Solid Oxide Research Articles

Computational Fluid Dynamics Analysis of Gas Crossover in an Alkaline Electrolyzer Using a Multifluid Model

Green hydrogen has emerged as a key solution for high-intensity energy storage, with various technologies introduced to facilitate its production, including alkaline electrolyzers (AWE), proton exchange membrane electrolyzers, and solid oxide electrolyzers. While each of these technologies presents unique strengths and weaknesses, alkaline electrolyzers are particularly noted for their cost-effectiveness and robust structure in hydrogen production. However, a comprehensive understanding of the internal dynamics of the electrolyzer during operation requires detailed modeling.This study aims to delve into the dynamics of AWE, optimizing operational parameters and cell design to enable higher current operation without increasing voltage losses, thereby enhancing overall efficiency. Computational fluid dynamic modeling is employed to achieve this goal, focusing on gas bubble behavior within the electrolyzer, their impact on cell performance, and the dynamics of mass transfer between different phases.One drawback of alkaline electrolyzers is the crossover of hydrogen and oxygen through the membrane, resulting in reduced hydrogen purity and increased hydrogen loss. The preset study investigates the effect of electrolyte saturation levels on crossover, highlighting its significance. Additionally, a parametric study is conducted, varying bubble diameter across simulations to further understand its implications. Figure 1

Manufacturing of Proton Conducting Solid-Oxide Electrolysis Cells Based on Yttrium‐Doped Barium Zirconate Electrolyte

Proton-conducting solid oxide electrolysis cell (P-SOEC) has been recently recognized as a promising technology for delivering fast hydrogen production at lower temperature range to hold the promise of utilizing cheaper stack materials and reducing degradation. The current P-SOEC technology has been progressed into a new development stage with promising technical accomplishments. The operating temperatures have been effectively pushed down to 500~600°C to enable use of cheaper interconnects and to improve material system compatibility. However, the P-SOEC development is in its early stage due to low technology readiness level limited by several technical issues lying in material system, thermal processing, and efficiency. Based on comprehensive considerations on efficiency and durability, BaZr0.8Y0.2O3 (BZY) is considered as stable electrolyte candidate for electrolysis operation under extremely high steam concentration. However, the manufacturing of BZY electrolyte in half cells is challenging due to the refractory nature on sintering. In this work, we demonstrate the recent efforts in manufacturing BZY based P-SOEC for achieving the dense electrolyte with less sacrifice in proton conductivity. Several approaches are utilized and compared for validating the sintering activity and resulted properties. This work paves a solid foundation for our further investigation on electrolysis behaviors to meet the requirements on performances and durability.

Techno-Economic Analyses on Electric Ship By NH3 Fueled Solid Oxide Fuel Cells

We have been conducting an international collaboration study on “Green ammonia synthesis and utilization by solid electrolysis cells for maritime application” between Germany and Japan (term 2022-2024) under the SICORP program of the Japan Science and Technology Agency (JST). The contributors of this project are AIST, Kyoto University, and Morimura SOFC Technology from the Japanese side and Fraunhofer IKTS and EDL from the German side.The purpose of this project is to establish a new concept for an energy loop based on ammonia synthesis and utilization with maritime applications. One of the work packages of this project is to evaluate the feasibility of electric ships by using Solid Oxide Fuel Cells (SOFCs) with ammonia fuels. The important point of this project is to give a concept for such NH3-fuel SOFC ships based on techno-economic evaluation.As a preliminary evaluation of this concept, we have started the feasibility study on the SOFC system based on the literature data so far. A 200 kW SOFC system is considered for a small boat (less than 100 ton class) with an NH3 tank. Const evaluation and technical barriers are presented, and the technical target will be presented to achieve the realization of such a ship. Figure 1

Stability Enhancement of Direct Ammonia Solid Oxide Fuel Cells By Using Barium-Modified Ni/YSZ Anodes

Ammonia fuel is attracting interest as a hydrogen carrier gas in solid oxide fuel cells (SOFCs) due to its superior volumetric storage capacity. In this study, comparative analyses of hydrogen and ammonia fuel were conducted for SOFCs. Experiments using a Ni/YSZ-based button cell were conducted to investigate one of the major technical challenges encountered when using ammonia fuel: the nitridation of the Ni fuel electrode. We employed methods such as the addition of alkaline earth metals to prevent nitridation. Accordingly, two types of button cells were fabricated to compare their performance, including power density and ammonia conversion rates. The difference between these cells was in the composition of their anode support layer. One maintained the standard Ni/YSZ formulation, while the other was modified by adding BCZYYb to the Ni/YSZ base. This modification, specifically the addition of Ba, aims to enhance ammonia conversion and mitigate nitridation when operated with ammonia fuel. Both types of button cells were tested at 750℃. Current-voltage (IV) measurements and Electrochemical Impedance Spectroscopy (EIS) analysis were conducted to evaluate the electrochemical performance of the cells. X-Ray Diffraction (XRD) analysis was utilized to examine the presence of secondary phases. Gas Chromatography (GC) analysis was performed to measure the ammonia conversion rates.

