SwePub - search: WFRF:(Li Tingshuai)

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1.	Qi, Yuanxin, et al. (author) Temperature control strategy for polymer electrolyte fuel cells 2020 In: International Journal of Energy Research. - : Hindawi Limited. - 0363-907X .- 1099-114X. ; 44:6, s. 4352-4365 Journal article (peer-reviewed)abstract A polymer electrolyte fuel cell (PEFC) is an electrochemical device that converts chemical energy directly to electrical energy, and its performance greatly depends on its operating temperature. Therefore, in this paper, a novel thermodynamic PEFC model with the airflow cooling method is firstly developed for the PEFC system. Then, a novel model predictive control (MPC) controller is designed to control the stack temperature at an optimal value by adjusting the air flow rate on the basis of the developed thermodynamic PEFC model. The thermodynamic PEFC model and the designed controlling strategies are simulated and analysed in Matlab/Simulink. Three tests are conducted to estimate the reliability of the developed controllers concerning different operating conditions: (a) typical perturbation in the current load, (b) any perturbation in the current load, and (c) variation of the ambient temperature. The simulation results demonstrate that the MPC controller can effectively control the stack temperature at the desired value. Moreover, the MPC controller shows much superior effects compared with the conventional proportional integral derivative (PID) controller. In addition, the developed coolant circuit model can be easily applied to various PEFC systems. The MPC controller shows potential also for other controlling issues of PEFC systems due to its strong robustness and fast response.
2.	Zeng, Shumao, et al. (author) Thermal stress analysis of a planar anode-supported solid oxide fuel cell : Effects of anode porosity 2017 In: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 42:31, s. 20239-20248 Journal article (peer-reviewed)abstract A Fuel cell is a highly efficient device for converting chemical energy in fuels to electrical energy and the electrical efficiency is strongly affected by the porosity in electrodes due to its close couplings with mass transfer and active sites for the electrochemical reactions, which will also cause changes in distribution of thermal stresses inside the electrodes. A three-dimensional computational fluid dynamics (CFD) approach based on the finite element method (FEM) is used to investigate the effects of porosity on polarizations, temperatures and thermal stresses by coupling equations for gas-phase species, heat, momentum, ion and electron transport. It was found that the porosity in the anode remarkably affected the exchange current density and electrical current density, but it had an opposite effect on the anodic activation polarization compared to that in cathode. The first principle stress was enhanced from 0 to 2 MPa to 6-8 MPa by an increased anode porosity from 25% to 40%, and the increased porosity resulted in a decrease of the von mises stress along the main flow direction as well. The conclusions could be used to lay foundations for an improved performance and stabilization by optimizing electrode microstructures and by eliminating the stresses in electrodes.
3.	Espinoza Andaluz, Mayken, et al. (author) A-Asterisk Algorithm as an Alternative to Evaluate the Geometric Tortuosity in Digitally Created SOFC Anodes 2021. - 1 In: 17th International Symposium on Solid Oxide Fuel Cells, SOFC 2021. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; 103:1, s. 1665-1671 Conference paper (peer-reviewed)abstract A solid oxide fuel cell (SOFC) contains complex materials that facilitate the energy conversion process. The diffusion media play an important role in facilitating the reactant gases to reach the electrochemical active regions. Porosity and tortuosity are crucial parameters describing the diffusion to be analyzed in a SOFC anode. This paper aims to evaluate the feasibility of using the A-asterisk algorithm to compute the geometric tortuosity within SOFC anodes. A three-dimensional structure, which is digitally created, represents the SOFC anode, in which the possible paths that follow the fluid flow are analyzed. A-asterisk algorithm is used to generate possible paths, and therefore the geometric tortuosity can be computed considering an averaged distance. A tortuosity-porosity correlation is proposed, and the results are compared with previous studies. Results show that the A-asterisk algorithm is a capable algorithm to evaluate the geometric tortuosity values in SOFC anodes with different particle size distribution and porosities.
4.	Larsson, Tara, et al. (author) Co-fabrication of nickel-YSZ cermet nanofibers via an electrospinning technique 2017 In: Materials Research Bulletin. - : Elsevier BV. - 0025-5408. ; 86, s. 38-43 Journal article (peer-reviewed)abstract Abstract In this study, we co-fabricated the Ni-based nanofibers using an electrospinning technique. The effects of viscosity, applied voltage and distance from needle to the collection plate on the fiber morphology were investigated. The fibers were sintered at temperatures ranging from 350 °C to 1200 °C and the results indicated that the crystallization was completed at 800 °C and the particle size increased with the temperature. The porosity of nanostructure can reach over 50% before reduction of the nickel oxide, which increased firstly with the temperature and then decreased over 800 °C. The nanocrystallization of an anode was helpful to maximize the electrochemical reaction sites for restraining the activation polarization and also to enlarge pores for rapid gas diffusion in fuel cells.
