SOFC Anode Research Articles

Analytical and numerical models for impedance of a button SOFC anode

We report a physics–based model for the impedance of a button–type anode–supported SOFC. The model includes ion and electron charge conservation equations and a Fick’s diffusion transport equation for hydrogen in the anode support layer. In the limit of small overpotentials, an analytical solution for the anode impedance is derived. For typical SOFC anode parameters, this solution is valid from open–circuit voltage (OCV) up to the cell current density of about 5 mA cm−2. Fast least–squares fitting of the model impedance to an experimental spectrum measured at OCV is demonstrated and the resulting fitting parameters are compared with literature data. A high–current numerical version of the model is also suitable for fast fitting of experimental impedance spectra.

The effect of the nature of pore former on the microstructure of SOFC anodes based on NiO and 10YSZ formed by hybrid 3d printing

The effect of the nature of pore former on the microstructure of SOFC anodes based on NiO and 10YSZ formed by hybrid 3d printing

Comprehensive numerical investigations on direct ammonia-fed planar solid oxide fuel cell

This study aims at presenting comprehensive insights into the ammonia-utilization in SOFCs using a numerical model developed in 3D for a laboratory-size SOFC and also enlarged to a commercial-size to provide more realistic insights. The verification of the model using the experimental data, and the description of the Ammonia Decomposition Reaction (ACR) kinetics using a rate equation derived from a real SOFC anode make the model, computations, and analyses more accurate. Temperature appears as the most effective on the ACR rate, whereas the impacts of the cell potential and fuel feed rate are insignificant. The ACR rate and endothermic cooling peak around the fuel inlet. However, the distributions of the ACR rate, concentration of species, temperature, and current depend strongly on the active area. In the commercial-size SOFC, except the fuel inlet region, the remaining area exhibits the characteristics which are usually observed when a SOFC is fed by hydrogen.

Enhancement of redox cycling stability of Ni/GDC cermets for intermediate-temperature SOFC anodes through Ge incorporation in the ceramic phase

In this study, Ge4+ was incorporated into the ceramic matrix of nickel-based anode materials, synthesizing anode materials NiO-Gd0.1Ce0.9-xGexO1.95 (x = 0.01, 0.04, 0.07) and NiO-Ce0.9Gd0.1O2–δ. Corresponding anode support samples were also prepared, designated as A-CGDC, A-C1Ge, A-C4Ge, and A-C7Ge. Additionally, single cell samples using the newly co-doped anode materials were prepared, identified as C-CGDC, C-C1Ge, C-C4Ge, and C-C7Ge. The research indicates that after doping the ceramic phase framework with Ge4+, these composite anode materials exhibit the potential to withstand more redox cycles than C-CGDC without catastrophic mechanical structural damage or degradation in electrochemical performance. Particularly, after incorporating 7mol% Ge4+ into the ceramic backbone, the issue of 86 % strain accumulation in the anode support was mitigated. Additionally, the ion doping ratio is closely linked to the stability of the single cell samples, with the A-C7Ge sample able to withstand up to 11 extreme recycling sessions at 700 °C without complete structural failure, improving structural stability by approximately 57 % compared to A-C1Ge. In terms of electrochemical output performance, the impedance of C-C1Ge prior to complete failure was nearly double that before oxidation-reduction, with a maximum power density reduction of about 26.47 %. As the co-doping concentration in the ceramic phase reached 7mol%, the impedance increase during single cell cycle testing was about four times smaller, with C-C7Ge 's impedance before mechanical failure only 37 % higher than before cycling, and a reduction in maximum power density of just 11.11 %. Moreover, during consecutive cycling tests, the average damage to the open-circuit voltage was only 0.02V, showing almost no negative impact from the cycling operations, and it maintained efficient output performance after multiple cycles. Therefore, the newly synthesized nickel-based anode materials, modified via co-doping methods within the ceramic phase, can be considered as potential composite anode materials for intermediate-temperature solid oxide fuel cells.

Impact of SOFC anode carbon deposition and hydrogen adsorption on the cell performance by molecular simulation.

