Supported Solid Oxide Fuel Cells Research Articles

Tubular Metal Support Solid Oxide Fuel Cell Manufacturing and Characterization

Tubular metal supported SOFC technology has successfully been developed over the past years with the aim at domestic CHP systems below 3 kWe. The basic cell structure consists of a metal porous support, a protective barrier layer, an anode and an electrolyte cofired at 1350ºC. Cathode and contacting layers are subsequently sintered at lower temperatures. The most significant results to date include successful thermal cycling of the cell and anodic connection during 450 cycles and 2000 hours, oxidation testing of the metal support for more than 2500 hours and a comparison of influence of porosity during 100 hours oxidation of metal porous substrates under high water vapour atmospheres.

Powder extrusion moulding of 430L stainless steel thin tubes for porous metal supported SOFCs

Thin and thick walled tubes made of 430L stainless steel for porous metal supported solid oxide fuel cells (SOFCs) were prepared by powder extrusion moulding (PEM). A gas atomised metal powder and a binder composed by 50 vol.‐% high density polyethylene and 50 vol.‐% paraffin wax were chosen. The most suitable powder loading for feedstock (68 vol.‐%) was determined by means of torque experiments and rheological measurements. Mixing temperature was selected taking into account the results from differential scanning calorimetry. The extrusion of tubes was carried out in a single screw extruder and two kinds of tubes with two different wall thicknesses were obtained. In order to investigate the homogeneity of feedstock, microstructure of green tubes was evaluated by SEM. Thermal debinding was performed on the basis of thermogravimetric analysis results. After sintering, tubes with good dimensional stability and without defects were obtained. Different wall thicknesses extruded were 150 and 500 μm.

Anode supported solid oxide fuel cells (SOFC) by electrophoretic deposition

Solid oxide fuel cells (SOFC), with its ability to use hydrocarbon fuels and capability to offer highest efficiency, have attracted great attention in India in recent years as an alternative energy generation system for future. But a great deal of problems associated with SOFC is needed to be solved before it can find commercial application. The relatively high operating temperature of 800–1000 °C of SOFC imposes a stringent requirement on materials that significantly increases the cost of SOFC technology. Reducing the operating temperature of an SOFC to below 800 °C can reduce degradation of cell components, improve flexibility in cell design, and lower the material and manufacturing cost by the use of cheap and readily available materials such as ferritic stainless steel. The operating temperature can be reduced by two possible approaches: (i) developing alternative electrolyte materials with high ionic conductivity at lower temperature, and (ii) developing much thinner and denser electrolyte layer such that the ohmic losses are minimised.In this work we report the use of inexpensive Electrophoretic deposition (EPD) technique in making about 10 micron thin and dense YSZ electrolyte on NiO–YSZ substrate. The effect of different operating parameters such as applied voltage, deposition time etc have been optimised during deposition from YSZ suspension in acetylacetone. The YSZ/NiO–YSZ bi-layers were then co-sintered at 1450 °C for 5 h. The single SOFC cells were then fabricated by brush painting LSM:YSZ (50:50) paste on the electrolyte layer followed by sintering at 1200 °C for 2 h. The single SOFC cell when tested using H2 as fuel and ambient air as oxidant exhibited an open circuit voltage (OCV) of 1.03 V and the peak power density of about 624 mW/cm2 at 800 °C.

Tubular Metal Support Solid Oxide Fuel Cell Manufacturing and Characterization

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Nanostructured GDC-impregnated La 0.7Ca 0.3CrO 3−δ symmetrical electrodes for solid oxide fuel cells operating on hydrogen and city gas

Nanostructured Gd 0.1Ce 0.9O 1.95 (GDC)-impregnated La 0.7Ca 0.3CrO 3−δ (LCC) composites were investigated as symmetrical electrodes for La 0.9Sr 0.1Ga 0.8Mg 0.2O 3−δ (LSGM)-supported solid oxide fuel cells (SOFCs) without using interlayer at anode/electrolyte interface. The impregnation of aqueous Gd 0.1Ce 0.9(NO 3) x solution into the porous LCC electrode backbones was found to form nanosized GDC particles on LCC surfaces after calcining at 850 °C for 30 min. The optimized performance of electrodes for SOFCs had been achieved through the impregnation cycles of 3–7 times. The introduction of the ion conducting phase GDC in nanometer significantly enhanced the symmetrical electrode performance. The symmetrical cell with the impregnation of five times displayed the best performance and the maximum power densities were 521 mW cm −2 and 638 mW cm −2 at 850 °C and 900 °C with dry H 2 as fuel, respectively. Using commercial city gas containing H 2S as fuel, the maximum power densities of the cell reached 362 mW cm −2 and 491 mW cm −2 at 850 °C and 900 °C, respectively. The microstructure, valence state of Ce element and electrochemical stability of the nanostructured GDC-impregnated LCC composites were also discussed.

