(Invited) Gradient Ni-SDC Anode By Reactive Co-Sputtering for Low Temperature Solid Oxide Fuel Cells

Cycle analysis of planar SOFC power generation with serial connection of low and high temperature SOFCs

For the last few decades, alternative and sustainable energy sources have been approached which deplete the environmental issues and provides the clean energy conversion towards world energy demands. Fuel cells which convert chemical (Fuel) energy directly into electrical energy (electricity) via electro-chemical reaction mechanism are more advantageous when compared with the other conventional energy conversion technologies. Among the various available fuel cells, Solid oxide fuel cell (SOFC) has proven as most promising, efficient, eco-friendly energy conversion device due to its longer life time, variety choice of fuels and less environmental impact. The fundamentals of fuel cell technologies, background, working mechanism, different components of SOFC, brief note on traditional materials, and development of novel materials for the advanced SOFC were addressed. Working/operating temperature plays a key role in the development of SOFC because high operating temperature curbs the commercialization. Enormous efforts have been done in reducing the operating temperature by introducing various doped /co doped /triple-doped ceria based materials with enhanced electrical properties which led to the development of intermediate temperature SOFCs. On the way of reducing the operating temperature, R&D introduced a composite approach using doped ceria and alkali carbonates which pave a way for the development of low operating temperature SOFC. The recent developments regarding ceria-carbonate composites with emphasis on the ionic conductivity have been discussed towards the electrolytes for advanced SOFC applications at relatively lower temperatures

In this report, we present a study of using nitrogen‐doped graphene as the air electrode of low temperature solid oxide fuel cells (LT‐SOFCs) operating at 350 °C or lower. Three graphene derivatives were prepared through hydrothermal reactions and their electrochemical performance and material properties were characterized in the temperature range of 225–350 °C in atmospheric air. Nitrogen‐doped graphene was found to exhibit a decent air electrode performance comparable to a porous Pt electrode aged for 8 h at 350 °C, but only for a limited time. After ∼10 h of operation at 350 °C, the electrode performance degraded significantly due to carbon oxidation. However, alternative routes of synthesizing/doping graphene derivatives are expected to improve the viability of using these materials as a practical high temperature air electrode.

Solid Oxide Fuel Cells (SOFCs) are energy conversion devices known for their significantly higher power density compared to other fuel cell types. However, their high operating temperatures pose challenges related to thermal stability. To address this, research is focusing on Low-Temperature SOFCs (LT-SOFCs), which function at lower temperatures and exhibit enhanced electrochemical performance. While various electrode materials are utilized in SOFCs, platinum (Pt) stands out for its excellent electronic conductivity and catalytic activity. Unfortunately, at the operating temperatures of SOFCs, Pt tends to agglomerate, leading to a rapid reduction in the triple phase boundary (TPB) and a subsequent decline in electrochemical reactions. In this study, LT-SOFCs were fabricated with a Praseodymium Oxide (PrOx) capping layer applied to a porous Pt cathode using sputtering, with various thicknesses achieved by adjusting the deposition time. The electrochemical performance of the LT-SOFCs was measured at 500oC. Additionally, the degradation behavior of the LT-SOFCs was assessed by applying a constant voltage of 0.5 V for 48 hours. Scanning Electron Microscopy (SEM) analysis was also conducted on the PrOx capping layer thin films under the same operating conditions.