(Invited) Elucidation of Degradation Mechanisms of Ni Cermet Electrode during Co-Electrolysis Using Cross-Section Model Electrodes

One of the main problems in the commercialization of solid oxide H2O/CO2 co-electrolysis cells is performance degradation during long-term operation which mainly comes from the nickel migration and carbon deposition in the fuel electrode. In order to suppress the degradation, it is essential to understand its mechanism. However, practical porous cermet electrodes have a complex three-dimensional structure, making it difficult to separate the multiple causes of degradation. Therefore, a model electrode is used to understand the degradation phenomena. While previous studies used glid pattern electrodes [1], we use comb-shaped model electrodes. We developed a comb-shaped Ni electrode on the YSZ thin film that simulate a porous Ni/YSZ into a flat surface [2]. The comb model electrode has a structure in which anode and cathode thin-film electrodes are formed on a YSZ thin-film in the form of a comb. It allows the mechanism of Ni migration and carbon deposition to be revealed in the cross-sectional direction. To further understand the degradation mechanism, the morphological change of the electrode was captured in real-time by operando evaluation using a comb-shaped model cell to evaluate the distribution of migrated nickel and deposited carbon.The model electrode was fabricated by sputtering YSZ thin film on single-crystal MgO, on which thin-film patterned electrodes of Ni and Pt were fabricated by photolithography. Ni acts as WE (working electrode) and Pt as CE (counter electrode), WE and CE are 40 mm apart. To eliminate the contribution of the counter electrode, the Pt reference electrode was deposited in the middle of the YSZ electrolyte. The measurements were done under two different conditions: 1. Water electrolysis and 2. Co-electrolysis. The measurement was carried out at 1073 K with 10% H2O + 1% H2 + 99% Ar for water electrolysis and 10% H2O + 10% H2 + 20% CO2 + 70% Ar for co-electrolysis. The long-term measurements were performed for 100 h at -0.462 V from RE (reference electrode) to WE in water electrolysis, -0.516 V from RE to WE in co-electrolysis where the impedance measurements were taken for every 5 h by electrochemical workstation (Biologic SP-300). During the measurement, a laser microscope (Keyence VK-X3000, Japan) recorded the microstructure change for 100 h.In both steam electrolysis and co-electrolysis, the tip of the Ni electrode was raised by electrolysis, suggesting that Ni was exfoliated from the YSZ by the electrolysis of water vapor and carbon dioxide. In the co-electrolysis, carbon deposition was observed at the tip of the Ni electrode by EDX and EPMA results. This carbon deposition is concentrated at the tip of the comb, suggesting that the electrode reaction is concentrated at the interface between the fuel electrode and the electrolyte. The calculated reaction area length obtained from the transmission line model (TLM) was close to the range where the electrode was delaminated and carbon deposition was observed, suggesting that more quantitative analysis would allow the comb model electrode to reveal the conditions under which degradation phenomena occur. Acknowledgement This study was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan, grant number JPNP16002.

Oxygen Nonstoichiometry of Bulk and Thin Film of Mixed Ionic and Electronic Conductors

One of the most important properties of mixed ionic and electronic conductor is oxygen non-stoichiometry which defines the oxygen reduction reaction (ORR) process in solid oxide fuel cell (SOFC) cathode. Typically, to understand the ORR of SOFC cathode, a thin film electrode is preferred to be used than a porous electrode due to the simpler microstructure and geometry. However, one of the most used SOFC cathodes, La0.6Sr0.4CoO3-δ (LSC64), has been reported to have different oxygen nonstoichiometry in thin films and bulk [1][2]. This has been hypothesized that the discrepancy might be due to the segregation of Sr in the thin film resulting in an inhomogeneous distribution of the composition [2]. The cause of the Sr segregation could be due to the Sr having a larger cation radius than La. Instead of Sr, Ca that has a cation radius closer to the La is expected to have higher stability than Sr that have attracts attention recently [3]. Thus, the oxygen nonstoichiometry of LSC64 and La0.6Ca0.4CoO3 - δ (LCC64) was studied to understand the discrepancy factor in bulk and thin film electrodes. In this study, the oxygen nonstoichiometry of the LCC64 bulk material was measured by a high-temperature gravimetry (TG) (NETZSCH, STA449F1-K21Jupiter, Germany) and Coulometric titration (CT) as a function of temperature and oxygen partial pressure (p(O2). Meanwhile the oxygen nonstoichiometry for LSC64 bulk from reference [4] was used in this study. The thin film LSC64 and LCC64 electrodes were prepared by pulsed-laser deposition on the top of Ce0.9Gd0.1O1.95(GDC) substrate. The thin film electrodes were measured their electrochemical performance by electrochemical impedance spectroscopy as a function of temperature and p(O2). For the AC impedance method, an experimental system combining an impedance analyzer (Solartron, SI1255B) and a potentiogalvanostat (Solartron, SI1287) was used. The chemical capacitance from impedance measurement was used to determine the oxygen nonstoichiometry as reported by Kawada et al [1]. In addition, the compositions were analyzed by SEM-EDX (JEOL, JSM-7001F) and STEM-EDX (Jeol, JEM2100F). As a result, the oxygen nonstoichiometry in the LSC64 thin film were not significantly different from those in the bulk at low p(O2) (10-3 – 10-4 bar) range for all measured temperature, but at high p(O2) range, a large discrepancy was observed as reported in our earlier paper [1]. Oxygen vacancy formation enthalpy determined for the thin film was higher than the reported value for bulk of LSC64[4]. SEM-EDX and STEM-EDX observations on the LSC64 thin film confirmed that the as-prepared thin film was homogeneously formed on both surface and inside the thin film while the film after EIS showed segregation of Sr on the surface and Co3O4 near the interface with the substrate. The compositional deviation in thin film could be one of the factors of the discrepancy in oxygen nonstoichiometry. In the other side, careful measurement of the bulk nonstoichiometry of LCC64 was performed in its stability range which was narrower than LSC64. It showed that the oxygen vacancy concentration (δ) in the bulk was slightly smaller than that of LSC64. What is noteworthy is that the chemical capacitance of LCC64 thin film at 773 K matched with that estimated from oxygen nonstoichiometry of LCC64 bulk. To confirm the effect of compositional change on the discrepancy of oxygen nonstoishiometry, further study is necessary to determine by EIS at different temperatures with careful observation of compositional change before and after the measurement. The factor that governs the defect equilibrium of bulk and thin film electrode will be discussed.

