Journal articles on the topic 'Ni-YSZ Fuel electrode'
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1
Vibhu, Vaibhav, Izaak Vinke, Rudiger-A. Eichel, and L. G. J. (Bert) de Haart. "Performance and Electrochemical Behavior of LSM Based Fuel Electrode Materials Under High Temperature Electrolysis Conditions." ECS Transactions 111, no. 6 (May 19, 2023): 1401–6. http://dx.doi.org/10.1149/11106.1401ecst.
Abstract:
Ni-YSZ is known as the state-of-the-art fuel electrode material for solid oxide cells. However, this conventional fuel electrode experiences severe degradation due to Ni- agglomeration and migration away from the electrolyte. Therefore, to avoid such issues, we have considered Ni free electrodes i.e. La0.6Sr0.4MnO3 (LSM) based perovskite oxides as fuel electrode. Under reducing atmosphere, the LSM perovskite phase transforms into a Ruddlesden-Popper (La0.6Sr0.4)2MnO4±δ phase. In addition to pure LSM fuel electrode, we have also investigated the performance of LSM+YSZ (50:50 wt %) and LSM+GDC (50:50 wt %) composite electrodes. The electrolyte-supported single cells were prepared using 8YSZ electrolyte supports, and in all cases, LSM+YSZ/LSM oxygen electrodes were used. The current-voltage characteristics show good performance for LSM and LSM+GDC fuel electrode containing single cells. However, a lower performance is observed for LSM+YSZ fuel electrode containing single cell. For instance, a current density of 997, 1025, and 511 mA.cm-2 at 1.5 V, are obtained for LSM, LSM+GDC, and LSM+YSZ fuel electrode containing single cells respectively, with 50% N2 and 50% H2O feed gas mixture.
2
Grimes, Jerren, Yubo Zhang, Dalton Cox, and Scott A. Barnett. "Enhancement of Ni-YSZ Fuel Electrode Performance Via Pressurization and GDC Infiltration." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 9. http://dx.doi.org/10.1149/ma2023-01549mtgabs.
Abstract:
Solid oxide cell systems are often designed for operation with a pressurized stack. Although the cell performance is expected to improve with pressurization, the details of how pressure affects the performance of various technologically-relevant electrodes are typically not known. Here we investigate the electrochemical characteristics of Ni-YSZ and GDC-infiltrated Ni-YSZ fuel electrodes in Ni-YSZ-supported cells as a function of total pressure P from 1 to 5 atm in H2/H2O fuel mixtures with humidification of 25%, 50%, and 75% and temperatures of 600˚C and 700˚C. Using electrochemical impedance spectroscopy, the two limiting electrode processes are identified: charge transfer reactions and gas diffusion. The charge transfer resistance is significantly reduced for Ni-YSZ:GDC compared to Ni-YSZ for all conditions, with total polarization resistance RP reduced by 30 - 40%. Fitting the data to a power-law dependence, RP ∝ P−n, yields a power law exponent of n = 0.28 for Ni-YSZ and 0.36 for Ni-YSZ:GDC (at 600˚C) and n = 0.32 for Ni-YSZ and 0.39 (at 700˚C). That is, GDC infiltration improved electrode performance more at higher pressure. Increasing the total pressure from 1 to 5 atm results in a 42% and 47% reduction in RP for infiltrated electrodes at 600˚C and 700˚C; these values are averaged for all humidities. Increasing humidity from 25 to 50% at 1 atm resulted in a ~26% reduction in total RP. The Ni-YSZ:GDC electrode at 5 atm had a RP value 63% - 65% lower than that of the Ni-YSZ electrode at 1 atm, a very substantial combined effect. The impact of pressurization on overall cell area-specific resistance is assessed based on the present data combined with prior measurements of oxygen electrode pressurization effects.
3
Ouyang, Zhufeng, Anna Sciazko, Yosuke Komatsu, Nishimura Katsuhiko, and Naoki Shikazono. "Effects of Transition Metal Elements on Ni Migration in Solid Oxide Cell Fuel Electrodes." ECS Transactions 111, no. 6 (May 19, 2023): 171–79. http://dx.doi.org/10.1149/11106.0171ecst.
Abstract:
In the present study, Ni-M (M = Fe, Cu) bimetallic fuel electrodes are applied to investigate the effects of transition metal elements on nickel (Ni) migration and Ni coarsening under SOFC and SOEC operations. Ni-Fe, Ni-Cu and pure Ni patterned fuel electrodes are sputtered on YSZ pellets. The electrochemical performance of these Ni-M bimetallic fuel electrodes are lower than pure Ni fuel electrode, while the degradation rate of Ni-Fe fuel electrodes is smaller than the others. The spreading of Ni film on YSZ surface is observed for all samples under anodic polarization, and such Ni migration is suppressed by Fe doping, whereas it was enhanced by Cu doping. The adhesion between the electrode/electrolyte interface is weakened for Ni-Cu and pure Ni fuel electrodes under cathodic polarization, while good adhesion at the interface is maintained for Ni-Fe, which correlates with the smaller performance degradation rate.
4
Budiman, Riyan Achmad, Rikuto Konishi, Nanako Bisaka, Keiji Yashiro, and Tatsuya Kawada. "Time-Dependence of Microstructural Evolution and Performance Degradation of Ni/YSZ Electrode in Co-Electrolysis SOEC." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 231. http://dx.doi.org/10.1149/ma2023-0154231mtgabs.
Abstract:
Production of synthetic hydrocarbon fuels with Co-electrolysis using solid oxide electrolysis cell (SOEC) by Fischer-Tropsch reaction has attracted attention to solving energy and environmental problems. Reduction of CO2 and H2O to CO and H2 like a simple reaction process. However, carbon coking and microstructure alteration due to long-term operation could cause degradation performance, especially at Ni/YSZ fuel electrode. In this study, we determined the microstructure evolution and performance degradation of fuel electrode supported SOEC (Nexceris, USA) as function of temperature under 10% H2O:20%CO2 and applied voltage of -1.3 Volt. As a result, lower temperatures (1023 K) degradation showed faster degradation rate than higher temperatures (1073 K) despite similar fuel composition. Post-mortem analysis by SEM-EDX showed that the amount of carbon deposition is relatively low. However, the Ni average diameter increase by factor of two compared to as-reduced Ni/YSZ fuel electrode. Another measurement was conducted to confirm the effect of the water vapor only. It showed that the Ni average diameter was observed to be similar between co-electrolysis and water electrolysis conditions. This result indicated that the change of the Ni average diameter could be affected by the presence of water vapor only. There have been many reports on the change of Ni diameter in the Ni/YSZ for SOEC [1,2]. The Ni migration/diffusion in the Ni/YSZ fuel electrode is a complex mechanism, especially at the porous body because the complex geometry and morphology. Thus, it is so often to use model electrodes to simplify the geometry in order to understand the Ni migration [3]. The YSZ film was deposited on the MgO single crystal by pulsed-laser deposition (PLD). After that, the Ni film sputtered onto YSZ thin film, then patterned by photolithography. The Ni-pattern electrode can be viewed as a simplified cross-section of a porous electrode and simulated on a flat surface. It has two side Ni patterns in the opposite direction which are separated by a small gap on YSZ film which works as the electrolyte. At the edge of the Ni-pattern electrodes, the Pt electrodes were sputtered as a current collector. The model electrode was measured by applying a voltage on two-side of the Ni-patterned electrode where one Ni pattern was in fuel cell mode and another Ni pattern was in electrolysis mode. The measurement was completed under various gas composition at 1173 K. The measurement was taken every 20 h – 40 h before the laser microscope was used to observe the change in the Ni pattern electrode. The result on the model electrode will be corroborated with our study on Ni/YSZ porous. Acknowledgement This study was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan. Reference: [1] A. Hauch, S. D. Ebbesen, S. H. Jensen, M. Mogensen, J. Electrochem. Soc., 155(11) (2008) B1184-B1193. [2] D. The, S. Grieshammer, M. Schroeder, M. Martin, M. A. Daroukh, F. Tietz, J. Schefold, A. Brisse, J. Power Sources, 275 (2015) 901-911. [3] Z. Ouyang, Y. Komatsu, A. Sciazko, J. Onishi, K. Nishimura, N. Shikazono, J. Power Sources, 529 (2022) 231228.
5
Ouyang, Zhufeng, Anna Sciazko, Yosuke Komatsu, Nishimura Katsuhiko, and Naoki Shikazono. "Effects of Transition Metal Elements on Ni Migration in Solid Oxide Cell Fuel Electrodes." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 28. http://dx.doi.org/10.1149/ma2023-015428mtgabs.
Abstract:
Solid oxide cells (SOCs), both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC), have emerged and attracted more and more attentions due to its high energy conversion efficiency and fuel flexibility. However, degradation of fuel electrodes after long-term operation remains as one of the main challenges for their commercial application. Two major types of microstructure evolution, nickel (Ni) migration and Ni coarsening in Ni - yttria-stabilized zirconia (Ni-YSZ) fuel electrodes have been widely reported, which have strong impacts on both cell performance and durability. Therefore, materials-driven research has focused on developing more robust fuel electrodes with good electrocatalytic ability. Utilization of Ni alloys has immersed as a promising concept to enhance the performance and robustness of conventional Ni/YSZ. In the present study, Ni-M (M = Fe, Cu) bimetallic fuel electrodes are applied to investigate the effects of transition metal elements on the morphological evolutions under SOFC and SOEC operations. Ni-Fe, Ni-Cu and pure Ni patterned fuel electrodes are sputtered on YSZ pellets. The electrochemical performance of these Ni-M bimetallic fuel electrodes decreases compared with pure Ni fuel electrode, while the performance degradation rate of Ni-Fe fuel electrodes is smaller than others. Besides, the spreading of Ni film on YSZ surface is observed for all samples under anodic polarization and such Ni migration is suppressed by Fe doping, whereas enhanced by Cu doping. On the other hand, the adhesion is weakened at the electrode / electrolyte interface for Ni-Cu and pure Ni fuel electrodes under cathodic polarization, while good adhesion at the interface is maintained for Ni-Fe, which correlates with the smaller performance degradation rate.
6
Kamboj, Vipin, and Chinmoy Ranjan. "Mixed Metal Cathodes for CO2 Electroreduction Using Solid Oxide Electrodes." ECS Meeting Abstracts MA2022-02, no. 64 (October 9, 2022): 2369. http://dx.doi.org/10.1149/ma2022-02642369mtgabs.
Abstract:
Electroreduction of CO2 to fuels through the use of renewable energy provides a beneficial route and it decreases the reliance on fossil fuels. The electrochemical reduction of CO2 to hydrocarbon fuels (CHx) is highly energy inefficient owing to kinetic limitations which are a direct consequence of multistep-multielectron transfer process. The selective formation of CO from CO2 is energy efficient. CO thus formed, serves as a valuable source of energy as it can be directly used as a fuel. Moreover, it can be further converted into hydrocarbon fuels via Fischer-Tropsch reactions using green hydrogen. We hereby propose Ni(M)x/YSZ based electrodes for electroreduction of CO2 on solid oxide cells at high temperature (~800∘C). Electrodes were fabricated on commercial standard YSZ supports using Ni(M)x/YSZ and LSM/YSZ mixtures which were respectively employed as materials for that cathode and anode. Characterisation of the developed electrode architecture was carried out via electron microscopy and X ray diffraction. The behaviour of electrodes during CO2 electrolysis was analysed through online mass spectrometry and operando Raman spectroscopy. Ni/YSZ electrodes displayed sustained performance only upon the addition of H2 to the fuel mixture. The reaction progressed through a reverse water gas shift reaction (RWGS) (CO2 + H2 à CO + H2O) along with water electrolysis where CO originates from non-electrochemical RWGS reaction. Electrochemical impedance spectroscopy was employed to analyse the reactions. Three electrode assembly was used to compare the electrochemical performance of the various electrodes. The pure Ni/YSZ cathodes showed deactivation under pure CO2 atmosphere. Mixed metal oxide electrodes such as Ni(M)x exhibit enhanced performance for CO2 electrolysis in both pure CO2 as well as in the presence of 5% H2. Catalytic performance of the electrodes was evaluated by varying fuel mixtures composition and temperature. Kinetics of electrode performance were evaluated using distribution of relaxation time formalism. Mixed metal oxide such as Ni(M)x showed improved kinetic with significant improvement in charge transfer resistance. Figure 1
7
Ranjan, Chinmoy. "Mechanistic Details of CO2 Electroreduction on Ni and Ni{Cu}-YSZ Electrodes Using Operando Spectroscopy." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 13. http://dx.doi.org/10.1149/ma2023-015413mtgabs.
