The effect of Mn on the oxidation behavior and electrical conductivity of Fe-17Cr alloys in solid oxide fuel cell cathode atmosphere

Four Fe-17Cr alloys with various Mn contents between 0.0 and 3.0 wt.% are prepared for investigation of the effect of Mn content on the oxidation behavior and electrical conductivity of the Fe-Cr alloys for the application of metallic interconnects in solid oxide fuel cells (SOFCs). During the initial oxidation stage (within 1 min) at 750 °C in air, Cr is preferentially oxidized to form a layer of Cr₂O₃ type oxide in all the alloys, regardless the Mn content, with similar oxidation rate and oxide morphology. The subsequent oxidation of the Mn containing alloys is accelerated caused by the fast outward diffusion of Mn ions across the Cr₂O₃ type oxide layer to form Mn-rich (Mn, Cr)₃O₄ and Mn₂O₃ oxides on the top. After 700 h oxidation a multi-layered oxide scale is observed in the Mn containing alloys, which corresponds to a multi-stage oxidation kinetics in the alloys containing 0.5 and 1.0 wt.% of Mn. The oxidation rate and ASR of the oxide scale increase with the Mn content in the alloy changes from 0.0 to 3.0 wt.%. For the application of metallic interconnects in SOFCs, Mn-free Fe-17Cr alloy with conducting Cr free spinel coatings is preferred.     

NiMn2O4 spinel as an alternative coating material for metallic interconnects of intermediate temperature solid oxide fuel cells

In an effort to improve the performance of SUS 430 alloy as a metallic interconnect material, a low cost and Cr-free spinel coating of NiMn₂O₄ is prepared on SUS 430 alloy substrate by the sol-gel method and evaluated in terms of the microstructure, oxidation resistance and electrical conductivity. A oxide scale of 3-4 μm thick is formed during cyclic oxidation at 750 °C in air for 1000 h, consisting of an inner layer of doped Cr₂O₃ and an outer layer of doped NiMn₂O₄ and Mn₂O₃; and the growth of Cr₂O₃ and formation of MnCr₂O₄ are depressed. The oxidation kinetics obeys the parabolic law with a rate constant as low as 4.59 × 10⁻¹⁵ g² cm⁻⁴ s⁻¹. The area specific resistance at temperatures between 600 and 800 °C is in the range of 6 and 17 mΩ cm². The above results indicate that NiMn₂O₄ is a promising coating material for metallic interconnects of the intermediate temperature solid oxide fuel cells.     

A promising NiCo2O4 protective coating for metallic interconnects of solid oxide fuel cells

The NiCo₂O₄ spinel coating is applied onto the surfaces of the SUS 430 ferritic stainless steel by the sol-gel process; and the coated alloy, together with the uncoated as a comparison, is cyclically oxidized in air at 800 °C for 200 h. The oxidation behavior and oxide scale microstructure as well as the electrical property are characterized. The results indicate that the oxidation resistance is significantly enhanced by the protective coating with a parabolic rate constant of 8.1 × 10⁻¹⁵ g² cm⁻⁴ s⁻¹, while the electrical conductivity is considerably improved due to inhibited growth of resistive Cr₂O₃ and the formation of conductive spinel phases in the oxide scale.     

Characterization of electrical properties of GDC doped A-site deficient LSCF based composite cathode using impedance spectroscopy

The composite cathode consisting of A-site deficient perosvkite material La_0.58Sr_0.4Co_0.2Fe_0.8O_3−δ (L58SCF) and Ce_0.8Gd_0.2O_2−δ (GDC) on YSZ electrolyte is studied for potential applications in intermediate/low-temperature solid oxide fuel cells (SOFCs). Impedance spectroscopy measurements are performed in air over the temperature range of 600–800 °C under open circuit potential. The results show that the addition of 40 wt.% GDC to L58SCF (L58SCF–GDC40) results in the lower polarization resistance (0.07 Ω cm² at 800 °C, 0.11 Ω cm² at 750 °C and 0.22 Ω cm² at 700 °C) than other composite cathodes and its activation energy values calculated for the low- and high-frequency arcs are 0.86 and 1.10 eV, respectively. The composite cathode exhibit high exchange current density and low charge-transfer resistance.     

