Temperature Solid Oxide Fuel Cells Research Articles

Design of a High Temperature Solid Oxide Fuel Cell: A Review

Design of a High Temperature Solid Oxide Fuel Cell: A Review

An efficient Sm and Ge co-doped ceria nanocomposite electrolyte for low temperature solid oxide fuel cells

In this study we present a new nanocomposite electrolyte based on samarium (Sm) and germanium (Ge) co-doped ceria Ce0.7Sm0.15Ge0.15O2-δ (SGeDC). The nanocomposite electrolyte was prepared using co-precipitation method. The crystal structure and surface morphology were determined using x-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Four probe dc conductivity indicated the value of 0.074S/cm at 650°C. The Fuel cell performance was carried out using hydrogen as fuel. The maximum OCV observed was 0.95V while the peak power density came out to be 600mW/cm2 at 600°C. It is suggested that adding Ge, the conductivity as well as performance of this new nanocomposite electrolyte is comparatively enhanced and it can find potential applications in low temperature solid oxide Fuel cells (LTSOFCs).

Electrochemical Characteristics of La0.65Sr0.3 MnO3 and La0.8Sr0.2MnO3 Nanoceramic Cathode Powders for Intermediate Temperature Solid Oxide Fuel Cell (SOFC) Application

Electrochemical Characteristics of La0.65Sr0.3 MnO3 and La0.8Sr0.2MnO3 Nanoceramic Cathode Powders for Intermediate Temperature Solid Oxide Fuel Cell (SOFC) Application

(Invited) Understanding Anode and Cathode Reaction Mechanisms for Proton Conducting Intermediate Temperature Solid Oxide Fuel Cells

The anode and cathode reaction processes for conventional solid oxide fuel cells (SOFC) have been widely studied. In comparison, there are many unknowns about the basic electrochemical behaviors and mechanisms for the anode and cathode reactions of proton conducting SOFC, especially at intermediate temperature (IT) range of ~400-700oC when the cells approach ideal proton conducting behaviors. At intermediate temperature, due to the change of the dominating ionic conducting species from oxide ion to proton, the fundamental reaction pathways would change for both the anode and cathode reactions. Accompanied with such changes, many interesting electrochemical behaviors arise for proton conducting IT-SOFC. For example, it is well known that the Ni-based cermet anode for conventional oxide ion SOFC are susceptible to poisoning by sub-ppm level hydrogen sulfide (H2S) and not very sensitive to carbon monoxide (CO). In comparison, literature seems to suggest that the Ni-proton conducting oxide cermet as the anode for proton conducting IT-SOFC shows much better resistance against low ppm-level H2S but is poisoned by percentage level CO. This study aims to understand the fundamental reaction processes for both the anode (hydrogen electrode) and cathode (air electrode) of proton conducting IT-SOFCs. Electrochemical tests are carried out based on the concept of “controlled poisoning”, which is to selectively slow down a specific part of the electrode reaction using a specially chosen “poison” in order to help understand the fundamentals about the electrode reactions for proton-conducting IT-SOFCs. In particular, for the anode, H2S is used as a “Ni poison” and CO2 as a proton conducting oxide poison, while for the cathode, either H2O or CO2 is used. The measured electrochemical behaviors for different anode- or electrolyte-supported full cells and symmetrical cells including those with patterned (metal) electrodes are compared with those of conventional oxide ion based SOFCs. The results for those experiments aimed at understanding the similarity and differences between proton conducting SOFC and conventional oxide ion conducting SOFC will be presented, and their implications on the anode and cathode reaction mechanisms and the roles (including electrocatalytic roles) of proton conducting oxides in those electrode reactions for proton conducting IT-SOFC will be discussed.

