Intermediate Temperature Solid Oxide Fuel Cells Research Articles

Five‐layer reverse tape casting of IT‐SOFC

AbstractTape casting is a well‐established method for manufacturing thin ceramic layers with controllable thickness and porosity. This study investigates the potential of 10Sc1CeSZ material for the electrolyte and anode layers for intermediate‐temperature solid oxide fuel cells (IT‐SOFC) in an anode‐supported cell (ASC) geometry. In order to use La0.6Sr0.4Co0.2Fe0.8 Oxide (LSCF) cathode material, a Gd0.2Ce0.8 Oxide (GDC) barrier layer is needed; however, thermal expansion coefficient mismatch results in delamination of the GDC from the electrolyte during high temperature sintering when fabricated by conventional tape casting procedures. For the first time, ASCs have been manufactured by a five‐layer tape casting technique; barrier layer, novel composite layer, electrolyte, anode functional layer, and anode substrate. Ni‐ScCeSZ composite cells were tested between 650 and 800°C in H2:N2 fuel (85% H2) on the anode and air on the cathode to yield a maximum power density of .46 W/cm2. These results demonstrate the feasibility of this new five‐layer tape casting technique to produce IT‐SOFC.

Dopant Induced-Modulation in Reducing Ability of Cerium in Doped Ceria System and Its Effect on Oxy-Ion Conductivity: Core Study by XPS and XANES Probes

Acceptor-doped ceria systems are potential materials forelectrolytes in intermediate temperature solid oxide fuel cells (IT-SOFCs), but the reduction of Ce4+ to Ce3+ in the ceria-based electrolytes limits such functionality. Reduction is accompanied by the release of one electron + oxygen vacancy; leading to electronic contribution and making short circuiting critical. Suppressing the reducing ability of cerium is thus a core challenge in optimizing its use. We developed acceptor (Sm3+, Gd3+) singly and doubly doped ceria, as valence and size of dopants are key in altering ionic conductivity. The oxidation state of dopant and host is revealed by XPS spectroscopy and XANES. XPS confirms the existence of Sm in two states, while Gd exists in one. The existence of Ce in Ce3+ and Ce4+ states are confirmed by both techniques, which also show that Ce4+ content in Sm-Gd doubly doped system is more than singly doped, and pure ceria, i.e. reduction ability of cerium in ceria is found to be suppressed by Sm and Gd double dopant. Effects of doping on the geometric and electronic structure have been studied using first-principles density functional theory. Ionic conductivity of a doubly doped system is enhanced by one order with suppression of reduction of cerium. The study shows acceptor multiple dopants in ceria system have potential to suppress reducing ability of cerium and improve ionic conductivity at intermediate temperature (400 °C–700 °C).

High-performance and CO2‑resistant cathode toward electrocatalytic oxygen reduction for solid oxide fuel cells: Doped ceria and SrCo0.7Nb0.1Ni0.2O3-δ composite

High oxygen reduction reaction (ORR) activity and sufficient stability are main challenges for high performance cathodes for solid oxide fuel cells (SOFCs) operated at medium temperature (550-700°C). In this study, ionic conducting Sm0.2Ce0.8O2-δ (SDC) are incorporated into perovskite SrCo0.7Nb0.1Ni0.2O3-δ (SCNN) cathode to synergistically improve its ORR activity as well as CO2 tolerance. A series of composite oxide, SCNN-xSDC (x=0, 20, 30, 40 and 50 wt %), were systematically evaluated as candidate cathodes for intermediate temperature SOFCs. Among all cathodes, SCNN-40SDC has the lowest polarization resistance (0.019 Ω cm2), only ∼30% of SCNN (0.066 Ω cm2) at 700°C. Introduction appropriate SDC boosts ORR activity of the composite cathodes, which is owing to enhanced oxygen surface exchange process, as evidenced by higher oxygen surface exchange coefficient (Kchem) and bulk diffusion coefficient (Dchem). Furthermore, the composite cathode shows much enhanced stability under CO2 poisoning, which was ascribed to the suppression of Sr segregation from SrCo0.7Nb0.1Ni0.2O3-δ and alleviated formation of carbonate in condition of SDC addition. Introducing ionic conductor Sm0.2Ce0.8O2-δ to construct a dual-phase cathode is a promising way to improve stability and ORR activity of perovskite oxides for SOFCs.