Effect of Co doping on the properties of Sr0.8Ce0.2MnO3−δ cathode for intermediate-temperature solid-oxide fuel cells

The effect of the Co doping on the structure, electrical conductivity and electrochemical properties of Sr_0.8Ce_0.2MnO_3−δ was investigated. The Co doping decreased the sintering temperature by about 100 °C and cubic structure was synthesized for Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3−δ. The electrical conductivity of Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3−δ reached 102 S cm⁻¹ at 700 °C, which was sufficient to provide low ohmic losses at the cathode. In comparison with Sr_0.8Ce_0.2MnO_3−δ, the area-specific resistance of Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3−δ was 0.10 Ω cm² at 750 °C, which was about 20 times lower than that of Sr_0.8Ce_0.2MnO_3−δ. While the exchange current density i₀ of Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3−δ was 0.49 A cm⁻² at 800 °C, that for Sr_0.8Ce_0.2MnO_3−δ was 0.11 A cm⁻². The results show that the Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3−δ cathode had high catalytic activity for oxygen reduction reaction in the temperature range of 700–800 °C.     

Ethane dehydrogenation over nano-Cr2O3 anode catalyst in proton ceramic fuel cell reactors to co-produce ethylene and electricity

Ethane and electrical power are co-generated in proton ceramic fuel cell reactors having Cr₂O₃ nanoparticles as anode catalyst, BaCe_0.8Y_0.15Nd_0.05O_3−δ (BCYN) perovskite oxide as proton conducting ceramic electrolyte, and Pt as cathode catalyst. Cr₂O₃ nanoparticles are synthesized by a combustion method. BaCe_0.8Y_0.15Nd_0.05O_3−δ (BCYN) perovskite oxides are obtained using a solid state reaction. The power density increases from 51 mW cm⁻² to 118 mW cm⁻² and the ethylene yield increases from about 8% to 31% when the operating temperature of the solid oxide fuel cell reactor increases from 650 °C to 750 °C. The fuel cell reactor and process are stable at 700 °C for at least 48 h. Cr₂O₃ anode catalyst exhibits much better coke resistance than Pt and Ni catalysts in ethane fuel atmosphere at 700 °C.     

Electrochemical performances of NdBa0.5Sr0.5Co2O5+x as potential cathode material for intermediate-temperature solid oxide fuel cells

Layered perovskite oxide NdBa_0.5Sr_0.5Co₂O_5+x is investigated as a cathode material for intermediate-temperature solid oxide fuel cells. The NBSC cathode is chemically compatible with the electrolyte La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) at temperatures below 1000 °C. It is metallic in nature and the maximum and minimum conductivities are 1368 S cm⁻¹ at 100 °C and 389 S cm⁻¹ at 850 °C. The area specific resistance (ASR) value for the NBSC cathode is as low as 0.023 Ω cm² at 850 °C. The electrolyte-supported fuel cell generates good performance with the maximum power density of 904, 774 and 556 mW cm⁻² at 850, 800 and 750 °C, respectively. Preliminary results indicate that NBSC is promising as a cathode for IT-SOFCs.     

BaCo0.7Fe0.2Nb0.1O3−δ as cathode material for intermediate temperature solid oxide fuel cells

