Analysis of Design Parameters in Anode‐Supported Solid Oxide Fuel Cells Using Response Surface Methodology

Achieving high performance from a solid oxide fuel cell (SOFC) requires optimal design based on parametric analysis. In this paper, design parameters, including anode support porosity, thicknesses of electrolyte, anode support, and cathode functional layers of a single, intermediate temperature, anode‐supported planar SOFC, are analyzed. The response surface methodology (RSM) technique based on an artificial neural network (ANN) model is used. The effects of the cell parameters on its performance are calculated to determine the significant design factors and interaction effects. The obtained optimum parameters are adopted to manufacture the single units of an SOFC through tape casting and screen‐printing processes. The cell is tested and its electrochemical characteristics, which show a satisfactory performance, are discussed. The measured maximum power density (MPD) of the fabricated SOFC displays a promising performance of 1.39 W cm^–2. The manufacturing process planned to fabricate the SOFC can be used for industrial production purposes.     

Micro‐Scale Modeling of a Functionally Graded Ni‐YSZ Anode

A mathematical model was developed to investigate the coupled transport and electrochemical reactions in a nickel‐yttrial‐stablized zirconia (Ni‐YSZ) anode for use in solid oxide fuel cells (SOFCs). The modeling results were consistent with experimental data from the literature. Comparison between conventional non‐graded (uniform random composites) and two types of functionally graded electrodes (FGE), namely particle size graded and porosity graded SOFC anodes were conducted to evaluate the potential of FGE for SOFC. Improved performance of both types of FGE was observed due to reduced mass transport resistance and increased volumetric reactive surface area close to the electrode‐electrolyte interface. It was found that the particle size graded SOFC anode showed the best performance. This paper demonstrates that the SOFC performance could be enhanced by modifying the microstructures of the electrodes. The results presented in this paper provide a better understanding of the working mechanisms of SOFC electrodes and could serve as an important reference for design optimizations.     

质子传导陶瓷电解质燃料电池特性分析

An electrolyte model for the solid oxide fuel cell (SOFC) with proton conducting perovskite electrolyte is developed in this study, in which four types of charge carriers including proton, oxygen vacancy (oxide ion), free electron and electron hole are taken into consideration. The electrochemical process within the SOFC with hydrogen as the fuel is theoretically analyzed. With the present model, the effects of some parameters, such as the thickness of electrolyte, operating temperature and gas composition, on the ionic transport (or gas permeation) through the electrolyte and the electrical performance, i.e., the electromotive force (EMF) and internal resistance of the cell, are investigated in detail. The theoretical results are tested partly by comparing with the experimental data obtained from SrCe0.05M0.05O3-α(M=Yb, Y) cells.     

Mn‐Stabilised Microstructure and Performance of Pd‐impregnated YSZ Cathode for Intermediate Temperature Solid Oxide Fuel Cells

The effect of Mn alloying on PdO powder and Pd‐impregnated Pd + YSZ cathode for the O₂ reduction reaction in intermediate temperature solid oxide fuel cells has been studied in detail. The microstructure, thermal stability, electrochemical activity and performance stability of the powder and cathode were analysed using thermal gravimetric analysis, X‐ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and electrochemical impedance spectroscopy. The results indicate that an addition of 5 mol.‐% Mn effectively inhibits the growth and coalescence of Pd and PdO particles at high temperatures and stabilises the microstructure of the powders and the electrode; as a consequence, the electrochemical performance and stability of the cathode are significantly improved. The electrochemical performance of the Pd + YSZ and Pd_0.95Mn_0.05 + YSZ cathodes so prepared is much better than that of the conventional LSM‐based cathodes and is also comparable with the mixed ionic and electronic conducting oxide cathodes such as LSCF.     