Investigation of surficial and interfacial properties of BaCo0.4Fe0.4Zr0.1Y0.1O3-δ cathode directly on yttria-stabilized zirconia electrolyte for solid oxide fuel cell

The cobalt/iron-containing perovskites are the most promising cathodes for the intermediate-temperature solid oxide fuel cell (IT-SOFC). However, these cathodes are generally not directly applied on the currently available commercial yttria-stabilized zirconia (YSZ) electrolyte due to the issues of over-firing, harmful reaction and thermal incompatibility. BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) which contains both zirconium and yttrium ions can theoretically be more compatible with the YSZ electrolyte. This paper focuses on the surficial and interfacial properties of BCFZY directly prepared with YSZ under different conditions. The surface of BCFZY by the glycine-nitrate process (GNP) can form the nanoparticles in contrast to that by solid-state reaction (SSR). The peak power density of the cell with BCFZY-GNP cathode directly on YSZ electrolyte can reach 1250 mW cm−2 at 750 °C, which is hardly achieved on the reported traditional cobalt/iron-containing cathodes. It is proved that BCFZY-GNP cathode fired at 900 °C can show more distinct nanoparticles with extensive specific surface area and better BCFZY|YSZ interface, which can promote both oxygen exchange and ion incorporation processes.

Structure and performance of Pr, Sm, Y co-doped cerium-based electrolyte for intermediate temperature solid oxide fuel cells

In this paper, Pr, Sm, Y co-doped CeO2-based PrxYxSm0.2-2xCe0.8O2-δ (x = 0.025, 0.05, 0.075, abbreviated as PYSC1, PYSC2 and PYSC3) electrolytes were successfully synthesized and investigated its properties as intermediate-temperature Solid oxide fuel cells (IT-SOFCs). The PrxYxSm0.2-2xCe0.8O2-δ electrolytes have formed a cubic fluorite structure after calcined at 600 °C. Raman spectra show that Sm, Pr, Y co-doped effectively increases the oxygen vacancy concentration. At 800 °C, the conductivity of PYSC1 electrolyte is about 0.125 Scm−1, higher than that of Sm0.2Ce0.8O1.9 (SDC) (∼0.096 Scm−1) electrolyte. The conductivity of PYSC1 electrolyte maintains good stability within 60 h in air. The open circuit voltage and maximum power density of single cell with the configuration of Ni0.9Cu0.1O-Sm0.2Ce0.8O1.9/PYSC1/La0.6Ba0.4Co0.8Fe0.2O3-δ are 0.74 V and 674.6mWcm−2, respectively. Therefore, PYSC1 would be a promising electrolyte material in IT-SOFCs.

An Overview on the Novel Core-Shell Electrodes for Solid Oxide Fuel Cell (SOFC) Using Polymeric Methodology.

Lowering the interface charge transfer, ohmic and diffusion impedances are the main considerations to achieve an intermediate temperature solid oxide fuel cell (ITSOFC). Those are determined by the electrode materials selection and manipulating the microstructures of electrodes. The composite electrodes are utilized by a variety of mixed and impregnation or infiltration methods to develop an efficient electrocatalytic anode and cathode. The progress of our proposed core-shell structure pre-formed during the preparation of electrode particles compared with functional layer and repeated impregnation by capillary action. The core-shell process possibly prevented the electrocatalysis decrease, hindering and even blocking the fuel gas path through the porous electrode structure due to the serious agglomeration of impregnated particles. A small amount of shell nanoparticles can form a continuous charge transport pathway and increase the electronic and ionic conductivity of the electrode. The triple-phase boundaries (TPBs) area and electrode electrocatalytic activity are then improved. The core-shell anode SLTN-LSBC and cathode BSF-LC configuration of the present report effectively improve the thermal stability by avoiding further sintering and thermomechanical stress due to the thermal expansion coefficient matching with the electrolyte. Only the half-cell consisting of 2.75 μm thickness thin electrolyte iLSBC with pseudo-core-shell anode LST could provide a peak power of 325 mW/cm2 at 700 °C, which is comparable to other reference full cells’ performance at 650 °C. Then, the core-shell electrodes preparation by simple chelating solution and cost-effective one process has a potential enhancement of full cell electrochemical performance. Additionally, it is expected to apply for double ions (H+ and O2−) conducting cells at low temperature.

