Electrophoretic Deposition of Zirconia Thin Film on Nonconducting Substrate for Solid Oxide Fuel Cell Application

Electrophoretic deposition (EPD) of 8 mol% yttria‐stabilized zirconia (YSZ) electrolyte thin film has been carried out onto nonconducting porous NiO‐YSZ cermet anode substrate using a fugitive and electrically conducting polymer interlayer for solid oxide fuel cell (SOFC) application. Such polymer interlayer burnt out during the high‐temperature sintering process (1400°C for 6 h) leaving behind a well adhered, dense, and uniform ceramic YSZ electrolyte film on the top of the porous anode substrate. The EPD kinetics have been studied in depth. It is found that homogeneous and uniform film could be obtained onto the polymer‐coated substrate at an applied voltage of 15 V for 1 min. After the half‐cell (anode + electrolyte) is co‐fired at 1400°C, a suitable cathode composition (La_0.65Sr_0.3MnO₃) thick film paste is screen printed on the top of the sintered YSZ electrolyte. A second stage of sintering of such cathode thick film at 1100°C for 2 h finally yield a single cell SOFC. Such single cell produced a power output of 0.91 W/cm² at 0.7 V when measured at 800°C using hydrogen and oxygen as fuel and oxidant, respectively.     

Formation of sol–gel derived (Cu,Mn,Co)3O4 spinel and its electrical properties

An (Mn,Co)₃O₄ spinel layer effectively suppresses Cr outward diffusion, but the occurrence of spallation between coating and metal interfaces and the increasing oxidation rate over time significantly deteriorate cell performance. A transition metal cation, particularly Cu, is added into the (Mn,Co)₃O₄ to improve the long-term stability of the interconnect materials for low-to-intermediate-temperature solid oxide fuel cells (SOFCs). In this work, fine-crystalline (Cu,Mn,Co)₃O₄ spinel powders with an average crystallite size of 21 nm were successfully synthesized via the citric acid–nitrate method. The potential for use as a coating material for low-to-intermediate-temperature SOFC interconnects was explored. According to the TG curves, IR spectra, and XRD patterns, 800 °C is recommended as the minimum calcination temperature for (Cu,Mn,Co)₃O₄ spinel materials. Compared with (Mn,Co)₃O₄ spinel materials, the addition of Cu does not induce significant changes in the crystal structure but markedly improves the electrical conductivity (116 Scm⁻¹) and the activation energy (0.394 eV) of the (Cu,Mn,Co)₃O₄ spinel. Overall, the sol–gel derived (Cu,Mn,Co)₃O₄ spinel can be used as a coating material for low-to-intermediate-temperature SOFC interconnects and is superior to (Mn,Co)₃O₄ spinel because high electrical conductivity is preferred to minimize ohmic losses between the electrodes of adjacent cells.     

Oxygen Dissociation and Interfacial Transfer Rate on Performance of SOFCs with Metal‐Added (LaSr)(CoFe)O3‐(Ce,Gd)O2 – δ Cathodes

A solid oxide fuel cell (SOFC) unit is constructed with Ni‐Ce_0.9Gd_0.1O_{2 – δ} (GDC) as the anode, yttria‐stabilised zirconia (YSZ) as the electrolyte and Pt, Ag or Cu‐added La_0.58Sr_0.4Co_0.2Fe_0.8O_{3 – δ} (LSCF)–GDC as the cathode. The current–voltage measurements are performed at 800 °C. Cu addition leads to best SOFC performance. LSCF–GDC–Cu is better than LSCF–GDC and much better than GDC as the material of the cathode interlayer. Cu content of 2 wt.‐% leads to best SOFC performance. A cathode functional layer calcined at 800 °C is better than that calcined at higher temperature. Metal addition increases the O₂ dissociation reactivity but results in an interfacial resistance for O transfer. A balance between the rates of O₂ dissociation and interfacial O transfer is needed for best SOFC performance.     

