Area Specific Resistance Values Research Articles

Characterization of a 100 W SOFC stack fed by carbon monoxide rich fuels

This paper presents the evaluation of the performance of a 100 W Solid Oxide Fuel Cell (SOFC) stack with CO rich fuels as anode gas. The study aims at measuring the Open Circuit Voltage (OCV) and the Area Specific Resistance (ASR) when the amount of CO in the anode flow varies from 0 to 40% in volume. At the same time, the FCTestQA procedures were applied and evaluated as methodology for Solid Oxide Fuel Cell testing. The theoretical OCV was measured considering both H2 and CO oxidation and the water gas shift reaction. The OCV values, as a function of CO concentration, resulted closely related to theoretical ones and the ASR value, calculated for different mixtures of fuel, did not change with anode gas composition and it seemed to be a function of the temperature and the degradation of the materials only.

Strontium Doping Effect on High-Performance PrBa1-xSrxCo2O5+ as a Cathode Material for IT-SOFCs

The strontium effect in PrBa1–xSrxCo2O5+δ (x = 0, 0.25, 0.5, 0.75, and 1.0) oxides was investigated based on their structural characteristics, electrical properties, and electrochemical performance. Electrical conductivities increase with increasing strontium content due to the higher oxygen content and coordination number. The area specific resistance (ASR) of PrBa1–xSrxCo2O5+δ were measured on Ce0.9Gd0.1O1.95 (GDC) and the minimum ASR values were observed at x = 0.5 and 0.75. Electrochemical performance of PrBa1–xSrxCo2O5+δ cathodes was measured using Ni-GDC anode-supported cell. The maximum power density was 1.08 W cm −2 at 600 ◦ Cf orx = 0.5 and 0.75.

Effect of B2O3–Bi2O3–PbO frit on the performance of LaBaCo2O5+δ cathode for intermediate-temperature solid oxide fuel cells

The effects of B 2 O 3 –Bi 2 O 3 –PbO (BBP) frit on the electrochemical performance, electrical conductivity, and thermal expansion of LaBaCo 2 O 5+ δ (LBCO) cathode were investigated. BBP frit was found to be effective in lowering the sintering temperature of LBCO cathode by about 200 °C and in improving its electrochemical performance within the intermediate-temperature range of 600–800 °C. LBCO with 5 wt.% BBP frit cathode based on Sm 0.2 Ce 0.8 O 1.9 electrolyte showed the best electrochemical performance, i.e., the lowest area-specific resistance (ASR) and cathodic overpotential. The ASR values were about 64.1%, 66.1%, and 74.5% lower than those of LBCO at 700, 750, and 800 °C, respectively. The cathodic overpotential decreased from 51.0 mV for LBCO to 8.2 mV at a current density of 0.2 A cm −2 at 700 °C. The electrical conductivity of LBCO with 5 wt.% BBP frit was about 320–330 S cm −1 at 600–800 °C in air. ► B 2 O 3 –Bi 2 O 3 –PbO (BBP) frit is proven to be an effective sintering agent for cathode. ► The addition of 5 wt.% BBP reduces the sintering temperature of LaBaCo 2 O 5+ δ by 200 °C. ► BBP is effective for improving the performance of LaBaCo 2 O 5+ δ cathode for IT-SOFCs. ► The addition of 5 wt.% BBP to LaBaCo 2 O 5+ δ reduce the thermal expansion at 600–800 °C.

Preparation and performance of triple-layer graded LaBaCo2O5+δ–Ce0.8Sm0.2O1.9 composite cathode for intermediate-temperature solid oxide fuel cells

The triple-layer graded LaBaCo2O5+δ–Sm0.2Ce0.8O1.9 (LBCO–SDC) composite cathode was prepared by screen-printing method for intermediate-temperature solid oxide fuel cells. The result of X-ray diffraction indicated the LBCO cathode was chemically stable with the SDC electrolyte. Through optimizing the composition and microstructure, the electrochemical performance of cathode was significantly improved. For triple-layer graded LBCO–SDC composite cathode, the area-specific resistance (ASR) values were 0.881Ωcm2 at 600°C, 0.174Ωcm2 at 700°C and 0.047Ωcm2 at 800°C in air, about 14.8%, 41.0% and 65.7% lower than that of the monolayer LBCO cathode, respectively. The cathodic overpotential was also decreased from 51.0mV for the monolayer cathode to 33.6mV at a current density of 0.20Acm−2 at 700°C. The graded composite cathode showed great potential in improving the cathode performance for IT-SOFCs.

