Ceramic Fuel Cells Research Articles

Fuel-Flexible Ceramic Fuel Cells at Reduced Operating Temperatures

Ceramic fuel cells are uniquely capable of generating power using a wide range of fuels, including hydrogen, hydrocarbons, and ammonia. One of the primary issues of ceramic fuel cells for large-scale power generation originates from the high operating temperature, which leads to limited material choices for interconnects and sealants, expensive balance of plants, slow start-up and shutdown cycles, and high degradation rates, inevitably limiting their scaleup and commercialization. Reducing the temperature to <600 °C could transform the architecture and operation of ceramic fuel cells. However, the internal reforming of hydrocarbons is endothermic, which is thermodynamically and kinetically unfavorable at lowered operating temperatures, necessitating the development of internal reforming catalysts to enhance the anode catalytic activity. This talk will first focus on presenting the approaches that have been validated for designing and synthesizing internal reforming catalysts, with a particular focus on internal steam reforming and dry reforming of methane. Additionally, the characterization of high-performance ceramic fuel cells equipped with these catalysts will also be discussed. The associated challenges and proposing strategies from different perspectives will also be provided in this talk.

Strong Metal-Support Interactions Stabilize Pt Nanocatalysts for Ceramic Fuel Cells

Nano-sized metal particles are widely used in various chemical/electrochemical fields due to their excellent catalytic activity, but they still suffer from deactivation by sintering, and this leads to serious issues regarding the price and lifespan of catalysts. In this study, we demonstrate that the introduction of nanoscale amorphous TiOx via atomic layer deposition can significantly improve the dispersion and durability of supported Pt nanocatalysts. An ultrathin TiOx layer (< 1 nm) deposited on a conductive Pr0.5Ba0.5MnO3 electrode, with a deposition time of less than 1 min, provides nucleation sites for the Pt nanocrystals impregnated thereon and promotes the migration of TiOx to the Pt surface, creating a metal-oxide interface. As a result, when applied to ceramic fuel cells, the TiOx undercoat achieves remarkable power density increases of over 100% and 400%, respectively, for wet (3% H2O) H2 and CH4 fuels without degradation at 700 °C for 120 h. These observations provide an innovative direction for the design of supported metal catalysts for high-temperature applications.

Effect of Water Vapor and Hydrogen Concentration on Power Generation Characteristics of Protonic Ceramic Fuel Cell

The proton and hole conductivities of BaZrO3-based perovskites depend on partial pressures of oxygen and water vapor. These conductivities affect the power generation characteristics of Proton Ceramic Fuel Cells (PCFCs) using the perovskite as an electrolyte. In this study, the effect of humidification conditions on the power generation characteristics of an anode-supported PCFCs was investigated.The configuration of the anode-supported PCFC was La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode/BaZr0.8Yb0.2O3-δ(BZYb) electrolyte/Ni-BZYb anode. The diameter of the effective cathode area was approx. 10 mm. The cathode gas composition was fixed at 97% concentration of air and 3% concentration of water vapor. The concentration of water vapor in the anode gas was controlled to be 3-69%. The current density-voltage characteristics and AC impedance were measured by Bio-Logic SP-150.In all water vapor concentration conditions, the cell showed the highest OCV (approximately 1 V) at 3% concentration of water vapor. However, the maximum power density was highest at 30% concentration of water vapor (346 mW/cm2). The highest maximum power density at 30% concentration of water vapor can be explained by the following reason. The OCV values decrease with increasing the concentration of water vapor because of decreasing the concentration of hydrogen. On the other hand, from the results of impedance measurements, the ohmic resistance of the cell decrease with increasing the concentration of water vapor because of increase of proton conductivity of the cell. Thus, the increase of cell voltage by increase of proton conductivity should be higher than the decrease of OCV values.【Acknowledgements】This presentation is the result of the research and development of ultra-efficient proton-conducting ceramic fuel cell devices, JPNP20003, funded by the New Energy and Industrial Technology Development Organization (NEDO), Japan. We would like to express our gratitude to all parties involved.