Geometric structure distribution and oxidation state demand of cations in spinel NixFe1-xCo2O4 composite cathodes for solid oxide fuel cells

Slow oxygen reduction reaction (ORR) is a key obstacle of intermediate-temperature solid oxide fuel cells (IT-SOFCs). In this study, we prepared a complex spinel oxide (Fe3+Co2+)(Fe2+Fe3+Co3+)2O4 as good ORR catalyst for IT-SOFCs. Inducing oxidation state optimization of Fe and Co ions, the strategy of Ni doping at octahedral sites of FeCo2O4 with narrow band gap can effectively facilitate small polaron hopping of valence electrons, resulting in high electrical conductivity. In the p-type semiconductor NixFe1-xCo2O4 (NFCOx), the strong oxidant Ni3+ and highly electronegative Ni2+ would capture electrons to increase hole concentration and decrease resistance. The substitution of Ni that is smaller in size for Fe of bigger size at B-sites would cause lattice distortion and structure defects, which are beneficial to the promotion of oxygen transport capacity. The analysis of ORR kinetics based on the distribution of relaxation time (DRT) method reveals that the migration of adsorbed oxygen from NFCOx surface to the triple-phase boundary (TPB) is the rate-determining step. Owing to high electronic conductivity and fast oxygen transport, power density as high as 1.93 W/cm2 at 800 °C could be obtained when NFCO2-60GDC composite was used as cathode for IT-SOFCs, which is superior to (75.5% higher) that of using commercial LSM-based cathode (1.10 W/cm2 at 800 °C). The electrochemical performance of NFCO2-based IT-SOFCs is better than that of the other SOFCs with cathodes reported.

Impedance and Electric Modulus Spectroscopy of Polycrystalline La0.5Sr0.5Bi0.2Co0.4Fe0.4O3–d Cathode Ceramic for Intermediate Temperature SOFCs

In the present research work, La 0.5 Sr 0.5 Bi 0.2 Co 0 . 4 Fe 0.4 O 3– d cathode ceramic powder is synthesized through cost-effective flash pyrolysis process and further conventional heat treatment for sintering for IT-SOFCs. The crystal structure, unit cell parameters and bond length are determined by using the Rietveld refinement program. The XRD result indicates existence of a pure single phase with R C space group symmetry detected from the sample which has been sintered at 700 ℃. SEM images of fracture surface of sample sintered at 700 ℃ showed a high porosity and nano grain sizes (50-100 nm). Impedance and electric modulus spectroscopic methods are used to identify the relaxation phenomena in La 0.5 Sr 0.5 Bi 0.2 Co 0 . 4 Fe 0.4 O 3– d ceramic over a broad range of temperature and frequency. A single relaxation peak is observed in the imaginary part of impedance and electric modulus spectra, which could be due to the contribution of grain boundary of La 0.5 Sr 0.5 Bi 0.2 Co 0 . 4 Fe 0.4 O 3– d ceramic. The imaginary part of modulus ( ) spectra is analyzed with help of non-exponential decay function or Kohlrausch–Williams–Watts (KWW) parameter ( β ). In the combined plot of the imaginary part of impedance and electric modulus spectra at 210 ℃, only a single peak of and is observed at the same frequency which indicates that the conduction process is a long-range motion of the charge carriers. The frequency-dependent conductivity is followed by the Jonscher’s double power law in the temperature range 30-210 ℃.

