Time-Resolved Characterization of Electrochemically-Induced Solid Oxide Cell Microstructure Evolution

The global, macro-scale description of degradation phenomena in solid oxide cells (SOC) reaches limitations when dealing with localized, micro-scale processes. For example, it is established that carbon deposition and transformation of the active area in nickel containing electrodes in electrolysis mode depend strongly on the local overpotential and gas composition. The state-of-the-art long-term characterization of a full SOC however relies on macroscopic measurements of DC polarization and electrochemical impedance spectroscopy (EIS), which are capturing the average response of the entire cell. The deconvolution of impedance spectra allows to separate the electrolyte resistance from electrode electrochemistry, gas conversion, and diffusion contributions. Nonetheless, heterogeneous, and local degradation cannot be described deploying commonly used tools of EIS analysis, such as equivalent electric circuit models, transmission line models, or the analysis of distribution of relaxation times.Multi-physics based numerical models on the other hand open new opportunities in gaining advanced insights into the complex degradation mechanisms in SOCs. In the model proposed here, combining simulations of transient and frequency domain into one framework allows the description of measured long-term durability of an SOC in terms of voltage-current and impedance characteristic. In addition, the framework enables a local, micro-scale description of the degradation process based upon physical properties confirmable in experiments.The modelling framework is validated with the durability measurements of the SOC in Sun et al. [1]. In this study, a fuel electrode supported cell with an active area of 16 cm2 was tested in galvanostatic operating conditions as an electrolysis cell with the constant current of -1 A/cm2 over 4383 h. Simultaneously to the voltage measurements over the test duration, the impedance response of the cell was tracked every eight hours. The evolution of the measured impedance spectra of the cell can be seen in the attached figure.Comparing the outcomes of the model to the experimental data showcases the benefits of the model in describing the degradation induced increase in voltage over time and the evolution of impedance spectra. In particular, the effect of higher activation overpotential at the fuel inlet to the outlet of the cell is analyzed enabling the generation of local insights concerning the observed degradation. The model establishes an improved validation of equations describing degradation of SOCs encompassing overpotential gradients and relating to postmortem observed micro-structural changes. Reference [1] Sun, X., et al. "Degradation in solid oxide electrolysis cells during long term testing." Fuel Cells 19.6 (2019): 740-747. Figure 1

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Fatigue resistance of steels: Boardman, B. Metals Handbook 10th Edn (ASM International, Materials Park, Ohio, 1990) Vol. 1, pp 673–688

Mathematical approaches to modelling the mass transfer process in solid oxide fuel cell anode

Different solutions adopted in producing Solid Oxide Cells (SOCs) have proven to be scalable and the technology is now approaching commercialization. The high energy conversion efficiency, coupled with the fuel flexibility and the reduced use of expensive catalyst materials promoted by the favorable thermodynamics at the operative temperatures, are making the technology increasingly attractive and stacks are finding applications in more fields. Large scale power-to-X plants, particularly the ones devoted to hydrogen production (Solid Oxide Electrolysis Cells – SOEC), are among the solutions that are gaining most momentum in the energy market. X-to-power (Solid Oxide Fuel Cells – SOFC) solutions such as decentralized heat and electricity production, auxiliary power systems and heavy duty transport propulsion are spreading as well, facing challenges such as power density and dynamic load operation.Advancement in the SOC technology is opting at substituting ceramic materials with mechanical support function, in favor of metal. A lower amount of ceramic materials not only reduces the raw material costs, but also allows rapid thermal cycling without compromising the mechanical integrity of the cells – hence allowing faster start-ups and load regulations. Furthermore, our recent studies demonstrated a scalable and innovative layer integration process that allows to fabricate complex 3D multilayer structures with internal gas channels and cavities of different geometries, using conventional tape casting. The monolithic SOC stacks rising from this process, combined with the integration of metallic