Direct Applicability of La0.6Sr0.4CoO3 – δ Thin Film Cathode to Yttria Stabilised Zirconia Electrolytes at T ≤ 650 °C

For investigating the direct applicability of highly active cobalt containing cathodes on YSZ electrolytes at a lower processing and operating temperature range (T ≤ 650 °C), we fabricated a thin film lanthanum strontium cobalt oxide (LSC) cathode on an yttria stabilised zirconia (YSZ)‐based solid oxide fuel cell (SOFC) via pulsed laser deposition (PLD). Its electrochemical performance (5.9 mW cm^–2 at 0.7 V, 650 °C) was significantly inferior to that (595 mW cm^–2 at 0.7 V, 650 °C) of an SOFC with a thin (t ∼ 200 nm) gadolinium doped ceria (GDC) buffer layer in between the LSC thin film cathode and the YSZ electrolyte. It implies that even though the cathode processing and cell operating temperatures were strictly controlled not to exceed 650 °C, the direct application of LSC on YSZ should be avoided. The origin of the cell performance deterioration is thoroughly studied by glancing angle X‐ray diffraction (GAXRD) and transmission electron microscopy (TEM), and the decomposition of the cathode and diffusion of La and Sr into YSZ were observed when LSC directly contacted YSZ.     

Oxygen Dissociation and Interfacial Transfer Rate on Performance of SOFCs with Metal‐Added (LaSr)(CoFe)O3‐(Ce,Gd)O2 – δ Cathodes

A solid oxide fuel cell (SOFC) unit is constructed with Ni‐Ce_0.9Gd_0.1O_{2 – δ} (GDC) as the anode, yttria‐stabilised zirconia (YSZ) as the electrolyte and Pt, Ag or Cu‐added La_0.58Sr_0.4Co_0.2Fe_0.8O_{3 – δ} (LSCF)–GDC as the cathode. The current–voltage measurements are performed at 800 °C. Cu addition leads to best SOFC performance. LSCF–GDC–Cu is better than LSCF–GDC and much better than GDC as the material of the cathode interlayer. Cu content of 2 wt.‐% leads to best SOFC performance. A cathode functional layer calcined at 800 °C is better than that calcined at higher temperature. Metal addition increases the O₂ dissociation reactivity but results in an interfacial resistance for O transfer. A balance between the rates of O₂ dissociation and interfacial O transfer is needed for best SOFC performance.     

Microscale Modeling of an Anode‐Supported Planar Solid Oxide Fuel Cell

A microscale model of a solid oxide fuel cell (SOFC) involving the mass transfer together with the electrochemical reaction, the transportation of electrons and ions through the respective spherical shaped electron conducting and ion conducting particles inside the electrodes was mathematically developed. Couples of useful parameters were introduced in order to represent the characteristics of the cell. The predicted cell performance was showed according to various operating and design conditions. The effects of microscale electrode geometry on the cell performance were also taken into account. Parametric study according to the volumetric fraction of ionic and electronic conducting particles was conducted in order to examine the effects of operating conditions on the cell overpotentials. The study results substantiate the fact that SOFC overpotential could be effectively decreased by increasing the operating temperature as well as operating pressure. This present study reveals the working mechanisms of SOFC at the microscale level, while demonstrating the use of microscale relations to enhance the SOFC performance. The accuracy of the presented model was validated by comparing with already existing experimental results from the available literatures.     

Wet Atomisation of Gd‐doped CeO2 Electrolyte Slurries for Intermediate Temperatures' Microtubular SOFC Applications

A wet atomising system has been employed as a novel method to prepare ultrafine Gd‐doped CeO₂ (GDC) electrolyte slurries. By changing the fluid flow pressure and repeating the atomisation process several times for the same atomised slurries, we have obtained optimised ultrafine GDC slurry with high‐dispersed and homogeneous distribution. The sizes of the particles of GDC were in the range of tens of nanometres. A highly dense electrolyte layer (membrane) was prepared using the ultrafine GDC slurries for intermediate temperatures microtubular solid oxide fuel cell (SOFC) applications. The SOFC was fabricated by using supporting porous anode tubes of NiO and GDC, and the cathode consisted of La_0.6Sr_0.4Co_0.2Fe_0.8O_3–y and GDC. A dense 10 μm GDC electrolyte layer was obtained at a lower sintering temperature of 1,250 °C for 1 h. The SOFC was tested with humidified (3% H₂O) hydrogen as a fuel and the static air as an oxidant, and the tubular cell maintained its high performance even at 500 °C.     

