bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic Evaluation of Integrated Heat-Pipe Reformer SOFC System
Authors: Herrmann Stephan , Jimenez Arreola Manuel , Gaderer Matthias , Spliethoff Hartmut
Published: February 2020

In the presented work a medium-sized integrated system based on a sodium heat pipes powered allothermal fluidized bed gasification and SOFC is introduced, simulated and validated in Aspen Plus. Suitable feedstocks for such fluidized bed gasification systems are for example waste and biomass, especially wood. The concept development and evaluation have been conducted as part of the EU FCH-JU project SOFCOM.

During the allothermal heat pipes gasification process heat for the endothermic gasification reactions is transported into the gasification chamber via the heat pipes. The heat pipes allow low temperature differences using mainly latent heat transport. Inside the heat pipes sodium is evaporated on the hot side by a heat source (i.e. combustion chamber) and condensed on the cold side (i.e. gasification chamber). Heat pipes based gasification has proven to be a reliable technology at different installations by the company Agnion energy GmbH and others. The gasifier model has been validated against data from this type of gasifier. The SOFC model applied is a thermodyamic model, which has been developed in the frame of SOFCOM and already described in detail in other works.

In the presented system configuration the product gas from the gasifier is cleaned during several process steps at an intermediate temperature of 350°C. After the cleaning procedure the gas is introduced into the SOFC anode where it is converted into electricity and high temperature heat at a fuel utilization rate of 80%. At the same time preheated air is fed to the cathode of the SOFC. The SOFC exhaust is fed into a fluidized bed post combustion chamber where residual fuel is burned with residual oxygen. Heat is extracted via the heat pipes from the combustion chamber, as well as the SOFC itself. Combustion exhaust gases are used to preheat the cathode air. Residual exhaust heat is used to generate high pressure superheated steam, which in turn is expanded in a steam turbine. At this point, the steam necessary for the fluidization of the gasifier and gasification agent is not produced in a separate steam generator but instead extracted from the steam turbine. Especially by means of utilization of excess heat from the SOFC and its exhaust gases via the heat pipes and full integration of the steam cycle the electrical efficiency of the combined system reaches up to 62%LHV.

Figure 1
Accelerated Lifetime Tests for SOFCs
Authors: Weber André , Szász Julian , Dierickx Sebastian , Endler-Schuck Cornelia , Ivers-Tiffée Ellen
Published: February 2020

Considering the expected lifetimes for Solid Oxide Fuel Cells of 5 to 10 years, durability is still a major issue. Even though quite a number of research institutions and companies have proven an acceptable degradation rate of cells, stacks and systems for periods ranging from a few hundred hours to several years, neither reliable degradation models nor methodologies to evaluate the durability in a short timeframe are available. Thus any kind of modification on the cell or stack level, which might affect the durability, requires an expensive and time consuming repetition of the durability test. Accelerated lifetime tests, which enable a rapid degradation analysis, and degradation models, that enable an extrapolation of the results, would be highly desirable.  

In most durability investigations a cumulative degradation rate is evaluated from the cell voltage decrease in a galvanostatic operating mode. In addition, extensive post test analysis is performed to detect the failure causes. This approach does not reveal any quantitative information on the different underlying degradation mechanisms. If aggravated stress is applied by increasing operating temperature, current density or gas utilization, the degradation of cathode, electrolyte, anode, contact layers and interconnects is accelerated in different ways. Therefore the cell voltage alone is insufficient to understand the performance degradation and its acceleration due to aggravated stress.

To deconvolute the degradation of cathode, electrolyte and anode (i) electrochemical impedance spectroscopy, (ii) impedance data analysis by the distribution of relaxation times and, (iii) a subsequent CNLS-Fit to a physically meaningful equivalent circuit model is suggested. Cell tests were performed at different stress levels by varying temperature and current density as well as fuel and oxidant composition. Based on this extensive data set, the interplay between stress level and impact of the different stresses on degradation mechanisms in cathode, electrolyte and anode will be presented and guidelines for the design of accelerated tests will be discussed.
Towards the Design-Led Optimization of Solid Oxide Fuel Cell Electrodes
Authors: Kishimoto Masashi , Lomberg Marina , Ruiz-Trejo Enrique , Brandon Nigel P.
Published: February 2020

Electrode microstructure plays an important role in determining the performance and durability of solid oxide fuel cells (SOFCs). It needs to be tailored towards a variety of requirement for the electrodes, such as transport properties and electrochemical activity. Long-term stability of the microstructure is also important to guarantee the durability of SOFC systems. In order to satisfy the growing demand for their performance and durability, an improved understanding of the microstructure-performance relationships is desired, along with optimization of the microstructure, through a design-led approach.

The focus of this study is on electrodes fabricated with the nano-particle infiltration techniques. Porous framework structures (scaffolds) were first fabricated with gadolinium-doped ceria (GDC), and then nickel metal particles were introduced into the structures in the form of nano particles. 3D microstructural analysis using focused ion beam and scanning electron microscope (FIB-SEM) was carried out and revealed that the infiltration technique has a greater potential, compared with the conventional approach based on powder mixing and sintering, to control the electrode microstructure, helping satisfy multiple requirements for the electrodes. Most notably, the triple-phase boundary (TPB) density in the infiltrated electrodes was found to be one order of magnitude larger than that typically found in the conventional electrodes.

