Solid oxide fuel cells produced at Riso National Laboratory have been tested as electrolysis cells by applying an external voltage. Results on initial performance and durability of such reversible ...solid oxide cells at temperatures from 750 to 950 deg C and current densities from -0.25 A/cm2 to - 0.50 A/cm2 are reported. The full cells have an initial area specific resistance as low as 0.27 Omegacm2 for electrolysis operation at 850 deg C. During galvanostatic long-term electrolysis tests, the cells were observed to passivate mainly during the first ~ 100 h of electrolysis. Cells that have been passivated during electrolysis tests can be partly activated again by operation in fuel cell mode or even at constant electrolysis conditions after several hundred hours of testing.
Metal‐supported solid oxide fuel cells are expected to offer several potential advantages over conventional anode (Ni‐YSZ) supported cells. For example, increased resistance against mechanical and ...thermal stresses and a reduction in material costs. When Ni‐YSZ based anodes are used in metal supported SOFC, elements from the active anode layer may inter‐diffuse with the metallic support during sintering. This work illustrates how the inter‐diffusion problem can be circumvented by using an alternative anode design based on porous and electronically conducting layers, into which electrocatalytically active materials are infiltrated after sintering. The paper presents the electrochemical performance and durability of the novel planar metal‐supported SOFC design. The electrode performance on symmetrical cells has also been evaluated. The novel cell and anode design shows a promising performance and durability at a broad range of temperatures and is especially suitable for intermediate temperature operation at around 650 °C.
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3.
Break Down of Losses in Thin Electrolyte SOFCs Barfod, R.; Hagen, A.; Ramousse, S. ...
Fuel cells (Weinheim an der Bergstrasse, Germany),
April, 2006, Volume:
6, Issue:
2
Journal Article
Peer reviewed
The contributions of the individual components of the cell (anode, cathode, and electrolyte) to the cell resistance were determined experimentally, directly from impedance spectra obtained from a ...full cell. It was an anode supported thin electrolyte cell, consisting of a YSZ electrolyte, a Ni/YSZ cermet anode, and a LSM composite cathode. Additional, qualitative information was obtained using symmetric cells with LSM composite electrodes. The investigations were carried out in the temperature interval from 700 to 850 °C. The electrolyte and anode activation energies obtained were 0.9 and 1.1 eV, respectively, which is in relatively good agreement with literature values. The anode resistance was 0.24 Ω cm2 and the cathode resistance was 0.58 Ω cm2 at 700 °C, corresponding to 23% and 56% of the total resistance, respectively.
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The sintering of asymmetric CGO bi-layers (thin dense membrane on a porous support; Ce0.9Gd0.1O1.95−δ=CGO) with Co3O4 as sintering additive has been optimized by combination of two in situ ...techniques. Optical dilatometry revealed that bi-layer shape and microstructure are dramatically changing in a narrow temperature range of less than 100°C. Below 1030°C, a higher densification rate in the dense membrane layer than in the porous support leads to concave shape, whereas the densification rate of the support is dominant above 1030°C, leading to convex shape. A flat bi-layer could be prepared at 1030°C, when shrinkage rates were similar. In situ van der Pauw measurements on tape cast layers during sintering allowed following the conductivity during sintering. A strong increase in conductivity and in activation energy Ea for conduction was observed between 900 and 1030°C indicating an activation of the reactive sintering process and phase transformation of cobalt oxide.
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The potential of MS‐SOFCs was demonstrated through the previous EU METSOFC project, which concluded that the development of oxidation resistant novel metal‐supported solid oxide fule cell (MS‐SOFC) ...design and stack is the requirement to advance this technology to the next level. The following EU METSAPP project has been executed with an overall aim of developing advanced metal‐supported cells and stacks based on a robust, reliable and up‐scalable technology. During the project, oxidation resistant nanostructured anodes based on modified SrTiO3 were developed and integrated into MS‐SOFCs to enhance their robustness. In addition, the manufacturing of metal‐supported cells with different geometries, scalability of the manufacturing process was demonstrated and more than 200 cells with an area of ∼150 cm2 were produced. The electrochemical performance of different cell generations was evaluated and best performance and stability combination was observed with doped SrTiO3 based anode designs. Furthermore, numerical models to understand the corrosion behavior of the MS‐SOFCs were developed and validated. Finally, the cost effective concept of coated metal interconnects was developed, which resulted in 90% reduction in Cr evaporation, three times lower Cr2O3 scale thickness and increased lifetime. The possibility of assembling these cells into two radically different stack designs was demonstrated.
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Many years of close collaboration between Topsoe Fuel Cell A/S (TOFC) and Risø (to day DTU Energy Conversion) on SOFC development have ensured an efficient transfer of SOFC basic know how to ...industrial technology. The SOFC development in the consortium includes material development and manufacturing of materials, cells and stacks based on state of the art as well as innovative strategies. Today TOFC provides the SOFC technology platform: Cells, stacks, integrated multi stack module and PowerCore units that integrate stack modules with hot fuel processing units for high electrical efficiency. TOFC collaborates with integrator partners to develop, test and demonstrate possibilities and challenges in case of CHP, distributed generation, transportation application and electrolysis. Aiming at improved reliability, robustness and low material cost, TOFC has in the collaboration with DTU increased the efforts on development of next generation cells with metallic support including novel infiltrated nano-structured electrodes for operation in the temperature range 600-700 oC. Recently, record-breaking results have been obtained on cell level as well as on stack level.
In the present paper, anode supported solid oxide fuel cells (SOFCs), produced on a pre‐pilot plant scale in ten batches of ∼100 cells, are characterised with respect to performance. The main purpose ...was to evaluate the reproducibility of the scaled‐up process. Based on 20 tests, the average area specific cell resistance at 850 °C was found to be 0.24 Ω cm2 with a standard deviation of 0.05 Ω cm2. The variation in performance between the cells can be largely attributed to variations in the cathode performance. Experimental evidence will be presented on full 4 × 4 cm2 cells, symmetric cells with two cathodes on a YSZ strip, and a special cell with a divided cathode.
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The degradation behavior of anode supported solid oxide fuel cells (SOFCs) was investigated as a function of operating temperature and current density. Degradation rates were denned and shown to be ...mainly dependent on the cell polarization. The combination of a detailed evaluation of electrochemical properties by impedance spectroscopy, in particular, and post-test microscopy revealed that cathode degradation was the dominant contribution to degradation at higher current densities and lower temperatures. The anode was found to contribute more to degradation at higher temperatures. Generally, the degradation rates obtained were lower at higher operating temperatures, even at higher current densities. A degradation rate as low as 2%/1000 h was observed at 1.7 A/cm2 and 950 deg C over an operating period of 1500 h.
The sintering behavior of porous Ce0.9Gd0.1O1.95 (CGO10) tape cast layers was systematically investigated to establish fundamental kinetic parameters associated to densification and grain growth. ...Densification and grain growth were characterized by a set of different methods to determine the dominant sintering mechanisms and kinetics, both in isothermal and at constant heating rate (iso-rate) conditions. Densification of porous CGO10 tape is thermally activated with typical activation energy which was estimated around 440–470kJmol−1. Grain growth showed similar thermal activation energy of ∼427±22kJmol−1 in the temperature range of 1100–1250°C. Grain-boundary diffusion was identified to be the dominant mechanism in porous CGO10 tapes. Grain growth and densification mechanism were found strictly related in the investigated temperature range. Porosity acts as a grain growth inhibitor and grain boundary mobility in the porous body was estimated around 10−18–10−16m3N−1s−1 at the investigated temperature range.
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