Abstract:
Electroreduction of CO2 to fuels using renewable energy can significantly help in reducing emissions and dependence of fossil fuels. Electrochemical reduction of CO2 to hydrocarbon fuels (CHx) is energy inefficient owing to multistep-multielectron transfer process which posses many kinetic limitations. The selective conversion of CO2 to CO is energy efficient. CO as product can be directly used as a fuel or converted to hydrocarbon fuels by using green hydrogen via Fischer-Tropsch reactions. Well known Ni/YSZ electrode architectures have both well-established lifetimes, performance benchmarks and optimised manufacturing protocols when it comes to use as SOFC. Unfortunately, using these electrodes as CO2 reduction electrodes requires use of H2 at the inlet. The reaction proceeds through a reverse water gas shift reaction (RWGS) (CO2 + H2 à CO + H2O) in conjunction with water electrolysis. Most of the CO originates from non-electrochemical RWGS reaction. Use of pure CO2 streams at currents exceeding 240mA/cm2 leads to catastrophic electrode failure. In the literature, it is believed that transformation of Ni metal to NiOx and carbon deposition via Bouduard reaction are the causes of electrode failure in pure CO2. We have adapted this well-known Ni/YSZ electrode by impregnation of Cu into the Ni architecture. The Ni{Cu}/YSZ electrode not only does not deactivate but also shows improved performance in every aspect compared to the pure Ni/YSZ electrode. We have developed a unique setup for operando Raman Spectroscopy and online mass spectroscopy which can be used to study electrode reactions under both steady state and transient conditions. Using this setup, we have shown that Ni-YSZ and Ni{Cu}/YSZ electrodes go through an oxide mediated mechanism of CO2 reduction. Metal oxides such as NiOx and Ni{Cu}Ox are the active catalyst species and not the metals. Upon applying strongly reducing conditions (currents > 240mA/cm2), NiOx reduces to Ni metal which can no longer catalyse the reaction, whereas the oxide on Ni{Cu}Ox is much stronger and does not reduce under even the most reducing of conditions (reducing currents >480mA/cm2). Such an electrode remains active for reducing pure CO2. Supporting studies using SEM, TEM, XPS, operando EIS, TPR and DFT modelling were also carried out. We believe that enabling CO2 reduction Ni/YSZ architecture using Cu impregnation is a game changer as all aspects of electrode manufacturing and device compatibility for Ni/YSZ have been extensively tested and market proven. This will allow for quick adaptation for this electrode in the CO2-SOEC market. Besides this, such a mechanistic study remains unique in the field of solid oxide-based research. Figure 1
8
Mogensen, Mogens Bjerg, and Gurli Mogensen. "(Invited) On Degradation Mechanisms of Ni-YSZ Fuel Electrodes in Solid Oxide Cells." ECS Meeting Abstracts MA2023-02, no. 46 (December 22, 2023): 2236. http://dx.doi.org/10.1149/ma2023-02462236mtgabs.
Abstract:
The solid oxide cell (SOC) is reversible. It has about equally good performance both in solid oxide fuel cell (SOFC) and in solid oxide electrolyzer cell (SOEC) mode. The classical Ni-YSZ cermet SOC fuel electrode has an excellent initial performance provided that it has a good structure in terms of particle size of both Ni and YSZ, and a suitable porosity with sufficient contact between Ni-Ni, YSZ-Ni, YSZ-YSZ particles, and in absence of certain impurities such as silica and sulfur. The essential entity of the Ni-YSZ electrode is the length of the three phase boundary (3pb) between the three phases of Ni electron conductor, YSZ oxide ion conductor, and H2-H2O gas, which have electronic contact to the main Ni electrode, ionic contact to the bulk YSZ electrolyte, and access to the the main gas atmosphere, respectively. Nano-particular Ni is an excellent electrocatalyst for the reduction of H2O to H2 + O2- and for the oxidation. It seems that it is generally accepted that at operation temperatures (above 650 °C and above) the initial nano-sized Ni particles, which are in electric contact with each other, will over time continue to sinter into larger and larger Ni particles until all the Ni has become one dense body or the growth of the Ni particles has been blocked by particles of another phase like YSZ. Thus, the relative high mobility of Ni continues to pose a problem towards the lifetime of a highly functional Ni-YSZ electrode. A most serious type of degradation of Ni-YSZ electrodes in solid oxide electrolysis cells (SOEC) seems to be the one coupled to Ni-migration, which is regarded as an important obstacle for the commercialization of SOEC. Post mortem scanning electron microscopy investigations of the degraded Ni-YSZ electrode reveal that a thin (up to 3 – 5 µm) zone of the original nano-structured active Ni-YSZ cathode has been significantly been depleted in Ni. This degradation is clearly driven by the electrochemical polarization of the Ni-YSZ electrode [1], but the mechanism is highly discussed. Several researchers have the hypothesis that the Ni depletion is a result of Ni migration in a gradient in Ni/YSZ interface energy, see e.g. [2,3]. However, a review of relevant literature points out that this hypothesis cannot explain several reported clear experimental results, whereas our hypothesis based on Ni+ ions from Ni particles, which have lost electrochemical contact, migrate as NiOH across the YSZ particles to new active 3pbs formed further away from the bulk electrolyte. This hypothesis may qualitatively explain all reported results from steam electrolysis cells and H2 fuel cells so far [1]. However, our hypothesis does not directly explain the similar migration of Ni away from the YSZ bulk electrolyte in case of CO2 electrolysis. Therefore, a revision of our hypothesis will be presented. The essential change is simply to propose that it is the Ni+-ion that migrates in the YSZ-surface layer as either NiOH in case of steam electrolysis, or as “Ni2CO3” in case of CO2 electrolysis. A monolayer of “Ni2CO3” on a YSZ surface is not assumed to be any kind of crystalline Ni2CO3, but rather a layer of adsorbed Ni+ and “CO3 1-“ in which CO3 2- has one of its oxygen atoms incorporated into the YSZ surface crystalline structure which is formed by reaction between CO2 from gas and an unsaturated surface oxygen with a “dangling” electron with similarity to CO2 reduction on ceria [4]. Furthermore, the possible role of SiO2 impurities in the loss of contact between Ni and YSZ at negatively polarized Ni will be presented as another revision of the hypothesis together with further new details. References M.B. Mogensen et al., Fuel Cells, (2021), 1–15; DOI: 10.1002/fuce.202100072, and references therein. M. Trini et al., Acta Materialia, 212 (2021) 116887; DOI: 10.1016/j.actamat.2021.116887. L. Rorato et al., J. Electrochem. Soc., 170 (2023) 034504, DOI: 10.1149/1945-7111/acc1a3, and references therein. E.M. Sala et al., Phys. Chem. Chem. Phys. (2023), DOI: 10.1039/d2cp05157e.
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Kamboj, Vipin, and Chinmoy Ranjan. "Mixed Metal Ni(M)/YSZ for High-Temperature CO2 Electroreduction to CO." ECS Meeting Abstracts MA2022-01, no. 55 (July 7, 2022): 2312. http://dx.doi.org/10.1149/ma2022-01552312mtgabs.
Abstract:
Electroreduction of CO2 to fuels using renewable energy can significantly help in reducing emissions and dependence on fossil fuels. Electrochemical reduction of CO2 to hydrocarbon fuels (CHx) is energy inefficient owing to the multistep-multielectron transfer process, which possesses many kinetic limitations. The selective conversion of CO2 to CO is energy efficient. CO as product can be directly used as a fuel or converted to hydrocarbon fuels by using green hydrogen via Fischer-Tropsch reactions. We have used Ni(M)x/YSZ based electrodes to study electroreduction of CO2 on solid oxide cells at high temperature (~800∘C). Electrodes were developed on commercial standard YSZ supports using Ni(M)x/YSZ mixtures for cathode and LSM/YSZ mixtures for the anode. Electron microscopy and X-ray diffraction were used to characterize the electrode architecture and material. The electrodes were tested using online mass spectroscopy and operando Raman spectroscopy. Ni/YSZ electrodes showed sustained performance only when H2 was added to the fuel mixture, and the reaction proceeded through a reverse water gas shift reaction (RWGS) (CO2 + H2 → CO + H2O) in conjunction with water electrolysis with the CO originating from non-electrochemical RWGS reaction. The reactions were also analyzed using electrochemical impedance spectroscopy. The pure Ni/YSZ cathodes showed deactivation under a pure CO2 atmosphere with the formation of NiOx species with the catastrophic breakdown at high current densities around 400 mA/cm2. The behaviour could be verified using both mass spectroscopy and operando Raman Spectroscopy. The electrochemical performance of various electrodes was compared using a 3-electrode geometry. Mixed metal oxide electrodes such as Ni(M) showed improved kinetics, with significant improvement seen in the charge transfer resistance measured. Figure 1
10
Grimes, Jerren, Yubo Zhang, Dalton Cox, and Scott A. Barnett. "Enhancement of Ni-YSZ Fuel Electrode Performance Via Pressurization and GDC Infiltration." ECS Transactions 111, no. 6 (May 19, 2023): 51–59. http://dx.doi.org/10.1149/11106.0051ecst.
Abstract:
Ni–(Y2O3)0.08(ZrO2)0.92 (YSZ) and Ce0.8Gd0.2O2 - δ (GDC) infiltratedNi-YSZ fuel electrodes are investigated using impedance spectroscopy as a function of total pressure P from 1 to 5 atm in 25%, 50%, and 75% humidified H2 mixtures at a temperature of 600˚C. The charge transfer resistance decreases significantly with infiltration for all conditions, and the total polarization resistance RP is reduced by ~20%. Fitting the P dependence to a power-law, RP ∝ P−n, yields an exponent of ~0.21 for both un-infiltrated and infiltrated tests. Increasing the total pressure from 1 to 5 atm results in an average 29% reduction in RP for both electrodes. Increasing the humidification from 25 to 75% generally results in a reduction in RP. The Ni-YSZ:GDC electrode at 5 atm had a RP value ~44% lower than that of the Ni-YSZ electrode at 1 atm, a substantial combined effect.
11
Yu, Miao, Xiaofeng Tong, Karen Brodersen, and Ming Chen. "Electrochemical Performance and Durability of a Solid Oxide Cell with Nanoparticles-Modified Electrodes for CO2 Electrolysis." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 212. http://dx.doi.org/10.1149/ma2023-0154212mtgabs.
Abstract:
Solid oxide electrolysis cell (SOEC) is one of the most effective technologies for converting carbon dioxide to carbon monoxide using renewable energy sources. Improving the electrode performance of an SOC by manufacturing nanocomposite electrodes via infiltration has attracted growing interest in recent years. This work investigated the electrochemical performance and long-term durability of a Ni/yttria-stabilized zirconia (YSZ)-supported planar-type SOEC cell (CGO@Ni/YSZ|YSZ|CGO|LSC/CGPO@CGO) infiltrated with nano-catalysts for CO2 electrolysis. The Ni/YSZ fuel electrode was infiltrated with Ce0.8Gd0.2O2−δ (CGO) solution, and the porous CGO scaffold was co-infiltrated with La0.6Sr0.4CoO3-δ (LSC) and Gd, Pr co-doped CeO2 (CGPO) nano-sized electrocatalysts. The cells were operated at 800 °C and -1 A/cm2 for 1548 h with a mixture of 24 L/h CO2/CO (83/17) supplied to the Ni/YSZ fuel electrode and pure O2 to the oxygen electrode. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) analysis were conducted. Cell activation occurred at ⁓400 h of the durability testing due to the gas resupply from an unexpected power outage at ⁓360 h. During the durability testing period, the cell voltage increased from 1246 mV to 1400 mV with a degradation rate of 99.1 mV/kh (7.95%/kh). Furthermore, the cell showed a much lower degradation of ohmic resistance R s (7.14 mΩ cm2/kh) compared to that of polarization resistance R p (129.05 mΩ cm2/kh) after the gas resupply. DRT reveals that the degradation originates mainly from the Ni/YSZ fuel electrode during durability testing. Results from the current work demonstrate the potential of modifying SOECs for CO2 electrolysis at a high current density through the infiltration technique.
12
Kamboj, Vipin, and Chinmoy Ranjan. "CO2 Electroreduction to Fuels Using Solid Oxide Electrodes: Beyond Ni-YSZ." ECS Meeting Abstracts MA2022-02, no. 49 (October 9, 2022): 1946. http://dx.doi.org/10.1149/ma2022-02491946mtgabs.
Abstract:
Ni-YSZ electrodes form the benchmark in Carbon Dioxide electroreduction to CO. Ni-YSZ due its popular use in Solid Oxide Fuel Cells forms the basis of various process steps. Unfortunately, this material remains active only if a certain amount of hydrogen is supplied along side CO2 to the inlet of the reaction. Consequently, the Ni-YSZ results in CO production via reverse water gas shift (RWGS) reaction when H2 is supplied at the inlet. The currents for the electrode originate from electrolysis of H2O which is formed as a result of reverse water has shift. We have quantified the amount of CO produced from RWGS vs direct CO2 electrolysis in such a system using online mass spectrometry (MS). Electrochemical impedance spectroscopy measurements where analysed using distribution of relaxation times analysis. Under low concentration of H2 the overall impedance is dominated by H2 mass transfer. Effects of concentration of various reactants were measured using online MS. The process of pretreatment of the electrodes and catalyst surface development during reaction were tracked using in situ Raman Spectroscopy and optical spectrocopy. Electrodes were structurally characterised using SEM, TEM, XPS and ICP-OES measurememts. Various new combination of mixed metal oxide electrodes Ni(M)-YSZ were tested and compared with the performance of pure Ni-YSZ. Ni-YSZ electrode when used under pure CO2 results in catastrophic failure of the electrode performance. We have investigated this failure using in situ Raman and Mass spectrometry. The mechanism of CO2 production in pure CO2 stream was found to be drastically different from when a small amount of H2 is used. Figure 1
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Barnett, Scott A. "(High-Temperature Energy, Materials, & Processes Division Outstanding Achievement Award Address) Mechanisms of Oxide Exsolution and Electrode Applications in Solid Oxide Cells." ECS Meeting Abstracts MA2022-02, no. 47 (October 9, 2022): 1769. http://dx.doi.org/10.1149/ma2022-02471769mtgabs.
Abstract:
Solid oxide cell fuel electrodes based on perovskite oxides are desirable to avoid problems with Ni-based anodes, including coking in hydrocarbon fuels and degradation due to fuel impurities or redox cycling. However, oxide anode electrochemical performance is often lacking, limited by surface processes such as 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 cation exsolution and nucleation of metallic nanoparticles on oxide surfaces during cell startup and operation. For example, substitution of small amounts of Ni or Ru on the B-site of Sr(Ti,Fe)O3 results in the formation of Ni-Fe or Ru-Fe nanoparticles, respectively, during exposure of the electrode to fuel during cell operation. This talk will examine the microstructural evolution of these exsolution anodes, making use of in situ x-ray diffraction measurements to detect formation of exsolved metal alloys and oxide phase changes. Exsolved metal nanoparticles enhance electrochemical performance, usually by promoting hydrogen dissociation on electrode surfaces. Changes in perovskite stoichiometry resulting from B-site exsolution can also impact the phase stability of the oxide, in some cases resulting in the formation of Ruddlesden-Popper phases that deleteriously affect electrochemical performance. The application of exsolution in fuel electrodes in novel thin-electrolyte oxygen-electrode-supported cells is discussed; the results indicate that performance in H2/H2O fuel is superior to Ni-YSZ in both electrolysis and fuel cell modes. Electrochemical characteristics of the exsolution electrodes are especially superior to Ni-YSZ when operated in CO/CO2 fuel.