Metallic Interconnects for Solid Oxide Fuel Cell: Performance of Reactive Element Oxide Coating During 10, 20 and 30 Months Exposure

One of challenges in improving the performance and cost-effectiveness of SOFCs (Solid Oxide Fuel Cells) is the development of suitable interconnect materials. Chromia-forming alloys and especially ferritic stainless steels, like Crofer22APU, are considered to be among the most promising candidate materials as interconnects in SOFC stacks. However, the performance of chromia-forming materials can be limited by the low electronic conductivity of the oxide scale (high ASR—area specific resistance—value). Such degradation is unacceptable regarding the long-term operation (>40,000 h). A previous study demonstrated that in air, the addition of a nanometric reactive element oxide (La2O3) layer applied by Metal Organic Chemical Vapour Deposition (MOCVD) drastically improved both corrosion rate and electrical properties of Crofer22APU for 100 h at 800 °C. In the present study, coating performances were checked after 10 months (7,700 h), 20 months (15,400 h) and 30 months (23,100 h) exposure in air at 800 °C. The corrosion products were characterized by SEM, EDX and XRD. ASR measurements are realized after long time exposure. The study demonstrates that the Crofer22APU alloy has a good oxidation resistance after 23,100 h in air but this alloy has a high ASR value equal to 0.410 Ω cm2. The coatings composed of thin reactive element oxides made of La2O3 or Y2O3 resulted in an important improvement in the high temperature oxidation resistance; the ASR values are equal to 0.180 and 0.160 Ω cm2 respectively.

LaCoO3: Promising cathode material for protonic ceramic fuel cells based on a BaCe0.2Zr0.7Y0.1O3−δ electrolyte

Symmetric cells (cathode/electrolyte/cathode) were prepared using BaCe0.2Zr0.7Y0.1O3−δ (BCZY27) as proton conducting electrolyte and LaCoO3 (LC) infiltrated into a porous BCZY27 backbone as cathode. Single phased LC was formed after annealing in air at 600 °C for 2 h. Scanning electron micrographs showed the presence of the infiltrated LC in the full cathode depth. Transmission electron micrographs revealed LC grains (60–80 nm) covering partly the BCZY27 grains (200 nm–1 μm). Impedance spectra were recorded at 500 °C and 600 °C, varying the oxygen partial pressure and the water vapour pressure. Two arcs correspond to the cathode contribution: a middle range frequency one (charge transfer) and a low frequency one (oxygen dissociation/adsorption). The area specific resistances (ASRs) of both contributions increase when decreasing the oxygen partial pressure. The low frequency arc is independent on the water vapour pressure while the charge transfer ASR values increase with higher pH2O. The cathode ASRs of 0.39 and 0.11 Ω cm2 at 500 and 600 °C respectively, in air (pH2O = 0.01 atm) are the lowest reported to the authors’ knowledge for PCFC cathodes. Furthermore, this work shows that the presence of oxide ion conduction in the cathode material is not necessary for good performance.

Ba and Gd Doping Effect in (BaxSr1–x)0.95Gd0.05Co0.8Fe0.2O3–δ (x = 0.1–0.9) Cathode on the Phase Structure and Electrochemical Performance

