Search

Rare earth element-doped bismuth oxides with the fluorite structure (δ-Bi2O3) exhibit high oxygen ion conductivity at low temperature, which is promising electrolyte materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). However, traditional co-sintering process is not applicable to the manufacturing of IT-SOFCs using low melting point Bi2O3-based electrolyte, while further high-temperature processing is not required for deposition Bi2O3-based electrolytes. In this study, plasma spraying was used to examine the possibility to deposit high-performance Bi2O3-based electrolytes without the following high-temperature process. (Bi2O3)0.75 (Y2O3)0.25 (YSB) spray powders were prepared by the sinter-crushing method. The YSB electrolytes were fabricated by plasma spraying at different deposition temperatures. The effects of deposition temperature on the coating microstructure, crystalline stability, and ion conductivity were investigated. Results showed that the as-sprayed YSB electrolytes present a dense microstructure with well-bonded lamellar interfaces. The pure δ-phase YSB electrolyte was deposited with 37.5-75 μm powders at a deposition temperature of 350 °C. The deposited YSB electrolyte presented the excellent ionic conductivity of 0.19 S cm−1 at 700 °C in comparison with 0.21 S cm−1 for sintered bulk. [ABSTRACT FROM AUTHOR]

For tubular solid oxide fuel cells (SOFCs), individual cells are connected in series by the interconnector to obtain desired voltage and power output. As the most widely used ceramic interconnector for high-temperature SOFCs, lanthanum chromite-based material is quite difficult to sinter to high density due to the high vapor pressure of the chromium component. In this paper, dense strontium-doped lanthanum chromite (LSC) membranes with enhanced lamellar interface bonding were achieved at an elevated deposition temperature over the critical bonding temperature by atmospheric plasma spraying (APS). The effects of molten droplet particle size on the chemical composition and phase structure of LSC deposits were studied. The preferential vaporization of Cr during plasma spraying was of the greatest interest here. When the particle size of molten droplet was smaller than 30 μm, the vaporization loss of Cr increased remarkably with the decrease in particle size, resulting in impurity phases. When the particle size was larger than 30 μm, the vaporization loss of Cr was greatly reduced. The electrical conductivity of plasma-sprayed LSC deposits reached 8.7 and 2.1 S/cm at 850 °C in oxidizing and reducing atmospheres, respectively. The optimized LSC deposits exhibited good stabilities of phase structure and properties under operation conditions, which is adequate for SOFC interconnector application. [ABSTRACT FROM AUTHOR]

The La 0.8 Sr 0.2 MnO 3 Zr 0.92 Y 0.16 O 2-δ (LSM-YSZ) composite is the most widely used oxygen electrode for solid oxide electrochemical cells (SOCs). However, operating temperatures >700 °C are required for good performance since oxygen reactions are limitied to three-phase boundaries (TPBs) because of poor ionic conductivity of LSM. Furthermore, LSM-YSZ electrodes typically delaminate during electrolysis operation leading to cell degradation. One strategy to improve SOCs with LSM-YSZ electrodes is to infiltrate a mixed ionically and electronically conducting (MIEC) material that promotes oxygen exchange. However, infiltrated materials have a nano-scale structure that may not be stable under SOC operating temperatures. Here, we report results on the infiltration of SrTi 0.3 Fe 0.6 Co 0.1 O 3-δ (STFC), a recently reported high performance MIEC, into LSM-YSZ to improve its electrochemical performance and stability at intermediate temperatures. The infiltrated STFC enhances LSM-YSZ and cell performance, typically yielding a decrease in electrode polarization resistance by a factor >3 times, resulting in an increase in fuel cell maximum power density and electrolysis current density (at 1.3 V) by a factor > 2 times. Perhaps more significantly, the infiltrated electrodes show good performance stability, with suppression of electrode delamination during electrolysis and no evidence of coarsening or segregation induced degradation. Image 1 • First application of STFC infiltration to improve LSM-YSZ performance and stability. • A factor of >3 reduction in polarization resistance by the infiltration of STFC. • A factor of >2 improvement in single cell performance by the STFC infiltration. • STFC-infiltration eliminates the delamination of LSM-YSZ electrodes in electrolysis. [ABSTRACT FROM AUTHOR]