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Mulligan, Jillian Rix, Emily Ghosh, John In Lee, Ayesha Akter, Srikanth Gopalan, Uday Pal, and Soumendra Basu. "Quantifying Microstructural Degradation in GDC-Infiltrated Fuel Electrodes in Reversible Solid Oxide Cells." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 312. http://dx.doi.org/10.1149/ma2023-0154312mtgabs.
Abstract:
Reversible solid oxide cells (RSOCs) can convert between hydrogen or other fuels and electricity in both directions, offering a promising application as tools for mitigating gaps between renewable energy supply and demand in the electric grid. Many advanced RSOC electrode materials achieve good performance stability during operation—for example, NNO | NNO-NDC50 | GDC10 | YSZ | Ni-YSZ cells have been shown to exhibit excellent performance stability over 500hr testing periods when operated reversibly. However, infiltration of a nanocatalyst species, such as GDC10, into the fuel electrode may further improve electrode performance and stability by mitigating Ni coarsening and offering more resilient paths to active reaction sites. In this study, the microstructural degradation of baseline and GDC10-infiltrated RSOC fuel electrodes are quantitatively compared in the context of in-depth electrochemical characterizations. Scanning electron microscopy (SEM) analysis of cell cross sections elucidates the role of GDC10 in improving and stabilizing electrode performance over long-term operation.
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Macalisang, Christine Mae, James Francis Imperial, and Rinlee Butch Cervera. "Facile Preparation of Porous Ni-YSZ Electrode Composite Material: From Highly Dense to Desirable Electrode Porosity Even without Pore Former." ECS Meeting Abstracts MA2023-02, no. 46 (December 22, 2023): 2274. http://dx.doi.org/10.1149/ma2023-02462274mtgabs.
Abstract:
Ni-YSZ is a key electrode material for solid oxide electrochemical cells (SOC) applications, such as fuel or electrolysis cell applications. The number of active sites, specifically the triple-phase boundaries (TPB), strongly affects the electrode performance. Thus, in order to achieve good electrode performance, a desirable microstructure of the electrode is essential. This study investigated the effect of precursor particle size without using pore former in developing porous Ni-YSZ electrode materials. Precursors were prepared with different particle sizes using a planetary ball mill. In comparison, Ni-YSZ with carbon black as a pore former was also prepared. From the XRD patterns, major peaks can be attributed to the cubic phases of NiO and YSZ. SEM images revealed that a highly dense as-sintered NiO-YSZ electrode was achieved; however, a desirable porous microstructure was obtained after reduction to Ni-YSZ, even without a pore former. In comparison, the prepared electrode with carbon black pore former has a larger pore size than the sample prepared without pore former. The obtained total bulk conductivities for the reduced Ni-YSZ without pore former at 700 oC is 3.94x10-1 S/cm with Ea of 0.02 eV at 500-700 oC. Thus, a desirable porous Ni-YSZ electrode with more TPBs and high total conductivity can be achieved even without a pore former. Figure 1
16
Vibhu, Vaibhav, Izaak C. Vinke, Rüdiger-A. Eichel, and L. G. J. (Bert) de Haart. "La0.6Sr0.4MnO3-Based Fuel Electrode Materials for Solid Oxide Electrolysis Cells Operating under Steam, CO2, and Co-Electrolysis Conditions." Energies 16, no. 20 (October 17, 2023): 7115. http://dx.doi.org/10.3390/en16207115.
Abstract:
The conventional Ni–YSZ (yttria-stabilized zirconia) fuel electrode experiences severe degradation due to Ni- agglomeration and migration away from the electrolyte. Therefore, herein, we have considered Ni free electrodes, i.e., La0.6Sr0.4MnO3-δ (LSM)-based perovskite oxides as fuel electrodes. The LSM perovskite phase transforms into a Ruddlesden–Popper LSM (RP-LSM) phase with exsolved MnOx under reducing atmospheres. The RP-LSM is mainly interesting due to its good electrical conductivity, redox stability, and acceptable electrochemical behaviour. In this work, we synthesized the LSM powder and characterized it using several methods including X-ray diffraction (XRD), thermogravimetry analyses (TGA), four-probe conductivity, and scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX). Finally, the electrolyte-supported single cells were fabricated and electrochemically characterized using AC and DC techniques under electrolysis conditions. In addition to pure LSM fuel electrodes, we have also investigated the electrochemical behaviour of LSM + YSZ (50:50) and LSM + GDC (50:50) composite fuel electrodes. The single cells containing LSM and LSM + GDC fuel electrodes show higher cell performance than LSM + YSZ. For instance, current densities of 1, 1.03, and 0.51 A·cm−2 at 1.5 V are obtained for LSM, LSM + GDC, and LSM + YSZ fuel electrodes containing single cells, respectively, with a 50% N2 and 50% H2O feed gas mixture. Moreover, the performance of the cell was also investigated under co-electrolysis with 50% CO2 and 50% H2O and under direct CO2 electrolysis conditions with 100% CO2 fuel gas.
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Unachukwu, Ifeanyichukwu Daniel, Vaibhav Vibhu, Jan Uecker, Izaak C. Vinke, Rudiger-A. Eichel, and L. G. J. (Bert) de Haart. "Comparison of the Electrochemical and Degradation Behaviour of Ni-YSZ and Ni-GDC Electrodes Under Steam, Co- and CO2 Electrolysis." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 219. http://dx.doi.org/10.1149/ma2023-0154219mtgabs.
Abstract:
Abstract The mixed ionic and electronic conductive property of Ni-GDC has ensured that the electrochemical reaction zones of the electrode extend beyond the triple phase boundary of Ni/GDC/fuel gas to the double phase boundary of the GDC and the fuel gas [1, 2]. In addition, ceria has shown good carbon suppression properties when operated in carbon-containing fuels[3, 4]. For these reasons, Ni-GDC has emerged as a possible replacement for the conventional Ni-YSZ electrode. However, a direct comparison of the performance and long-term degradation of Ni-GDC with literature values of the Ni-YSZ would be ambiguous. On one hand, different reports utilize different fuel gas compositions, operating temperatures as well as current densities. On the other hand, the fabrication of fuel electrode-supported Ni-GDC is still a challenge due to the well-known inter-diffusion [5, 6] between the YSZ and the GDC oxide phase at a high sintering temperature (1400 °C) of YSZ electrolytes. Hence, most of the electrode fabrication has remained on electrolyte support. Thus, a direct comparison of electrolyte-supported Ni-GDC with the conventional fuel electrode-supported Ni-YSZ is ineffective due to different degradation behaviour. Therefore, this present study aims to investigate and compare the long-term stability of Ni-GDC and Ni-YSZ under three different electrolysis modes; steam-electrolysis, co-electrolysis and CO2-electrolysis. Firstly, electrolyte-supported single cells of Ni-GDC (NiO-GDC//8YSZ//GDC//LSCF) and Ni-YSZ (NiO-GDC//8YSZ//GDC//LSCF) were fabricated and investigated using electrochemical impedance spectroscopy (EIS) from 750-900 °C temperature range. Furthermore, the impedance data were also recorded under polarization (0.7 to 1.4V) as well as at OCV by varying the partial pressure of steam, CO2 and oxygen (, pH20, pCO2 and pO2). Finally, stability tests of the single cells were carried out under steam electrolysis (H2O: H2, 50:50) and co-electrolysis (H2O: CO2:H2, 40:40:20) conditions at 900 °C with 0.5 A/cm2 current density for 500 h [7]. For the CO2-electrolysis (CO2:CO, 80:20), the stability test was performed up to 1000 h. The post-test characterization of the operated cells was carried out using both SEM-EDX as well as FIB-SEM. The results reveal that Ni-GDC exhibits higher current density than Ni-YSZ in all the electrolysis modes. In the post-test analysis, loss of GDC percolation was observed and the Ni particles were observed to be covered by the GDC oxide phase. Furthermore, both electrodes demonstrate that Ni is migrating away from the electrolyte in all the electrolysis modes. The detailed electrochemical and microstructural properties of the operated cells will be presented and discussed. References [1] R. GREEN, et al, Solid State Ionics 2008, 179, 647–660. [2] D. Chen, et al, Nano Energy 2022, 101, 107564. [3] H. He, et al, MSF 2007, 539-543, 2822–2827. [4] H. He, et al, Hill, Applied Catalysis A: General 2007, 317, 284–292. [5] Y. J. Sohn et al, Inter. Conference on Solid State Ionics 2019, SSI-22 [6] T. SHIMURA, et al, Solid State Ionics 2019, 342, 115058. [7] I. D. Unachukwu, et al, Journal of Power Sources 2023, 556, 232436.
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Li, Xiaoxiao, Yuqing Wang, Yinan Wang, and Yixiang Shi. "Studying the Sulfur Poisoning Mechanism of Solid Oxide Fuel Cells by Means of Patterned Nickel/Yttrium-Stabilized Zirconia Electrodes." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 330. http://dx.doi.org/10.1149/ma2023-0154330mtgabs.
Abstract:
Sulfur causes Ni-based ceramic anode poisoning and thus shortens the life of the cell. Therefore, it is important to clarify the mechanism of sulfur poisoning to improve cell performance and lifetime. However, there is still some controversy about the mechanism of sulfur poisoning. In this work, Ni-patterned electrodes were used for electrochemical experiments to investigate the mechanism of sulfur poisoning under different operating parameters. First, the Ni pattern electrode is operated in H2 fuel containing H2S with the H2S concentration gradually increasing from 5 ppm to 50 ppm. As the concentration of H2S increases, the electrode performance decreases faster. The effect of high oxygen ion flux on the degree of sulfur poisoning was investigated by regulating the operating current of the Ni-patterned electrode SOFC. The results show that the operating current has a large effect on poisoning. This work provides empirical evidence for the mechanism of Ni/YSZ anode sulfur poisoning, and a possible mechanism for Ni/YSZ anode poisoning under sulfur exposure conditions was established.
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Wilson, James R., Marcio Gameiro, Konstantin Mischaikow, William Kalies, Peter W. Voorhees, and Scott A. Barnett. "Three-Dimensional Analysis of Solid Oxide Fuel Cell Ni-YSZ Anode Interconnectivity." Microscopy and Microanalysis 15, no. 1 (January 15, 2009): 71–77. http://dx.doi.org/10.1017/s1431927609090096.
Abstract:
AbstractA method is described for quantitatively analyzing the level of interconnectivity of solid-oxide fuel cell electrode phases. The method was applied to the three-dimensional microstructure of a Ni–Y2O3-stabilized ZrO2 (Ni-YSZ) anode active layer measured by focused ion beam scanning electron microscopy. Each individual contiguous network of Ni, YSZ, and porosity was identified and labeled according to whether it was contiguous with the rest of the electrode. It was determined that the YSZ phase was 100% connected, whereas at least 86% of the Ni and 96% of the pores were connected. Triple-phase boundary (TPB) segments were identified and evaluated with respect to the contiguity of each of the three phases at their locations. It was found that 11.6% of the TPB length was on one or more isolated phases and hence was not electrochemically active.
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Laguna-Bercero, Miguel A. "Degradation Issues in Solid Oxide Electrolysers." ECS Meeting Abstracts MA2023-02, no. 46 (December 22, 2023): 2234. http://dx.doi.org/10.1149/ma2023-02462234mtgabs.
Abstract:
One of the crucial aspects to achieving long lifetime and high-efficient SOCs (Solid oxide cells) is to enhance durability of the current devices. Degradation issues are typically associated with problems in both electrodes. For example, nickel-yttria stabilized zirconia (Ni-YSZ) hydrogen electrodes present under extreme conditions of high steam partial pressures, a low durability due to Ni oxidation resulting in lowered electronic conductivity and catalytic activity of the electrode. Ni agglomeration, depleting and micro crack in Ni-containing hydrogen electrode can also occur leading to a lower activity of the Ni-based electrodes as an SOEC fuel electrode. Furthermore, carbon deposition and sulfur poisoning on the Ni surface are also lead to cell performance degradation and poor durability. In addition, the performance of the oxygen electrode is also particularly more important in electrolysis mode than in fuel cell mode, as it is well established that electrochemically induced oxygen pressure increase at the electrolyte-oxygen electrode interface and subsequent membrane failure have been theoretically predicted and experimentally observed in SOEC mode. For example, several examples in the literature reported the presence on voids at the YSZ electrolyte, leading to delamination of the oxygen electrode. In this sense, lanthanide nickelates (Ln = La, Nd, Pr) have received considerable interest as materials for IT-SOFC electrodes and oxygen separation membranes, and they seem to be very attractive for electrolysis applications. The hyperstoichiometry of some oxygen electrode materials such as these Ruddlesden-Popper phases is believed to be favourable for effective oxygen evolution, as performance of these electrodes is enhanced in SOEC mode. Different strategies to develop optimized electrode structures as well as controlled operating conditions will be discussed in order to improve the durability of SOCs.
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Diaz Lacharme, Maria Carmenza, and Alessandro Donazzi. "Characterization and Testing of Exsolution-Based Solid Oxide Cells for Reversible Operations in CO2 Electrolysis." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 290. http://dx.doi.org/10.1149/ma2023-0154290mtgabs.