A 1D numerical model for Ni-GDC electrodes was also developed assuming that the GDC phase has mixed ionic and electronic conductivity and hence that the electrochemical reaction takes place on the GDC-pore double-phase boundary (DPB), and successfully reproduced the overpotential characteristics obtained from the experiment. Sensitivity analysis was also conducted with the developed model at 700 °C to investigate the effect of electrode microstructure on electrode performance. This revealed that the electrochemical reaction on the DPB is the rate-determining process within the electrodes; therefore increasing the DPB density is recommended as the most effective route to improving performance of ceria-based electrodes, rather than improving species transport rate.

Using the insights from the experiment, microstructural analysis and numerical simulation, guidelines for further optimizing the electrode microstructure are proposed

Figure 1
A Time Resolved Study of Precoated AISI 441 for SOFC Interconnects Using STEM-EELS - Part I
Authors: Karlsson Lisa S , Lundberg Mats W , Berger Robert , Westlinder Jörgen
Published: February 2020

Precoated AISI441 for SOFC interconnectors were investigated by STEM-EELS looking at the diffusion processes in the initial stage of the oxidation. The PVD coating contained Ce and Co/Mn-alloy in two layers with at total thickness of 800nm. The samples were exposed up to 1000 hours at 800°C then characterized by TEM. Multiple linear least squares (MLLS) fitting of reference spectra aids the interpretation of the elemental maps due to overlapping edges (Figure 1). Within 4 min heat treatment the oxidation front has reached the substrate steel and Cr2O3 is forming at the stainless steel interface. CeO2 acts as the barrier line for Cr and is situated between the Cr-containing spinels and the (Co,Mn)-spinel after 72 h heat treatment.

Figure 1
Electrochemical Investigation of a Large SOFC Fed with n-Dodecane Reformate
Authors: Trocino Stefano , Lo Faro Massimiliano , Campagna Zignani Sabrina , Monforte Giuseppe , Aricò Antonino S.
Published: February 2020

In recent years, solid oxide fuel cells (SOFCs) have been extensively studied because of its potential as clean and efficient electric generators. Recently, SOFCs coupled with an external reforming have been suggested for the utilization in marine on-board applications. Diesel marine is the conventional fuel actually used; however, the stability of a conventional SOFC fed with a diesel reformate is not yet proven. Furthermore, the testing of a large area SOFC has a specific importance with the aim of the subsequent scaling up to a stack.

This study deals with the investigation of the degradation effects occurring onto the anode of a large area cell in presence of n-dodecane reformate. A commercial anode supported SOFC (10 × 10 cm2) with planar configuration having the composition Ni-YSZ/YSZ/YDC/LSFC, has been investigated in-situ electrochemically. The test bench used for this experiment is the conventional ECN test station showed in Figure 1. The electrochemical experiments concerned I-V curves (Figure 2) and impedance spectroscopy (Figure 3) carried out at OCV and at 0.9 V. Ex situ tests were also carried out in order to evaluate morphological and and physico-chemical modification on the discharged cell.

In the case of anodes (Ni-YSZ cermets), the degradation phenomena are recognized due to Ni agglomeration and carbon deposition. These microstructural changes in anode is expected to be highly dependent on operating conditions, such as operating temperature, operating voltage and water content in the feed.

Figure 1: ECN test bench (a) and commercial large area cell (b)

Figure 1
Fabrication of a Ni/MgO Nanocomposite Catalyst by Exolution
Authors: Lim Ye Sol , Yoon Jong Seol , Choi Byung Hyun , Seo Won Seon , Hwang Hae Jin
Published: February 2020

Methane steam reforming reaction is the most important chemical process to produce hydrogen or synthesis gas. Hydrogen is heavily consumed for ammonia production, the cryogenics industry and methanol production. Recently, the hydrogen demand is expected to increase as fuel cells become more widely accepted and are used more in the near future. For effective production of hydrogen or synthesis gas, the role of the reforming catalyst becomes more significant. Especially, highly active and stable catalyst is necessary for an on-site reformer for fuel cell systems.

 In conventional technology, the methane steam reforming reaction is conducted on supported noble metals- (Pt, Pd, Rh, Ru, and Ir) or nickel-based catalysts at temperature up to 700~800°C and steam to methane rations between 2 and 4. However, these catalysts suffer from the deactivation by agglomeration and carbon deposition. Noble metal-based catalysts are less sensitive to carbon deposition than nickel-based catalyst. However, high cost and limited availability are major concern.

 In this study, nickel-based nanocomposite catalysts were fabricated by exolution process. The exsolution means the process to precipitate particles from solid solution by means of the heat treatment in a specially-controlled atmosphere. This process is distinguished from the infiltration in which particles are precipitated from solutions by evaporation. First, Mg1-xNixO solid solution powders were synthesized from aqueous magnesium and nickel nitrate solution by precipitation technique and then the powder was heat-treated in reducing atmosphere at 600 to 900°C. SEM and TEM images revealed that the nano-sized nickel particles were homogeneously dispersed in the Mg1-xNixO solid solution matrix and the size and morphology of nano nickel particles can be controlled by the heat-treatment condition. Catalytic activity for the methane steam reforming or methane particle oxidation reaction and durability of the Ni/Mg1-xNixO was investigated in terms of nickel contents and sizes.