5.	Yu, Guangsen, et al. (author) Fabrication of Nickel-YSZ cermet nanofibers via electrospinning 2017 In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 693, s. 1214-1219 Journal article (peer-reviewed)abstract Abstract The Ni-YSZ cerment as a promising anode for solid oxide fuel cells and its performance strongly depends on its miscrocture. This work focused on fabrication of Ni-8YSZ nanofibers via an electrospinning technique using yttria and zirconia nanoparticles as precussors. The effects of viscosity on the quality of fibers were assessed by adjusting the polymer and solid contents in slurry. The fibers sintered at different temperatures showed varying morphologies and a bead-like chain at temperatures higher than 800 °C was obtained. Crystalization of the YSZ was completed above 1400 °C and NiO was above 800 °C. The porosity of the fiber structure can reach high up to 45% before NiO reducation. The nanocrystallization of an anode for SOFCs was beneficial to enhance the electrochemical reaction sites and also to reduce the difficulties for gas diffusion.
6.	Zhang, Xiaoqiang, et al. (author) Mechanism of chromium poisoning the conventional cathode material for solid oxide fuel cells 2018 In: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 381, s. 26-29 Journal article (peer-reviewed)abstract Chromium poisoning the La0.875Sr0.125MnO3 (LSM) cathode for solid oxide fuel cells is a critical issue that can strongly affect the stability. In this study, we evaluate the temperature distribution in a SOFC based on a 3D model and then combine conductivity test and material computation to reveal the effects of chromium in SUS430 stainless steels on LSM conductivities. The starch concentration in LSM pellets and the applied pressure on the contact with interconnect materials show close relationships with the chromium poisoning behavior. The density functional theory (DFT) computing results indicate that chromium atoms preferably adsorb on the MnO2-terminated and La (Sr)-O-terminated (001) surfaces. The resulting conclusions are expected to deeply understand mechanism of chromium deactivating conventional cathodes at some typical operational conditions, and offer crucial information to optimize the structure to avoid the poisoning effect.
7.	Andersson, Martin, et al. (author) Review on Dimensionless Numbers Relevant for Polymer Electrolyte Fuel Cells 2016 In: ECS Transactions. - : The Electrochemical Society. - 1938-6737 .- 1938-5862. ; 75:14, s. 547-552 Journal article (peer-reviewed)abstract With the concern about global warming, air pollution and energy security, the prospect of using polymer electrolyte fuel cells (PEFCs) in future sustainable and renewable energy conversion systems has achieved substantial momentum. Dimensionless numbers can be determined before construction of a model is started, to make simple estimations on the transport processes, for example, within the porous PEFC GDL. Microstructural parameters, such as tortuosities and contact angles, are frequently treated as fitting parameters used in the respective governing equations, such that unrealistic values could be assumed or properties could not be representative of the corresponding microstructure. This treatment can be avoided if the origin of the expression is clearly clarified and if geometric properties are not used for fitting. Instead, it is recommended to, when needed, introduce parameters, without a geometrical meaning used only for fitting the model to experimental data, such as the pre-exponential factor in the advanced microstructural approach.
8.	Andersson, Martin, et al. (author) SOFC Cathode Design Optimization using the Finite Element Method 2014 Conference paper (peer-reviewed)abstract Solid oxide fuel cells (SOFCs) are promising as an energy producing device, which at this stage of development will require extensive analysis and benefit from numerical modeling at different time- and length scales. A 3D model is developed based on the finite element method (FEM), using COMSOL Multiphysics, of a single SOFC operating at an intermediate temperature range. Ion, electron, heat, gas-phase species and momentum, transport equations are implemented and coupled to the kinetics of the electrochemical and internal reforming reactions. High current density spots were identified in our previous work, at positions where the electron transport distance is short and the oxygen concentration is high. The electron transport especially within the cathode is found to be limiting for the electrochemical reactions at positions far from the channel walls (interconnect). New cathode designs are proposed, for the cathode/air channel interface, to be able to reduce the maximum electron current density (decreasing the ohmic polarization due to electron transport), i.e., to increase the fuel utilization, with constant inlet conditions, compared to a standard approach. The two cases with a modified cathode structure presents 1 % higher average ion current density as well as 1 % higher fuel utilization, keeping the inlet conditions similar.
9.	Congress on Research, Development and Innovation in Renewable Energies : Selected Papers from CIDiER 2021 2022 Editorial collection (peer-reviewed)
10.	Espinoza-Andaluz, Mayken, et al. (author) Computational simulation data using the Lattice Boltzmann method to generate correlations for gas diffusion layer parameters 2019 In: Data in Brief. - : Elsevier BV. - 2352-3409. ; 27 Journal article (peer-reviewed)abstract Analyzing the fluid behavior in complex porous media like gas diffusion layers (GDLs) in polymer electrolyte fuel cells (PEFCs) can be accurately done using the lattice Boltzmann method (LBM). This article shows the data obtained from a study in which diffusion parameters such as porosity, gas phase tortuosity and diffusibility are computed considering simulated porous media [1]. The data were computed when a water drop obstacle is placed inside the GDL domain and the size of the water-drop is varied. Additionally, figures showing the evolution of the flow velocity field are presented alongside graphics that presents the change in local and bulk porosity for each obstacle size. Finally, there is a detailed method explanation concerning the implementation of the lattice Boltzmann method and a general description of computational codes for the domain and obstacle generation as well as the boundary conditions simulation. Data and processes in this article can be exploited in new attempts to solve real case problems in complex mesoscale media.