A novel CO2-tolerant Ba0.5Sr0.5Co0.8Fe0.1Ta0.1O3-δ cathode with high performance for proton-conducting solid oxide fuel cells

The application of traditional MIEC cathode material Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) in the solid oxide fuel cell (SOFC) field is limited due to its susceptibility to CO2 and high thermal expansion coefficient. Therefore, improving the stability of BSCF cathode in CO2-containing environments and the matching degree between BSCF and electrolyte are the key factors to achieve its excellent electrochemical and stable performance for intermediate temperature solid oxide fuel cells (IT-SOFCs). Herein, the cathode materials Ba0.5Sr0.5Co0.8Fe0.2-xTaxO3-δ (X = 0, 0.1, 0.2) are successfully prepared and the effects of Ta-doped content are investigated systematically. With the increase of Ta-doped content, the thermal expansion coefficient of BSCF0.2-xTx decreases from 25.1 × 10−6 K−1 to 16.5 × 10−6 K−1, which indicated that Ta-doped enhanced the combination of cathode material and electrolyte. In single-cell applications, the maximum power density of 926.4 mW cm−2 and the lowest polarization resistance of 0.06 Ω cm2 at 700 °C are achieved. Furthermore, theoretical calculations show that the CO2 adsorption energy of BSCFT is 0.12 eV higher than that of BSCF, indicating that BSCFT exhibited improved resistance to CO2 corrosion compared with BSCF. It is indicated that the Ta-doping strategy has the advantage of improving both the performance and stability of BSCF cathode materials.

Praseodymium based double-perovskite cathode nanofibers for intermediate temperature solid oxide fuel cells (IT-SOFC)

In this work, praseodymium based double perovskite oxide, PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) cathode nanofibers were fabricated by electrospinning for intermediate-temperature solid oxide fuel cell (IT-SOFC). The three-dimensional nanofiber network cathode provides high porosity coupled with the large interfacial contact areas, leading to an improved oxygen reduction reaction (ORR) kinetics. The nanofiber cathode showed a polarization resistance of ∼0.025 Ω cm2 at 750 °C. The resulted low resistance is smaller than the commercial LSCF cathode showing polarization resistance of ∼0.041 Ω cm2 at 750 °C. The peak power densities of the PBSCF fibers are ∼2539, 1580 and 993 mW/cm2 at 750, 700, and 650 °C, respectively when compared to LSCF cathode performance of ∼1974, 1304 and 769 mW/cm2 at same temperature. Such promising performance of fiber cathode IT-SOFCs in this study was achieved via careful selection of the catalyst structure and composition, electrode structure for efficient ORR, and through process optimizations. The results obtained in this study illustrates that one-dimensional nanostructures obtained by adopting nanofibers could be an appropriate cathode material choice for intermediate-temperature SOFCs suitable for high power density applications such in automotive, stationary, APU and aviation fields.

PrBaCo2O5+δ-Sm0.5Sr0.5CoO3 Composite Oxide as Active Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