Integrated Autothermal Reformer, Heat Exchanger and Solid Oxide Fuel Cell in Single-Stack for Aircraft Gas-Turbine Applications

To take advantage of carbon-neutral aviation fuels such as synthetic liquified natural gas, aircraft engines must increase their efficiency through novel approaches, such as hybrid electric gas-turbine/solid oxide fuel cells (GT/SOFCs). To date, most hydrocarbon-fueled SOFC stack designs utilize rigid architectures and independent pre-reformers that require complex manifolding and rigid sealing. To enable SOFCs to operate effectively and robustly within an aircraft GT engine flow path upstream of a combustor, our team is developing an innovative integrated SOFC stack with an inline autothermal reformer/heat exchanger (ATR/HX) to provide adequate operating conditions for high-power (W/cm2) performance. The ATR/HX, integrated upstream of the stack, provides preheating of the cathode air through mildly exothermic reforming of the fuel with a bleed of combustor air and recycling of some anode exhaust. The exothermic ATR provides adequate heat to the cathode air to allow intermediate-temperature SOFCs, with either gadolinium-doped ceria (GDC) electrolytes or thin-film yttria-stabilized zirconia (YSZ) electrolytes, to operate on GT compressor outlet temperatures just above 400 °C. To enable rapid thermal response of the integrated ATR/HX/SOFC, the stack design eliminates rigid seals to mitigate the risks of SOFC failure due to thermomechanical stresses. This paper presents the design and preliminary testing of the integrated ATR/HX/SOFC under rapid heating conditions to suggest the potential for SOFCs for next generation hybrid-electric aircraft application.The ATR/HX/SOFC stack design is supported by 441 stainless steel plates with electrochemically etched, air-flow channels through the upstream HX and the SOFC cathode. The plates also include a pocket for the ATR, which consists of a woven metal-mesh with an Al2O3-washcoat supported Pt catalyst that can light off with CH4/bleed air/H2O inlet temperatures of 400 °C. The SOFC membrane electrode assembly (MEA), 10 cm*10 cm with 81 cm2 active cathode area, rest within a frame that supports the MEA as well as a silver mesh cathode collector and a nickel mesh anode current collector. The cell is sealed by compressing a thermiculite seal that extends over the full area of the stack and compresses on the exposed electrolyte area bordering the cathode. Testing at operating temperatures indicated minimal leakage (<1%) from the anode and from the cathode to the external environment. This design, which lacks rigid seals or confinement of the MEA, enables ease of assembly and disassembly and minimizes external stresses on the MEA to enable rapid heating during ATR light-off.Integrated ATR/HX/SOFC stack has been initially incorporated into a low-pressure test facility shown in Figure 1a), which provides steam generation for the ATR inlet and premixing and preheating for the ATR inlet and air-side HX inlet flows. The ATR/HX/SOFC stack is preheated to 400 °C or more to achieve rapid light-off that rapidly preheats the SOFC inlet to desirable temperatures. For a 3-cell ATR/HX/SOFC short stack, light-off test to SOFC operating temperatures of 550 °C for thin-film YSZ-electrolyte MEAs from Elcogen are achieved in < 1 h. Such start-up times are expected to be reduced for larger ATR/HX/SOFC stacks with reduced heat loss per stack volume. Tests to date have only achieved maximum MEA power densities of 0.26 W/cm2 at 0.65 V/cell operating on the ATR outlet. Simulated performance shows pathway to higher power densities > 1.0 W/cm2 with higher temperature operation that will be achieved with coated interconnect materials. Tests to date show that the thin-film YSZ cells avoid cracking after undergoing multiple assembly and disassembly cycles, as well as high-temperature ATR light-off and fuel cell testing. These results indicate that both mechanical and thermal stresses remain sufficiently low to prevent cell cracking throughout start-up, normal operation, and shut-down processes, thus affirming the robustness and reliability of our integrated stack design. Figure 1