Influence of Copper‐based Anode Composition on Intermediate Temperature Solid Oxide Fuel Cells Performance

AbstractPlanar solid oxide fuel cells (SOFCs), which are intended to be used in the intermediate temperature range (600–800 °C) and whose supporting anode contains various amount of Cu in Li‐doped gadolinia‐doped ceria matrix, are produced and characterized in the present work. Intermediate temperature solid oxide fuel cell (IT‐SOFC) performances are investigated by recording polarization and power density at different temperatures. Electrochemical impedance spectroscopy (EIS) measurements are carried out to analyze how internal resistances change as function of temperature and, above all, for variable Cu content. The gadolinia‐doped ceria electrolyte microstructure and the cell integrity after sintering are also shown to depend on the initial CuO content in the anode. The electronic conductivity increases with Cu content within the anodic cermet. When the anode contains more than 25 vol.% CuO, a dense Li‐doped gadolinia‐doped ceria electrolyte can be obtained by sintering at 900 °C. Conversely, CuO load in excess to 50% in the anode is detrimental because of the formation of macroscopic cracks within the electrolyte. Intermediate temperature solid oxide fuel cells produced with an anodic layer containing 50 vol.% CuO show the lowest impedance parameters.

Sputtered Nanoporous PtNi Thin Film Cathodes with Improved Thermal Stability for Low Temperature Solid Oxide Fuel Cells

Nanoporous PtNi alloy thin film was demonstrated to effectively improve the thermal stability of cathode under high temperature fuel cell operation. The grain growth, which indicates the agglomeration of the nanoparticles, were constrained, as observed by comparing the surface morphologies and grain sizes in bulk of film between pure Pt and PtNi alloy cathodes. The constrained grain growth by alloying with Ni maintained the porosity in bulk of cathode film for sufficient cathode oxygen diffusion and adsorption/dissociation processes. Fuel cell using Pt67-Ni33 cathode better maintained the output current density than the cell using pure Pt cathode by 26% after 48hours of continuous operation.

Nickel foam anode-supported solid oxide fuel cells with composite electrolytes

In this paper, three composite electrolytes (Ce0.8Sm0.2O1.9/Na2CO3) SDC, (Ce0.8Gd0.2O1.9/Na2CO3) GDC and (La0.8Sr0.2Ga0.8Mg0.2O3−δ/Na2CO3) LSGM have been studied to review the effect of Na2CO3, present as second phase, and effect of Ni support, sintering and pressure for dry pressing for fuel cell performance. The electrolytes were prepared through a co-precipitation method. Different techniques were used to characterize the prepared electrolytes. The crystal structures were determined using x-ray diffraction (XRD) and structural morphologies were analyzed through scanning electron microscopy (SEM). The four-probe dc conductivity and two probe AC impedance analysis were carried out in open air. The fuel cell performance was determined with and without Ni support on anode side which resulted in a considerable difference in obtained peak power densities. It is suggested that prepared electrolytes can find potential applications in low temperatures Solid Oxide Fuel Cells (LT-SOFCs).

An Efficient Ge and Sm Co-Doped Ceria Nanocomposite Electrolyte for Low Temperature Solid Oxide Fuel Cells

Electrochemical studies of Fuel cell with different composite electrolyte In this paper, three composite electrolytes (Ce0.8Sm0.2O1.9/Na2CO3) SDC, (Ce0.8Gd0.2O1.9/Na2CO3) GDC and (La0.8Sr0.2Ga0.8Mg0.2O3−δ/Na2CO3)LSGM nanocomposite electrolytes have been studied, also see the effect of Na2CO3, present as second phase, and effect of Ni support, sintering and pressure for dry pressing for fuel cell performance. The electrolytes were prepared through co-precipitation method. Different techniques were used to characterize the prepared electrolytes. The crystal structures were determined using x-ray diffraction (XRD) and structural morphologies were analyzed through scanning electron microscopy (SEM). The four probe dc conductivity and two probe AC impedance analysis were carried out in open air. The fuel cell performance was determined with and without Nickel support on anode side which resulted in a considerable difference in obtained peak power densities. It is suggested that prepared electrolytes can find potential applications in low temperatures Solid Oxide Fuel Cells (LT-SOFCs). Key words: nanocomposite, LTSOFCs, Crystal structure, SDC, Sintering

Electrochemical Properties of YSZ/GDC Bi-Layer Produced by One-Side Dip Coating Method for the Intermediate Temperature Solid Oxide Fuel Cell