Tuning the Interfacial Reaction Between Bismuth‐Containing Sealing Glasses and Cr‐Containing Interconnect: Effect of ZnO

The interfacial reaction between sealing glasses and Cr‐containing interconnect presents a challenge for the development of solid oxide fuel cell (SOFC). In this work, we report that the interfacial reaction between bismuth‐containing sealing glasses and Cr‐containing interconnect can be tailored by ZnO dopant. The addition of ZnO contributes to a more open glass structure, resulting in the facilitated diffusion of ions in glass and thus the increase in the interfacial reaction. On the other hand, the further increase in ZnO content enhances the Bi³⁺→Bi⁵⁺ transition in glasses and reduces the redox interfacial reaction by consuming the oxygen available at the glass/metal interface. In addition, good joining can be observed at the sealing interface between ZnO‐containing glass‐ceramics and Crofer 22 APU, held in air at 700°C for 1400 h. Moreover, the glass‐ceramics show considerable electrical stability in oxidizing and reducing atmospheres. The reported results support the suitability of prepared glass‐ceramics as sealing materials for SOFC applications.     

Electrical Properties,Cation Distributions,and Thermal Expansion of Manganese Cobalt Chromite Spinel Oxides

As the oxidation and chromium volatilization of chromia‐forming alloy interconnects can cause Solid oxide fuel cells (SOFC) cathode poisoning and cell degradation, spinel coatings like Mn_1.5Co_1.5O₄ have been applied as a barrier to oxygen and chromium diffusion. To evaluate their long‐term stability, the properties of the reaction layer between the Mn_1.5Co_1.5O₄ coating and Cr₂O₃ scale formed on the alloy surface need to be characterized. Therefore, compositions of Mn_1.5?0.5xCo_1.5?0.5xCr_xO₄ (x = 0–2) were prepared to investigate their electrical properties, cation distributions, and thermal expansion behavior at high temperature. With increasing Cr content in manganese cobalt spinel oxides, the cubic crystal structure is stabilized and the electrical conductivity and coefficient of thermal expansion both decrease. The cation distributions determined from neutron diffraction show that Cr and Mn have stronger preference for octahedral sites in the spinel structure as compared with Co.     

Evaluation of Using LaNi0.6Fe0.4O3–δ Contact Layer Between La0.6Sr0.4FeO3 Cathode and Crofer22APU Interconnect for Solid Oxide Fuel Cells

Interconnect‐cathode interfacial adhesion is important for the durability of solid oxide fuel cell (SOFC). Thus, the use of a conductive contact layer between interconnect and cathode could reduce the cell area specific resistance (ASR). The use of La_0.6Sr_0.4FeO₃ (LSF) cathode, LaNi_0.6Fe_0.4O_3–δ (LNF) contact layer and Crofer22APU interconnect was proposed as an alternative cathode side. LNF‐LSF powder mixtures were heated at 800 °C for 1,000 h and at 1,050 °C for 2 h and analyzed by X‐Ray power diffraction (XRD). The results indicated a low reactivity between the materials. The degradation occurring between the components of the half‐cell (LSF/LNF/Crofer22APU) was studied. XRD results indicated the formation of secondary phases, mainly: SrCrO₄, A(B, Cr)O₃ (A = La, Sr; B = Ni, Fe) and SrFe₁₂O₁₉. Scanning electron microscopy with energy dispersive X‐Ray spectroscopy (SEM‐EDX) and the X‐Ray photoelectron spectroscopy (XPS) analyzes confirmed the interaction between LSF/LNF and the metallic interconnect due to the Cr vaporization/migration. An increment of the resistance of ∼0.007 Ω cm² in 1,000 h is observed for (LSF/LNF/Crofer22APU) sample. However, the ASR values of the cell without contact coating, (LSF/Crofer22APU), were higher (0.31(1) Ω cm²) than those of the system with LNF coated interconnect (0.054(7) Ω cm²), which makes the proposed materials combination interesting for SOFC.     