Performance Improvement of Proton Ceramic Fuel Cells through Surface Treatment of Cobalt Oxide Nanoparticles on Perovskite Oxide

Ceramic fuel cells, such as solid oxide fuel cells (SOFCs) have attracted substantial attention as next-generation power generators. However, SOFCs exhibit high activation energy required for ion conduction (0.8–1 eV), which considerably increases the resistance upon decreasing the driving temperature. Therefore, the operating temperature of a typical SOFC is 800 °C or higher. However, such high-temperature driving conditions are associated to several challenges, such as heat-induced cell-structure deformation , rapid degradation of the material due to bonding stress, and the need for an insulation structure to prevent energy loss. Therefore, efforts have been made to lower the operating temperatures. Common methods use proton-conductive ceramics for proton-ceramic fuel cells (PCFCs). Unlike SOFCs, where the oxide ions pass through the electrolyte, in PCFC, protons pass through the electrolyte. Given that the activation energy (0.3–0.5 eV) of proton conduction is lower than that of oxide ions, most proton-conductive ceramics have very high ion conductivity at a lower temperature than oxygen-conductive ceramics. Therefore, compared with SOFCs, PCFCs exhibit a relatively high performance in the temperature range of 600 °C or less. As described above, efforts have been made to lower the driving temperature by promoting the oxygen reduction reaction (ORR) at the cathode, as well as by changing the ion transferred from the electrolyte.PrBa0.5Sr0.5Co2xFexO5+δ (PBSCF), a typical co-doping (Sr on the A-site and Fe on the B-site) cathode material, formed rapid oxygen diffusion and surface oxygen exchange through crystalline channels. However, most perovskite oxides, including PBSCF, exhibit poor chemical surface stability in high-temperature oxidation environments. In particular, Sr aggregation is considered a major reason for cathode degradation; however, the exact mechanism of this phenomenon has not yet been elucidated and a solution has not yet been established. Currently, it is known that elements such as Ba and Sr are larger size than other elements. During the stretch compression process inside the lattice, they are pushed out via the strain effect; moreover, the electrostatic phenomenon between the oxygen vacancies and cations may be an additional reason. Surface-treatment techniques are suitable for suppressing these phenomena. Through surface coating, the secondary phases generated by Ba and Sr aggregation may be suppressed to prevent electrode degradation. In addition, surface treatment technology is used to increase the catalytic activity of the cathode. Among the various surface treatment techniques, atomic layer deposition (ALD) is a surface thin-film coating technology suitable for ceramic cell electrodes. ALD proceeds in a chemical manner, such as chemical vapor deposition; however, it has several advantages. This may limit the deposition thickness per cycle to less than that of the atomic layer units through self-limiting reaction characteristics during material synthesis. In addition, the ALD reaction proceeded at the same rate along the surface of the substrate, which enabled uniform coating along a complex surface shape. Therefore, it may be considered an effective process to uniformly deposit a surface film and material inside a porous ceramic cell electrode structure.Herein, we attempted to improve electrode performance by applying ALD CoOx to a porous PBSCF cathode surface. CoOx has gained popularity as a high-performance electrochemical catalyst owing to its excellent ORR performance, low cost, and high chemical stability. As a result, we confirmed that the ohmic and polarization resistances were reduced by approximately 50 % and 34 %, respectively, at 600 °C by treating with CoOx, and through this, we confirmed a performance improvement of approximately 32 %. In addition, the inhibition of Ba or Sr segregation was confirmed through long-term testing. These results show that CoOx acts as an ORR catalyst in a PBSCF cathode with a perovskite structure and that ALD is a suitable method for coating porous cathode structures. In addition, H2O as a by-product of the cathode generates an oxygen reduction reaction in PBSCF, and a large amount of OH- is generated. As the number of oxygen vacancies increased, the movement of active oxygen species and electrons was promoted. This further improves the reaction with the catalyst by facilitating movement to the catalyst surface via overall electron migration and the overall spillover effect.