This study primarily investigates the changes in carbon adsorption capacity and hydrogen adsorption capacity on the anode catalyst surface when using methane fuel and mixed gas fuel as the anode fuel for SOFC systems. To reduce the carbon adsorption capacity of the commonly used anode catalyst-nickel-based catalysts-towards hydrocarbon fuels, copper and gold are doped into the nickel-based catalysts to compare the effects on carbon and hydrogen adsorption capacities. Moreover, aside from calculating the carbon and hydrogen adsorption capacities, this project also evaluates the impact of mixed gas effects and doping effects on SOFC performance through the analysis of hydrogen diffusion coefficients and performance polarization curves. The findings reveal a noteworthy enhancement in the diffusion coefficient of syngas within the Au-doped Ni catalyst, showing an improvement of up to 45.46% at 973K. Furthermore, the electrical power generated by syngas in the Au-doped Ni catalyst at 973K demonstrates an increase of up to 12.06%. This study primarily employs DFT to calculate the carbon and hydrogen adsorption energies on methane, utilizing CASTEP for the calculations. During these calculations, the adsorption energy is determined through a three-layer surface approach, in conjunction with the Kohn-Sham equations, combining the Generalized Gradient Approximation and ultrasoft pseudopotentials for TS-search calculations. On the other hand, this project will analyze the diffusion coefficient of hydrogen on the anode catalyst using MD methods combined with the ReaxFF potential field, with GULP being utilized to complete all dynamics calculation theories. Finally, the project will analyze the performance of SOFC cells, incorporating relevant numerical equations with Matlab for numerical analysis.

Optimization of SOFC Anode Microstructure for Performance and Highly Scalable Cells Through Graded Porosity

Anode porosity is fundamental to the performance and durability of SOFCs. This research evaluated the role of pore former loading in the anode layer to optimize the trade-off between cell performance and flatness. It was found that intermediate levels of organic loading through pore former resulted in the highest performance while also the greatest degree of curvature. Grading the porosity such that it decreases towards the electrolyte improved the performance at lower temperatures and fuel ratios. Graded anodes only improved flatness when larger loadings of pore former were used, but this resulted in a loss of performance. When considering both flatness and curvature, graded anodes resulted in cells that were flat and had decent but not the highest performance. Based on our results, the anode microstructure closest to the electrolyte strongly affects performance, while the microstructure towards the fuel affects flatness.

Multiphase engineering regulation of double perovskite and RP structure heterojunction interfaces for solid oxide fuel cells

In the rigorous testing environment of fuel electrodes, surface-modified and element-doped Sr2Fe1.5Mo0.5O6-δ (SFMO6) experiences RP phase decomposition, thereby significantly improving performance - an aspect often underexplored and underutilized. Therefore, the design of a multiphase structure with complementary advantages and the exploration of their interactions become crucial. In the present investigation, SFMO6, which has outstanding redox stability, high conductivity, and catalytic activity, was combined with Sr3Fe1.8Ni0.2O7-δ (SFNO7) in different proportions. SFNO7, characterized by thermodynamic stability, absence of phase transitions, and mixed electrical conductivity, serves as an anode material. XRD results reveal structural stability, with minimal exsolution in a hydrogen environment, and good chemical compatibility. TEM confirms the hetero-interface, while ECR results show a complementary role of Dchem and Kex values for the two structures. At 800 °C, a composition comprising 70% SFMO6 and 30% SFNO7 demonstrates a notably low polarization resistance (Rp) of 0.12 Ω cm2. The maximum power density (MPD) reaches 725.7 mW cm−2 at 800 °C, a 20% improvement compared to single-phase single-cell counterparts (578.9 and 574.1 mWcm−2). This research provides a valuable strategy for the preparation of complementary hetero-interface materials for SOFC anodes and supports the improvement of performance by controlling the decomposition of SFMO6 into the RP phase in a reducing atmosphere.