From decreasing the cost and the reliability of solid oxide fuel cells (SOFCs), increase in power density is strongly required. In order to achieve these requirements, decrease in operating temperature is the most effective way. However, reduced operating temperature leads to significant decrease in electrode activity, particularly cathode. Therefore, the development of novel and highly active cathode is strongly required for intermediate temperature (873-1073 K). In this study, we studied cathodic performance of double perovskite oxide of PrBaCo2O5 as active cathode of SOFC. Because of delamination of PrBaCo2O5 cathode is easily occurred because of larger thermal expansion coefficient. Mixing effects of PrBaCo2O5 with another perovskite oxide were investigated using a LaGaO3-based electrolyte. The electrochemical performance of the cell was measured using electrolyte-supported single cell at 873, 973 and 1073 K and humidified H2 was used as fuel and O2 as oxidant.Among the oxides mixed with PrBaCo2O5 (PBCO), it was found that mixing Sm0.5Sr0.5CoO3 (SSC)shows the smallest cathodic overpotential and the most suitable for increase in cathodic activity. Therefore, composite oxide of PBCO with SSC is active as cathode for SOFC. However, the cells with composite cathodes show lower performance at 1073 K comparing with PBCO cathode and this could be explained by small cathodic internal resistance at 873 K. On the other hand, the cell with PBCO-SSC (1:1) shows small overpotential at 873 K and much larger power density. Therefore, it was found that mixing PBCO with SSC shows the positive effects on the oxygen dissociation on the cathode at decreased temperature and suitable for low temperature operation SOFC. The optimization of SSC content on the cathodic activity of PBCO-SSC mixed oxide was further studied. The cathodic overpotential at 50 mA/cm2 was decreased with increasing amount of SSC and the smallest overpotential was achieved at 1:1 composition at all temperature studied. Positive effects of mixing PBCO and SSC could be assigned to the increased three phase boundary and increased activity to oxygen dissociation. Since cathodic overpotential was decreased significantly by mixing PBCO-SSC, power density of the cell using PBCO-SSC cathode at 1:1 composition shows 232 mW/cm2 at 873 K which is two times larger than that of the cell using PBCO single oxide cathode. Application of PBCO-SSC composite oxide for anode of steam electrolyser was also studied and it was found that PBCO-SSC is also active to oxygen association under applied voltage. Therefore, this study reveals that PBCO-SSC composite is potential air electrode material for intermediate-temperature solid oxide cells.

Electrochemical Characterization of Intermediate-Temperature Solid Oxide Fuel Cells with PVD-Coated Electrolyte

Intermediate temperature solid oxide fuel cells (SOFCs) working in the range of 600–800°C are interesting because they allow the expansion of the choice of materials that can be used, decrease system cost, and reduce the corrosion rate of system components [1]. The thickness of the electrolyte should be reduced, so reducing the area-specific resistance of the fuel cell for working in this temperature range. Physical vapor deposition methods, such as magnetron sputtering are used to produce thin-film electrolytes [2]. This work is an extension of our previous efforts focusing on scaling the technology of magnetron deposition of electrolyte to large-area cells [3]. It is known that area-specific resistance of small button cells is much less than that of industrial-sized planar anode-supported SOFC cells (10 cm×10 cm or greater). Such difference in ASR is due to large ohmic losses in a SOFC stack that are highly dependent on contact resistance at the cathode/bipolar plate interface. For example, the power density of our 10 cm×5 cm cell with magnetron sputtered yttria-stabilized zirconia (YSZ)/gadolinium-doped ceria (GDC) bilayer electrolyte and La0.6Sr0.4Co0.2Fe0.8O3/Gd0.1Ce0.9O1.95 (LSCF/GDC) cathode was 430 mW/cm2 at 0.7 V and at 750°C [4]. This value was about 40% of that of the 2 cm diameter button cell (1025 mW/cm2) with a similar structure and composition. The area-specific resistance of the former cell was 0.54 Ohm·cm2, while it was 0.2 Ohm·cm2 for the latter one. The goal of this work is to increase the performance of the large-area cell with PVD-deposited electrolyte by improving the structure and composition of the cathode active and contact layers. 4-µm-thick YSZ electrolyte and 2-µm-thick GDC barrier layer were deposited on the 5 cm×5 cm commercial NiO/10ScCeSZ anodes (KCERACELL CO., Korea) by means of reactive magnetron sputtering. LSCF/GDC cathode active layer with an active area of 4 cm×4 cm was screen printed onto the electrolyte. Electrochemical investigations were performed in the temperature interval of 600–800 °С. Figure shows the resulting performance – I–V–P curves of the large-area (5 cm×5 cm) cell with PVD-deposited electrolyte. High power densities of 0.29, 0.55, 0.83, 1.16 и 1.4 W/cm2 were achieved at 0.7 V and at 600, 650, 700, 750 and 800°C, respectively. Acknowledgements. This work was funded by the Russian Science Foundation (Grant No. 17-79-30071).[1] D. J. L. Brett et al., Chem. Soc. Rev., 37, 1568 (2008)[2] S. Sønderby et al., Surf. Coat. Technol., 240, 1 (2014)[3] A. Solovyev et al., J. Electrochem. En. Conv. Stor., 15(4), 044501 (2018)[4] A. Solovyev et al., Fuel Cells, 17(3), 378 (2017) Figure 1: I–V–P curves of the large-area (5 cm×5 cm) cell with PVD-deposited electrolyte. Figure 1

