Symposium CK
Solid Oxide Fuel Cells: Materials and Technology Challenges
ABSTRACTS
CK-1:IL03 Nanoscale Investigation of Long-term Operated Solid Oxideelectrolysis Cells
J. Villanova, ESRF The European Synchrotron, Grenoble Cedex, France; S. Schlabach, Institute for Applied Materials and Karlsruhe Nano Micro Facility, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany; A. Brisse, A. LEON, European Institute for Energy Research, Karlsruhe, Germany
The degradation processes in solid oxide cells have been investigated by applying nanoscale X-ray fluorescence spectroscopy on a cathode and an electrolyte supported cell that have been in electrolysis mode for 6,100 and 23,000 hours, respectively. 2D map with 50 nm resolution were acquired for Ni, Y, Ce, Gd, La, Sr, Co, Fe that provides high-resolution compositional analysis in combination with high lateral resolution. It will be shown that during the sintering process, different elements are diffusing to form additional layers at different interfaces of the functional layers. After long-term operation, some of the layer thickness only evolves. The cobalt is the element that is highly segregating from the LSCF electrode in both type of cell. The gadolinium from the CGO layer shows an accumulation at the CGO/electrolyte interface on the oxygen electrode side and on the hydrogen electrode side in the electrolyte supported cell. The concentration significantly increases during the cell operation to form a layer of a few micrometers. The Ni depletion seems to be prevented by the contact layer inserted between the hydrogen electrode and the electrolyte.
CK-1:IL05 Hydride Superionic Conduction in Ba1.75LiH2.7O0.9
GENKI KOBAYASHI, Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Japan
Hydride ions (H–) can act as charge carriers as they exhibit several features suitable for fast ion conduction: monovalence, the moderate ionic size comparable to O2– and F–, and high polarizability. Furthermore, hydride ions exhibit strong reducing properties through the standard H–/H2 redox potential (–2.3 V vs. SHE), which can be expected to be applied to novel electrochemical devices. Following some investigations on H– conduction in alkaline earth metal hydrides, we reported H– conduction in an oxide- based framework structure for the first time by finding a series of H–conductive oxyhydrides, La2–x–ySrx+yLiH1–x+yO3–y. The discovery has triggered the exploration of materials for H– conductors such as K2NiF4-type Ln2LiHO3 (Ln = Pr, Nd), and Ba2MHO3 (M = Sc, Y). However, H– conductors exhibiting both high conductivity and low activation energy had not been developed yet. In the present study, we report a new H– conductive oxyhydride, Ba1.75LiH2.7O0.9, containing a high amount of barium and anion vacancies and exhibiting long-range ordering at room temperature. Increasing the temperature above 315 °C disorder the ordered vacancies, triggering superionic conduction with a high H– conductivity of over 0.01 S cm–1 nearly independent of the temperature. Such a remarkable H– conducting nature at intermediate temperatures is anticipated to provide a breakthrough for energy and chemical conversion devices.
CK-1:L06 Modulating the Composition of Bimetallic Fe-Ni Exsolved Nanoparticles
A. Tsiotsias1, 2, B. Ehrhardt1, B. Rudolph1, L. Nodari3, Seunghyun Kim4, WooChul Jung4, N. Charisiou2, M. Goula2, S. Mascotto1, 1Institut für Anorganische und Angewandte Chemie, Universität Hamburg, Hamburg, Germany; 2Department of Chemical Engineering, University of Western Macedonia, Koila, Kozani, Greece; 3Department of Chemical Science, University of Padua, Padova, Italy; 4Department of Materials Science and Engineering, KAIST, Daejeon, South Korea
Exsolution represents an attractive preparation method for high performance supported metal nanoparticles for SOFC applications. The exsolution of bimetallic systems, e.g. Fe-Ni alloys, has been diffusely reported in the literature. However, clear understanding of the segregation mechanism of two distinct ions needs still to be achieved. This is of pivotal importance to design intermetallic nanoparticles with tailored properties like size and composition. In the present work, we show how the bimetallic exsolution of Fe and Ni can be modulated both by controlling the exsolution temperature and the concentration of oxygen vacancies in A-site deficient (La,Sr)(Ti,Fe,Ni)O3. In particular, the different concentration of oxygen vacancies associated with iron, i.e. pentacoordinated Fe3+, has been found as the real determiner for the metal exsolution, especially of Fe. Due to the different segregation energy of the two metallic species, different Ni/Fe ratios were also obtained depending by varying the exsolution temperature (600-850 °C). Bimetallic nanoparticles with different composition had a remarkable effect on catalysis being able to tune the reforming and dehydrogenation pathways in the SOFC-relevant CO2-assisted ethane conversion.
CK-1:L07 High Temperature Mechanical Properties of Zirconia Thin Ceramic Foils for SOFCs
I. BOMBARDA, F. Dömling, T. Liensdorf, C. Sitzmann, N. Langhof, S. Schafföner, Universität Bayreuth, Bayreuth, Germany
For the cost-optimization of high temperature solid oxide fuel cells (SOFCs), an important role is played by the mechanical stability of the cell, which is mainly provided by the cell electrolyte. In this study, the mechanical performances of 90 µm thick Yttrium-stabilized 3YSZ electrolytes were investigated with a Ring-On-Ring (RoR) flexural test. The electrolytes were tested at room temperature and at T = 850 °C, which corresponds to SOFCs operational temperature. To calculate the material strength, a FEM simulation model was implemented. It was found that the electrolyte strength at T = 850 °C is reduced to half of the strength at room temperature. After the test, a fractographic analysis of the fracture surface was conducted by scanning electron microscopy (SEM) to individuate and characterize the crack initiation. It was found that for both the room temperature and high temperature tests, the fracture initiation often corresponds to a substrate defect, of dimensions up to 3 µm depth and 10 µm length. The finding demonstrates how, for both room and high temperature measures, surface irregularities have a large impact in the electrolyte strength when tested with the RoR flexural test.
CK-1:L08 Solid Oxide Fuel Monocell Based on Calcium Aluminate obtained by Functionally Gradient Materials
V.C. SOUSA1, F.C.T. Veiga1, J.J. Egea2, S.S. Cava3, 1UFRSG/PPGE3M/LABCAV, Porto Alegre, RS, Brazil; 2CSIC/ UFRSG-(CNPQ/Research PVE), Brazil; 3UFPEL/CCAF, Brazil
Solid oxide full cells (SOFC) have been developed using unusual types of oxide materials and innovative processes. The use of alternative materials and processes in order to reduce costs and guarantee good performance is of great interest for the development of new solid oxide fuel cells. Therefore, in this work, synthetic materials based on calcium aluminate and the functionally gradient material (FGMs) method were used for the manufacturing of the anode/electrolyte/cathode structure. Dense CA (calcium aluminate) was used as electrolyte, NiO/CA and LSM/CA porous were used as electrodes. As a result, the anode/electrolyte/cathode mono cell was manufactured. By scanning electron microscopy (SEM) of the SOFC it wasn’t observed cracks and other microstructural defects. In addition, the polarization curve at 650°C was obtained to evaluate the SOFC performance and presented at 0.6 V a density current of 1µA/cm2. The experimental values are relatively low in relation to the SOFC found in the literature; however, this material based in CA has about 3 orders of magnitude lower conductivity than zirconia stabilized with yttria. So, it presents potential to be used in full cells oxide solid with some adjustments in the processing.
