Conducting Solid Oxide Fuel Cells Research Articles

BaCo0.4Fe0.4Zr0.1Y0.1O3−σ Cathode Performance for Proton Conducting Solid Oxide Fuel Cells with BaZr0.8−xCexY0.1Yb0.1O3−δ Electrolytes

BaCo0.4Fe0.4Zr0.1Y0.1O3−σ (BCFZY) is a proton, oxygen-ion, and electron-hole conducting cathode material for intermediate temperature solid oxide fuel cells. Its electrode reaction mechanism in air with moisture is not well understood. In this study, three types of symmetrical cells with the same BCFZY cathode were fabricated over three related proton conducting electrolytes: BaZr0.8−xCexY0.1Yb0.1O3−δ (x = 0.1, 0.4, and 0.7). The cathode shows similar performance over three different electrolytes in dry air but different responses to moisture introduction. The differences are hypothesized to relate to the mutual diffusion at the cathode/electrolyte interface. Such a hypothesis is supported by different techniques such as XRD Rietveld refinement of BCFZY cathode in mixtures with different electrolytes after firing, energy-dispersive X-ray spectroscopy (EDS) line scanning for element concentration distribution at the cathode/electrolyte interface, as well as electrochemical test for a related BaCoFeO-type cathode with Zr replaced by Ce.

Cathode Surface Segregating Modification for Boosting Oxygen Reduction Reactions: Coupling Theory and Experiment in Proton Conducting Solid Oxide Fuel Cells (H-SOFCs)

The surface electrochemical catalysis reaction is complex due to the unpredictable surface morphology and severe reaction environment, especially for cathodes in proton conducting solid oxide fuel cells (H-SOFCs) where water vapor is generated and evaporated at a high operating temperature. The first-generation cathode materials (LaxSr1-xMO3-δ, M=Fe, Co, Mn) tend to have A-site cation segregation, and this segregation layer reduces the performance. Surface segregation phenomena tends to be ignored by computer simulations because surface termination is described as a highly crystallized layer, misleading the development of material computing science. Therefore, a combination of theory and surface investigation is essential for future work in this community. In this work, we use density functional theory (DFT) for designing a higher-performing cathode material, La0.35Bi0.15Sr0.5FeO3-δ (LBSF), for improvement of both bulk and surface electrochemical character in an intrinsic manner, predicting a candidate material with good performance that can be used in solid oxide proton conducting fuel cells (H-SOFCs). By combining a sensitive surface analysis technique, low energy ion scattering (LEIS), surface segregation is finely considered and determined that the particles are fully covered with a Sr segregation layer on the outer most surface. Aberration-Corrected transmission electron microscopy (ACTEM) is also applied and shows an amorphous structure at the particle edge. With the determination of this segregation layer, a reality-closed model is given, and related surface reactions are modelled based on this layer instead of a conventional cleaved, well-crystallized surface. Also, as bismuth diffuses towards the surface due to the lone pair effect, the segregation becomes an oxygen reduction reaction preferred layer instead of a blocking layer. After computational prediction and surface analysis, LBSF is successfully applied into H-SOFCs and shows excellent performance with a peak power density of 1630 mW cm−2 at 700 oC. In addition, long term stability tests were conducted to ensure stability in future commercial use, and the experimental results show that LBSF works stable under extremely high temperature operating environments. In addition, a full cell was stabilized for about 300 hours, indicating a potential commercial application in the future.

BaCo0.4Fe0.4Zr0.1Y0.1O3-Σ Cathode Performance for Proton Conducting Solid Oxide Fuel Cells with BaZr0.8-XCexY0.1Yb0.1O3-Δ Electrolytes

BaCo0.4Fe0.4Zr0.1Y0.1O3-σ (BCFZY) is a proton, oxygen-ion, and electron-hole triple conducting cathode material for solid oxide fuel cells. Its electrode reaction mechanism including the rate-limiting step in air with moisture are not well understood. Therefore, we fabricated three types of symmetric cells with the same BCFZY cathode over three related proton conducting electrolytes: BaZr0.8-xCexY0.1Yb0.1O3-δ (x = 0.1, 0.4, and 0.7; Fig.1 are SEM images showing the surface of three different electrolytes). The cathode shows different electrochemical behaviors for the three electrochemical cells including the response to the introduction of moisture. The differences are hypothesized to relate to mutual diffusion at the cathode/electrolyte interface, which are tested by various techniques such as XRD Rietveld refinement of BCFZY cathode in mixtures with different electrolytes after firing, thermogravimetric analysis (TGA) for oxygen vacancy concentration and hydration behavior, electrical conductivity relaxation (ECR) for conductivity changes between dry and moist atmosphere, and energy-dispersive X-ray spectroscopy (EDS) line scanning for element concentration distribution at the cathode/electrolyte interface.Fig1. SEM images of electrolytes (a) BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (Ce-rich), (b) BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (ZrCe-bal) and (c) BaZr0.7Ce0.1Y0.1Yb0.1O3-δ (Zr-rich) Figure 1