Pore orientation of the gadolinia‐doped ceria cathode interlayer for a tubular SOFC using dip‐coating

An active region of cathode interlayer in a tubular solid oxide fuel cell (SOFC) is structurally analyzed using a dual‐beam focused ion beam/scanning electron microscope (FIB/SEM). The GDC (10 mol% gadolinia‐doped ceria) cathode interlayer (about 1 μm in thickness) is dip‐coated, and then sintered on YSZ (8 mol% yttria‐stabilized zirconia) electrolyte. At 1150°C sintering temperature, the pores oriented more along the axial direction than the radial direction. The anisotropy of pore shape is accounted for the withdrawal force during the dip‐coating of the GDC interlayer.     

Development and Fabrication of a New Concept Planar‐tubular Solid Oxide Fuel Cell (PT‐SOFC)

The paper reports a new concept of planar‐tubular solid oxide fuel cell (PT‐SOFC). Emphasis is on the fabrication of the required complex configuration of Ni‐yttria‐stabilised zirconia (YSZ) porous anode support by tert‐butyl alcohol (TBA) based gelcasting, particularly the effects of solid loading, amounts of monomers and dispersant on the rheological behaviour of suspension, the shrinkage of a wet gelcast green body upon drying, and the properties of final sample after sintering at 1350 °C and reduction from NiO‐YSZ to Ni‐YSZ. The results show that the gelcasting is a powerful method for preparation of the required complex configuration anode support. The anode support resulted from an optimised suspension with the solid loading of 25 vol% has uniform microstructure with 37% porosity, bending strength of 44 MPa and conductivity of 300 S cm^—1 at 700 °C, meeting the requirements for an anode support of SOFC. Based on the as‐prepared anode support, PT‐SOFC single cell of Ni‐YSZ/YSZ/LSCF has been fabricated by slurry coating and co‐sintering technique. The cell peak power density reaches 63, 106 and 141 mW cm^—2 at 700, 750 and 800 °C, respectively, using hydrogen as fuel and ambient air as oxidant.     

Chemical compatibility of Al2O3-added glass sealant with bare and coated interconnect in oxidizing and reducing environments

Chemical compatibility in oxidizing and reducing environments between sealants and interconnects for planar solid oxide fuel cells (SOFC) are investigated. (Co,Mn)₃O₄, Co-Mn, and Al coatings were prepared on the FeCr-based ferritic-stainless-steel (SUS430). The (Co,Mn)₃O₄ coating exhibited water vapor bubble formation at the outer sealing edges when exposed to H₂, indicating reactions between the coating and sealant. Co-Mn metal coating was found readily oxidized in an oxidizing environment. The glass with 5 wt% Al₂O₃ addition helped mitigate the Cr diffusion into sealant based on bare SUS430 substrate. Moreover, the Al metal layer effectively blocked the diffusion of Cr into the sealant at the interface and environment for 100 h, with a thickness of only 1 µm. At the constant discharge current of 24 A, the voltage is stabilized at about 4.2 V for 48 h using H₂ as fuel gas in 5-cell stack.     

Effect of GDC addition method on the properties of LSM–YSZ composite cathode support for solid oxide fuel cells

Equal amounts of Gd_0.1Ce_0.9O_2−δ (GDC) were added to La_0.65Sr_0.3MnO_3−δ/(Y₂O₃)_0.08(ZrO₂)_0.92 (LSM/YSZ) powder either by physical mixing or by sol–gel process, to produce a porous cathode support for solid oxide fuel cells (SOFCs). The effect of the GDC mixing method was analyzed in view of sinterability, thermal expansion coefficient, microstructure, porosity, and electrical conductivity of the LSM/YSZ composite. GDC infiltrated LSM/YSZ (G-LY) composite showed a highly porous microstructure when compared with mechanically mixed LSM/YSZ (LY) and LSM/YSZ/GDC (LYG) composites. The cathode support composites were used to fabricate the button SOFCs by slurry coating of YSZ electrolyte and a nickel/YSZ anode functional layer, followed by co-firing at 1250 °C. The G-LY composite cathode-supported SOFC showed maximum power densities of 215, 316, and 396 mW cm⁻² at 750, 800, and 850 °C, respectively, using dry hydrogen as fuel. Results showed that the GDC deposition by sol–gel process on LSM/YSZ powder before sintering is a promising technique for producing porous cathode support for the SOFCs.     