Figure 1
Numerical Assessment of SOFC Anode Polarization with Microstructure Evolution
Authors: Jiao Zhenjun , Shimura Takaaki , Shikazono Naoki
Published: February 2020

A phase field method was introduced to simulate the microstructural evolution of nickel-yttria stabilized zirconia composite anode of solid oxide fuel cell in high temperature sintering based on three-dimensional microstructures reconstructed by focused ion beam-scanning-electron-microscopy technique. Nickel phase morphology and crystal structure evolutions and the change of nickel network percolation in operation were simulated simultaneously. In order to quantitatively study the correlation between anode microstructure change and the anode electrochemical performance degradation, the evolution of three-phase boundary density and nickel specific surface area were calculated. Corresponding degradation experiments have been conducted to compare with the simulation results. The experimental results showed good agreement to the simulation results.

Figure 1
Development of Robust SOFC Anode Materials Using La-Doped SrTiO3
Authors: Shen Xuesong , Sasaki Kazunari
Published: February 2020

We utilize the very stable Sr0.9La0.1TiO3 (SLT) to fabricate robust anode for SSZ electrolyte-supported SOFC single cell. The anode consisted of three layers: a layer of 60wt% GDC-SLT or 40wt% SSZ-SLT as functional layer and two layers of SLT as current conducting layer. Cathode was composed of a layer of 50wt% SSZ-LSM as functional layer and a layer of LSM as current conducting layer. Impregnation method was employed to decorate nano-sized Ni and CeO2 into the ceramic anode. We measured electrochemical properties of the single cells in 3%-humidified H2at 800°C, and investigated redox stability of the nano-sized catalyst impregnated ceramic anodes by fuel interruption method described in our previous publication.

The homogeneously dispersed nano-sized catalyst provides sufficient catalytic activity for the conductive ceramic backbones, GDC-SLT or SSZ-SLT, to work as effective anodes, and remarkable improvement of cell performance could be achieved. Compared with the traditional Ni-SSZ cermet anode, the catalyst impregnated ceramic anodes have prominent advantage against the redox cycling test. Cell performance drops 0.52% and 0.45% when using catalyst impregnated 60wt% GDC-SLT and 40wt% SSZ-SLT as anode in the first 10 redox cycles respectively, whereas, the degradation rate of Ni-SSZ in the first 10 redox cycles is 14%. The excellent stability of the impregnated anodes against redox cycling test mainly comes from two aspects: firstly, the electronic conducting path provided by ceramic backbone maintains completely during redox cycling, whereas, conducting path in traditional Ni-SSZ, the connected Ni particles, will be dislocated when Ni particles suffer shrink and expansion during redox cycling. Moreover, CeO2used in the anode works as inhibitor preventing Ni particles from further agglomeration, meanwhile it supports Ni particles to maintain sufficient catalytic activity for fuel oxidation at constant current loading.

In conclusion, we have developed robust SLT-based ceramic anodes using impregnation method, which demonstrated excellent stability in redox cycling test compared with traditional Ni-Zirconia cermet.
Chemical Compatibility of A-site Deficient La Substituted SrTiO3
Anode and Stabilized Zirconia Electrolyte
Authors: Chen Gang , Luo Yifei , Gao Yu , Guo Ruifeng , Ma Wanqing , Liu Man , Geng Shujiang
Published: February 2020

Rapid performance degradation occurred during the initial stage of the cells test with (La0.25Sr0.75)0.9TiO3(LST-0.9)/ScSZ composite anode and (La0.25Sr0.75)0.85(LST-0.85)TiO3/ScSZ composite anode, respectively, has been reported in previous study. Diffusion of Zr and Sc from ScSZ into LST-0.9 and Ti from LST-0.85 into ScSZ occurred during anode preparation processes and the performance tests were respectively considered as dominant degradation mechanism for the cells with LST-0.9/ScSZ anode and LST-0.85/ScSZ anode. Based on this, a LST with A-site deficiency between LST-0.85 and LST-0.9 possess chemical stability with ScSZ at elevated temperature might be existed. In this study, series A-site deficient (La0.25Sr0.75)xTiO3 (x varies from 0.89 to 0.86) were prepared by sol-gel method to develop A-site deficient LST with better chemical compatibility with ScSZ. Chemical stability between as-prepared A-site deficient LST with ScSZ and long term stability of LST-x/ScSZ composite anode were investigated.
Gas Composition Analysis on Ni-YSZ Anode in Direct Internal Reforming Solid Oxide Fuel Cell
Authors: Muroyama Hiroki , Ando Daiki , Okanishi Takeou , Matsui Toshiaki , Eguchi Koichi
Published: February 2020

Solid oxide fuel cell (SOFC) is one of the most promising power generation devices. In Japan, the residential SOFC cogeneration systems have been commercialized since 2011. In this system, the supplied methane-rich fuel is reformed in an external reactor and the pre-reformed gas (hydrogen-rich fuel) is introduced to the anode chamber. In contrast, high operating temperature of SOFCs provides the possibility of a direct internal reforming operation, in which the anode material plays a role in the promotion of fuel reforming and fuel oxidation. Because the supplied fuel is reformed over anode catalyst, the concentration distribution of reactants and products appears along the direction of gas flow. Moreover, under discharge operation, the exothermic reaction of electrochemical oxidation as well as the endothermic reaction in the fuel reforming proceed simultaneously at the anode. In this case, the temperature distribution is more complicated than that in a supply of hydrogen fuel. Up to now, there are few reports on the direct evaluation of gas composition and temperature distributions over the anode although the theoretical calculation have been conducted.