Preparation of Model SOFCs with Proton-Conducting Electrolyte on Metal Support Using Pulse Laser Deposition

Introduction Solid oxide fuel cells (SOFCs) have advantages including no need for using expensive noble metal catalysts, and higher energy conversion efficiency compared to the other types of fuel cells. On the other hand, since their operating temperature ranges from 600 to 1000°C, heat resistance is required for the components, and the materials that can be used for fuel cells are limited to ceramics. Therefore, intermediate temperature (500 to 600°C) SOFCs are of technological interest1-3. Proton-conducting electrolytes such as Yb-doped barium zirconate exhibit sufficiently high protonic conductivity at intermediate temperatures4,5. Furthermore, SOFCs using the proton-conducting electrolytes (p-SOFCs) can operate at a high fuel utilization, because water vapor is formed on the cathode side so that the fuel gas is not diluted on the anode (fuel electrode) side. Previous numerical study has revealed that the p-SOFCs can theoretically generate electric power from the fuels with a conversion efficiency even beyond 80% LHV6. Here in this study, metal-supported p-SOFC model cells are fabricated using Pulse Laser Deposition (PLD) technique, in which p-SOFCs are prepared on supporting porous metal plates with mechanical strength and chemical stability. Technical issues and various fabrication conditions are examined. Experimental Figure 1 schematically shows the structure of a metal-supported p-SOFC model cell prepared in this study. Electrodes were prepared by a screen printing method using NiO-Gd0.1Ce0.9O2-δ (Gd-doped CeO2 denoted as GDC) as the anode material, and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) as the cathode material. As the electrolytes, three types of electrolyte materials were applied, prepared by PLD: oxygen-ion conducting Y2O3-stabilized ZrO2 (YSZ), and proton conducting BaZr0.8Yb0.2O3-δ (BZYb). The model cells were prepared by the following steps: (i) After filling the fuel-supplying holes of the metal support plates, the anode layer was prepared on the plates by the screen printing method. (ii) Using the PLD method, thin electrolyte was deposited on the anode layer. (iii) The cathode layer was then prepared on the electrolyte by the screen printing method. Microstructural characterization and electrochemical measurements were made for the cells prepared by these procedures. Results and discussion A three-layer electrolyte structure of GDC / BZYb / GDC was prepared by using the PLD technique. Figure 2 shows a cross-sectional SEM image of the electrolyte. From this figure, it was confirmed that a dense multi-layer (GDC / BZYb / GDC) electrolyte membrane with a thickness of a few mm could be prepared by the PLD method on the support structure. Electrochemical properties and detailed microstructural observation of such metal-supported p-SOFC model cells fabricated by these procedures will be reported and discussed. References B. C. H. Steele, and A. Heinzel, Nature, 414, 345 (2001).R. Doshi, V. L. Richards, J. D. Carter, X. Wang, and M. Krumpelt, J. Electrochem. Soc., 146 (4), 1273 (1999).M. Gödickemeier, K. Sasaki, L. J. Gauckler, and I. Riess, J. Electrochem. Soc., 144 (5), 1635 (1997).K. D. Kreuer, Chem. Mater., 8 (3), 610 (1996).Y. Matsuzaki, Y. Tachikawa, Y. Baba, K. Sato, H. Iinuma, G. Kojo, H. Matsuo, J. Otomo, H. Matsumoto, S. Taniguch, and K. Sasaki, ECS Trans., 91 (1), 1009 (2019).Y. Matsuzaki, Y. Tachikawa, T. Somekawa, T. Hatae, H. Matsumoto, S. Taniguchi, and K. Sasaki, Sci. Rep., 5, 12640 (2015). Acknowledgement This study is partially supported by the Center of Innovation (COI) program (JPMJCE1318) of the Japan Science and Technology Agency (JST). Figure 1