Gd0.1Ce0.9O1.95 impregnated with Ba(Ce0.9Y0.1)0.8Ni0.2O3–δ@CuO as SOFC anode with increased carbon-deposition resistant for direct hydrocarbon fuels

Solid oxide fuel cells are thought to be capable of a wide range of fuels, but the direct utilization of hydrocarbon fuels increases the risk of carbon deposition at the anode. In this research, a novel full cell structure supported by porous Gd0.1Ce0.9O1.95 (GDC) skeleton is proposed and anode material Ba(Ce0.9Y0.1)0.8Ni0.2O3–δ (BCYN) is proposed to be impregnated on the skeleton to form a multi-functional anode. In the operating reductional atmosphere, Ni is reduced from the BCYN and provides electrochemical catalyticity, and BCYN can absorb water on its surface to prevent carbon deposition. 5% Cu is also applied to the anode to increase electron conductivity by impregnation, and it doubles the peak power density. The composite Ba(Ce0.9Y0.1)0.8Ni0.2O3–δ@CuO anode is evaluated and found to have good carbon deposition resistance with 3% humidified C2H6 in constant current operation for 120 h, and withstand 3% humidified CH4 in OCV condition for nearly 160 h.

Ni-doped Fe-based perovskite to obtain multifunctional and highly efficient electrocatalytic active IT-SOFC electrode

This paper systematically studies Ni doping at Fe sites in La0.6Sr0.4Co0.3Fe0.7O3-δ (LSCF) as an intermediate temperature solid oxide fuel cell (IT-SOFC) electrode. The electrocatalytic activity of Ni-doped electrodes in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) modes was analyzed, rather than individual cathode or anode. The results indicate that Ni doping increases the internal vacancies, ORR activity, and charge transfer ability of La0.6Sr0.4Co0.3Fe0.6Ni0.15O3-δ (LSCFN15). In addition, compared to LSCF, LSCFN15 also reduces the energy barriers for surface oxygen exchange and bulk diffusion, thereby increasing the overall ORR kinetic rate. Combined with the distribution of relaxation time (DRT) analysis, it was confirmed that Ni-doped LSCFN15 increased the adsorption and dissociation rates of oxygen. At 750 ℃, the area-specific resistance (ASR) of LSCFN15 reached 0.045 Ω cm2, which is only 58.4 % of LSCF (0.077 Ω cm2). As a SOFC cathode, the peak power density (PPD) reached 1175 mW cm−2, 1.31 times that of LSCF (898 mW cm−2). As a SOFC anode, the current exchange density of LSCFN15 in OER mode reaches 164 mA cm−2, which is higher than the 125 mA cm−2 of LSCF, indicating that LSCFN15 also has the potential to serve as an anode for SOFC. In addition, Ni doping reduces the thermal expansion coefficient of the electrode and improves its thermal compatibility with traditional electrolytes. As an electrode, LSCFN15 exhibits excellent long-term stability in both SOFC and SOEC modes. Overall, Ni-doped Fe-based perovskite can improve the ORR and OER activities while enhancing the stability of cell operation and is expected to obtain multifunctional SOFC electrode materials.

A novel approach to tailoring the microstructure and electrophysical properties of Ni/GDC-based anodes by combining 3D-inkjet printing and layer-by-layer laser treatment

This work proposes an original method for tailoring the microstructure and electrical properties of Ni/GDC anodes by using 3D inkjet printing of high-viscosity functional compositions with intermediate laser treatment of each layer after each printing pass. Based on a mixture of highly dispersed oxides NiO and CeO2 doped with gadolinium (GDC), paste formulations for 3D inkjet printing have been developed. The effects of 3D printing and laser treatment conditions on the porosity and shrinkage ratio of the NiO/GDC anodes during sintering were investigated. The reduction of the anode support workpieces to produce Ni/GDC cermet was carried out and the effect of laser exposure on the morphology and electrical characteristics of the resulting samples was studied. It was found that an increase in the laser exposure values during layer-by-layer laser treatment of printing compositions leads to a two-fold increase in the porosity of the solid oxide fuel cell components, an increase in the average pore size from 0.2 to 0.3 to 2–5 μm, and to a five-fold decrease in the sintering shrinkage ratio. It was also found that the electrical conductivity of the Ni/GDC cermet, produced by the reduction of the laser treated NiO/GDC, increased by 5–10 times as the laser exposure values increased. The influence mechanism of the layer-by-layer laser treatment of the original NiO/GDC samples on the electrical conductivity of their reduced counterparts, Ni/GDC cermet anodes, has been proposed. An increase in the electrical conductivity was shown to be due to in situ reduction of NiO, partial sintering of Ni nanoparticles and the formation of a percolation network. This new method of hybrid 3D printing opens up great prospects for tailoring the morphological and electrical characteristics of SOFC anode supports.