This study, therefore, aimed to investigate the methane steam reforming and electrochemical oxidation over Ni–YSZ anode in an anode-supported cell. The distribution of gas composition over the anode surface along the direction of gas flow was examined by gas chromatograph under the open circuit and discharge conditions in a direct internal reforming SOFC.

The effect of total flow rate on the reaction process was studied under the open circuit condition. Regardless of total flow rate, the methane conversion remarkably increased at the upstream part. The extent of conversion enhancement was more significant at slower flow rates. In contrast, the correlation between the obtained methane conversion and the gas-catalyst contacting time agreed well in all flow rate conditions. The temperatures of anode surface at all measurement positions were lower than that under supplying only hydrogen due to the endothermic reaction in methane reforming process. The temperature variation against the direction of gas flow corresponded to the methane conversion. The surface temperature decreased at the upstream parts and then gradually rose toward the downstream parts.

During discharge, the enhancement of methane conversion and the decrement of CO concentration were accomplished with an increase in current density. This result suggests that the steam reforming reaction and water gas shift reaction were promoted by the consumption of hydrogen and the formation of steam in the electrochemical hydrogen oxidation.
Characterization and Stack Testing of Solid Oxide Fuel Cells with Cathodes Prepared by Infiltration
Authors: Küngas Rainer , Hertz Thomas B. , Heiredal-Clausen Thomas
Published: February 2020

Recently, the use of infiltration as a method for SOFC electrode preparation has gathered significant scientific interest (1-6). The results thus far have been mostly obtained on button cells with electrode active areas on the order of 1 cm2 or less. Here, we report the physical characterization and stack testing of 12 x 12 cm2 planar cells with cathodes prepared by infiltration of a perovskite precursor solution into a stabilized zirconia backbone.

    As the first step in the development of the new cell design, a stabilized zirconia backbone layer with high surface area and good mechanical compatibility with the rest of the cell was developed. After an optimized sintering procedure was introduced, batches of about 90 cells could reproducibly be manufactured with high yields. The optimized blank cells were infiltrated with a precursor solution of (La0.8Sr0.2)0.95FeO3 and the resulting cells were characterized thoroughly using XRD, van der Pauw in-plane conductivity, BET specific surface area, and electrochemical single-cell measurements. As the in-plane conductivity, the BET surface area as well as the pore-size distribution of the cathode are thought to play a key role in determining the long-term performance and stability of infiltrated cells in a stack, changes in these properties were mapped out as a function of the cathode sintering temperature.

    Electrochemical testing on both cell and stack level confirmed the enhanced performance of cells with cathodes prepared by infiltration. Results on degradation testing will be reported separately.

    This work was partly funded by EUDP project J 64012-0225, “SOFC Accelerated”.

References

S.P. Jiang, Mater. Sci. Eng. A, 418, 199 (2006).

J.M. Vohs, R.J. Gorte, Adv. Mater., 21, 943 (2009).

A.J. Samson, P. Hjalmarsson, M. Søgaard, J. Hjelm, N. Bonanos, J. Power Sources, 216, 124 (2012).

D. Ding, X. Li, S.Y. Lai, K. Gerdes, M. Liu, Energy Environ. Sci., 7, 552 (2014).

T.Z. Sholklapper, H. Kurokawa, C.P. Jacobson, S.J. Visco, L.C. De Jonghe, Nano Lett. 7, 2136 (2007).

M. Shah, S.A. Barnett, Solid State Ionics, 179, 2059 (2008).

Figure 1
Dusty-Gas Model with Uniform Pressure: A Numerical Study on the Impact of a Frequent Inconsistent Assumption in SOFC Electrode Modeling
Authors: Bertei Antonio , Nicolella Cristiano
Published: February 2020

One of the most popular models adopted to describe the gas transport in porous electrodes is the dusty-gas model. Such a model is commonly applied in the literature under the assumption of uniform pressure. However, as we recently summarized in a short communication [A. Bertei, C. Nicolella, J. Power Sour. 279 (2015) 133-137], this assumption is incompatible with the dusty-gas model formulation and leads to serious inconsistencies, for example, fluxes that do not obey reaction stoichiometry. In such a case the model fails to predict partial pressure profiles, concentration overpotentials and limiting currents.

In this study, we report the quantification of the error in the prediction of partial pressure profiles and concentration overpotential due the inconsistent assumption of uniform pressure in a broad range of conditions, focusing mainly on SOFC anodes. Simulations show that an inconsistent use of the dusty-gas model may lead to relative errors in the prediction of concentration overpotential as large as 60%. In H2/H2O/N2 mixtures, the error increases as the molar fraction of the inert species decreases and is maximum in binary H2/H2O mixtures. In addition, the error increases as porosity, pore size and water molar fraction increase while it decreases as the current density and the electrode thickness increase. These results are helpful to quantify the impact of an inconsistent use of the dusty-gas model in the literature and to promote a coherent gas transport modeling.
Stability of Nickel-Infiltrated Anodes in Intermediate Temperature SOFCs
Authors: Miller Elizabeth C , Sherman Quentin , Gao Zhan , Voorhees Peter W , Barnett Scott A
Published: February 2020