BaCo_0.7Fe_0.2Nb_0.1O_3−δ (BCFN) has been synthesized and characterized as cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) using La_0.8Sr_0.2Ga_0.83Mg_0.17O_3−δ (LSGM) electrolyte. X-ray diffraction results show that pure cubic BCFN perovskite phase can be obtained at 950 °C through solid state reactions of BaCO₃, Co₃O₄, Fe₂O₃ and Nb₂O₅. The electrical conductivity of BCFN increases with the increase in oxygen partial pressure, indicating that BCFN is a p-type semiconductor. The polarization resistance of the BCFN cathode with LSGM electrolyte is only 0.06 Ω cm² at 750 °C in air under open-circuit conditions. The overpotential at a current density of 1 A cm⁻² in oxygen was only about 0.04 V at 750 °C. Peak power densities of 550, 770 and 980 mW cm⁻² have been achieved on LSGM-electrolyte supported single cells with the configuration of Ni-Gd_0.1Ce_0.9O_1.95|La_0.4Ce_0.6O₂|LSGM|BCFN at 700, 750 and 800 °C, respectively. These results indicate that BCFN is a very promising cathode candidate for IT-SOFCs with LSGM electrolyte.     

Low-temperature synthesis of Na2Mn5O10 for supercapacitor applications

The romanechite-like sodium manganese oxide Na₂Mn₅O₁₀ is synthesized through alkaline hydrolysis of [Mn₁₂O₁₂(CH₃COO)₁₆(H₂O)₄] followed by thermal calcination. Amorphous Na₂Mn₅O₁₀ is obtained at relatively low temperature (200 °C). Increasing the calcination temperature leads to highly crystalline nano-rods. Electrochemical studies demonstrate that Na₂Mn₅O₁₀ is a good candidate as positive electrode materials for supercapacitor: specific capacitances of 178, 173 and 175 F g⁻¹ are obtained for Na₂Mn₅O₁₀ calcined at different temperatures (200, 400 and 600 °C), respectively, by charge-discharge tests at 0.1 A g⁻¹. Moreover, capacitance losses of all the products in 1000 cycles are less than 3%.     

Improved electrochemical performance and thermal compatibility of Fe- and Cu-doped SmBaCo2O5+δ-Ce0.9Gd0.1O1.95 composite cathode for intermediate-temperature solid oxide fuel cells

Fe- and Cu-doped SmBaCo₂O_5+δ (FC-SBCO)-Ce_0.9Gd_0.1O_1.95 (CGO) composites with various CGO contents (0-40 wt.%) are investigated as new cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on a Ce_0.9Gd_0.1O_1.95 electrolyte. The effect of CGO incorporation on the thermal expansion coefficient (TEC), electrochemical properties and thermal stability of the FC-SBCO-CGO composites is investigated. A composite cathode of 30 wt.% CGO-70 wt.% FC-SBCO (CS30-70) coated on a Ce_0.9Gd_0.1O_1.95 electrolyte shows the lowest area specific resistance (ASR), i.e., 0.049 Ω cm² at 700 °C. The TEC of the CS30-70 cathode is 14.1 × 10⁻⁶ °C⁻¹ up to 900 °C, which is a lower value than that of the FC-SBCO (16.6 × 10⁻⁶ °C⁻¹) counterpart. Long-term thermal stability and thermal cycle tests of the CS30-70 cathode are performed. Stable ARS values are observed during both type of test. An electrolyte-supported (300-μm thick) single-cell configuration of CS30-70/CGO/Ni-CGO delivers a maximum power density of 535 mW cm⁻² at 700 °C. The unique composite composition of CS30-70 demonstrates improved electrochemical performance and good thermal stability for IT-SOFCs.     

Fabrication and performance of membrane solid oxide fuel cells with La0.75Sr0.25Cr0.5Mn0.5O3−δ impregnated anodes

La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCrM)-impregnated anodes have been fabricated by infiltrating 70% porous yttria-stabilized zirconia (YSZ) matrixes with an LSCrM solution. In these anodes, LSCrM is a primary electronic conducive phase while the well-sintered YSZ provides an ionic-conducting pathway throughout the electrode. The maximum power densities of a single cell with YSZ + 35 wt.% LSCrM composite anode reach 567 and 561 mW cm⁻² at 850 °C in dry H₂ and CH₄, respectively. Further, Ag and Ni are added via nitrate impregnating method for improving electronic conductivity and catalytic activity. With the addition of 6 wt.% Ni and 2 wt.% Ag to the YSZ + 32 wt.% LSCrM composite anode, the maximum power densities at 850 °C increase to 1302 mW cm⁻² in dry H₂ and 769 mW cm⁻² in dry CH₄. No carbon deposition is detected in the tested anodes, even with the presence of Ni.     