High Stability/Catalytic Activity Co-based Perovskite as SOFC Anode: In-situ Preparation by Fuel Reducing Method

High Stability/Catalytic Activity Co-based Perovskite as SOFC Anode: <i>In-situ</i> Preparation by Fuel Reducing Method

Study on the Degradation of SOFC Anodes Induced by Chemical and Electrochemical Sintering Using EIS and µ-CT

The goal of the present study was to quantify degradation phenomena on anodes that can be attributed to chemical (thermal) and/or electrochemical sintering, to find out the underlying mechanisms, and to propose countermeasures. The samples were thermally aged for times from 0 to 1000 h, and additional samples of the same type were subjected to electrochemical loading over the same period. The cells were then examined for microstructural changes using FE-SEM/EDS and micro-computed tomography (µ-CT), and the results are correlated with electrochemical impedance spectroscopy (EIS) parameters of long-term electrochemical experiments under dry and humid conditions. It has been shown that it is possible to distinguish between the thermal (chemical) and the electrochemical part of the microstructure degradation. Humidity is an important factor that affects the microstructure in the long term. Tortuosity, porosity, and specific resistance change with time, depending on the humidity of the fuel. Tortuosity changes by one order of magnitude in the direction perpendicular to the electrode surface, while in the other two directions in the plane, the changes are only moderate. Porosity increases in all electrochemically treated samples by 1–5% depending on dry ore humidity conditions and time. As all other experimental parameters are the same in all experiments, the EIS results confirm through the increasing specific resistance, mainly the influence of the changes on the microstructure on the electrochemical properties of the cells.

Fracture of Ni/YSZ Porous Material Under Water Vapor Environment in SOFC Anode: Reactive Molecular Dynamics Simulation

