Proton Solid Oxide Research Articles

Production of La0.6Sr0.4Co0.2Fe0.8O3-δ cathode with graded porosity for improving proton-conducting solid oxide fuel cells

Utilization of 500-nm-diameter polystyrene (PS) nanospheres as pore former in a screen printing process to tailor the porous structure of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode for improving the performance of protonic solid oxide fuel cells is reported. The effects of PS nanosphere amount on cathode microstructure and cell performance are investigated. It is found that PS nanospheres can undergo a self-organized distribution in the screen-printed LSCF cathode due to the large difference in density between PS and LSCF, resulting in a porosity gradient in the cathode structure. The fuel cell with a 15 wt% PS-tailored cathode exhibits a much higher power density compared to that without tailoring by PS. The enhanced cell performance can be ascribed to the graded porosity in the cathode structure, which significantly reduces the ohmic and polarization resistances. It seems that such a graded-porosity cathode structure not only facilitates the generation and migration of O−ad from catalytic sites to triple phase boundaries (TPBs) but also promotes transfer of protons from the electrolyte to the TPBs.

Synthesis and Characterization of a New Electrolyte Composition for Protonic SOFC

This work focuses on the research of high efficiency and durability materials for use in protonic solid oxide fuel cells. The focused material on this stage of research is BaZr0.4Ce0.4Y0.1Gd0.1O3-δ (BZCYG); it attempts to join the good proton conductivity of barium cerate with the chemical stability of barium zirconate. Its synthesis is done via the modified Pechini method (1) using nitrates of the desired ions. The property characterization methods used were TGA/DSC, to determine the calcination temperature; dilatometry to assess the sintering behavior with and without sintering aid (NiO, as found in the literature (2)); X-ray diffraction (XRD) to make sure the desired phase was obtained; and Electrochemical Impedance Spectroscopy (EIS) to assess the protonic conductivity. The main problem faced while dealing with materials of this kind is their poor sinterability (3). The ideal composition was obtained, with single phase formation being identified through XRD.

Assessing Substitution Effects on Surface Chemistry by in Situ Ambient Pressure X-ray Photoelectron Spectroscopy on Perovskite Thin Films, BaCe xZr0.9- xY0.1O2.95 ( x = 0; 0.2; 0.9).

Performance of proton-solid oxide fuel cells (H+-SOFC) is governed by ion transport through solid/gas interfaces. Major breakthroughs are then intrinsically linked to a detailed understanding of how parameters tailoring bulk proton conductivity affect surface chemistry in situ, at an early stage. In this work, we studied proton and oxygen transport at the interface between H+-SOFC electrolyte BaCe xZr0.9- xY0.1O2.95 ( x = 0; 0.2; 0.9) thin films and the gas (100 mTorr of H2O and O2) by using synchrotron-based ambient pressure X-ray photoelectron spectroscopy at operating temperature (>400 °C). We developed highly textured BaCe xZr0.9- xY0.1O2.95 epitaxial thin films, which exhibit high level of in-plane proton conductivity, that is, up to 0.08 S cm-1 at 500 °C for x = 0.9. Upon applying 100 mTorr water partial pressure above 300 °C, major changes are observed only in the O 1s and Y 3d core level spectra, with a clear Zr/Ce ratio dependency. OH- formation is favored by Ce content while initiated near Y. Hydration is also associated with surface secondary phase growth comprising oxygen-under-coordinated yttrium and/or yttrium hydroxide. With BaCe0.2Zr0.7Y0.1O2.95, high levels of ionic conductivities and chemical stability are obtained as a result of the optimized surface reaction kinetics, with low activation energy barrier for proton transport while restraining formation of OH-/SO42- adsorb species.

Characterization and polarization DRT analysis of a stable and highly active proton-conducting cathode

The development of high active cathode materials owning low activation energy (Ea) is the most critical core for protonic solid oxide fuel cells (P-SOFCs). Considering this challenge, we herein develop Ba0.9La0.1Co0.4Fe0.4Zr0.1Y0.1O3-δ-BaZr0.1Ce0.7Y0.2O3-δ (BLCFZY-BZCY) composite as a new proton conducting cathode for P-SOFCs. Anode supported single cells with BLCFZY-BZCY cathode show remarkable performance and low electrode Ea of 83.41 kJ mol−1. High power densities of 752 and 206 mW cm−2 are achieved at 700 and 500 °C, respectively, while corresponding electrode interfacial polarization resistances (Rp) are 0.08 and 1.2 Ω cm2. Interestingly, the electrode polarization processes with a high resolution based on the impedance spectra data were further analyzed using the distribution function of relaxation time (DRT). Three same polarization peaks (P1, P2, P3) meaning three rate-limiting steps are existed in the DRT curves with different temperature, where P3 resulting from the cathode-electrolyte interfacial resistance with oxygen species involved reactions is the dominant rate-limiting step with a proportion of over 49.6% while the anode-electrolyte interfacial resistance corresponding to P1 has almost no increase, from 0.03 Ωcm2 to 0.09 Ωcm2. The experimental results demonstrate BLCFZY-BZCY composite can be a promising proton conducting cathode for P-SOFCs.