High performance metal-supported intermediate temperature solid oxide fuel cells fabricated by atmospheric plasma spraying

The LSGM(La_0.8Sr_0.2Ga_0.8Mg_0.2O₃) electrolyte based intermediate temperature solid oxide fuel cells (ITSOFCs) supported by porous nickel substrates with different permeabilities are prepared by plasma spray technology for performance studies. The cell having a porous nickel substrate with a permeability of 3.4 Darcy, an LSCM(La_0.75Sr_0.25Cr_0.5Mn_0.5O₃) interlayer on the nickel substrate, a nano-structured LDC(Ce_0.55La_0.45O₂)/Ni anode functional layer, an LDC interlayer, an LSGM/LSCF(La_0.58Sr_0.4Co_0.2Fe_0.8O₃) cathode interlayer and an LSCF cathode current collector layer shows remarkable electric output power densities such as 1270 mW cm⁻² (800 °C), 978 mW cm⁻² (750 °C) and 702 mW cm⁻² (700 °C) at 0.6 V cell voltage under 335 ml min⁻¹ H₂ and 670 ml min⁻¹ air flow rates. SEM, TEM, EDX, AC impedance, voltage and power data with related analyses are presented here to support this high performance. The durability test of the cell with the best power performance shows a degradation rate of about 3% kh⁻¹ at the test conditions of 400 mA cm⁻² constant current density and 700 °C. Results demonstrate the success of APS technology for fabricating high performance metal-supported and LSGM based ITSOFCs.     

Performance of LaBaCo2O5+δ-Ag with B2O3-Bi2O3-PbO frit composite cathodes for intermediate-temperature solid oxide fuel cells

The composite cathodes LaBaCo₂O_5+δ-x wt.% Ag (LBCO-xAg, x = 20, 30, 40, 50) were prepared by mechanical mixing method for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The experiment results indicated that the addition of a small amount of B₂O₃-Bi₂O₃-PbO (BBP) frit to LBCO-xAg can effectively improve the adhesion and strength of cathode membrane without damaging its porous structure. The BBP frit was proved effective for lowering the sintering temperature of LBCO-xAg to 900 °C. According to the electrochemical impedance spectroscopy and cathodic polarization analysis, the LBCO-30Ag exhibited the best performance and the optimal BBP frit content was 2.5 wt.%. For LBCO-30Ag with 2.5 wt.% BBP frit, the area-specific resistance based on Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte decreased by about 57.6% at 700 °C, 60.5% at 750 °C and 75.9% at 800 °C compared to LBCO, and its cathodic overpotential was 10.7 mV at a current density of 0.2 A cm⁻² at 700 °C, while the corresponding value for LBCO was 51.0 mV. The addition of Ag and BBP frit to LBCO had no significant effect on the thermal expansion.     

Influence of multiple oxide (Cr2O3/Nb2O5) addition on the sorption kinetics of MgH2

The influence of multiple additions of two oxides, Cr₂O₃ and Nb₂O₅, as additives on the hydrogen sorption kinetics of MgH₂ after milling was investigated. We found that the desorption kinetics of MgH₂ were improved more by multiple oxide addition than by single addition. Even for the milled MgH₂ micrometric size powders, the high hydrogen capacity with fast kinetics were achieved for the powders after addition of 0.2 mol% Cr₂O₃ + 1 mol% Nb₂O₅. For this composition, the hydride desorbed about 5 wt.% hydrogen within 20 min and absorbed about 6 wt.% in 5 min at 300 °C. Furthermore, the desorption temperature was decreased by 100 °C, compared to MgH₂ without any oxide addition, and the activation energy for the hydrogen desorption was estimated to be about 185 kJ mol⁻¹, while that for MgH₂ without oxide was about 206 kJ mol⁻¹.     

