bluuebunny/crossref_metadata_2025_split huggingface dataset:
Efficiency Optimization of SOFC Subject to Degradation and Minimum Power Constraint
Authors: Li Hangyue , Han Minfang 
Published: September 2023

Solid Oxide Fuel Cell (SOFC) is a developing energy conversion technology featuring high efficiency, power density, durability, and fuel compatibility. With these advantages, SOFCs are combined frequently with heat engines such as gas turbines, for higher system efficiency and power density.
In practice, SOFCs are often required to deliver certain power. Considering economical aspects, power generation efficiency is critical to the running cost of energy conversion systems. However, high power and high efficiency are likely reached under different operating conditions. For example, to meet peak power demands, higher operating currents and fuel flowrates are necessary, while SOFCs are generally more energy efficient at lower current densities and fuel flowrates. Hence, the ideal operating condition is the solution to a power-constrained efficiency optimization problem. Moreover, SOFCs degrade as they operate, introducing gradual changes to SOFC characteristics. Thus, the optimization needs to be solved dynamically.
To analyze the above-mentioned problem, a 10 cm by 10 cm planar SOFC was repeatedly tested for polarization characterizations and electrochemical impedance spectra. A 2-dimentional multi-physics model was developed and calibrated using both polarization and impedance data. To account for the lower open circuit voltage at lower fuel flowrates, an equivalent leakage current is included in the model. The model was thereafter employed for efficiency optimization given power constraints. At each required power output, the optimal fuel flowrate and the corresponding voltage, current, and efficiency was calculated. The electrical efficiency peaks globally at around 0.1 Standard Liter per Minute (SLM) hydrogen flowrate, while at higher power, the optimal efficiency is reached at fuel utilizations between 65% and 90%. Accounting for degradation in terms of growing ohmic resistance and decreasing electrode exchange current densities, the optimal efficiency is reached at lowering fuel utilization and lowering voltage, which may result in local oxidization of the anode.
Moreover, an easy and straight-forward way was proposed to estimate the optimal fuel flowrate given polarization data. Further studies involving the safety constraints will be carried out in the future.

Figure 1
Mechanistic Details of CO2 Electroreduction on Ni and Ni{Cu}-YSZ Electrodes Using Operando Spectroscopy
Authors: Ranjan Chinmoy 
Published: September 2023

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
Modeling Delamination of Electrodes of Solid Oxide Electrolyzers with Fuel Electrode as a Support
Authors: Kupecki Jakub , Niemczyk Anna , Jagielski Stanisław 
Published: September 2023

Solid oxide electrolyzers (SOE) are the most efficient yet not fully mature devices for electrochemical production of hydrogen. These devices offer a great advantage in applications which make it possible to utilize process heat or steam to feed SOE for direct conversion of steam instead of water. However, the technology is prone to a degradation, as it combines advanced materials, requires dedicated fabrication techniques and it operates at elevated temperature, typically above 650ºC. One of the biggest challenges is the mitigation of degradation of solid oxide electrolyzers due to the delamination of the electrode. Several measures can be proposed to limit the process, however full elimination of this type of degradation is not yet possible. The good understanding of the mechanisms and consecutive steps which lead to deterioration of the interface between the electrolyte and air electrode of SOE is based on thorough experimental studies supported by the numerical modeling.
In the study we present a delamination model, which can be used to identify the safe operating envelope of SOEs with a given structure and material composition. The mechanisms behind degradation through delamination are discussed with respect to the chemical and electrochemical potentials. This is complement by the discussion of criteria for the formation and propagation of cracks, taking into account the oxygen potential at the electrolyte-electrode interface. Moreover, the microstructural modifications of the electrodes, e.g. increase of its porosity, are discussed as one of the potential measures to substantially reduce the risk of delamination under design point and off-design operation of SOEs. The methodology of manipulating the porosity of the electrode by varying the content and type of pore forming agents was proposed in order to adjust the parameters of electrodes to the required microstructure. Results of the experimental characterization of cells fabricated in such a way are presented, and the guidelines for fine-tuning the microstructure are discussed with respect to the degradation mechanisms.
Tracking Localized Degradation of Solid Oxide Cells Via Multi-Physics Modelling of Impedance Spectroscopy
Authors: Taubmann Julian , Sun Xiufu , Chatzichristodoulou Christodoulos , Frandsen Henrik Lund 
Published: September 2023

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

Reference

[1] Sun, X., et al. "Degradation in solid oxide electrolysis cells during long term testing." Fuel Cells 19.6 (2019): 740-747.

