Cermet Anode Research Articles

Infiltrated NiCo Alloy Nanoparticle Decorated Perovskite Oxide: A Highly Active, Stable, and Antisintering Anode for Direct-Ammonia Solid Oxide Fuel Cells.

Direct ammonia solid oxide fuel cell (DA-SOFC) is superior to low-temperature direct ammonia fuel cell using anion exchange membrane because of much improved anode reaction kinetics at elevated temperature. However, significant performance degradation due to severe sintering of conventional nickel cermet anode under operating conditions is a big challenge for realizing its practical use. Herein, a high-performance anode based on La0.55 Sr0.30 TiO3- δ (LST) perovskite substrate with its surface decorated with in situ exsolved and strongly coupled NiCo alloy nanoparticles (NPs) is designed and fabricated for DA-SOFCs, exhibiting superior catalytic activity for NH3 decomposition reaction due to balanced NH3 adsorption and N2 desorption processes. An electrolyte-supported single cell with infiltrated NiCo/LST on Sm0.2 Ce0.8 O1.9 scaffold anode delivers a maximum power density of 361 mW cm-2 at 800 °C in NH3 fuel, superior to similar SOFCs with Ni or Co NP-decorated LST based anodes (161 and 98 mW cm-2 ). Furthermore, the SOFC with this newly developed anode displays favorable operational stability without obvious performance degradation at 700 °C for a test period of ≈120 h, attributed to its high antisintering capability. This study provides some strategies to develop highly active, stable, and antisintering perovskite-based nanocomposite for DA-SOFCs, facilitating the practical use of this technology.

Improving fuel cell performance via optimal parameters identification through fuzzy logic based-modeling and optimization

Improving the performance of solid oxide fuel cell via maximizing its available peak power density is a key requirement of research in the field of renewable energy. This could be achieved through identifying the optimal controlling parameters such as, the deposition instrument power (P), the temperature (T), and the electrolyte thickness (Thick). Nickel–Gadolinium Doped Ceria cermet anode films are deposited on one side of the Zirconia electrolyte by radio frequency sputtering. The sputtering plasma power is varied at 50, 100, 150, and 200 W. Lanthanum Strontium Manganite cathodes were screen-printed on the other side of the electrolyte supports to complete the configuration. Cells were electrochemically tested at various intermediate solid oxide fuel cell temperatures of 600, 700 and 800 °C using different electrolyte thicknesses. The cell’s current density, I (A/cm2) and voltage (V) and hence the power density (W/cm2) are recorded in each case. Based on the obtained experimental results, a fuzzy model is built using different control parameters. Then, the particle swarm optimization technique is used for obtaining the best parameters of the cell that maximizes its power density. The results show that by utilizing the optimized conditions, the power density can be increased to 0.39 (W/cm2), which is almost two times higher than the maximum power density obtained experimentally.

(Invited) Designing SOC for Power-to-X Applications: A Multi-Physical Modelling Approach