parts in the great majority of their volume, may achieve groundbreaking power densities and the dynamic load operation desired for the mentioned applications, while decreasing CapEX and resources necessary to produce high performing SOCs of the future.The monolithic SOC stacks obtained within this work are made of three standard repetitive units (SRUs). Each SRU consists of a SOC backbone, composed by two porous zirconia based electrode backbones to be infiltrated with appropriate electro-catalysts, a dense thin zirconia based electrolyte, two sets of ferritic steel gas channel structures – one at the fuel side and one at the oxygen side – conferring enhanced gas diffusion to the triple phase boundaries, mechanical support and electronic conductivity and composite metal/ceramic interconnect plates connecting in series the SRUs. The total number of layers co-fired to produce monoliths within this work is 19 and the monoliths are denoted as “MNx3” (nomenclature defined for a monolith stack with 3x SRUs). The cross section is showed in Figure, where scanning electron microscopy is complemented by qualitative energy dispersive x-ray spectroscopy (EDS) to highlight the material composition of the three SRUs. This work presents the challenges and a solid framework for the solutions adopted to fabricate monolithic stacks aimed at hydrogen production, using the conventional tape casting shaping technique integrated with the innovative assembly process developed. Among the challenges, focus is given to i) the shaping of internal gas channels, ii) structural integrity during fabrication and operation and iii) the use of non-critical raw materials. Detailed electrochemical characterization is currently in progress and the results will be presented at the conference. Besides the real initial performance of the stacks at this development stage, it is speculated that SRU cells performance could get close to the ones of state of the art metal supported cells, also relying on electrocatalyst infiltration. Figure 1

Electrocatalytic reduction of CO2 to CO have been performed in a high temperature solid oxide electrolysis cell (SOEC). Solid oxide cell was fabricated using ceramic cathode, Ce0.9Pr0.1O2-δ (PDC), infiltrated into yettria stabilized zirconia (YSZ) scaffold. Lanthanum strontium manganite (LSM) as anode was brush coated on dense YSZ electrolyte. Physical characterization of infiltrated PDC cathode was performed by X-Ray diffraction (XRD) and scanning electron microscopy (SEM). XRD pattern indicated the phase purity of PDC cathode, Figure 1(a). The porous cathode and dense electrolyte layers of thickness 600 µm and 700 µm respectively, were perfectly adhered as suggested by the SEM image of Figure 1(b). Electrochemical characterizations of SOEC were performed at 750 ºC, using impedance spectroscopy (IS) and current voltage (I-V) measurements. Open circuit impedance spectra of SOEC were obtained with varying ratio of CO2/CO gas in the inlet flow, as shown in Figure 1(c). As the CO concentration in the fuel side environment of SOEC was increased from 0% to 90%, the measured ohmic losses were observed to decrease from 3.5 to 1.5 Ωcm2. This might occurred because of the reducing environment in which Ce4+ may partially be reduced to Ce3+, resulting in mixed ion-electron conduction leading to higher ionic transport at the electrode-electrolyte interface. Similarly, the polarization resistances were decreased by increasing the CO content in reaction atmosphere (CO2/CO) on the cathode side. This might be because of the faster reaction kinetic of CO oxidation as compared to the CO2 reduction kinetics. Furthermore, open circuit potential (OCP) was observed to be increased from 0.06 V to 0.90 V as the CO2 percentage was decreased from 100 to 10%, possibly due to the same reason. Chronoamperometry (CA) were performed at certain a potential and corresponding reduction current was observed to be constant. Products of CO2 reduction reaction were analysed in gas chromatogram (GC). In order to understand the reaction mechanism of CO2 reduction on ceria, density function theory (DFT) calculations were performed to study the formation of CO from CO2 reduction on CeO2 surface. CO2 molecule adsorbed on the neighbor site of oxygen vacancy on the reduced surface, was activated and form a bent carbonate CO3 δ- like structure which ultimately dissociates into CO via the incorporation of the oxygen atom into the vacancy. The activation barrier and reaction energy for this redox mechanism, calculated from DFT studies, were of 258.9 kJ/mole and 238.6 kJ/mole respectively. The effect of lateral interactions were studied by performing calculations for the same reaction step on two oxygen vacancy (di-vacancy) on 2x2 supercell unit. The activation barrier and reaction energy on a di-vacancy were significantly reduced to 134.3 and 127.3 kJ/mole respectively. Furthermore, the hydrogen atom co-adsorbed on the surface could assist the CO2 dissociation reaction. In the presence of a hydrogen atom the dissociation reaction occurs in two exothermic steps: CO2+H→COOH, COOH→CO+OH. The intrinsic activation barriers of two hydrogen assisted elementary steps were 39.0 and 47.4 kJ/mole (Figure 1D) respectively, which were significantly lower than the barrier of redox mechanism of CO2 dissociation reaction. The experimental and theoretical studies could suggest a feasibility of CO2 reduction reaction on ceria based materials. Figure 1