Physicochemical Impedance Modelling of Porous Electrodes in All-Solid-State Electrochemical Devices

Fundamental knowledge about performance limiting processes in electrochemical devices like battery-, fuel- and electrolyzer-cells is mandatory for a model-aided development. The method of choice to analyze these processes is electrochemical impedance spectroscopy, enabling a separation of electrochemical processes differing in their relaxation frequencies. In order to improve the deconvolution of these processes in the impedance spectrum, the distribution of relaxation times (DRT) analysis is a well-established method [1].In case of porous, multiphase electrodes, the DRT usually doesn’t enable a simple correlation of a peak in the DRT with a single polarization process in an electrode. The complex coupling of electronic and ionic charge transport via charge transfer reactions, often described by a transmission line model (TLM) [2-4], induces a number of peaks in the DRT. TLM parametrization just by operating and/or electrode parameter variations is often insufficient. Since different parameter sets can result in identical spectra [3], a straightforward CNLS-fit is insufficient and a pre-parameterization by determining at least a few model parameters independently is required.In this study, impedance spectra of two all-solid-state electrochemical devices, an all-solid-state battery and a solid oxide cell, are analyzed by the distribution of relaxation times. Physicochemically motivated impedance models based on the TLM-approach were derived, pre-parameterized and applied to quantify different loss processes in the cells. The pre-parameterization included microstructural parameters obtained by focus ion beam tomography and conductivity data. The model development and areas of application will be discussed in detail within this contribution, focusing on the differences between the two investigated all-solid-state electrochemical devices.

Influence of Morphology and Surface Chemistry on Ni-Exsolved Perovskite Oxides for Direct Ammonia Solid Oxide Fuel Cells

Ni-YSZ as an anode material for solid oxide fuel cells (SOFCs) has shown excellent catalytic, electrical, and thermal properties. However, when applied to direct ammonia (DA) fed SOFCs, Ni coarsening and microstructural degradation caused by Ni nitrification resulted in a decrease in the electrode reactivity and an increase in contact resistance, thereby reducing the performance of DA-SOFCs. Nano-size metal exsolved perovskite oxides have been intensively investigated as an alternative anode due to superior catalytic activity and anti-coarsening under various fuel conditions. In this study, Ni exsolution behavior, ammonia decomposition, and surface chemistry on Ni substituted (La,Sr)0.8TiO3- δ oxides were analyzed. Then it was applied to the anode of DA-SOFCs to evaluate cell performance and durability. Ni exsoluted oxides were efficient to decompose ammonia at reduced temperatures due to enlarged catalytic sites and electronic donation. The cell using Ni exsoluted perovskite anode indicated a significant improvement of durability for excellent catalyst stability while the cell performance was comparable with that of Ni-YSZ based DA-SOFC.

Redox Stability of Co-Doped Barium Niobate Thin Films in Reducing Conditions Analyzed Using Cyclic Voltammetry Measurements

Perovskite anodes (general chemical formula ABO3) for the high temperature (>750 °C) electrolysis of methane to ethylene in a ceramic solid oxide electrolysis cell require both high activity, chemical and mechanical stability as well as durability for future commercialization efforts. We have previously shown co-doped barium niobate perovskites as stable anode materials for electrochemical oxidation of methane (E-OCM)1 . The mechanism for the excellent chemical stability is highly connected to the flexible oxidation state switching of Nb4+/Nb5+ cations associated with changes in lattice oxygen concentration2 ,3. To further evaluate their chemical stability in highly reducing conditions to understand their applicable potential window , this work utilizes the Ca and Fe codoped perovskite BaCa0.33Nb0.67-xFexO3-δ (BCNF). BCNF has shown very good methane activation properties and higher activities in E-OCM operation via increased conductivity and ethylene selectivity4. We deposited BCNF thin films utilizing pulsed laser deposition on various substrates such as quartz glass and yttria stabilized zirconia (YSZ) and analyzed their electrical properties using electrochemical impedance spectroscopy (EIS) in various oxygen partial pressures and cyclic voltammetry (CV) in a homemade test setup that allow for redox stability under controlled gas environments to be examined. This advanced screening methodology allows for holding at desired operating temperatures while altering the applied potential bias to simulate electrode reduction in various gas environments (for a single test). The results of these measurements along with physical characterization of the thin films by TEM, SEM, AFM will be presented to demonstrate the utility of BCNF perovskites in E-OCM applications.