Rapidly Direct Laser 3D Printing of High-Performance Protonic Ceramic Fuel Cells

Fuel cells with a dense ionic conducting electrolyte layer sandwiched between two porous electrode layers are one of the most efficient fuel-to-electricity energy conversion devices. Their reversible operation can also efficiently electrolyze water to hydrogen, reduce carbon dioxide to fuels, synthesize ammonia, upgrade fuels, and store energy on large scales. Compared with the popular low-temperature (~80 oC) proton exchange/polymer electrolyte membrane fuel cells and the high-temperature (700-1000 oC) oxygen ion-conducting solid oxide fuel cells (SOFCs), initially used in electric vehicles, auxiliary powers, power plants, and hydrogen electrolyzers, the rising star of protonic ceramic fuel cells (PCFCs) based on proton conducting oxide electrolytes offers excellent suitability for operating at 400-700 oC, the optimum temperature range for electrochemical energy devices, enabling extensive superiorities (high efficiency and performance, long thermal and chemical stabilities, flexible fuels, and cost-effective compatible materials) compared to their counterparts. In recent ten years, many high-performance PCFCs have been reported. However, most performances were achieved using small-area button cells (<0.5cm2) fabricated using spin coating, drop coating, manual brushing, and screen printing of electrolytes on the dry-pressed anode supports, followed by co-firing. There are challenges to transferring the excellent microstructures and materials chemistries/properties obtained from small-area cells to large-area cells and stacks. Furthermore, the decrease in cell component layer thickness for high volumetric cell performance and the requirement for more efficient, faster, and more cost-effective manufacturing motivated the advanced manufacturing of PCFCs.This work will focus on the direct laser 3D printing (DL3DP) of PCFCs performed at Clemson University. The DL3DP integrated 3D printing (microextrusion and ultrasonic spraying) and laser processing (drying, sintering, and machining), allowing for manufacturing PCFC components, single cells, and stacks with the desired microstructures and geometries irrelevant to the area. The DL3DP could rapidly and cost-effectively manufacture PCFCs without conventional long-term furnace processing. The processing speed could be 2 orders of magnitude faster than the conventional tape-casting and furnace co-firing method. The achieved cells and stacks showed excellent fuel cell performance and less dependence on the effective area. The cells showed peak power densities 1.6-2.6 times that of the conventionally processed samples. The stacks demonstrated a peak power of 7 W and constant power outputs of 0.5-3.1 W for 110-260 hours. This DL3DP can be expanded to manufacturing other heterogeneous ceramics for energy conversion and storage devices. Figure 1

Numerical Analysis of Humidification Condition Effects on Protonic Ceramic Fuel Cell Performance Considering Concentration Overpotential

Protonic ceramic fuel cells (PCFCs) show relatively high performance at intermediate temperature range (400–600 °C) due to high proton conductivity in electrolyte. However, besides proton, other charges such as electron hole and oxygen vacancy can also be conductive in PCFCs. Especially, the hole conductivity will induce a hole current leakage so that current efficiency and power density will decrease. Besides the operating temperature, the conductivities of proton and hole are also strongly affected by the partial pressures of steam and oxygen in the PCFC [1,2]. Higher steam partial pressure leads higher proton conductivity, so that a higher power density can be expected. However, other influences such as concentration overpotential may be non-negligible. Furthermore, the proton and hole current density are affected by defect concentrations differences between two surfaces of the electrolyte membrane. Numerical simulation method is powerful tool for dealing with the complicated conditions in a PCFC mentioned above.In the present study, the influences of steam partial pressure on a BaZr0.8Yb0.2O3− δ (BZYb20) electrolyte are investigated. Specifically, to reveal the currents induced by the electrostatic potential and gas concentrations, Nernst-Planck model is selected. To relatively obviously reveal the steam concentration influences on the PCFC performances, low (3%) and high (69%) humidification conditions of H2 fuel gas are adopted. The results in Fig. 1(a) and 1(b) show the simulation and experimental current-voltage characteristics under 3% and 69% humidification conditions, respectively. The green solid and dotted lines are external and proton current densities considering concentration overpotential influence, respectively. The blue lines express external current density when no concentration overpotential in the numerical model. The red circles are the measured data. At low steam partial pressure, the simulation results well reproduced the experimental data without concentration overpotential consideration. However, an obvious deviation was found between simulation and experimental results when neglecting concentration overpotential in the simulation model. The performances such as open circuit voltage (OCV) and hole current leakage (difference between proton and external current density) are influenced by the steam partial pressure.