Figure 1
Theoretical Prediction of the Vapor Pressure of Solid Oxide Fuel Cell Components
Authors: Hu Yang , Wang Kai , Spatschek Robert , Müller Michael , Wessel Egbert 
Published: September 2023

Due to the high operation temperature solid oxide fuel cells, various chemical reactions can lead to degradation, e.g. based on Cr2O3 gas phase evaporation from the interconnect and subsequent reaction with SrO which originates from LSCF cathodes. Therefore, investigations of the potential chemical reactions and the sublimation process play an extremely important role to study the related chemical reactions in SOFCs.
Here we propose a practical physical model based on density functional theory calculations and statistical mechanics, which is used to predict the vapor pressure of pure substances, which allows to extend thermodynamic database and to analyse the resulting chemical reactions inducing the new phase formation which leads to the degradation of SOFCs. These investigations serve as theoretical basis to understand and reduce degradation phenomena from a thermodynamic and kinetic perspective.
Perovskite-Based Materials As Alternative Fuel Electrodes for Solid Oxide Electrolysis Cells (SOECs)
Authors: Winterhalder Franziska Elisabeth , Alizad Farzin Yousef , Guillon Olivier , Weber Andre , Menzler Norbert H. 
Published: September 2023

Enhancing the lifetime of SOECs is a challenge to overcome regarding their commercialization. A major impact on the lifetime of a cell during electrolysis operation, particularly under thermoneutral potential and high current densities, is the degradation of the currently used electrode materials, mainly the Ni-based fuel electrode. Among other things, nickel migration, as well as agglomeration, is leading to a significant performance loss after a certain operating time. Hence, preventing degradation mechanisms of the fuel electrode during operation is a necessity to be tackled for using it commercially. Therefore the development of alternative materials which combine sufficient performance with the lowest possible degradation rate is needed. Perovskite-based materials have been investigated in the last years as all-ceramic possible substitutes.
In this work, four perovskites (i.e., strontium-iron-niobate double perovskite (SFN), a strontium-iron-titanate material (STF), a lanthanum-strontium-titanate (LST) and a lanthanum-strontium-iron-manganese (LSFM)) were examined as alternative electrode materials. The aim is to substitute the active fuel electrode, at the moment commonly consisting of Ni cermets, with a perovskite-based electrode while at the same time using state-of-the-art materials for the remaining cell components.
The first task here was to look at the chemical stability between the new electrode material and the electrolyte under the standard conditions used to manufacture fuel electrode-supported SOECs.
Therefore, the compatibility between these perovskites with a yttria-stabilized-zirconia (8YSZ) electrolyte and how nickel inside the fuel electrode affected the chemical stability during sintering in air at 1400 °C for 5 h was investigated. At this point, SFN double perovskite shows the lowest interaction between the electrode and electrolyte after thermal treatment.
A thorough evaluation of all preliminary tests (including compatibility, stability in reducing atmospheres and redox stability tests) indicates that SFN shows so far the best results of the four materials in terms of application as fuel electrode material, followed directly by STF.
Thus SFN and STF were chosen to be evaluated in single cell tests. The tests of pure SFN and STF electrodes are carried out with electrolyte-supported single cells exhibiting an LSCF air electrode and symmetrical cells, respectively. CV-characteristics and impedance spectra are measured at varied operating conditions. Impedance spectra are evaluated by the distribution of relaxation times (DRT). These examinations are carried out to give an insight into the electrochemical properties of pure perovskite-based fuel electrodes in order to obtain a base for further optimization.
High-Performance Solid Oxide Electrochemical Cells with Ultrathin and Dense Double-Doped Ceria Interlayers
Authors: Yu Hyeongmin , Im Ha-Ni , Lee Kang Taek 
Published: September 2023

To mitigate the drastic global climate change, which mainly originated from the indiscriminate use of fossil fuels, various alternative eco-friendly energy conversion technologies have been studied. Among them, solid oxide electrochemical cells (SOCs) are one of the most promising devices with superior power and energy densities and low environmental impact. The current main objective of the SOCs research field is lowering the operating temperature to secure thermal cycling stability and minimize system costs. To achieve a feasible performance for commercial usage at reduced temperatures, it is inevitable to use state-of-the-art cobalt-based oxygen electrode materials. However, cobalt-based materials inherently react with conventional zirconia-based electrolytes at high temperatures forming insulating phases at the interface. Thus, the ceria interlayer is essentially required to prevent unwanted chemical reactions.
In this study, we newly developed thin and dense doubly doped ceria interlayers (~250 nm) using a non-vacuum solution deposition process with gelatin. The SOCs with the thin-film ceria interlayers achieved superior electrochemical performance both in the fuel cell (FC) and the electrolysis cell (EC) mode (~3.5W/cm2 and ~2.1A/cm2 at 750°C for the FC and EC modes, respectively) compared to the SOC with a conventional porous and thick interlayer. The mechanistic analyses showed that the thin-film interlayer provides a much shorter route for oxygen ionic conduction and more active sites for oxygen reduction reaction (ORR) and oxygen evolution reaction (ORR) at the interface compared to the porous interlayer. Our results suggest that the thin-film doubly-doped ceria interlayer fabricated using the gelatin-assisted process has a high potential for development of high-performance SOCs.
Role of Dopants in Fine-Tuning the Electrical and Catalytic Properties of Barium Niobate Perovskites Towards High-Temperature Electrolyzer Application
Authors: Ramaiyan Kannan , Denoyer Luke H , Benavidez Angelica , Garzon Fernando H. 
Published: September 2023