The sluggish kinetics of oxygen reduction reaction (ORR) at low temperatures and the fast degradation of the cathode are the main obstacles to the commercialization of solid oxide fuel cells (SOFCs). However, it is still very challenging to achieve both high catalytic activity and favorable stability for single‐phase materials. Herein, a highly active and durable nanocomposite cathode (Ba0.5Sr0.5)0.75Pr0.25Co0.575Fe0.3W0.125O3‐δ (BSPCFW) for low‐temperature SOFC (≤650 °C) is presented, which self‐assembles into two cubic perovskites: the simple perovskite Pr0.38Ba0.25Sr0.37Co0.62Fe0.38O3‐δ (PBSCF‐c) and the B‐site cations ordered double perovskite Ba1.30Sr0.70Co1.0Fe0.25W0.75O6‐δ (BSCFW‐c). The former PBSCF‐c serves as the highly conductive and active catalyst for ORR, while the latter BSCFW‐c with a large lattice parameter introduces a key beneficial lattice tensile strain into the PBSCF‐c phase through a coherent interface, which significantly promotes the ORR activity at low temperatures with the area specific resistance of 0.034 Ω cm2 at 650 °C, and the long‐term stability of 2 years storage and 1280 h operation in symmetrical cell. The introduction of the beneficial lattice tensile strain in self‐assembled composite catalysts is an effective way to synergistically enhance the electrochemical activity and durability of the electrode materials for electrochemical devices.

Effects of In substitution in Y1−xInxBaCo3ZnO7+δ (0 ≤ x ≤ 0.5) cathodes for intermediate temperature solid oxide fuel cells

Density functional theory was used to design a non-noble metal catalyst for low temperature oxygen reduction. A core–shell catalyst of Ag|AgxCu5-xZn8 was found to have an electronic structure predicted to be near optimal for weak oxygen bonding, and the activation energy for dissociation was low. This catalyst was made via evaporation and sputtering and tested as the anode and cathode of low temperature solid oxide fuel cells. The new catalyst showed charge transfer resistance 16 times higher than platinum on the cathode side, and five times lower on the anode side at 400 °C. The resistance to common catalyst poisons CO and H2S is enhanced compared to Pt. Further, the catalyst was tested as the cathode of a proton exchange membrane fuel cell by testing the half cell reaction in a rotating disk electrode. The exchange current density was within a factor of 3 lower than Pt, while the charge transfer coefficient was a factor of 3 higher than Pt. The Ag|AgxCu5-xZn8 catalyst is a promising start to develop non...

Fabrication and characterization of low-temperature SOFC stack based on GDC electrolyte membrane

Development of nickel based cermet anode materials in solid oxide fuel cells – Now and future

Mixed metallic oxides are getting increasing attention as novel electrode materials for energy conversion devices. However, low mixed ionic-electronic conductivity and high operating temperature hamper the practical applications of these devices. This study reports an effective strategy to improve the conductivity and performance of the fuel cell at low temperature by partially incorporating graphene in the Li0.1Cu0.2Zn0.7-oxide (LCZ) composite. The proposed cathode material is synthesized via the cost effective conventional solid-state route. Graphene incorporated LCZ shows excellent performance, which is attributed to the favorable charge transport paths offering low area-specific resistance. An X-ray diffractometer (XRD) and scanning electron microscope (SEM) are employed for microstructural and surface morphological analyses, respectively. Electrical conductivities of all the materials are determined by the DC four probe method, and interestingly, LCZ-1.5% graphene exhibits an excellent conductivity of 3.5 S/cm in air atmosphere at a temperature of 450 °C with a minimum value of 0.057 Ωcm2 area-specific resistance (ASR) that demonstrates significantly good performance. Moreover, the three-layer fuel cell device is fabricated using sodium carbonated Sm0.2Ce0.8O (NSDC) as an electrolyte, which can operate at low temperatures exhibiting open circuit voltage 0.95 V and shows a peak power density, i.e., 267.5 mW/cm2 with hydrogen as the fuel.

: Using DFT and experimental methods, the following topics have been deeply explored. (1) Interaction between oxygen and molten carbonate; (2) Fabrication and test of SOFCs with MC modified LSM cathodes; (3) Low-temperature SOFCs using MC modified LSCF/GDC cathode; (4) Spectroscopic and DFT evidence of pyrocarbonate. The results point out that molten carbonate modified cathodes can significantly reduce the operating temperature of SOFCs by enhancing the ORR process at low temperatures of 500-650 deg C. The mechanism of ORR with the presence of MC was proposed through DFT modeling and the theoretical results agree well with the experiments.