Fabrication of Mn–Co Spinel Coatings on Crofer 22 APU Stainless Steel by Electrophoretic Deposition for Interconnect Applications in Solid Oxide Fuel Cells

This study investigates the microstructure, oxidation kinetics, and electrical behavior of Mn–Co spinel coating for interconnect applications in solid oxide fuel cells. A relatively dense, uniform, and well‐adherent Mn–Co (Mn_1.5Co_1.5O₄) spinel coating with good oxidation resistance and stable conductivity was successfully prepared on the surface of Crofer 22 APU stainless steel using electrophoretic deposition followed by sintering at 1150°C. During further thermal treatment at 800°C, the chromium oxide (Cr₂O₃) sublayer formed at the substrate/coating interface during sintering showed a very slow growth, and no chromium penetration was detected in the Mn–Co coating. The oxidation kinetics of the Mn–Co‐coated substrate obeyed the parabolic law with the a parabolic rate constant k_p of 5.20 × 10^?15 g²/cm⁴/s, which was 1–2 orders of magnitude lower than that of the uncoated Crofer 22 APU stainless steel substrate. For oxidation (at 800°C) times ≥50 h, the area‐specific resistance of the Mn–Co‐coated Crofer 22 APU substrate became ~17 mΩ·cm² and was almost constant after further oxidation.     

Efficiently enhance the proton conductivity of YSZ-based electrolyte for low temperature solid oxide fuel cell

Yttrium stabilized zirconia (YSZ) as a typical oxygen ionic conductor has been widely used as the electrolyte for solid oxide fuel cell (SOFC) at the temperature higher than 1000 °C, but its poor ionic conductivity at lower temperature (500–800 °C) limits SOFC commercialization. Compared with oxide ionic transport, protons conduction are more transportable at low temperatures due to lower activation energy, which delivered enormous potential in the low-temperature SOFC application. In order to increase the proton conductivity of YSZ-based electrolyte, we introduced semiconductor ZnO into YSZ electrolyte layer to construct heterointerface between semiconductor and ionic conductor. Study results revealed that the heterointerface between ZnO and YSZ provided a large number of oxygen vacancies. When the mass ratio of YSZ to ZnO was 5:5, the fuel cell achieved the best performance. The maximum power density (P_max) of this fuel cell achieved 721 mW cm^?2 at 550 °C, whereas the P_max of the fuel cell with pure YSZ electrolyte was only 290 mW cm^?2. Further investigation revealed that this composite electrolyte possessed poor O^2? conductivity but good proton conductivity of 0.047 S cm^?1 at 550 °C. The ionic conduction activation energy of 5YSZ-5ZnO composite in fuel cell atmosphere was only 0.62 eV. This work provides an alternative way to improve the ionic conductivity of YSZ-based electrolytes at low operating temperatures.     

Influence of mixing time during glycine–nitrate process on the structural properties and reducibility of a dual-phase Ni–Cu–Mn spinel catalyst

The potential of Ni–Cu–Mn spinels as methane reforming catalysts for hydrocarbon-fueled solid oxide fuel cell (SOFC) applications is highly dependent on its catalytic properties, particularly reducibility. The reducibility of a spinel-structured catalyst is often correlated with its structural properties and fabrication processes. In this work, the structural properties and reducibility of a Ni–Cu–Mn spinel catalyst was evaluated on the basis of mixing time during the glycine–nitrate process. Phase analysis results showed that Ni_0.4Cu_0.6Mn_2.0O₄ and (Cu, Mn)₃O₄ in normal or inversed spinel structures were observed in GNP-produced Ni–Cu–Mn spinel catalyst powders. Distortion in inverse spinel structures enhanced the reducibility of the spinel catalyst. Morphological analysis results showed that complete nitrate binding occurred at a minimum mixing time of 24 h and resulted in homogenous particle size distribution and uniform elemental distribution. Furthermore, the Ni–Cu–Mn spinel catalyst produced after 24 h of mixing was fully reduced at 450 °C. The reducing pattern of the Ni–Cu–Mn spinel catalyst produced after 24 h of mixing time showed strong metal–support interaction and the fast adsorption of reactants. These effects were due to either the distribution of divalent cations in octahedral sites or large amounts of bulk pores. In conclusion, a minimum mixing time of 24 h is sufficient to produce the desired structural properties and reducibility of Ni–Cu–Mn spinel catalysts for SOFC applications.     