Effect of Ni-GDC AFL Composition on Performance of IT-SOFCs

Anode supported solid oxide fuel cells (SOFCs) with various NiO content in the anode function layer (AFL) were fabricated and investigated. For AFLs with lower NiO content, the observed open circuit potential was higher. However, the highest maximum power density of 1.15 W/cm2 at 650 °C was achieved at 60 wt% of NiO in the AFL, which is a 1:1 volume ratio of Ni to GDC phase. The optimal composition was valid in the intermediate temperature range from 450 to 650 °C. The effect of the optimal composition on power density was retained for 200 hours with high power density of 1.1 W/cm2. Electrochemical impedance tests supported this result by showing the lowest electrode area specific resistance at 60 wt% NiO, which has a linear relationship with maximum power density.

Fabrication and evaluation of the thin NiFe supported solid oxide fuel cell by co-firing method

Abstract Metal supported solid oxide fuel cells (SOFCs) are one of the most promising candidates for power plants as well as portable applications due to their good mechanical and thermal properties. In this study, the thin NiFe supported SOFC, which consisted of thin metal support (NiFe, ∼70 μm), anode functional layer (Ni-YSZ, ∼30 μm), electrolyte (YSZ, ∼15 μm), and cathode (LSCF, ∼30 μm), was fabricated through tape casting and co-firing method. The cell showed 1.05–1.1 V of open circuit voltage and 1.4 W cm −2 of maximum power density at 800 °C with the ohmic resistance ( R ohm ) of 0.12 Ω cm 2 and the polarization resistance ( R p ) of 0.38 Ω cm 2 . The high performance and the successful measurement of thin metal supported cell showed the possibility for mobile applications through the large area cell fabrications.

Investigation of Various Factors Affecting the Gas Conversion Overpotential in Planar Type Anode Supported Solid Oxide Fuel Cells (SOFCs)

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Comparison of ultra-fast microwave sintering and conventional thermal sintering in manufacturing of anode support solid oxide fuel cell

Ultra-fast microwave sintering in a multi-mode domestic microwave oven with selective susceptor and spacer has been proved to be an effective and facile method in the manufacturing of anode support solid oxide fuel cell (SOFC). Two anode support SOFCs were fabricated by using ultra-fast microwave sintering and conventional thermal sintering techniques, separately. The performances of the two cells were measured and compared in a temperature range of 700–800 °C. The microstructures of the two cells after the measurements were compared qualitatively based on SEM images. FIB-SEM technique was used to reconstruct the 3-D microstructure of both anode and cathode. The quantitative comparison of 3-D reconstructions shows the application potential and the advantages of microwave technique in SOFCs manufacturing.

Comparison of the multicomponent mass transfer models for the prediction of the concentration overpotential for solid oxide fuel cell anodes

In this study, multicomponent mass diffusion models, namely the Stefan–Maxwell model (SMM), the Dusty Gas model (DGM) and the Binary Friction model (BFM) have been compared in terms of their predictive capabilities of the concentration polarization of an anode supported solid oxide fuel cell (SOFC) anode. The results show that other than the pore diameter, current density and concentration of reactants, which have a high importance in concentration polarization predictions, the tortuosity (or porosity/tortuosity) term, has a substantial effect on the model predictions. Contrary to the previous discussions in the literature, for the fitted value of tortuosities, SMM and DGM predictions are similar, even for an average pore radius as small as 2.6e−07 and current density as high as 1.5 A cm −2. Also it is shown that the BFM predictions are similar to DGM for the case investigated in this study. Moreover, in this study, the effect of the pressure gradient term in the DGM and the BFM has been investigated by including and excluding this term from the model equations. It is shown that for the case investigated and model assumptions used in this study, the terms including the pressure coefficient have an insignificant effect on the predictions of both DGM and BFM and therefore they can be neglected.

Nickel–Zirconia Anode Degradation and Triple Phase Boundary Quantification from Microstructural Analysis

AbstractMicrostructural evolution of anode supported solid oxide fuel cells (SOFC) during medium‐term stack testing has been characterised by scanning electron microscopy (SEM). Low acceleration voltage SEM imaging is used to separate the three anode phases (nickel, yttria‐stabilised zirconia and porosity). Microstructural quantification is obtained using a software code that yields phase proportion, particle size, particle size distribution and a direct measure of triple phase boundary (TPB) density (μm–2). In addition, an anode degradation model is proposed. The model describes the gradual degradation of the anode due to nickel particle sintering and the concomitant loss of TPB. Fundamental operational and structural parameters of the anode can be used to estimate the TPB length change with time from the degradation rate. The combination of experimental results and modelling allows separating the degradation due to sintering of nickel particles from total stack degradation. Anode degradation occurs principally during the first 500 operating hours. For stack tests carried out over more than 1,000 h, anode degradation was responsible for 18 to 41% of the total degradation depending on initial microstructure.