CK-2:IL01 Innovative Architectured Oxygen Electrodes for IT-SOFC using Electrostatic Spray Deposition
E. Djurado, N.I. Khamidy, R.K. Sharma, Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble, France
Intermediate temperature solid oxide fuel cells are efficient energy-conversion systems for electrical power generation. In order to design novel optimized cathodes with improved mixed ionic-electronic properties, it is of high importance to control (i) the electrode microstructure and composition to obtain large surface areas, increasing the number of active sites for the oxygen reduction reaction, (ii) the electrode/electrolyte interface to enhance the charge transfer. Recent developments are discussed in the design of Pr doped lanthanum nickelates, La2-xPrxNiO4+δ (LPNO) with 0 ≤ x ≤ 2 using electrostatic spray deposition, a unique method capable of creating special microstructures. This talk will end with our latest results incorporating a composite sub-layer to the double layer LPNO electrode, to investigate the role of the electrode/electrolyte interface. The correlation between microstructure, composition, interfaces and electrochemical properties is discussed in detail.
CK-2:IL02 Perovskite Oxide Exsolution Anodes for Solid Oxide Fuel Cells
S.A. Barnett, T. ZHU, S. ZHANG, Northwestern University, Evanston, IL, USA
Solid oxide cell anodes that contain only oxide phases are desirable to avoid problems with Ni-based anodes, including coking in hydrocarbon fuels and degradation due to fuel impurities or redox cycling. This talk will describe various perovskite oxides that provide useful alternatives to Ni-YSZ. It is shown that oxide anode performance is often limited by the dissociative adsorption of hydrogen. One way to improve such anodes is by the addition of a reducible cation in the oxide formulation, resulting in the ex-solution of metallic nanoparticles on oxide surfaces in situ during cell startup and operation. This talk will examine the microstructural evolution of these “exsolution anodes,” and discuss how exsolved metal nanoparticles enhance electrochemical performance by promoting hydrogen dissociation. In particular,, Sr(Ti,Fe,Ni)O3 anodes where Ni-Fe nanoparticles form during cell operation will be discussed.
CK-2:IL04 Partial Conductivities in Proton-conducting Oxide Systems
G.C. Mather, D. Pérez Coll, G. Heras-Juaristi, Á. Triviño-Peláez, Instituto de Cerámica y Vidrio, CSIC, Campus de Cantoblanco, Madrid, Spain
The efficiency of an ion-conducting device component is highly dependent on the relative proportions of ionic and electronic partial conductivities, the determination of which has long been recognised as important for developing appropriate materials and understanding their behaviour under particular working conditions. Proton-conducting ceramic membranes for protonic ceramic fuel cells (PCFCs) and protonic ceramic electrolyser cells (PCECs) operate best with purely protonic conduction, whereas other applications require significant ionic and electronic (mixed) conductivity, including fuel-cell electrodes and membrane components. More recently, the requirement of co-ionic (proton and oxide ion) conductivity has been recognized as key to certain membrane reactor processes. Here we describe two methods of determining partial conductivities in mixed protonic, oxide-ionic and electronic conducting systems. The first involves emf measurements with correction of the electrode polarisation as applied to the SrZr0.9Y0.1O3- system. Secondly, the method of defect-chemistry analysis involving the examination of electrical conductivity data in different oxygen and water-vapour partial pressures as applied to the BaZr0.7Ce0.2Y0.1O3- and Ba1-xCe0.8Y0.2O3- systems will be described.
CK-2:IL05 Proton Conducting Solid Oxide Cells
M.E. IVANOVA1, W. Deibert1, C. Lenser1, O. Guillon1, 2, N.H. Menzler1, 1Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research (IEK-1), Jülich, Germany; 2JARA Jülich-Aachen Research Alliance – Energy, Germany
Ceramic proton conductors (PC) with tailored properties gain increasing scientific and industrial interest due to their multifaceted low temperature applications. PC solid oxide cells have high potential to produce electrical energy in a very efficient way. Reversible PC electrolysis/fuel cell devices can convert and store electrical surplus from renewables into H2 or NH3, which is then used as fuel when power generation is required. Renewably electrified PC co-electrolysers utilize CO2 emissions electrochemically to produce i.e. CH4, CH3OH, or syngas, while natural gas fuelled PC ceramic cells can co-generate electricity and valuable chemicals, e.g. olefins or aromatics (i.e. C2H4, C2H2, or C6H6). Such concepts for integration of PC ceramics offer significant process intensification resulting in higher overall energy efficiency, products selectivity and yields. The present talk will give an overview on different functional and utilization aspects of selected proton conductors (e.g. BaZr1-x(Ce,Y)xO3-δ, La5.5WO12-δ) [1] and ceramic composites (BaZr1-x(Ce,M)xO3-δ:Ce1-xMxO2-δ) in the light of achieving green and sustainable economy.
[1] W. Deibert, M. E. Ivanova, et al., J. Mater. Chem. A (2021) doi.org/10.1039/D1TA05240C
CK-2:IL08 Electrocatalysis at Nano-scaled Electrodes in Solid Oxide Fuel Cells
D.B. Drasbæk, M.L. Traulsen, B.R, Sudireddy, P. Holtappels, Technical University of Denmark, Kgs. Lyngby, Denmark
Low dimensional structures such as nano scaled electro catalysts and fibre structures can lead to electrodes with high electrochemical activity and are thus considered as promising electrode concepts for solid oxide fuel with operation temperatures below 800 C. At these operation temperatures electrocatalytic and catalytic processes are becoming important, and impedance spectroscopy in combination with Raman spectroscopy is a powerful tool to get an insight into the electrode processes. Based on a comparative study, Fe, Co in addition to Ni have been identified as promising electrocatalyst materials and have been investigated as regards their behavior in carbon containing gas atmospheres. The results show a clear decrease in carbon formation when Co was present in the electrode. In-situ experiments confirmed in general an electrode deactivation when carbon was built up. The influence on the impedance as well the detailed impact of operation parameters will be discussed in this contribution as regards the electrocatalytic activity of the different metals.
CK-2:L09 Novel In Situ Isotope Exchange Raman Spectroscopy for Improved Understanding of Physiochemical Processes
A. STANGL1, D. Pla1, C. Pirovano2, O. Chaix1, S. Ambrosio1, F. Baiutti3, F. Chiabrera3, M. Mermoux4, A. Tarancón3, C. Jimenez1, M. Burriel1, 1Univ. Grenoble Alpes, CNRS, Grenoble-INP, LMGP, Grenoble France; 2Univ. Lille, CNRS, Centrale Lille, ENSCL, Lille, France; 3Catalonia Institute for Energy Research (IREC), Barcelona, Spain; 4Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble, France
Thorough understanding of elementary physicochemical processes is the ultimate key in the performance enhancement of electrochemical devices such as solid oxide cells. We have developed a novel in situ methodology using Raman spectroscopy for the characterization of kinetic transport properties, such as self-diffusion and surface exchange coefficients of electrode and electrolyte materials based on isotopic exchange using a conventional temperature cell and Raman setup. Raman Spectroscopy is sensitive to molecular vibrational states. Isotopic substitution leads to changes in these vibrational states, translating into a shift of the corresponding Raman modes. Hence, changes in the isotopic composition due to isotopic exchange can be directly followed in situ, with spatial and temporal resolution, not accessible with conventional methods, such as isotope exchange depth profiling. This innovative approach therefore enables complementary insights for the study of ion transport properties of functional materials. Captivating benefits of this elegant in situ approach are its cost efficiency, speed, simple setup and sample preparation and its non-destructive nature. The strengths of this new approach will be showcased with our proof of concept study on (La,Sr)(Mn,Co)O3 thin films.