The Gadolinium Doped Ceria (GDC) diffusion barrier layer was formed on the Yttrium Stabilized Zirconia (YSZ) electrolyte to apply La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode system for lowering the operating temperature of Solid Oxide Fuel Cell. In this study, YSZ and GDC layers were coated by one-side dip coating method which possibly coat one-side of anode substrate. Cu(NO3)2 was infiltrated into pre-sintered substrate of anode and electrolyte as a sintering aid for lowering the co-firing temperature which was enough to produce dense electrolyte layer. LSCF-GDC cathode was coated on the GDC layer by screen printing method. The cells were operated at 600℃ and 650℃. The microstructures of the surface and cross-section were observed by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). The ohmic and polarization resistance were measured by the Electrochemical Impedance Spectroscopy (EIS).

Comparison of Pr-Based Cathodes for IT-SOFCs in the Ruddlesden-Popper Family

The present study is focused on alternative oxygen electrodes for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs). Among the K2NiF4 type compounds, the nickelates Ln2NiO4+δ (Ln = La, Pr or Nd) have already shown their suitability as oxygen electrode due to their mixed ionic and electronic conductivity (i.e. MIEC properties). Pr2NiO4+δ showed the best electrochemical properties [1] at intermediate temperature among the three nickelates: R p = 0.15 Ω∙cm² at 600 °C for instance, for screen printed electrode. Interestingly, the ageing of the Pr2NiO4+δ//CGO//8YSZ symmetrical half cells during 1 month under air shows no significant change in the R p value at i dc = 0 condition, despite the decomposition of Pr2NiO4+δ into the third term of the R.P. series (Prn+1NinO3n+1), Pr4Ni3O10+δ, the perovskite PrNiO3-δ and Pr6O11. Such decomposition was observed after one month at different SOFC operating temperatures, namely 600, 700 and 800 °C under air [2]. Aiming at further understanding the relationship between the electrochemical behavior and the phase stability, the physico-chemical and electrochemical properties of Pr4Ni3O10+δ and PrNiO3-δwere thoroughly studied. PrNiO3-δ is chemically very stable at operating temperatures up to one month while the electrochemical properties remain limited. The symmetrical half-cell with PrNiO3-δ electrode shows relatively high R p value, for instance R p = 0.9 Ω∙cm² at 600 °C, which is almost six times higher than the one of Pr2NiO4+δ [3]. On the other hand, Pr4Ni3O10+δ is a very promising material. In addition, Pr4Ni3O10+δ is highly chemically stable during long term up to 1 month under air at 600, 700 and 800 °C, contrarily to Pr2NiO4+δ [4]. Moreover, a single cell Pr4Ni3O10+δ//CGO//8YSZ//Ni-YSZ produces a very high power density of 1.60 W·cm-2 at 800 °C and 0.68 W·cm-2 at 700 °C. Hence, the electrochemical behaviors of Pr4Ni3O10+δ and Pr2NiO4+δ are similar, but Pr4Ni3O10+δis a more promising oxygen electrode since it is highly chemically stable. Herein, the comparison of Pr-based cathodes, and more especially their chemical stability, conductivity and electrochemical properties will be presented and discussed in details.