11.	Espinoza-Andaluz, Mayken, et al. (author) Diffusion parameter correlations for PEFC gas diffusion layers considering the presence of a water-droplet 2019 In: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. Journal article (peer-reviewed)abstract A polymer electrolyte fuel cell (PEFC) produces electrical energy according to the electrochemical reactions carried out inside the cell. During the energy conversion, water molecules are also produced at the cathode side, which affects the gas diffusion layer (GDL) diffusion parameters. The generated water-drops from the reaction may give partial or total blockage of the reactant gases and also material oxidation. The mentioned phenomena influence the performance of the PEFCs. This paper aims to describe and quantify the impact on diffusion parameters of GDLs when the size of the formed water-drops inside the layer is varying. This study considers digitally generated GDLs, in which the porosity, gas-phase tortuosity and diffusibility are studied. The fluid flow behavior through the three-dimensional porous domain representing the GDL is obtained with the lattice Boltzmann method (LBM). Depending on the water-drop size, the impact of the mentioned parameters can be computed. For the current study a spherical water-drop whose radius varies between the 15 and 35% of the size of the domain was considered. The studied parameters showed a dependency of the water-drop radius, each changing independently and several correlations to predict the behavior of the mentioned diffusion transport parameters are proposed.
12.	Espinoza-Andaluz, Mayken, et al. (author) Impact of water drop presence on diffusion parameters of PEFC gas diffusion layers 2019 In: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 158, s. 1400-1405 Conference paper (peer-reviewed)abstract A polymer electrolyte fuel cell (PEFC) produces electrical energy thanks to the electrochemical reaction carried out inside the cell. During the energy conversion, water molecules are also produced in the cathode side and this can affect the diffusion parameters of the gas diffusion layers (GDLs). The generated water-drops due to the reaction may block the reactant gases and produce material oxidation. The mentioned phenomena influence the performance of the PEFCs. This paper aims to describe and quantify the impact on diffusion parameters of GDLs when the presence of formed water-drops inside the layer is considered. This study considers digitally generated GDLs, and the parameters considered are porosity, gas-phase tortuosity and diffusibility. The fluid flow behavior through the three-dimensional porous domain representing the GDL is obtained by using the lattice Boltzmann method (LBM). Depending on the water-drop size, the impact over the mentioned parameters can be computed. For the current study, a single water-drop has been placed into the GDL domain and its impact has been analyzed.
13.	Espinoza-Andaluz, Mayken, et al. (author) Performance experimental data of a polymer electrolyte fuel cell considering the variation of the relative humidity of reactants gases 2019 In: Data in Brief. - : Elsevier BV. - 2352-3409. ; 27 Journal article (peer-reviewed)abstract The data collected in this article is based on a performance test of a polymer electrolyte fuel cell (PEFC). The behavior the different parameters of a PEFC is analyzed considering different aspects relative to the inlet gases temperatures. The fuel cell was evaluated by means of a current sweep at different percentages of relative humidity between the feed gas and the cell. The relative humidity values were established by means of the temperature setting. The data presented show the experimental response of the cell in real time, which can be used to perform a depth analysis or they can be a starting point for material and performance investigation. In addition, charts presenting the voltage and power density behavior as a function of the volumetric flows of the anode (H2) as well as cathode (O2). The data presented in this article are originally from our research performed in [1].
14.	Hu, Peiji, et al. (author) In-situ exsolution of FeCo nanoparticles over perovskite oxides for efficient electrocatalytic nitrate reduction to ammonia via localized electrons 2024 In: Applied Catalysis B: Environmental. - 0926-3373. ; 357 Journal article (peer-reviewed)abstract FeCo nanoparticles exsolved from Co-doped Sm0.9FeO3 nanofibers with abundant oxygen vacancies (Vos) are proposed as an efficient electrocatalyst to promote nitrate reduction reaction (NITRR). Such catalyst achieves a maximum Faradaic efficiency (FE) of 90.3 % and a large NH3 yield of 17.2 mg h−1 mg−1cat. at a negatively shifted potential of −0.9 V in 0.1 M PBS with 0.1 M NaNO3, and the alloy nanoparticles socketed into nanofibers remain extremely stable during long-term electrolysis. The reaction pathway favoring the formation of NH2OH is uncovered by in situ electrochemical tests and theoretical calculations reveal the exsolution of FeCo alloy combined with the generation of Vos enhances nitrate adsorption and lowers energy increase of the potential determining step. Finite-element simulations unveil the applied current and charges are localized on the alloys along the nanofiber, which confirms the exsolved FeCo nanoparticles are the main active sites for NITRR.