PrBa 0.5 Sr 0.5 Co 2–x Fe x O 5+δ (PBSCF) (X = 0, 0.3, 0.4, and 0.5) is investigated as cathode material for intermediate-temperature solid oxide fuel cells. Suspension plasma spraying is used as a low cost and large-scale manufacturing process to prepare PBSCF cathodes. Fe substitution effects on the crystal structure and electrochemical performance are characterized. All plasma-sprayed PBSCF cathodes exhibit a pure and stable cubic structure. The suspension plasma-sprayed PBSCF deposits show a porous and fine structure, and the microstructures are insensitive to Fe substitution. Subsequent to Fe doping, the polarization resistance of PBSCF cathodes rapidly decreases for increasing Fe substitution concentration from 0 to 0.4. Further increase of the Fe doping concentration increases the cathode polarization instead. At 600 and 700 °C, a 20% Fe-doped (x = 0.4) PBSCF cathode exhibits remarkably low area-specific polarization resistances (R p ) of 0.074 Ω cm 2 and 0.012 Ω cm 2 , respectively. Moreover, the R p of all cathodes remains almost identical after isothermal annealing at 600 °C for 300 h. Furthermore, the thermally-sprayed porous metal-supported cell assembled with the optimal PBSCF cathode shows excellent performance with peak power densities of 0.37, 0.8, and 1.35 W cm −2 at 500, 600, and 700 °C, respectively. [ABSTRACT FROM AUTHOR]

Active three-phase boundaries (TPBs) significantly influence cathode performance in solid oxide fuel cells, but obtaining long TPBs and understanding the mechanism underlying the improved cathode performance when the electrolyte is prepared with a smooth surface by a high-temperature sintering process remain essential challenges. In this work, we used flame spraying to deposit single-layer semimolten particles on a smooth electrolyte to build a three-dimensional surface with enlarged active surface area and thus increased TPBs. Meanwhile, LaSrMnO (LSM) cathodes with fine microstructure were deposited by solution-precursor plasma spraying (SPPS) on the designed electrolyte to establish a three-dimensional cathode-electrolyte interface. The deposition behavior of the semimolten particles on the smooth electrolyte and LSM cathodes on the three-dimensional electrolyte surface was studied. The effects of the area enlargement factor ( α ) on the polarization resistance of the SPPS LSM cathodes were investigated, using three-dimensional electrolytes with α from 1.29 to 2.48. The results indicated that convex particles with different molten states bonded well with the electrolytes. SPPS LSM cathodes also showed good interfacial bonding with convex particles. Finally, the cathode polarization ( R ) decreased linearly with increase of α . At 800 °C, R decreased from 0.98 to 0.32 Ω cm when α was increased from 1.29 to 2.48. [ABSTRACT FROM AUTHOR]

Here, we investigate the feasibility of using a liquid plasma spray process as a novel method for the cost-effective fabrication of a nanonetwork of La 0.4 Sr 0.6 Co 0.2 Fe 0.8 O 3−δ (LSCF) and Ce 0.8 Gd 0.2 O 2−δ (GDC) composite as a high-performance cathode for intermediate-temperature solid oxide fuel cells. A suspension containing well-dispersed nanosized GDC particles in an LSCF precursor solution is designed as the feedstock. The effects of GDC concentration in the suspension on the phase composition, microstructure, and electrochemical performance of the resulting cathode are studied. When the GDC concentration increases to 15 g L −1 , the nanosized GDC particles distribute uniformly and continuously on the LSCF backbone to form a porous network structure. The electrochemical studies further indicate that the cathode polarization decreased with the increase in GDC concentration from 0 g L −1 to 15 g L −1 , whereas a further increase in the GDC concentration increases the cathode polarization instead. At 600 and 750 °C, the cathode prepared using 15 g L −1 GDC concentration exhibits an impressive area-specific polarization resistance (R p ) of 0.1 Ω cm 2 and 0.009 Ω cm 2 , respectively. Finally, the R p of the optimal cathode almost does not change after the isothermal dwelling at 650 °C for 350 h. [ABSTRACT FROM AUTHOR]

Porous metal-supported solid oxide fuel cells (SOFCs) have attracted much attention because their potential to dramatically reduce the cost while enhancing the robustness and manufacturability. In particular, 430 ferritic steel (430L) is one of the popular choice for SOFC support because of its superior performance and low cost. In this study, we investigate the oxidation and diffusion behavior of the interface between a Ni-based anode and porous 430L support exposed to a humidified (3% H 2 O) hydrogen atmosphere at 700 °C. The Ni-GDC (Ce 0.8 Gd 0.2 O 2−δ ) cermet anodes are deposited on the porous 430L support by atmospheric plasma spraying (APS). The effect of exposure time on the microstructure and phase structure of the anode and the supports is studied and the element diffusion across the support/anode interface is characterized. Results indicate that the main oxidation product of the 430L support is Cr 2 O 3 , and that Cr and Fe will diffuse to the anode and the diffusion thickness increases with the exposure time. The diffusion thickness of Cr and Fe reach about 5 and 2 μm, respectively, after 1000 h exposure. However, the element diffusion and oxidation has little influence on the area-specific resistance, indicating that the porous 430L steel and plasma sprayed Ni-GDC anode are promising for durable SOFCs. [ABSTRACT FROM AUTHOR]