Increasing demand for long-term energy storage, reduced carbon emissions, more resilient grid, and the lowest cost grid balancing solutions promotes solid oxide electrolysis cell (SOEC) and reversible solid oxide cell (RSOC) technologies. These systems can achieve high hydrogen production rates with near 100 percent stack electrical efficiency while co-electrolysis of carbon dioxide and water leads to production of syngas. RSOC can serve as a grid storage device (hydrogen production) and power production plant (provide electricity during peak demand). With over 25 years’ experience building and testing solid oxide cell materials, components and stacks, Nexceris has a proven track-record of commercializing products to major OEMs. The established manufacturing platforms at Nexceris enable smooth expansion into new applications.In this talk, development of cells, stack components and stacks will be discussed. Performance and durability improvements from single cell to short stacks will be addressed. Cells with downselected electrode sets were implemented into short stacks with active cell area of 42 cm2 and 96 cm2. Stacks were operated continuously in SOEC mode at ~1.3 V for ≥ 500 hours with <5%/kh degradation and improving. The resulting short stack demonstrations show promising baseline performance and durability platform for future cell and stack development. RSOC tests were recently initiated with dynamic operation. Nexceris’ ChromLok coatings for bipolar plates were also integrated to stacks to enhance durability.

An electrode supported Ni-YSZ/YSZ/Ni-YSZ symmetric cell was studied with direct-current operation, with one electrode operating in electrolysis mode, and another electrode in fuel cell mode. The 1000 h life tests were carried out at different current densities in 97% H2 / 3% H2O. At a current density ≤ 0.4 A/cm2, the cell total resistance value was reasonably constant, with a slight increase in ohmic resistance; no changes in microstructure were observed relative to the as-prepared cell. At current densities ≥ 0.6 A/cm2, there was a steady increase in ohmic resistance that was offset by a decrease in polarization resistance, resulting in a total resistance that was approximately stable. However, these higher current densities resulted in significant damage to the electrolyte microstructure. First, fracture was observed within the electrolyte near the electrolysis operation side. Second, fracture SEM images showed pronounced intergranular fracture that resulted because voids had formed at grain boundaries during the life tests. These changes presumably explain the observed ohmic resistance increase. In addition, nanoparticles formed in the electrode after electrolysis operation, probably explaining the decrease of polarization resistance. The constant-current results are compared with those from similar cells life tested in reversing-current operation. The critical current density values for onset of signification degradation were similar: between 0.4 and 0.6 A/cm2. At the same values of current densities ≥ 0.6 A/cm2, the rate of increase in ohmic resistance were comparable during direct-current and reversing-current operation, while the rate of decrease in polarization resistance with direct-current operation were less than half of that with reversing-current operation. The microstructure changes after life tests at higher current densities were different: First, reversing-current operation resulted in damage to the electrode/electrolyte interface, but the electrolyte appeared to be intact. Second, highly concentrated Ni and YSZ nanoparticles were observed at both side of electrodes after reversing-current operation. Numerical analysis was carried out to determine the effective oxygen partial pressure versus position within the electrolyte. The results show that the oxygen partial pressure near the electrolysis operation side decreased with increasing current density. The values may be low enough to reduce zirconia and form a Ni-Zr alloy. Subsequent oxidation of zirconium presumably causes the observed structural changes near the Ni-YSZ/YSZ interface.