Abstract:
Reversible solid oxide cells (rSOCs) are a promising electrochemical technology able to work both as energy storage devices in solid oxide electrolysis (SOEC) mode, and as power generators in solid oxide fuel cell (SOFC) mode. rSOCs implemented for CO2 electroreduction into valuable CO-rich steams through electrolysis would provide opportunities for CO2 utilization, and hence become useful tools for the reduction of greenhouse gases emissions. High-temperature co-electrolysis of CO2/H2O mixtures has recently become of interest since high conversion and energy efficiency are thermodynamically favored in addition to the reduction in cell area-specific resistance when compared to pure CO2 electrolysis [1]. However, reversible operation with CO2-containing feeds requires developing flexible, high-performing, and long-lasting materials for the rSOCs Managing issues such as coking and low redox tolerance in the state-of-the-art (SoA) Ni-Yttria-stabilized-zirconia (Ni-YSZ) cermet fuel electrode in the rSOCs is crucial. Ni-YSZ cermet exhibits high electronic conductivity and electrochemical activity in hydrogen. Nonetheless, Ni is prone to oxidation due to operation under high steam concentrations, and rapid variations in the fuel supply. Additionally, Ni is well-known for its coke-formation tendency which becomes detrimental in CO2-rich mixtures for electrolysis [2]. Thus, ceramics with mixed ionic and electronic conductivity (MIEC) have emerged as alternative fuel electrodes thanks to the larger electrochemically active area compared to standard cermets. Among the MIEC electrodes, the SrTi0.3Fe0.7O3 (STF) perovskite has proven to give low polarization resistances especially when modification techniques such as exsolution of metal nanoparticles are employed [3]. This work focuses on the investigation of the electrocatalytic properties of exsolution-based STF electrodes operating with CO/CO2 and H2O/CO2 mixtures. The mixtures used were 50% CO2/50% CO, 25% H2O/25% CO2/25%H2/25%CO, and 45% H2O/45% CO2/10% H2. A comparison between the performance and microstructure of the studied electrode formulation is provided. Electrolyte-supported cells were manufactured via screen-printing of the electrode inks on scandia-stabilized zirconia (ScSZ) electrolytes. STF perovskite-based electrodes were used, namely: SrTi0.3Fe0.7O3 (STF), Sr0.95(Ti0.3Fe0.63Ni0.07)O3 (STF-Ni), and Sr0.95(Ti0.3Fe0.63Ru0.07)O3 (STF-Ru). The latter two formulations allowed the enhancement of the perovskite structure via exsolution of catalytic nanoparticles (Ni, Co alloyed with Fe) on the oxide surface during cell operation. Each cell configuration included a gadolinium-doped ceria (GDC) buffer layer coupled with an LSCF-GDC (La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O1.95) oxygen electrode. Baseline performances of cell mounting the Ni-YSZ cermet electrode were also evaluated for comparison with the perovskite alternatives, both in the short and long term. Electrochemical characterization was done via impedance spectroscopy, polarization experiments, and durability tests in potentiostatic mode. Chemical characterization was performed via X-ray diffraction, scanning electron microscopy, and temperature-programmed reduction analyses. Compared to Ni-YSZ, significant improvement in terms of reversibility and maximum current densities of the current-voltage (I/V) curves in both SOFC and SOEC modes is found on the STF-based cells at 750°C under CO/CO2 mixtures (Figure 1B). The initial difference in the performance of the STF cells with respect to the Ni-YSZ cermet in humidified H2 (SOFC mode, Figure 1A) was overcome by using the exsolved electrode formulations. Aging experiments up to 100 h performed in alternating operation modes from SOFC (6 h) to SOEC (6 h) indicated an initial performance degradation within the first 24 h for both the cermet and perovskite-based fuel electrodes which later stabilized in time. Compared to the undoped STF formulation, improvement in performance stability was observed for the exsolved STF-Ni and STF-Ru fuel electrodes while working under the target CO/CO2 mixture. This was attributed to the combination of the STF structure benefits (low polarization resistance towards CO/CO2 and H2O/CO2 mixtures) with the boost that metallic nanoparticles provide to the electrode’s heterogeneous catalytic reactivity and overall stability over time. References [1] C. Graves, S. D. Ebbesen, M. Mogensen, Solid State Ionics. 192 (2011) 398–403. [2] Y. Zheng et.al., Chemical Society Reviews. 46 (2017) 1427–1463. [3] T. Zhu, H. E. Troiani, L. V. Mogni, M. Han, S. A. Barnett, Joule. 2 (2018) 478–496. Figure 1 Comparison of polarization curves from STF fuel electrode vs. SoA Ni-YSZ (A): Operation in SOFC mode under 3% humidified H2 (B): Operation in rSOC mode under CO/CO2 mixture Figure 1
22
Kamboj, Vipin, Soham Raychowdury, and Chinmoy Ranjan. "Mechanistic Studies on CO2 Electroreduction on Ni{M}x-YSZ and Ce{M}Ox-YSZ." ECS Meeting Abstracts MA2023-01, no. 40 (August 28, 2023): 2757. http://dx.doi.org/10.1149/ma2023-01402757mtgabs.
Abstract:
The conversion of CO2 to fuels via electroreduction can be instrumental in reducing dependence on fossil fuels and contributes to the global targets of CO2 reduction. The electrochemical reduction of CO2 to hydrocarbons, however, is kinetically limited by the fact that it is a multi-step process, with each step requiring the transfer of multiple electrons. On the other hand, the high temperature electrochemical reduction of CO2 to CO using a solid oxide electrolysis cell (SOEC) provides a route that is both energy efficient and cost effective. The CO thus produced can act as a value added product, as it can be directly used as a fuel, or it can be reduced into hydrocarbons via the well-known Fischer-Tropsch process. Ni/YSZ based electrodes are fairly ubiquitous in the field of solid oxide technologies. We have proposed the infiltration of Cu into Ni/YSZ to generate Ni{Cu}x-YSZ type cathodes, which exhibit improved performance for CO2 electroreduction at high temperature (~800 oC). The electrodes are prepared on commercial standard YSZ supports using Ni{Cu}x-YSZ mixtures for cathode and LSM-YSZ mixture for anode. Most of the existing studies on high temperature reduction of CO2 on Ni/YSZ have been in the presence of safe gases, such as H2 or CO. The presence of H2 in the inlet stream created a reducing atmosphere on the electrode surface, and the reduction of CO2 proceeded through a thermochemical reverse water gas shift (RWGS) mechanism. (CO2 + H2 à CO + H2O). The presence of CO could lead to catalyst deactivation by Carbon deposition through Boudouard reaction (2CO à CO2 + C). Observations from such experiments led to the belief that metallic Ni in Ni/YSZ acts as the active species for CO2 reduction; and that the oxidation of the Ni to NiO leads to deactivation of the catalyst. By using operando Raman spectroscopy and online mass spectrometry, we have countered this idea and demonstrated that the electroreduction of CO2 on Ni-YSZ is mediated by a layer of NiOx on the electrode surface, which is the actual active species. CeOx is a well-known cathodic material for pure CO2 electroreduction. We have attempted to study the mechanistic aspects associated with CO2 electroreduction on Ce{M}Ox based systems as well. Figure 1
23
Vibhu, Vaibhav, Izaak Vinke, Rudiger-A. Eichel, and L. G. J. (Bert) de Haart. "Performance and Electrochemical Behavior of LSM Based Fuel Electrode Materials Under High Temperature Electrolysis Conditions." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 213. http://dx.doi.org/10.1149/ma2023-0154213mtgabs.
Abstract:
High-temperature solid oxide electrolysis cells (SOECs) have gained considerable attention due to more favourable thermodynamic and electrochemical kinetic conditions over low-temperature electrolysis. The SOECs can be used for the production of hydrogen from steam electrolysis, syngas (H2 + CO) from co-electrolysis, and carbon mono-oxide from pure CO2 electrolysis. Despite several advantages, the long-term durability of SOECs is still an issue. The long-term durability of SOEC depends on the stability of electrodes as well as on the operational conditions, for example current load, temperature, and fuel gas composition. The conventional cermet-based fuel electrode i.e. Ni-YSZ shows good initial performance, however, it experiences severe degradation during long-term due to Ni- agglomeration and migration away from the electrolyte. Therefore, searching for new electrode materials is crucial in order to enhance the overall performance and durability of SOECs. In this work, we have considered Lanthanum strontium manganite-based perovskite oxides as fuel electrodes i.e. La0.6Sr0.4MnO3 (LSM). LSM is very stable chemically under oxidizing atmosphere, however, it undergoes phase transformation into a Ruddlesden-Popper (La0.6Sr0.4)2MnO4±δ phase under reducing atmosphere. We have first prepared the electrolyte-supported single cells using 8YSZ electrolyte and LSM+YSZ/LSM oxygen electrodes. The single cells were then electrochemically characterized using AC- and DC-techniques under steam electrolysis, co-electrolysis, and CO2-electrolysis conditions in 800-900 °C temperature range. Moreover, the electrochemical behaviour of LSM+GDC (50:50) and LSM+YSZ (50:50) composite electrodes containing single cells were also investigated. The LSM and LSM+GDC fuel electrode containing single cells show good electrochemical performance in all three electrolysis modes. However, lower performance is observed for LSM+YSZ fuel electrode containing single cell. For example, a current density of 997, 1025, and 511 mA.cm-2 at 1.5 V, are obtained for LSM, LSM+GDC, and LSM+YSZ fuel electrode containing single cells respectively, with 50% N2 and 50% H2O feed gas mixture at 900 °C. Furthermore, the impedance spectra were also recorded for all these cells under OCV and polarization conditions, and fitted with an equivalent circuit model using an inductor, a series resistance and 4 R//CPE elements. The impedance spectra vary significantly with the gas compositions. The detailed electrochemical results will be presented and discussed in detail.
24
Klitkou, Morten Phan, Albert Lopez de Moragas, Julian Taubmann, Peyman Khajavi, Stéven Pirou, Henrik Lund Frandsen, and Peter Vang Hendriksen. "Development of Fuel Electrode Supported Solid Oxide Cell with Ni/CGO Active Layer." ECS Transactions 111, no. 6 (May 19, 2023): 1407–13. http://dx.doi.org/10.1149/11106.1407ecst.
Abstract:
A half-cell comprising of a Ni/3YSZ support, a Ni/CGO10 active fuel electrode, a thin ScYSZ electrolyte and a CGO10 barrier layer was realized through tape casting, lamination and co-sintering. After screen printing of air electrode and contact layer, the cell was electrochemically tested using EIS at open circuit voltage. At 750°C in 50/50 H2O/H2 ohmic resistance (Rs) was encouraging at 0.18 Ω.cm2. Polarization resistance (Rp) was however significantly larger than state of the art (SoA) cells at 0.45 Ω.cm2. From electrochemical analysis the causes for the large Rp are hypothesized to be poor air electrode performance and low fuel electrode performance. This transaction paper includes a description of ongoing activities to improve the electrochemical performance of this cell concept to approach or surpass SoA fuel electrode supported solid oxide cells (FE-SOC) relying on Ni/YSZ electrodes.
25
Li, Qiangqiang, Dingxi Xue, Chongyang Feng, Xiongwen Zhang, and Guojun Li. "Fracture Simulation of Ni–YSZ Anode Microstructures of Solid Oxide Fuel Cells Using Phase Field Method." Journal of The Electrochemical Society 169, no. 7 (July 1, 2022): 073507. http://dx.doi.org/10.1149/1945-7111/ac7c3f.
Abstract:
The performance degradation of solid oxide fuel cells (SOFC) is directly related to the damage and fracture of electrode microstructures. In this study, the phase field fracture method is used to simulate the fracture of anode microstructures, and the effects of boundary constraints, thermal load, and Ni phase on the fracture of Ni–YSZ anode microstructures are investigated. Results show that tensile stresses occur in the Ni and YSZ phases whether above or below the reference temperature. The cracks propagate along the direction perpendicular to the first principal stress, showing a brittle fracture characteristic. When the microstructure is cooled, all cracks appear in YSZ phase, and almost all cracks initiate at the lowest point of YSZ–pore concave interface. When the microstructure is heated, the tensile first principal stress induces few cracks at local positions but will not make the cracks propagate continuously. The thermal mismatch between Ni and YSZ is not enough to induce cracks, and the fracture of electrode microstructure is more likely to be caused by external tensile load or the thermal mismatch between anode and electrolyte layers. The presence of Ni increases the stiffness of the microstructure, and solid phase’s disconnection reduces the strength of the microstructure.
26
Diaz Lacharme, Maria Carmenza, and Alessandro Donazzi. "Characterization and Testing of Exsolution-Based Solid Oxide Cells for Reversible Operations in CO2 Electrolysis." ECS Transactions 111, no. 6 (May 19, 2023): 1867–76. http://dx.doi.org/10.1149/11106.1867ecst.
Abstract:
Reversible solid oxide cells (rSOCs) are promising electrochemical devices, able to work both in energy storage mode as solid oxide electrolyzes (SOECs), and in power generation mode as solid oxide fuel cells (SOFCs). rSOCs dedicated to high-temperature co-electrolysis of CO2/H2O mixtures are of interest since they could foster the utilization and consequent reduction of CO2 gas emissions while converting it and H2O into valuable fuels (i.e. syngas and H2). However, operation under CO2-rich feeds requires alternatives to the state-of-the-art Ni-Yttria-stabilized-zirconia (Ni-YSZ) cermet fuel electrode in view of its low coking and redox resistance. Perovskites with mixed ionic and electronic conductivity are major alternatives, especially when the functionality of their active surface is enhanced via metal nanoparticle exsolution. This work focuses on the investigation of the electrocatalytic properties of the SrTi0.3Fe0.7O3 (STF), and exsolution Sr0.95(Ti0.3Fe0.63Ni0.07)O3 (STF-Ni) perovskite-based fuel electrodes together with Ni-YSZ while operating with CO2-rich mixtures both in the short and long term.
27
Barnett, Scott A., Qian Zhang, Jerren Grimes, Dalton Cox, Junsung Hong, Beom-Kyeong Park, Tianrang Yang, and Peter W. Voorhees. "(Keynote) Degradation Processes in Solid Oxide Cell Ni-YSZ Electrodes." ECS Meeting Abstracts MA2022-01, no. 38 (July 7, 2022): 1669. http://dx.doi.org/10.1149/ma2022-01381669mtgabs.