Influence of Oxygen Partial Pressure on Cathodic Polarization of LaNiO3/GDC Composite Cathode

LaNiO3/GDC composite is one of the potential cathodic materials for intermediate temperature SOFCs. In order to evaluate its electrochemical performance, influence of oxygen partial pressure on cathodic polarization is examined with an electrolyte supported symmetric cell and a frequency response analyzer. An electrolyte disk made of GDC is used for the electrochemical symmetric cell. The operating temperature was controlled from 773K to 1073K, and the partial pressure was controlled between −4 < log(pO2) atm < 0 in this study.Polarization resistance increased with decreasing oxygen partial pressure at any temperature. In addition, the characteristic frequency (the summit frequency) of the impedance arc decreased with decreasing oxygen partial pressure. In order to search for the reaction mechanism, the rate-determining step approximation is applied to the experimental results. As a result, a rate-determining step is not dissociative adsorption of oxygen, but apparent oxygen reduction (charge transfer) reaction at temperature in the range from 773K to 973K. However, activation energy of the interfacial conductivity which is a reciprocal of polarization resistance is lower than 100 kJ/mol. Therefore, the rate-determining step is presumably a surface diffusion step, which is a migration step of dissociative oxygen from active point on the LaNiO3 surface to double phase boundary. At 1073K and higher oxygen partial pressure condition, the rate-determination step is still apparent oxygen reduction (charge transfer) reaction. Whereas at 1073K and lower oxygen partial pressure condition, the rate-determining step may be dissociative adsorption of oxygen.

Relationships between mechanical stability of the anode supports and electrochemical performance of intermediate-temperature SOFCs

Mechanical strength and microstructure of the anode supports are among the most critical factors affecting the long-term stability and performance of the intermediate-temperature solid oxide fuel cells (IT-SOFCs). In this work, the anode supports made of Ni/NiO and 10 mol.% Sc2O3 and 1 mol.% Y2O3 co-stabilized zirconia (10Sc1YSZ) were fabricated by tape casting, followed by sintering and screen-printing of the anode functional layer of 10 mol.% Gd2O3 doped ceria (10GDC) and NiO. Then two dense solid-electrolyte layers, 8 mol.% Y2O3 stabilized zirconia (8YSZ) and 10GDC, were deposited by the reactive pulsed dual magnetron sputtering. Mechanical properties of as-sintered and reduced anode supports were estimated employing three-point bending technique. The power density of model anode-supported SOFCs, where mechanical stability of the support was kept after complete reduction in hydrogen, achieved 0.3 W/cm2 at 800°C and 0.6 V under air/hydrogen gradient.

Performance and reaction process of Ba1−xCo0.7Fe0.2Nb0.1O3-δ cathode for intermediate-temperature solid oxide fuel cell

Perovskite-type cathode Ba1-xCo0.7Fe0.2Nb0.1O3-δ (B1-xCFN, x = 0.0-0.15) are proposed for intermediate-temperature solid oxide fuel cell(IT-SOFC). The changes in crystal structure, thermal expansion and electrochemical reaction through XRD, SEM, ac impedance spectroscopy and single-cell test are studied. The results show that except for the B0.95CFN has a small amount of impurity，B1-xCFN oxides present cubic perovskite structure. The porosity decreases as A-site deficiency increases, B0.9CFN has a lowest porosity. The interfacial polarization resistance of B0.9CFN drops nearly 66.2% than BCFN at 800 ◦C. The process of generating lattice oxygen is the major rate-limiting step when oxygen partial pressure is higher than 0.01 atm. Ba deficiency mainly accelerates the ionization process of oxygen atoms in the cathode bulk. The performance of single-cell B0.9CFN/SDC/Ni0.9Cu0.1-SDC is higher than other cathodes in the operation temperature, which means B0.9CFN is a better cathode for IT-SOFC.