Solid oxide fuel cells (SOFCs) with a thin La1-xSrxGa0.8Mg0.2O3-
δ (LSGM) electrolyte plus Ni-infiltrated LSGM anode functional layer and Sr0.8La0.2TiO3 (SLT) anode support have shown high power density (> 1 W cm-2) at temperatures ≤ 650°C and good stability in short-term testing (< 100 h).  However, the long term stability of these cells is still largely unstudied. In this work, ex situ studies on the evolution of aqueous infiltrated Ni(NO3)2 to NiO and finally to Ni metal nanoparticles on LSGM pellets determined that the size and number of Ni particles can be controlled by dehydrating the samples before calcination, which could be used to advantageously control the microstructure of infiltrated anodes. SOFCs with Ni-infiltrated anodes were tested in humidified hydrogen and air at open circuit voltage (OCV) to determine stability for durations up to 600 h. Scanning electron microscopy indicated that Ni nanoparticles coarsened over time, which negatively affected performance. The polarization resistance of the anode doubled in magnitude over the course of the test, and ohmic polarization was found to increase with time, which could result from coarsening Ni closing off active areas in the anode functional layer. OCV remained within ~0.05 V of the theoretical OCV by the end of the test. In all cases, the majority of the polarization resistance resulted from degradation of the La0.6Sr0.4Fe0.8Co0.2O3-δ-Ce0.8Gd0.2O1.95 (LSCF-GDC) cathode.  To better understand the effect of Ni coarsening on cell performance, a model was developed to predict the changes in triple phase boundary (TPB) length during coarsening and its effect on cell performance. Additional testing is required to determine how these preliminary results will extend to operating lifetimes and how to use the ex situ test results to control microstructures in processed cells.
Durability Assessment of SOFC Stacks with Several Types of Structures for Thermal Cycles during Their Lifetimes on Residential Use
Authors: Hatae Toru , Sato Koki , Somekawa Takaaki , Matsuzaki Yoshio , Amaha Shinji , Yoshikawa Masahiro , Mugikura Yoshihiro , Miyara Kengo , Oshima Toshihiro , Taniguchi Shunsuke , Sasaki Kazunari , Shimazu Megumi , Takahashi Yuya , Kawakami Akira , Mori Naoya , Yokokawa Harumi
Published: February 2020

New Energy and Industrial technology Development Organization (NEDO) in Japan started a project “Fundamental study on rapid evaluation method of SOFCs”. In the project, we try to develop a rapid evaluation method for durability of SOFC stacks with several types of structures for thermal cycles during their lifetimes based on the assumption of residential use. The durability of SOFC stacks for thermal cycles is expected to be affected by the degradation during their long-term operation. In order to accelerate the evaluation, a treatment to intentionally cause a rapid degradation is investigated. A degradation factor is determined depending on the SOFC stacks with different structures respectively because each degradation mechanism during their long-term operation also depends on them. Four types of SOFC stacks were selected for the assessment which have been developed by respective stack manufactures in Japan. In the presentation, we investigates the Cr-poisoning treatment for tubular SOFC manufactured by TOTO and the SO2-poisoning for co-fired type planer SOFC manufactured by Murata Manufacturing.
Morphological Modelling of a Metal Foam Supported SOFC Configuration
Authors: Masson David , Abdallah Bassam , Willot François , Jeulin Dominique , Mercadelli Elisa , Sanson Alessandra , Chesnaud Anthony , Thorel Alain
Published: February 2020

The EVOLVE cell, named after a running FP7 project, is an innovative SOFC concept that integrates advanced materials, providing multiple functionalities (electrochemical activity, ion or/and electron conduction, gas diffusion…), and an inventive anode current collector made of a NiCrAl preoxidized foam impregnated with a conductive perovskite. Therefore, this anode combines the beneficial characteristics of MSC and ASC technologies, and strong improvements in terms of reliability and durability (inter-diffusion, Ni coarsening and agglomeration, sulphur tolerance, mechanical robustness and chemical stability under redox cycling in temperature) are expected.

In order to enhance the electrode efficiency, the 3D microstructure needs to be precisely described at the microscopic scale by a morphology model. An optimized microstructure (controlled pores size, morphology and connectivity, grains size distribution, 3D tortuosity and 3D percolation of phases, volume fraction of phases, final thickness of components …) is closely related to the starting parameters (nature and quantity of starting powder, binder, shaping aids…) and to the control of the shaping process parameters (sintering treatment and atmosphere). It should meet the best compromise between a good electrocatalytic activity and a low ohmic resistivity while ensuring a stisfactory long term thermomechanical stability on the life time of the device.

Based on a mathematical morphology approach applied on symmetrical LST/CGO anode layers, the present work aims at showing how a morphology model can be establised and 3D microstructural data relevant for shaping and performances can be derived from back-scattered electrons (BSE) SEM observations. For each sample, a series of images were used as input information for the microstructural modelling. All the original images were first filtered to remove the noise, thresholded and finally a series of morphological operators (openings, surface openings, closings and reconstruction with markers) were applied to remove artefacts. A 3D pluri-Gaussian model has been generated from 2D images, and then computed to predict volume fraction of the 3 phases, 3D tortuosity, gas permeation and ionic conductivities. These results were used for the optimization of the shaping process that includes the integration of the metal foam.
Hexis and the SOFC System Galileo 1000 N: Experiences from Lab and Field Testing
Authors: Mai Andreas , Schuler J. Andreas , Fleischhauer Felix , Nerlich Volker , Schuler Alexander
Published: February 2020

Hexis is developing and manufacturing SOFC-based micro-CHP systems for single-family or small multi-family houses. The current system Galileo 1000 N has an output of 1 kW electrical power. It furthermore covers the full heat demand of a standard single family house. More than 250 Galileo 1000 N systems have been installed up to now and are operated at customer's sites and in the lab.