Developing Redox Stability of Ceramic Anode Supported Intermediate Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are eco-friendly and promising electrochemical devices which can convert chemical energy of fuel to electrical energy. They have many advantages including high conversion efficiency (45~65%) and fuel flexibility [1]. However they have to stand under harsh condition such as frequent load cycles, operational temperature fluctuations, and pump malfunctions. They should also operate over 40,000h on combined head and power (CHP) plants for commercial uses [2]. Mixed ionic and electronic conductors (MIEC) normally (particularly, Ni-YSZ cermets) use for the anode material of SOFCs, because of their good electrical conductivity and high catalytic activity for hydrogen oxidation. However Ni is likely to agglomerate at high temperature, thus resulting in reducing electrical conductivity with the significant loss of Ni-Ni contacts [3]. In addition, when SOFCs are exposed on the fuel starvation condition in the anode side, it can occur mechanical failure of anode substrates with the significant chemical expansion due to oxidation of Ni to NiO [4]. Furthermore Ni is not albe to use hydrocarbon fuel because of carbon deposition and has low tolerance to Sulphur.[4] In order to solve those issues, ceramic anode materials, La0.75Sr0.25Cr0.5Mn0.5O3- δ(LSCM), have been considered as a candidate material for the SOFC anode due to high chemical stability and good electrical conductivity. Furthermore, LSCM anode materials are fabricated with the highly conductive Nd0.1Ce0.9O2(NDC) electrolytes to investigate the practicability of SOFCs at the intermediate temperature (IT), since decreasing the operating temperature of SOFCs is one of possible solutions to enhance operational stability and long-term durability. In this work, LSCM anode-supoorted cells are fabricate by the using uniaxial pressing and drop-coating methods. For the electrical characterizations of LSCM-based cells electrochemical impedance spectra (EIS) and I-V (current-voltage) polarization curves are measured by using the Potentiostat/Galvanostatntequipped with impedance spectroscopy (Biologic) field emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD) spectroscopy are used for the physicochemical analysis of LSCM anode-cells. [1] Steele, Brian CH, and Angelika Heinzel. "Materials for fuel-cell technologies." Nature 414.6861 (2001): 345-352. [2] Wachsman, Eric D., and Kang Taek Lee. "Lowering the temperature of solid oxide fuel cells." Science 334.6058 (2011): 935-939. [3] Simwonis, D., F. Tietz, and D. Stöver. "Nickel coarsening in annealed Ni/8YSZ anode substrates for solid oxide fuel cells." Solid State Ionics 132.3 (2000): 241-251. [4] Sarantaridis, D., and A. Atkinson. "Redox Cycling of Ni‐Based Solid Oxide Fuel Cell Anodes: A Review." Fuel cells 7.3 (2007): 246-258. [5] Yokokawa, Harumi, et al. "Fundamental mechanisms limiting solid oxide fuel cell durability." Journal of Power Sources 182.2 (2008): 400-412. [6] Tao, Shanwen, and John TS Irvine. "A redox-stable efficient anode for solid-oxide fuel cells." Nature materials 2.5 (2003): 320-323. * Corresponding author: jyoung@sejong.ac.kr (J.-Y. Park). Keywords : solid oxide fuel cells, ceramic anode, La0.75Sr0.25Cr0.5Mn0.5O3- δ, electrochemical performances, durability.

Sodium Doped Strontium Silicates as Electrolyte for Intermediate Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are considered as important green energy devices for the 21st century due to its high chemical to electrical energy conversion efficiency, modular design and fuel flexibility. However, the widespread commercialization of SOFCs has not been realized due to its cost associated with cell fabrication, electrode/ electrolyte materials and its maintenance. The conventional electrolyte, Yttria-stabilized Zirconia requires high operating temperature (800 - 1000 0C) to achieve sufficient oxide-ion conductivity, which increases the cost and exacerbates the instability between the components [1]. Therefore, there is considerable interest in developing alternative electrolytes with oxide ion conductivity > 10−2 S/ cm at intermediate temperature (IT) (500 - 700 0C). Hence, here we successfully synthesized IT electrolytes Sr1−xNaxSiO3− d (x = 0.0, 0.45) by solid state reactions. XRD, Solid state NMR, FE-SEM/ EDS and impedance spectroscopy are used for the structural and electrical studies. From the XRD, it is evident that both the samples can be indexed in monoclinic c2/c space group (15) [2]. 29Si solid state NMR reveals a sharp single peak at −86 ppm for SrSiO3. Broadening of the peak at ~ −89 ppm indicates the presence of glassy Na2Si2O5 phase in Sr0.55Na0.45SiO3− d [3]. FE-SEM image of Sr0.55Na0.45SiO3− d clearly shows the amorphous Na2Si2O5 dispersed in SrSiO3 insulating crystalline phase. EDS analysis confirms that grain is Na-deficient (SrSiO3) and grain boundary (GB) is Na-rich phase (Na2Si2O5). The doping of Na into SrSiO3 leads to the formation and segregation of glassy Na2Si2O5 along the GBs, which is the main reason for high electrical conductivity. Among, Sr1−xNaxSiO3− d (x = 0.0, 0.45), SrSiO3 behaves as an insulator and Sr0.55Na0.45SiO3− d exhibits highest conductivity in the measured temperature range, which makes it as electrolyte for intermediate temperature SOFCs. Figure 1