15.	Ohrelius, Mathilda, et al. (author) Electrochemical Synthesis of Ammonia Based on a Perovskite LaCrO3 Catalyst 2020 In: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 12:3, s. 731-735 Journal article (peer-reviewed)abstract Electrochemical synthesis of ammonia through the nitrogen reduction reaction (NRR) has the possibility to revolutionize our production of ammonia and to save our planet from both emissions and large energy consumption. In this study, a perovskite structured lanthanum chromite catalyst (LaCrO3) is synthesized, characterized as well as electrochemically evaluated for NRR. The highest ammonia yield is obtained at −0.8 V vs. reversible hydrogen electrode with an ammonia formation rate of 24.8 μg h−1 mg−1 cat, and a Faradaic efficiency of 15 %. Material calculation further confirms the possible mechanism of ammonia formation with the aid of LaCrO3 catalyst. The resulting conclusion offers a great alternative with the easily produced and low-cost perovskite structured electrocatalysts for ammonia production.
16.	Parbey, Joseph, et al. (author) Electrospun fabrication of nanofibers as high-performance cathodes of solid oxide fuel cells 2020 In: Ceramics International. - : Elsevier BV. - 0272-8842. ; 46:5, s. 6969-6972 Journal article (peer-reviewed)abstract The oxygen reduction reaction (ORR) activity can strongly affect the performance of solid oxide fuel cells (SOFCs). To improve the electron transfer and enhance active sites for reactions in cathode, La0.8Sr0.2MnO3 mixed with Y2O3-stabilized ZrO2 (LSM/YSZ) nanofibers were co-fabricated by the electrospinning method. The fibers were well characterized and the electrochemical properties were evaluated by preparing a symmetrical sample with yttria-stabilized Zirconia (YSZ) pellet as electrolyte. The electrochemical impedance spectra reveal that appropriate grinding time can benefit an improved electrical conductivity and this nanostructure also has a porosity of up to 50%, which is expected to reduce the resistance of mass transfer and enhance the electron and ion transportation.
17.	Parbey, Joseph, et al. (author) High-performance solid oxide fuel cells with fiber-based cathodes for low-temperature operation 2020 In: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 45:11, s. 6949-6957 Journal article (peer-reviewed)abstract Low-temperature operation of solid oxide fuel cells (SOFCs) results in deterioration in electrochemical performance due to sluggish oxygen reduction reaction (ORR) at the cathode. To enhance the reaction pathway for ORR, La0.8Sr0.2MnO3 (LSM) nanofibers were fabricated by electrospinning and used for low-temperature solid oxide fuel cells operated at 600–700 °C. The morphological and structural characteristics show that the electrospun LSM nanofiber has a highly crystallized perovskite structure with a uniform elemental distribution. The average diameter of the LSM nanofiber after sintering is 380 nm. A symmetric cell of nanofiber-based LSM cathode on scandia-stabilized zirconia (SSZ) electrolyte pellet exhibits much lower area specific resistances compared to commercial LSM powder-based cathode. A single cell based on the nanofiber LSM cathode on yttrium-doped barium cerate-zirconia (BCZY) electrolyte exhibits a power density of 0.35 Wcm−2 at 600 °C, which increases to 0.85 Wcm−2 at 700 °C. The cell has an area specific resistance (ASR) of 0.46 Ωcm2 at 600 °C, which decreases to 0.07 Ωcm2 at 700 °C. The results indicate that the LSM electrode fabricated by the electrospinning process produces a nanostructured porous electrode which optimizes the microstructure and significantly enhances the ORR at the cathode of SOFCs.
18.	Parbey, Joseph, et al. (author) Progress in the use of electrospun nanofiber electrodes for solid oxide fuel cells : A review 2019 In: Reviews in Chemical Engineering. - : Walter de Gruyter GmbH. - 2191-0235 .- 0167-8299. ; 36:8, s. 879-931 Journal article (peer-reviewed)abstract The application of one-dimensional nanofibers in the fabrication of an electrode greatly improves the performance of solid oxide fuel cells (SOFCs) due to its advantages on electron transfer and mass transport. Various mixed ionic-electronic conducting materials with perovskites and Ruddlesden-Popper-type metal oxide structures are successfully electrospun into nanofibers in recent years mostly in solvent solution and some in melt forms, which are used as anode and cathode electrodes for SOFCs. This paper presents a comprehensive review of the structure, electrochemical performance, and development of anode and cathode nanofiber electrodes including processing, structure, and property characterization. The focuses are first on the precursor, applied voltage, and polymer in the material electrospinning process, the performance of the fiber, potential limitation and drawbacks, and factors affecting fiber morphology, and sintering temperature for impurity-free fibers. Information on relevant methodologies for cell fabrication and stability issues, polarization resistances, area specific resistance, conductivity, and power densities are summarized in the paper, and technology limitations, research challenges, and future trends are also discussed. The concluded information benefits improvement of the material properties and optimization of microstructure of the electrodes for SOFCs.