CK-2:L11 Nano-columnar La2NiO4+d Films with Multifold Active Surface Area for Enhanced Electrode Performance
A. RIAZ, A. Stangl, L. Rapenne, C. Jiménez, M. Burriel, Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, Grenoble, France; M. Mermoux, Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble, France
Micro-solid oxide fuel cells (μ-SOFC) are electrochemical devices composed of multilayered thin films which convert chemical energy into electrical power, and which could be used in low power portable electronic devices. Their integration into these devices requires low working temperatures (<500 oC), where the electrochemical performance is intrinsically reduced due to the sluggish oxygen reduction reaction at the cathode. La2NiO4+δ (L2NO4) is a promising cathode material for low temperatures due to its good electronic and ionic conductivity and high oxygen exchange activity with a low activation energy. In this work we report an innovative strategy to tune intrinsic and apparent surface activity by tailoring the nanostructure of L2NO4 thin films deposited by pulsed injection-MOCVD. The microstructure changes from a dense layer in the thinnest film (33nm) to a nano-columnar structure in thicker films (100-540 nm). Electrical conductivity relaxation measurements showed significantly enhanced surface activity in thicker, nano-columnar structured films, as compared to dense ones. Our results demonstrate that the increased surface area, in combination with the exposure of different surface terminations, leads to a significant enhancement of the total exchange activity in the films.
CK-3:IL01 Highly Performing and Stable Proton-conducting Steam Solid Oxide Electrolysis Cell with Triple-conductive Ruddlesden-Popper Phase Anode
Wenyuan Li, Xingbo Liu, West Virginia University, Mechanical & Aerospace Engineering Department, Morgantown, WV, USA
Triple-conducting Pr2NiO4+δ (PNO) is investigated as anode for the proton-conducting electrolysis cell. Good chemical compatibility is verified between PNO and BZCY proton-conducting electrolyte. Excellent catalytic activity towards water splitting is observed for PNO anode, 0.52 Ωcm2 for 550oC, 0.057 Ωcm2 for 700oC. Due to proton conduction in PNO, the PNO surface is activated for electrochemical reactions. The non-charge transfer processes account little for the electrode resistance. The performance of the PNO anode is determined by two charge transfer processes whose kinetics is governed the electrolyzing potential. This charge transfer-limiting nature is relatively benign since the electrode resistance has been found to exponentially reduce with increasing overpotential. To further improve the cell stability, proton conductors BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and La2Ce2O7 (LDC) are combined to create an interface active and steam-tolerant electrolyte for H-SOECs. LDC shows good chemical compatibility with BZCYYb. BZCYYb layer in the electrolyte promotes the HER at the cathode, resulting in a 108% improvement over the cell without this layer. The LDC layer, on the other hand, effectively protects BZCYYb from high concentration of vapor in a practical SOEC operation condition.
CK-3:IL02 Ex-situ Artificial Aging – An Effective Tool for Solid Oxide Cells Accelerated Stress Tests
D. VLADIKOVA, B. Burdin, A. Sheikh, M. Krapchanska, IEES-BAS, Sofia, Bulgaria; P. Piccardo, University of Genoa, Genoa, Italy; D. Montinaro, SOLIDpower S.p.A, Mezzolombardo, Italy
Solid Oxide Cells (SOC) are under intensive development for fulfilling the 2030 targets for decarbonization, since they ensure opportunities for integration of renewable energy sources into the overall energy system. Taking into account the target for commercial lifetime of 80000 hours, intensive work is performed for decreasing the degradation rate. Obviously experiments lasting years are not acceptable for market needs. This work aims at development of accelerated stress tests (AST) for SOC by artificial aging of the fuel electrode via redox cycling which in principle follows the degradation processes of calendar aging (Ni coarsening and migration).The advantages of the developed procedure are that it ensures reproducible and fine-tuned level of oxidation which can be regulated by direct impedance monitoring of the Ni network resistance changes during oxidation/reduction performed on anode sample. Once the redox cycling conditions are adjusted, the artificial aging is introduced for AST in full cell configuration. The developed methodology is evaluated by comparative analysis of current-voltage and impedance measurements of pristine, artificially aged and calendar aged cells. The experimental results register more than 100 times acceleration.
CK-3:L05 A Simple Approach to make the Commercial Solid Oxide Fuel Cells Flexible in the Use of Fuels
s. campagna zignani, M. Lo Faro, A.S. Aricò, Institute of Advanced Energy Technologies (ITAE) of the Italian National Research Council (CNR), Messina, Italy
This communication will compare the electrochemical performances of a commercial cell fed with dry ethanol with various coating layers ad-hoc prepared. The addition of a protective layer based did not imply a substantial modification for the cell. In our experiments, the protective layer was deposited by spray coating but, the approach is amenable also for other coating methods. Suitable electrochemical performances, achieved in the presence of dry ethanol, indicate that the direct oxidation of ethanol can occur at good reaction rates in the presence of an appropriate catalytic pre-layer at the anode. The increased activity towards these processes allows for a simplification of the SOFC system since no external reforming step appears strictly necessary. Acknowledgements The authors acknowledge the Italian Ministry of Research and Education for the financial support of the DIRECTBIOPOWER project within the program "PROGRAMMI DI RICERCA SCIENTIFICA DI RILEVANTE INTERESSE NAZIONALE- PRIN PROGRAMMA DI RICERCA - Anno 2017 - prot. 2017FCFYHK_002".
CK-4:IL03 Freeze Tape-casted and In Situ-decorated Solid Oxide Cells for Reversible Applications
P. CARPANESE1, D. Cademartori1, D. Clematis1, A.M. Asensio1, S. Presto2, M. Viviani2, A. Barbucci1, 2, 1Department of Civil, Chemical and Environmental Engineering (DICCA), University of Genova, Genova, Italy; 2Institute of Condensed Matter Chemistry and Technology for Energy (ICMATE), National Research Council (CNR), c/o DICCA-UNIGE, Genova, Italy
Solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) constitute important technologies to reach the low carbon economy planned for 2050. >From a macroscopic point of view SOFCs and SOECs do not exhibit significant differences, nevertheless an appropriate choice of materials and design must be accomplished, since degradation over time is a matter not solved yet. In light of these considerations, a cell with a symmetrical structure through the freeze tape-casting technique was manufactured [1], to be operated with high efficiency as reversible system. The body of the cell is made of yttria-stabilised zirconia (YSZ) at the fuel side and gadolinia-doped ceria (GDC) at the oxygen side, and is characterised by an anisotropic porosity. This feature improves ionic tortuosity and favours the gas evacuation in electrolysis operation, preventing delamination of the oxygen electrode, being this one of the main modes of failure especially in SOEC mode. Furthermore, the symmetry of the assembly minimizes the risk of fractures during the sintering phase, which is indeed carried out in a single step. On this electrolytic frame, the electrocatalyst has been grown up through in-situ decoration methods.