In SOFC anodes, the concentration of water vapor in the hydrogen fuel increases when the hydrogen fuel supply is insufficient due to an accident. Here, when Ni/YSZ porous material is used for anodes, the high concentration of water vapor causes oxidation and volume expansion of Ni particles, leading to the destruction of the anode structure. To develop an anode material with high durability against such oxidation-induced fracture, it is necessary to elucidate the fracture process of Ni/YSZ porous materials due to the oxidation by water and the stress by the volume expansion of Ni particles. In this study, the fracture processes induced by the oxidation are investigated by reactive molecular dynamics method, which can handle chemical reactions. Especially, fatigue simulation by cyclic tension and compression is performed on the Ni/YSZ porous structures under water vapor environment to elucidate the effects of water-induced oxidation and fatigue on fracture.A Ni/YSZ porous model of about 2 million atoms is constructed with Ni and YSZ particles. A mass ratio of Ni particles to YSZ particles is 46:54, and a porosity is set to 40%. To consider water vapor environment, water molecules are placed in the vacancies (Fig. 1). Here, amount of water molecules is equivalent to 1500 times normal pressure to accelerate the oxidation by water. In fatigue processes, cyclic stress induces crack generation, crack propagation, and fracture of materials. Therefore, to investigate the fatigue fracture process, cyclic tension and compression by controlling the strain along the x-axis direction is applied to the Ni/YSZ porous model with a temperature of 1073 K, a pressure of 1.0 atm, and a strain rate of 1.0 x 10-9 s-1.The fatigue simulation was performed by changing the strain (i) from 0.00 to 1.50 for the 1st tension, (ii) from 1.50 to -1.50 for the 1st compression, and (iii) from -1.50 to 1.50 for the 2nd tension. The stress-strain curve during the fatigue simulation is shown in Fig. 2. To clarify the effect of oxidation by water on the fracture of Ni/YSZ porous structure, we first compared the stress-strain curves during the 1st tension of the Ni/YSZ porous models under vacuum and water vapor environment. Under water vapor environment, the tensile strength is 0.57 GPa at the strain of 0.10. This indicates that the water vapor environment leads to the fracture of the Ni/YSZ porous structure when the tensile stress is more than 0.57 GPa. On the other hand, under vacuum environment, the stress-strain curve raises and the tensile strength does not appear. Here, the tensile stress reaches 0.60 GPa at the strain of 1.50. Then, the fracture will ocuur by the tensile stress higher than 0.60 GPa under vacuum environment.Next, we compared the stress-strain curves during the 2nd tension after the 1st compression. The tensile strengths are 0.90 and 1.07 GPa under water vapor and vacuum environment, respectively. The lower tensile strength under water vapor environment indicates that fracture of the Ni/YSZ porous structure during fatigue is more likely to occur under water vapor environment than under vacuum environment.To discuss the reason why the water vapor environment induces the fracture of the Ni/YSZ porous structure, we investigated the structural change in the Ni/YSZ porous models in the fatigue simulations. Figure 3 shows the structural change around the interface between the Ni and YSZ particles during the 1st tension under water vapor and vacuum environment. Under water vapor environment, some cracks are generated at the interface between the Ni and YSZ particles (Fig. 3b). Around the cracks, H atoms and OH groups derived from water molecules are adsorbed on the Ni atoms and on the Zr and Y atoms of the YSZ particles. On the other hand, under vacuum environment, the Ni particles are stretched and no crack is generated by tension (Fig. 3c). These results suggest that the chemical reaction by water promotes the formation and growth of cracks at the Ni/YSZ interface during the tension of Ni/YSZ porous structures. Moreover, plastic deformation occurs within the Ni particles during tension under vacuum environment. On the other hand, there is less plastic deformation under water vapor environment, because the Ni particles are not stretched due to the crack generation at the interface between the Ni and YSZ particles. Therefore, the tensile strength under water vapor environment is lower than that under vacuum environment. Then, we suggest that water vapor environment induces crack generation and propagation at the interface between the Ni and YSZ particles and fracture of the Ni/YSZ porous material during fatigue. Figure 1

Study on Exsolution Process of Sr2FeMo0.6Ni0.4O6 via in Situ Cathodic Polarization