In the current global energy transition, the Solid Oxide Cell (SOC) represents a promising technology for stationary energy generation and storage, since it facilitates highly efficient and low-emission energy conversion. Besides converting hydrogen or hydrocarbon fuels directly into electricity in fuel cell mode, the SOC can also be operated in a reverse mode as a Solid Oxide Electrolyzer Cell (SOEC). By operating the SOC as an electrolyzer, any surplus electrical energy produced from fluctuating renewable energy sources (e.g. solar or wind energy) can be utilized to synthesize syngas and subsequently hydrocarbon fuels. The outlet syngas composition is directly correlated to the applied operating conditions as H2O/CO2-ratio, temperature and current. Therefore, it is of utmost importance to gain a deep understanding of these relationships in order to establish optimal operational strategies for different applications.During electrolyzer operation the key component of the SOC is the fuel electrode (anode), since it facilitates the (i) electrochemical charge transfer reaction and (ii) the chemical reaction kinetics (cf. Fig. 1(c)). In state-of-the-art, anode-supported SOCs the anode relies on two porous, Ni / stabilized zirconia layers with specified phase compositions and microstructural characteristics: (i) the highly porous and catalytically active anode substrate (AS) and (ii) the electrochemically active anode functional layer (AFL) (cf. Fig. 1(a)). To raise fuel conversion efficiency, we must first gain a profound understanding of the optimal double-layer design for the desired application. Numerical simulations enable an efficient variation of geometrical, microstructural and material parameters over wide ranges and provide correlations between anode design and SOEC performance.In this contribution, we demonstrate a multi-physical modelling approach to predict the SOC performance in both fuel cell and electrolyzer operation. To do so, we combine two of our recently published modelling approaches: (i) the physically meaningful, three-channeled transmission line model for double-layered cermet anodes [1,2] and (ii) the non-isothermal FEM stacklayer model [3,4]. For the first time, a powerful mode framework is realized (cf. Fig. 1(b)), which is capable of spatially resolving all of the above mentioned processes, in both anode layers, within a complete stacklayer. The model considers the complex interplay of (i) multi-component gas transport coupled with (ii) catalytic reforming reactions, (iii) charge carrier transport, (iv) electrochemical charge transfer, (v) coupled heat release and consumption as well as (vi) heat transport in the individual stack components.We demonstrate a comprehensive, model-based optimization of Ni-based cermet anodes in a SOC stack layer with respect to (i) the selection of the electrolyte material, (ii) the modification of the microstructure and (iii) adapting of the layer thicknesses. Furthermore, the impact of the operating conditions on the optimal cell configuration will be discussed. Finally, we derive operational strategies for efficient SOEC operation by investigating the impact of (i) the inlet gases, (ii) the operating temperature and (iii) the applied current on the produced syngas composition.[1] S. Dierickx, J. Joos, A. Weber, E. Ivers-Tiffée, Advanced impedance modelling of Ni/8YSZ cermet anodes, Electrochim. Acta. 265 (2018) 736–750.[2] S. Dierickx, T. Mundloch, A. Weber, E. Ivers-Tiffée, Advanced impedance model for double-layered solid oxide fuel cell cermet anodes, J. Power Sources. 415 (2019) 69–82.[3] H. Geisler, A. Kromp, A. Weber, E. Ivers-Tiffée, Stationary FEM Model for Performance Evaluation of Planar Solid Oxide Fuel Cells Connected by Metal Interconnectors, J. Electrochem. Soc. 161 (2014) F778–F788.[4] N. Russner, S. Dierickx, A. Weber, R. Reimert, E. Ivers-Tiffée, Multiphysical modelling of planar Solid oxide fuel cell stack layers, J. Power Sources (in press). Figure 1

Improved Electrochemical Properties of an Ni-Based YSZ Cermet Anode for the Direct Supply of Methane by Co Alloying with an Impregnation Method

To avoid the proneness to degradation due to coking in the operation of solid oxide fuel cells (SOFCs) directly running on methane (CH4) fuels, a modified porous anode of the Ni1−XCoX/YSZ (yttria-stabilized zirconia) cermet prepared by an impregnation method is presented. The influence of the Co alloying content on the cermet microstructure, SOFC characteristics, and prolonged cell performance stability has been studied. Co was incorporated into Ni and formed a solid solution of Ni1−XCoX alloy connected with the YSZ as the cermet anode. The porous microstructure of the Ni1−XCoX/YSZ cermet anode formed by sintering exhibited a grain growth with an increase in the Co alloying content. The electrochemical performance of the cells consisting of the Ni1−XCoX/YSZ cermet anode, the YSZ electrolyte, and the LSM (La0.8Sr0.2MnO3) cathode showed an enhancement by the Ni1−XCoX impregnation treatment for the respective supply of H2 and CH4 to the anode. The cell using the Ni0.75Co0.25/YSZ cermet anode (the Ni0.75Co0.25 cell) showed the highest cell performance among the cells tested. In particular, the performance enhancement of this cell was found to be more significant for CH4 than that for H2; a 45% increase in the maximum power density for CH4 and a 17% increase for H2 at 750 °C compared with the performance of the cell using the Ni/YSZ cermet anode. Furthermore, the prolonged cell performance stability with a continuous CH4 supply was found for the Ni0.85Co0.15 and Ni0.75Co0.25 cells at least for 60 h at 750 °C. These enhancement effects were caused by the optimum porous microstructure of the cermet anode with the low anodic polarization resistance.