Abstract:
Solid oxide cells (SOCs) can have a significant impact on climate change over the next decade and beyond, in applications such as balancing renewable grid electricity via electrolytic fuel production, and producing electricity from bio-fuels combined with CO2 product sequestration. However, long-term performance degradation remains a key variable that may limit further implementation of SOCs. This talk focuses on the Ni-YSZ fuel electrode that is widely used but is known to be an important contributor to SOC degradation. Various processes that cause Ni-YSZ degradation are discussed. Results on 3D tomography measurements of accelerated Ni coarsening are described and a quantitative model is developed to predict long-term degradation. Although the results indicate that coarsening effects can be minimized in well-designed Ni-YSZ microstructures, degradation can still occur, especially during high-current-density electrolysis operation. For operation under low H2O/H2 conditions, high electrolysis current density can yield reduction of zirconia to form Ni-Zr compounds, along with substantial microstructural damage. For operation under high H2O/H2conditions, high electrolysis current density can yield Ni migration away from the electrolyte. A phase-field simulation is described that predicts this Ni migration, using actual Ni-YSZ microstructures measured using 3D tomography as the starting point, and compared with experimental observations. The model assumes that Ni transport is driven by a spatial gradient in surface tensions, i.e., a decrease in the Ni/YSZ contact angle with increasing distance from the electrolyte. Recent results on electrolysis and reversibly operated SOCs, making use of Ceria-infiltrated Ni-YSZ to improve stability, are described.
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Ozaki, Ryota, Kei Yamada, Kazutaka Ikegawa, Tsutomu Kawabata, Chie Uryu, Yuya Tachikawa, Junko Matsuda, and Kazunari Sasaki. "A Study on Electrochemical Properties of Fuel-Electrode-Supported Reversible Solid Oxide Cells." ECS Transactions 112, no. 5 (September 29, 2023): 141–47. http://dx.doi.org/10.1149/11205.0141ecst.
Abstract:
Reversible solid oxide cells (r-SOCs) enable both fuel cell power generation and steam-electrolysis hydrogen production by changing the direction of the current in the cells. They are attractive electrochemical devices because of their ability to regulate power supply derived from renewable energy sources. In this study, initial performance was evaluated, and an electrolyte-supported cell and fuel-electrode-supported cells were compared and evaluated with changing operating temperatures. The performances for fuel-electrode-supported cells with various combinations of fuel electrode and electrolyte materials were also evaluated. In addition, the Ni-YSZ/YSZ fuel-electrode-supported cell, which exhibited the highest current-voltage characteristics, was subjected to r-SOC cycling tests to evaluate the cycle durability.
29
Heenan, Thomas M. M., Antonis Vamvakeros, Chun Tan, Donal P. Finegan, Sohrab R. Daemi, Simon D. M. Jacques, Andrew M. Beale, Marco Di Michiel, Dan J. L. Brett, and Paul R. Shearing. "The Detection of Monoclinic Zirconia and Non-Uniform 3D Crystallographic Strain in a Re-Oxidized Ni-YSZ Solid Oxide Fuel Cell Anode." Crystals 10, no. 10 (October 16, 2020): 941. http://dx.doi.org/10.3390/cryst10100941.
Abstract:
The solid oxide fuel cell (SOFC) anode is often composed of nickel (Ni) and yttria-stabilized zirconia (YSZ). The yttria is added in small quantities (e.g., 8 mol %) to maintain the crystallographic structure throughout the operating temperatures (e.g., room-temperature to >800 °C). The YSZ skeleton provides a constraining structural support that inhibits degradation mechanisms such as Ni agglomeration and thermal expansion miss-match between the anode and electrolyte layers. Within this structure, the Ni is deposited in the oxide form and then reduced during start-up; however, exposure to oxygen (e.g., during gasket failure) readily re-oxidizes the Ni back to NiO, impeding electrochemical performance and introducing complex structural stresses. In this work, we correlate lab-based X-ray computed tomography using zone plate focusing optics, with X-ray synchrotron diffraction computed tomography to explore the crystal structure of a partially re-oxidized Ni/NiO-YSZ electrode. These state-of-the-art techniques expose several novel findings: non-isotropic YSZ lattice distributions; the presence of monoclinic zirconia around the oxidation boundary; and metallic strain complications in the presence of variable yttria content. This work provides evidence that the reduction–oxidation processes may destabilize the YSZ structure, producing monoclinic zirconia and microscopic YSZ strain, which has implications upon the electrode’s mechanical integrity and thus lifetime of the SOFC.
30
Yu, Miao, Xiaofeng Tong, Karen Brodersen, and Ming Chen. "Electrochemical Performance and Durability of a Solid Oxide Cell with Nanoparticles-Modified Electrodes for CO2 Electrolysis." ECS Transactions 111, no. 6 (May 19, 2023): 1389–99. http://dx.doi.org/10.1149/11106.1389ecst.
Abstract:
Solid oxide electrolysis cell (SOEC) is one of the most effective technologies for converting carbon dioxide to carbon monoxide using renewable energy sources. This work investigated the electrochemical performance and long-term durability of a Ni/yttria-stabilized zirconia (YSZ)-supported planar-type SOEC cell (CGO@Ni/YSZ|YSZ|CGO|LSC/CGPO@CGO) infiltrated with nano-catalysts for CO2 electrolysis. The Ni/YSZ fuel electrode was infiltrated with Ce0.8Gd0.2O2−δ (CGO) solution, and the porous CGO scaffold was co-infiltrated with La0.6Sr0.4CoO3-δ (LSC) and Gd, Pr co-doped CeO2 (CGPO) nano-sized electrocatalysts. The cells were operated at 800 °C and -1 A/cm2 for 1548 h with a mixture of 24 L/h CO2/CO (83/17) supplied to the fuel electrode and pure O2 to the oxygen electrode. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) analysis were conducted. During the entire durability testing period, the cell voltage increased from 1246 mV to 1400 mV with a degradation rate of 99.1 mV/kh (7.95%/kh). Following the recovery after an unexpected power outage, the cell demonstrated an activation process over ⁓110 h, with a voltage decrease from 1337 mV to 1263.9 mV. Furthermore, the cell showed a much lower degradation of ohmic resistance R s (7.14 mΩ cm2/kh) compared to that of polarization resistance R p (129.05 mΩ cm2/kh). DRT reveals that the degradation originates from both electrodes. The present study reveals that it is crucial to carefully select the appropriate electrocatalyst candidate considering the specific operating conditions.
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Cox, Dalton, and Scott A. Barnett. "Microstructural Changes in Ni-YSZ Electrodes Operated in Fuel Cell and Electrolysis Modes: Effect of Gas Diffusion Limitations." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 295. http://dx.doi.org/10.1149/ma2023-0154295mtgabs.
Abstract:
Lifetime performance stability is a key issue for the commercialization of solid oxide cells. Ni migration in Ni-YSZ electrode supported cells is an important degradation mechanism. Here we present the results of life tests on symmetric Ni-YSZ electrode-supported cells. These symmetric cells have similar processing and microstructure as conventional Ni-YSZ-supported cells, but the symmetric structure provides information on the Ni-YSZ electrode operating as both an anode and a cathode in the same test. Life tests of up to 1000 h were carried out at 800 ˚C in 50-50 H2-H2O at current densities of 0, 0.75, 1.00, and 1.50 A/cm2. Total applied voltage to each cell was tracked over the lifetime, and small portions of the cells were removed during the life tests to study the time-dependent changes in microstructure. Figure 1 summarizes the microstructural results from a Ni-YSZ cell operated at 1.0 A/cm2, observed at 100, 500, and 1000 h. 2D and 3D microstructure characterization was used to show the volume fractions of pore and active (electrically connected) Ni versus position. Somewhat surprisingly, the cathode microstructure remains relatively unchanged compared to a non-polarized cell, with no evidence of Ni migration or isolation. In contrast, Ni migration and isolation was observed to increase with time at the anode in polarized cells, with the thickness of the Ni deactivated region growing from ~5 mm at 500 h to ~15 mm at 1000 h for 1.0 A/cm2 and ~2 μm at 500 h and ~8 μm at 1000 h for 0.75 A/cm2. In addition, total cleavage at the anode-electrolyte interface occurs at 1.5 A/cm2 by 100 h, and at 1.0 A/cm2 by 1000 hr. The increase of porosity in the altered zones clearly shows where Ni is depleted. There is no evidence of Ni enrichment adjacent to the depleted region, as might be expected if Ni was moving via surface diffusion. Although there have been numerous recent reports of Ni migration/isolation in Ni-YSZ cathodes during electrolysis cell operation1, Ni migration has also been reported in Ni-YSZ fuel cell anodes2,3. Here we suggest that such results can be explained by a relatively high steam content in the Ni-YSZ anode functional layer. Conversely, the lack of Ni migration in the electrolysis cathode can be explained by a relatively low steam content in the cathode functional layer. To quantitatively assess the gas compositions, one-dimensional modeling of the electrochemical and gas diffusion processes of these cells was performed using a finite difference method (FDM) with modified Butler-Volmer kinetics and the dusty-gas model respectively. Using diffusivity values calculated via electrochemical impedance spectroscopy and microstructural measurements, the modeling reveals that electrochemically active Ni sees significantly different gas composition than the inlet, creating steam-rich anodes (PH2O = 0.73, 0.8, and 0.95 atm for 0.75, 1.0 and 1.5 A/cm2 respectively) and steam-depleted cathodes (PH2O = 0.27, 0.2, and 0.05 atm for 0.75, 1.0 and 1.5 A/cm2 respectively). This is in accord with results and models suggesting that Ni migration is important mainly under high steam conditions, probably due to vapor transport. Note that these effects are exacerbated by the relatively low porosity and small pore size in the present electrodes that lead to asymmetric Knudsen diffusion, wherein H2O diffuses at ~1/3 the rate of H2. These results suggest that the nature of the porosity in Ni-YSZ supports can lead to significant variations in the extent and directionality of Ni migration. Figure 1: (a, b, c) Polished cross sectional backscatter electron (BSE) images and (d,e,f) low voltage secondary electron (LV-SE) images of an electrode-supported symmetric Ni-YSZ cell at 100, 500, and 1000 h of galvanostatic operation at 1.00 A/cm2 in 50-50 H2-H2O and T = 800 ˚C. BSE images reveal a depletion of total Ni at the anode-electrolyte interface (AEI) by a net increase in porosity, and eventual cleavage at that line. LV-SE images reveal that near total deactivation of Ni occurs near the AEI as well. (g,h,i) Quantitative image analysis reveals the extent of porosity increase (via Ni depletion) and Ni deactivation at 100, 500, and 1000 hours. The regimes for both events exactly overlap, with the depletion/deactivation extending 0, 5, and 15 μm from the AEI, respectively. M. B. Mogensen et al., Fuel Cells, 21, 415–429 (2021). J. Geng et al., J. Power Sources, 495, 229792 (2021). Z. Jiao and N. Shikazono, J. Power Sources, 396, 119–123 (2018). Figure 1
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Ozaki, Ryota, Kei Yamada, Kazutaka Ikegawa, Tsutomu Kawabata, Chie Uryu, Yuya Tachikawa, Junko Matsuda, and Kazunari Sasaki. "A Study on Electrochemical Properties of Fuel-Electrode-Supported Reversible Solid Oxide Cells." ECS Meeting Abstracts MA2023-02, no. 46 (December 22, 2023): 2259. http://dx.doi.org/10.1149/ma2023-02462259mtgabs.
Abstract:
Introduction Reversible solid oxide cells (r-SOCs) enable both power generation and steam electrolysis, and have attracted attention as a solid state electrochemical energy device for a decarbonized society (1). R-SOCs have the advantage of high efficiency due to high temperature operation, but there exist various technical issues remained in materials selection, start-up and shutdown, and long-term durability. Therefore, reducing operating temperature is desirable for practical applications (2,3). Electrode-supported cells, in which the electrode acts as a structural support, enable lower temperature operation by reducing the thickness of the electrolyte, which has certain electrical resistivity. Here in this study, the current-voltage characteristics and reversible cycle durability under r-SOC operating conditions are evaluated using fuel-electrode-supported cells, with the aim of developing r-SOCs capable of highly efficient fuel cell power generation and steam electrolysis. Experimental For the experiments, fuel-electrode-supported cells were fabricated using fuel electrode-supported half-cells (Japan Fine Ceramics, Japan), schematically shown in Fig. 1. The half-cell consists of scandia-stabilized zirconia (ScSZ: 10 mol%Sc2O3-1mol%CeO2-89 mol%ZrO2) or yttria-stabilized zirconia (YSZ: 8 mol%Y2O3-92 mol%ZrO2) electrolyte and a Ni-cermet fuel electrode, such as Ni-ScSZ or Ni-YSZ. (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) was applied for the air electrode, and Gd0.1Ce0.9O2 (GDC) was inserted between the electrolyte and the air electrode to suppress interdiffusion and chemical reactions. Four types of cells were used with different combinations of the electrolyte component (YSZ or ScSZ) in the electrolyte layer or the supporting fuel electrode. In electrochemical tests, 50%-humidified hydrogen (100 ml min-1) was supplied to the fuel electrode, and air (150 ml min-1) was supplied to the air electrode. R-SOC initial performance tests were conducted using an electrochemical analyzer (1255B, Solartron). Cell voltage and impedance were measured at 700-800°C at current densities ranging from -0.5 A cm-2 to +0.5 A cm-2. Positive current density means the value in SOFC mode, while negative current density means the value in SOEC mode. In r-SOC 1,000 cycle durability tests, cycles of switching between SOFC and SOEC operation were repeated 1,000 times by varying current density. The range of current density in the cycle tests was between -0.2 A cm-2 and +0.2 A cm-2. The cell impedance was measured before the cycling test and every 100 cycles. After each test, the cells were analyzed by using a focused-ion beam scanning electron microscopy (FIB-SEM) to observe and evaluate the electrode microstructure. Results and discussion Figure 2 (a) shows the r-SOC initial performance of each fuel-electrode-supported cell. The cell with the Ni-YSZ fuel electrode and the YSZ electrolyte showed better current voltage characteristics than other cells. Figure 2 (b) shows the r-SOC 1000-cycle durability of the cell with the Ni-YSZ fuel electrode and the YSZ electrolyte. The results showed a decrease in power generation and electrolysis performance with increasing the number of cycles in both SOFC and SOEC modes. Possible degradation mechanisms will be discussed. Acknowledgments This paper is based on results obtained from a project (Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration), JPNP20005, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Collaborative support by Prof. H. L. Tuller and Prof. B. Yildiz at Massachusetts Institute of Technology (MIT) is gratefully acknowledged. References (1) Venkataraman, M. Pérez-Fortes, L. Wang, Y. S. Hajimolana, C. Boigues-Muñoz, A. Agostini, S. J. Mcphail, F. Mar échal, J. V. Herle, and P. V. Aravind, J. Energy Storage, 24, 100782 (2019). (2) Subotić, S. Pofahl, V. Lawlor, N. H. Menzler, T. Thaller, and C. Hochenauer, Energy Proc., 158, 2329 (2019). (3) B. Mogensen, Current Opinion Electrochem., 21, 265 (2020). Figure 1
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Wang, Shu, Peter Vang Hendriksen, and Bhaskar Reddy Sudireddy. "Ni and Fe Doped (La,Sr)TiO3 Fuel Electrodes for Solid Oxide Cells – Electrical and Electrochemical Properties." ECS Meeting Abstracts MA2023-02, no. 46 (December 22, 2023): 2214. http://dx.doi.org/10.1149/ma2023-02462214mtgabs.