Solid oxide cells (SOCs) are nowadays one of the most promising energy conversion technologies, to accelerate and promote the ongoing energy transition1,2, based on the use of renewable resources. These devices in fact allow the development of valuable low carbon footprint power-to-X (X= power, fuels) chains of energy conversion and storage3. In this respect is crucial the design of innovative, cost-effective materials and processes for more and more versatile and reversible devices.In the last decade, simple perovskite (ABO3) and double perovskite (A2BBʹO6) oxide have been proved to be a valuable alternative to cermet SOC electrodes, thanks to their relative ease of functionalization via doping and exsolution and their mixed ionic-electron conduction4-6. Exsolution process is strongly dependent on the type of metal and perovskite and on methodology adopted to induce the reduction7. Cathodic electrochemical polarization has been demonstrated to be a valuable approach to boost the exsolution especially from titanate based structures, obtaining higher dispersions than that derived from thermal reduction8.In this work, we explored for the first time the behaviour of the double perovskite Sr2FeMo0.6Ni0.4O6-δ (SFMN) under cathodic polarization and we investigated the impact of the structural evolution on the electrochemical performances of a multi-functional electrode for H2-SOFC and CO2-SOEC applications.SFMN was prepared by sol gel method and used to prepare supported SFMN/ La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM)/La0.6Sr0.4Fe0.8Co0.2O3-δ:Ce0.9Gd0.1O2-δ (LSFCo:GDC) cells that were tested either before and after thermal or electrochemical reduction at 850°C.As already reported the thermal reduction of SFMN leads to the exsolution of metal nanoparticles (of Ni or Ni-Fe alloys) and the in situ formation of Ruddlesden-Popper phase9 (RP). HRTEM, SEM and XRD characterizations of tested cells allowed to observe an acceleration of the structural transformation of perovskite under cathodic polarization in comparison to what observed under thermal reduction. This allows to gain insights on the role of entire transformation on the electrochemical behaviours of cells. Electrochemical properties of SFNM were investigated by EIS analysis. Distribution of relaxation times (DRT) analyses was also used to obtain further insights on the impedance of the different cell mechanisms according to their characteristic frequency.The exsolved metal nanoparticles contributed to improve the conductivity and activity of the electrode, however, also the formation of RP phase seems have a significant role, especially in the electroreduction of CO2. Further studies are in progress to better understand the mechanisms of interaction between the phases formed during the exsolution process and their role on SOC electrodes activity. References 1 Hauch et al., Science 370, eaba6118 (2020). 2 M.B. Mogensen et al. Clean Energy, 3 (2019) 175–2013 F. Salomone et.al Chem. Eng. Journal 377 (2019), 1202334.Irvine, J. T. S. Perovskite Oxide Anodes for SOFCs. In Perovskite Oxide for Solid Oxide Fuel Cells; Ishihara, T., Ed.; Springer US: Boston, MA, 2009; pp 167–182.5. W. Yin, et al. Energy Environ. Sci. 12 ( 2019) 442–4626. Q. Islam, et al. J. Power Sources 492 ( 2021) , 229626.7. O. Kwon et.al. J. Phys. Energy2, ( 2020), 0320018. Jh, Myung, Jh. et al. Nature 537, (2016) 528–5319. Z.; Du et.al ACS Nano 10, 2016, 8660–8669

Electrochemical Activation and NAP-XPS As Well As EIS Characterization of La0.31Sr0.58Ti0.97Ni0.03O3-δ Thin Film Electrode

Mixed conductive perovskites, like LaxSr0.9-xTiyNi1-yO3-d, LaxSr1-xCryMn1-yO3-d are attractive materials for SOFC anodes. These structures are flexible to adopt different cations into the structure. To improve catalytic activity of these materials, doping of perovskite B-site with metals like Ni, Co, Mo or Cu has been proposed. It has been demonstrated, that at elevated temperatures and in reducing atmosphere these dopants exsolve to perovskite surface to form nanometre scale catalyst particles [1,2]. Exsolution process could be accelerated by using electrochemical polarization. Other phenomena which has been observed in the case of these materials is the segregation of A-site elements because of elastic and electrostatic interactions of ions in the surface layer [3]. The extent of aforementioned effects is connected to the oxidation state of the B-site elements, which is a function of the chemical composition and the stoichiometry of the electrode material, the oxygen partial pressure in electrode compartment and temperature. To improve the understanding how the chemical composition of electrode surface depends on the electrode stoichiometry and environmental conditions it’s necessary to carry out in situ or operando characterization of electrode materials.In the present study thin film electrodes with La0.31Sr0.58Ti0.97Ni0.03O3-δ composition was deposited using pulsed laser deposition (PLD) technique. Current collectors were made from Pt (using magnethron sputtering) and placed under the thin film electrode layer.Electrodes were characterized usin XPS and EIS method at near ambient pressure conditions (1-5 mbar) at 650 °C, activated electrochemcally and characterized again to see the effect of activation. Changes on the electrochemical performance as well as on XPS data caused by electrochemical activation were observed and analyzed.[1] Homel et al., J. Power Sources 195, 6367 (2010)[2] Steiger, P., et al., Mater, 31, 748−758 (2019).[3] Lee et al., J. Am. Chem. Soc. 135, 7909 (2013).