Fabrication and Operation of Tubular Segmented‐In‐Series (SIS) Solid Oxide Fuel Cells (SOFC)

A tubular segmented‐in‐series (SIS) solid oxide fuel cell (SOFC) sub module for intermediate temperature (700–800 °C) operation was fabricated and operated in this study. For this purpose, we fabricated porous ceramic supports of 3 YSZ through an extrusion process and analyzed the basic properties of the ceramic support, such as visible microstructure, porosity, and mechanical strength, respectively. After that, we fabricated a tubular SIS SOFC single cell by using dip coating and vacuum slurry coating method in the case of electrode and electrolyte, and obtained at 800 °C a performance of about 400 mW cm^–2. To make a sub module for tubular SIS SOFC, ten tubular SIS SOFC single cells with an effective electrode area of 1.1 cm² were coated onto the surface of the prepared ceramic support and were connected in series by using Ag + glass interconnect between each single cell. The ten‐cell sub module of tubular SIS SOFC showed in 3% humidified H₂ and air at 800 °C a maximum power of ca. 390 mW cm^–2.     

Integration of Spin‐Coated Nanoparticulate‐Based La0.6Sr0.4CoO3–δ Cathodes into Micro‐Solid Oxide Fuel Cell Membranes

Thin cathodes for micro‐solid oxide fuel cells (micro‐SOFCs) are fabricated by spin‐coating a suspension of La_0.6Sr_0.4CoO_3–δ (LSC) nanoparticulates obtained by salt‐assisted spray pyrolysis. The resulting 250 nm thin LSC layers exhibit a three‐dimensional porous microstructure with a grain size of around 45 nm and can be integrated onto free‐standing 3 mol.% yttria‐stabilized‐zirconia (3YSZ) electrolyte membranes with high survival rates. Weakly buckled micro‐SOFC membranes enable a homogeneous distribution of the LSC dispersion on the electrolyte, whereas the steep slopes of strongly buckled membranes do not allow for a perfect LSC coverage. A micro‐SOFC membrane consisting of an LSC cathode on a weakly buckled 3YSZ electrolyte and a sputtered Pt anode has an open‐circuit voltage of 1.05 V and delivers a maximum power density of 12 mW cm^–2 at 500 °C.     

Investigation of Impactors on Cell Degradation Inside Planar SOFC Stacks

The impactors on cell degradation inside planar SOFC stacks were investigated using both coated and uncoated Fe–16Cr alloys as the interconnects under stable operating conditions at 750 °C and thermal cycling conditions from 750 to 200 °C. It was found that cell degradation inside the stack is primarily dependent on the interfacial contact between the cathode current‐collecting layer and the interconnect. Additionally, cell degradation is found to be independent of the high‐temperature oxidation and Cr vaporization of the interconnects during stack operation, as the stacks are well sealed. The coating on the interconnect can further improve the contact between the cell cathode and the interconnect when the latter is properly embedded into the current‐collecting layer.     