The aim of this presentation is to address three fundamental questions related to solid oxide cells: Are the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) indeed the rate-limiting steps in the high-performance of solid oxide cells, and how can we accurately quantify the area specific resistance of the oxygen electrode?What causes the phenomenon known as “electrochemically driven phase transformation,” and how can our understanding of this process be applied to create electrodes that are both high-performing and durable?How can we develop reliable accelerated testing protocols for both solid oxide fuel cells and solid oxide electrolysis cells, and which physical processes are being accelerated through these tests? The accurate quantification of electrode polarization in fuel cells and electrolyzers holds critical importance but presents a significant challenge due to the extensive overlap in polarizations from both the anode and cathode, whether in DC or AC measurements. This overlap creates a notable gap in our understanding of electrode behavior and in the development of electrochemical devices that are both high-performing and durable. In this presentation, I will introduce a reliable method for measuring the polarization of individual electrodes within a solid oxide cell. This technique is versatile and can be easily adapted for use in various types of electrochemical cells. Additionally, we will explore the limitations associated with using the distribution of relaxation times analysis for determining the polarization of individual electrodes.We will then address the origin for the phase transformation observed in an oxygen electrode during operation, as opposed to what is seen with thermally annealed materials. By integrating electronic conduction at the interface layer, we can significantly reduce the occurrence of phase transformation. This understanding of “electrochemically driven phase change” is crucial for the development of reliable accelerated testing protocols. Such protocols are essential in solid oxide fuel cell research to speed up the investigation of durability issues, quickly identify potential failure mechanisms, and ultimately estimate the lifespan of electrochemical cells. In our study, we compared solid oxide fuel cells operated at constant current density with those subjected to accelerated testing methods, which involve intermittent current injections. We have formulated a general accelerated testing framework, which will be presented in detail.Finally, we will present a theoretical model that underlies those three questions and can be used to address stability and durability issues in solid oxide cells. Acknowledgements: The presenter would like to thank Prof. Anil Virkar, Dr. Emir Dogdibegovic, and Dr. Yudong Wang, for their invaluable contributions to the work presented. This work was made possible through the support of projects DE-FE0026097, DE-FE0031667, DE-AR0001346, and DE-FE0032110.

High-temperature solid oxide cells (SOCs) is in the center of scientific attention for a while as a promising technology related to sustainable society. In this case, SOCs consist of two closely interlinked technologies: solid oxide fuel cells and solid oxide electrolysis cells. Both technologies share several similar traits such as high electrical efficiency and fast reaction kinetics due to the high operating temperature (600–900 °C) without the need for PGM catalysts. These cells basically consist of two porous composite electrodes and a dense ion conducting electrolyte. In particular, the inner microstructure of the electrodes predetermines the SOCs performance owing to its governing effect on the electrical conductivity and/or electrocatalytic activity. Despite its importance, contemporary understanding of the development of the emerging microstructure during the fabrication of these composite materials is far from sufficient.Lanthanum-strontium-manganite (LSM, La1-xSrxMnO3-δ) paired with yttria stabilized zirconia (YSZ, ZrO2:Y2O3) is the typical example of the state-of-the art porous oxygen electrode exhibiting a mixed ion-electron conductivity suitable for SOCs. The fabrication process of LSM:YSZ electrodes involves a crucial step – the sintering, which principle lies in the thermal treatment of the precursor particles for a defined period of time. The LSM:YSZ composite is usually sintered at 1150 °C. At this temperature, exclusively LSM particles tend to soften and form an interlinked solid framework between individual particles, while the YSZ particles remain unaffected by the temperature treatment due to their high melting point (around 2500 °C).Despite the sintering process belongs among the oldest known fabrication techniques, there is no hard evidence on how the sintering proceeds over time at different temperatures while employing materials with significantly different melting points, such as LSM and YSZ. In addition, the sintering temperature along with the sintering time directly influences the resulting inner microstructure and consequently the electrical conductivity of such electrode. Prediction of the resulting inner microstructure is frequently performed by postmortem analyses of multiple samples sintered at different temperatures. However, such practice results only in indirect proofs of the impact of the sintering temperature and is significantly time consuming. The goal of this study is, therefore, to investigate the sintering process of LSM:YSZ composite in situ and to set into relation the resulting inner microstructure with the applied thermal treatment.To answer the present goal, a novel combination of SEM paired with inbuilt MEMS