[1] T. L. Cable, S. W. Sofie, J. Power Sources 2007, 174, 221.
CK-4:IL06 SOFC Development in Jülich / Utilization of Bio-Syngas in Solid Oxide Fuel Cell Stacks
C. Lenser1, H. Jeong1,3, M. Hauser2, S. Fendt2, F. Fischer2, M. Hauck2, S. Herrmann2, H. Spliethoff2, O. Guillon4, N.H. Menzler1, 1Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research - Materials Synthesis and Processing (IEK-1), Jülich, Germany; 2Technische Universität München, Chair of Energy Systems, Garching, Germany; 3Korea Institute of Ceramic Engineering and Technology (KICET), Engineering Ceramic Center, Seoul, South Korea; 4Jülich Aachen Research Alliance: JARA-Energy, Jülich, Germany
The main focus of SOC development at Forschungszentrum Jülich is on optimized, mass-production compatible manufacturing technologies of anode-supported fuel cells (ASCs) and on understanding the degradation phenomena of fuel cells during long-term stack operation. Primary achievements include the continuous operation of a planar SOFC stack for > 93.000 hours as well as new insights into the mechanisms of chromium-related cathode degradation. The coupling of a biomass gasifier with an SOFC stack has been demonstrated within a joint project with TU Munich, and the degradation effects on cell and stack level have been investigated with tar-containing model gases as well real bio-syngas. The drastic degradation effects observed demonstrate that substantial improvements of the coking resistance of the fuel side of the stack are necessary if the economically attractive operation of such a system without a gas cleaning system is to be realized. In further work, an electrolyte based on doped ceria was developed that enables the incorporation of Ni-GDC fuel electrodes into the co-sintered ASC. The continuation in the SynSOFC 2 project aims to further distinguish the influence of chemical and electro-chemical interactions of the cell with the contaminants.
CK-5:IL02 Characterisation of Materials for Solid Oxide Cells by Means of Model-type Thin Film Samples
a.k. opitz, TU Wien, Institute of Chemical Technologies and Analytics, Vienna, Austria
For a knowledge-based optimisation of solid oxide cells (SOCs) basic electrochemical parameters such as conductivities or reaction resistances of the used materials are needed. Extracting these parameters from porous electrodes is challenging, since their exact geometry is difficult to assess. Model-type systems based on thin films are a powerful tool, since they offer a well-defined, adjustable, and thus known geometry. Here, 3 cases will be discussed, where model-type thin film samples are employed to study SOC materials: i) Micro-patterned Ni/YSZ electrodes are used for separation of two different reaction pathways of H2 oxidation. The defined variation of the electrode geometry allows quantifying a triple phase boundary (TPB) length related and an area related reaction resistance. ii) The p(O2) dependent ionic grain boundary conductivity of Gd-doped CeO2 (GDC) films is separated from the p(O2) independent grain interior conductivity by means of impedance measurements using interdigitating electrodes. Moreover, the poisoning effect of H2S on GDC is studied and the result is transferred to the impedance analysis of real 3D porous Ni/GDC fuel electrodes. iii) Perovskite-type thin film electrodes are used to study the electrochemical switchability of exsolution-based catalysts.
CK-5:IL03 Modelling and Characterization of Solid Oxide Cells: Impact of Microstructure and Reaction Mechanisms on Cell Performances and Degradation
m. hubert, A. Abaza, L. Rorato, G. Sassone, L. Yefsah, J. Laurencin, Univ. Grenoble Alpes – CEA/LITEN/DTCH, Grenoble, France
Solid Oxide Cells (SOCs) are electrochemical devices working at high temperature. In the recent years, they have gained interest due to their advantages such as high electrical efficiency, reversibility and fuel flexibility. However, the durability still needs to be improved for a large-scale deployment of this technology. Indeed, the high temperatures and the polarization activates degradation phenomena that lead to various material and mechanical instabilities in the electrodes limiting the SOCs durability. To date, the basic degradation mechanisms associated to the complex electrode multi-steps reaction pathways are still not precisely understood. To address this issue, a trifold approach has been developed coupling electrochemical tests with advanced post-mortem characterizations and multi-physic modelling. This methodology has been applied to the typical fuel electrode made of Nickel and Yttria Stabilized Zirconia (Ni-YSZ) and air electrode composed of a Lanthanum Strontium Cobalt Ferrite (LSCF) or Lanthanum Nickelate (LNO). For each case, a better understanding of the reaction mechanism has been proposed. Moreover, the microstructural evolutions, the material decompositions as well as mechanical damage in the electrodes have been studied.
CK-5:IL04 Model Experiments for Bridging the Gap between Fundamentals and Applied SOFC Research
A. Nenning1, A.K. Opitz1, C. Bischof2, M. HOLZMANN1, M. Gerstl1, M. Doppler1, M. Bram2, 1Technical University Vienna, Institute of Chemical Technologies and Analytics, Vienna, Austria; 2Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research, Materials Synthesis and Processing (IEK-1), Jülich, Germany
Electrochemical impedance spectroscopy (EIS) is a powerful tool to investigate the kinetics of electrochemical model systems or entire SOFC stacks. At an intermediate degree of abstraction, EIS studies on symmetrical model cells allow mechanistic, detailed insight into electrochemical properties and reaction mechanisms of electrodes with the same materials, processing and microstructures that are used in SOFC stacks. From impedance studies of Gd-doped Ceria (GDC) – Nickel cermet anodes we can quantify parameters such as the effective oxide ion conductivity of the porous structure, gas diffusion kinetics and the rate of hydrogen oxidation at the GDC surface as well as the electrochemically active thickness. Quantitative knowledge of these parameters allows us to predict how microstructural modifications, e.g. by Ni content, particle size, thickness or sintering temperature will influence the electrode performance and deliver targeted optimization strategies. For example, we can explain why electrodes with a thin, Ni-free GDC functional layers can even exceed the performance of the very good Ni-GDC cermets, which were employed in metal supported cells and deliver a power density of 2.5 W/cm2 at 700°C with negligible degradation for 1000 hours.
CK-5:IL05 Computational Modeling and Simulation of Ion Transport in Oxide Electrolytes for Energy Conversion
M. MARTIN, RWTH Aachen University, Aachen, Germany
Ion transport in oxides plays an important role in energy and environmental applications. Important examples are oxygen ion or proton conducting oxides for electrolytes in electrolyzers and fuel cells. I will present our recent theoretical approaches to understand these ionic transport processes in detail. We use density-functioal theory (DFT) to calculate on a microscopic level defect interaction energies and migration energies of the defects that enable ionic motion. By means of Kinetic Monte Carlo (KMC) simulations we then predict macroscopic ion mobilities and ion conductivities on an ab initio level, i.e. without any adjustable parameters. As first example we will discuss rare-earth doped ceria. We show that all interactions between defects contribute to the so-called conductivity maximum of the ionic conductivity [1]. The second example concerns BaZrO3-based oxides which are proto-type proton conductors. We show that the proton mobility is determined by nanoscale percolation of dopant ions which enables high proton mobility along [2].