AbstractIn this study, BaxSr1–xCo0.8Fe0.2O3–δ (BSCF) doped with trace of Gd were studied for phase structures and properties about thermal expansion, electrical conductivity, and electrocatalytic activity. The solution range of barium in BaxSr1–xCo0.8Fe0.2O3–δ can be extended to 0.1 ≤ x ≤ 0.7 after the introduction of small amount of Gd3+ ions (only for 5%) into the Ba/Sr‐site. The calculation results of the crystal structure and the crystal lattice energy show that the ratio of Ba/Sr and doping of Gd3+ lead to increase the lattice parameter and the Co/Fe ionic average valence state in B‐site. Moreover, the ratio of Ba/Sr and doping of Gd3+ were found to have significant impacts on the high‐temperature physical properties and electrochemical characteristics. All oxides exhibited decreases in the thermal expansion coefficient (TEC) and electrical conductivity with increasing Ba/Sr ratio. Barium insertion was found to change the area‐specific resistance (ASR) of porous (not dense) cathodes. An ASR values of 0.048, 0.072, 0.064, 0.121, and 0.059 Ω cm2 under air condition were observed at 650 °C for BSGCF with x = 0.1, 0.2, 0.3, 0.5, and 0.7, respectively.

Synthesis, structure and electrochemical performance of cobaltite‐based composite cathodes for IT‐SOFC

AbstractThe development of novel and high‐performance cathodes is a critical issue to be addressed in order to reduce Solid Oxide Fuel Cells (SOFCs) operation temperature to the 600‐800 °C range or less. The performance of CeO2‐based composite cathodes is very attractive to such operational temperatures. In this work, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and Ce0.8Sm0.2O1.9 (SDC) powders were synthesized by different synthesis methods and mechanically mixed to prepare LSCF‐SDC composite cathodes. Screen‐printed LSCF‐SDC/CGO/LSCF‐SDC symmetrical cells were sintered at 1150 °C for 4 h and characterized by electrochemical impedance spectroscopy in static air. X‐ray diffraction and scanning electron microscopy were employed to characterize the powders. Area specific resistance values of 0.72 and 2.77 Ω cm2 at 800 °C were found for composite cathodes containing SDC powder synthesized by modified Pechini and microwave‐assisted combustion methods, respectively. Furthermore, the activation energy of the composite cathode containing SDC derived from modified Pechini method is 1.18 eV, i.e., much lower than 1.73 eV, value determined for LSCF with SDC from microwave‐combustion method.

Synthesis and characterization of GdCoO3 as a potential SOFC cathode material

Gadolinium cobaltite (GdCoO3) powder has been synthesized by solution polymerization method and characterized for its application as cathode material in gadolinia doped ceria (GDC) electrolyte based intermediate temperature SOFC (IT-SOFC). Perovskite structured phase pure and nanocrystalline GdCoO3 powder was obtained after calcining the precursor at 800°C. The powder was found to start sintering at about 850°C on heating and could be sintered to near theoretical density at 1200°C. The electrical conductivity of the sintered material was measured to be 580Scm−1 at 800°C and its coefficient of thermal expansion varied from 16×10−6 to 25×10−6K−1 in the temperature range from 200 to 1000°C. GdCoO3–GDC (1:1wt.%) composite cathode was found to have coefficient of thermal expansion that match closely with GDC electrolyte. Symmetric cells were prepared using GDC electrolyte and GdCoO3–GDC composite as the electrode and the area specific resistance (ASR) for interfacial polarization was evaluated by AC impedance spectroscopic technique. ASR values of 1.1, 0.55 and 0.2Ωcm2 have been obtained at 800, 850 and 900°C, respectively.

Effects of pre-oxidation on the microstructural and electrical properties of La0.67Sr0.33MnO3−δ coated ferritic stainless steels

LaxSr1−xMnO3 (LSM) is commonly used as a protective layer on the metallic interconnects of solid oxide fuel cells (SOFCs) to prevent surface oxidation and chromium poisoning. However, the volume shrinkage at elevated temperatures causes the LSM coatings to crack, resulting in chromium diffusion. Therefore, this paper investigates the effects of pre-oxidation on the microstructure and electrical properties of ferritic stainless steels coated with La0.67Sr0.33MnO3 (LSM). Four ferritic stainless steels were selected for use as interconnect substrates: Crofer22APU, Crofer22H, ss441, and ZMG232L. The candidate materials were pre-oxidised at 850°C for 25 and 50h, respectively. After the pre-oxidation process, the LSM films with a thickness of 3–4μm were deposited on the surface of samples by using Pulsed DC magnetron sputtering. After aging the coated specimens at elevated temperatures, the morphologies and crystalline structures were examined using SEM/EDX and XRD, respectively. The results indicated that the pre-oxidised layer, (Mn, Cr)3O4, could significantly suppress chromium penetration from the interior to the surface of the specimens. Moreover, the area specific resistance (ASR) values for the 25-h pre-oxidised specimens were 2.24, 12.21, 2.30, and 6.77mΩcm2 for Crofer22APU, Crofer22H, ss441, and ZMG232L, respectively, at 800°C for 500h in an air atmosphere.