Comparison of Different Synthesis Methods to Obtain GDC as Nanoparticulated Electrolytic Material for SOFCs Operating at Intermediate Temperature (~500°C)

Solid Oxide Fuel Cells (SOFCs) are a promising technology to produce electric energy from chemical energy. To achieve this, the development of new materials with enhanced properties are still needed. In this work, the synthesis of nanostructured powders to be used as components of an Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC) was carried out through different synthesis methods. So, co-precipitation, sol-gel combustion, and hydrothermal synthesis methods were compared in the synthesis of the Gadolinium Doped Cerium G0,2C0,8O1,9 (GDC) used as electrolytic material. Cathodic material (La0.6Sr0.4Co0.8Fe0.2O3 (LSCF) cobaltite type perovskite) was obtained by coprecipitation method. The materials were characterized by Fourier Transformed Infrared Spectroscopy (FTIR), Thermal Gravimetrical Analysis (TGA), Scanning Electron Microscopy (SEM-EDS), X-ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). The synthesized materials showed to be nanostructured. The chemical composition measured by EDS was constant in the entire sample and it has the expected stoichiometry in both materials. On the other hand, X-ray patterns exhibited well-defined peaks characteristic of ordered structures and with a high degree of crystallinity, corresponding with the information reported in the literature. From FTIR results, the characteristic peaks related to the presence of perovskites can be observed in the case of LSCF when it was compared to the results found in the literature. Nanostructured LSCF cathodic material was effectively synthesized by coprecipitation method. In the case of GDC highly crystalline material was obtain by sol-gel combustion method. Based on the results, the employed method allows to obtain homogeneous materials suitable to be used in IT-SOFC.

PrBaCo2O5+δ-Sm0.5Sr0.5CoO3 Composite Oxide as Active Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

Cathodic performance of double perovskite oxide of PrBaCo2O5 as an active catalyst for SOFC was investigated. Because delamination of PrBaCo2O5 cathode is easily occurred by larger thermal expansion coefficient, mixing effects of PrBaCo2O5 with another perovskite oxide were investigated using a LaGaO3-based electrolyte. Among the oxides mixed with PrBaCo2O5 (PBCO), it was found that mixing Sm0.5Sr0.5CoO3 (SSC) with PBCO shows the smallest cathodic overpotential and the most suitable for increase in cathodic activity. Increase in cathodic performance can be assigned to the high activity of oxygen dissociation on SSC and the fast oxide ion diffusivity in PBCO. Therefore, composite oxide of PBCO with SSC is highly active as cathode for SOFC at intermediate temperature.

Electrochemical Characterization of Intermediate-Temperature Solid Oxide Fuel Cells with PVD-Coated Electrolyte

Anode-supported solid oxide fuel cells with thin electrolytes show good electrochemical performance. In this work, 4-μm-thick YSZ electrolyte with 2-μm-thick GDC barrier layer is deposited onto the substrates by reactive magnetron sputtering. It is shown that high power density can be obtained for 5 × 5 cm2 cells under planar stacks conditions with stainless steel current collectors. Electrochemical investigations are performed in the temperature range of 600-800°C. High power density of 0.29, 0.83, 1.4 W cm-2 is achieved at a voltage 0.7 V and 600, 700, and 800°C, respectively.

Perovskites Doped with Small Amounts of Noble Metals for IT-SOFCs

Noble metal-doped lanthanum strontium ferrite (La0.6Sr0.4Fe0.99M0.01O3-d M=Ru, Pt) powders were developed as active electrodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). The as low as 1% mol doping sensitively improved the electrochemical performance. Structural, electrical, and electrochemical properties are discussed in detail. Fuel cell tests in H2 show promising performance in the 700-750°C temperature range.