Up to now, Solid Oxide Fuel Cell (SOFC) materials and processing does not meet the cost goals for commercialization. This resulted in a worldwide increase in R&D activities dealing with advanced materials and effective manufacturing methods. The present paper describes efforts to process novel SOFC materials as well as optimization of well known ones. The R&D trends are explained for key components such as anode, electrolyte, cathode, contact- and protective layers. Typical SOFC manufacturing methods include tape casting, extrusion, calendaring and axial pressing. Each of these techniques has advantages and limitations. Examples for the highly efficient use of these methods are given for electrolyte supported cells as well as anode and cathode supported designs. An evaluation in reference to automation, process complexity and costs is given under the present limiting factors. Exemplary the processing by tape casting and the micro structural fine tuning of an advanced anode-supported system is discussed in detail. To produce the layered components of an SOFC, techniques like screen printing, wet powder spraying, PVD and CVD are under development. While the layer properties are excellent, PVD and CVD are nowadays too expensive in some cases, due to the low deposition rates. If thin layers are required, these techniques become interesting under cost considerations. The effectiveness of a PVD interlayer between electrolyte and high power density cathodes is shown in comparison to a sintered layer. In thin electrolyte concepts, the cathode becomes the power limiting component at operating temperatures below around 750°C. Thus new cathode materials and adjusted processing parameters are under development. The possibilities to manufacture advanced cathode layers by screen printing, wet powder spraying and other wet chemical methods are discussed. As an example screen printing of LSCF is described which results in a high power density cathode layer for low temperature SOFC operation. Finally, future needs to achieve the technical and economic goals are summarized.

Proc. 6 th International Symposium on Solid Oxide Fuel Cells (SOFC-VI) ed. S. C. Singhal et al., Honolulu, Hawaii, Oct. 17-22, 1999 LBNL-43185 May, 1999 PROMISES AND PROBLEMS WITH METALLIC INTERCONNECTS FOR REDUCED TEMPERATURE SOLID OXIDE FUEL CELLS Peggy Y. Hou, Keqin Huang † and Wate T. Bakker* Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley, CA 94720 Texas Materials Institute, ETC 9.102 The University of Texas at Austin Austin, TX 78713 *Electric Power Research Institute 3412 Hillview Avenue Palo Alto, CA 94304 ABSTRACT The oxidation kinetics and electrical properties of oxide scales thermally grown on the surface of a commercial iron-based alloy have been investigated up to 1000 o C. The effect of surface coating to improve performance was studied, and it was found that a double coating of Y and Ni oxide was most beneficial. While the Y oxide reduced the oxidation rate, the Ni oxide increased the Cr 2 O 3 scale conductivity. Different electrodes were applied to the alloy or to pre-oxidized samples. Some of the electrodes, such as LaSrCoO 3 (LSCo), reacted strongly with the alloy upon oxidation by increasing the oxidation rate and forming a mixed Fe/Co/Cr interlayer that impeded conduction. Application of these electrodes to a pre-oxidized surface eliminated these problems. Preliminary results in reducing atmosphere using Ce 0.8 +Sm 0.2 O 1.9 +Ni and Pt electrodes are also reported. The possibility of using Cr 2 O 3 forming alloys as interconnects for low temperature solid oxide fuel cell is discussed in light of these results. INTRODUCTION The trend in planar solid oxide fuel cell (SOFC) development is towards lower temperature operation. This has several advantages such as the elimination of interdiffusion between electrodes and electrolytes, ease of internal reforming and the use of relatively low cost metallic interconnects and balance of plant components. Several methods to operate at low temperatures have been identified and demonstrated at a single cell level. The most prominent are the use of thin film, conventional doped zirconia electrolytes (1,2) and the use of a recently discovered new electrolyte, doped lanthanum