Modelling Microstructural and Chemical Degradation of Ferritic Stainless Steels for SOFC Interconnects

Ferritic Fe-based (FeCrX) alloys forming a protective chromium oxide film are used for providing electrical interconnection in high temperature Solid Oxide Fuel Cells (SOFC) are susceptible to degradation mechanisms in the presence of high temperatures (>600oC), and humid air. These translate by the increase in interconnect electrical contact resistance and the formation of volatile chromium species causing poisoning of the adjacent cathode. Modelling tools and techniques are increasingly becoming popular to gain better understanding of the degradation mechanisms that lead to the formation of volatile chromium species. This research work examines the oxidation behaviour of uncoated ferritic stainless steels system operated at temperature of 700oC in both wet (3% humidity) and dry conditions. A model is presented based on the physical processes involved. The model is able to predict the weight gain of the samples upon oxidation, the oxide film thickness, the volatilization of chromium and the useable lifetime of interconnects based on chromium depletion. Parameter determination from standard experiments is discussed along with the physical and design insights from the model. Perhaps most importantly the model provides recommendations regarding accelerated testing of FeCrX interconnects and control of the Chromia film thickness. Acknowledgements: This work was supported by the European FCH JU in project SCORED 2:0 under contract no. 325331 and the EPSRC.

Study on the ORR Mechanism and CO2-Poisoning Resistance of La0.8Sr0.2MnO3-δ-coated Ba0.5Sr0.5Co0.8Fe0.2O3-δ Cathode for Intermediate Temperature Solid Oxide Fuel Cells

The LSM-coated BSCF cathode with 3D core-shell architecture had been fabricated by the solution impregnation technology and presented the excellent CO2-poisoning resistance at the operating temperature. The LSM shell limited the combination of CO2 and BSCF, making that the 3D core-shell cathode present the great CO2-poisoning resistance. The three-electrode measurement was carried out to investigate the ORR mechanism. As the intervention of LSM shell, the LSM-coated BSCF presented the different ORR rate-determining step comparing with the BSCF cathode. The formation of lattice oxygen was the rate-determining step for the LSM-coated BSCF cathode, while molecular oxygen surface adsorption for the BSCF cathode. In addition, the electrochemical stability was promoted greatly with the protection of LSM shell. The LSM-coated BSCF cathode could get the stable state at about 11 h under cathodic current passage of 400 mAcm-2 at 650 °C, while it was about 70 h for the BSCF cathode. The excellent electrochemical performance and CO2-poisoning resistance made that the LSM-coated BSCF cathode appears to be a promising cathode for IT-SOFCs.

Nanoparticle Surface Modification Enhanced Anode Performance in La1.7Sr0.3Fe0.9Ru0.1O4 for Intermediate Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) have drawn remarkable attention in recent years due to their distinctive advantages of high efficiency, fuel variety and low environment pollution. Along the way to designing of new cathode materials for SOFCs, an understanding of the mechanism of oxygen reduction reaction (ORR) plays a key role, especially the interaction between O2 molecule and surface of cathode. The results of the first principles calculations of the atomic and electronic structure of a layered perovskite LaSrCo0.5Feo.5O4-δ used as a cathode material for solid oxide fuel cells (SOFCs) are presented and discussed. The oxygen vacancy formation energies is found to be smaller than LaSrCoO4 and slightly lower than the other perovskite, e.g. (La, Sr)MnO3, which widely used as a cathode because of its excellent catalytic activity. From a detailed analysis of difference electron densities, the presence of oxygen vacancies can induce local charge redistribution. Furthermore, a strong hybridization between Co-Oad and Fe-Oad for molecular adsorption was obtained by analysis of density of states. Our results show how the mixed B-site ions produce the excellent adsorption and conduction performance of LaSrCo0.5Feo.5O4-δ and fully support its potential application in next-generation SOFCs.