19.	Qi, Yuanxin, et al. (author) Dynamic modelling and controlling strategy of polymer electrolyte fuel cells 2020 In: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 45:54, s. 29718-29729 Journal article (peer-reviewed)abstract A comprehensive dynamic control oriented model of a polymer electrolyte fuel cell (PEFC) is developed, considering the mixed effects of temperature, gas flow and capacitance. The fractional relationship between the dynamic output voltage and the capacitance, which escaped the attention in most previous studies is also addressed. Moreover, based on the developed PEFC model, a proportional integral and derivative (PID) controller is designed to stabilize the output voltage at a determined value by regulating the input hydrogen mass flow rate under a series of disturbance in the input. The dynamic PEFC model and controller are simulated in Matlab/Simulink. The simulation results illustrate that the PEFC system model is capable of characterizing dynamic properties of PEFCs. Additionally, the developed PID controller is effective in stabilizing the output voltage with a rather small overshoot and rather faster response, which also proves that the developed model is suitable for PEFC control algorithms development.
20.	Santana, Jordy, et al. (author) A Detailed Analysis of Internal Resistance of a PEFC Comparing High and Low Humidification of the Reactant Gases 2020 In: Frontiers in Energy Research. - : Frontiers Media SA. - 2296-598X. ; 8 Journal article (peer-reviewed)abstract Polymer electrolyte fuel cells (PEFCs) have shown a great potential to be used in several applications, e.g., portable, mobile and stationary systems. Each of the mentioned applications demands from PEFCs different operating conditions to perform in the best possible manner. Knowing in detail the behavior of their internal components will help to improve the mechanical and thermal properties of the different constitutive layers. The objective of this research is to analyze in detail the behavior of the internal resistances of a PEFC, using the impedance spectroscopy technique. A single cell is evaluated in a broad range of current densities, i.e., from 0.2 to 2.0 A.cm–2, to evaluate the resistances that cause loss of performance. The analyzed resistances correspond to the ohmic, charge transfer and mass transport resistance. The results were obtained after the interpretation of the data taking from Nyquist diagrams, and they were analyzed considering high and low conditions of relative humidity (RH). The obtained results showed that the ohmic resistance (attributed to membrane Nafion® 212), is independent of the load applied for fully humidified conditions, with a value of 0.0725 Ω.cm2. On the other hand, it is strongly dependent on low humidification conditions, with values between [0.198–0.132] Ω.cm2, for current density of [0.2–2.0] A.cm–2, respectively. It was also found that the charge transfer resistance decreases with respect to the applied load until a saturation value, and further it represents the major participation to the total resistance of the cell. The charge transfer resistance represents around 50–75% of the total resistance in conditions of high RH, and among 30–65% for conditions of low RH. In addition, it was found that the mass transport resistance appears early at low RH and triples for full humidification conditions.
21.	Santana, Jordy, et al. (author) Temperature Impact on the Internal Resistance of a Polymer Electrolyte Fuel Cell Considering the Electrochemical Impedance Spectroscopy Diagnosis 2020. - 1 In: Fuel Cell Seminar and Energy Exposition 2019. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; 96:1, s. 183-190 Conference paper (peer-reviewed)abstract A polymer electrolyte fuel cell (PEFC) is an electrochemical device that converts the chemical energy presents in the hydrogen into electricity and heat having as by product only water. The energy conversion process is carried out in a clean and noiseless manner. Depending on the applications, a PEFC works at different operating temperature. In this study, the internal resistance of a PEFC is evaluated by using Electrochemical Impedance Spectroscopy (EIS) at moderate low current density, i.e., 0.5 A/cm2, in the temperature range of 40-80°C. The evaluation is carried out considering frequencies between 3.1kHz and 1Hz. An equivalent Randle circuit is considered as adjusted model and the Nyquist and Bode diagram were obtained to analyze the internal resistance. Results show that the ohmic resistance and charge transport increase when the operating temperature is low, decreasing the cell performance. A voltage drop of 42 mV was obtained for the evaluated temperature sweep. At the same time, it was demonstrated that the double layer capacitance increases at high temperatures, increasing its operating performance.
22.	Xu, Min, et al. (author) Modeling of an anode supported Solid Oxide Fuel Cell focusing on Thermal Stresses 2016 In: International Journal of Hydrogen Energy. - : Elsevier BV. - 1879-3487 .- 0360-3199. ; 41:33, s. 14927-14940 Journal article (peer-reviewed)abstract A mechanical failure of a single component is sufficient to cause a solid oxide fuel cell (SOFC) breakdown. As an unfavorable issue for interfering the stable operation of SOFCs, thermal stress stemming from temperature gradient and mechanical mismatch can result in crack damage. Therefore, it is strongly significant to clarify the relationship of mechanical properties of the cell materials with distribution of the stress by taking into account the electrochemical reactions. A complete three-dimensional model for a planar anode-supported SOFC has been proposed and established in this study, which includes governing equations for momentum, gas-phase species, heat, electron and ion transport. The thermal gradients caused by the electrochemical reactions and heat transport processes of the counterflow leading to a maximum thermal stress is slightly larger than that is induced by the coflow. The influence of mechanical mismatch is analyzed and the results indicate that the strength of stress at two sides of a cell tends to be enlarged under fixed constraint conditions. Furthermore, the functional buffer layers can affect the stress between different components and inhibit the extent of degradation. This investigation is expected to offer a path to improve the matches of SOFC components and optimize the stack design.