Direct Ammonia SOFC-Gas Turbine Hybrid Systems Modeling for Heavy-Duty Transportation Sector

Ammonia currently stands as being the second most produced chemical in the world [1]. While it is prominently used in the manufacturing of fertilizers, increase in production capacity through renewable sources such as green hydrogen and its potential as a carbon-neutral energy carrier make it a promising candidate to replace fossil fuels for power generation in the future [2]. Moreover, when compared to liquid hydrogen, ammonia can be stored at more practical temperatures (-253⁰C vs -33⁰C at 1 bar) and has a higher volumetric energy density (8.5 MJ/L vs 12.7 MJ/L) [3]. Though the toxicity of ammonia as a fuel is well known, there are well established safety and handling procedures for storage and transport, given its ubiquitous existence as an essential commodity required for agriculture.From a systems perspective, residual chemical exergy available in the SOFC anode gas exhaust can be utilized through a gas turbine to enable increased efficiency [4]. Direct ammonia SOFCs (DASOFCs) can eliminate the need for external cracking to hydrogen, thereby reducing system complexity. In addition, heat loss and thermal management in the stack periphery may be effectively managed via in-situ endothermic decomposition of ammonia [5]. Integration in a hybrid system is also beneficial to SOFCs due to the associated heat of compression for pressurized operation. The different physicochemical timescales of electrochemical fuel cells and mechanical turbomachinery are advantageous to dynamic operation which is important because of fluctuating power loads in a mobile application.In this work, the potential of an ammonia-based hybrid SOFC/GT system concept is assessed. A multiscale stack simulation using constitutive relations for heat, mass and charge transfer based on high power density SOFCs is integrated with turbomachinery and other auxiliary system components within the gPROMS process simulation framework. State variables for each point can then be defined to estimate the operating boundaries of the system.This presentation discusses the thermodynamics of SOFC operation and system concepts to utilize ammonia in a hybrid system for a kW-scale transportation application. This involves evaluation of system indicators such as thermodynamic efficiency, fuel utilization and specific power which can help determine optimal performance. The efficiency and specific power are dictated by the operating temperature of the fuel cell, preheating requirements and the relative utilization of fuel between the SOFC and gas turbine. The proposed system concept is shown to achieve LHV efficiencies of up to 60% (LHV) within reasonable operating limits. The presentation includes an examination of the prospects of ammonia as a power source for the mobility sector in comparison to contemporary and future renewable fuels, and concludes with practical challenges for deployment.

Optimization of SOFC Anode Microstructure for Performance and Highly Scalable Cells through Graded Porosity

The performance and durability of anode supported solid oxide fuel cells is heavily dependent on the porosity of their anode layer. An optimal amount of porosity is needed to achieve high performance without compromising the flatness, and by extension, the hermetic sealing of the cell. This presents challenges for commercialization, as anode porosity heavily influences the densification of the cells during sintering. In this work, the effect of pore former loading was evaluated on both cell performance and curvature. It was also found that anodes with an intermediate amount of pore former had the best performance but also the most curvature. The mechanism behind this was evaluated with an optical dilatometer. As expected, when cells were sintered with thicker anode support layers, they resulted in significantly flatter cells. Improvements to performance but not flatness were achieved with the use of graded porosity in the anode, with high porosity at the fuel side that decreased closer to the electrolyte. This effect was more pronounced at lower temperatures and fuel ratios, further demonstrating that this is a more efficient microstructure for the anode than a typical anode with uniform porosity. The use of graded porosity was then evaluated as a means of improving the performance of thicker anodes, to take advantage of their greater flatness and mechanical strength. Unfortunately, thicker anodes exhibited a significant drop in performance. It was found that the greater distance for gas diffusion in thicker anodes means that a different microstructure is needed for efficient gas flow and charge transfer. In the case of thicker anodes, it was found that having two anode regions, one thinner region with moderate porosity adjacent to the anode functional layer and one with high porosity making up the bulk of the anode resulted in the best performance. This allows sufficient fuel flow in a thicker anode, without significantly reducing the activity of the anode. In this way, this anode microstructure behaves similarly to an anode functional layer, which is well known to improve fuel cell performance. While graded anode microstructures have been reported before, there have been few, if any, studies that evaluated both their performance and flatness simultaneously. Optimization of anode porosity in anode supported cells is essential to improving both their performance and reliability, which are necessary for widespread adoption of SOFCs.