La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3 (LSGM) is considered a promising electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to its high ionic conductivity and stability under fuel cell operating conditions. Here we report our findings in investigating the feasibility of using a high velocity oxygen fuel flame (HVOF) spraying process for cost-effective fabrication of dense LSGM electrolyte membranes. The flame and in-flight particle behavior were simulated numerically to optimize the microstructure and phase compositions of the LSGM deposits. The measured gas leakage rate of an LSGM deposit is ∼7 × 10 −7 cm 4 gf −1 s −1 . The single cell assembled with 50–55 μm HVOF-sprayed LSGM electrolyte shows open circuit voltage (OCV) of 1.08 V at 800 °C, suggesting that the as-sprayed LSGM deposit is dense enough for direct application as SOFC electrolyte. At 800 °C, the ionic conductivity of the sprayed LSGM deposit is ∼0.04 S cm −1 , indicating that the HVOF spraying is a promising process for low-temperature fabrication of dense LSGM electrolyte membranes for IT-SOFCs. [ABSTRACT FROM AUTHOR]

Perovskite-structured (LaSrCoFeO) LSCF has been widely studied as a cathode material for intermediate-temperature solid oxide fuel cells. However, the application of LSCF cathode is likely to be limited by its sluggish surface catalytic properties and long-term stability issues. Oxygen hyper-stoichiometric LaNiO with KNiF structure exhibits higher catalytic properties, ionic conductivity, and stability in comparison with LSCF cathode. Due to the good chemical compatibility of these two cathode materials, it is possible to prepare a composite cathode by the infiltration of LaNiO in the porous LSCF. This composite structure fully utilizes the advantages of the two cathodes and enhances the LSCF cathode performance. In this study, the LSCF cathode was deposited by using an atmospheric plasma spray technique, and the porous LSCF cathode was then infiltrated by LaNiO. The atmospheric plasma spray technique was used to reduce the SOFC manufacturing cost. The microstructure of coatings was characterized by SEM and EDS. The cathode polarization resistance was found to decrease by ~40% after the LaNiO infiltration. Also, the activation energy decreased from 1.53 to 1.40 eV. [ABSTRACT FROM AUTHOR]

Abstract: La-doped strontium titanate (LST) is a promising, redox-stable perovskite material for direct hydrocarbon oxidation anodes in intermediate-temperature solid oxide fuel cells (IT-SOFCs). In this study, nano-sized LST and Sm-doped ceria (SDC) powders are produced by the sol–gel and glycine–nitrate processes, respectively. The chemical compatibility between LST and electrolyte materials is studied. A LST–SDC composite anode is prepared by suspension plasma spraying (SPS). The effects of annealing conditions on the phase structure, microstructure, and chemical stability of the LST–SDC composite anode are investigated. The results indicate that the suspension plasma-sprayed LST–SDC anode has the same phase structure as the original powders. LST exhibits a good chemical compatibility with SDC and Mg/Sr-doped lanthanum gallate (LSGM). The anode has a porosity of ∼40% with a finely porous structure that provides high gas permeability and a long three-phase boundary for the anode reaction. Single cells assembled with the LST–SDC anode, La0.8Sr0.2Ga0.8Mg0.2O3 electrolyte, and La0.8Sr0.2CoO3–SDC cathode show a good performance at 650–800 °C. The annealing reduces the impedances due to the enhancement in the bonding between the particles in the anode and interface of anode and LSGM electrolyte, thus improving the output performance of the cell. [Copyright &y& Elsevier]