Effects of Microstructural Functional Layers on Flat‐Tubular Solid Oxide Fuel Cells

The functional layer of a flat‐tubular solid oxide fuel cell (SOFC) is examined using a three‐dimensional microscale electrode model. SOFC electrodes essentially include two types of layers: a structural layer and a functional layer. The structural layers, which are the anode support layer and the cathode current collector layer, are composed of large particles with a high porosity that facilitates gas diffusion. The functional layers consist of small particles with a low porosity that increases the triple phase boundary (TPB) reaction area and reduces the activation overpotential. In the model, the particle diameter and functional layer thickness are adjusted and analyzed. The effects of the two parameters on the performance of the functional layer are monitored in the contexts of several multilateral approaches. Most reactions occurred near the electrode–electrolyte interface; however, an electrode design that included additional TPB areas improved the electrode performance. The role of the functional layer in a flat‐tubular SOFC is examined as a function of the functional layer particle size and thickness. The performance of a cell could be enhanced by preparing a functional layer using particles of optimal size and thickness, and by operating the device under conditions optimized for these parameters.     

Numerical Investigation into Thermofluidic and Electrochemical Characteristics of Tubular‐type SOFC

Three‐dimensional simulations based on a multi‐physics model are performed to examine the thermofluidic and electrochemical characteristics of a tubular, anode‐supported solid oxide fuel cell (SOFC). The simulations focus on the local transport characteristics of the cathode and anode gases and the distribution of the temperature field within the fuel cell. In addition, the electrochemical properties of the SOFC are systematically examined for a representative range of inlet gas temperatures and pressures. The validity of the numerical model is confirmed by comparing the results obtained for the correlation between the power density and the current density with the experimental results presented in the literature. Overall, the present results show that the performance of the tubular SOFC is significantly improved under pressurised conditions and a higher operating temperature.     

Cu-Ce-Zr-O／YSZ阳极材料以甲烷为燃料时的抗积炭性能

为研究甲烷在固体氧化物燃料电池中操作稳定性,分别采用共沉淀法和柠檬酸溶胶.凝胶法制备了10%CuO-Ce0.15Zr0.85O2催化剂,并以此为阳极催化剂、LSM为阴极制成了YSZ电解质支撑的SOFC单电池.用XRD对材料进行表征;用SEM对阳极,阴极进行表征.以甲烷为燃料对单电池发电性能进行测试,研究了两种不同方法制备的Cu-Ce-Zr-O阳极催化剂的抗积炭性能.相对于共沉淀法,溶胶-凝胶法制备的阳极结构和发电性能都要优于前者.长期稳定性方面,共沉淀法和溶胶.凝胶法制备的Cu-Ce-Zr-O/YSZ阳极都较传统的Ni-YSZ阳极更能够长期稳定运行.     

Electrochemical Performance of a Ni and YSZ Composite Synthesised by Ultrasonic Spray Pyrolysis as an Anode for SOFCs

The electrochemical performance of an anode material for a solid oxide fuel cell (SOFC) depends highly on microstructure in addition to composition. In this study, a NiO–yttria‐stabilised zirconia (NiO–YSZ) composite with a highly dispersed microstructure and large pore volume/surface area has been synthesised by ultrasonic spray pyrolysis (USP) and its electrochemical characteristics has been investigated. For comparison, the electrochemical performance of a conventional NiO–YSZ is also evaluated. The power density of the zirconia electrolyte‐supported SOFC with the synthesised anode is ∼392 mW cm^–2 at 900 °C and that of the SOFC with the conventional NiO–YSZ anode is ∼315 mW cm^–2. The improvement is ∼24%. This result demonstrates that the synthesised NiO–YSZ is a potential alternative anode material for SOFCs fabricated with a zirconia solid electrolyte.     