[1] J. Koettgen, S. Grieshammer, P. Hein, B. Grope, M. Nakayama, M. Martin, Phys. Chem. Chem. Phys. 20, 14291 (2018) [2] F.M. Draber, C. Ader, J.P. Arnold, S. Eisele, S. Grieshammer, S. Yamaguchi, M. Martin, Nature Mater. 19, 338 (2020)
J. Villanova, ESRF The European Synchrotron, Grenoble Cedex, France; S. Schlabach, Institute for Applied Materials and Karlsruhe Nano Micro Facility, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany; A. Brisse, A. LEON, European Institute for Energy Research, Karlsruhe, Germany
The degradation processes in solid oxide cells have been investigated by applying nanoscale X-ray fluorescence spectroscopy on a cathode and an electrolyte supported cell that have been in electrolysis mode for 6,100 and 23,000 hours, respectively. 2D map with 50 nm resolution were acquired for Ni, Y, Ce, Gd, La, Sr, Co, Fe that provides high-resolution compositional analysis in combination with high lateral resolution. It will be shown that during the sintering process, different elements are diffusing to form additional layers at different interfaces of the functional layers. After long-term operation, some of the layer thickness only evolves. The cobalt is the element that is highly segregating from the LSCF electrode in both type of cell. The gadolinium from the CGO layer shows an accumulation at the CGO/electrolyte interface on the oxygen electrode side and on the hydrogen electrode side in the electrolyte supported cell. The concentration significantly increases during the cell operation to form a layer of a few micrometers. The Ni depletion seems to be prevented by the contact layer inserted between the hydrogen electrode and the electrolyte.
CK-1:IL05 Hydride Superionic Conduction in Ba1.75LiH2.7O0.9
GENKI KOBAYASHI, Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Japan
Hydride ions (H–) can act as charge carriers as they exhibit several features suitable for fast ion conduction: monovalence, the moderate ionic size comparable to O2– and F–, and high polarizability. Furthermore, hydride ions exhibit strong reducing properties through the standard H–/H2 redox potential (–2.3 V vs. SHE), which can be expected to be applied to novel electrochemical devices. Following some investigations on H– conduction in alkaline earth metal hydrides, we reported H– conduction in an oxide- based framework structure for the first time by finding a series of H–conductive oxyhydrides, La2–x–ySrx+yLiH1–x+yO3–y. The discovery has triggered the exploration of materials for H– conductors such as K2NiF4-type Ln2LiHO3 (Ln = Pr, Nd), and Ba2MHO3 (M = Sc, Y). However, H– conductors exhibiting both high conductivity and low activation energy had not been developed yet. In the present study, we report a new H– conductive oxyhydride, Ba1.75LiH2.7O0.9, containing a high amount of barium and anion vacancies and exhibiting long-range ordering at room temperature. Increasing the temperature above 315 °C disorder the ordered vacancies, triggering superionic conduction with a high H– conductivity of over 0.01 S cm–1 nearly independent of the temperature. Such a remarkable H– conducting nature at intermediate temperatures is anticipated to provide a breakthrough for energy and chemical conversion devices.
CK-1:L06 Modulating the Composition of Bimetallic Fe-Ni Exsolved Nanoparticles
A. Tsiotsias1, 2, B. Ehrhardt1, B. Rudolph1, L. Nodari3, Seunghyun Kim4, WooChul Jung4, N. Charisiou2, M. Goula2, S. Mascotto1, 1Institut für Anorganische und Angewandte Chemie, Universität Hamburg, Hamburg, Germany; 2Department of Chemical Engineering, University of Western Macedonia, Koila, Kozani, Greece; 3Department of Chemical Science, University of Padua, Padova, Italy; 4Department of Materials Science and Engineering, KAIST, Daejeon, South Korea
Exsolution represents an attractive preparation method for high performance supported metal nanoparticles for SOFC applications. The exsolution of bimetallic systems, e.g. Fe-Ni alloys, has been diffusely reported in the literature. However, clear understanding of the segregation mechanism of two distinct ions needs still to be achieved. This is of pivotal importance to design intermetallic nanoparticles with tailored properties like size and composition. In the present work, we show how the bimetallic exsolution of Fe and Ni can be modulated both by controlling the exsolution temperature and the concentration of oxygen vacancies in A-site deficient (La,Sr)(Ti,Fe,Ni)O3. In particular, the different concentration of oxygen vacancies associated with iron, i.e. pentacoordinated Fe3+, has been found as the real determiner for the metal exsolution, especially of Fe. Due to the different segregation energy of the two metallic species, different Ni/Fe ratios were also obtained depending by varying the exsolution temperature (600-850 °C). Bimetallic nanoparticles with different composition had a remarkable effect on catalysis being able to tune the reforming and dehydrogenation pathways in the SOFC-relevant CO2-assisted ethane conversion.
CK-1:L07 High Temperature Mechanical Properties of Zirconia Thin Ceramic Foils for SOFCs
I. BOMBARDA, F. Dömling, T. Liensdorf, C. Sitzmann, N. Langhof, S. Schafföner, Universität Bayreuth, Bayreuth, Germany
For the cost-optimization of high temperature solid oxide fuel cells (SOFCs), an important role is played by the mechanical stability of the cell, which is mainly provided by the cell electrolyte. In this study, the mechanical performances of 90 µm thick Yttrium-stabilized 3YSZ electrolytes were investigated with a Ring-On-Ring (RoR) flexural test. The electrolytes were tested at room temperature and at T = 850 °C, which corresponds to SOFCs operational temperature. To calculate the material strength, a FEM simulation model was implemented. It was found that the electrolyte strength at T = 850 °C is reduced to half of the strength at room temperature. After the test, a fractographic analysis of the fracture surface was conducted by scanning electron microscopy (SEM) to individuate and characterize the crack initiation. It was found that for both the room temperature and high temperature tests, the fracture initiation often corresponds to a substrate defect, of dimensions up to 3 µm depth and 10 µm length. The finding demonstrates how, for both room and high temperature measures, surface irregularities have a large impact in the electrolyte strength when tested with the RoR flexural test.
CK-1:L08 Solid Oxide Fuel Monocell Based on Calcium Aluminate obtained by Functionally Gradient Materials
V.C. SOUSA1, F.C.T. Veiga1, J.J. Egea2, S.S. Cava3, 1UFRSG/PPGE3M/LABCAV, Porto Alegre, RS, Brazil; 2CSIC/ UFRSG-(CNPQ/Research PVE), Brazil; 3UFPEL/CCAF, Brazil
Solid oxide full cells (SOFC) have been developed using unusual types of oxide materials and innovative processes. The use of alternative materials and processes in order to reduce costs and guarantee good performance is of great interest for the development of new solid oxide fuel cells. Therefore, in this work, synthetic materials based on calcium aluminate and the functionally gradient material (FGMs) method were used for the manufacturing of the anode/electrolyte/cathode structure. Dense CA (calcium aluminate) was used as electrolyte, NiO/CA and LSM/CA porous were used as electrodes. As a result, the anode/electrolyte/cathode mono cell was manufactured. By scanning electron microscopy (SEM) of the SOFC it wasn’t observed cracks and other microstructural defects. In addition, the polarization curve at 650°C was obtained to evaluate the SOFC performance and presented at 0.6 V a density current of 1µA/cm2. The experimental values are relatively low in relation to the SOFC found in the literature; however, this material based in CA has about 3 orders of magnitude lower conductivity than zirconia stabilized with yttria. So, it presents potential to be used in full cells oxide solid with some adjustments in the processing.