(Invited) Mathematical Modeling of Electrochemical Cells: Promises, Problems, and Progress

Fuel cells and electrolyzers are key components in the energy transformation from non-renewable fossil fuels, to technologies based on renewable energy, such as solar and wind, which utilize or synthesize hydrogen (and oxygen) rich fuels/feedstocks in place of hydrocarbons. Following a brief introduction, a description of modeling activities, past, present and future, developed by the authors over many years, are described.Electrochemical conversion cells may be considered as natural problems in combined heat and mass transfer with the electrochemical reactions functioning as the main driving force for the interconversion of chemical and electrical energy, and heat. Ionic and electronic charge transfer within the electrodes and electrolyte must be considered, and multi-phase flow (liquid-gas) is also frequently present. The authors have led development of a suite of object-oriented open source models for both polymer electrolyte membrane cells (PEMCs) and solid oxide cells (SOCs), the emphasis being on generic (rather than specific) algorithms. The implementation is based around the popular open-source finite-volume-based software library, OpenFOAM. This allows the user access to a flexible framework/library of C++ classes, thereby allowing for further model research, as well as development appropriate to practical real-life applications. The main features of the methodology are described and explored both, with the benefit of hindsight from past experiences, and foresight to the problems to be tackled in the future.In addition to the above cell-level macro-homogeneous analysis, substantial work is being devoted to micro-scale analysis; for example, detailed studies of flow phenomena within the porous transport layers and electrodes of electrochemical cells as well as construction of digital twins of physical morphologies. These are necessary, not only for basic qualitative understanding and control of the underlying 3-D processes, but also to provide quantitative closure parameters for quantifying the dynamics of macro-scale equations (multi-scale models).The state-of-the art of CFD-based modeling in electrochemical science is presented with examples of PEMC (and SOC) technologies together with a discussion of the important issues and limitations of the present generation of models as well as examples of success stories. Some of the issues for concern include degradation and evolution of material properties, code stability and numerical issues, suitability of present-generation existing two-phase models (mixture, Euler-Euler, volume of fluid methods, etc.) to electrochemical applications, and computational issues such as parallel efficiency. In spite of numerous unexpected problems encountered over the years, great progress was, is, and will continue to be made in this quest for mathematical descriptions and prototypes of complex electrochemical processes and products, based on physical modeling.Artificial neural network techniques have found applications in tackling scientific and industrial challenges involving the concept of digital twins. In the domain of electrochemical cells, data-driven models or physically informed data-driven methods have been shown to provide valuable insight into issues that were traditionally explored using physical models. Areas for investigation include; material properties, performance prediction, and control strategies. By integrating physical/mathematical models with data-driven counterparts, a more comprehensive suite of methodologies should become capable to address ever more complex issues in the field.

In-Situ Exsolved Nico Alloy Nano Catalyst for Direct Utilization of Ammonia Fuel in Solid Oxide Fuel Cells

Ammonia (NH3) is regarded as an innovative hydrogen (H2) carrier for diverse energy conversion systems with its clean nature, high energy density, and widespread availability. Solid oxide fuel cells (SOFCs) are attracting attention for direct utilization of NH3 fuel due to thier high temperature operating (~900 oC) and conversion efficiency. The electrode materials for direct NH3 SOFCs (DA-SOFCs) are still limited to traditional Ni-based cermet materials. These materials suffer from additional overpotential during NH3 decomposition steps and the potential nitriding of pure Ni metal catalysts. In this study, we suggest in-situ prepared single and alloy nano metal catalysts exsolved from La0.43Ca0.37M1-xO3-d (M: Ni, Co, Fe, NiCo, NiFe, and CoFe) perovskite electrodes. Homogenously distributed NiCo alloy nano exsolution catalyst exhibits synergistically enhanced powder density under both H2 and NH3 fuel conditions, compared to that of single Ni exsolution and conventional Ni-YSZ electrode. Hydrogen production efficiencies of exsolution catalysts via NH3 decomposition reaction are characterized to determine the optimal composition of exsolution catalysts for DA-SOFCs electrode design. The electrochemical properties of different catalytic materials and fuels are also investigated to understand the effect of exsolution catalysts under DA-SOFCs operating conditions. The results obtained here are expected to improve the catalytic activity and durability of electrode materials for DA-SOFCs applications.

High Surface Proton Conductivity of Epitaxial CeO2- δ Thin Film below Medium Temperature Range

Fluorite-type oxide such as Yttria-stabilized zirconia (YSZ) or doped-CeO2- δ ceramics are good electrolyte candidates for solid oxide fuel cells (SOFC) due to their high oxygen ion conductivity in high temperature range above 700 ºC[1]. Furthermore, porous and nanocrystalline CeO2- δ exhibit proton conduction at the surface below 100 °C[2]. This surface proton conduction is believed to the Grotthuss mechanism caused by the adsorption of water molecules. Since protons are produced by adsorbed water molecules and conduct through the layer of adsorbed water, oxygen vacancies and lattice constant are important parameters to enhance proton conduction. If high surface proton conduction can realize in CeO2- δ thin film, this may be more suitable than porous or nanocrystalline materials for new electrochemical devices and smart fuel cells.Recently, our group reported that the higher ion conductivity depends on the lattice constant and grain size for YSZ and Sm-doped CeO2- δ thin films[3,4]. However, the effect of crystallinity on the ion conductivity is not clarified. In this study, we have prepared the CeO2- δ thin films on YSZ (002) substrates by RF magnetron sputtering and probed their surface proton conduction below 300 °C in terms of electrical conductivity and electronic structure.The CeO2- δ ceramics target was prepared by solid-state reaction method. The CeO2- δ thin films with thicknesses of ~20 and ~120 nm were prepared by RF magnetron sputtering by adjust the deposition time. The sputtering conditions is followed; The base pressure was kept at 5.0×10-8 Torr and the deposition pressure was kept at 3.5 mTorr to control the Ar flow rate of ~2.67 sccm. The RF power was fixed at 30 W. The crystal and electrical structure of CeO2- δ thin films were evaluated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The electrical characteristics was evaluated by A.C. impedance method.The prepared CeO2- δ thin films on the YSZ substrates were due to the exhibited 200 and 400 peaks. Figure shows the Arrhenius plot of the conductivity of the as-deposited and wet-annealed CeO2- δ thin films, indicating thermally activated behavior in the medium temperature range but different behavior below 100 °C. The conducting carrier in the medium and room temperature range is considered to be oxide ion and proton, respectively. In this poster, we will show that the surface proton conduction of CeO2- δ thin film is closely related to the lattice distortion and oxygen vacancies concentration at the surface.

