Protonic Ceramic Fuel Cells Research Articles

A novel triple-conductive cathode with high efficiency and stability for protonic ceramic fuel cells

The sluggish kinetics of cathodic oxygen reduction reaction is one of the key barriers to the development of protonic ceramic fuel cells (PCFCs), while the appearance of triple-conductive material reported in recent years has brought a new dawn for the commercialization of PCFCs. These materials need to have excellent hydration ability and water tolerance to expand the active sites and prolong the operation lifespan. Herein, a highly efficient and stable cathode material, BaCo0.4Fe0.4Zr0.1Sc0.1O3-δ (BCFZSc) with cubic perovskite structure, is proposed for PCFCs. Electrical conductivity relaxation measurements reveal that the oxygen surface exchange coefficient of BCFZSc can reach the value of 1.8 × 10−3 cm s−1 at 700 °C, almost an order of magnitude larger than those of most reported cathodes. Applying BCFZSc as cathode, single cell exhibits an excellent peak power density of 1.334 W cm−2 with a small polarization resistance of 0.044 Ω cm2 at 700 °C, and a decent durability over 150 h at 600 °C is demonstrated. This research highlights that BCFZSc is a promising candidate for PCFCs cathode.

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

Although cobalt-containing cathode materials are widely used in protonic ceramic fuel cells (PCFCs) because of its high catalytic activity, cobalt diffuses into the proton-conducting electrolyte, thereby decreasing the power generation performance. To achieve a higher power generation performance in PCFCs with a cobalt-free cathode, we fabricate anode-supported PCFCs using BaZr0.8Yb0.2O3–δ as the electrolyte, and composite cathodes of La0.65Ca0.35FeO3−δ (LCaF) and BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb). The mixing weight ratios of LCaF and BZCYYb are varied to 80:20, 70:30, 60:40, 50:50, and 30:70. The PCFC with LCaF–BZCYYb (60:40) composite cathode exhibits the highest power generation performance in the operating temperature range of 500–700 °C with a maximum power density (MPD) of 0.41 W cm−2 at the operating temperature of 600 °C. This MPD value is higher than that obtained in our previous study using a PCFC with a La0.6Sr0.4Co0.2Fe0.8O3−δ –BZCYYb composite cathode.

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.

Examination of Morphological and Chemical Properties of Ni-BZY Anodes and their Influence upon Methane Reactivity and Electrochemical Performance of Protonic-Ceramic Fuel Cells

Ni-BZY (yttrium-doped barium zirconate) has drawn recent interest for application in protonic ceramic fuel cells (PCFCs) due to BZY’s superior protonic conductivity and stability in reforming environments containing CO2 and H2O. Additionally, Ni and BZY form unique nano/microstructures thought to synergistically facilitate reforming. While PCFCs with Ni-BZY anodes have demonstrated stable long-term performance, little is known about the material’s transformations during operation and subsequent impact on electrochemical metrics. To address this knowledge gap, we constructed PCFCs consisting of Ni-BZY anodes sintered onto a ~600 μm BZY electrolyte complete with a LSCF/BCZY cathode. The electrochemical performance of these cells is compared at 600-700 °C while operating with humidified hydrogen, neat methane, and steam reformed methane (1CH4:1H2O). Insights into morphological and chemical changes are provided by pre- and post-mortem analysis of the anode via Raman spectroscopy, X-ray diffraction, and SEM. Phase transformations, agglomeration and coking all appeared to contribute to performance degradation.

Inkjet Printing of PrBa0.5Sr0.5Co1.5Fe0.5O5+ δ Cathode for High-Performance Proton Ceramic Fuel Cells

This study reports on the fabrication of the perovskite materials for anod-supported proton ceramic fuel cells (PCFCs) using inkjet-printing (IJP) method. The ceramic ink source was synthesized by dissolving PrBa0.5Sr0.5Co1.5Fe0.5O5+d (PBSCF) as a cathode nanopowder as a pigment material in ethanol and propylene methyl ether based solvents with a variety of surfactants. We could optimized the precise cathode microstructure through grayscale control using commercial software. We achieved high performance in the low-temperature region. Moreover, it was stable even under long-term operation condition. A peak power density of 728 mWcm-2 at 600 C was achieved. This verified that the performance was maintained without significant degradation for 80 h at 500 C. We propose an efficient method for fabricating high-quality and precise PBSCF cathodes in PCFCs using IJP.