Abstract:
Development of robust and impurity tolerant solid oxide cells (SOCs) has attracted a significant R&D-effort in recent years. The shortcomings of Ni-YSZ fuel electrodes in terms of redox stability, carbon and sulfur tolerance and long-term durability under strong polarization has spurred the search for alternative fuel electrode materials. Among them, doped strontium titanate materials has shown promising performance due to their good electrical transport properties, chemical and redox stability and tolerance towards impurities. In the present study, the electrical properties of the La0.477Sr0.33Ni0.03Fe0.03Ti0.94O3- δ (LSFNT) material, which is designed with the potential for exsoluting Ni and Fe nanoparticles, is investigated in detail. In addition, the performance of LSFNT based fuel electrodes is characterized in a symmetrical cell configuration. The electrical conductivity measurements are performed on both dense and porous LSFNT layers, as a function of temperature and pO2. The pre-reduced (1100oC, 24 hours, dry 5%H2/N2) dense LSFNT sample showed an electrical conductivity of ca. 10 S/cm at 850 oC in dry 5%H2/N2. The “in-situ reduced” (850oC, 700 hours) porous LSFNT layer showed a conductivity 10 times smaller. The conductivity was tracked as a function of pO2 showing an approximate pO2 -1/6 dependence. Also the ionic conductivity of the material was determined using an electron blocking method. At 850oC at a pO2 of 10-20 bar the ionic conductivity is ca. 0.05 S/cm at which is similar to that of Y2O3 doped ZrO2 electrolytes demonstrating that LSFNT is indeed a very good mixed ion- and electron-conducting material. Motivated by the observed conductivities SOC fuel electrodes of LSFNT were prepared by incorporating Gd-doped CeO2 electrocatalyst into LSFNT porous backbones and their electrochemical performance was measured in 50% H2 / 50% H2O at OCV. An electrode polarization resistance of 0.05 Ω cm2 at 850oC and 0.26 Ω cm2 at 650 oC is measured for these electrodes. The polarization resistance at 850 oC is comparable to that of Ni-YSZ fuel electrodes; while at 650oC it is significantly lower in similar atmospheres. This promising electrochemical performance shows the potential of the LSFNT fuel electrodes, as an alternative to Ni-YSZ fuel electrodes, in solid oxide cell applications.
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Kamboj, Vipin, and Chinmoy Ranjan. "Operando Studies on High-Temperature CO2 Electrolysis to Fuels." ECS Meeting Abstracts MA2022-01, no. 36 (July 7, 2022): 1603. http://dx.doi.org/10.1149/ma2022-01361603mtgabs.
Abstract:
High temperature CO2 electroreduction of one of the most promising technologies for converting CO2 to fuels. Electroreduction can typically result in various reduced products but interms of energy efficiency a electrolytic reduction to CO followed by Fischer Tropsch (along with H2) based conversion to hydrocarbon fuels is most preferred. Nickel-Yttria Stabilized Zirconia cermet (Ni/YSZ) is one of the most common electrodes used in solid oxide fuel cells. Lately, various groups have essentially repurposed the same electrode for CO2 electrolysis. However, it suffers from catalyst degradation and poor activity. Successful operation of these electrodes requires presence of H2 in the CO2 stream. In presence of hydrogen CO2 undergoes reverere water gas shift reaction leading to production of CO (non electrochemically) in combination with electrochemical water splitting. Using operando Raman and online Mass Spectroscopy we have followed the evolution of catalyst from preatreatment in various atmospheres to its performance under conditions of operation. The mentioned electrodes were operated at current densities between 100-400 mA/cm2. The operando studies show that Ni active sites oxidize to NiOx in the presence of pure CO2. The poor electronic conductivity of NiO adversely affects the activity of the electrode. The failure is rather drastic at higher current densities. Apart from this, mass spectroscopy confirmed the formation of coke during CO2 electrolysis through Bouduard reaction. The absence of any Raman signal for carbon indicated that the reaction only proceeds to a small extent and the primary deactivation occurs through oxidation of Ni. Small amounts of H2 (~5%) in the mixture prevented the deactivation, but the reaction seemed to proceed through Reverse Water Gas Shift reaction followed by Water electrolysis. Furthermore, we have explored the performance of Ni(Mx)/YSZ type cathodes for CO2 reduction. The electrode performances were compared using three electrode configuration based measurements. Our results indicate that catalysts development in situ is drastically different for mixed metal oxides often resulting in different type of spatial distribution of the metals compared to the pure Ni/YSZ. Many electrodes show promising behavior in terms of both enhanced activity and catalyst stability. Figure 1
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Yashiro, Keiji, Kota Watanabe, Riyan Achmad Budiman, Masami Sato, Mayu Muramatsu, and Tatsuya Kawada. "Analysis of Interfacial Capacitance of Ni-YSZ Anode By Transient Simulation." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 128. http://dx.doi.org/10.1149/ma2023-0154128mtgabs.
Abstract:
An electrochemical impedance and equivalent circuit analysis are frequently used for electrochemical evaluation of SOFC cells. The impedance analysis enables to obtain the resistance and the capacitance components of the electrode reaction. The electrode resistance is directly related to the cell performance. The electrode capacitance can be sometimes give information about the active electrode reaction site. As to Ni-YSZ electrode, we've tried to elucidate the physical meaning of the capacitance [1]. However, it is not easy to clarify the physical origin of the electrode capacitance. Thus, the capacitance has not been used to evaluate the active reaction zone so far. In this study, the capacitance of Ni-YSZ interface will be simulated by calculating the chemical capacitance derived from YSZ. Then, the origin of the capacitance will be discussed through comparison with the previous studies [1]. The structural model to simulate the Ni-YSZ model cell [1] are shown in Fig. 1., which shows simplified model according to symmetry of the cell. In order to limit the electrochemical reaction zone (triple phase boundary), a virtual reaction zone was introduced. Cell conditions for the calculation are following: temperature: 765ºC; oxygen partial pressure of the air electrode: 0.21 bar;hydrogen partial pressure: 1.00 bar, and water vapor partial pressure: 0.03 bar for fuel electrode. Transient simulation was performed to obtain the chemical capacitance by an in-house code, SIMUDEL, where mixed ionic electronic conduction and oxygen nonstoichiometry were taken into consideration [2,3] using the reported conductivity data of YSZ [4]. The measured capacitance of the model cell [1] was 5×10-4 Fcm-2. On the other hand, the calculated chemical capacitance of YSZ was 2×10-3 Fcm-2. Even though the oxygen nonstoichiometry of YSZ was small, calculated chemical capacitance was much larger than the observed interfacial capacitance. These difference implies there was unknown factors to promote the response of electron in the actual Ni-YSZ interface. If a thin resistive layer was inserted between Ni and YSZ interface, the calculated chemical capacitance became smaller than that of observed. Sasaki et al. observed an incoherent interface between Ni and YSZ by TEM [5]. This kind of interface structure may be the potential cause of the complicated capacitance. This study was partially supported by NEDO, Japan. [1] M. Takeda, et. al., submitted to J. Electrochem. Soc. [2] K. Terada, et. al., ECS Trans. 35(1), 923 (2011). [3] M. Sato, et. al., Trans. Jpn. Soc. Comp. Eng. Sci. 2017, 14 (2017). [4] J.H. Park, et. al., J. Am. Ceram.Soc.,72[8],1485-87(1989). [5] T. Sasaki, et. al., Mater. Trans. 45(7), 2137 (2004). Fig. 1 Schematic diagrams of the structural model to simulate the chemical capacitance of Ni-YSZ. Figure 1
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Lee, Myongjin, Yun Gan, Chunyang Yang, Chunlei Ren, and Xingjian Xue. "Fabrication and Characterization of Thin-Film SOFC Supported by Microchannel-Structured Zirconia Substrate for Direct Methane Operation." International Journal of Petroleum Technology 8 (October 12, 2021): 80–92. http://dx.doi.org/10.15377/2409-787x.2021.08.6.
Abstract:
Ni-cermet anode demonstrates excellent catalytic activity and electrical conductivity but suffers from carbon deposition issue. To utilize Ni-cermet anode while preventing carbon deposition, a synergic strategy is employed to design anode electrode. In particular, Zr is incorporated into Ce0.8Sm0.2O2-δ lattice to tailor oxygen storage and catalytic properties of Ni-Ce0.8-xSm0.2ZrxO2-δ anode for improving electrochemical oxidizations of various fuel species. An inert thick YSZ microtubular substrate with radially well-aligned microchannels open at the inner surface is used to support multi thin functional layers of solid oxide cell, i.e., Ni current collector, Ni-Ce0.8-xSm0.2ZrxO2-δ anode, YSZ/SDC electrolyte, and LSCF cathode. The thick YSZ substrate is able to inhibit the ratio of fuel to product gases in the thin anode functional layer, which favors the prevention of carbon buildup in the thin anode layer when synergistically combined with Ni-Ce0.8-xSm0.2ZrxO2-δ anode material. The microchannels embedded in the YSZ substrate can also avoid too much dilutions of the fuel in the anode functional layer. The cell is fabricated and tested with both hydrogen and methane as the fuel. A short-term test is conducted with methane as fuel and good stability is obtained. The fundamental mechanisms for the prevention of carbon buildup in anode functional layer are also discussed.
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Williams, Nicholas J., Robert Leah, Subhasish Mukerjee, Debbie Zhuang, Martin Z. Bazant, and Stephen J. Skinner. "Multiphase Porous Electrode Theory for the Next Generation of SOFC/SOEC Electrodes." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 59. http://dx.doi.org/10.1149/ma2023-015459mtgabs.
Abstract:
The mixed-ionic electronic conduction (MIEC) of gadolinium doped ceria (CGO) under reduced oxygen conditions makes it an excellent fuel electrode material for SOFC/SOEC applications. As part of a composite electrode (Ni/CGO), the nickel phase offers a fast electronic conduction pathway to the current collector and may act as an electrocatalyst at the three-phase boundary. Although the Ni/CGO cermet provides superior electrochemical performance compared with older technologies such as Ni/YSZ, the models used to study MIEC materials do not capture the unique transport and kinetic physics which makes them an excellent choice for the next generation of fuel electrodes. Within the framework of multiphase porous electrode theory, this work provides a novel set of differential-algebraic equations which captures the effects of the activation overpotential on electronic defect concentration, electrostatic surface potential and ionic transport to accurately predict the current-voltage behaviour of the Ni/CGO electrode. Moreover, through concerted electron and proton tunnelling events, we unify the theory of the electrostatic surface potential with proton-coupled electron transfer kinetics.
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Muto, Seina, Ryuji Uno, and Hirotatsu Watanabe. "Carbon Deposition Mechanisms on Ni-Based Anode for SOFC: A Comparison Between Non-Discharge and Discharge Modes." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 62. http://dx.doi.org/10.1149/ma2023-015462mtgabs.