Highly dense and chemically stable proton conducting electrolyte sintered at 1200 °C

The BaCe0.7Zr0.1Y0.2−xZnxO3−δ (x = 0.05, 0.10, 0.15, 0.20) has been synthesized by the conventional solid state reaction method for application in protonic solid oxide fuel cell. The phase purity and lattice parameters of the materials have been studied by the room temperature X-ray diffraction (XRD). Scanning electron microscopy (SEM) has been done for check the morphology and grain growth of the samples. The chemical and mechanical stabilities have been done using thermogravimetric analysis (TGA) in pure CO2 environment and thermomechanical analysis (TMA) in Argon atmosphere. The XRD of the materials show the orthorhombic crystal symmetry with Pbnm space group. The SEM images of the pellets show that the samples sintered at 1200 °C are highly dense. The XRD after TGA in CO2 and thermal expansion measurements confirm the stability. The particles of the samples are in micrometer ranges and increasing Zn content decreases the size. The conductivity measurements have been done in 5% H2 with Ar in dry and wet atmospheres. All the materials show high proton conductivity in the intermediate temperature range (400–700 °C). The maximum proton conductivity was found to be 1.0 × 10−2 S cm−1 at 700 °C in wet atmosphere for x = 0.10. From our study, 10 wt % of Zn seems to be optimum at the B-site of the perovskite structure. All the properties studied here suggest it can be a promising candidate of electrolyte for IT-SOFCs.

High performance of protonic solid oxide fuel cell with BaCo0.7Fe0.22Sc0.08O3−δ electrode

Solid oxide fuel cells (SOFCs) have attracted tremendous attention for their combination of environmental power generation and fuel flexibility. Proton conducting SOFCs (P-SOFCs) demonstrate advantages over oxygen-ion conducting SOFCs, such as less activation energies on ionic transport and higher fuel utilization efficiency. Central to the devices is a suitable cathode with high catalytic activity. Herein, a cubic perovskite BaCo0.7Fe0.22Sc0.08O3−δ (BCFSc) has been applied as the cathode in proton-conducting solid state fuel cell (SOFC) with BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte. Peak power densities of 760, 591, 452 and 318 mW cm−2 are obtained at 650, 600, 550 and 500 °C with humidified hydrogen as the fuel and air as the oxidant. A low polarization resistance of 0.05 Ω cm2 under open circuit at 650 °C is observed.

Structural, thermal and microstructural studies of the proton conductor BaCe0.7Zr0.1Y0.05Zn0.15O3 for IT-SOFCs

The specimen of BaCe0.7Zr0.1Y0.05Zn0.15O3, a perovskite-type electrolyte, has been synthesized for application in an anode-supported protonic solid oxide fuel cell by the conventional solid state reaction in air at 1200°C for 12 hours. Structural and thermal characterization has been performed using room temperature X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA). Rietveld analysis of the XRD data has been analyzed by FullProf program and confirmed the single phase of the sample with an orthorhombic crystal structure in the Pbnm space group. To understand the temperature dependent behaviour TG/DTA scan of the precursor was recorded. The TG/DTA scan was performed under constant flow of Argon which exhibits a gradual weight loss up to 900oC. The SEM image of the pellet surface of the sample shows that the sample sintered at 1200oC was dense and suitable to use as electrolyte in solid oxide fuel cells (SOFCs).

Location of deuterium sites at operating temperature from neutron diffraction of BaIn0.6Ti0.2Yb0.2O2.6-n(OH)2n, an electrolyte for proton-solid oxide fuel cells.