Evaluation of Properties of La1-XCexCr0.5Ni0.5O3-Δ for Internal Dry Reforming of Solid Oxide Fuel Cells

Dry reforming of methane (DRM) has environmental benefits because it uses CH4 and CO2, two major greenhouse gases that contribute to global warming. Additionally, SOFCs operate at high temperatures, so the DRM reaction can be performed directly internally without a separate reformer. However, the carbon coking generated after the reaction is produced through the pyrolysis of methane and the Boudouard reaction, which can be a major disadvantage of DRM. In this study, La1-xCexCr0.5Ni0.5O3-δ (LCCN) perovskite was investigated as a material to minimize carbon coking and improve catalytic activity for DRM inside SOFCs. LCCN was synthesized through the Pechini method, and Ce was substituted for La in the A-site. At 800℃, the conversion rates of LCCN55, LCCN64, and LCCN82 were high and stable at over 90 % for 40 hours. Oxygen vacancies were 53.3, 40.80, and 34.41 % in LCCN55, LCCN64, and LCCN82, respectively. These oxygen vacancies are important for increasing resistance to carbon deposition. Based on the results of this experiment, we plan to manufacture a fuel cell and measure its electrochemical performance, and as shown in the GC results, it is believed that LCCN55 will show excellent and stable long-term performance.

Influence of the Transition Metal Doping on the Properties of Sr2Fe1.5Mo0.5O6 Double Perovskite for Solid Oxide Fuel Cells

The increase in environmental awareness has led to a significant worldwide trend for the development of alternative energy sources other than conventional use of the fossil fuels. One of the alternatives is the use of Solid Oxide Fuel Cells (SOFCs), which are capable of converting chemical energy of the fuel into electricity. In SOFCs, dense electrolyte is covered with two porous electrodes. So far, the most widely used fuel electrode material is Ni-YSZ composite, which degrades significantly when is fed with the fuels other than hydrogen. Thus, the development of a substation for Ni cermet is desirable. Among many materials, one may find perovskite families, which are known for their high stability and ionic conductivity. Unfortunately, their catalytic performance is rather low and needs to be increased. This can be done by introducing catalytically active materials as dopants and force them to form nanoparticles via the exsolution phenomenon. Main advantages of exsolving nanoparticles, rather than their deposition, are better connection with the surface and lower tendency for agglomeration.Perovskites may be divided into several sub-groups and one of them are double perovskites with general formula of A2BB’O6. Strontium ferrite molybdate (SFM – Sr2Fe1.5Mo0.5O6) is one of the most prominent compounds in this family. It is well known for its high ionic and electronic conductivity as well as stability in both reducing and oxidizing atmospheres. Those properties make it a promising material for not only the anode, but also a cathode, hence SFM-based compounds can be considered prominent candidates for symmetrical fuel cells. On the other hand, our previous work has shown that, in highly reducing atmospheres, this double perovskite can partially transform into the Ruddlesden-Popper layered perovskite. This transition could increase the amount of exsolved nanoparticles due to internal strain.Herein, the SFM-based compounds were co-doped with La at A-site and one of transition metals - Co or Ni, (with x being doping level within 5-20 mol.%) - giving the composition of La0.3Sr1.7Fe1.5-0.75xMo0.5-0.25xMexO6. Fixed Fe:Mo ratio was maintained to prevent formation of either Fe-, or Mo-rich phases. Based on our previous studies, La-doping was found to suppress the phase transition and to simultaneously increase the electrical conductivity. Transition metals were incorporated during the synthesis to boost the catalytic performance of the compound. After the reduction at 800 °C in hydrogen, the surface of the grains was almost fully covered with nanoparticles of one metal (Co or Ni) or bimetallic alloys with co-exsolved iron. Even small amount (10 mol.%) of introduced transition metal resulted in enormous amount of nanoparticles. The electrical conductivity measurements were performed in both air and hydrogen. It was found that the mechanism of electrical conductivity is different in both atmospheres: in the air, the electrical conduction occurs by the polaron hopping mechanism through Fe/Mo-O-Fe/Mo bonds. Selected samples underwent several cycles of electrical measurements in air and hydrogen, alternately, to determine their stability for several redox cycles and to study the degradation. To better understand how Fe3+/4+-Mo5+/6+ redox pairs are influenced by transition doping, the XPS technique was used for as-synthesized and reduced compounds. After the reduction, both iron and transition metals were present also in Me0 form, hence the amount of Mo6+ cations increased. Finally, TPR/TPO measurements were performed to understand the reducibility of the compounds and to have a better understanding of the formation of exsolved nanoparticles. Acknowledgements: The research project was supported by the National Science Center under grant No. NCN 2022/45/N/ST5/02933.