Cathode Surface Segregating Modification for Boosting Oxygen Reduction Reactions: Coupling Theory and Experiment in Proton Conducting Solid Oxide Fuel Cells (H-SOFCs)

Computational simulation, based on Density Functional Theory (DFT), was carried out to develop a more powerful cathode material, La0.35Bi0.15Sr0.5FeO3-δ (LBSF), based on a first-generation cathode material, La0.5Sr0.5FeO3-δ (LSF) for use in proton-conducting solid oxide fuel cells (H-SOFCs). The calculation results show that the Bi substitution causes an oxygen p band center shift, which accelerates the oxygen reduction reaction (ORR). To prove this prediction, LBSF and LSF was synthesized successfully, and each surface was also characterized with X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS), observing a surface Sr segregation and change after Bi substitution. The change proves an effective modification of surface segregation component. Subsequently, LBSF, applied into H-SOFCs, shows excellent performance with a peak power density of 1630 mW cm-2 at 700 ℃ when this material was employed as a cathode in a full H-SOFC.

Study of BaCe0.4Zr0.4Y0.2O3-δ/BaCe0.8Pr0.2O3-δ (BCZY/BCP) bilayer membrane for Protonic Conductor Solid Oxide Fuel Cells (PC-SOFC)

This paper address the blocking of the electronic conductivity for a BaCe0.8Pr0.2O3-δ (BCP) material due to the addition of a BaCe0.4Zr0.4Y0.2O3-δ (BCZY) thin layer. Barium cerates (BCP and BCZY) show interesting features as electrolytes for Proton Conducting Solid Oxide Fuel Cells (PC-SOFC). BCP perovskite displays good mechanical properties associated to its sintering capability, typically proposed as a possible electrolyte. However, this compound shows poor CO2 tolerance above 500 °C and presents mixed conductivity under wet synthetic air. Protonic transport is the main feature of BCZY perovskite and it presents an excellent CO2 tolerance. However, the drawback of this compound is its high grain boundary resistance. In this work, a BCZY film was grown by Pulsed Laser Deposition (PLD) on BCP in order to block its electronic conductivity and improve CO2 tolerance. From the electrochemical characterization of materials, it is proposed that BCP dominates transport mechanisms on the BCZY/BCP bilayer membranes under wet synthetic air and wet diluted hydrogen. Our measurements confirm that the BCZY film blocks the electronic conductivity of BCP under wet synthetic air and protects it from CO2-containig atmospheres. Due to this set of properties, the BCZY/BCP bilayer membrane represents a possible candidate as electrolyte for PC-SOFC operating between 400 and 600 °C.

Synthesis and Characterization of Zn-doped LiCoO2 Material Prepared via Glycinenitrate Combustion Method for Proton Conducting Solid Oxide Fuel Cell Application

Synthesis and Characterization of Zn-doped LiCoO2 Material Prepared via Glycinenitrate Combustion Method for Proton Conducting Solid Oxide Fuel Cell Application

H2S Poisoning of Proton Conducting Solid Oxide Fuel Cell and Comparison with Conventional Oxide-Ion Conducting Solid Oxide Fuel Cell

The electrochemical response of proton conducting solid oxide fuel cells (PC-SOFC) with Ni-BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) cermet anode by low-ppm(v) level hydrogen sulfide (H2S) was studied using both electrolyte-supported cells and anode symmetrical cells at 750–450°C. Upon the introduction of H2S, both types of cells show small but observable increase in the electrode apparent interfacial resistance (Rai) with no change in ohmic resistance. In addition, secondary-ion mass spectroscopy (SIMS) analysis on Ni-BZCYYb composite pellets after exposure to H2S showed a strong correlation between the distributions of barium and sulfur species, yet both were complementary to the distribution of nickel species. The results indicate that PC-SOFC are still subjected to poisoning by low ppm(v)-level H2S at intermediate temperature. However, the H2S poisoning effect (in terms of relative increase in interfacial resistance) for PC-SOFC appears much smaller than for conventional oxide-ion conducting SOFC with Ni-yttria stabilized zirconia (Ni-YSZ) cermet anode and YSZ electrolyte. Such a difference in H2S poisoning behavior is hypothesized to be related to the different anode reaction process for PC-SOFC versus conventional oxide-ion conducting SOFC and the potential (electro-)catalytic role that proton conducting ceramic electrolyte might play in the anode reaction. The directions for future study are also pointed out.

Characterization and Performance of Proton Conducting Solid Oxide Fuel Cells Manufactured Using Reactive Spray Deposition Technology

Proton conducting solid oxide fuel cells (SOFCs) have received attention as a possible alternative to traditional oxygen anion conducting SOFCs. The reason is existing proton conducting perovskites display ionic conductivity similar to yttria-stabilized zirconia at lower temperatures. Lower operating temperatures alleviate durability issues and open the door for the use of low cost stainless steels in cell construction. This study examines the use of reactive spray deposition technology (RSDT) as a means of producing a low cost, metal supported proton conducting SOFC by directly depositing layer after layer onto a metal substrate and with a no need for additional sintering steps. The deposited materials are characterized using SEM, STEM, and XRD techniques.