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

A highly efficient power generation system was designed by minimizing leakage current in protonic ceramic fuel cells (PCFCs) using bilayer electrolytes. The best electrolyte designs are achieved by optimizing the cell efficiency based on the transport properties of electrolyte materials assuming hydrogen as fuel. In parallel, the effect of the electrodes on the overall cell performance was also considered. Additionally, a PCFC system was modeled using the designed cells. Two PCFC systems were investigated. One based on hydrogen as a fuel, and another based on methane as fuel. It was found that a bilayer electrolyte consisting of BaZr0.8Y0.2O3−δ (BZY) with a thin layer of lanthanum tungstate (La28-xW4+xO54+3x/2v2-3x/2) is the most effective at reducing leakage current at 600°C. For this cell, a system efficiency of 69% (LHV, DC) and 65% (LHV, AC) were obtained under the cell voltage of 0.93 V, with a leakage current ratio of less than 1%, and fuel utilization of 95% when using hydrogen as fuel. On the other hand, when methane was used as fuel, the efficiency increased up to 78% (LHV, DC) and 74% (LHV, AC).

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

Protonic ceramic fuel cells (PCFCs) operating at an intermediate temperature range (400–600 °C) show high performance due to high proton conductivity in the electrolyte. Especially, because the water steam is generated at the oxygen side, so there is less dilution effect on fuel. Therefore, one of the main merits of PCFCs is that it can operate with extremely high fuel utilization. Furthermore, a higher fuel humidification rate leads to higher proton conductivity. However, under relatively high steam partial pressure, the concentration overpotential effect on cell performance may become non-negligible. In the present study, the performance of PCFC under several fuel humidification conditions is investigated by considering the influence of concentration overpotential by numerical analysis.

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

The durability of protonic ceramic fuel cells (PCFC) using Yb-doped BaZrO3 (BZYb) as electrolyte was investigated by 1000 h power generation tests and EPMA analysis of Co from cathode and Ni from anode. In addition, the effect of buffer layer of BaCeZrYYbO3-δ (BCZYYb) between the cathode and the electrolyte on durability and elemental diffusion was also investigated. In the cell with the buffer layer, the degradation of polarization resistance was suppressed in 1000 h power generation test. From EPMA analysis, Ni and Co segregation was observed in the electrolyte and the cathode after 1000 h power generation test in the cell without the buffer layer, which was suppressed in the cell with the buffer layer. These results suggested that the suppression of the segregation by use of BCZYYb buffer layer might have reduced the degradation of polarization resistance.

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 due to its higher energy conversion efficiency. We evaluated the electric efficiency using a Φ60mm anode supported BZYb cell and a newly designed jig. The Φ60mm BZYb cell performed almost as well as the Φ20mm cell, and the maximum power reached 7 W at 12.9 A at 600ºC. In addition, we obtained the cell performance of 0.3 A cm–2 current density under various Uf (fuel utilization) condition. We demonstrated that a BZYb based PCFC could be operated at a high Uf condition (i.e., Uf = 90%), and the maximum electric efficiency was 55% (DC).

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

Improving the activity of the cathode is important for the practical use of Protonic Ceramic Fuel Cells (PCFCs). We developed BaZr0.375Yb0.125Co0.500O3-δ as a new cathode material for the PCFCs using BaZr0.8Yb0.2O3-δ as the electrolyte. Anode supported cells using these materials were fabricated and the electrochemical performances were investigated. The maximum power density was 0.60 W/cm2 at 600°C. The voltage degradation rate over 1000 hours in the durability test under the constant current mode was 7.3%/kh. After 1000 hours of durability test, diffused Ni and Co were unevenly distributed in the electrolyte of the cell. Therefore, prevention of diffusion of electrode-derived elements such as Ni and Co is considered to be one solution to improve durability.

Sr3Fe1.5Zn0.5O7-δ as Cathode for Protonic-Conducting Solid Oxide Fuel Cells with Enhanced Oxygen Reduction Reaction Activity

Perovskite oxides have attracted intensive attention for their good electrochemical performance and stability as electrodes for protonic ceramic fuel cells (PCFCs). However, operating under high temperatures and various atmospheres results in a large polarization resistance and sluggish oxygen reduction reaction (ORR) in cathodes. Here, Zn was successfully doped into Sr3Fe2O7-δ (SFO) Ruddlesden-Popper (RP) perovskite cathode and the Sr3Fe1.5Zn0.5O7-δ (SFZ05) shows a superior ORR activity. The polarization resistance of SFZ05 is 0.072 Ω·cm-2, which is 47% lower than that of the undoped SFO, and the maximum peak power density of the single-cell of NiO-BaZr0.1Ce0.7Y0.2O3-δ(BZCY)|BZCY|SFZ05 reaches 523.56 mW·cm-2 at 750℃, increased by 22% than SFO. The improvement is attributed to the formation of oxygen vacancies and the increase of proton conductivity. These results display that SFZ05 is a promising candidate for a highly active and stable cathode for PCFCs.