Abstract:
The nickel/yttria-stabilized zirconia (Ni/YSZ) and nickel/scandia-stabilized zirconia (Ni/ScSZ) have widely used as an anode for solid fuel cells (SOFCs). When hydrocarbon gas is supplied to the Ni-based fuel electrode of SOFCs, carbon is deposited on the anode, and it causes anode destruction. Therefore, carbon deposition control is required. The purpose of this study is to clarify carbon deposition mechanisms to understand how the carbon resistance appears on the Ni-based electrode in non-discharge and discharge modes. NiO/8XSZ powder with a binder was uniaxially pressed to form 0.7mm thick pellet (Ni : XSZ=50:50 vol%, X(dopant)=Y, Sc) which were subsequently sintered. After a reduction in H2 atmosphere, Ni/8XSZ sintered cells were heated in CH4/Ar (S/C ratio (Steam to Carbon) =0, CH4/Ar=0.25) and CH4/H2O/Ar atmosphere (S/C ratio=0.15, CH4/Ar=0.25) using a thermobalance, and the carbon deposition rates were measured from the weight change of the cell at 1173 K and 973 K. In this experiment, the S/C ratio was adjusted by bubbling CH4/Ar gas to set the saturated water vapor pressure at a given temperature. In addition, a power generation experiment of SOFC was conducted at 1073 K to investigate the effect of electrochemical reactions on the carbon deposition. The SOFC cells were prepared as follows. YSZ suspension was spin-coated on the NiO/8YSZ substrate. The electrolyte/electrode bilayer was co-sintered at 1673K. Then, a paste of LSM/YSZ was coated on electrolyte and sintered at 1473K. The cell was sealed to the alumina tube in the electric furnace. The anode side was fed with CH4/Ar/H2O (S/C ratio = 0.15) and the cathode side was exposed to O2. Current density was set to 126mA/cm2 for 30 min. After discharge, the anode surface was observed using SEM/EDS. As a result, the carbon deposition rate of Ni/ScSZ was lower than that of Ni/YSZ by 34 % at 1173 K and S/C=0 under non-discharge mode. This result indicated that the Ni/ScSZ exhibited superior carbon deposition tolerance than the Ni/YSZ at 1173 K. Steam reforming reaction was also different between the Ni/YSZ and Ni/ScSZ. Previous studies showed that carbon deposition tended to progress easily at the metal/solid electrolyte interface. The difference in carbon deposition behavior between Ni/YSZ and Ni/ScSZ was caused by the difference in the interface structure. On the other hand, the carbon deposition rate of Ni/ScSZ was higher than that of Ni/YSZ at 973 K which was opposite to that at 1173 K. Moreover, the rate of carbon reforming reaction (C+H2O→CO+H2) of Ni/YSZ was higher than that of Ni/ScSZ. In fact, the Ni/YSZ anode showed superior carbon tolerance than the Ni/ScSZ at lower temperature. XRD (X-ray Diffraction) analysis showed that the ScSZ with cubic structure was partially changed to the rhombohedral structure after the carbon deposition at high temperature while YSZ cubic structure was unchanged. This implied that the rhombohedral structure at the interface inhibited the carbon deposition reaction, suggesting that the electrolyte structure influenced the carbon deposition and steam reforming reactions. Therefore, it was shown that the electrolyte structure can control the carbon deposition while the same Ni was used. These findings give an useful hint to design the carbon tolerance electrode. Meanwhile, carbon deposition was not found on the Ni/YSZ surface after discharge at 1073 K. This indicated O2- ion improved the carbon tolerance during discharge. Comparison of carbon deposition between Ni/YSZ and Ni/ScSZ will be discussed using DFT (Density Functional Calculation).
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Sun, Yanhua, Christabel Adjah-Tetteh, Yudong Wang, Zhiyong Jia, Xingwen Yu, and Xiao-Dong Zhou. "Achieving High-Efficiency CO2 Electro-Conversion in a Solid Oxide Cell." ECS Meeting Abstracts MA2022-02, no. 49 (October 9, 2022): 1939. http://dx.doi.org/10.1149/ma2022-02491939mtgabs.
Abstract:
Carbon dioxide (CO2) emissions have been steadily increasing since the beginning of human civilization. The greenhouse effect and climate change aroused by the cumulative CO2 are severely impacting the global sustainable development and pose serious concerns for our future life. Strategies toward reducing the CO2 level encompass a series of processes of carbon capture, storage, utilization, and conversion; among them the conversion of CO2 to fuels and valuable chemicals is appealing toward the development of new sustainable technologies. As the highest oxidized form of carbon, CO2 is thermodynamically stable. The breaking of its strong C=O double bonds is an endergonic process, which requires highly active and expensive catalysts for activation at ambient temperatures. Therefore, conversion of CO2 with high-temperature electrolysis technologies represents a promising strategy, which is garnering increasing attention. In this study, we present a solid oxide electrolysis cell (SOECs) design for high-efficiency CO2 conversion. The fuel electrode in an SOEC is a critical component where CO2 reduction occurs. Therefore, we focus on the design and optimization of the fuel electrode from the perspectives of chemistry (composition) and architecture (especially the thickness) to enhance the efficiency of CO2 electrolysis. A Ni-based cermet layer was developed as an ideal CO2/CO fuel electrode, based on which the cell architecture was strategically optimized with prototype Ni-YSZ/YSZ/GDC/LSCF cells (YSZ: yttria-stabilized zirconia; GDC: gadolinium-doped ceria; LSCF: lanthanum strontium cobalt ferrite). Over the course of optimization, the Ni-YSZ cermet fuel electrode was methodologically fabricated with various thickness and the cells were operated at contracting temperatures. Meanwhile, the fuel was managed with different ratios of CO2 to CO and the O2 was supplied with different flow rates at the opposite electrode. At an exemplarily optimized condition, a high electrolysis current of 1.33 A cm-2 was achieved at 750 oC with a fuel comprising of 99% CO2 and 1% CO. To assist the cell optimization, electrochemical impedance spectroscopy (EIS) was particularly used to investigate the electrochemical properties of SOECs. Meanwhile, cell components were analyzed with scanning electron microscope (SEM) before and after the electrolysis operation to study the degradation behavior of SOECs that were operated under high-current electrolysis. The detailed cell design and experimental results will be comprehensively demonstrated and presented.
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Thieu, Cam-Anh, Jongsup Hong, Hyoungchul Kim, Kyung Joong Yoon, Jong-Ho Lee, Byung-Kook Kim, and Ji-Won Son. "Incorporation of a Pd catalyst at the fuel electrode of a thin-film-based solid oxide cell by multi-layer deposition and its impact on low-temperature co-electrolysis." Journal of Materials Chemistry A 5, no. 16 (2017): 7433–44. http://dx.doi.org/10.1039/c7ta00499k.
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Park, Beom-Kyeong, Roberto Scipioni, Dalton Cox, and Scott A. Barnett. "Enhancement of Ni–(Y2O3)0.08(ZrO2)0.92 fuel electrode performance by infiltration of Ce0.8Gd0.2O2−δ nanoparticles." Journal of Materials Chemistry A 8, no. 7 (2020): 4099–106. http://dx.doi.org/10.1039/c9ta12316d.
Abstract:
GDC nanoparticles reduce the reaction resistance associated with three-phase boundaries and improve oxygen transport in the Ni–YSZ electrode, as measured by electrochemical impedance spectroscopy under actual solid oxide cell operating conditions.
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Kim, Taeyoung, Hyong June Kim, Dohyun GO, Jeong woo Shin, Byung Chan Yang, Ji-Won Son, and Jihwan An. "(Invited) Gradient Ni-SDC Anode By Reactive Co-Sputtering for Low Temperature Solid Oxide Fuel Cells." ECS Meeting Abstracts MA2022-02, no. 47 (October 9, 2022): 1742. http://dx.doi.org/10.1149/ma2022-02471742mtgabs.
Abstract:
Solid oxide fuel cells (SOFCs) are attracting attention as next-generation energy conversion devices due to their high efficiency, eco-friendliness, and scalability. However, the high operation temperature of conventional SOFCs (> 800°C) has posed several practical issues such as thermal degradation and limited material choice. To overcome this limitation, low-temperature SOFC (LT-SOFC, operation temperature <600°C) is actively being researched these days. Ni-YSZ (nickel-yttria stabilized zirconia) is commonly used as anode material in SOFCs. Ni-YSZ anodes are reasonably conductive at high operating temperatures and stable under harsh reducing conditions. However, at lower operating temperatures, the low conductivity of Ni-YSZ becomes an issue for use as an anode. Using doped ceria instead of YSZ is considered an alternative because the doped ceria has higher conductivity compared to YSZ due to the co-existence of multivalent states, i.e., Ce3+ and Ce4+, which can be further improved by doping. Moreover, if one adopts a carefully designed anode structure, e.g., gradient structure, the electrochemical performance of Ni-doped ceria anode can be further improved. Employing nanoscale components, e.g., thin films, are also one of the strategies to improve the electrode kinetics at the low operating temperature of LT-SOFCs. Thin film electrodes with short electronic and ionic paths as well as high surface area contribute to low ohmic and activation resistances. While high uniformity, reproducibility and throughout are practical concerns in thin film fabrication, reactive sputtering, which can produce uniform ceramic thin films from metal target in reactive gas environment in high reproducibility ad deposition rate, is a suitable candidate for thin film components for SOFCs. In this study, we fabricate a Ni-Samaria doped ceria(SDC) gradient anode by reactive co-sputtering. We prepare and characterize the cells with homogeneous and gradient-structured Ni-SDC thin film anodes. The gradient Ni-SDC thin film anode is composed of three layers, whose compositions are graded in a way that the Ni content increases from bottom (near electrolyte-anode interface) to top (anode top-surface). Possibly due to the combination of facilitated ionic conduction near electrolyte-anode interface and higher catalytic activity at anode surface, we observe the improved anode kinetics with lower activation resistance in the cell with gradient-structured Ni-SDC anode compared to the one with homogeneous anode.
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Yang, Meiting, Changjiang Yang, Mingzhuang Liang, Guangming Yang, Ran Ran, Wei Zhou, and Zongping Shao. "Solid Oxide Cells with Phase-Inversion Tape-Casted Hydrogen Electrode and SrSc0.175Nb0.025Co0.8O3−δ Oxygen Electrode for High-Performance Reversible Power Generation and Hydrogen Production." Molecules 27, no. 23 (December 1, 2022): 8396. http://dx.doi.org/10.3390/molecules27238396.
Abstract:
Solid oxide cells (SOCs) have been considered as a promising energy conversion and storage device. However, state-of-the-art cells’ practical application with conventionally fabricated Ni-(Y2O3)0.08(ZrO2)0.92 (YSZ) cermet hydrogen electrode and La0.8Sr0.2MnO3 perovskite oxygen electrode is strongly limited by the unsatisfactory performance. Instead, new advances in cell materials and fabrication techniques that can lead to significant performance enhancements are urgently demanded. Here, we report a high-performance reversible SOC that consisted of a combination of SrSc0.175Nb0.025Co0.8O3−δ (SSNC) and phase-inversion tape-casted Ni-YSZ, which served as the oxygen and hydrogen electrode, respectively. The hydrogen electrode synthesized from phase-inversion tape-casting showed a high porosity of 60.8%, providing sufficient active sites for hydrogen oxidation in the solid oxide fuel cell (SOFC) mode and H2O electrolysis in the solid oxide electrolysis cell (SOEC) mode. Accordingly, it was observed that the maximum power density of 2.3 W cm−2 was attained at 750 °C in SOFC mode and a current density of −1.59 A cm−2 was obtained at 1.3 V in SOEC mode. Hence, these results reveal that the simultaneous optimization of oxygen and hydrogen electrodes is a pragmatic strategy that improves the performance of SOCs, which may significantly accelerate the commercialization of such an attractive technology.
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Christensen, Jens Ole, Gino Longo, Holger Bausinger, Andreas Mai, Bhaskar Reddy Sudireddy, and Anke Hagen. "Long-Term Sulfur Tolerance of Solid Oxide Fuel Cells with Alternative Titanate-Based Fuel Electrodes." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 40. http://dx.doi.org/10.1149/ma2023-015440mtgabs.
Abstract:
The future renewable energy system relies on devices capable of energy conversion and storage. Solid oxide fuel cells (SOFCs) convert the chemical energy of a fuel into electricity and heat with high electrical efficiency. The fuel flexibility of SOFCs allows for the use of not only hydrogen, but also C-containing fuels, including biogas and green fuels from power-to-X. Such fuels contain trace amounts of sulfur, either being present from the original source or added for safety reasons as odorant, which causes loss of performance in state-of-the-art (SoA) SOCFs with Ni-based cermet fuel electrodes, due to sulfur adsorption on the Ni. An upstream desulfurization unit mitigates this problem in commercial SOFC-systems, increasing CAPEX and system complexity. Hence, alternative S-tolerant fuel electrode materials are highly desirable. All-ceramic doped strontium titanates perovskite compounds (ABO3) are interesting candidates due to their high electronic conductivity and chemical stability. Among these, La0.4Sr0.4Fe0.03Ni0.03Ti0.94O3 (LSFNT), is particularly interesting, due to its B-site exsolution of electrocatalytically active Fe and Ni nanoparticles under reducing conditions. However, the electrochemical activity from the exsoluted catalyst is not sufficient and integration of additional electrocatalyst by infiltration ensures electrochemical performance comparable to SoA. In this study, the electrochemical performance and sulfur tolerance of three different, electrolyte supported cells are examined: Cell 1 contains a standard Ni/CGO cermet fuel electrode, Cell 2 contains a LSFNT electrode backbone with Ni:CGO electrocatalyst and Cell 3 contains LSFNT electrode backbone with Fe-Ni:CGO electrocatalyst.. Fe is added to the Ni:CGO to investigate if alloy formation on the nanoscale can improve the sulfur tolerance. All the cells contain LSM-YSZ oxygen electrodes. The cells were integrated in a short, 5-cell stack and tested at HEXIS AG. The fuel was a natural gas directly supplied from the grid, pre-reformed in a catalytic partial oxidation (CPOx) unit, where a desulfurization unit was connected or by-passed for determining the sulfur tolerance. The electrochemical performance was investigated for each cell in the stack individually by iV-curves and electrochemical impedance spectroscopy (EIS) with and without the use of an upstream desulfurization unit. This was followed by a durability test for ca. 400 hours with sulfur exposure. While the initial performances with short term exposure to sulfur indicate reversible degradation on both types of infiltrated LSFNT fuel electrodes, Cell 1 with the Ni/CGO cermet fuel electrode experiences loss of performance related to an increase in the Ohmic resistance. Cell 1 together with Cell 2 (LSFNT infiltrated with Ni:CGO) are both stable over several hundred hours of operation in sulfur, whereas accelerated degradation of cell voltage is observed on Cell 3 where Fe is present in the infiltrate. Details on electrochemical behavior during the durability test and origins of degradation will be presented together with a microstructural analysis. Figure 1
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Padinjarethil, Aiswarya Krishnakumar, Fiammetta Rita Bianchi, Barbara Bosio, and Anke Hagen. "Degradation of Ni-YSZ and Ni-GDC fuel cells after 1000 h operation: Analysis of different overpotential contributions according to electrochemical and microstructural characterization." E3S Web of Conferences 334 (2022): 04011. http://dx.doi.org/10.1051/e3sconf/202233404011.