heating chip was developed. This setup allows for online monitoring of the LSM:YSZ sintering process. The results show that at 900 °C the LSM particle agglomerates begin to shrink as the individual LSM particles start to adhere to each other. At this point, significant porosity emerges in the composite, which is considered essential to ensure a sufficient mass transfer during the SOCs operation. On the other hand, the degree of the emerged porosity can be beyond the threshold of mechanical stability of the electrode body, rendering such an electrode unusable. At 1150 °C the densification of the composite occurs, which is essentially a self-healing process resulting in a well-interlinked and mechanically stable composite. The densification is related to the adhesion of the LSM particles to the YSZ particles, thus forming a solid framework, ensuring ample mixed ionic-electronic conductivity of the fabricated electrode. Based on the results, a slight variation in sintering temperature and/or time leads to a significant difference in the electric conductivity of the electrode due to a different sintering degree or, in other words, due to the different void fraction in the body of the electrode. Within the literature, this outcome is reflected by a major inconsistency in reported electric conductivity of the commonly utilized 50:50 wt.% ratio of LSM:YSZ.An interesting insight into the sintering process of the LSM:YSZ composite has provided the SEM paired with inbuilt MEMS heating chip. This experimental technique is very promising for in situ studies of sintering and/or synthesis processes of various materials related to numerous technologies.This work was supported by the Technology Agency of the Czech Republic under project no. TK04030143.

Clean and high-efficiency energy conversion devices are receiving great attention to address the global energy problem and achieve carbon neutrality. In recent years, solid oxide electrolysis cells (SOECs), an energy conversion device, have been widely studied for H2O reduction. However, the degradation under long operation is one of the biggest challenges for the commercialization of SOEC. Thus, it is important to clarify the mechanisms and relevant factors contributing to performance degradation of SOEC.One of the most studied degradation phenomena in SOECs is Ni microstructural change in the Ni-YSZ cathode. For example, the coarsening of Ni particles leads to the decrease of TPB and the Ni recedes from the electrolyte leading to an increase of the electrolyte’s thickness that increasing the R ohmic [1,2]. Both of the degradation caused by the Ni migration that led to microstructure change. Nevertheless, the microstructure of Ni-YSZ porous electrode is so complicated that it is difficult to understand the microstructure changes by direct observation. Thus, instead of the porous electrode, the model electrode can be utilized to simplify the microstructure and geometry, which can make the observation of Ni morphological change more intuitive.To avoid the complexity of Ni-YSZ porous electrode, in this study, a three-dimensional porous electrode is flattened into a two-dimensional comb-shaped model electrode, which allows direct observation of the morphological changes that take place in a complex electrode structure.In this study, laser microscope and scanning electron microscope (SEM) were used to observe the morphological change of Ni electrode. Under different conditions, no obvious Ni migration was found after the long-term operation. However, the Ni and YSZ interface was partially separated. This phenomenon may be caused by low wettability in SOEC mode, or it may be caused by the accumulation of oxygen vacancies leading to an increase of Ni contact angle to form a gap.Chronoamperometry (CA) and Impedance electrochemical measurements were used to study the electrochemical degradation of patterned cells during long term operation. The polarization resistance increased under different H2O and H2 concentration at 1073 K. At 10% H2O concentration, impedance results show that degradation mainly occurred in the first 25 hours. However, at 5% H2O concentration, the increase in polarization resistance was more uniform during 125h. Similarly, the CA results also show that the current decreased more significantly in the first 25 hours at 10% H2O concentration but maintains a certain upward trend at 5% H2O concentration until 125 hours. This result suggests that higher H2O concentration may lead to faster initial cell degradation. Because higher H2O concentration can cause the microstructural change of Ni/YSZ in a shorter period of time, such as Ni coarsening or Ni-YSZ interface detachment. Experiments with other oxides materials are currently underway. Different ceramics may possess different ionic and electronic conductivity and shows the effect of the interaction between Ni and the ceramics that may affect the Ni microstrutural change. The results will be compared with YSZ electrolyte in the future.AcknowledgementThis study was supported by JST, the establishment of university fellowships for the creation of science technology innovation, grant number JPMJFS2102 and NEDO, grant number JPNP16002.Reference[1] D. The, S. Grieshammer, M. Schroeder, M. Martin, M. Al Daroukh, F. Tietz, J. Schefold, A. Brisse, Microstructural comparison of solid oxide electrolyser cells operated for 6100 h and 9000 h, J . P ower Sources , 275 (2015) 901-911.[2] M.P. Hoerlein, M. Riegraf, R. Costa, G. Schiller, K.A. Friedrich, A parameter study of solid oxide electrolysis cell degradation: Microstructural changes of the fuel electrode, Electrochim . Acta , 276 (2018) 162-175.