Thin film YSZ coatings on functionally graded freeze cast NiO/YSZ SOFC anode supports

Intermediate temperature (600–800 °C) solid oxide fuel cell (SOFC) technology is often limited by inadequate gas transport in electrodes, and high ion transport resistance electrolytes. In this study, large area filtered arc deposition (LAFAD) and hybrid filtered arc-assisted e-beam physical vapor deposition (FA-EBPVD) technologies, in combination with freeze-tape-casting, were used to fabricate SOFC anode/electrolyte bi-layers with functionally graded porous anode microstructures and thin film electrolytes favorable for both gas transport and low resistance. Traditionally-processed NiO/YSZ in addition to freeze-tape-cast NiO/YSZ anode substrates were fabricated and subsequently coated with thin film (<1–20 μm) YSZ via LAFAD and FA-EBPVD. LAFAD was found to be effective in applying thin (~1 μm) dense YSZ films on porous substrates at ~400 °C. FA-EBPVD produced relatively thick (~10–20 μm) dense YSZ coatings on porous substrates, with columnar morphology and nano-metrical grain size. A ~10 μm FA-EBPVD YSZ coating was observed to bridge NiO/YSZ surface pores of ~10 μm, which typically requires pre-filling prior to conventional thin film coating processes. Coated substrates exhibited negligible curvature, yielding flat anode/electrode bi-layers up to 2.5 cm in diameter. These results are presented with conderations for future SOFC development discussed.     

Infiltration of SOFC Stacks: Evaluation of the Electrochemical Performance Enhancement and the Underlying Changes in the Microstructure

Experimental SOFC stacks with 10 SOFCs (LSM‐YSZ/YSZ/Ni‐YSZ) were infiltrated with CGO and Ni‐CGO on the air and fuel side, respectively in an attempt to counter degradation and improve the output. The electrochemical performance of each cell was characterized (i) before infiltration, (ii) after infiltration on the cathode side, and (iii) after the infiltration of the anode side. A significant performance enhancement was observed after the infiltration with CGO on the cathode, while the infiltration of the anode side with Ni‐CGO had no significant effect on the electrochemical performance. After testing the cells were characterized by SEM and TEM/EELS. A thin layer of CGO nanoparticles around the LSM‐YSZ back bone structure was found after infiltration. On the anode side nano sized Ni particles were found embedded in a CGO layer formed around the Ni‐YSZ structure. EELS analysis showed that the oxidation state of the Ce ions is identical on the air and the fuel side.     

铋离子掺杂固体氧化物燃料电池阴极材料的研究进展

固体氧化物燃料电池(SOFC)是一种可以将燃料中的化学能直接转化为电能的发电装置,具有燃料选择灵活、效率高、环境友好等优点。基于SOFC运行成本和长期稳定性的要求,降低工作温度已成为当前研究的热点。传统阴极较低的催化活性制约了SOFC的技术发展,因此开发具有良好催化性能的阴极材料至关重要。大量的研究表明,铋离子的掺杂能够有效提高材料的电导率和氧催化活性。从铋离子掺杂的角度出发,综述了铋离子掺杂对阴极材料的制备、结构、电导率和电化学性能的影响,并对掺铋SOFC阴极材料未来的发展趋势进行了展望。     

Synthesis of LSM–YSZ–GDC dual composite SOFC cathodes for high-performance power-generation systems

This article investigates a method in further improvement of a (La_0.8,Sr_0.2)MnO₃ (LSM)-Yttria-stabilized zirconia (YSZ) dual composite cathode by adding material with high ionic conductivity such as gadolinia-doped ceria (GDC). A nano-porous composite cathode containing LSM, YSZ, and GDC was prepared by a two-step polymerizable complex (PC) method which minimizes the formation of YSZ–GDC solid solution. The structure of the resulting LSM/GDC–YSZ dual composite cathode was such that the LSM and GDC phases were present on the YSZ core particles without formation of the La₂Zr₂O₇, SrZrO₃, and GDC–YSZ solid solution. At 800 °C, the electrode polarization resistance of the LSM/GDC–YSZ dual composite cathode decreased to 0.266 Ω cm², compared with 0.385 Ω cm² for the LSM/YSZ–YSZ dual composite cathode. In addition, the Ni–YSZ anode-supported single cell using a LSM/GDC–YSZ dual composite cathode with H₂ as the fuel achieved a maximum power density of 0.65 W cm⁻² at 800 °C.