Abstract:
Solid Oxide Fuel Cell (SOFC) technologies are emerging as potential power generation units with limited environmental impacts. However, the main challenges towards large scale commercial applications are high costs and low lifetime compared to currently used technologies. The present study aims at understanding degradation mechanisms in SOFCs through both experimental and modelling approaches. For this purpose, two state of the art fuel cell configurations based on Ni cermet fuel electrode (either YSZ-Yttrium Stabilised Zirconia or GDC-Gadolinium Doped Ceria), YSZ electrolyte and LSCF (Lanthanum Strontium Cobalt Ferrite oxide) air electrode were chosen. The cells were tested for 1000 hours with H2 rich mixture as fuel feed and air as oxidant. Cells were characterised at several H2/H2O ratios and temperatures with air or oxygen fed to the air electrode using different techniques. These allowed the identification of kinetic parameters to be implemented in an in-house 2D Fortran based model. The model was able to successfully simulate global cell behaviour as a function of local features, and it was validated with experimental I-V curves recorded prior and post durability operation. Moreover, post-mortem microstructure characterisation was also performed to fine-tune the model towards a more accurate prediction of the degradation influence on cell performance.
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Esau, Daniel, Cedric Grosselindemann, Soeren Peter Sckuhr, Felix Kullmann, Lena Wissmeier, and Andre Weber. "Characterization of a Nickel / Gadolinia Doped Ceria Fuel Electrode for Co-Electrolysis." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 137. http://dx.doi.org/10.1149/ma2023-0154137mtgabs.
Abstract:
Modelling of the high temperature co-electrolysis process requires understanding of the underlying reaction pathways. These include the electrochemical steam reduction, the electrochemical CO2 reduction and their coupling via the catalytic (reverse-)water-gas-shift reaction (RWGS). The assumption of a very fast water-gas-shift reaction and therefore neglectable CO electro-oxidation is widely used. The validity of this assumption has been previously investigated and proven to be sufficient by Kromp et al. [1] for an anode supported cell (ASC) with a nickel / yttria-stabilized zirconia (Ni/YSZ) fuel electrode. Within this contribution we aim to extend the approach by Kromp et al. [1] towards an electrolyte-supported cell (ESC) with a nickel / gadolinium-doped ceria (Ni/CGO) fuel electrode. Previously, it has been proposed, that the electro-oxidation /-reduction of CO / CO2 can be present under reformate gas mixtures [2,3] on Ni/CGO fuel electrodes. However, a detailed comparison of pure activation resistance contributions during different operating modes has not been performed yet. We present results from a complex variation of operating parameters (such as various gas compositions, exemplarily shown in fig. 1) for process identification by the use of electrochemical impedance spectroscopy and the subsequent impedance analysis by the distribution of relaxation times (DRT). Visualization and deconvolution of gas diffusion impedance contributions is done via the evaluation of the polarization resistance differences with different inert gases. This has been successfully applied for binary gas mixtures of hydrogen and steam [4] and also CO2 and CO. [5] The applicability of this method towards more complex multicomponent gas mixtures incorporating hydrogen, steam, CO2 and CO will be shown. By subtracting the gas diffusion impedance contributions, it is possible to evaluate reaction kinetics of the underlying activation polarization and a meaningful comparison of operation modes is facilitated. The ratio of direct CO2electro-reduction and CO2-conversion by RWGS will be discussed for different compositions and temperatures to show a non-neglectable influence of the CO2 electroreduction at even lower pCO2 / pH2 ratios than previously reported. Furthermore, we compare our results with ones obtained from Ni/YSZ fuel electrodes, to investigate the influence of fuel electrode structure and material. References: [1] A. Kromp et al., J. Electrochem. Soc., 158 (8) B980-B986 (2011). [2] M. Riegraf et al., ACS Catal. 7 , 7760-7771 (2017). [3] E. Ioannidou et al., J.Catal. 404, 174-186 (2021). [4] C. Grosselindemann et al., J. Electrochem. Soc., 168, 124506 (2021). [5] C. Grosselindemann et al., Proceedings of the 15th EFCF, July 5th-8th (2022). Figure 1: Electrochemical impedance spectra recorded at open circuit and T = 860 °C of a symmetrical Ni/CGO fuel electrode under atmospheres of H2, H2O, CO and CO2 with varying CO/CO2-content. Gas mixtures have been applied in equilibrium compositions determined by the (reverse-)water-gas-shift reaction. Figure 1
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Zhang, Qian, Dalton Cox, Clarita Yosune Regalado Vera, Hanping Ding, Wei Tang, Sicen Du, Alexander F. Chadwick, et al. "Interface Problems in Solid Oxide Electrolysis Cells." ECS Meeting Abstracts MA2022-02, no. 47 (October 9, 2022): 2425. http://dx.doi.org/10.1149/ma2022-02472425mtgabs.
Abstract:
In this talk, I introduce topics, that I have been working on, in solid oxide electrolysis cells involving complicated interfacial structures and dynamics of interfaces. Then I will focus on my recent work on nickel (Ni) particle migration in electrodes consisting of Ni, yttria-stabilized zirconia (YSZ), and pores during the operation of oxygen-ion conducting solid oxide electrolysis cells (o-SOECs) and Faraday efficiency in proton-conducting solid oxide electrolysis cells (p-SOECs) under electrolysis operations. SOECs can have a significant impact on climate change over the next decade and beyond, in applications such as balancing renewable grid electricity via electrolytic fuel production. However, long-term performance degradation remains a key issue that may limit further implementation of O-SOECs, and the dependency of operation conditions on Faraday efficiency in P-SOECs has been under debate. In particular, in Ni/YSZ/pore electrode of O-SOEC, a phase-field model is proposed that employs the Ni-YSZ 3D microstructure as the initial condition and large-scale numerical simulation is implemented that predicts the directional Ni migration. The results are thus directly comparable to experimental observations. Quantitative predictions of the evolution of the Ni/YSZ/pore system's microstructures due to Ni particles' migration are studied through theoretical analysis and data analysis. In P-SOECs, an electrochemical model is proposed to study the dependency of Faraday efficiency on operation conditions for P-SOECs with yttrium-doped barium zirconates (BZY) and co-doping barium zirconate-cerate oxides with ytterbium and yttrium (BCZYYb) as electrolytes respectively. Our numerical predictions are verified by experimental results obtained in INL. An optimal structure of electrolyte is proposed to boost the Faraday efficiency in P-SOECs.
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Wolf, Stephanie E., Vaibhav Vibhu, Carla L. Coll, Niklas Eyckeler, Izaak C. Vinke, Rudiger-A. Eichel, and L. G. J. (Bert) de Haart. "Long-Term Stability of Perovskite-Based Fuel Electrode Material Sr2Fe2-XMoxO6-δ – GDC for Enhanced High-Temperature Steam and CO2 Electrolysis." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 329. http://dx.doi.org/10.1149/ma2023-0154329mtgabs.
Abstract:
Solid oxide electrolysis cells (SOECs) have proven to be a highly efficient key technology to produce valuable gases (H2, CO). SOECs utilize renewably generated electricity at temperatures between 600 - 900 °C, thereby providing a carbon-neutral method for energy storage. However, the successful industrial implementation of this technology requires long-term stability of all system components and is mainly delayed by the degradation of the electrodes over time. The state-of-the-art Ni-YSZ fuel electrode has been extensively studied and exhibits severe performance loss due to Ni particle agglomeration and Ni migration away from the active sites at the electrolyte/electrode interface under real operating conditions [1]. To mitigate this issue, we have investigated the Ni-free perovskite Sr2Fe2-xMoxO6-δ + 30% GDC as fuel electrode material. As mixed ionic and electronic (MIEC) perovskite structured oxides, these materials have shown excellent short-term redox stability in oxidizing and reducing atmospheres in addition to high conductivity and outstanding coking resistance [2]. These characteristics meet exactly the targeted requirements for new solid oxide electrolyzer materials. We have compared the long-term degradation of an SFM fuel electrode to an electrode made of SFM-GDC (Figure 1). The degradation was less severe for the mixed electrode of SFM-GDC. Impedance and post-test SEM-EDX analysis clarified the main degradation mechanisms of SFM as well as SFM-GDC in steam and CO2 electrolysis. The tested button cells showed demixing of the SFM phase and particle aggomeration in the fuel electrode. [1] S. E. Wolf, V. Vibhu, E. Tröster, I. C. Vinke, R.-A. Eichel and L. G. J. de Haart, Energies, 15(15), 5449 (2022). [2] L. Bernadet, C. Moncasi, M. Torrell and A. Tarancón, Int. J. Hydrog. Energy, 45(28), 14208–14217 (2020). Figure 1
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Wehner, Luzie, Christian Lenser, Krzysztof Dzieciol, Egbert Wessel, Jürgen Malzbender, and Ruth Schwaiger. "Three-Dimensional Microstructural Analysis for the Characterization of Failure Mechanisms of a Novel SOEC." ECS Transactions 111, no. 6 (May 19, 2023): 231–39. http://dx.doi.org/10.1149/11106.0231ecst.
Abstract:
A novel fuel electrode-supported electrolysis cell has been developed as promising candidate for hydrogen production at intermediate temperatures. It contains a Ni-GDC electrode functional layer, a three-layer GDC-YSZ-GDC electrolyte and an LSC air electrode. Although this cell enables improved performance compared to state-of-the-art YSZ electrolyte-based cells, especially at lower operation temperatures, 700 °C and below, and electrolysis currents around 1.2-1.7 A cm-2 a voltage drop and subsequently crack formation in the electrolyte was observed in initial studies. In the current work, FIB/SEM and X-ray computed tomography are used for microstructural investigations. Based on calculated microstructural parameters the suitability of the methods for an assessment of the failure mechanisms are discussed.
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Nagatomo, Yohei, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, and Kazunari Sasaki. "Distribution of Relaxation Times of Fuel Electrodes for Reversible Solid Oxide Cells Fabricated Under Various Conditions." ECS Meeting Abstracts MA2023-02, no. 46 (December 22, 2023): 2257. http://dx.doi.org/10.1149/ma2023-02462257mtgabs.
Abstract:
Introduction Reversible solid oxide cells (r-SOCs) are electrochemical energy devices that can switch reversibly between power generation as a solid oxide fuel cell (SOFC) and hydrogen production as a solid oxide electrolysis cell (SOEC). It is important to systematically understand the electrode reaction processes and degradation factors in these two modes to tailor high-performance and durable r-SOC electrodes. The dependence of polarization resistance on cell fabrication conditions and operating conditions has been individually investigated for SOFC and SOEC by impedance measurement and distribution of relaxation times (DRT) analysis [1-4], but it is necessary to evaluate r-SOC as a whole [5]. Here in this study, we aim to systematically clarify the similarities and differences in the electrode reaction processes at the fuel electrodes of both SOFC and SOEC modes of r-SOCs, with respect to fuel electrode fabrication conditions. Experimental Several types of cells were fabricated with different fuel electrode constituent materials, thicknesses, and sintering temperatures. Three types of fuel electrode materials were used: Ni-GDC cermet, a composite of Ni and mixed ionic-electronic conductor Gd0.9Ce0.1O3 (GDC); Ni-YSZ cermet, a composite of Ni and pure ionic conductor YSZ (8 mol% Y2O3 - stabilized ZrO2); and Ni-GDC co-impregnated electrode with LST-GDC as a backbone support (LST: La0.1Sr0.9TiO3). Scandia-stabilized zirconia (ScSZ) was used as the electrolyte plate, and (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) was used as the air electrode. GDC buffer layer was prepared between the electrolyte and the air electrode to suppress the formation of interfacial insulting layers. Electrochemical impedance measurements were performed for the fuel electrode of the fabricated cell under SOFC and SOEC modes by supplying H2-H2O mixture and varying operating temperature, fuel humidification, and current density. The DRT analysis was conducted to separate various polarization resistance components of the fuel electrode with different relaxation times. The area of each DRT peak corresponds to the resistance of each electrode reaction process. In this study, activation energy was derived based on the assumption that the electrical conductance is of an Arrhenius-type thermally activated character. Its dependence on the fuel electrode fabrication conditions was investigated. Furthermore, electrode microstructure was observed by using focused-ion beam scanning electron microscopy (FIB-SEM). Results and Discussion Figure 1 shows typical DRT peaks of the Ni-GDC cermet fuel electrode in (a) SOFC and (b) SOEC modes, measured at different temperatures. In the range of 10-1 to 106 Hz where the frequency response was measured, three DRT peaks appeared, P1: 10-1 to 100 Hz, P2: 100 to 102 Hz, and P3: 102 to 103 Hz, all with a DRT peak area decreasing with increasing operating temperature. This indicates that there are at least three electrode reaction processes with different relaxation times, which are thermally active processes. Activation energies of 0.1-0.3 eV (SOFC mode) and 0.2-0.5 eV (SOEC mode) were obtained for P1, and 0.9-1.0 eV (SOFC mode) and 1.1-1.3 eV (SOEC mode) for P2. The activation energies in SOEC mode were higher than those in SOFC mode for both P1 and P2. In the presentation, the dependence of activation energies on the fuel electrode constituent materials and related electrode reaction processes will be discussed. References [1] A. Leonide, V. Sonn, A. Weber, and E. Ivers-Tiffée, J. Electrochem. Soc., 155, B36 (2007). [2] C. Graves, S. D. Ebbesen, and M. Mogensen, Solid State Ionics, 192, 398 (2011). [3] H. Sumi, T. Yamaguchi, K. Hamamoto, T. Suzuki, Y. Fujishiro, T. Matsui, and K. Eguchi, Electrochim. Acta, 67, 159 (2012). [4] N. Endo, T. Fukumoto, Y. Tachikawa, S. M. Lyth, J. Matsuda, and K. Sasaki, ECS Trans., 109 (11), 3 (2022). [5] V. Subotić, B. Königshofer, Ð. Juričić, M. Kusnezoff, H. Schröttner, C. Hochenauer, and P. Boškoski, Energy Convers. Manag., 226, 113509 (2020). Acknowledgment This paper is based on results obtained from a project (Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration), JPNP20005, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Collaborative support by Prof. H. L. Tuller and Prof. B. Yildiz at Massachusetts Institute of Technology (MIT) is gratefully acknowledged. Figure 1