Characteristic of (La0.8Sr0.2)0.98MnO3 coating on Crofer22APU used as metallic interconnects for solid oxide fuel cell

This study reports the high temperature oxidation kinetics, area specific resistance (ASR), and interfacial microstructure of metallic interconnects coated by (La_0.8Sr_0.2)_0.98MnO₃ (LSM) in air atmosphere at 800 °C. An efficient LSM conductive layer was fabricated on metallic interconnects for solid oxide fuel cells (SOFCs) by using a wet spray coating method. The optimum conditions for slurries used in the wet spray coating were determined by the measurement of slurry viscosity and coated surface morphology. The surface roughnesses of the substrates were increased through sandblast treatment. The adhesive strength of the interface between the coated layer and the metal substrate increased with increased surface roughness of the metallic interconnects. The electrical conductivities of the coated substrates were measured by using a DC two-point and four-wire method under air atmosphere at 800 °C. Of note, the Crofer22APU treated at 1100 °C in N₂ with 10 vol.% H₂ showed long-term stability and a lower ASR value than other samples(heat-treated at 800 °C and 900 °C). After an 8000-h oxidation experiment the coated Crofer22APU substrate, the ASR showed a low value of 23 mΩ cm². The thickness of the coated conductive oxide layer was about 10-20 μm. These results show that a coated oxide layer prevents the formation and the growth of scale (Cr₂O₃ and (Mn, Cr, Fe)₃O₄ layer) and enhances the long-term stability and electrical performance of metallic interconnects for SOFCs.     

Novel Al2O3-based compressive seals for IT-SOFC applications

Novel compressive Al₂O₃-based seals were developed and characterized under simulated intermediate temperature solid oxide fuel cell (IT-SOFC) environment. The seals were prepared by tape casting, mainly composed of fine Al₂O₃ powder with various contents of fine Al powder addition. The leakage rates were determined at 800 °C under 0.14–0.69 MPa compressive stresses, and the stabilities were evaluated at 750 °C under constant 0.35 MPa compressive stress. The leakage rates at 800 °C were in range of 0.2–0.01 sccm cm⁻¹, decreasing with increasing the compressive stress and Al content; Al addition significantly improved the stability, the leakage rate with 20 wt% Al addition was as low as 0.025 sccm cm⁻¹ at 800 °C under 0.35 MPa compressive stress with a gauge pressure of 6.9 kPa, and exhibited good stability at 750 °C. Single cell test also confirmed the effectiveness of the tape cast Al₂O₃-based seal for planar IT-SOFC applications.     

Lithium difluoro(oxalato)borate/ethylene carbonate + propylene carbonate + ethyl(methyl) carbonate electrolyte for LiMn2O4 cathode

Lithium difluoro(oxalato)borate (LiODFB) was investigated as a lithium salt for non-aqueous electrolytes for LiMn₂O₄ cathode in lithium-ion batteries. Linear sweep voltammetry (LSV) tests were used to examine the electrochemical stability and the compatibility between the electrolytes and LiMn₂O₄ cathode. Through inductively coupled plasma (ICP) analysis, we compared the amount of Mn²⁺ dissolved from the spinel cathode in 1 mol L⁻¹ LiPF₆/EC + PC + EMC (1:1:3 wt.%) and 1 mol L⁻¹ LiODFB/EC + PC + EMC (1:1:3 wt.%). AC impedance measurements and scanning electron microscopy (SEM) analysis were used to analyze the formation of the surface film on the LiMn₂O₄ cathode. These results demonstrate that ODFB anion can capture the dissolution manganese ions and form a denser and more compact surface film on the cathode surface to prevent the continued Mn²⁺ dissolution, especially at high temperature. It is found that LiODFB, instead of LiPF₆, can improve the capacity retention significantly after 100 cycles at 25 °C and 60 °C, respectively. LiODFB is a very promising lithium salt for LiMn₂O₄ cathode in lithium-ion batteries.     