Multiscale model for solid oxide fuel cell with electrode containing mixed conducting material

Solid oxide fuel cells (SOFCs) with electrodes that contain mixed conducting materials usually show very different relationships among microstructure parameters, effective electrode characteristics, and detailed working processes from conventional ones. A new multiscale model for SOFCs using mixed conducting materials, such as LSCF or BSCF, was developed. It consisted of a generalized percolation micromodel to obtain the electrode properties from microstructure parameters and a multiphysics single cell model to relate these properties to performance details. Various constraint relationships between the activation overpotential expressions and electric boundaries for SOFC models were collected by analyzing the local electrochemical equilibrium. Finally, taking a typical LSCF‐SDC/SDC/Ni‐SDC intermediate temperature SOFC as an example, the application of the multiscale model was illustrated. The accuracy of the models was verified by fitting 25 experimental I‐V curves reported in literature with a few adjustable parameters; additionally, and several conclusions were drawn from the analysis of simulation results. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3786–3803, 2015     

Tailoring Electrochemical Property of Layered Perovskite Cathode by Cu‐doping for Proton‐Conducting IT‐SOFCs

Layered perovskite oxide YBaCuCoO_5+x (YBCC) was synthesized by an EDTA‐citrate complexation process and was investigated as a novel cathode for proton‐conducting intermediate temperature solid oxide fuel cells (IT‐SOFCs). The thermal expansion coefficient (TEC) of YBCC was 15.3 × 10⁻⁶ K⁻¹ and the electrical conductivity presented a semiconductor‐like behavior with the maximum value of 93.03 Scm⁻¹ at 800 °C. Based on the defect chemistry analysis, the electrical conductivity gradually decreases by the introduction of Cu into Co sites of YBaCo₂O_5+x and the conductor mechanism can transform from the metallic‐like behavior to the semiconductor‐like behavior. Thin proton‐conducting (BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3–δ) BZCYYb electrolyte and NiO–BZCYYb anode functional layer were prepared over porous anode substrates composed of NiO–BZCYYb by a one‐step dry‐pressing/co‐firing process. Laboratory‐sized quad‐layer cells of NiO‐BZCYYb / NiO‐BZCYYb / BZCYYb / YBCC with a 20 μm‐thick BZCYYb electrolyte membrane exhibited the maximum power density as high as 435 mW cm⁻² with an open‐circuit potential (OCV) of 0.99 V and a low interfacial polarization resistance of 0.151 Ωcm² at 700 °C. The experimental results have indicated that the layered perovskite oxide YBCC can be a cathode candidate for utilization as proton‐conducting IT‐SOFCs.     

Planar Metal‐Supported SOFC with Novel Cermet Anode

Metal‐supported solid oxide fuel cells are expected to offer several potential advantages over conventional anode (Ni‐YSZ) supported cells. For example, increased resistance against mechanical and thermal stresses and a reduction in material costs. When Ni‐YSZ based anodes are used in metal supported SOFC, elements from the active anode layer may inter‐diffuse with the metallic support during sintering. This work illustrates how the inter‐diffusion problem can be circumvented by using an alternative anode design based on porous and electronically conducting layers, into which electrocatalytically active materials are infiltrated after sintering. The paper presents the electrochemical performance and durability of the novel planar metal‐supported SOFC design. The electrode performance on symmetrical cells has also been evaluated. The novel cell and anode design shows a promising performance and durability at a broad range of temperatures and is especially suitable for intermediate temperature operation at around 650 °C.     

Modeling and Optimization of Anode‐Supported Solid Oxide Fuel Cells on Cell Parameters via Artificial Neural Network and Genetic Algorithm

An artificial neural network (ANN) and a genetic algorithm (GA) are employed to model and optimize cell parameters to improve the performance of singular, intermediate‐temperature, solid oxide fuel cells (IT‐SOFCs). The ANN model uses a feed‐forward neural network with an error back‐propagation algorithm. The ANN is trained using experimental data as a black‐box without using physical models. The developed model is able to predict the performance of the SOFC. An optimization algorithm is utilized to select the optimal SOFC parameters. The optimal values of four cell parameters (anode support thickness, anode support porosity, electrolyte thickness, and functional layer cathode thickness) are determined by using the GA under different conditions. The results show that these optimum cell parameters deliver the highest maximum power density under different constraints on the anode support thickness, porosity, and electrolyte thickness.     