Sr(Ti 1-x Fe x)O 3−δ (STF) perovskite has been developed as one of the alternatives to Nickel-base fuel electrodes for solid oxide electrochemical cells (SOCs) that can provide good tolerance to redox cycling and fuel impurities. Recent results on STF fuel electrodes present excellent electrochemical performance and outstand stability both under H 2 fuel cell mode and H 2 O electrolysis mode, however, the electrochemical characteristics in other fuel gases, such as CO, CO–H 2 mixture, CH 4 , and CO–CO 2 mixture have not been investigated. Herein, we report the electrochemical performance of Sr(Ti 0.3 Fe 0.7)O 3−δ fuel electrode on La 0.8 Sr 0.2 MnO 3−δ -Zr 0.92 Y 0.16 O 2−δ (LSM-YSZ) oxygen electrode supported SOCs with thin YSZ electrolyte using different fuel gases. At 800 °C, the peak power density slightly decreased from 0.9 W/cm2 in wet H 2 to 0.68 W/cm2 in wet CO under fuel cell mode. However, the cell only showed a peak power density of 0.27 W/cm2 at 800 °C in wet CH 4 , reaching 0.75 W/cm2 at 850 °C, when the open-circuit voltage increased from 0.9 V to 1.02 V. STF fuel electrode exhibited much worse CO 2 electrolysis performance than steam electrolysis, especially in high CO 2 concentration due to the increased ohmic resistance and electrode polarization resistance. [ABSTRACT FROM AUTHOR]

The potential application of plasma spraying in the preparation of ceramic electrolyte for porous metal-supported solid oxide fuel cells (SOFCs) is highlighted by its ability to eliminate the need for a high-temperature sintering process. However, the challenge of achieving highly dense electrolytes through plasma spraying remains to be addressed. In this study, a novel electrolyte for porous metal-supported SOFCs (PMS-SOFCs) is developed. This involved the preparation of a highly dense structure of gadolinium-doped ceria (GDC)-lanthanum strontium gallium magnesium oxide (LSGM) composite coating using plasma spraying under atmospheric conditions. The composite electrolyte is prepared using atmospheric plasma spraying (APS). The addition of the low-melting-point LSGM phase enhanced the microstructural densification of the GDC-based composite coating and diminished electron loss in a reducing atmosphere, thereby improving the cell's open-circuit voltage. At 36 kW plasma arc power, the single cell with composite electrolyte exhibited a maximum power density of 371 mw/cm2 at 750 °C and achieved the highest open-circuit voltage (1.03 V) at 600 °C. Moreover, the open-circuit voltage remained stable over a 100-h test. These findings suggest that using APS to deposit a composite electrolyte with added low-melting-point secondary phases presents a promising approach for achieving relatively high OCV in PMS-SOFCs based on cerium oxide electrolytes. [Display omitted] • Bulk-like composite electrolyte directly fabricated by atmospheric plasma spray. • OCV can reach 1.03V at 600 °C for ceria-based composite electrolyte. • LSGM splats effectively blocked the electron conducting in GDC deposits. • Low melting point LSGM could enhance the interface bonding of plasma-sprayed GDC electrolyte. [ABSTRACT FROM AUTHOR]

Very low pressure plasma spraying (VLPPS) is an attractive method for metal-supported solid oxide fuel cells, wherein it can significantly avoid the oxidation of metal substrate. In this study, scandia-stabilized zirconia electrolyte was fabricated by VLPPS. To investigate the microstructure of coatings, the spraying distances were set to 150, 250 and 350 mm. The fractured morphology suggests that, at a relatively low deposition temperature (< 350 °C), typical lamellar structure was replaced by trans-granular structure. The apparent porosity of coatings ranges from 4.75 to 6.83%, as per the image analysis method. The ionic conductivity of coating at 250 mm was 0.068 S cm−1, which was ~ 68% of bulk. The ratio of surface area to projected area of coatings surface could reach 6.53-8.30 measured by a 3D confocal laser microscope. Finally, testing cells showed a maximum output power density of 1112 mW cm−2 and an OCV of 1.07 V at 750 °C. The ohmic resistance of whole cell was 0.1 Ω cm2, and the total resistance was 0.15 Ω cm2. The results suggest that very low pressure plasma spraying is a promising approach for the manufacturing of high-performance MS-SOFCs. [ABSTRACT FROM AUTHOR]

How to obtain dense La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3 (LSGM) electrolyte at low sintering temperature (<1300 °C) is a challenge to improve solid oxide fuel cell (SOFC) performance at intermediate operation temperature. In this study, a double-layer design method for vacuum cold spray (VCS) prepared-LSGM electrolyte assisted with two-step sintering at a low temperature was proposed. The sintering behavior of VCS deposited LSGM layers at 1200 °C was investigated. The LSGM layers became denser in most regions except the appearance of some cracks. Subsequently, the effect of a second LSGM layer on the sintered top layer was studied to block cracks. Results showed that the co-sintered layer with a thickness of approximately 5 μm presented a maximum open circuit voltage of ∼0.956 V at 650 °C and a maximum power density of 592 mW/cm 2 at 750 °C. Result indicates that the sintering assisted VCS is a promising method to prepare the LSGM electrolyte applied in intermediate temperature SOFCs. [ABSTRACT FROM AUTHOR]