CK-2:IL01 Innovative Architectured Oxygen Electrodes for IT-SOFC using Electrostatic Spray Deposition
E. Djurado, N.I. Khamidy, R.K. Sharma, Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble, France
Intermediate temperature solid oxide fuel cells are efficient energy-conversion systems for electrical power generation. In order to design novel optimized cathodes with improved mixed ionic-electronic properties, it is of high importance to control (i) the electrode microstructure and composition to obtain large surface areas, increasing the number of active sites for the oxygen reduction reaction, (ii) the electrode/electrolyte interface to enhance the charge transfer. Recent developments are discussed in the design of Pr doped lanthanum nickelates, La2-xPrxNiO4+δ (LPNO) with 0 ≤ x ≤ 2 using electrostatic spray deposition, a unique method capable of creating special microstructures. This talk will end with our latest results incorporating a composite sub-layer to the double layer LPNO electrode, to investigate the role of the electrode/electrolyte interface. The correlation between microstructure, composition, interfaces and electrochemical properties is discussed in detail.
CK-2:IL02 Perovskite Oxide Exsolution Anodes for Solid Oxide Fuel Cells
S.A. Barnett, T. ZHU, S. ZHANG, Northwestern University, Evanston, IL, USA
Solid oxide cell anodes that contain only oxide phases are desirable to avoid problems with Ni-based anodes, including coking in hydrocarbon fuels and degradation due to fuel impurities or redox cycling. This talk will describe various perovskite oxides that provide useful alternatives to Ni-YSZ. It is shown that oxide anode performance is often limited by the dissociative adsorption of hydrogen. One way to improve such anodes is by the addition of a reducible cation in the oxide formulation, resulting in the ex-solution of metallic nanoparticles on oxide surfaces in situ during cell startup and operation. This talk will examine the microstructural evolution of these “exsolution anodes,” and discuss how exsolved metal nanoparticles enhance electrochemical performance by promoting hydrogen dissociation. In particular,, Sr(Ti,Fe,Ni)O3 anodes where Ni-Fe nanoparticles form during cell operation will be discussed.
CK-2:IL04 Partial Conductivities in Proton-conducting Oxide Systems
G.C. Mather, D. Pérez Coll, G. Heras-Juaristi, Á. Triviño-Peláez, Instituto de Cerámica y Vidrio, CSIC, Campus de Cantoblanco, Madrid, Spain
The efficiency of an ion-conducting device component is highly dependent on the relative proportions of ionic and electronic partial conductivities, the determination of which has long been recognised as important for developing appropriate materials and understanding their behaviour under particular working conditions. Proton-conducting ceramic membranes for protonic ceramic fuel cells (PCFCs) and protonic ceramic electrolyser cells (PCECs) operate best with purely protonic conduction, whereas other applications require significant ionic and electronic (mixed) conductivity, including fuel-cell electrodes and membrane components. More recently, the requirement of co-ionic (proton and oxide ion) conductivity has been recognized as key to certain membrane reactor processes. Here we describe two methods of determining partial conductivities in mixed protonic, oxide-ionic and electronic conducting systems. The first involves emf measurements with correction of the electrode polarisation as applied to the SrZr0.9Y0.1O3- system. Secondly, the method of defect-chemistry analysis involving the examination of electrical conductivity data in different oxygen and water-vapour partial pressures as applied to the BaZr0.7Ce0.2Y0.1O3- and Ba1-xCe0.8Y0.2O3- systems will be described.
CK-2:IL05 Proton Conducting Solid Oxide Cells
M.E. IVANOVA1, W. Deibert1, C. Lenser1, O. Guillon1, 2, N.H. Menzler1, 1Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research (IEK-1), Jülich, Germany; 2JARA Jülich-Aachen Research Alliance – Energy, Germany
Ceramic proton conductors (PC) with tailored properties gain increasing scientific and industrial interest due to their multifaceted low temperature applications. PC solid oxide cells have high potential to produce electrical energy in a very efficient way. Reversible PC electrolysis/fuel cell devices can convert and store electrical surplus from renewables into H2 or NH3, which is then used as fuel when power generation is required. Renewably electrified PC co-electrolysers utilize CO2 emissions electrochemically to produce i.e. CH4, CH3OH, or syngas, while natural gas fuelled PC ceramic cells can co-generate electricity and valuable chemicals, e.g. olefins or aromatics (i.e. C2H4, C2H2, or C6H6). Such concepts for integration of PC ceramics offer significant process intensification resulting in higher overall energy efficiency, products selectivity and yields. The present talk will give an overview on different functional and utilization aspects of selected proton conductors (e.g. BaZr1-x(Ce,Y)xO3-δ, La5.5WO12-δ) [1] and ceramic composites (BaZr1-x(Ce,M)xO3-δ:Ce1-xMxO2-δ) in the light of achieving green and sustainable economy.
[1] W. Deibert, M. E. Ivanova, et al., J. Mater. Chem. A (2021) doi.org/10.1039/D1TA05240C
CK-2:IL08 Electrocatalysis at Nano-scaled Electrodes in Solid Oxide Fuel Cells
D.B. Drasbæk, M.L. Traulsen, B.R, Sudireddy, P. Holtappels, Technical University of Denmark, Kgs. Lyngby, Denmark
Low dimensional structures such as nano scaled electro catalysts and fibre structures can lead to electrodes with high electrochemical activity and are thus considered as promising electrode concepts for solid oxide fuel with operation temperatures below 800 C. At these operation temperatures electrocatalytic and catalytic processes are becoming important, and impedance spectroscopy in combination with Raman spectroscopy is a powerful tool to get an insight into the electrode processes. Based on a comparative study, Fe, Co in addition to Ni have been identified as promising electrocatalyst materials and have been investigated as regards their behavior in carbon containing gas atmospheres. The results show a clear decrease in carbon formation when Co was present in the electrode. In-situ experiments confirmed in general an electrode deactivation when carbon was built up. The influence on the impedance as well the detailed impact of operation parameters will be discussed in this contribution as regards the electrocatalytic activity of the different metals.
CK-2:L09 Novel In Situ Isotope Exchange Raman Spectroscopy for Improved Understanding of Physiochemical Processes
A. STANGL1, D. Pla1, C. Pirovano2, O. Chaix1, S. Ambrosio1, F. Baiutti3, F. Chiabrera3, M. Mermoux4, A. Tarancón3, C. Jimenez1, M. Burriel1, 1Univ. Grenoble Alpes, CNRS, Grenoble-INP, LMGP, Grenoble France; 2Univ. Lille, CNRS, Centrale Lille, ENSCL, Lille, France; 3Catalonia Institute for Energy Research (IREC), Barcelona, Spain; 4Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble, France
Thorough understanding of elementary physicochemical processes is the ultimate key in the performance enhancement of electrochemical devices such as solid oxide cells. We have developed a novel in situ methodology using Raman spectroscopy for the characterization of kinetic transport properties, such as self-diffusion and surface exchange coefficients of electrode and electrolyte materials based on isotopic exchange using a conventional temperature cell and Raman setup. Raman Spectroscopy is sensitive to molecular vibrational states. Isotopic substitution leads to changes in these vibrational states, translating into a shift of the corresponding Raman modes. Hence, changes in the isotopic composition due to isotopic exchange can be directly followed in situ, with spatial and temporal resolution, not accessible with conventional methods, such as isotope exchange depth profiling. This innovative approach therefore enables complementary insights for the study of ion transport properties of functional materials. Captivating benefits of this elegant in situ approach are its cost efficiency, speed, simple setup and sample preparation and its non-destructive nature. The strengths of this new approach will be showcased with our proof of concept study on (La,Sr)(Mn,Co)O3 thin films.