Ceramic high-temperature fuel cells and electrolysers are efficient energy conversion systems for electrical power generation and hydrogen production. Their core components are constituted by a stack of electroactive Solid Oxide Cells (SOCs) in which the electrochemical reactions take place. Thanks to their flexibility, the same stack can be alternatively operated in both fuel cell and electrolysis modes. However, the insufficient durability of SOCs still constitutes a major limitation for the technology. The present study addresses this issue and aims to bring some new insights on the effect of the Solid Oxide Fuel Cell (SOFC) versus Solid Oxide Electrolysis Cell (SOEC) operating modes on degradation of a typical Ni-YSZ//YSZ//CGO//LSCF-CGO cell. The electrochemical degradations are generally attributed to several underlying phenomena such as electrode microstructural evolution, material chemical decomposition or electroactive sites poisoning by contaminants. Among them, it is generally considered that Ni agglomeration in the Ni-YSZ cermet and Lanthanum Strontium Cobalt Ferrite (LSCF) material destabilization are two prevalent mechanisms involved in the cell performance deterioration. Therefore, these two mechanisms have been specifically investigated by a coupled approach of long-term testing in both SOFC and SOEC modes (1000 ≤ t (h) ≤9000) and post-test characterizations. The experimental results have then been analyzed in the frame of an in-house multi-scale model with the purpose to interpret them and to quantify the effect of material ageing on cell performances. The extent of Ni agglomeration has been characterized by three-dimensional electrode reconstructions obtained by X-ray nano-holotomography at European Synchrotron Radiation Facility (ESRF) (on the new Nano-Imaging beamline ID16A-NI). The new set-up and protocol enable the reconstructions of valuable 3D volumes (Fig. 1) with a large field of view (~50 µm) along with a high spatial resolution (~50 nm). The electrode morphological properties, which have been measured on the 3D volumes, have revealed a substantial Ni coarsening over time at 850°C and 750°C, whereas no Ni depletion was detected at the electrolyte interface. The increase of the Ni particle size is found to induce a decrease in both (i) the density of Triple Phase Boundary (TPBs) lines and (ii) the interfacial surface area between Ni and gas. Moreover, it was found that the Ni/YSZ interfacial surface area does not evolve during the experiments. This statement indicates that the ceramic backbone in the cermet prevents a massive Ni agglomeration at the SOFC/SOEC operating temperature. The compilation of all experimental data have allowed fitting the parameters of a physically-based law for Ni coarsening that was introduced in the modelling framework. The simulations have revealed that Ni agglomeration explains around 20-25% of the electrochemical degradation at 850°C after 1000 hrs of operation. However, the electrode microstructural evolution is found not to be affected by the cell polarizations. Therefore, the mechanism cannot explain the higher degradation rates recorded in electrolysis mode compared to the fuel cell ones. To explain the impact of the operating modes (SOFC or SOEC) on the degradation rates, several post-test analyses (i.e. Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray µfluorescence and µdiffraction techniques) have been employed to investigate the phase reactivity in the region of the CGO barrier layer. The characterizations have revealed that Sr diffusion across the barrier layer and formation of SrZrO3 secondary phase occur mainly during electrolysis operation, whereas the process is very limited in fuel cell mode (Fig. 2). As a consequence, LSCF destabilization is found not to be involved in the degradation of cell performances during fuel cell operation while it could explain the highest degradation rates recorded in electrolysis mode. The post-test analyses have also revealed a diffusion and an accumulation of Co in the region of the barrier layer which is concomitant with the formation of SrZrO3. The formation of these Co-rich segregates