A fundamental understanding of the doping effect on the hydration mechanism and related proton diffusion pathways are keys to the progress of Proton-Solid Oxide Fuel Cell (H(+)-SOFC) technologies. Here, we elucidate the possible interplay between the crystal structure upon hydration and the conductivity properties in a promising perovskite type H(+)-SOFC electrolyte, BaIn0.6Yb0.2Ti0.2O2.6-n(OH)2n. Thermal X-ray and neutron diffractions, neutron time-of-flight scattering along with thermal gravimetric analysis reveal the structural features of BaIn0.6Ti0.2Yb0.2O2.6-n(OH)2n at fuel cell operating temperatures. Between 400-600 °C, BaIn0.6Yb0.2Ti0.2O2.6-n(OD)2n (n < 0.042) remains in a disordered perovskite structure with high anisotropies in the form of oblate spheroids for oxygen. At 400 °C, the presence of oxygen and proton static disorder is clearly established. Yet, the insertion of mobile protons in 24k sites does not induce long-range structural distortion while facilitating both inter- and intra-octahedral proton transfers via quasi-linear O-DO bonds, strong hydrogen bonding, and octahedral tilting. This experimental evidence reveals that the co-doping approach on Ba2In2O5 enhances greatly protonic conductivity levels by enabling a continuous proton diffusion pathway through BaIn0.6Yb0.2Ti0.2O2.6-n(OH)2n. These new insights into the doping effect on the proton-transfer mechanism offer new perspectives for the development of H(+)-SOFC electrolyte materials.

Analysis Proton Conducting Electrolyte IT-SOFC Hybrid System Exhaust Gas With External Reforming of Biofuel

In this analysis, a hybrid system containing proton SOFC (P-SOFC) combine with micro gas turbine (MGT) with biofuel external reforming is investigation to decrease the greenhouse gases problem facing in electrical power plant. The hybrid system consist of a proton solid oxide fuel cell stack, a micro gas turbine, a combustor, compressors, heat exchangers and external reformer. The main operating parameter such as, fuel utilization and steam - carbon ratio is determined in this analysis.

Anode Supported Protonic Solid Oxide Fuel Cells Fabricated Using Electrophoretic Deposition

AbstractIntermediate temperature solid oxide fuel cells (IT‐SOFCs) were fabricated depositing proton conducting BaCe0.9Y0.1O3–x (BCY10) thick films on cermet substrates made of nickel oxide–yttrium doped barium cerate (NiO–BCY10) using electrophoretic deposition (EPD) technique. The influence of the EPD parameters on the microstructure and electrical properties of BCY10 thick films was investigated. Deposited BCY10 thick films together with green anode substrates were co‐sintered in a single heating treatment at 1,550 °C for 2 h to obtain dense electrolyte and suitably porous anodes. The half‐cells were characterised by field emission scanning electron microscopy (FE‐SEM) and by X‐ray diffraction (XRD) analysis. A composite cathode specifically developed for BCY electrolytes, made of La0.8Sr0.2Co0.8Fe0.2O3(LSCF, mixed oxygen‐ion/electronic conductor) and BaCe0.9Yb0.1O3–δ (10YbBC, mixed protonic/electronic conductor), was used. Fuel cells were prepared by slurry coating the composite cathode on the co‐sintered half‐cells. Fuel cell tests and electrochemical impedance spectroscopy (EIS) were performed in the 550–700 °C temperature range. A maximum power density of 296 mW cm–2 was achieved at 700 °C for electrolyte deposited at 60 V for 1 min.

Perovskite and A 2MO 4-type oxides as new cathode materials for protonic solid oxide fuel cells

Solid state ionic devices based on high-temperature proton conductors can be used for various applications, especially in a new class of fuel cells, the Protonic Ceramic Fuel Cell (SOFC-H +). These systems are currently operating at intermediate temperatures (500–600 °C) and one of the major problems is the overpotential at the cathode side. In this context, various perovskite oxides AMO 3 − δ (A = La, Ba, Sr; M = Mn; Fe, Co, Ni) and A 2MO 4-type compounds (A = La, Nd, Pr or Sr; M = Ni) have been investigated. Their properties under moist cathodic atmosphere have been studied. Actually, they are stable and exhibit high electrical conductivity ( σ > 100 S cm −1) as well as good electrocatalytic properties towards oxygen reduction. The electrochemical properties of these oxides deposited on the protonic electrolyte BaCe 0.9Y 0.1O 3 − δ have been studied and the Area Specific Resistances have been measured under air/H 2O (3%) atmosphere. The obtained values at 600 °C, especially for Ba 0.5Sr 0.5Fe 0.8Co 0.2O 3 − δ and Pr 2NiO 4 + δ show to be promising cathode materials for Protonic Ceramic Fuel Cell applications.