Noise suppressed and bias field corrected image segmentation method for porous Ni-YSZ anode microstructure

Accurate three-phase identification from Solid Oxide Fuel Cell (SOFC) anode micrograph is challenged by both noise and intensity inhomogeneity. In this paper, a novel framework is proposed for porous Ni-YSZ cermet anode Optical Microscopy (OM) image segmentation. The proposed framework takes advantage of a statistical model in which an observed image is decomposed into two multiplicative components (bias field and true image) and one additive component (noise). A two-stage Principal Component Analysis with Local Pixel Grouping (LPG-PCA) denoising algorithm is firstly performed to suppress additive noise, it can preserve more image local structural features by modeling a pixel and its nearest neighbors as a vector variable and selecting training samples with similar contents to this variable in a local window for PCA transformation. In order to enhance the robustness to noise, uneven illumination and other outliers, a kernel metric is introduced into fuzzy clustering method embedded with bias field correction for image segmentation. The proposed method has been compared to other state-of-the-art segmentation algorithms on both simulated images and real SOFC anode OM images. Extensive experiments results have demonstrated that the proposed framework can successfully eliminate the influence of both uneven illumination and noise on real Ni/YSZ anode OM images to obtain a better three-phase identification accuracy. The high-quality segmentation results lay firm foundation for accurate microstructural parameter extraction.

The Relation of Microstructure, Materials Properties and Impedance of SOFC Electrodes: A Case Study of Ni/GDC Anodes

Detailed insight into electrochemical reaction mechanisms and rate limiting steps is crucial for targeted optimization of solid oxide fuel cell (SOFC) electrodes, especially for new materials and processing techniques, such as Ni/Gd-doped ceria (GDC) cermet anodes in metal-supported cells. Here, we present a comprehensive model that describes the impedance of porous cermet electrodes according to a transmission line circuit. We exemplify the validity of the model on electrolyte-supported symmetrical model cells with two equal Ni/Ce0.9Gd0.1O1.95-δ anodes. These anodes exhibit a remarkably low polarization resistance of less than 0.1 Ωcm2 at 750 °C and OCV, and metal-supported cells with equally prepared anodes achieve excellent power density of >2 W/cm2 at 700 °C. With the transmission line impedance model, it is possible to separate and quantify the individual contributions to the polarization resistance, such as oxygen ion transport across the YSZ-GDC interface, ionic conductivity within the porous anode, oxygen exchange at the GDC surface and gas phase diffusion. Furthermore, we show that the fitted parameters consistently scale with variation of electrode geometry, temperature and atmosphere. Since the fitted parameters are representative for materials properties, we can also relate our results to model studies on the ion conductivity, oxygen stoichiometry and surface catalytic properties of Gd-doped ceria and obtain very good quantitative agreement. With this detailed insight into reaction mechanisms, we can explain the excellent performance of the anode as a combination of materials properties of GDC and the unusual microstructure that is a consequence of the reductive sintering procedure, which is required for anodes in metal-supported cells.