in contact with SrZrO3 grains have been identified as cobalt-ferrite type compound. The in-house multi-scale model has been used to interpret the role of the cell operating mode on the LSCF destabilization mechanism. The cell polarization curves and the local quantities within the O2 electrode have been computed in both fuel cell and electrolysis modes. The simulations have shown that the electrolysis operation leads to a strong depletion of oxygen vacancies in the LSCF material. It has been proposed that the depletion in oxygen vacancies under electrolysis polarization could drive the Sr release from the structure, and in turn, could explain the experimental results. Based on this proposition, a possible mechanism for the LSCF destabilization and SrZrO3 formation has been detailed. Figure 1

The fabrication of solid oxide electrolysis cells (SOECs) depends critically on the microstructural integrity of their electrodes and electrolytes, which influence ionic/electronic transport and long-term durability. Conventional sintering techniques involve prolonged thermal exposure at high temperatures, resulting in high energy consumption and extended processing times. This study investigates Ultra-Fast High-Temperature Sintering (UHS) as an alternative approach, focusing on the effects of rapid thermal exposure on grain growth, defect formation, and electrochemical performance in standard SOEC electrodes materials, including NiO-YSZ, GDC, and LSCF. Samples were sintered using Joule-heated carbon felts under controlled argon atmospheres, with temperatures reaching up to 1300 °C within seconds.UHS employs rapid Joule heating of carbon fibers to achieve heating rates exceeding 1000 °C/min, significantly reducing total sintering times while maintaining structural integrity. In this study, fuel electrode (NiO-YSZ), air electrode (LSCF-GDC/ LSCF), and barrier layer (GDC) materials were sintered via UHS under vacuum and argon atmospheres at temperatures up to ~1300°C. Preliminary tests were also conducted on Ba-based proton-conducting membranes (e.g., BaCeₓFeᵧO₃₋δ, BCF) to evaluate the compatibility of UHS with protonic ceramics. The effects of sintering rate, chemical stability and applied current (ranging from 20 A to 31 A) were analyzed through scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS).UHS enabled significant densification within 120–200 seconds, reaching relative densities of 90–97% for GDC and up to 96% for LSCF. SEM imaging (Figure 1) revealed well-sintered LSCF structures with average grain sizes of ~5 µm, highlighting the accelerated grain growth kinetics induced by rapid thermal exposure. In contrast, conventional sintering required ~20 hours to achieve comparable densification, underscoring the efficiency of UHS. For NiO-YSZ, early tests showed surface nickel precipitation due to direct interaction with carbon fibers; this phenomenon was confirmed via SEM and elemental mapping using EDS (Figure 2), which showed localized Ni enrichment near the pellet surface. The issue was mitigated using 3D-printed NiO spacers, which provided a chemically compatible interface. No secondary phases were detected by XRD in any of the sintered samples. Electrochemical impedance spectroscopy revealed reduced polarization resistance and improved ionic conductivity in GDC-LSCF layers processed via UHS, indicating a strong correlation between grain connectivity and electrochemical performance. While detailed defect characterization is ongoing via XPS and TEM, the observed trends suggest that UHS-induced microstructural changes—particularly grain growth and phase purity—play a pivotal role in the functional properties of SOEC materials.These findings establish UHS as a viable and scalable sintering technique for SOEC manufacturing, offering substantial reductions in energy consumption and processing time while maintaining desirable electrochemical properties. On the other hand, initial results from UHS-processed BCF membranes further suggest the technique's broader applicability to proton-conducting ceramic systems. Further optimization of heating parameters and atmospheric conditions will be essential to fully exploit the benefits of UHS in next-generation SOEC fabrication. Acknowledgements This work was partially supported through federal project number W912CH-24-9-0006, as part of a partnership with the Center for Clean Hydrogen (CCH) at the University of Delaware. The authors would also like to acknowledge Mr. Ethan Ness and Mr. Daniel Schlaffer for experimental support, and Dr. Qiang Wang and Dr. Marcela Redigolo of WVU Shared Research Facilities (SRF) for assistance in characterization and technical input. Figure 1