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

This study reports on the performance improvement of a protonic ceramic fuel cell (PCFC) after a CoOx nanoparticle treatment has been applied to a PrBa0.5Sr0.5Co2-xFexO5+δ(PBSCF) cathode with a perovskite structure. CoOx nanoparticles are deposited on the sintered PBSCF surface using a plasma-enhanced (PE) atomic layer deposition (ALD) process, thereby avoiding any unwanted reactions or phase changes. The CoOx nanoparticles are successfully deposited uniformly onto the entire surface of the porous and complex cathode structure. A constant deposition rate is observed because of the self-limiting characteristics of the ALD process by a thickness difference as a function of a change in the cycle count. In our experiment, the performance of the fuel cells increases by approximately 36 % compared with the untreated cells at an operating temperature of 650 °C. In addition, all cells feature long-term stability. Impedance analysis reveals that the CoOx nanoparticle treatment results in a significant polarization and some ohmic loss improvement within all temperature regions. This is due to the synergistic effect with PBSCF and self-catalytic effects. The results imply that the proposed method enables high-performance PCFC fabrication; additionally it helps lowering the operating temperature.

Additive Manufacturing of Single-Layer Protonic Ceramic Fuel Cells

Single-layer proton conducting ceramic fuel cells (PCFCs) were fabricated through a hybrid of extrusion-based 3D printing utilizing BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (BZCYYb) as an ionic conductor, and BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) as the electrode material. The rheological properties of the printable pastes were investigated in detail. The 3D printed single-layer cell produced a maximum power density of 283 mW/cm2 at 550oC. The performance was mainly limited due to limited surface area on both sides of the cell. The performance improved by 17% (331 mW/cm2) when porous layers were added on both sides of the cell. In addition, cells with traditional 3-layer structure were fabricated using NiO-BZCYYb as anode, BZCYYb as electrolyte, and BCFZY-BZCYYb as cathode. The cell produced a maximum power density of 426 mW/cm2 at 650OC. The performance improved by 120% (938 mW/cm2) when a composite of BZCYYb and a eutectic mixture of Li2CO3, Na2CO3 and K2CO3 was used as electrolyte.

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

To investigate the effect of water vapor in the feed gas on the power generation characteristics of PCFCs, the water vapor concentration was changed to 3%, 15%, 30%, and 50%, while the hydrogen concentration in the gas fed to the anode was fixed at 50%. The impedance measurements showed that the ohmic resistance decreased with increasing water vapor concentration, which was attributed to the increase in the proton conductivity of the electrolyte. The measured current density-voltage characteristics showed that the power output increased with increasing water vapor concentration, which was attributed to the decrease in ohmic overvoltage caused by the increase in proton conductivity. In addition, as a more practical condition, the power generation characteristics were measured when the water vapor concentration was varied while the hydrogen concentration was varied in an anode gas consisting only of hydrogen and water vapor.

Fluorine Anion-Doped Ba0.6Sr0.4Co0.7Fe0.2Nb0.1O3-δ as a Promising Cathode for Protonic Ceramic Fuel Cells

The widespread application of protonic ceramic fuel cells is limited by the lack of oxygen electrodes with excellent activity and stability. Herein, the strategy of halogen doping in a Ba0.6Sr0.4Co0.7Fe0.2Nb0.1O3-δ (BSCFN) cathode is discussed in detail for improving cathode activity. Ba0.6Sr0.4Co0.7Fe0.2Nb0.1O3-x-δFx (x = 0, 0.05, 0.1) cathode materials are synthesised by a solid-phase method. The XRD results show that fluorine anion-doped BSCFN forms a single-phase perovskite structure. XPS and titration results reveal that fluorine ion doping increases active oxygen and surface adsorbed oxygen. It also confines chemical bonds between cations and anions, which enhances the cathode’s catalytic performance. Therefore, an anode-supported single cell with the configuration of Ni-BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb)|BZCYYb|Ba0.6Sr0.4Co0.7Fe0.2Nb0.1O3-0.1-δF0.1 (BSCFN-F0.1) achieved a high peak power density of 630 mW cm−2 at 600 °C. Moreover, according to the symmetrical cell test, the BSCFN-F0.1 electrode demonstrated a superb stability for nearly 400 h at 600 °C. This work focuses on the influence of fluorine anion incorporation upon the performance of cathode materials. It also analyses and discusses the effects of different fluorine ion incorporation amounts to occupy different oxygen positions.

Proton conductivity in Yb-doped BaZrO3-based thin film prepared by pulsed laser deposition

For increasing the performance of PCFC (Protonic Ceramic Fuel Cells), it is important to prepare high-quality thin films of electrolyte materials. In this study, the preparation condition of the thin film of BaZr0.8Yb0.2O2.9 (BZYb) by pulsed laser deposition (PLD) method was optimized and the electrical conductivities of the obtained films were measured. The thin film was prepared by PLD using two kinds of BZYb targets, which were prepared by solids state reaction and Pechini method. Both thin-film samples have the single phase of the cubic perovskite-type structure, however, morphology as well as the orientation of the BZYb film was significantly different. The thin film using the target material by Pechini method is a high crystalline orientation and partially oriented [211] direction. The electrical conductivities of the obtained thin films at reduction atmosphere are dominated by proton conductivity, which is almost the same as that of the bulk sample despite [211] orientation.