Improving SOFC Anode Electrocatalytic Activity Using Nanoparticle Infiltration into MIEC Compositions

Mitigating activation polarization in the anode is one of the major challenges in intermediate-temperature operation of solid oxide fuel cells (SOFCs). Liquid phase infiltration of nanoscale electrocatalysts has been shown to result in significant reductions in activation polarization in SOFC anodes. In this study, we explore liquid-phase infiltration of nickel, gadolinium doped ceria (GDC), and Ni/GDC electrocatalysts into two different types of cermet anodes: one with a conventional Ni-YSZ composition, and the other with a Ni-MIEC cermet anode where the YSZ has been doped with 3 mol% TiO2 to impart electronic conductivity. The principal goal of this study is to explore the role of electronic transport in the MIEC phase in effective utilization of the infiltrated nanoscale electrocatalysts. The role of temperature, infiltration cycles and the type of electrocatalysts have been experimentally studied in symmetric cells using electrochemical impedance spectroscopy (EIS). Distribution of relaxation times (DRT) modeling has been used to elucidate the contributions of various charge transfer processes.

Improved Redox Cycling Durability in Alternative Ni Alloy-Based SOFC Anodes

Repeated reduction and oxidation of metallic nickel in the anodes of solid oxide fuel cell (SOFC) causes volume changes and agglomeration. This disrupts the electron conducting network, resulting in deterioration of the electrochemical performance. It is therefore desirable to develop more robust anodes with high redox stability. Here, new cermet anodes are developed, based on nickel alloyed with Co, Fe, and/or Cr. The stable phases of these different alloys are calculated for oxidizing and reducing conditions, and their electrochemical characteristics are evaluated. Whilst alloying causes a slight decrease in power generation efficiency, the Ni-alloy based anodes have significantly improved redox cycle durability. Microstructural observation reveals that alloying results in the formation of a dense oxide film on the surface of the catalyst particle (e.g. Co-oxide or a complex Fe–Ni–Cr oxide). These oxide layers help suppress oxidation of the underlying nickel catalyst particles, preventing oxidation-induced volume changes/agglomeration, and thereby preserving the electron conducting pathways. As such, the use of these alternative Ni-alloy based cermets significantly improves the redox stability of SOFC anodes.

Highly Durable, Surface Modified SOFCs Running on Hydrocarbon Fuels at 600 °C

Fuel flexibility is a unique feature of solid oxide fuel cells (SOFCs), the instability of Ni-based cermet anodes in hydrocarbon fuels impede the advancement of low-temperature solid oxide fuel cells (LT-SOFCs). Here we demonstrate highly stable LT-SOFCs prepared by catalytically modifying the surface of a conductive ceramic oxide, SrFe0.2Co0.4Mo0.4O3 (SFCM), using Ni-GDC nanoparticles (<100 nm). The nano-sized Ni-GDC electrocatalysts, resulting from careful optimization of Ni-to-GDC ratio, and subsequent low-temperature calcination process, enhance the fuel oxidation kinetics and stability of SFCM anode significantly. An optimized Ni-to-GDC ratio of 1:10 on SFCM-supported SOFC delivered peak power density of 0.75, 0.65 and 0.36 W cm−2 at 650 °C, 600 °C and 550 °C, respectively, in humidified H2 and 0.62, 0.39 and 0.22 W cm−2 at 650 °C, 600 °C and 550 °C, respectively, in CH4/H2 gas mixtures, nearly 4× higher than GDC as electrocatalyst. Remarkably, for the same Ni-to-GDC ratio, a stable cell voltage of 0.82 V is maintained over 200 h of operations (under current) at 600 °C in CH4/H2 gas mixtures.

Characterizing Performance of Electrocatalyst Nanoparticles Infiltrated into Ni-YSZ Cermet Anodes for Solid Oxide Fuel Cells

The infiltration of nanoparticle electrocatalysts into solid oxide fuel cell (SOFC) electrodes has been proven to produce a high density of electrochemically active sites, and reduce charge transfer polarization losses for SOFC electrodes. This is crucial for intermediate temperature operation, as these losses increase greatly at lower temperatures. Nickel-yttria stabilized zirconia (Ni-YSZ) cermets are low-cost, and exhibit excellent stability, but their main disadvantage stems from nickel coarsening and performance loss over their operational lifetimes. Infiltration of electrocatalyst nanoparticles has been shown to mitigate nickel coarsening and the consequent anode degradation. In this study, the effects of these infiltrants are observed in a standard Ni-YSZ electrode. In addition to nickel, mixed ionic and electronic conducting (MIEC) phases were infiltrated into Ni-YSZ scaffolds and their performances were characterized using electrochemical impedance spectroscopy (EIS). Cross-sectional microscopy of fractured cells was used to compare electrode microstructure and particle statistics. A model is proposed for how the nanoparticle electrocatalysts improve the anode performance.