Optimizing the modification method of zinc-enhanced sintering of BaZr0.4Ce0.4Y0.2O3−δ-based electrolytes for application in an anode-supported protonic solid oxide fuel cell

Abstract The effects of zinc modification methods on membrane sintering, electrical conductivity of BaZr0.4Ce0.4Y0.2O3−δ (BZCY4) and the thermo-mechanical match of the BZCY4 electrolyte with anode were systematically investigated. Three modification methods are pursued, including the physical mixing of BZCY4 with a ZnO solid (method 1), introducing zinc during the solution stage of the sol–gel synthesis (method 2) and doping zinc into a perovskite lattice by synthesis of a new compound with a nominal composition of BaZr0.4Ce0.4Y0.16Zn0.04O3−δ (method 3). Method 1 turned out to be the most effective at reducing the sintering temperature, which can mainly be attributed to a reactive sintering although ZnO doping into the BZCY4 lattice also facilitates the sintering. While all three modification methods facilitated the membrane sintering, only the electrolyte from method 3 had similar shrinkage behavior to the anode. An anode-supported thin-film BZCY4-3 electrolyte solid oxide fuel cell (SOFC) was successfully fabricated, and the fuel cell delivered an attractive performance with a peak power density of ∼307 mW cm−2 at 700 °C.

A novel Ba 0.6Sr 0.4Co 0.9Nb 0.1O 3− δ cathode for protonic solid-oxide fuel cells

Ba 0.6Sr 0.4Co 0.9Nb 0.1O 3− δ (BSCN), originated from SrCo 0.9Nb 0.1O 3− δ (SCN), is investigated as a cathode material in a protonic solid-oxide fuel cell (SOFC-H +) with a BaZr 0.1Ce 0.7Y 0.2O 3 (BZCY) electrolyte. The surface-exchange and bulk-diffusion properties, phase reaction with the electrolyte, electrochemical activity for oxygen reduction, and performance in the real fuel cell condition of SCN and BSCN electrodes are comparatively studied by conductivity relaxation, XRD, EIS and I–V polarization characterizations. Much better performance is found for BSCN than SCN. Furthermore, water has a positive effect on oxygen reduction over BSCN while it has the opposite effect with SCN. A peak power density of 630 mW cm −2 at 700 °C is achieved for a thin-film BZCY electrolyte cell with a BSCN cathode compared to only 287 mW cm −2 for a similar cell with an SCN cathode. The results highly recommend BSCN as a potential cathode material for protonic SOFCs.

Focus on innovation in ceramics research in East Asia

Ceramics, as broadly defined, include all materials other than organic substances and metals, either crystalline or amorphous. They have been used by humans since early history and have contributed considerably to improving the quality of our life. In most cases, however, high-temperature treatment is necessary to prepare ceramics. This burdens the environment and there is therefore a great need for new ceramics processing methods. Recent technologically advanced ceramics are often composed of nanocrystallites, which have great potential for innovation in terms of exploring practical applications of nanomaterials and, consequently, reducing the environmental load. The ceramics industry had long flourished in Asia, particularly in East Asia, and even today, this region is leading the development of related materials. In line with these traditions, Japanese and Korean ceramics societies have been co-sponsoring seminars on ceramics since the 1980s. Having become more international in scope and context, a series of these seminars is now known as the International Japan–Korea Seminar on Ceramics. This focus issue contains eight key articles presented at the 26th International Japan–Korea Seminar on Ceramics held on 24–26 November 2009 at the Tsukuba International Congress Center. In particular, Fabbri et al review electrode materials for protonic solid-oxide fuel cells, and Kamiya et al outline the present situation and future prospects for transparent transistors, particularly those based on amorphous In-Ga-Zn-O films. Eitel et al discuss the progress in engineering high-strain lead-free piezoelectric ceramics. Kim and Kumar review a simple processing method for producing porous ceramics using polysiloxane precursors, Kamiya and Iijima focus on surface modification and characterization of nanomaterials, and Wan et al briefly review the strategy of reducing lattice thermal conductivity of thermoelectric materials and propose new materials for thermoelectric devices. Aubert et al introduce a novel technique of synthesizing composite nanomaterials and Cross and coworkers characterize Pb(Zr,Ti)O3 (PZT) ferroelectric thin films co-doped with Bi and Fe to enhance PZT capacitor ferroelectric properties. These articles are closely related to the global environmental load and energy issues that require solutions in modern ceramics technology. We hope that this focus issue will help advance not only ceramics-related but also other fields of materials science.