Thermodynamic Analysis of Methane-fueled Solid Oxide Fuel Cells Considering CO Electrochemical Oxidation

abstract Thermodynamic analyses in the literature have shown that solid oxide fuel cells (SOFCs) with proton conducting electrolyte (H-SOFC) exhibited higher performance than SOFC with oxygen ion condu...     

Spatial Distribution of Electrochemical Performance in a Segmented SOFC: A Combined Modeling and Experimental Study

Spatially inhomogeneous distribution of current density and temperature in solid oxide fuel cells (SOFC) contributes to accelerated electrode degradation, thermomechanical stresses, and reduced efficiency. This paper presents a combined experimental and modeling study of the distributed electrochemical performance of a planar SOFC. Experimental data were obtained using a segmented cell setup that allows the measurement of local current‐voltage characteristics, gas composition and temperature in 4 × 4 segments. Simulations were performed using a two‐dimensional elementary kinetic model that represents the experimental setup in a detailed way. Excellent agreement between model and experiment was obtained for both global and local performance over all investigated operating conditions under varying H₂/H₂O/N₂ compositions at the anode, O₂/N₂ compositions at the cathode, temperature, and fuel utilization. A strong variation of the electrochemical performance along the flow path was observed when the cell was operated at high fuel utilization. The simulations predict a considerable gradient of gas‐phase concentrations along the fuel channel and through the thickness of the porous anode, while the gradients are lower at the cathode side. The anode dominates polarization losses. The cell may operate locally in critical operating conditions (low H₂/H₂O ratios, low local segment voltage) without notably affecting globally observed electrochemical behavior.     

In Situ X‐Ray Diffraction and Stress Analysis of Solid Oxide Fuel Cells

To increase the long term stability and performance of solid oxide fuel cell (SOFC) materials, it is important to understand the main degradation processes in their functional layers. In this work, the interface between electrolyte and anode material was investigated by in situ X‐ray diffraction (XRD) stress and phase analysis. It has been found that the determining process for the initial degradation of SOFC is the reduction of the anode material with hydrogen. During this process a tensile strength of 600–700 MPa is measured. These stresses are induced in the electrolyte material and produce crack networks. The reduction from nickel oxide to pure nickel was monitored by in situ phase analysis. This reaction induces tensile stress at the interface between electrolyte and anode. The stress produced in the electrolyte material was also confirmed by the observation of crack networks detected using scanning electron microscopy (SEM). Finally, the reducing process was optimized using different process gases, decreasing the destructive tensile stress level.     

Improved Electrodes/Electrolyte Interfaces for Solid Oxide Fuel Cell by Using Dual‐Sized Powders in Electrolyte Slurry

The dense electrolyte film with the rough surfaces for solid oxide fuel cell (SOFC) was fabricated on NiO/yttria‐stabilized zirconia (YSZ) anode substrate by using dual‐sized YSZ powders without additional effort to roughen electrolyte film. The dual‐sized YSZ powders consisted of the fine YSZ powder and the coarse YSZ powder at different weight ratios. Incorporation of the coarse YSZ powder into the fine YSZ powder is in order to increase the surface roughness of electrolyte film, and the surface roughness obviously increased with the increase of coarse YSZ powder. The rough surfaces resulted in an enlargement of the electrochemical active area. It was found that electrode polarization was reduced evidently and cell electrochemical performance was enhanced, as the surface roughness increased. However, the excessive coarse YSZ powder was not beneficial for densification of electrolyte film and thus the open‐circuit voltage (OCV) was declined. The cell with 17 wt.% coarse YSZ powder in the electrolyte exhibited the best performance and the maximum power density was 1,930 mW cm^–2 at 800 °C.