CK-2:L11 Nano-columnar La2NiO4+d Films with Multifold Active Surface Area for Enhanced Electrode Performance
A. RIAZ, A. Stangl, L. Rapenne, C. Jiménez, M. Burriel, Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, Grenoble, France; M. Mermoux, Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble, France
Micro-solid oxide fuel cells (μ-SOFC) are electrochemical devices composed of multilayered thin films which convert chemical energy into electrical power, and which could be used in low power portable electronic devices. Their integration into these devices requires low working temperatures (<500 oC), where the electrochemical performance is intrinsically reduced due to the sluggish oxygen reduction reaction at the cathode. La2NiO4+δ (L2NO4) is a promising cathode material for low temperatures due to its good electronic and ionic conductivity and high oxygen exchange activity with a low activation energy. In this work we report an innovative strategy to tune intrinsic and apparent surface activity by tailoring the nanostructure of L2NO4 thin films deposited by pulsed injection-MOCVD. The microstructure changes from a dense layer in the thinnest film (33nm) to a nano-columnar structure in thicker films (100-540 nm). Electrical conductivity relaxation measurements showed significantly enhanced surface activity in thicker, nano-columnar structured films, as compared to dense ones. Our results demonstrate that the increased surface area, in combination with the exposure of different surface terminations, leads to a significant enhancement of the total exchange activity in the films.
CK-3:IL01 Highly Performing and Stable Proton-conducting Steam Solid Oxide Electrolysis Cell with Triple-conductive Ruddlesden-Popper Phase Anode
Wenyuan Li, Xingbo Liu, West Virginia University, Mechanical & Aerospace Engineering Department, Morgantown, WV, USA
Triple-conducting Pr2NiO4+δ (PNO) is investigated as anode for the proton-conducting electrolysis cell. Good chemical compatibility is verified between PNO and BZCY proton-conducting electrolyte. Excellent catalytic activity towards water splitting is observed for PNO anode, 0.52 Ωcm2 for 550oC, 0.057 Ωcm2 for 700oC. Due to proton conduction in PNO, the PNO surface is activated for electrochemical reactions. The non-charge transfer processes account little for the electrode resistance. The performance of the PNO anode is determined by two charge transfer processes whose kinetics is governed the electrolyzing potential. This charge transfer-limiting nature is relatively benign since the electrode resistance has been found to exponentially reduce with increasing overpotential. To further improve the cell stability, proton conductors BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and La2Ce2O7 (LDC) are combined to create an interface active and steam-tolerant electrolyte for H-SOECs. LDC shows good chemical compatibility with BZCYYb. BZCYYb layer in the electrolyte promotes the HER at the cathode, resulting in a 108% improvement over the cell without this layer. The LDC layer, on the other hand, effectively protects BZCYYb from high concentration of vapor in a practical SOEC operation condition.
CK-3:IL02 Ex-situ Artificial Aging – An Effective Tool for Solid Oxide Cells Accelerated Stress Tests
D. VLADIKOVA, B. Burdin, A. Sheikh, M. Krapchanska, IEES-BAS, Sofia, Bulgaria; P. Piccardo, University of Genoa, Genoa, Italy; D. Montinaro, SOLIDpower S.p.A, Mezzolombardo, Italy
Solid Oxide Cells (SOC) are under intensive development for fulfilling the 2030 targets for decarbonization, since they ensure opportunities for integration of renewable energy sources into the overall energy system. Taking into account the target for commercial lifetime of 80000 hours, intensive work is performed for decreasing the degradation rate. Obviously experiments lasting years are not acceptable for market needs. This work aims at development of accelerated stress tests (AST) for SOC by artificial aging of the fuel electrode via redox cycling which in principle follows the degradation processes of calendar aging (Ni coarsening and migration).The advantages of the developed procedure are that it ensures reproducible and fine-tuned level of oxidation which can be regulated by direct impedance monitoring of the Ni network resistance changes during oxidation/reduction performed on anode sample. Once the redox cycling conditions are adjusted, the artificial aging is introduced for AST in full cell configuration. The developed methodology is evaluated by comparative analysis of current-voltage and impedance measurements of pristine, artificially aged and calendar aged cells. The experimental results register more than 100 times acceleration.
CK-3:L05 A Simple Approach to make the Commercial Solid Oxide Fuel Cells Flexible in the Use of Fuels
s. campagna zignani, M. Lo Faro, A.S. Aricò, Institute of Advanced Energy Technologies (ITAE) of the Italian National Research Council (CNR), Messina, Italy
This communication will compare the electrochemical performances of a commercial cell fed with dry ethanol with various coating layers ad-hoc prepared. The addition of a protective layer based did not imply a substantial modification for the cell. In our experiments, the protective layer was deposited by spray coating but, the approach is amenable also for other coating methods. Suitable electrochemical performances, achieved in the presence of dry ethanol, indicate that the direct oxidation of ethanol can occur at good reaction rates in the presence of an appropriate catalytic pre-layer at the anode. The increased activity towards these processes allows for a simplification of the SOFC system since no external reforming step appears strictly necessary. Acknowledgements The authors acknowledge the Italian Ministry of Research and Education for the financial support of the DIRECTBIOPOWER project within the program "PROGRAMMI DI RICERCA SCIENTIFICA DI RILEVANTE INTERESSE NAZIONALE- PRIN PROGRAMMA DI RICERCA - Anno 2017 - prot. 2017FCFYHK_002".
CK-4:IL03 Freeze Tape-casted and In Situ-decorated Solid Oxide Cells for Reversible Applications
P. CARPANESE1, D. Cademartori1, D. Clematis1, A.M. Asensio1, S. Presto2, M. Viviani2, A. Barbucci1, 2, 1Department of Civil, Chemical and Environmental Engineering (DICCA), University of Genova, Genova, Italy; 2Institute of Condensed Matter Chemistry and Technology for Energy (ICMATE), National Research Council (CNR), c/o DICCA-UNIGE, Genova, Italy
Solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) constitute important technologies to reach the low carbon economy planned for 2050. >From a macroscopic point of view SOFCs and SOECs do not exhibit significant differences, nevertheless an appropriate choice of materials and design must be accomplished, since degradation over time is a matter not solved yet. In light of these considerations, a cell with a symmetrical structure through the freeze tape-casting technique was manufactured [1], to be operated with high efficiency as reversible system. The body of the cell is made of yttria-stabilised zirconia (YSZ) at the fuel side and gadolinia-doped ceria (GDC) at the oxygen side, and is characterised by an anisotropic porosity. This feature improves ionic tortuosity and favours the gas evacuation in electrolysis operation, preventing delamination of the oxygen electrode, being this one of the main modes of failure especially in SOEC mode. Furthermore, the symmetry of the assembly minimizes the risk of fractures during the sintering phase, which is indeed carried out in a single step. On this electrolytic frame, the electrocatalyst has been grown up through in-situ decoration methods.
[1] T. L. Cable, S. W. Sofie, J. Power Sources 2007, 174, 221.