Effect of Nano Ion Conductor Infiltration on the Performance of Anode Supported Solid Oxide Fuel Cells

A high performance anode supported solid oxide fuel cell (SOFC) is developed by low-cost tape casting, co-sintering and nano-ion conductor infiltration techniques. The mixture of gadolinium and cerium nitrate solution is infiltrated into both anode and cathode layers and fired at a temperature that gadolinium nitrate and cerium nitrate undergoes a solid state reaction and forms nano ion conductor phase in both electrodes. The effect of molar concentrations and firing temperature of nano ion conductor phase on the cell performance are investigated. The measurements show that nano-sized ion conductor infiltration significantly improves the cell performance. The cell provides 1.718Wcm-2 maximum power density at an operation temperature of 750{degree sign}C. The high performance is attributed to increase in the oxide ion conductivity and three phase boundaries of both anode and cathode layers by nano ion-conductor infiltration.

Non-Ionic Conduction Phenomena in Yttria Stabilised Zirconia Electrolyte in SOFC operated in the Electrolysis Mode

Anode supported solid oxide fuel cells (SOFCs) with yttria stabilised zircona (YSZ) electrolytes were operated at ~800{degree sign}C as solid oxide H2O electrolyser cells (SOECs). Typical operation voltages were 1.0 to 1.3 V. When operation was extended to current densities j corresponding to a steam conversion rate above 100%, or when the steam supply was interrupted under constant current conditions, cell voltages saturated at about 1.8 to 2.0 V. Cells survived long-term current polarisation with j ~ -0.3 to -0.5 Acm-2 without steam supply. The mechanism limiting the cell voltage is attributed to electronic conduction in the YSZ electrolyte. Electrolyte conduction in the normal SOEC mode (with reasonable steam conversion rates) remains predominantly ionic in the investigated temperature range. Depending on the cell characteristics and the operation conditions (notably the temperature), however, the ionic transfer number may be significantly lower compared to the SOFC operation.

Performance Study of Alternative (La,Sr)FeO3-δ and (La,Sr)(Co,Fe)O3-δ MIEC Cathode Compositions

In this study two cathodes, La0.68Sr0.3FeO3-δ and La0.68Sr0.3Co0.2Fe0.8O3-δ, are characterized by electrochemical impedance spectroscopy. The chemical surface and diffusion coefficients of both cathode materials are obtained directly from impedance measurements performed on full anode supported solid oxide fuel cells (SOFC). This is done by a combined distribution of relaxation times and equivalent circuit impedance analysis method, which allows a high resolved identification and deconvolution of each single polarization mechanisms contributing to the overall loss of the cell.

Solid Oxide Fuel Cells damage mechanisms due to Ni-YSZ re-oxidation: Case of the Anode Supported Cell

The effects of Ni-YSZ cermet re-oxidation in anode supported Solid Oxide Fuel Cells (SOFCs) have been investigated. Damage mechanisms have been studied in both cases of direct oxidation in air (i.e., fuel shutdown) or by an ionic current (i.e., fuel starvation). Direct oxidation tests show that the electrolyte cracks for a conversion degree of Ni into NiO ranging between similar to 58 and similar to 71%. This failure mode has been modelled considering both the bulk expansion of the cermet induced by the transformation of the Ni phase and the change of mechanical stresses in the multilayered cell. In the case of fuel starvation, a thin layer of the cermet was electrochemically re-oxidised at 800 degrees C and then reduced under a hydrogen stream. This 'redox' cycle was repeated until the degradation of the cell. The evolution of the impedance diagrams recorded after each cycle suggests that the cermet damages in an area close to anode/electrolyte interface. The mechanical modelling states that a delamination can occur along the interface between the Anode Functional Layer(AFL) and the Anode Current Collector (ACC) substrate. This theoretical result confirms the experimental trends observed by impedance spectroscopy. (C) 2009 Elsevier B.V. All rights reserved.

Series Connection of Thick-Film (<20 μm) Electrolyte-Supported Solid Oxide Fuel Cells

Thick-film electrolyte (<20 μm)-supported solid oxide fuel cells (SOFCs) have the advantages of both electrolyte-supported and anode-supported cells due to their thin and self-supporting electrolyte layer. A multicell stacking design using a series connection of thick-film electrolyte-supported cells was adopted to avoid the bipolar plates of planar SOFCs. The cell structure of series-connected electrolyte-supported SOFCs (SES-SOFCs) is similar to the segmented-in-series SOFC design but is based on the self-supporting electrolyte. Two cells with 16 μm thick yttria-stabilized zirconia electrolytes connected in series achieved high performance, i.e., open-circuit voltage of 2.10 V and maximum power density of ∼460 mW/cm 2 at 800°C.