23.	Xu, Min, et al. (author) Modeling of Solid Oxide Fuel Cell with Anisotropic Conductivity 2015 In: ECS Transactions. - : The Electrochemical Society. - 1938-6737 .- 1938-5862. ; 68:1, s. 3003-3011 Conference paper (peer-reviewed)abstract In recent years, significant advances have been made in the understanding of fabricated technology of solid oxide fuel cells (SOFCs). A three-dimensional model based on the finite element method (FEM) is developed for a single planar SOFC. The uniqueness of this paper is that both anode support electrode and anode active electrode layer fabricated by the freeze-tape-casting process with anisotropic conductivity property is taken into account. The parameter study demonstrates that grading the electron conductivity (increased in both anode and cathode active layers and support layers), in the principle direction to the electrode/electrolyte interface will increase the performance. On the other hand, the results also indicate that increased conductivity perpendicular with fuel transform of active electrode could significantly enhance the gas transport current density. It is concluded that an increased electric conductivity parallel to the electrode/electrolyte and perpendicular to the fuel and gases transport path in the active electrode raises the current density efficiently. Optimization of cell performance requires consideration of anisotropic conductivity that is needed to develop three-dimensional models.
24.	Xu, Min, et al. (author) Solid Oxide Fuel Cell Interconnect Design Optimization considering the Thermal Stresses 2016 In: Science Bulletin. - : Elsevier BV. - 2095-9273. ; 61:17, s. 1333-1344 Journal article (peer-reviewed)abstract The mechanical failure of solid oxide fuel cell (SOFC) components may cause cracks with consequences such as gas leakage, structure instability and reduction of cell lifetime. A comprehensive 3D model of the thermal stresses of an anode-supported planar SOFC is presented in this work. The main objective of this paper is to get an interconnect optimized design by evaluating the thermal stresses of an anode-supported SOFC for different designs, which would be a new criterion for interconnect design. The model incorporates the momentum, mass, heat, ion and electron transport, as well as steady-state mechanics. Heat from methane steam reforming and water–gas shift reaction were considered in our model. The results examine the relationship between the interconnect structures and thermal stresses in SOFC at certain mechanical properties. A wider interconnect of the anode side lowers the stress obviously. The simulation results also indicate that thermal stress of coflow design is smaller than that of counterflow, corresponding to the temperature distribution. This study shows that it is possible to design interconnects for an optimum thermal stress performance of the cell.
25.	Xu, Yilin, et al. (author) Analysis of Thermal Stress in a Solid Oxide Fuel Cell Due to the Sulfur Poisoning Interface of the Electrolyte and Cathode 2021 In: Energy and Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 35:3, s. 2674-2682 Journal article (peer-reviewed)abstract The interface of an electrolyte and cathode strongly determines the oxygen reduction reaction and cell stability, but it is susceptible to sulfur impurities like SO2 in air. In this study, a 3D solid oxide fuel cell model is developed based on experimental characterization to reveal sulfur-deactivating active cathodes. The results indicate that both the average values for electric and ionic current densities drastically decrease after sulfur poisoning; meanwhile, their distributions are also changed, suggesting that the involved oxygen reduction reaction is detrimentally affected. Moreover, the temperature decreases after poisoning due to electrochemical reaction slowdown near the interface of the active cathode and electrolyte. The pronounced temperature changes together with differences in the thermal expansion coefficient of neighboring components, further resulting in uneven stress distributions at the active cathode, possibly bringing out cracks and bending. Thermal stresses are reduced after sulfur poisoning, especially for the third principal stress, which produces a decrement of 154 MPa. The visualized results of the current density, temperature, and stresses are helpful to understand the sulfur poisoning behavior and also to better understand the internal changes of some crucial electrochemical processes beneficial for further optimization of the microstructural stability.
26.	Zeng, Shumao, et al. (author) Effect of the electrochemical active site on thermal stress in solid oxide fuel cells 2018 In: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 165:2, s. 105-113 Journal article (peer-reviewed)abstract A 3D model is developed by coupling the equations for momentum, gas-phase species, heat, electron and ion transport to analyze cell polarization, current density and temperature in solid oxide fuel cells (SOFCs). The increase of active sites is beneficial to improve efficiency of electrochemical reactions, but it can be also detrimental to SOFCs’ stability as it will induce changes in strength and distribution of the thermal stresses. The variation of thermal stresses is systematically studied by grading the active site along the main flow direction. The results indicate that the first principle stress increases with the active site at the interface of electrolyte and electrode, but the shear stress mainly appears in the vicinity of gas inlets, which both suffer from a dramatic change when the active site is enhanced from the initial state to 1.5 times. Moreover, the electrolyte is subjected to large contrary tensile stresses, and the first principle stress is responsible for crack possibly occurring to the electrolyte. We also confirm that the sharp fluctuation of stress caused by the active sites can be relieved through adjusting thickness of the anode active layer.