Multiscale Simulation of Internal Reforming Solid Oxide Fuel Cells to Capture Complex Reaction Phenomena

In our previous work, we successfully employed a multiscale modelling approach to simulate solid oxide fuel cells (SOFCs) fuelled by pure hydrogen [1]. This approach effectively captured the interplay between electrochemical and transport phenomena at various scales within the SOFC. Here, we extend this framework to investigate the complexities of internal reforming SOFCs (IR-SOFCs) fuelled by hydrocarbon fuels, such as methane. IR-SOFCs offer fuel flexibility but introduce significant modelling challenges due to the inclusion of steam methane reforming (SMR) within the anode[2]. Accurately capturing this process requires accounting for several complexities.A multiscale modelling approach that can handle the interplay of several complex phenomena in IR-SOFCs. SMR involves a series of interconnected reactions with intricate mechanisms [3]. Unlike SOFCs working with pure hydrogen fuel, SMR reactions in IR-SOFCs may operate far from chemical equilibrium under certain operating conditions. To capture this condition, rigorous kinetic modelling across different length scales is needed. Finally, a significant challenge lies in describing the coupling between the electrochemical reactions at the anode and the chemical reactions of SMR. These phenomena are intrinsically linked, as the reforming process consumes reactants (steam and methane) that are also crucial for the electrochemical oxidation at the anode. An effective modelling framework must seamlessly integrate the transport and reaction phenomena occurring at both micro and macro scales within the SOFC electrodes. By addressing these challenges, our multiscale modelling framework aims to provide a more comprehensive understanding and optimization of IR-SOFC performance.

Surface Oxide Ion Conduction of a - Axis Oriented Ce0.75Sm0.25O2- δ Thin Film Prepared on (200) YSZ Substrate

Fuel cells are attracting attention as a clean energy source because their only waste product is water. Solid oxide fuel cells (SOFC), which use oxide with oxygen ion conductivity as the electrolyte, can simplify the configuration of the power generation system and facilitate management, but they require a high operating temperature of 800 ℃ or higher [1]. Yttria-stabilized zirconia, which is currently in practical use as an electrolyte, exhibits high oxygen ion conductivity at temperatures above 800 ºC. Therefore, an electrolyte that exhibits high ion conductivity at low temperatures is required.Fluorite-type CeO2-δ oxides are good solid electrolyte candidates for solid oxide fuel cells due to their high oxygen ion conductivity in high-temperature regions above 800 ℃ because they take on a mixed valence state of Ce3+ and Ce4+ in the high temperature. Furthermore, it is known that doping CeO2 with trivalent dopants increases the amount of oxygen defects and improves ionic conductivity [2-4]. While we have reported the surface ionic conduction Sm-doped CeO2 thin films, the conductivity was not sufficiently high for practical applications [5].In this study, in order to realize high surface oxide ion conductivity, we prepared a - Axis Oriented Sm-doped CeO2 (Ce0.75Sm0.25O2- δ : SDC) Thin Film without lattice distortion and investigated its surface oxide ion conduction.The SDC thin films were prepared on YSZ (200) substrates by RF magnetron sputtering using ceramic targets. The flow rate of Ar gas controlled by a mass-flow controller was kept at approximately 2.81 sccm. The pressure of Ar gas was fixed at 3.5 × 10−3 Torr during the deposition. The prepared thin films were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and A.C impedance method using a frequency response analyzer.The prepared SDC thin films showed a 200 peak and a 400 peak on the YSZ substrates, indicating no change in lattice constants with the ceramics. Figure shows an Arrhenius plot of the conductivity of the As-deposited and Wet-annealed SDC thin films. As a reference, the Arrhenius plot of the conductivity of the YSZ substrate and ceramics is shown. The conductivity of the SDC thin film is much higher than that of the YSZ substrate and ceramics because the amount of oxygen vacancies increased more than those. The conductivity does not much change by wet annealing and depends on the film thickness. The conducting carrier above 200 °C is considered to be oxide ion. In this presentation, the author will show the details of the conductivity and discuss including XPS results as well as details of the conductivity.

