both cerium and gadolinium and uses excess hexamethylenetetramine (HMT) to produce crystalline GDC at 80 ºC. As-produced powders were found to be GDC crystalline fluorite-type structure, with crystallite size ≤ 10 nm. Thermalgravimetric analysis show a small mass loss and dilatometry profiles show a total retraction of ˃ 20% up to 1400 °C. The electrical properties of the material were studied by impedance spectroscopy measurements of sintered samples in a controlled atmosphere. The samples sintered for 2 hours at 1400 °C exhibited electrical conductivity comparable to previously reported data for GDC.
Fabrication of BaZr1-XYxO3 Powder by Freeze Drying Method
Authors: Kato Tohru , Momma Akihiko , Yoshioka Ayumi , Terayama Takeshi , Tanaka Yohei
Published: February 2020

BaZr1-xYxO3 is an attractive electrolyte material for low operating temperature SOFCs and SOECs because of its high proton conductivity at temperature less than 600 oC and good chemical stability under CO2 and steam atmospheres. However, its high synthetic temperature more than 1100 oC and the high sintering temperature more than 1,600 oC to get a dense electrolyte membrane cause mismatch of the shrinkage behavior and reaction with other SOFC or SOEC component materials at the fabrication process.

Therefore, in this paper, reducing the synthesizing temperature of BaZr1-xYxO3 powders by freeze dry method has been tried. In the freeze dry process, Ba(NO3)2, ZrO(NO3)2 nH2O, Y(NO3)3 nH2O were chosen as low materials. The hydration numbers of ZrO(NO3)2 nH2O and Y(NO3)3 nH2O were measured by using a differential thermogravimetric analyzer. These nitrates were mixed to produce solution with the molar ratio of metal ions what we desired. The solution was atomized and frozen rapidly by using liquid nitrogen to avoid segregation. The frozen solution was dried under vacuum condition at temperature of about -40 oC. After finishing sublimation, obtained frozen powder was heated and synthesized at the temperatures of 600 to1000 oC. As a result of X-ray diffraction analysis and energy dispersive X-ray spectrometry, it is clarified that BaZr1-xYxO3 can be synthesized at 800 oC which is lower more than 300 oC than conventional synthetic temperature. We are to report the possibility of reducing the sintering temperature of BaZr1-xYxO3 by using obtained powders and properties of the sintered BaZr1-xYxO3 such as the conductivity.
Study of Sr2MgMo0.9Ni0.1O6-δ as SOFC Anode
Authors: Dager Paola Katherine , Mogni Liliana Veronica , Zampieri Guillermo , Caneiro Alberto
Published: February 2020

The double perovskite Sr2MgMoO6 (SMMO) has attracted the attention to be used as SOFCs-anode because, despite its poor electrical conductivity, it exhibits high electrocatalytic performance for H2-oxidation, sulphur tolerance and thermal stability. This mixed oxide provides multiple positions for doping (Sr, Mg and Mo-sites) and promotes oxygen vacancies formation, which allows to improve its properties such as chemical stability, electrical conductivity, etc. In present work, the Mo-site of SMMO was doped with Ni, in order to gain understanding of the structure, chemical and electrochemical properties of Sr2MgMo0.9Ni0.1O6-δ
 (SMMNi). The undoped sample (SMMO) was tested to comparison. The SMMNi and SMMO powders were synthesised by combustion method and thermally treated in air at 1000 and 1100 ºC respectively during 12 h. These materials were characterised by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). XRD patterns for SMMNi powders confirmed the formation of a well-defined double perovskite phase belonging to the space group I-1. TEM micrographs show that SMMNi powders had a mean grain size around 340 nm. The surface analysis of SMMNi and SMMO powders were carried out by XPS on as-synthesised and post-reduced at 800 ºC in 10%H2-Ar for 10 h. Results demonstrated that Mo6+ ions in SMMNi had been reduced to Mo5+after calcined in 10%H2-Ar. Furthermore, XPS spectra exhibited no apparent change in oxidation state of Nickel after subjecting to SMMNi-powders to a reducing atmosphere. The stability studies indicate that SMMNi is more unstable in comparison to SMMO, under 10%H2-Ar. Whereas SMMO remains stable until 1000 ºC, SMMNi decompose above 900 ºC. Additionally, electrochemical impedance spectroscopy (EIS) measurements on symmetrical SMMNi/GDC/SMMNi under reducing atmosphere at 700 ºC allowed seeing the influence of the time and environment conditions (H2 content) in the anode polarisation resistance (Rpa). The aforementioned could be seen in Fig. 1, where the Rpa decreases from 3 to 0.4 Ωcm-2 as pH2 increases from 0.05 to 1 atm. These values are up 5 times higher than those for SMMO in the same conditions.