Perovskite materials are being studied for high temperature electrochemical applications such as solid oxide fuel cells (SOFC) and electrolyzers due to their tunable conductivity and catalytic activity. However, high temperature operation poses significant challenges in both fabrication and durable operation that is further complicated by the operating environment.1 We studied barium niobates with various dopants such as Fe, Ni, Ca, Y, and Mg for B site doping while Sr, K, and La are studied for A site doping. These niobates showed enhanced chemical stability in SOFC relevant conditions and catalytic activity towards methane activation. Nb4+/5+ redox couple seem to be a key reason behind this chemical stability while the size and electronegativity of the dopants affect the electrical properties.2 Catalyst exsolution is explored with dopants such as Fe, Ni, and Co under reducing conditions along with surface bound metallic nanoparticles prepared by an incipient wet synthesis method. Chemical stability of these perovskites was analyzed by an in situ TGA measurements under various gas environments followed by analysis of the powders using PXRD, XPS, SEM, and TEM methodologies.3 Methane activation properties are further analyzed in a temperature programmed reaction setup while Electrochemical properties were evaluated in a home-made setup using different electrolyte materials in the temperature range of 700°C to 900°C. Cyclic voltammetry, impedance spectroscopy, and chronoamperometry measurements coupled with continuous mass spectra analysis was utilized to diagnose any correlation between product distribution and applied potential. Our results demonstrate doped barium niobates as a promising candidate for stable operation in high temperature electrochemical applications. The presentation will discuss these results and provide a correlation between dopants and catalytic activity and chemical stability of doped barium niobate perovskites.

References

(1) Ramaiyan, K. P.; Denoyer, L. H.; Benavidez, A.; Garzon, F. H. Selective Electrochemical Oxidative Coupling of Methane Mediated by Sr2Fe1.5Mo0.5O6-δ and Its Chemical Stability. Commun. Chem.
2021, 4 (1), 139. https://doi.org/10.1038/s42004-021-00568-1.
(2) Denoyer, L. H.; Benavidez, A.; Garzon, F. H.; Ramaiyan, K. P. Highly Stable Doped Barium Niobate Based Electrocatalysts for Effective Electrochemical Coupling of Methane to Ethylene. Adv. Mater. Interfaces
2022, 9 (27), 2200796. https://doi.org/10.1002/admi.202200796.
(3) Denoyer, L. H.; Benavidez, A.; Garzon, F. H.; Ramaiyan, K. P. Chemical Stability of BaMg0.33Nb0.67-XFexO3-δ in High Temperature Methane Conversion Environments. under communication - ECS Journal of Solid State Science and Technology.
Electrochemical Deposition of Nanocatalysts on an Oxide Scaffold Enhances the Activity of Oxygen Reduction
Authors: Nam Seongwoo , Kim Jinwook , Kim Hyunseung , Jeon SungHyun , Ahn Sejong , Choi Yoonseok , Park Beom-Kyeong , Jung WooChul 
Published: September 2023

Solid oxide fuel cells (SOFCs) are devices that directly convert the chemical energy of hydrogen and oxygen into electrical energy, and are attracting attention for their high efficiency and eco-friendliness. Since the recent research trend is to lower the operating temperature of the device, there is a considerable demand for a way to effectively introduce a catalyst to overcome the poor electrochemical activity of the most commercially available lanthanum strontium manganite–yttria-stabilized zirconia (LSM-YSZ) composite electrode.
Praseodymium oxide (PrOx) is an excellent catalyst for the ORR and has also been applied to LSM-YSZ electrodes via infiltration, the most widely used catalyst fabrication method. However, this previously well-established method still experiences time-consuming and energy-intensive limitations; therefore, other catalyst fabrication approaches are required.
Cathodic electrochemical deposition (CELD) is chosen as a central strategy to decorate the PrOx catalyst which strongly empowers the exclusive ORR activity of the LSM-YSZ electrode. CELD is an excellent catalyst fabrication method that combines electroplating and chemical precipitation, and is simple, fast, cost-effective, and capable of deposition at room temperature and ambient pressure.
Herein, we present an electrochemical deposition method that fabricating a PrOx overlayer significantly improves the catalytic activity of composite electrodes with only a short process of less than 4 min, even in an ambient environment. Moreover, it does not require additional processes such as heat treatment. The PrOx-coated electrode exhibits a decrease in initial polarization resistance compared to the bare, and maintained an oxygen reduction reaction characteristic by more than 10 times even after about 400 hours of operation at 650 °C. Transmission line model analysis with impedance spectra describes how PrOx improves the reactivity of the oxygen reduction reaction of composite electrodes. Finally, we demonstrate that a two-element material, (Pr, Ce)Ox, was electrochemically deposited. Electrochemical deposition considerably improves the catalytic properties of the cathode via a concise and straightforward process.