Development of Protonic Ceramic Fuel Cell Using BaZr0.2Yb0.8O3-δ as the Electrolyte

Protonic Ceramic Fuel Cells (PCFCs) are attracting attention as next-generation fuel cells that are expected to have lower operating temperatures and higher power generation efficiency than SOFCs. We have reported that BaZr0.8Yb0.2O3-δ does not chemically react with NiO used as a fuel electrode at 1475°C, which is the sintering temperature of the cell, and that the fuel cell can be fabricated by the tape casting method and the fuel electrode and electrolyte co-firing method used in industrial production processes for SOFCs and electronic components. This report describes issues that need to be resolved for the practical application of this cell.Fuel cells were fabricated by laminating green sheets prepared by the tape casting method and co-firing the electrolyte and fuel electrode together. For the air electrode, La0.6Sr0.4Co0.2Fe0.8O3-δ and La0.6Sr0.4CoO3-δ, which are widely used in SOFCs, and newly developed BaZr0.375Yb0.125Co0.5O3-δ were sintered at 900°C to 1000°C. The electrochemical performance of the planar cell was investigated at 600°C under the conditions of a humid fuel gas (i.e., 3% H2O and 97% H2) and humid air (i.e., 3% H2O, 20% O2 and 77% N2). The active area of the planar cell was 0.785 cm2.To evaluate the durability of each cell, continuous power generation tests were conducted at constant current. The durability test was conducted by generating power for 1000 hours at a constant current that resulted in a voltage of 0.85 V at the start of the test, and durability was evaluated by the rate of voltage drop per 1000 hours. As a result, the voltage reduction rate per 1000 hours for the cell using BaZr0.375Yb0.125Co0.5O3-δ as the air electrode was 7.3%/kh. The results clearly show that one of the most significant issues for practical use is the suppression of the rate of voltage drop. The resistance of the cell before and after the durability test were analyzed by electrochemical impedance method, and the ohmic resistance and electrode resistance increased. EPMA analysis of the cell cross section to investigate the cause of degradation revealed diffusion of Ni from the fuel electrode and Co from the air electrode in the electrolyte. Therefore, in order to further improve durability, there is a need to consider adding an anti-diffusion layer to prevent the diffusion of these elements and developing air electrode materials that do not contain Co.

Additive Manufacturing of Single-Layer Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) or proton conducting solid oxide fuel cells (p-SOFCs) have been emerging as a potential low-temperature (400-600oC) fuel cell technology. Generally, the proton conducting ceramic electrolyte materials have a lower activation energy (< 50 eV) and lower electronic conductivity than the conventional oxygen-ion conducting ceramic materials, which are beneficial for improving the fuel cell efficiency and the power output. The additive manufacturing has the potential to transform the manufacturing of PCFCs since it can fabricate both the dense and porous structures with good mechanical and electrochemical properties. In this work, we fabricated single-layer PCFCs through a hybrid of extrusion-based 3D printing utilizing BaZr0.3Ce0.5Y0.15O3-δ and BaZr0.4Ce0.4Y0.1Yb0.1O3-δ as electrolytes, their composite with NiO as anode, and their composite with BaCo0.4Fe0.4Zr0.1Y0.1O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ as cathode. The rheological properties of the printable pastes were investigated in detail with the dynamic light scattering, viscometer, tensiometry, differential scanning calorimetry and thermal gravimetric analysis. Furthermore, the cells are characterized with current-voltage measurements and electrochemical impedance spectroscopy. In addition, other spectroscopic and microscopic measurements (HR-TEM-EELS, SEM-EDX, XPS) were conducted to better understand the mechanisms in the cells. A systematic study was conducted to optimize the sintering temperature for optimal fuel cell performance. Finally, the degradation mechanisms in the cells were investigated in order to improve their stability.Dr. Asghar thanks Academy of Finland (Grant No. 13322738, 13329016, 13352669) for the financial support. Figure 1

Investigation of La0.65Ca0.35FeO3−δ as a Co-Free Cathode for Protonic Ceramic Fuel Cells with Yb-Doped BaZrO3 Electrolyte