Direct Conversion of Ammonia to Electricity on a PCFC and an SOFC

A protonic ceramic fuel cell (PCFC) and a solid oxide fuel cell (SOFC) using NiO/BZCY and NiO/YSZ anodes, respectively, were compared in H2 and NH3 fuels at 600 °C. The effect on the cell performance by adding lanthanum strontium ruthenium titanate (LSRT) into the anode were investigated. The performance of PCFCs in NH3 was found to resemble that in H2 and remain stable; by contrast, the SOFC was subject to a rigorous fluctuation of voltages in NH3, followed by performance loss. Surface characterization evidenced that phase separation between nickel and electrolyte YSZ is a major reason to the deactivation of SOFCs. The structure degradation occurred due to repetitive nitridation of nickel and subsequent oxidation reaction. Despite containing nickel in the anode too, the PCFC experienced the little effect since the oxidation reaction occurs at the cathode. Furthermore, the addition of the LSRT helped stabilize the PCFC anode by facilitating decomposition of ammonia with exsolved ruthenium sites, which are characterized by temperature programmed reaction studies.

Carbon resistant Ni1-xCux-BCZY anode for methane-fed protonic ceramic fuel cell

This research aims to develop a better carbon resistant anode compared to conventional Ni-BCZY anode for methane fueled protonic ceramic fuel cell (PCFC). Solid-state reaction process is used to prepare alloy Ni1-xCux-BCZY anode in PCFC. Ni is doped with Cu for better carbon resistance. Results show that, Ni0·9Cu0.1-BCZY anode calcined at 800 °C for 0.5 h exhibit an electrical conductivity of 2054 S/cm at 600 °C, which is 8.4% less than traditional Ni-BCZY anode. XPS, and Raman data show that Ni0·9Cu0.1-BCZY anode exhibit resistance to carbon deposition compared to traditional anode. The best carbon deposition resistance is observed for the Ni0·7Cu0.3-BCZY sample. This work demonstrates the suppression of carbon deposition and inhibition of anode deformation in methane fueled PCFC with Ni1-xCux-BCZY anode. This work is helpful for development of carbon-resistant materials for energy generation with solid oxide fuel cells.

System analysis of a protonic ceramic fuel cell and gas turbine hybrid system with methanol reformer

The performance of a methanol-fed protonic ceramic fuel cell (PCFC)/gas turbine (GT) hybrid system is investigated in this work. To build the system, Thermolib software is employed with input parameters obtained from references. Effects of air stoichiometry on system performance are analyzed. Results show that, as air stoichiometry is increased, the reformer temperature and CO concentration decrease, while H2 concentration increases. High air stoichiometry decreases PCFC temperature and performance. GT output power increases with increasing air flow. But, the power consumption by compressor also increases. Overall, to achieve higher system efficiency for this hybrid system, the optimum values of air stoichiometry are from 2.7 to 2.9. An additional heat recovery steam generator can also improve the overall system efficiency from 66.5% to 71.7%. This work helps in understanding the modeling and optimum functioning parameters of high power generation systems.

Effect of cobalt content on electrochemical performance for La0.6Sr0.4CoxFe1-xO3-δ and BaZr0.8Yb0.2O3-δ composite cathodes in protonic ceramic fuel cells

This study compares the electrochemical performance of the composite cathodes of La0.6Sr0.4CoxFe1-xO3-δ and BaZr0.8Yb0.2O3-δ (BZYb) sintered at 900 and 1100 °C in anode-supported protonic ceramic fuel cells (PCFCs) using a BZYb electrolyte. For materials composited with BZYb, La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF), La0.6Sr0.4CoO3–δ (LSC), and La0.6Sr0.4FeO3–δ (LSF) were used. The composite cathodes sintered at 1100 °C showed higher performance than those sintered at 900 °C, because the number and thickness of proton conductive network paths of BZYb within the composite cathodes increase with increasing sintering temperature. The PCFCs with LSCF-BZYb, LSC-BZYb, and LSF-BZYb composite cathodes exhibit power densities of 0.25, 0.19, and 0.07 W cm−2, respectively, at an operating temperature of 600 °C. The polarization resistance of the Co-free LSF-BZYb composite cathodes is originally higher than those of the Co-containing LSC-BZYb and LSCF-BZYb cathodes, suggesting that Co plays an important role in obtaining high catalytic activity for cathode reactions in PCFCs as well as conventional solid oxide fuel cells.