Introduction For many potential mobile robot applications, current power supply technology (such as the lithium ion battery technology) is in fact a key limiting factor due to its low energy density. Solid oxide fuel cells (SOFCs) are a promising alternative and can overcome limitations of current battery technology. This is because SOFCs can, in principle, use not only hydrogen but also hydrocarbon fuels which have high energy density such as gasoline and so on.Ni-YSZ cermet is the most promising anode material for SOFCs because of its low cost, chemical stability, and closely matched thermalexpansion coefficients with the dense YSZ electrolyte. Ni is an excellent catalyst for hydrocarbon fuel reforming and cracking, which leads to rapid carbon deposition inside the SOFC anode and causes coking and deactivation1). In principle, the carbon deposition on Ni can be depressed by adding steam in the hydrocarbon fuel2,3), whereas few detailed investigations of SOFCs that operate on gasoline fuel have been reported.In this work, we studied the effect of steam content and demonstrated the direct operation of SOFCs by octane which is a main ingredient of gasoline. In the case of the Ni-YSZ anode, the operation temperature must be high in order to avoid sulfur poisoning4 -6 ), because most commercially available fuels contain sulfur. Therefore, in this study, the SOFCs operation was conducted at high temperature of 950 oC. Experimental Surface-polished YSZ pellets of 2 mm in thickness were used for the electrolyte. Pt cathode electrode and Pt reference electrode were prepared on the surface and side of the pellets, respectively, by firing Pt paste at 1300 oC. Then, NiO powder and GDC powder (NiO/YSZ=6/4 (wt)) were thoroughly mixed in a vacuum using the planetary ball mill (200 rpm, 12 h), and made into NiO-YSZ pastes using ethyl-cellulose and organic solvent. The NiO-YSZ paste was screen-printed in diameter of 8 mm on the YSZ pellets and sintered at 1200 oC for 1 h.Octane and steam were supplied to the SOFC cell by bubbling carrier gas (He) at a constant rate. Octane bubbler temperature was 30 oC, and Steam/Carbon ratio (S/C) were controlled by changing the temperature of the water bubbler from 40 to 70 oC. Electrochemical properties (open circuit voltage, anode electrode resistance, I - V and I - P characteristics, stable power generation property) were measured over a temperature range of 950-700 oC. During the constant current generation, exhaust gas was analyzed by gas chromatography. Results and Discussion Figure 1 shows I - V and I - P characteristics for the cells at 950 oC in wet octane. Maximum power density of 35 mW/cm2 was obtained by S/C of 8.9. The power density decreased with S/C quickly.Figure 2 shows the time course of cell voltage at a drawn current density of 5.2 mA/cm2 for S/C of 3.5. The cell voltage was stable. That is, carbon deposit does not arise even in the cell of the Ni-YSZ anode in low S/C of 3.5 when the operation temperature is high of 950 oC. References 1) S. Mclntosh and R.J. Gorte, “Direct Hydrocarbon Solid Oxide Fuel Cells,” Chemical Reviews, 104 (2004) 4845- 4865.2) K. Sasaki and Y. Teraoka, “Equilibria in Fuel Cell Gases: I. Equilibrium Compositions and Reforming Conditions,” Journal of Electrochemical Society, 850 (7) (2003) A878-A884.3) K. Sasaki and Y. Teraoka, “Equilibria in Fuel Cell Gases: II. The C-H-O Ternary Diagrams,” Journal of Electrochemical Society, 850 (7) (2003) A885-A888.4) K. Sasaki, K. Susuki, A. Iyoshi, M. Uchimura, N. Imamura, H. Kusaba, Y. Teraoka, H. Fuchino, K. Tsujimoto, Y. Uchida, N. Jingo, “H2S Poisoning of Solid Oxide Fuel Cells,” J. Electrochem. Soc., 153 (2006) A2023–A2029.5) P. Lohsoontorn, D.J.L. Brett, N.P. Brandon, “Thermodynamic predictions of the impact of fuel composition on the propensity of sulphur to interact with Ni and ceria-based anodes for solid oxide fuel cells,” Journal of Power Sources, 175 (2008) 60–67.6) H. Kishimoto, Y-P Xiong, K. Yamaji, T. Horita, N. Sakai, M.E. Brito, H. Yokokawa, “Stability of Ni base anode for direct hydrocarbon SOFCs, ” Journal Chemical Engineering of Japan, 40 (13) (2007) 1178-1182.

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