In protonic ceramic fuel cells (PCFCs), the use of cobalt-free cathodes is expected to reduce manufacturing costs and improve durability performance. However, cobalt-free cathodes generally tend to have poor power generation performance due to their lower catalytic activity than cobalt-containing cathodes. Therefore, based on a previous study in which higher power generation performance was obtained with SOFCs using La0.65Ca0.35FeO3−δ (LCaF) than with SOFCs using La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) containing cobalt, we focused on LCaF as a cobalt-free cathode. In this study, we attempted to apply cathodes with LCaF to anode-supported PCFCs using a BaZr0.8Yb0.2O3-δ (BZYb) electrolyte in order to improve the power generation performance and durability of PCFCs.The proton-conducting oxides used for composite cathodes were investigated. BZYb, which is the same as the electrolyte, was used, but the adhesion between the electrolyte and the cathode was poor. When, BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb), which has good sinterability compared with BZYb, was therefore used, reading to improvement in the adhesion. Moreover, process parameters such as composite ratio and sintering temperature were also optimized. As a result, a maximum power density of 0.4 W cm-2 at an operating temperature of 600 °C was obtained for PCFCs using a composite cathode of LCaF and BZCYYb at a weight ratio of 6:4 sintered at 1100 °C, which is equivalent to PCFCs using a cathode with LSCF. In addition, the voltage drop rate of PCFCs using a composite cathode of LCaF and BZCYYb in the constant current durability test (0.26 A cm-2) at an operating temperature of 600 °C was 4% per 1000 hours, less than 1/10 that of PCFCs using a cathode with LSCF. Based on these results, LCaF is one of the candidate materials of cobalt-free cathode for PCFCs.Acknowledgements: This work is based on the results obtained from a project (JPNP20003) commissioned by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Bilayer Cell Model and System Design of Highly Efficient Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) are promising devices for highly efficient next-generation fuel cell systems. PCFCs provide several benefits. Water formation at the cathode can improve fuel utilization. Also, lowering operation temperature using proton-conducting solid electrolyte membranes will enable a long lifetime and low system costs. On the other hand, ionic and electronic transport properties, i.e., proton, oxide ion, hole, and electron conductions, in PCFCs induce leakage current in electrolyte membranes and decrease energy conversion efficiency. Therefore, controlling the transport properties and designing cell structures to prevent them are important issues for developing highly efficient PCFCs. In this study, a comprehensive design approach was conducted from a bilayer cell to a PCFC system.It has been reported that bilayer electrolytes can improve the interface between cathode and electrolyte and also prevent nickel diffusion (1). Additionally, it has been reported that bilayer electrolytes can suppress leakage current by using a hole blocking layer (2, 3). Therefore, the use of bilayer electrolytes can help improve the efficiency and performance of PCFCs. In this study, a bilayer PCFC consisting of BaZr0.8Y0.2O3−δ (BZY) and BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) was modeled by considering the transport properties of each electrolyte. The main objective of the modeling was to determine the best cell design and operating conditions that maximize PCFC efficiency. Calculations were done by solving the set of integral equations described by Choudhury and Patterson (4) but extended for bilayer electrolytes (3) to obtain the cell potential, and the total and proton current densities.It was found that higher efficiencies were obtained when using a thin layer of BZY with a thicker layer of BZCYYb. The calculations suggest that the thin BZY layer acts as an electron-blocking layer. For example, leakage currents of less than 5% can be achieved by using a BZY(1 µm)|BZCYYb (19 µm). It was also found that the PCFC efficiency increased with decreasing temperature. Thus, higher efficiencies were obtained at 500°C than at 600°C.In addition, the energy conversion efficiency of a 5kW(DC)-class PCFC system was evaluated. In this study, the fuel in an anode was assumed to be hydrogen obtained by steam reforming of methane. Gas compositions in the streams of the PCFC system were calculated based on thermodynamic equilibrium at atmospheric pressure. The operating temperature of PCFC module was set as 500°C-600°C, and the external current density was assumed to be 300 mA/cm2. Here, the leakage current ratio was defined as a percentage of the leakage current to the total ion current density. The system efficiency was defined as an extracted power of the PCFC to the combustion heat of methane (25°C, LHV).The results are described as a standard case of 600°C as follows. A system efficiency of 69.5％ (LHV, DC) was attainable, assuming the cell voltage of 0.85 V, leakage current ratio of 1%, and fuel utilization of 94.2％. In this case, the steam-to-carbon ratio (S/C) was 2.5. In addition, a system efficiency of over 70％ (LHV, DC) was obtained under the cell voltage of 0.9 V, leakage current ratio of less than 5%, and fuel utilization of over 90％. Based on the above results, a cell design with bilayer electrolyte was discussed considering electrode/electrolyte materials and physical properties (e.g., transport number and conductivity). Acknowledgments This work was supported by a project, (JPNP20003), commissioned by the New Energy and Industrial Technology Development Organization (NEDO) and JSPS KAKENHI JP21H04938 and JP21J14251.