Characterisation and optimisation of the cathode/electrolyte couple for SOFC LSCF/BIT07

BaIn0.3Ti0.7O2.85 (BIT07) is a new electrolyte material for solid oxide fuel cells (SOFC). Its use with the cathode material La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF) is advantageous due to their reaction (above 1000°C) that leads to the formation of perovskite compounds called BLSITCFx (BaxLa0.58(1−x)Sr0.4(1−x)In0.3xTi0.7xCo0.2(1−x)Fe0.8(1−x)O3−δ, with 0≤x≤1) at the cathode/electrolyte interface. In this study, the influence of the cathode microstructure on its performance has been investigated, by varying the cathode parameters. An area specific resistance (ASR) value of 0.07Ωcm2 at 700°C has been reached and more generally the cathodes exhibit good performance (below 0.2Ωcm2) for a large range of thermal treatments, cathode grain sizes and thicknesses. An ageing study realised at 700°C for 320h showed an ageing rate of 0.125%h−1.

Correlation between Slurry Pore Former Content and Electrochemical Performance of Solid Oxide Fuel Cells with an Aqueous Tape Casted Anode

Nickel oxide/yttrium stabilized zirconia (NiO/8YSZ) anodes with different amounts of pore formers for anode used for solid oxide fuel cell have been prepared by aqueous tape casting technique. The zeta potential of NiO/8YSZ aqueous suspensions with and without dispersants was characterized. Moreover, the viscosity of NiO/8YSZ aqueous suspensions with different amount of dispersants and pore formers were studied by the concentric cylindrical rotational viscometer. The microstructures of the anode with different amounts of pore formers were also studied by SEM. The electrochemical performance of the single cell with different amounts of pore formers( modified by 0.8 wt% of polyvinyl pyrrolidone (PVP) over graphite) was evaluated between 700 and 800 °C with hydrogen as the fuel and air as the oxidant. It was observed that the maximum power density of the single cell with the optimum amount of graphite content (20wt%) measured was over 0.8 Wcm-2 at 800 °C and the area specific resistance value was as low as 0.79Ωcm2. The study allowed identifying optimum amount of graphite modified by PVP as the most promising pore formers for the production of supporting anodes prepared by aqueous tape casting for intermediate temperature solid oxide fuel cell application.

Novel Ba0.5Sr0.5(Co0.8Fe0.2)1 − xTixO3 − δ (x = 0, 0.05, and 0.1) cathode materials for proton-conducting solid oxide fuel cells

Ba0.5Sr0.5(Co0.8Fe0.2)1−xTixO3−δ (x=0, 0.05, and 0.1) materials were successfully prepared via an improved solid-state reaction route in an attempt to get better chemical stability for Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF). Stability tests showed that the novel Ti-doping strategy can effectively increase the chemical stability for Ba0.5Sr0.5Co0.8Fe0.2O3−δ in CO2-containing environments. The larger the Ti doping amount, the better the chemical stability. Ti-doped samples showed only a slight increase in area specific resistance (ASR) values, as shown from electrochemical tests performed on symmetrical cells. Therefore, anode-supported single fuel cells using BaZr0.4Ce0.4Y0.2O3−δ (BZCY) as the electrolyte and BZCY-Ba0.5Sr0.5(Co0.8Fe0.2)0.9Ti0.1O3−δ as the composite cathode, were fabricated and tested. The measured maximum power density values were 181, 116, and 49mWcm−2 at 700, 600, and 500°C, respectively.