CK-4:IL06 SOFC Development in Jülich / Utilization of Bio-Syngas in Solid Oxide Fuel Cell Stacks
C. Lenser1, H. Jeong1,3, M. Hauser2, S. Fendt2, F. Fischer2, M. Hauck2, S. Herrmann2, H. Spliethoff2, O. Guillon4, N.H. Menzler1, 1Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research - Materials Synthesis and Processing (IEK-1), Jülich, Germany; 2Technische Universität München, Chair of Energy Systems, Garching, Germany; 3Korea Institute of Ceramic Engineering and Technology (KICET), Engineering Ceramic Center, Seoul, South Korea; 4Jülich Aachen Research Alliance: JARA-Energy, Jülich, Germany
The main focus of SOC development at Forschungszentrum Jülich is on optimized, mass-production compatible manufacturing technologies of anode-supported fuel cells (ASCs) and on understanding the degradation phenomena of fuel cells during long-term stack operation. Primary achievements include the continuous operation of a planar SOFC stack for > 93.000 hours as well as new insights into the mechanisms of chromium-related cathode degradation. The coupling of a biomass gasifier with an SOFC stack has been demonstrated within a joint project with TU Munich, and the degradation effects on cell and stack level have been investigated with tar-containing model gases as well real bio-syngas. The drastic degradation effects observed demonstrate that substantial improvements of the coking resistance of the fuel side of the stack are necessary if the economically attractive operation of such a system without a gas cleaning system is to be realized. In further work, an electrolyte based on doped ceria was developed that enables the incorporation of Ni-GDC fuel electrodes into the co-sintered ASC. The continuation in the SynSOFC 2 project aims to further distinguish the influence of chemical and electro-chemical interactions of the cell with the contaminants.
CK-5:IL02 Characterisation of Materials for Solid Oxide Cells by Means of Model-type Thin Film Samples
a.k. opitz, TU Wien, Institute of Chemical Technologies and Analytics, Vienna, Austria
For a knowledge-based optimisation of solid oxide cells (SOCs) basic electrochemical parameters such as conductivities or reaction resistances of the used materials are needed. Extracting these parameters from porous electrodes is challenging, since their exact geometry is difficult to assess. Model-type systems based on thin films are a powerful tool, since they offer a well-defined, adjustable, and thus known geometry. Here, 3 cases will be discussed, where model-type thin film samples are employed to study SOC materials: i) Micro-patterned Ni/YSZ electrodes are used for separation of two different reaction pathways of H2 oxidation. The defined variation of the electrode geometry allows quantifying a triple phase boundary (TPB) length related and an area related reaction resistance. ii) The p(O2) dependent ionic grain boundary conductivity of Gd-doped CeO2 (GDC) films is separated from the p(O2) independent grain interior conductivity by means of impedance measurements using interdigitating electrodes. Moreover, the poisoning effect of H2S on GDC is studied and the result is transferred to the impedance analysis of real 3D porous Ni/GDC fuel electrodes. iii) Perovskite-type thin film electrodes are used to study the electrochemical switchability of exsolution-based catalysts.
CK-5:IL03 Modelling and Characterization of Solid Oxide Cells: Impact of Microstructure and Reaction Mechanisms on Cell Performances and Degradation
m. hubert, A. Abaza, L. Rorato, G. Sassone, L. Yefsah, J. Laurencin, Univ. Grenoble Alpes – CEA/LITEN/DTCH, Grenoble, France
Solid Oxide Cells (SOCs) are electrochemical devices working at high temperature. In the recent years, they have gained interest due to their advantages such as high electrical efficiency, reversibility and fuel flexibility. However, the durability still needs to be improved for a large-scale deployment of this technology. Indeed, the high temperatures and the polarization activates degradation phenomena that lead to various material and mechanical instabilities in the electrodes limiting the SOCs durability. To date, the basic degradation mechanisms associated to the complex electrode multi-steps reaction pathways are still not precisely understood. To address this issue, a trifold approach has been developed coupling electrochemical tests with advanced post-mortem characterizations and multi-physic modelling. This methodology has been applied to the typical fuel electrode made of Nickel and Yttria Stabilized Zirconia (Ni-YSZ) and air electrode composed of a Lanthanum Strontium Cobalt Ferrite (LSCF) or Lanthanum Nickelate (LNO). For each case, a better understanding of the reaction mechanism has been proposed. Moreover, the microstructural evolutions, the material decompositions as well as mechanical damage in the electrodes have been studied.
CK-5:IL04 Model Experiments for Bridging the Gap between Fundamentals and Applied SOFC Research
A. Nenning1, A.K. Opitz1, C. Bischof2, M. HOLZMANN1, M. Gerstl1, M. Doppler1, M. Bram2, 1Technical University Vienna, Institute of Chemical Technologies and Analytics, Vienna, Austria; 2Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research, Materials Synthesis and Processing (IEK-1), Jülich, Germany
Electrochemical impedance spectroscopy (EIS) is a powerful tool to investigate the kinetics of electrochemical model systems or entire SOFC stacks. At an intermediate degree of abstraction, EIS studies on symmetrical model cells allow mechanistic, detailed insight into electrochemical properties and reaction mechanisms of electrodes with the same materials, processing and microstructures that are used in SOFC stacks. From impedance studies of Gd-doped Ceria (GDC) – Nickel cermet anodes we can quantify parameters such as the effective oxide ion conductivity of the porous structure, gas diffusion kinetics and the rate of hydrogen oxidation at the GDC surface as well as the electrochemically active thickness. Quantitative knowledge of these parameters allows us to predict how microstructural modifications, e.g. by Ni content, particle size, thickness or sintering temperature will influence the electrode performance and deliver targeted optimization strategies. For example, we can explain why electrodes with a thin, Ni-free GDC functional layers can even exceed the performance of the very good Ni-GDC cermets, which were employed in metal supported cells and deliver a power density of 2.5 W/cm2 at 700°C with negligible degradation for 1000 hours.
CK-5:IL05 Computational Modeling and Simulation of Ion Transport in Oxide Electrolytes for Energy Conversion
M. MARTIN, RWTH Aachen University, Aachen, Germany
Ion transport in oxides plays an important role in energy and environmental applications. Important examples are oxygen ion or proton conducting oxides for electrolytes in electrolyzers and fuel cells. I will present our recent theoretical approaches to understand these ionic transport processes in detail. We use density-functioal theory (DFT) to calculate on a microscopic level defect interaction energies and migration energies of the defects that enable ionic motion. By means of Kinetic Monte Carlo (KMC) simulations we then predict macroscopic ion mobilities and ion conductivities on an ab initio level, i.e. without any adjustable parameters. As first example we will discuss rare-earth doped ceria. We show that all interactions between defects contribute to the so-called conductivity maximum of the ionic conductivity [1]. The second example concerns BaZrO3-based oxides which are proto-type proton conductors. We show that the proton mobility is determined by nanoscale percolation of dopant ions which enables high proton mobility along [2].
[1] J. Koettgen, S. Grieshammer, P. Hein, B. Grope, M. Nakayama, M. Martin, Phys. Chem. Chem. Phys. 20, 14291 (2018) [2] F.M. Draber, C. Ader, J.P. Arnold, S. Eisele, S. Grieshammer, S. Yamaguchi, M. Martin, Nature Mater. 19, 338 (2020)