Electrochemical performance of $$\hbox {La}_{0.8}\hbox {Sr}_{0.2}\hbox {MnO}_{3-\delta }$$ (LSM) for $$\hbox {CO}_{2}$$ reduction in solid oxide cell is studied by performing impedance spectroscopy measurement and current-voltage characterizations for varying ratio of $$\hbox {CO}_{2}/\hbox {H}_{2}$$ . Ohmic resistance $$(\hbox {R}_{\Omega })$$ is observed to be slightly increased from 2.59 to $$2.70\, \Omega \hbox { cm}^{2}$$ , however; the cathode polarization resistance $$(\hbox {R}_{2})$$ decreased significantly from 16.20 to 4.70 $$\Omega \hbox { cm}^{2}$$ as the $$\hbox {H}_{2}$$ percentage increased from 8 to 82%, respectively. As the $$\hbox {H}_{2}$$ content increased in feed gas, the improved polarization resistance indicated an enhanced activity of LSM for $$\hbox {CO}_{2}$$ reduction reaction. Furthermore, the cathode polarization resistance for $$\hbox {CO}_{2}/\hbox {H}_{2}$$ of 92/08, is observed to be decreased from 16.20 $$\Omega \hbox { cm}^{2}$$ (OCV 0.89 V) to 1.90 $$\Omega \hbox { cm}^{2}$$ (2.0 V) as the applied potential increased in the electrolysis mode of operation. A maximum conversion of $$\hbox {CO}_{2}$$ of 6.0% with 55% of faradaic efficiency for the production of CO is achieved for $$\hbox {CO}_{2}/\hbox {H}_{2}$$ ratio of 38/62, which is supported by improved current-voltage polarization, i.e., an increase in reduction current from $$-0.28$$ to $$-0.32\hbox { A cm}^{-2}$$ (at 2.5 V) as the $$\hbox {CO}_{2}/\hbox {H}_{2}$$ ratio decreased from 92/08 to 38/62 respectively. These results demonstrate LSM as an active electrocatalyst to reduce $$\hbox {CO}_{2}$$ , which could further be improved by increasing the $$\hbox {H}_{2}$$ concentration in the feed composition to the cathode. Synopsis: Solid oxide cell is fabricated with strontium doped lanthanum manganite electrodes and yttria stabilized zirconia electrolyte. Electrochemical performance in terms of impedance spectroscopy and current-voltage characteristics of the cell are reported for the reduction of carbon dioxide into carbon monoxide in presence of hydrogen with varying ratio of $$\hbox {CO}_{2}/\hbox {H}_{2}$$ .

Reversible solid oxide electrochemical cell (RSOC) is a competitive option which has attracted increasing focus on alleviating some environmental problems and energy crisis with the capability of reversibly operating in solid oxide fuel cell (SOFC) mode and solid oxide electrolysis cell (SOEC) mode [1].Solid oxide cells (SOCs) have received increasingly attention due to their high efficiency and broad applications. However, electrodes with rapid hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), oxygen evolution reaction (OER) and sufficient durability play a key role in solid oxide cells. A multifunctional perovskite oxide La0.6Ca0.4Fe0.8Ni0.2O3-δ (LCFN) has been investigated as an electrode for SSOCs in our previous work. The results confirm that LCFN shows excellent ORR, OER, CO2-RR and HOR catalytic activity [2-3]. However, the investigation of LCFN for SOCs has been hindered due to the lack of stability. Herein, a novel perovskite La0.6Ca0.4Fe0.7Sc0.1Ni0.2O3-δ (LCFSN) is investigated as an electrode of SOCs. Its structural stability has been improved under H2 atmosphere. The polarization resistance (Rp) of the electrode LCFSN is only 0.147 Ω cm2 at 800 °C under air. The single cell Ni-YSZ/YSZ/GDC/LCFSN displays a peak power density of 1.36 W/cm2 in fuel cell mode and a low Rp value of 0.131 Ω cm2. Most importantly, the cell exhibits admirable durability of 130 h without apparent degradation. All these results suggest that LCFSN is a promising candidate electrode for SOCs.