Thermal performance and capillary limit of a ceramic wick applied to LHP and CPL

Abstract The performance of a ceramic wick working as a capillary evaporator of a Loop Heat Pipe (LHP) and a Capillary Pumped Loop (CPL) is analyzed. The LHP and the CPL have a capillary evaporator with 10 mm of inner diameter and 25 mm of length. The LHP compensation chamber has the same diameter as the evaporator and a length of 50 mm. The ceramic wick was sintered from alumina and mullite powders, achieving 50% of porosity, 1–3 μm pore size distribution and permeability of 35 × 10 −15 m 2 , and then machined to properly fit the evaporators. The performance tests were carried out using deionized water as the working fluid for power inputs of up to 30 W. The thermal performance, capillary limit and area-specific thermal resistance of these systems were analyzed with the support of basic heat transfer and fluid flow lumped models. The lowest area-specific thermal resistance values of 31.7 °C/W/cm 2 for CPL and 25.0 °C/W/cm 2 for LHP were reached when dissipating 3.18 W/cm 2 , while the highest values of 52.8 °C/W/cm 2 for CPL and 38.8 °C/W/cm 2 for LHP were reached while dissipating 0.53 W/cm 2 and 1.06 W/cm 2 , respectively. The analysis shows that the systems operate well at their capillary limit and their performance is equivalent to similar devices operating with acetone and ammonia reported in the literature.

Characterization of Ba-deficient PrBa1−xCo2O5+δ as cathode material for intermediate temperature solid oxide fuel cells

A-site Ba-deficient PrBa1−xCo2O5+δ (PB1−xCO, x=0–0.08) oxides are synthesized and evaluated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) with respect to crystal structure, chemical stability, thermal expansion behavior, electrical conduction and electrochemical performance. PB1−xCO with Ba-deficiency x=0–0.08 has an orthorhombic structure, which shows lattice shrinkage with bigger x; higher Ba-deficiency x=0.1 causes formation of impurity phases. The PB1−xCO oxides are chemically stable with Gd0.1Ce0.9O1.95 (GDC) electrolyte at 1050°C in air. Thermal expansion coefficient of PB1−xCO decreases slightly with higher Ba-deficiency. Electrical conductivity of PB1−xCO exhibits an initial decrease with higher Ba deficiency to x=0.03 and then increases gradually to a maximum at x=0.08. Introduction of Ba deficiency greatly improves electrochemical performance of PB1−xCO, characterized by decreased area specific resistances (ASRs) with higher Ba deficiency. The ASR values as low as 0.115Ωcm2 and 0.093Ωcm2 have been obtained at 600°C in air for PB1−xCO with x=0.05 and 0.08 respectively. These results have demonstrated that the Ba-deficient PB1−xCO (x=0.03–0.08) oxides are promising cathode materials for IT-SOFCs.

Synthesis and characterisation of oxyanion-doped manganites for potential application as SOFC cathodes

In this paper we report the successful incorporation of borate and phosphate into CaMnO3 and borate into La1−ySryMnO3−δ. For CaMnO3, an increase in the electronic conductivity was observed, which can be correlated with electron doping due to the oxyanion doping favoring the introduction of oxide ion vacancies (as well as the higher valence of P5+ compared to Mn4+ in the case of phosphate doping). The highest conductivity at 800 °C was observed for CaMn0.95P0.05O3−δ, 43.0 S cm−1, in comparison with 7.6 S cm−1 for undoped CaMnO3 at the same temperature. For La1−ySryMnO3−δ the conductivity suffers a decrease for all compositions on borate doping, attributed to a reduction in the hole (Mn4+) concentration. In order to investigate the potential of these materials as SOFC cathodes, the chemical compatibility with Gd0.1Ce0.9O1.95 (CGO10) has also been investigated. For the calcium manganites, the lowest temperature examined without reaction was 900 °C, with minor amounts of Ca4Mn3O10 observed at 1000 °C. Composites of these cathode materials with 50% CGO10 were examined on dense CGO10 pellets and the area specific resistances (ASR) in symmetrical cells were determined. The ASR values, at 800 °C, were 1.50, 0.37 and 0.30 Ω·cm2 for CaMnO3, CaMn0.95B0.05O3−δ and CaMn0.95P0.05O3−δ, respectively. For the lanthanum strontium manganites, the B-doped compositions showed an improvement in the ASR values with respect to the parent compounds, despite the lower electronic conductivity. This may be due to an increase in ionic conductivity due to borate incorporation leading to the formation of oxide ion vacancies. Thus these preliminary results show that oxyanion doping has a beneficial effect on the performance of perovskite manganite cathode materials, and suggests that this doping strategy warrants further investigation in other perovskite cathode systems.