Investigation of Cr Poisoning on the LSCF Cathode Under Different Temperatures for Solid Oxide Fuel Cell

The Cr poisoning effect on cathode is identified as a considerable negative factor for the long-term performance of Solid Oxide Fuel Cells(SOFCs). With the lowering of the operating temperature of SOFCs, more high performance cathode materials could be used. In this study, the relation between testing temperature of SOFC and the Cr poisoning effect on La0.6Sr0.4Fe0.8Co0.2O3-δ - Ce0.9Gd0.1O2-δ symmetric cells is investigated . Combined with the SEM and XRD , a secondary phase, identified as SrCrO4 is found formed on the surface of cathode to cause serious cathode degradation. The EIS shows that as the increasing of performance temperature from 550°C to 750°C, the Cr poisoning effect firstly increases to the maximal poisoning effect on 650°C and then decreases as the increasing of testing temperature. The evaporation of Cr from metallic interconnect could increase with the rising of testing temperature, However , the surface incorporation and exchange of Cr or O2 may not obey the tendency of temperature. With the DRT calculation, the Cr is more easily to occupy the Co sites on the LSCF but O is more tend to occupy the Sr sites, which may lead to the existence of the peak performance temperature for the remarkable Cr poisoning effect on LSCF.

Electrochemcial Performances of La-Doped SrTiO3 Anode Materials for Intermediate Temperature-Solid Oxide Fuel Cells

Anode plays a very important role in the performance of solid oxide fuel cells (SOFCs) [1, 2]. In order to improve the cell performance proper anode materials should be selectd with suitable cell fabrication techniques. La-doped SrTiO3 (La0.4Sr0.6TiO3, LST) has received many attentions as an alternative anode material to state-of-art Ni-cermets anode for solid oxide fuel cells (SOFCs), because of its high redox stability, good electrical conductivity, and similar thermal expansion properties of yttria-stablized zirconia (YSZ) elecrolytes [3, 4]. Nowdays, decreasing the operating temperature of SOFCs down to intermediate temperature (IT) range (less than 800) is required to improve long-term durability and operational stability with economical advantages [5]. Hence, in this work, LST anode materials are fabricated with the highly conductive Nd0.1Ce0.9O2 (NDC) electrolytes and characterized to investigate the feasibility of SOFCs at the IT. In addition, LST is composited with the NDC to improve the ionic conductivity and decrease the thermal expansion mismatch of anode materails to the electrolyte. The Electrochmical impedance spectra (EIS) analysis shows that the polarization resistance of LST-NDC composite anode decreases with increasing of NDC concentrations, and 60:40 (LST:NDC in weight fraction) exhibits the lowest polarization resistance value at 650. The maximum power density of LST-NDC composite anode-cell is 143 mW cm-2 at 650, and thus we confirm the possbilty of LST as an anode material for the application of IT-SOFCs.

Microstructural and Electrochemical Characterisation of Degradation in Nickel Impregnated Scandia-Stabilised Zirconia Electrode during Isothermal Annealing