Protonic Ceramic Fuel Cells with Stoichiometric Electrolytes

Among various types of solid oxide electrochemical cells, protonic ceramic fuel cells (PCFCs) have been expected to reduce the operating temperature below 600 °C with their significantly high ionic conductivity and activation energy. For example, recently developed proton conductor (BaZr0.4Ce0.4Y0.1Yb0.1O3-δ, BZCYYb) ideally has ~12-fold higher ionic conductivity (2.810-2 S/cm at 600 °C) and low activation energy (Ea < 0.4 eV) than those of conventional oxide ion conductor (Y0.08Zr0.92O2-δ; 2.810-3 S/cm at 600 °C and Ea ~0.87 eV). However, the low chemical and physical stabilities of proton conducting oxides during fabrication processes, primarily due to the high mobility and volatility of Barium (Ba), induce the substantially lower electrochemical performance than their predictions, limiting their utilization and application. Here, we present the chemically and physically stable BZCYYb electrolyte with the desired stoichiometry and the average grain size of ~10 µm by controlling the chemical potential of the A-site cation, Ba, near the BZCYYb electrolyte surface during the sintering process. A stoichiometric BZCYYb-based PCFC in an anode-supported configuration exhibits 1.90/cm2 and 1.01 W/cm2 with an extremely low ohmic resistance of ~0.060 ohm·cm2 at 650 °C and ~0.082 ohm·cm2 at 550 °C, respectively. Our results may open the possibility of finding a technical breakthrough for various next-generation electrochemical systems having desirable material properties without the requirement for complicated and expensive fabrication processes.

Evaluation of Hydrogen Ions Flowing through Protonic Ceramic Fuel Cell Using Ytterbium-Doped Barium Zirconate as Electrolyte

Protonic ceramic fuel cells (PCFCs) are clean power generation devices that do not emit carbon dioxide, and generate electricity when protons (hydrogen ions) pass from the fuel electrode through the electrolyte to form water vapor at the air electrode. As a fuel cell, PCFC is expected to be a highly efficient fuel cell because it can operate at medium to low temperatures of around 600°C and no fuel dilution occurs. However, proton-conducting ceramics can conduct not only protons but also a small amount of holes, which can cause electron leakage and lower the power generation efficiency. Therefore, it is very important to understand the ionic and hole conductivity in a fuel cell.To evaluate the electronic leakage of PCFC, the amount of proton current flowed in PCFC can be measured by an apparatus developed based on the electromotive force of an electrochemical cell using 10 mol% In-doped CaZrO3 (hydrogen sensor) and Y stabilized zirconia (oxygen sensor). Water vapor pressure on cathode was change when hydrogen ion passes thorough PCFC. The current of hydrogen ion can be determined by monitoring water vapor pressure. We measured the current of hydrogen flowing through protonic ceramic fuel cell using ytterbium-doped barium zirconate as electrolyte. Hydrogen ion and hole were found to leak at OCV at 700°C. Then electronic leakage was estimated form the current of hydrogen ion and external current. The electronic leakage was found to be suppressed with increasing electrolyte film thickness. On the other hand, no leakage of hydrogen and holes was observed at 500°C.

Experimental Demonstration of the Electric Efficiency with BZYb based Protonic Ceramic Fuel Cell