The newest achievements in the field test and in the lab on durability and cyclability of SOFC stacks and complete micro-CHP systems are reported. Achievements are total system efficiencies of 95% (LHV) and electrical efficiencies of 35% (AC net, LHV). In tests with steam reforming, electrical efficiencies of more than 55 % (DC) have been shown on short-stack level. The longest system test had been running for more than 40 000 h. More recently, power degradation rates of approx. 0.5% per 1 000 h over more than 20 000 hours on short-stack level and over more than 12 000 h on full-system level have been demonstrated which were also confirmed in field tests. Cycling tests have shown a tolerance against 100 complete redox-cycles on short-stack level and 50 on-off cycles on system level. Summarized, stack lifetimes of 7 to 8 years are considered to be realistic. All-in-all, the technical market readiness has been achieved with the Galileo 1000 N. Consequently, an introduction into pilot-markets in Europe was started in autumn 2013.
Li/Na Modified Ni-SDC Anode for Methane-Fueled Solid Oxide Fuel Cells
Authors: Liu Lilu , Yang Qi , Yang Wei , Qi Xingguo , Sun Chunwen , Chen Liquan
Published: February 2020

Solid oxide fuel cells (SOFCs) have the potential to direct use hydrocarbon fuels without pretreatment due to its high operating temperature [1]. The most common used nickel/yttria-stabilized zirconia (Ni/YSZ) anodes have showed excellent performance in H2 fuel, however, there is serious carbon deposition when hydrocarbon fuels are used. In recent years, great efforts have been devoted to develop alternative anodes to alleviate carbon deposition issue encountered in Ni-based cermets anode. However, the performance of the proposed alternative anode materials is still not satisfactory yet when hydrocarbon fuels are used. Alkali or alkaline earth oxides have been used to enhance the activity of catalysts for reforming [2] and water-gas shift reactions [3]. In this work, a facile chemically lithium/sodium insertion method has been developed to prepare Li/Na doped-NiO composites (Li/Na-NiO). The single cells were fabricated with a Li/Na doped NiO-Ce0.8Sm0.2O1.9 (SDC) composite anode screened on a 250um La0.9Sr0.1Ga0.8Mg0.2O3-
d
(LSGM) electrolyte and a composite cathode consisting of Sr0.95Ce0.05CoO3-
d and SDC (30wt%). When CH4 was used as fuel, the peak power density of the cells with the Li and Na doped NiO anode reaches about 126 mW cm-2 and 106mW cm-2 at 800oC, respectively. Compared with that of the cell with the pristine NiO-SDC anode, the cells with Li/Na doped NiO anode material shows that it gives much higher open circuit voltage (OCV) and better long-term stability at 800oC than that of the cell with the pristine Ni-based anode. The preliminary results demonstrate that the Li/Na doped NiO anode materials are promising alternative anode for hydrocarbon-fueled solid oxide fuel cells.
Micro-SOFC with High Performance and Fast Thermal-Cycling Ability
Authors: Kim Kun Joong , Park Byung Hyun , Kim Sun Jae , Bae Hongyeul , Choi Gyeong Man
Published: February 2020

Due to a limited energy density of Li-ion batteries, miniaturized solid-oxide fuel cells (micro-SOFCs) have received growing attention for use in portable devices or vehicles. Conventional design has adopted a freestanding membrane supported by Si substate and used pure metal electrode which has shown poor thermomechanical-stability. Recently we have developed a new design of micro-SOFC consisting of robust metal support and ceramic-based electrode. Porous stainless-steel (STS) is used as a substrate to support a thin-film membrane electrode assembly (MEA) to achieve thermally-robust cell. A composite of nano-porous (La,Sr)(Ti,Ni)O3 conductor and electrolyte is applied as a contact layer between the macro-porous STS and the thin-film MEA. Excellent performance and thermal cycling ability at or below 550oC  for this novel cell are shown and will be further discussed.
Prediction of SOFC Performance with or without Experiments: A Study on Minimum Requirements for Experimental Data
Authors: Yang Tao , Sezer Hayri , Celik Ismail Bektas , Finklea Harry O. , Gerdes Kirk
Published: February 2020

A comprehensive analysis of solid oxide fuel cells (SOFCs) should consider polarization curve and impedance behavior simultaneously, as well as the cell performances at different air/fuel utilization cases and operating conditions. In the present study, a physics based protocol, combining experiments and multi-physics numerical simulations, is developed for overall analysis of SOFCs operational diagnostics and performance predictions.  In this protocol, essential information for the fuel cell is extracted first by utilizing empirical polarization analysis in conjunction with experiments and refined by multi-physics numerical simulations via simultaneous analysis and calibration of polarization curve and impedance behavior. The performance at different utilization cases and operating currents is also predicted to confirm the accuracy of the proposed model.  Furthermore, we also propose the requirements to determine the cell properties and model parameters with less uncertainty. It is demonstrated that, with the present electrochemical model, three air/fuel flow conditions are needed to produce a set of complete data for better understanding of the processes occurring within SOFCs. The detailed calibration procedure and performance prediction at different conditions of button cells are presented. It is also demonstrated that the methodology can be used to assess performance of planar cell without further calibration. The proposed methodology would accelerate the calibration process and improve the efficiency of design and diagnostics analysis.
Reversible Oxygen-Ion Storage for Solid Oxide Cells
Authors: Berger Cornelius M. , Hospach Andreas , Menzler Norbert H. , Guillon Olivier , Bram Martin
Published: February 2020

In a rechargeable oxide battery (ROB) a solid oxide cell (SOC) is combined with a component that acts as storage for oxygen ions. The cell is operated at 800°C in turns as fuel cell and as electrolyser. Yet, there is no need for the delivery of fuel because of the integrated iron oxide base storage component. This material regulates the oxygen partial pressure at the fuel electrode in a range of approximately 10-21-10-18 bar, which at 800°C corresponds to water vapor to hydrogen ratios between 1:4 and 4:1.