Figure 1
Nanostructured SOFC Electrode Scaffolds Prepared via High Temperature in situ Carbon Templating of Hybrid Materials
Authors: Muhoza Sixbert P , Barrett Taylor E , Soll Sydney E. , Gross Michael D
Published: February 2020

High surface area, nanostructured solid oxide fuel cell (SOFC) electrode scaffold materials were prepared at traditional sintering temperatures by heating hybrid inorganic-organic gels in an inert atmosphere. The prepared materials were yttria-stabilized zirconia (YSZ, 8 mol% Y2O3), gadolinium doped ceria (GDC, Gd0.2Ce0.8O3-δ) and strontium titanate (STO, SrTiO3). YSZ, GDC, and STO were prepared via the citric acid gel (Pechini) method; in addition, YSZ and GDC were prepared via the propylene oxide gel method. Gels were sintered between 1050oC and 1350oC in argon, leaving behind a hard carbon template which created and preserved the scaffold nanostructure. This carbon template was completely removed upon heating in air to 700oC. Surface areas up to 83, 95, and 99 m2/g were achieved for YSZ, GDC, and STO, respectively. The tunability of this method was assessed by varying the carbon template concentration. For the propylene oxide gels, this was accomplished by controlling the amount of glucose added to the gel formulation while the amount of citric acid was controlled for the citric acid gels. In all cases, the surface areas increased with increasing carbon template concentration. In some cases, amorphous or impure phases were obtained upon sintering as determined by x-ray diffraction. However, the desired phases formed upon heating to 700°C in air (Fig. 1). This in situ carbon templating approach creates high surface area, nanostructured SOFC scaffolds at traditional sintering temperatures without unusual processing steps or complex deposition techniques. As expected, preliminary data suggests that SOFC electrodes comprised of these materials have improved performance (Fig. 2).

Figure 1
Metal-Supported Solid Oxide Fuel Cell with High Power Density
Authors: Tucker Michael C
Published: February 2020

Metal-supported solid oxide fuel cells (mSOFC) display a number of advantages over conventional all-ceramic SOFCs, including low-cost structural materials (e.g. stainless steel), mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. Challenges for mSOFCs include: oxidation of the metal support, especially at 800°C and above; the possibility of the stainless steel exacerbating Cr poisoning of the cathode catalyst; fabrication and materials set restrictions arising from the requirement that stainless steel be sintered in reducing atmosphere; and, only moderate performance and lifetime have been demonstrated to date.

These advantages and challenges suggest that mSOFCs may be well-suited for portable, ruggedized, fast-start, intermittent-fuel, or other unique and innovative applications. Nissan has developed the world’s first light-duty vehicle with a conventional SOFC stack for traction power, fueled by bio-ethanol reformate. Because of the desire for rapid-start capability, developing mSOFC cell and stack technology for this vehicular application is a priority. The small volume allowance for the SOFC stack on-board a small vehicle furthermore demands high power density from the mSOFC. In this work, we seek to maximize mSOFC power density.

This work is an extension of our previous efforts focusing on co-sintered, YSZ-based mSOFCs with porous metal supports on both anode and cathode sides, with catalysts deposited into both electrodes via infiltration. These features provide for a mechanically rugged cell that can be processed with low-cost scalable techniques, and high surface-area catalysts that provide excellent performance by avoiding interdiffusion or coarsening during cell sintering. To support the vehicular traction application, in this work we further develop catalyst infiltration processing for mSOFCs to dramatically increase power density. The goal is to increase cell performance by improving infiltration of conventional catalyst compositions (lanthanum strontium manganite (LSM), Ni, doped ceria) into electrode backbones of conventional yttria-stabilized zirconia (YSZ). Various aspects of the infiltration procedure were optimized, including: precursor composition and dilution with water; catalyst loading; and, crystallization temperature. Figure 1 shows the resulting high performance. Peak power of 1.1 and 1.9 W/cm2 is achieved at 700°C and 800°C, respectively, and the 800°C performance is the highest reported for mSOFCs to date. Cell stability in the operating temperature range 600 to 750°C will also be presented.

Acknowledgements

Funding for this work was provided by Nissan Motor Co., Ltd. This work was funded in part by the U.S. Department of Energy under contract no. DE-AC02-05CH11231.

Figure 1