Protonic Ceramic Fuel Cell (PCFC) is expected to be the next-generation fuel cell for its higher energy conversion efficiency and lower operation temperature. BaZrO3 based oxide are potential materials as PCFC electrolyte because they have a high chemical stability under CO2 condition and high proton conductivity. We have developed PCFC using BaZr0.8Yb0.2Ox (BZYb) as the electrolyte and performed max power density 0.49 W cm–2 at 873 K. For practical use of PCFC, it is needed to conduct the higher electric efficiency and to improve the durability. Especially, improving the electric efficiency of PCFC might be difficult due to the internal current leakage by the hole creation.In this work, we have evaluated the electric efficiency using a Φ60mm anode supported PCFC (active electrode area: Φ45mm, 15.9 cm2). Thin and dense BZYb electrolyte is supported on porous Ni-BZYb cermet anode and La0.6Sr0.4CoOx cathode. The effect of fuel utilization on PCFC cell was examined and the electric efficiency of PCFC was calculated as follows:η = V / (-ΔH / nF) × Ufwhere the n and F are the mole number and the Faraday constant, respectively. ΔH is the standard combustion enthalpy of hydrogen or methane. The value of -ΔH / nF is 1.24 V or 1.04 V in the case of hydrogen supply or methane supply respectively. V is the cell voltage and Uf is the fuel utilization.Φ60mm anode supported PCFC was fabricated by tape-casting process used for the industrial production of ceramic electronic devices. NiO-BZYb anode slurry and BZYb electrolyte slurry were prepared by mixing the powder, binder, solvents and plasticizer. And then, these slurries were tape-casted respectively. The anode green sheets and the electrolyte green sheets were stacked and pressed. The anode electrolyte half-cell was obtained by firing this laminate at 1673–1773 K for 2 h. La0.6Sr0.4CoO3-δ (LSC) paste was applied to the surface of the half-cell by screen–printing, and then, fired at 1223 K for 2 h to form a cathode.The electrochemical performance of the Φ60mm anode supported PCFC was investigated at 873 K under the conditions of a humid fuel gas (i.e., 3% H2O, 48.5% N2 and 48.5% H2) and a humid air (i.e. 3% H2O and 97% air). Fuel flow rate were determined by the operational current and the fuel utilization (Uf), and air flow rate were constant at 264 cc min–1, which the air utilization (Uair) was 30% at the current of 0.3 A cm–2.Figure 1 shows the comparison of the current-voltage (I-V) and current-power (I-P) characteristics of Φ60mm and Φ20mm BZYb cell. Fuel flow rate was 100 cc min–1 at this experiment. The same electrochemical performance was observed, and the maximum power reached 7 W at 12.9 A in the case of the Φ60mm cell.Figure 2 shows the cell performance of 0.3 A cm–2 current density under the various Uf condition. The theoretical voltage line was also drawn in the figure, which was calculated by Nernst equation used the PH2 in the anode outlet gas, PO2 and PH2O in the cathode outlet gas. Cell voltage followed the same path as the theoretical voltage in the low Uf condition (Uf≦70%). On the other hand, the gap between the cell voltage and theoretical one was larger in the higher Uf condition (Uf≧80%). Anode gas diffusion overvoltage might be increased by PH2 decreasing in anode gas or the imbalanced gas flow due to decreasing the anode gas flow rate. We demonstrated that BZYb based PCFC could be operated at high Uf condition (i.e., Uf=90%) and the maximum electric efficiency was 55% (DC). This presentation is partially based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Durability and Interfacial Elemental Diffusion about BZYb based Protonic Ceramic Fuel Cell

Protonic ceramic fuel cells (PCFCs) are expected to be a highly efficient next-generation fuel cell because the fuel is not diluted by the generated water vapor during power generation. In the past research, we have found that Yb-doped BaZrO3 (BZYb) is promising in terms of the durability against CO2, proton conductivity, and less reactivity with NiO used for the fuel electrode. We are currently developing improvement of power generation efficiency and durability of PCFCs using BZYb electrolyte. In terms of the durability of PCFCs, there is concern about degradation due to diffusion of transition metals such as Co and Ni used in the air and fuel electrodes. In this study, we evaluated the durability of PCFCs using BZYb electrolyte focusing on the diffusion of transition metals derived from electrodes. We also examined the effect of a buffer layer on the air electrode side. In this study, fuel electrode supported cells with BaZr0.8Yb0.2O3-δ(BZYb20) electrolyte and NiO-BZYb20 fuel electrode was used. The fuel electrode half cells were fabricated by integrally firing process of the laminated green sheets of the electrolyte and fuel electrode to densify the electrolyte. For air electrode, BaZr0.375Yb0.125Co0.50O3-δ was screen printed on the fuel electrode half cell and fired at 900°C. For the cell with buffer layer between the air electrode and the electrolyte, BaCe0.7Zr0.1Y0.1Yb0.1O3- δ was spin-coated on the half-cell and then fired at 1300°C. The air electrode was then prepared in the same way. Durability tests were conducted at constant-current mode at 600°C, and the elemental diffusion state of the cells before/after the test was observed by cross-sectional EPMA. During 1000h power generation, the increase of ohmic resistance and polarization resistance was observed, and the increase in resistance was found to be smaller in cells with buffer layer. The results of cross-sectional EPMA analysis after the power generation test showed differences in the segregation state of Co and Ni in the electrolyte, with a tendency for segregation to be suppressed in the presence of a buffer layer.Acknowledgement: This work is partially based on results obtained from a project (JPNP20003), commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Evaluation of Hydrogen Ions Flowing through Protonic Ceramic Fuel Cell Using Ytterbium-Doped Barium Zirconate as Electrolyte