Achieving high mechanical-strength CH4-based SOFCs by low-temperature sintering (1100 °C)

Despite much progress achieved in the past decades in the process of advancing the low-temperature sintering technologies for Solid oxide fuel cells (SOFCs), such as via the structure design of the electrode materials, the practical application of low-temperature sintered SOFCs (with disqualified mechanical strength) remains challenging. In this work, first, we demonstrate that the appropriate amount of CuO as sintering aids can successfully reduce the co-firing temperature of conventional micron size NiO-YSZ (yttrium-stabilized zirconia (Y2O3)0.08–(ZrO2)0.92) anode from about 1400 °C to only 1100 °C. Second, the quantitative structure-activity relationship among the mechanical strength (low-temperature sintering ability) of anode cermets with the inclusion of CuO contents and the densification of YSZ electrolyte was synthetically evaluated, and the optimal Cu–NiO-YSZ anode composition demonstrates almost the equal mechanical strength when compared with the traditional NiO-YSZ anode (sintering at 1400 °C). At last, by comprehensive assessment, 8%Cu–52NiO-40YSZ (8%CuO–NiO-YSZ) shows excellent low-temperature sintering ability, high mechanical strength, optimal power output, and anti-carbon deposition when using as hydrocarbon-based anode for SOFCs.

Detailed electrochemical performance and microstructural characterization of nickel – Yttria stabilized zirconia cermet anodes infiltrated with nickel, gadolinium doped ceria, and nickel – Gadolinium doped ceria nanoparticles

Infiltration of nickel nanoparticles into nickel – yttria-stabilized-zirconia (Ni-YSZ) cermet anodes improves anode performance by reducing the average nickel feature size of the electrode, thus increasing the density of triple phase boundaries (TPBs). However, the TPBs of nickel nanoparticles are not fully utilized because there is no conductive pathway between nanoparticles, and nickel nanoparticles suffer from rapid coarsening during operation. This work explores the infiltration of Gd0.1Ce0.9O2-δ (GDC) as a material for connecting and stabilizing infiltrated nickel nanoparticles. Anodes were infiltrated with Ni, GDC, and Ni-GDC to study their stability and electrochemical performance. Measurements show that the simultaneous infiltration of nickel and GDC results in a greater performance improvement than either nickel or GDC alone. From this result, it is speculated that GDC provides a conducting pathway between nickel nanoparticles, better utilizing their TPBs. Fitting of electrochemical impedance spectra with an equivalent circuit model is used to measure individual cell resistances, revealing that infiltration of GDC reduces the activation energy of the anodic charge transfer reaction from 1.29 eV to 0.74 eV. The Ni-GDC nanoparticles are also more durable than nickel nanoparticles, demonstrating microstructural stability after 120 h of constant current at 800 °C, while nickel alone shows extensive coarsening.

The effect of calcination temperature on the properties of Ni-SDC cermet anode

In order to improve the performance of the anode of solid oxide fuel cells, the cermet anodes were synthesized by employing a carbonate co-precipitation method and calcined at different temperatures (500 °C-800 °C). The fabrication of pellet from calcined powder was done by uniaxial pressing. These pellets were then characterized to investigate the effect of calcination temperature on their microstructure, thermal behavior, porosity, and carbonate bonding along with conductivity. The carbonates formed within the synthesis process has shown a strong effect over the properties of the Ni-SDC. It is observed that Ni-SDC maintained its chemical compatibility during each process. The thermal gravimetric analysis showed that more weight loss occurred for the specimen calcined at low temperature. Due to the porosity increases with calcination electronic conductivity and performance will also be enhanced.