Hierarchical porous cobalt-free perovskite electrode for highly efficient oxygen reduction

A 3D hierarchical porous ceramic electrode is fabricated directly from a carbon-oxides precursor by a general, cost-effective, and facile method. The oxygen reduction reaction activity of the electrode is significantly enhanced due to enlarged active areas and optimized gas transport channels. For the first time, this study demonstrates that a cobalt-free cathode is able to reach the target area specific resistance value of 0.15 Ω cm2 at 600 °C. The new material has been successfully used as the cathode for a SOFC and shows high power generation ability below 600 °C.

고온열을 이용한 고온수증기전기분해장치(HTSE)에 의한 수소생산 특성에 관한 전산유체해석적 연구

The characteristics for hydrogen production and the thermochemical properties of high temperature steam electrolysis(HTSE) device have been numerically analyzed in a two-dimension, steady-state with using the COMSOL . The main parameters for the calculation are applied voltage, ASR(Area-specific Resistance), temperature and pressure of the inlet gas flow. The results showed that thermal-neutral voltage was 1.2454 V and rather than the cell temperature increases or decreases with increasing applied voltage by thermal-neutral voltage starting this voltage the temperature in high voltage tended to rise and temperature in the low voltage tended to fall. And with, increasing the values of ASR, temperature inside the cell and the hydrogen production rate were decreased.

Highly enhanced electrochemical performance of PrBa0.92Co2O5+δ cathode by introducing Ba cationic-deficiency

An A-site Ba cation-deficient layered-perovskite oxide PrBa0.92Co2O5+δ (PB0.92CO) was evaluated as a new cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). PB0.92CO is chemically stable with Ce0.9Gd0.1O1.95 (GDC) electrolyte at temperatures up to 1100 °C. PB0.92CO has conductivities of 580–195 S cm−1 at temperatures of 200–800 °C in air. Area specific resistances (ASR) of PB0.92CO cathode on the GDC electrolyte layer range from 0.093 Ω cm2 at 600 °C to 0.0068 Ω cm2 at 800 °C with an activation energy of 1.05 eV. These ASR values are much lower than the results of the parent PrBaCo2O5+δ (PBCO) cathode, cation-doped PBCO cathodes and the PBCO-based composite cathodes. The preliminary results have demonstrated that PB0.92CO has excellent electrochemical performances at temperatures of 600 °C–800 °C and is a very promising cathode material for IT-SOFCs.

Compatibility of proton conducting La6WO12 electrolyte with standard cathode materials

Mixed ionic and electronic conductors (MIEC) such as LSM (La0.7Sr0.3MnO3−δ), LSCM (La0.75Sr0.25Cr0.5Mn0.5O3−δ) and BSCF (Ba0.5Sr0.5Co0.8Fe0.2O3−δ) have been investigated as potential cathode materials with La6WO12 (LWO) proton conducting electrolyte for use in protonic ceramic fuel cells (PCFC). Different cathode — LWO powder mixtures have been subjected to high temperature treatment (1150°C during 144h in air) and studied by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). The analysis of the results reveals that LWO is chemically and mechanically stable with LSM and LSCM but reacts with BSCF. Symmetrical cells cathode/LWO/cathode have been studied by electrochemical impedance spectroscopy (EIS). The minimum of area specific resistance (ASR) values have been found for LSM cathode (in humidified air at 750°C: ASRLSM=4.3Ω·cm2; ASRLSCM=15.5Ω·cm2; ASRBSCF=9.7Ω·cm2). Composite cathodes using a two-phase ceramic/ceramic (cer–cer) approach were also studied. In the case of LSM/LWO cathode cer–cer, it allows a significant decrease of the ASR value.