Zirconium doping effect on the performance of proton-conducting BaZryCe0.8−yY0.2O3−δ (0.0≤y≤0.8) for fuel cell applications

Abstract High-temperature proton conductors are promising electrolytes for protonic solid oxide fuel cells (H+-SOFCs). In this study, the relationship between the Zr doping content and structure, chemical stability, carbon dioxide resistivity, sinterability and electrochemical properties of BaZryCe0.8−yY0.2O3−δ (BZCYy), 0.0 ≤ y ≤ 0.8, are studied systemically using XRD, CO2-TPD, SEM, EIS and I–V polarization characterizations. Zr doping suppresses carbonate formation, CO2-TPD demonstrates that the formative rate of carbonate over BZCYy are 7.50 × 10−6 and 8.70 × 10−7 mol m−2 min−1 at y = 0.0 and 0.4, respectively. Investigation of sinterability shows that the anode-supported configuration helps the sintering of the thin-film electrolyte. Peak power densities of 220 and 84 mW cm−2 are obtained at 750 and 450 °C, respectively, with BZCY0.4 electrolyte. Due to the favorable chemical stability against CO2 and good sintering in the thin-film configuration, BZCY0.4 is a potential electrolyte material for H+-SOFCs.

Electrode Performance in Reversible Solid Oxide Fuel Cells

The performance of several negative (fuel) and positive (air) electrode compositions for use in reversible solid oxide fuel cells capable of operating both as a fuel cell and as an electrolyzer was investigated in half-cell and full-cell tests. Negative electrode compositions studied were a nickel/zirconia cermet and lanthanum-substituted strontium titanate/ceria composite, whereas positive electrode compositions examined included mixed ion- and electron-conducting lanthanum strontium ferrite (LSF), lanthanum strontium copper ferrite , lanthanum strontium cobalt ferrite , and lanthanum strontium manganite (LSM). While titanate/ceria and electrodes performed similarly in the fuel cell mode in half-cell tests, losses associated with electrolysis were lower for the titanate/ceria electrode. Positive electrodes gave generally higher losses in the electrolysis mode when compared to the fuel cell mode. This behavior was most apparent for mixed-conducting and electrodes, and discernible but smaller for LSM; observations were consistent with expected trends in the interfacial oxygen vacancy concentration under anodic and cathodic polarization. Full-cell tests conducted for cells with a thin electrolyte ( YSZ) similarly showed higher polarization losses in the electrolysis than fuel cell direction.

Charge transfer in mixed proton, oxygen ion and electron solid oxide conductor

Analysis of the equivalent scheme of the mixed proton-oxygen ion-electron conductor (MPOEC) allowed to obtain relationships between parameters of the membrane (total conductivity and transfer numbers) and parameters of the charge and mass transfer through the membrane (partial ion and electron currents, the specific flux of hydrogen at the cathode membrane surface) under regime of electrochemical reforming. It was stated that presence of proton conductivity in addition to oxygen ion conductivity led to increase of total flux of produced hydrogen. However, under conditions typical for the electrochemical reforming of methane into hydrogen, the specific hydrogen flux is about four times lower in the case when the membrane has proton-electron conductivity than in the case when the membrane has oxygen ion-electron conductivity.

Application of Solid Oxide Fuel Cells to Aircraft

Fuels Cells are being considered for various applications on airplanes and space vehicles. It is critical that fuel cells meet the performance and airplane system-level environmental requirements. Fuels cells are being considered for replacing batteries as a non-time limited emergency power source; as a replacement for the Auxiliary Power Units (APUs); and as the primary power source for propulsion on high altitude long endurance aircraft and high altitude airships. For high altitude long endurance airplane or airship applications, fuels cells are being considered as regenerative closed loop power sources. Two major types of fuel cells, Proton Exchange Membrane Fuel Cell (PEMFC) and Solid Oxide Fuel Cell (SOFC), are the most probable choices due to their relatively high level of development and potential for commercialization. For transportation applications, the PEMFC is in the forefront because of its compact size, quick startup time and low operating temperatures (∼80°C). In the future, for aerospace applications, the SOFC should become more common because of its ability to use converted hydrocarbon fuels along with some of the impurities such as CO, its high operating temperatures (∼1,000°C) and its potential to combine with a gas turbine to gain even higher efficiency (1). For use on present day airplanes, since the operators of commercial airplanes have no desire to maintain the logistics and carry another type of fuel (e.g. Hydrogen), fuel processing is required to convert current fuels, such as Jet A, JP-5 or JP-8 to hydrogen in order to drive the fuel cells. The complexity of the fuel processing is dependent on the purity required. Here, the SOFC seems to have a definite advantage over the PEMFC.