High-performance PrBaCo2O5+δ-Ce0.8Sm0.2O1.9 composite cathodes for intermediate temperature solid oxide fuel cell

PrBaCo₂O_5+δ-Ce_0.8Sm_0.2O_1.9 (PBCO-SDC) composite material are prepared and characterized as cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction result proves that there are no obvious reaction between the PBCO and SDC after calcination at 1100 °C for 3 h. AC impedance spectra based on SDC electrolyte measured at intermediate temperatures shows that the addition of SDC to PBCO improved remarkably the electrochemical performance of a PBCO cathode, and that a PBCO-30SDC cathode exhibits the best electrochemical performance in the PBCO-xSDC system. The total interfacial resistances R_p is the smallest when the content of SDC is 30 wt%, where the value is 0.035 Ω cm² at 750 °C, 0.072 Ω cm² at 700 °C, and 0.148 Ω cm² at 650 °C, much lower than the corresponding interfacial resistance for pure PBCO. The maximum power density of an anode-supported single cell with PBCO-30SDC cathode, Ni-SDC anode, and dense thin SDC/LSGM (La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ)/SDC tri-layer electrolyte are 364, 521 and 741 mW cm⁻² at 700, 750 and 800 °C, respectively.     

Structural and electrochemical properties of the doped spinels Li1.05M0.02Mn1.98O3.98N0.02 (M = Ga, Al, or Co; N = S or F) for use as cathode material in lithium batteries

The doped and milled spinels Li_1.05M_0.02Mn_1.98O_3.98N_0.02 (M = Ga³⁺, Al³⁺ or Co³⁺; N = S²⁻ or F⁻) are studied aiming at obtaining an improved charge/discharge cycling performance. These spinels are prepared by a solid-state reaction among the precursors ?-MnO₂, LiOH, and the respective oxide/salt of the doping ions at 750 °C for 72 h and milled for 30 min. The obtained spinels are characterized by XRD, SEM, and determinations of the average manganese valence n. In the charge and discharge tests, the doped spinels present outstanding initial values of the specific discharge capacity C (117-126 mA h g⁻¹), decreasing in the following order: C(Li_1.05Al_0.02Mn_1.98S_3.02O_3.98) > C(Li_1.05Al_0.02Mn_1.98F_3.02O_3.98) > C(Li_1.05Ga_0.02Mn_1.98S_3.02O_3.98) > C(Li_1.05Ga_0.02Mn_1.98F_3.02O_3.98) > C(Li_1.05Co_0.02Mn_1.98S_3.02O_3.98) > C(Li_1.05Co_0.02Mn_1.98F_3.02O_3.98). The doped spinel Li_1.05Ga_0.02Mn_1.98S_3.02O_3.98 presents an excellent electrochemical performance, with a low capacity loss even after 300 charge and discharge cycles (from 120 to 115 mA h g⁻¹ or 4%).     

Palladium and ceria infiltrated La0.8Sr0.2Co0.5Fe0.5O3−δ cathodes of solid oxide fuel cells

La_0.8Sr_0.2Co_0.5Fe_0.5O_3−δ (LSCF) cathodes infiltrated with electrocatalytically active Pd and (Gd,Ce)O₂ (GDC) nanoparticles are investigated as high performance cathodes for the O₂ reduction reaction in intermediate temperature solid oxide fuel cells (IT-SOFCs). Incorporation of nano-sized Pd and GDC particles significantly reduces the electrode area specific resistance (ASR) as compared to the pure LSCF cathode; ASR is 0.1 Ω cm² for the reaction on a LSCF cathode infiltrated with 1.2 mg cm⁻² Pd and 0.06 Ω cm² on a LSCF cathode infiltrated with 1.5 mg cm⁻² GDC at 750 °C, which are all significantly smaller than 0.22 Ω cm² obtained for the reaction on a conventional LSCF cathode. The activation energy of GDC- and Pd-impregnated LSCF cathodes is 157 and 176 kJ mol⁻¹, respectively. The GDC-infiltrated LSCF cathode has a lower activation energy and higher electrocatalytic activity for the O₂ reduction reaction, showing promising potential for applications in IT-SOFCs.