27.	Zeng, Shumao, et al. (author) Modeling of solid oxide fuel cells with optimized interconnect designs 2018 In: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 125, s. 506-514 Journal article (peer-reviewed)abstract A 3D model is developed to investigate solid oxide fuel cells (SOFCs) contacting with optimized interconnect designs and the results indicate that the current density and thermal stress are closely related to both the shape of tip in interconnects and the depth of it in the cathode. The interconnect with triangular rips can yield the best electrochemical performance compared to those with tips of rectangle and trapezium, and the current densities increase with the depth of tips in cathodes, except the trapezoidal ribs, which shows a concaving change with the depth. The 1st principle stress reaches around 21.9 MPa and 16.6 MPa at the interfaces of electrodes and electrolytes, but it rises to 60 MPa and 18 MPa for the rectangular tips at the air and fuel inlets, respectively, which sharply decreases to nearly 25 MPa and 10 MPa with the depth in cathodes approaching 5 μm. The maximum shear stresses are found to reach 34.4 MPa and 32.1 MPa at the two interfaces, and the triangular tips will induce the most intensive stresses at electrolyte-cathode interface. The resulting conclusions are beneficial to optimize interconnect design to improve the efficiency of current collection and also reduce the risk of generation of remarkable thermal stresses.
28.	Zeng, Shumao, et al. (author) Thermal stress analysis of sulfur deactivated solid oxide fuel cells 2018 In: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 379, s. 134-143 Journal article (peer-reviewed)abstract Hydrogen sulfide in fuels can deactivate catalyst for solid oxide fuel cells, which has become one of the most critical challenges to stability. The reactions between sulfur and catalyst will cause phase changes, leading to increase in cell polarization and mechanical mismatch. A three-dimensional computational fluid dynamics (CFD) approach based on the finite element method (FEM) is thus used to investigate the polarization, temperature and thermal stress in a sulfur deactivated SOFC by coupling equations for gas-phase species, heat, momentum, ion and electron transport. The results indicate that sulfur in fuels can strongly affect the cell polarization and thermal stresses, which shows a sharp decrease in the vicinity of electrolyte when 10% nickel in the functional layer is poisoned, but they remain almost unchanged even when the poisoned Ni content was increased to 90%. This investigation is helpful to deeply understand the sulfur poisoning effects and also benefit the material design and optimization of electrode structure to enhance cell performance and lifetimes in various hydrocarbon fuels containing impurities.
29.	Zhang, Xiaoqiang, et al. (author) Analysing Tortuosity for Solid Oxide Fuel Cell Anode Material : Experiments and Modeling 2023 In: Journal of the Electrochemical Society. - 0013-4651. ; 170 Journal article (peer-reviewed)abstract Solid oxide fuel cells (SOFCs) directly convert chemical energy to electricity with high electrical efficiency. It involves gas transport through the porous electrode to the three-phase boundaries (TPB). The tortuosity of gas transport relates the bulk diffusion of gas in free space to the effective diffusion coefficient of gas migrating through a porous material. Therefore, determining the tortuosity is of great importance. This paper tests button SOFCs with NiO-YSZ as anode material followed by dual beam-focused ion beam scanning electron microscopy (FIB-SEM) to obtain 2D serial slice images. Based on processed 2D images and reconstructed 3D microstructure, the tortuosity is calculated using three approaches i.e., porosity-tortuosity correlations, voxel-based, and path-length-based approaches. The test results show that a decrease in Ni content in the anode greatly decreases the cell performance due to a decreased percolated electronic phase. The sample with low performance has high tortuosity. Different approaches vary regarding the tortuosity value and computational time. The path-length-based approach can achieve reasonable accuracy in a relatively short time but is only valid for using the longest path length.