Development of Nano-Composite Structured Electrode for High Performance Metal-Supported Solid Oxide Cells

Solid oxide cells can reversibly operate with high conversion efficiency and fuel flexibility. Metal-supported SOCs (MS-SOCs) have attracted attention for their exceptional thermomechanical stability and cost-effectiveness. In this study, we present a precisely controlled metal-supported structure and Ni/YSZ-YSZ dual-nanocomposite catalyst to achieve high performance in various conditions. Controlling the Ni/Fe ratio allows for precise tailoring to the thermal behavior of NiFe, a crucial factor in its interconnectivity with the metal-ceramic interface. Nanocomposite electrodes, with a maximized density of triple-phase boundaries (TPBs), enhance cell performance in both the oxidation and reduction reactions of various fuels compared to micro-sized electrodes. The optimal cells with NiFe support (150 μm)|Ni/YSZ-YSZ electrode (20 μm)|ScSZ electrolyte (10 μm)|LSM-ScSZ electrode (20 μm) exhibited maximum power densities of 1.1 and 1.0 W cm-2 in fuel-cell mode and current densities of -0.61 and -0.5 A cm-2 in electrolysis-cell mode (1.3 V) at 650 °C under H2O/H2 and CO2/CO fuel systems, respectively. Our study suggests fundamental techniques for improving the structural stability and activity to operate in diverse fuel systems.

(Invited) Topsoe’s Vision on the Commercialization of Solid Oxide Electrolysis Cells: Challenges and Accomplishments in Upscaling to the MW Scale

Topsoe is strongly committed to drive the decarbonization of the so-called hard-to-abate sectors, such as iron and steel manufacturing and long-haul transportation, by implementing the industrial scale production of sustainable fuels and chemicals via solid oxide electrolysis cells (SOECs).To enable the upscaling of the SOEC technology at the pace required by the increasing green hydrogen demand and the company’s target of full climate neutrality by 2040, Topsoe is building a facility able to produce electrolysis stacks and modules with an annual capacity of 500 MW, equaling the production of 125,000 tonnes of hydrogen p.a. The construction of the production facility, covering an area of over 23,000 m2, was initiated at the end of 2022 in Herning, Denmark, and is progressing at an accelerated pace, aiming at full operation in 2025. The 2nd generation Topsoe Stack Platform (TSP-2) produced in the Herning facility consists of SOEC stacks designed for H2 production from the electrolysis of steam at pressurized conditions (>3 bar), while maintaining the ability to operate at ambient pressure to produce CO by CO2 electrolysis. The TSP-2 stack has a capacity of >15 Nm3 H2/h, to be further combined in a 12 stacks-core module totaling over 180 Nm3 H2/h.Exciting and solid results have been recently released by Topsoe on the SOEC core’s first demonstration test at industrially relevant conditions [1]. The demo unit, consisting of 12 stacks (1200 cells) operating at a constant pressure of 3.5 bar and a combined stack power of 350 kW, showed remarkable stability over 2250 hours of operation (Figure 1). These impressive durability results were obtained at a core efficiency of approximately 93% (LHV of hydrogen), with an electricity consumption of the core of around 36 kWh/kg H2 and a ramp-up time to reach 100% of the load (approximately 230 A throughout each stack in the core) of just three minutes.While providing an overview of the continuing demonstration tests ongoing at a stack and core level, this presentation will report the developments of the construction of the manufacturing facility in Herning, highlighting the major challenges and key factors playing a role in the large-scale commercialization of SOECs.

Sr Migration and Gd-Ce-Zr Interdiffusion in Solid Oxide Cells Under Different Fabrication and Testing Conditions

This work aims to understand how solid oxide cell (SOC) fabrication methods and SOC operating conditions affect Sr migration into the yttria stabilized zirconia (YSZ) electrolyte through the rare-earth doped ceria barrier layer. Ni-YSZ electrode-supported SOCs and coupons were fabricated using (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ-Gd0.1Ce0.9O2-δ (LSCF-GDC) oxygen electrode and GDC or samaria-doped ceria (SDC) barrier layer. Barrier layers were either screen printed and sintered to YSZ electrolyte layer at 1260 °C for 2h, or deposited using thin film deposition techniques such as PLD, electron beam and sputtering. LSCF-GDC electrode layer was sintered onto the GDC barrier at different temperatures from 950 to 1100°C for 2h to determine the effect of firing temperature and barrier layer thickness on Sr migration. Several SOCs were tested at 750°C in a wide range of operating conditions, both in SOFC and SOEC mode, for up to 12,000 hours. The GDC/YSZ interfaces in coupons and SOCs were examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Sr-Zr rich phase formation at GDC/YSZ interface was observed in coupons with LSCF-GDC sintered at 1100°C, but not in the other coupons sintered below 1100°C, unless the barrier layer was too thin and porous. Furthermore, no Sr migration into YSZ was observed in SOECs with varying testing time from 0 h to12,000 h. In addition, Gd and Ce diffusion into YSZ occurred when GDC was fired at 1260°C, but not in cells with GDC deposited using thin film techniques without additional high temperature firing. No significant difference was noted in the GDC-YSZ interdiffusion layer growth after SOC testing for 1,000-12,000 h. Aberration-corrected scanning transmission electron microscopy (STEM) was involved to identify the composition and crystal structure of the Sr-Zr rich phase, which was demonstrated to be SrZrO3 phase. After the long-term SOC tests, no SrZrO3 phase or Sr migration through GDC grain boundaries was observed in cells with 5-7 microns thick porous GDC barrier. This presentation will demonstrate how optimization of fabrication conditions, thermal treatment and fabrication techniques, could mitigate the formation of the insulating SrZrO3 phase.