However, repeated charging (electrolysis) and discharging (fuel cell mode) can result in coarsening of particles and external layer formation. Both effects are not desired because they decrease the overall surface and thus the reaction kinetics. Adding secondary oxides to the Fe2O3 base material can mitigate those degradation phenomena. In the present study the effect of additions of Al2O3, CeO2, Mn3O4, Cr2O3, TiO2, SiO2, and MgO to the Fe2O3 base on the degradation properties is analysed. To this end, compacted samples are repeatedly oxidised and reduced in a laboratory furnace, where the conditions present in the ROB are simulated. Using X-ray diffraction and scanning electron microscopy it was found that among the tested oxides only MgO and Al2O3 could mitigate the layer formation and the particle coarsening to some extent.
9000 Hours Operation of a 25 Solid Oxide Cells Stack in Steam Electrolysis Mode
Authors: Corre Gaël , Brisse Annabelle
Published: February 2020

Hydrogen production through water electrolysis is one of the key processes required in the conversion of electricity to fuels. Carbon free hydrogen produced through water electrolysis can be used as a fuel for hydrogen powered applications (such as fuel cell cars) or grid injection, or as a reactant in downstream processes to produce synthetic fuels such as SNG or methanol. Among available technologies, high temperature electrolysis potentially offers significantly higher electrical to chemical conversion efficiencies compared to alkaline and PEM electrolysers, with values in excess of 100% achievable if additional thermal energy is supplied to the system. High temperature electrolysers are essentially solid oxide fuel cells operated in reverse. Hence, the development of solid oxide electrolysers (SOE) has hugely benefited from the intensive research carried out for the development of Solid Oxide Fuel Cells (SOFCs) in the past decades.  A 25 cells stack manufactured by Topsoe Fuel Cells has been tested at EIFER in high temperature electrolysis mode at about 750°C and current densities of 0.57 and 0.72 A/cm2. The applied steam conversion rate was 50%, with a 90 % absolute humidity gas feed.  

The total duration of the test was almost 9100 hours, split between 8300 current hours and 800 standby hours induced by incidents that occurred during the test. Incidents included losses of the steam and current supplies. After each incident, the stack performance was recovered, indicating a good robustness of the stack towards unexpected and potentially damaging conditions.  The main issue during the test has been the considerable increase of the voltage drop between the positive end plate and the bottom stack repeat unit (SRU), before a sharp improvement occurred after about 2000 hours of operation, which has influenced the stack temperature distribution and in turn individual SRU degradation. The maximum observed voltage drop culminated at 2.73 V, before stabilising around 0.6V.

The stack has shown an overall voltage degradation of 2% per thousand hours, as can be seen on Figure 1. The corresponding voltage losses were 613 mV and 678 mV per thousand hours, for 0.57 and 0.72 A/cm2 current densities, respectively.  This in turn corresponds to an average degradation in the range 0.24 – 0.27 mV per thousand hours per SRU.

Moreover, the stack temperature has been adjusted on a few occasion during the test, which highlighted the possibility of using the wide operating temperature range of the solid oxide technology to counter balance the stack degradation and increase the lifetime. Indeed, allowing the stack to increase at a rate of 3°C per thousand hours produced a reduced degradation rate of 1.80 % per thousand hours.

Figure 1
A Study of 8YSZ/GDC Bi-Layered Electrolyte: The Effect of 2 Mol% Fe2O3 Dopant on Sintering and Conductivity
Authors: Mehranjani Alireza Soleimany , Cumming Denis J , Call Ann V , Elder Rachael H
Published: February 2020

The primary requirements for an electrolyte material in a Solid Oxide Cell (SOC) is the ability to provide a sufficiently high level of oxide ion conduction while preventing both the mixing of reactant gas species and leakage of current through the electrolyte. Commonly, 8 mol% Yttria-stabilised Zirconia (8YSZ) or Gd0.1Ce0.9O1.95 (GDC) are used in high performance cells. Whilst GDC has higher oxide ion conductivity than YSZ, it suffers from electronic conduction due to the partial reduction of Ce4+ to Ce3+ during operation which is detrimental to cell performance. In this work we present the use of a bi-layer 8YSZ/GDC electrolyte as an effective solution to avoid ceria reduction in a fuel (reducing) environment, thereby preventing current leakage across the electrolyte, while maintaining high oxide ion conduction.  Electrolytes were produced via tape-casting, a low-cost, mass-production technique.  A transition metal oxide sintering aid of 2 mol% Fe2O3 was used to reduce the sintering temperature while also mitigating the formation of a low conductivity interlayer. This study aims to determine the role of Fe2O3 during the sintering process and its subsequent influence on microstructure and the total conductivity of the bi-layer electrolyte.
Grain Size Effect on Conductivity of LSGM Thin Film Electrolyte for Solid Oxide Fuel Cell
Authors: Endo Yoichi , Dempoh Akishi , Terai Takayuki , Suzuki Akihiro
Published: February 2020

Solid oxide fuel cell (SOFC) consisting of ion conductive ceramics has various advantages such as the high generating efficiency, the utilization of hydrocarbon-containing fuel and the non-necessity of expensive rare metal catalyst. Sr and Mg dopoed Lanthunum Gallate (La0.9Sr0.1Ga0.8Mg0.2O3-δ, LSGM) is a well-known electrolyte for solid oxide fuel cell because of the high conductivity.