30.	Zhang, Xiaoqiang, et al. (author) Numerical simulation of solid oxide fuel cells comparing different electrochemical kinetics 2021 In: International Journal of Energy Research. - : Hindawi Limited. - 0363-907X .- 1099-114X. ; 45:9, s. 12980-12995 Journal article (peer-reviewed)abstract Solid oxide fuel cells (SOFCs) produce electricity with high electrical efficiency and fuel flexibility without pollution, for example, CO2, NOx, SOx, and particles. Still, numerous issues hindered the large-scale commercialization of fuel cell at a large scale, such as fuel storage, mechanical failure, catalytic degradation, electrode poisoning from fuel and air, for example, lifetime in relation to cost. Computational fluid dynamics (CFD) couples various physical fields, which is vital to reduce the redundant workload required for SOFC development. Modeling of SOFCs includes the coupling of charge transfer, electrochemical reactions, fluid flow, energy transport, and species transport. The Butler-Volmer equation is frequently used to describe the coupling of electrochemical reactions with current density. The most frequently used is the activation- and diffusion-controlled Butler-Volmer equation. Three different electrode reaction models are examined in the study, which is named case 1, case 2, and case 3, respectively. Case 1 is activation controlled while cases 2 and 3 are diffusion-controlled which take the concentration of redox species into account. It is shown that case 1 gives the highest reaction rate, followed by case 2 and case 3. Case 3 gives the lowest reaction rate and thus has a much lower current density and temperature. The change of activation overpotential does not follow the change of current density and temperature at the interface of the anode and electrolyte and interface of cathode and electrolyte, which demonstrates the non-linearity of the model. This study provides a reference to build electrochemical models of SOFCs and gives a deep understanding of the involved electrochemistry.
31.	Zhang, Xiaoqiang, et al. (author) Parametric study for electrode microstructure influence on SOFC performance 2021 In: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 46:75, s. 37440-37459 Journal article (peer-reviewed)abstract A solid oxide fuel cell (SOFC) is a clean and high-efficiency energy conversion device, which undergoes improvement of performance continuously. The transport of gas species and charges proceed in the porous electrodes. The porous electrodes are also responsible for the removal of exhaust gases. In this paper, a fully coupled 3D single-channel multiphysics computational fluid dynamics (CFD) model was developed based on the finite element method (FEM). The governing equations for momentum, species, charges, and heat transport were solved by a segregated solver. The impact of decreased ionic, electronic, and pore phase tortuosity on the SOFC performance such as fuel utilization, current density, activation overpotential and temperature distribution are analyzed and compared with the base case. In addition to the tortuosity investigation, the volume fraction of the electronic phase in the active layer and the support layer is also investigated using a parametric sweep study. Of all the decreased tortuosity cases, there is an increase in ionic current density and temperature compared with the base case. Except for a decreased pore tortuosity, all other cases led to an increase of electronic current density compared with the base case. The consumption of hydrogen increased for all cases compared with the base case. The activation overpotential increased with decreased electronic phase and pore phase tortuosity, while a decrease of ionic phase tortuosity caused a decrease. Finally, when decreasing all phase tortuosity, both current density, temperature, activation overpotential, and hydrogen consumption increased. For the parametric sweep, there is an optimum electronic phase volume fraction value. This work allows for a better understanding of the relationship between the microstructure and performance of SOFCs. Meanwhile, it provides theoretical guidance for a better porous electrode design.
32.	Zhang, Xiaoqiang, et al. (author) Thermal stress analysis at the interface of cathode and electrolyte in solid oxide fuel cells 2020 In: International Communications in Heat and Mass Transfer. - : Elsevier BV. - 0735-1933. ; 118 Journal article (peer-reviewed)abstract A benign thermal stress in solid oxide fuel cell is of great importance for its stability and the interfaces between different components suffer from unexpected risks of instability such as electrode delamination and crack due to varying thermal expansion coefficients. Besides, chromium poisoning cathode materials leads to phase changes, which possibly induces thermal stresses at the interface of electrolyte and cathode. A three dimensional model at the microscale level is thus developed to unravel the effect of thermal stress on the interface. The model is constructed by governing equations including heat, species, momentum, ion and electronic transportation. The contact modes between the active cathode and electrolyte are studied to reveal the cell performance and thermal stresses, which are strongly related to the number of contact sites and the contact area. Moreover, chromium poisoning the contact causes the disordered distribution of thermal stresses with the increase of the contact sites, worsening the cell current density and durability. The resulting conclusions are expected to offer a solution to avoid possible fatal mechanical failure due to unfavorable interface design and chromium attack.
33.	Zhang, Xiaoqiang, et al. (author) Thermal stress analysis of solid oxide fuel cells with chromium poisoning cathodes 2018 In: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 165:14, s. 1224-1231 Journal article (peer-reviewed)abstract Chromium(Cr) poisoning of the traditional LSM cathode is one of the most critical issues that accounts for instability of solid oxide fuel cells (SOFCs). The poisoning course will introduce alien species in the cathode active regions and it causes phase change and structure deformation, reducing the sites for electrochemical reactions. A 3D model is thus developed by coupling the computational fluid dynamics (CFD) approach with the finite element method to unravel the involved electrochemical processes in chromium poisoning of SOFCs. A function is proposed based on the experimental results to describe the distribution of Cr-related compounds in cathode. The results indicate that chromium poisoning can induce a dramatic decrease in the electric current density, which can also lead to increase of activation polarizations and lower the temperature. Three kinds of thermal stresses are strongly affected by the invasion of chromium into cathodes, which are all significantly reduced with the poisoning extent. The resulting conclusions are beneficial to deeply understand the Cr poisoning of SOFCs and also to material design to prevent cathodes from Cr-based interconnect attack.

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