Internal reforming characteristics of cermet supported solid oxide fuel cell using yttria stabilized zirconia fed with partially reformed methane

Abstract In order to investigate the internal reforming characteristics in a cermet supported solid oxide fuel cell (SOFC) using YSZ as the electrolyte, the concentration profiles of the gaseous species along the gas flow direction in the anode were measured. Partially reformed methane using a pre-reformer kept at a constant temperature is supplied to the center of the cell which is operated with a seal-less structure at the gas outlet. The anode gas is sucked in via silica capillaries to the initially evacuated gas tanks. The process is simultaneously carried out using five sampling ports. The sampled gas is analyzed by a gas chromatograph. Most of the measurements are made at the cell temperature ( T cell ) of 750 °C and at various temperatures of the pre-reformer ( T ref ) with various fuel utilizations ( U f ) of the cell. The composition of the fuel at the inlet of the anode was confirmed to be almost the same as that theoretically calculated assuming equilibrium at the temperature of the pre-reformer. The effect of internal reforming in the anode is clearly observed as a steady decrease in the methane concentration along the flow axis. The effect of the water-gas shift reaction is also observed as a decrease in the CO 2 concentration and an increase of CO concentration around the gas inlet region, as the water-gas shift reaction inversely proceeds when T cell is higher than T ref . The diffusion of nitrogen from the seal-less outermost edge is observed, and the diffusion is confirmed to be more significant as U f decreases. The observations are compared with the results obtained by the SOFC supported by lanthanum gallate electrolyte. With respect to the internal reforming performance, the cell investigated here is found to be more effective when compared to the previously reported electrolyte supported cell.

Processing of YSZ screen printing pastes and the characterization of the electrolyte layers for anode supported SOFC

Screen printing pastes based on organic binder systems were developed for the production of dense electrolyte layers of Y 0.16Zr 0.84O 1.92(8YSZ) on Ni/YSZ anode substrates for anode supported solid oxide fuel cells (SOFCs). Pastes with a solid loading up to 50 vol.% (86 wt.%) of YSZ powder and the adequate thixotropic behaviour for screen printing could be produced. Dense layers were obtained by sintering at 1430 °C and were shown to be gas tight by window and He leakage test. The electrical conductivity of the dense layers and the resulting activation energy (96–99 kJ mol −1) were obtained from impedance spectra in the temperature range from 250 °C to 900 °C. The agreement with literature values indicates that performing layers have been obtained.

Effects of GDC interlayer on performance of low-temperature SOFCs

To bridge the sintering temperature gap between the electrolyte and the cathode, low-temperature anode supported solid oxide fuel cells (SOFCs) with various thickness of electrolyte interlayer were fabricated and investigated. The porous thin interlayer was dip-coated and fired onto the dense Ce 0.9Gd 0.1O 1.95 (GDC) electrolyte surface. With humidified hydrogen as the fuel and air as the oxidant, the single cell with a 0.15 μm interlayer achieved the maximum power density (MPD) of 0.9 W cm −2 at 600 °C. The higher open circuit voltages (OCVs) (>0.9 V at 600 °C) were obtained in this study. The impedance results showed that the porous interlayer not only improved the interfacial contact between electrolyte and cathode, but also increased electrochemically active surface area. The cathode/electrolyte polarization resistance exhibited minimum when a 0.15 μm interlayer was added. The apparent activation energies derived from the Arrhenius plots of interfacial polarization resistances were about the same when the added interlayer was thinner, which indicated that the reaction mechanism did not change. However, the corresponding values were higher as the thick interlayer was introduced, which could be ascribed to the retarded oxygen ion transfer in the added porous layer. The cell area specific resistance (ASR) obtained by linear fitting I– V plot in the region of 0.6–0.7 V was higher than the ohmic resistance tested at OCV condition, and it was potentially attributed to the increased oxygen partial pressure at the anode as well as the contribution from polarization resistance, i.e. polarization of mass transport.

Numerical study of mass and heat transport in solid-oxide fuel cells running on humidified methane

Internally reforming anode supported solid-oxide fuel cells (SOFC) running on humidified CH 4 is studied numerically. The computational framework employs detailed multi-step models for heterogeneous chemistry for Ni catalysts. The electrochemistry is implemented using a modified Butler–Volmer setting based on elementary charge transfer kinetics. Transport through the porous matrix is modeled using the dusty gas model (DGM). Parameters required for the electrochemical model are adjusted to reproduce experimentally observed data. Obtained parameters are then used to model a co-flow planar single cell under internally reforming conditions assuming the interconnect walls as adiabatic. Numerous runs with varying inlet conditions of cathode stream are carried out to deduce the behavior of temperature and current density distribution in the cell. Results show that internal reforming generally leads to a temperature drop near the inlet boundary.