To measure the proton current in a PCFC (protonic ceramic fuel cell), the proton current detector was developed using a proton conducting oxide. The amount of proton current that flowed in the PCFC can be measured by an apparatus developed based on the electromotive force of an electrochemical cell using 10 mol% In-doped CaZrO3 (hydrogen sensor) and Y-stabilized zirconia (oxygen sensor). The water vapor pressure on the cathode changed when hydrogen ions pass through the PCFC. The hydrogen ion current can be determined by monitoring the water vapor pressure. The electronic leakage was then estimated from the hydrogen ion current and external current. We measured the current of hydrogen flowing through protonic ceramic fuel cell using ytterbium-doped barium zirconate as the electrolyte. Hydrogen ions and holes were found to leak under the OCV at 700 °C. The electronic leakage was found to be suppressed with the increasing electrolyte film thickness. On the other hand, no leakage of hydrogen and holes was observed at 500 °C.

Comparison of Various Cathode Materials Fabricated by Pulsed Laser Deposition for Low-Temperature Ceramic Fuel Cells

Comparison of Various Cathode Materials Fabricated by Pulsed Laser Deposition for Low-Temperature Ceramic Fuel Cells

3D Printing Enabled Highly Scalable Tubular Protonic Ceramic Fuel Cells

3D Printing Enabled Highly Scalable Tubular Protonic Ceramic Fuel Cells

New Strategy for Boosting Cathodic Performance of Protonic Ceramic Fuel Cells Through Incorporating a Superior Hydronation Second Phase

For protonic ceramic fuel cells, it is key to develop material with high intrinsic activity for oxygen activation and bulk proton conductivity enabling water formation at entire electrode surface. However, a higher water content which benefitting for the increasing proton conductivity will not only dilute the oxygen in the gas, but also suppress the O2 adsorption on the electrode surface. Herein, a new electrode design concept is proposed, that may overcome this dilemma. By introducing a second phase with high‐hydrating capability into a conventional cobalt‐free perovskite to form a unique nanocomposite electrode, high proton conductivity/concentration can be reached at low water content in atmosphere. In addition, the hydronation creates additional fast proton transport channel along the two‐phase interface. As a result, high protonic conductivity is reached, leading to a new breakthrough in performance for proton ceramic fuel cells and electrolysis cells devices among available air electrodes.

Boosting Performance of a Protonic Ceramic Fuel Cell by the Incorporation of Active Nano-Structured Layers

Boosting Performance of a Protonic Ceramic Fuel Cell by the Incorporation of Active Nano-Structured Layers

Understanding the Impact of Sintering Temperature on the Properties of Ni–BCZY Composite Anode for Protonic Ceramic Fuel Cell Application

Understanding the impact of sintering temperature on the physical and chemical properties of Ni-BaCe0.54Zr0.36Y0.1O3-δ (Ni-BCZY) composite anode is worthy of being investigated as this anode is the potential for protonic ceramic fuel cell (PCFC) application. Initially, NiO–BCZY composite powder with 50 wt% of NiO and 50 wt% of BCZY is prepared by the sol–gel method using citric acid as the chelating agent. Thermogravimetric analysis indicates that the optimum calcination temperature of the synthesised powder is 1100 °C. XRD result shows that the calcined powder exists as a single cubic phase without any secondary phase with the lattice parameter (a) of 4.332 Å. FESEM analysis confirms that the powder is homogeneous and uniform, with an average particle size of 51 ± 16 nm. The specific surface area of the calcined powder measured by the Brunauer–Emmett–Teller (BET) technique is 6.25 m2/g. The thickness, porosity, electrical conductivity and electrochemical performance of the screen-printed anode are measured as a function of sintering temperature (1200–1400 °C). The thickness of the sintered anodes after the reduction process decreases from 28.95 μm to 26.18 μm and their porosity also decreases from 33.98% to 26.93% when the sintering temperature increases from 1200 °C to 1400 °C. The electrical conductivities of the anodes sintered at 1200 °C, 1300 °C and 1400 °C are 443 S/cm, 633 S/cm and 1124 S/cm at 800 °C, respectively. Electrochemical studies showed that the anode sintered at 1400 °C shows the lowest area specific resistance (ASR) of 1.165 Ω cm2 under a humidified (3% H2O) gas mixture of H2 (10%) and N2 (90%) at 800 °C. Further improvement of the anode’s performance can be achieved by considering the properties of the screen-printing ink used for its preparation.