The impregnation of nickel into porous ceramic scaffolds has been introduced as a promising alternative fabrication technique for solid oxide fuel cell (SOFC) anode as compared to conventional powder mixing [1]. Nevertheless, the stability of impregnated electrodes has not been extensively studied and understood [2]. SOFCs operate at a temperature range from 500 oC to 1000 oC and are expected to have a life time of 40,000 hours [3]. In this study, we examine the degradation of impregnated electrodes in a wet hydrogen atmosphere at a working temperature of SOFCs. Nickel was impregnated into a porous scandia-stabilised zirconia scaffold through 12 impregnation cycles. The impregnated electrodes contained approximately 40 wt% of nickel. Continuous van der Pauw measurement was carried out when the electrode was aged at 650 oC, 800 oC and 950 oC in an atmosphere with 5 vol% hydrogen and 95 vol% nitrogen, at open circuit. A fall in sheet conductivity was found in the electrode during ageing within 1000 min. The conductivity fall was attributed to nickel microstructural evolution during ageing. Electrochemical impedance spectra were collected at a constant time intervals during isothermal annealing at 650 oC, 800 oC and 950 oC for the impregnated electrode. Four resistance contributions were decoupled by equivalent circuit fitting, i.e. the ohmic resistance, the oxygen transfer resistance and the anodic reaction resistance, and the gas diffusion resistance. The increase in both the ohmic resistance and the polarisation resistances with time revealed the isothermal degradation brought about a diminishing active anode area. A more pronounced decrease in anodic polarisation resistance suggested a reduction in triple phase boundary (TPB) density. Secondary electron images of electrodes before and after ageing showed an increase in nickel particle size and a decrease in the number of particles, providing microstructural evidence of nickel coarsening. Nickel coarsening was identified as the main mechanism of degradation for the electrode in wet hydrogen as it caused a reduction in both TPB sites and percolating nickel paths. Combining time-dependent electrochemical performance with post-mortem electrode microstructure clarifies the physical processes behind the degradation quantified by increasing area specific resistances. [1] M. Lomberg, E. Ruiz-Trejo, G. Offer, and N. P. Brandon, “Characterization of Ni-infiltrated GDC electrodes for solid oxide cell applications,” J. Electrochem. Soc., vol. 161, no. 9, pp. F899–F905, 2014. [2] S. P. Jiang, “Nanoscale and nano-structured electrodes of solid oxide fuel cells by infiltration: Advances and challenges,” Int. J. Hydrogen Energy, vol. 37, no. 1, pp. 449–470, Jan. 2012. [3] H. Tu and U. Stimming, “Advances, aging mechanisms and lifetime in solid-oxide fuel cells,” J. Power Sources, vol. 127, no. 1–2, pp. 284–293, Mar. 2004.

Study on Nonlinear Identification SOFC Temperature Model Based on Particle Swarm Optimization–Least-Squares Support Vector Regression

In order to facilitate valid solid oxide fuel cell (SOFC) temperature control scheme, a nonlinear identification method of SOFC temperature dynamic behaviors is proposed using an autoregressive network with exogenous inputs (NARX) model, whose nonlinear function is described by a least-squares support vector regression (LSSVR) method with radial basis kernel function (RBF). During the identifying process, a particle swarm optimization (PSO) algorithm is introduced to optimize the parameters of LSSVR. On the other hand, a mechanism model is developed to sample the training data to regress the NARX model. Investigations are conducted to analyze the effects of training data size and PSO fitness function on the accuracy of the NARX model. The results demonstrate that the NARX model with tenfold cross-validation fitness function and large size data is precise enough in predicting the SOFC temperature dynamic behaviors. The maximum errors of cathode and anode outlet temperature are 0.3081 K and 0.3293 K, respectively. Furthermore, the simulation speed of NARX model is much faster than the mechanism model because NARX model avoids the internal complex computation process. The training time of the NARX model with large size data is about 1.2 s. For a 20,000 s simulation, the predicting time of the NARX model is about 0.2 s, while the mechanism model is about 36 s. In consideration of its high computational speed and accuracy, NARX model is a powerful candidate for valid multivariable model predictive control (MPC) schemes.

Identification of phase in-homogeneities in Na-SrSiO3 electrolytes for low temperature SOFCs

In this work we have synthesized and characterized sodium doped SrSiO3 electrolyte, for use in low and intermediate temperature solid oxide fuel cells (SOFCs). Great interest was placed onto this material after its first report in 2012, which was later dampened by conflicting reports about the properties of this class of materials. It is imperative to resolve this issue from the viewpoint of development of low and intermediate temperature SOFCs. Here, we report the most comprehensive data till date on the properties of this class of materials. Although it is desired to synthesize a single phase material, strong evidences presented here suggest that it is a multiphase material. The reason for obtaining a multiphase material is discussed considering the reaction thermodynamics. Additional data presented here establish that at the operating temperature (~750 °C) of SOFC devices, amorphous phases in the material transforms into a crystalline phase.