Atmospheric plasma spray is employed to deposit Mn 1.5 Co 1.5 O 4 (MCO) coatings onto T441 and porous 430L substrates respectively at room temperature and 400 °C. The coatings are then subjected to redox treatments to achieve a desirable gas tightness. The gas permeability, area specific resistance (ASR) and microstructure homogenization of MCO coatings are evaluated in different stages. The gas permeability of MCO coating deposited at 400 °C and exposed to redox treatments can be as low as ∼8.2 × 10 −8 cm 4 s −1 gf −1 , which is essential for sufficient protection of metallic substrate against oxidation. The MCO-coated T441 without pre-reduction presents a nonuniform microstructure characterized by isolated precipitates rich in Co and dark matrix rich in Mn. In comparison, the MCO coating with 5 h pre-reduction presents a uniform and dense spinel structure. The ASR tests indicates that a homogeneous structure has contributed to an increase in the overall conductivity. While bare T441 shows a substantial increase in interfacial ASR during the 200 h test, MCO-coated T441 exhibites a high stability and a much lower ASR value of 13 mΩ cm 2 . Besides, the dense MCO coatings effectively inhibit the oxide scale growth and block outward diffusion of Cr during the oxidation tests. Cr-rich oxide scale formed at the MCO/T441 interface is less than 1.2 μm and no further migration of Cr was detected. [ABSTRACT FROM AUTHOR]

In comparison to various power generating devices/energy conversion systems, solid oxide fuel cell (SOFC) has received much attention due to its remarkable efficiency, reliability and low pollution. Modified pechini method is used to synthesize La 0.7 Sr 0.3 Ti 0.1 Fe 0.6 Ni 0.3 O 3-δ (LSTFN) perovskite material and is utilized as cathode and anode for intermediate-temperature symmetrical solid oxide fuel cell (IT-SSOFC). The X-ray diffractometer (XRD) patterns reveals perovskite cubic structure with single phase for LSTFN. The maximum conductivity ~318 Scm−1 is obtained for LSTFN in air at a temperature of 700 °C, but is decreased with further increase in temperature due to small polaron mechanism. However, the conductivity is enhanced up to ~1.1 Scm−1 at the same temperature in the presence of dry H 2 , being capable to be utilized both as anode and cathode. Low polarization resistance (Rp) ~0.047 (with air) and 0.201Ωcm2 (with dry H 2) is exhibited by as prepared perovskite material at a temperature of 800 °C. The fabricated symmetrical cell maintains good stability with no apparent degradation during the tested hours ~300 in air and ~100 with dry H 2. Image 1 • Symmetrical Solid Oxide Fuel Cells (SOFCs) i.e.La 0.7 Sr 0.3 Ti 0.1 Fe 0.6 Ni 0.3 O 3-δ (LSTFN). • LSTFN shows a good conductivity of ~1.1 (in dry H 2) and ~318 Scm−1 (in air) at 700 °C. • LSTFN shows good stability for ~300 h in air and ~100 h in dry H 2. • LSTFN exhibits a maximum power density (Pmax) ~402 mWcm−2 at 800 °C. [ABSTRACT FROM AUTHOR]

La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) is a promising cathode material for solid oxide fuel cells (SOFCs). Hence, structured LSCF coatings were deposited in this study by atmospheric laminar plasma spraying (ALPS) at the spraying distances from 150 mm to 250 mm. Particles with high temperature were obtained at low plasma arc power of only 15 kW. The microstructural characterization of the coatings showed cluster-like morphologies on the top surfaces and columnar features with large-scale vertical cracks at the cross section. An evolution mechanism of the coatings was proposed based on particle size. The movement of particles during laminar plasma jet depended on particle size, which was studied experimentally and by simulation to explain the selective deposition. The coatings showed lower polarization resistance when compared to LSCF coatings deposited by atmospheric plasma spraying (APS) due to large vertical crack densities. The high output performance of the SOFCs with the LSCF cathode also proved this phenomenon. The results suggest that ALPS provides extensive options for SOFCs manufacturing. • LSCF coatings were deposited at the long spraying distances, although at low plasma arc power of only 15 kW. • The selective deposition depended on particle size was proposed to explain various structures of coatings. • Structured coatings with large-scale vertical cracks revealed lower polarization resistances compared to APS coatings. [ABSTRACT FROM AUTHOR]