It is said that thin film material can exhibit different characterization from bulk material. In our former study, we tried to reveal the mechanism of the conductivity change of LSGM thin film from the bulk. The LSGM thin films with different thickness deposited on sapphire substrate by radio frequency magnetron sputtering was studied. The grains in the thicker film were larger than those in the thinner film. The thicker the film was, the conductivity increased and the activation energy decreased. We suggested this was caused by the smaller bulk resistivity than the grain boundary resistivity. It is necessary to develop the method to separate the resistivity into the bulk resistivity and the grain boundary resistivity to confirm this hypothesis.

In this study, the radio frequency magnetron sputtering was used for obtaining LSGM films on LaSrGaO4 single crystal substrate. To crystallize and control the grain size in the LSGM film, we conducted post-annealing under various temperature. We evaluated the grain size in the LSGM film with a scanning electron microscope and measured the conductivity by electrochemical impedance spectroscopy. We try to separate the resistivity into the bulk resistivity and the grain boundary resistivity by using an equivalent circuit based on Brick-Layer model. In this paper, we report the grain size effect on the electrical conductivity in LSGM thin film.
High Ionic Conductivity in Composite Materials Under H2/Air Fuel Cell Condition
Authors: Lan Rong , Tao Shanwen
Published: February 2020

New ionic conducting electrolyte materials for solid oxide fuel cells (SOFCs), particularly intermediate temperature fuel cells have been attracting the interests of researchers in energy materials.  The typical electrolytes used for SOFCs are normally single phase oxides. Here we report a series of conductive composites with high ionic conductivity derived from an electronic conductor such as a-LiFeO2 and an insulator such as g-LiAlO2. High conductivity was observed in the composites when prepared by a solid state reaction method. These composites also exhibit O2- or/and H+ ionic conduction which was confirmed through H2/air fuel cell measurements. An exceptionally high conductivity of 0.50 S/cm at 650 °C was observed under H2/air fuel cell condition. This provides a new approach to discover novel ionic conductors in composite materials.

References:

[1] C. C. Liang, Journal of the Electrochemical Society, 120 (1973) 1289

[2] J. Maier, Nature Materials, 4 (2005) 805.

[3] S.W. Tao and J.T.S. Irvine, Advanced Materials, 18 (2006) 1581.

[4] R. Lan and S.W. Tao, Advanced Energy Materials, 4 (2014) 1301683.
SOFC Development in Huazhong University of Science and Technology
Authors: Li Jian
Published: February 2020

Solid oxide fuel cell is recognized as one of the promising technologies for green power generation in the 21th century. Extensive attention has been attracted on its development in last decade worldwide. In Huazhong University of Science and Technology, A R&D center for the development of solid oxide fuel cells was established in 2004, since then SOFC key materials (including cathodes, interconnects, contacts and seals), cell fabrications, stack designs and assembly as well as system integration have been focused. So far significant progresses have been achieved, including high performance key materials, large scale cells, kW stacks and a 5kW-scale system. In this talk, detailed developments are presented.
Direct Ceramic Inkjet Printing and Infiltration of Functional Coatings for Metal Supported SOFC
Authors: Tomov R I , Fakeeh A , Krishnan Venkatesan Venkata , Balasubramanian Krishnamurty , Kumar Vasant R , Glowacki B A
Published: February 2020

Direct Ceramic Inkjet Printing (DCIJP) was applied as a technology for the fabrication of anodes, electrolytes and cathodes coatings for metal-supported SOFCs. Drop-on demand electromagnetic nozzles with orifice diameter of 100 microns were utilized in dispensing nanoliter drops of suspension and sol inks with high frequency and high lateral resolution. An optimization procedure of the ink formulations and the major printing parameters was performed allowing routine production of coatings with thicknesses below 20 µm with an additional benefit of surface defects planarization. The drop-on-demand printing was also employed as a precision instrument for infiltration of the supports and the cathode scaffoldings with functional inks. Porous metal supports for SOFC applications were produced via conventional powder metallurgy routes. Commercially accessible low-cost stainless steel 430L and mixtures of NiO-Fe2O3 powders were chosen as source materials. The support sintering procedures was performed either in vacuum or air depending on the source material. The density and open porosity distribution of as-sintered supports were determined by Archimedes' method, optical image analysis and Hg-porosimetry. The relation between the vacuum/air sintering conditions and the micro-structural characteristics (porosity, Cr evolution, ink penetration) of the metal supports and the coatings were studied. The influence of the porosity parameters on the droplets penetration behaviour and coatings characteristics was explored. The microstructure and elemental distribution were investigated by Scanning Electron Microscope and energy dispersive X-ray spectrometry system. The analyses confirmed that DCIJP can be successfully applied for the production and modification of metal supported SOFCs.

Figure 1