An experimental investigation on flow-rate effects of internal CPOX reforming in SOFCs

Utilizing oxygen with methane as fuel is a feasible reforming strategy, more convenient and less costly in terms of configuration in solid oxide fuel cells (SOFC) systems. Current study addresses the issues related to the favorable operating conditions for the internal catalytic partial oxidation (CPOX) reforming of methane over Ni-YSZ cermet anode of SOFCs with a new analytical approach on the basis of Reynolds number (Re). The effect of the different flow rates of methane-oxygen mixed gas on the performances of SOFC are studied in fixed methane to oxygen ratio. The results indicated thatthe peak of power density (PPD) strongly depends upon the Reynolds number at the fuel channel inlet that controls the mixture of methane and air mass flow rate. The maximum value of PPD is obtained in Reynolds 10 and also the PPD is decreased by increasing Re. The electrochemical experiment showed stable performance of the SOFC in this condition and confirmed its durability after 120 h testing. The electron microscopy demonstrated that there is no trace of carbon in the anode which led to the durability of the SOFCs.

Nickel-copper based anodes for solid oxide fuel cells running on hydrogen and biogas: Study using ceria-based electrolytes with electronic short-circuiting correction

Cermet compositions based on Nickel–Copper alloys with gadolinium doped ceria as the ceramic matrix, Ni1-xCuxO (x = 0, 0.4 and 0.8 mol%) with 50 wt% CGO (Ce0.9Gd0.1O1.95), are assessed as possible anodes for SOFCs operating in H2 and biogas fuels. Equivalent circuit modelling is employed to evaluate the total polarisation resistance of cermet anodes with correction of data for electronic short-circuiting that may arise when using Ce0.9Gd0.1O1.95 (CGO) electrolytes under reducing conditions. Data analysis highlights that presence of electronic leakage in CGO electrolyte can lead to severe underestimation of total polarisation resistance in the case of H2 fuel, with this deviation becoming more serious with increasing temperature. In contrast, less significant effects are noted under biogas in similar conditions, due to a less reducing nature of this fuel. The results underscore that anode characteristics are highly dependent on the effective oxygen partial pressure of working gas atmosphere and that suitable correction of data is imperative before discussion. Corrected values for polarisation resistance in each fuel reveal the Nickel–Copper alloy cermet with copper content of x = 0.4 to be beneficial under the biogas atmosphere, while, conversely, the pure Ni-cermet is shown to be the peak performing composition in H2 fuel.

Co-infiltration of Nickel and Mixed Conducting Gd0.1Ce0.9O2−δ and La0.6Sr0.3Ni0.15Cr0.85O3−δ Phases in Ni-YSZ Anodes for Improved Stability and Performance

Liquid-phase infiltration of nickel (Ni) nanoparticles in Ni/yttria-stabilized-zirconia (YSZ) cermet anodes for solid oxide fuel cells can improve anode performance provided that the infiltrated nanoparticles on YSZ connect to form conducting pathways and the Ni nanoparticles do not coarsen significantly. This study explores liquid phase co-infiltration of Ni with mixed conducting oxides, the latter providing microstructural stability and conductive pathways between Ni nanoparticles. Two mixed conducting oxides have been studied: Gd0.1Ce0.9O2−δ (GDC), a predominantly ionic conductor, and La0.6Sr0.3Ni0.15Cr0.85O3−δ (LSNC), a predominantly electronic conductor. Experimental results show that both oxides improve the nickel nanoparticle stability and charge transfer kinetics. However, the electrochemical performance of the Ni-GDC-infiltrated electrode is much better than that of the Ni-LSNC-infiltrated electrode. This is attributed to the citrate–nitrate combustion reaction required to form LSNC, which fills the pores of the anode and inhibits gas diffusion, reducing the performance of the Ni-LSNC-infiltrated electrode.