Influence of A-Site Deficiency and B-Site Composition on the Electrical and Crystallographic Properties of (La0.25Sr0.25Ca0.45)yTi0.95Ni0.05-xMnxO3-δ Solid Oxide Fuel Cell Anode

(La,Sr)TiO3-δ has attracted specific attention over the past years due to its superior dimensional stability, high conductivity, and significant tolerance against sulfur poisoning and carbon depositions. To increase the catalytic activity and chemical stability, many different doping levels and stoichiometries for LaxSr1-xTiO3-δ (LST) have been investigated [1, 2]. Doping of B-site with Mn has been shown to promote electroreduction under SOFC conditions [3]. Furthermore, Mn is known to accept lower coordination numbers in perovskites, especially for Mn3+ (3d4), and so may enhance oxide-ion migration [4]. In addition, MnO is clearly stable under fuel conditions unlike Co or Ni oxides [4].In this research influence of A-site deficiency and B-site chemical composition on electrical performance of La0.25Sr0.25Ca0.45Ti0.95Ni0.05-xMnxO3-δ (x=0-0.05) (LSCTNM-x) hydrogen electrode has been studied. The crystal structure and microstructure have been studied using X-ray diffraction and SEM to confirm the phase purity and visualize the microstructure of studied electrode layers. To understand the influence of MIEC material composition on electrical conductivities of LSCTNM, the DC four-probe conductivity measurements of porous electrode layers has been performed. Conductivities have been measured at two different atmospheres: 1% H2 + 1.7% H2O + 97.3% Ar and 98.3% H2 + 1.7% H2O. It has been shown that all materials with LSCTNM compositions behave like semiconductor and the conductivity is significantly dependent on composition. The maximal total electrical conductivity of porous electrode layers was characteristic for the LSCTNM materials with 10% A-site deficiency, in 98.3% H2 + 1.7% H2O atmosphere. Keywords: solid oxide fuel cell; conductivity; perovskite; fuel electrode; MIEC.[1] X. Li, H. Zhao, X. Zhou, N. Xu, Z. Xie, N. Chen, Electrical conductivity and structural stability of La-doped SrTiO3 with A-site deficiency as anode materials for solid oxide fuel cells, international journal of hydrogen energy 35 (2010) 7913-7918.[2] A. Gondolini, E. Mercadelli, G. Constantin, L. Dessemond, V. Yurkiv, R. Costa, A. Sanson, On the manufacturing of low temperature activated Sr0.9La0.1TiO3-δ-Ce1-xGdxO2-δ anodes for solid oxide fuel cell, Journal of the European Ceramic Society, 38 (2018) 153–161.[3] P. Holtappels, J. Bradley, J.T.S. Irvine, A. Kaiser, M. Mogensen, Electrochemical characterization of ceramic SOFC anodes, J. Electrochem. Soc. A 148 (2001) 923–929.[4] S. Tao, J.T.S. Irvine, A redox-stable efficient anode for solid-oxide fuel cells, nature materials, 2 (2003) 320-323.

Methane Dehydrogenation and Coking Resistance on Ni(111) Surfaces of SOFC Anodes with Different Cu Doping Ratios under a Consistent DFT Framework

Methane Dehydrogenation and Coking Resistance on Ni(111) Surfaces of SOFC Anodes with Different Cu Doping Ratios under a Consistent DFT Framework

Material design and performance of carbon monoxide‐fueled solid oxide fuel cells: A review

AbstractSolid oxide fuel cells (SOFCs) are electrochemical energy conversion devices with fuel flexibility. Since carbon monoxide (CO) is a major product of SOFC anodes operating with hydrocarbon fuels, direct utilization of CO as a fuel is expected for more efficient operation of SOFCs. A review on CO‐fueled SOFC technologies is imperative to promote research activities in this important field, but it has not been published. In this review, we summarize and comment on literatures in this field, with respect to (1) materials developed for three fundamental components (anode, cathode, and electrolyte), (2) power output and stabilization strategies, and (3) critical challenges and directions in the development of CO‐fueled SOFCs.