Operando Studies of Carbon Removal and Partial Oxidation in Solid Oxide Fuel Cells

Operando methods, including thermal imaging, infrared emission and Raman spectroscopy, are combined with simultaneous electrochemical measurements to characterize carbon removal and partial oxidation of methane on Ni/YSZ anodes of operating solid oxide fuel cells (SOFCs). Results for carbon removal indicate that the CO2 to CO product ratio is higher for removal by oxygen than with steam. Also, steam removes carbon faster than oxygen and leads to slower oxidation of Ni in the cermet anode. Temperature changes are observed and explained in terms of the stronger adsorption for oxygen than water on the Ni anode. Related carbon oxidation studies are described for partial methane oxidation in operating cells in which Raman spectra show that graphite accumulation is strongly suppressed even at low ratios of oxygen or steam to methane (1:10). Simultaneous impedance measurements indicate that much of the effect is due to reduced polarization resistance.

Low Temperature Ammonia Decomposition Catalyst and Its Application for Direct Ammonia-Fueled Solid Oxide Fuel Cells

Ammonia regards as a promising alternative fuel for solid oxide fuel cell (SOFC) compare with hydrogen due to its low cost and ease for transportation and storage. Ni/yttria-stabilized zirconia (Ni/YSZ) anode of solid oxide fuel cells (SOFC) is only active for ammonia decomposition at high temperatures, and Ni in the cermet anode would be nitridized under concentrated ammonia atmosphere that leads to undesirably degradation. Here we report a low-temperature ammonia decomposition catalyst, Ba modified Ni/yttria-stabilized zirconia (Ba-Ni/YSZ) is synthesized by a facile solid-liquid (SL) method. Enhanced performance can be obtained for Ba-Ni/YSZ compare with that of Ni/YSZ catalysts, indicating that the addition of Ba promotes the catalytic activity. Besides, the Ba-Ni/YSZ catalyst is introduced in the flat-tube SOFC, and significantly improves the electrochemical performance of directly ammonia-fed SOFCs at low temperatures.

Hydrogen Oxidation Activity of SOFC Anodes with Metal Oxide Addition

Metal oxide addition is one of the major techniques to improve the performance of SOFC cermet anodes. However, the effects of the metal oxide addition on hydrogen oxidation activity of the anodes have not been clarified so far. In this study, Ni-CaO/YSZ anodes were prepared to examine the interaction between YSZ and Ca species. The hydrogen oxidation activities of the prepared anodes were investigated by introducing electrochemical impedance spectroscopy. The anodic resistance of the electrochemical hydrogen oxidation was determined by impedance fitting, and its temperature dependency was analyzed by means of Arrhenius plots. It was found that activation energy of the reaction was decreased with the CaO addition, suggesting the possibility of the SOFC operation at lower temperatures.

Novel SOFC Anodes Using Pyrochlore-Type Mixed Conducting Materials

In this study, four pyrochlore oxides such as (Gd0.9Ca0.1)2Ti2O7-δ, Gd2(Ti0.8Ru0.2)2O7-δ, (Sm0.9Ca0.1)2Ti2O7-δ, and (Y0.9Ca0.1)2Ti2O7-δ were investigated as new mixed ionic and electronic conductors for SOFC anodes. Cermets of nickel and the pyrochlores were fabricated as an anode, and current-voltage (I-V) characteristics were evaluated using yttria-stabilized zirconia and lanthanum manganite as an electrolyte and cathode, respectively. It was found that ohmic resistance and polarization resistance for the anodic reaction over some of the Ni-pyrochlore cermet anodes were smaller than those of Ni-YSZ, whereas the polarization resistance stemming from gas diffusion in the anode was significantly large over the pyrochlore anodes, leading to inferior I-V characteristics to Ni-YSZ. To improve the anode structure for better gas diffusion, pyrochlore oxides were prepared by solid-state synthesis method. The anode using these pyrochlore oxides exhibited smaller gas diffusion resistance and comparable I-V characteristics with Ni-YSZ anode.