Analisis Pemodelan Sistem Hibrid Proton Conducting Solid Oxide Fuel Cell (pSOFC) – Turbin Gas Mikro Pada Matlab-Simulink

This study simulated Proton Conducting Solid Oxide Fuel Cell (pSOFC) – Micro Gas Turbine (MGT) hybrid system on three different configuration. The first configuration use bypass hot gas from combustor going to fuel heater without pass the turbine first. The second configuration use bypass hot gas out of turbine going to fuel heater. The third configuration is combined bypass out of combustor and also bypass out of turbine. The performance of these system are analyzed by using variation of operating pressure, fuel utilization (Uf), steam to carbon ratio (S/C), and bypass valve. Moreover, the impact of different bypass position were also evaluated. The result shows that the efficiency of using a double bypass hot gas flow after combustor and turbine is about 67%. This configuration became the best one among of another two configuration which proposed in this research. The utilization of heat by using a double bypass hot flow gas after turbine and combustor has proven more effective to increase the system efficiency. Means that it can reduce the heat losses of the system.

Characterization and Performance of Proton Conducting Solid Oxide Fuel Cells Manufactured Using Reactive Spray Deposition Technology

Proton conducting solid oxide fuel cells (p-SOFC) have received attention recently as an alternative to traditional high temperature SOFCs [1]. This new class of p-SOFCs offer the potential to significantly reduce the cost of production due to the opportunity to lower the operating temperature from upwards of 800 °C down to as low as 500 °C. This shift is made possible by a modified class of ion conducting materials such as yttrium doped barium zirconate (BYZ) which has comparable ionic conductivity to yttria-stabilized zirconia at lower temperatures [2]. With a decrease in the operating temperature, it becomes possible to make use of inexpensive materials for cell construction such as stainless steels vs. expensive super alloys. This cost savings is a major driver towards practical commercialization of p-SOFCs. This work seeks to employ a novel flame based technique, Reactive Spray Deposition Technology (RSDT) [3], in manufacturing of a complete p-SOFC on a metal support. This technique involves dissolving organometallic precursor compounds (typically ethlyhexanoate ligands) into combustible solvents. The mixture is sprayed from an atomizing nozzle in an open atmosphere and ignited. The resulting heat of combustion due to the solvent is used to decompose the dissolved compounds and produce thin films via gas to particle conversion. The use of the flame eliminates the need for separate, costly sintering steps generally needed in traditional manufacturing processes. Secondary nozzles can be utilized to introduce different support and binder materials resulting in a single-step manufacturing process for the anode, electrolyte, and cathode of the p-SOFC. The current work focuses on the production and initial characterization of a p-SOFC using a Ni-BYZ anode, BYZ electrolyte, and lanthanum strontium cobalt ferrite (LSCF) cathode on a porous metal support. The deposited materials are characterized using SEM, STEM, and XRD techniques. Initial button cell performance is also reported.

Effects of Particle Size and Size Distribution on the Percolation Behavior of Composite Proton Conducting Solid Oxide Fuel Cells Cathode

The cathode is the key in improving the performance of solid oxide fuel cells (SOFCs) at an intermediate temperature (IT). High performance cathode requires not only large amount of reaction sites, but also efficient transport of gases, electrons and ions, which are characterized by the percolation properties of the cathode. In this paper, the effects of cathode material properties and microstructures on percolation behavior of a composite SOFC cathode are analyzed by a 3D numerically morphological dilation method with controlling contact angles between two types of particles. The proposed model is validated by comparing the present simulation results with data from our previous kinetic Monte Carlo (KMC) simulations. The model is used for calculating the effective conductivity and percolation behaviors of proton-conducting SOFC (H-SOFCs) cathode. Detailed simulations are conducted under different parameters (mean particle radius of composite cathode, volume fraction of electrode and electrolyte materials, bulk material conductivities) to investigate their effects on the important effective ionic conductivity and percolation behavior of the cathode at an IT. The results could help design high performance H-SOFC electrodes.

Development and understanding of La0.85Sr0.15Cr1−xNixO3−δ anodes for La5.6WO11.4−δ-based Proton Conducting Solid Oxide Fuel Cells

Porous electrodes based on the system La0.85Sr0.15Cr1−xNixO3−δ (x = 0.1 and 0.2) have been investigated as anodes for proton conducting solid oxide fuel cells based on the La5.6WO11.4−δ (LWO) electrolyte material. The microstructure of the anodes was optimized by varying both the starting powder morphology and the final anode sintering temperature. Two different electrode thicknesses were studied, i.e. 15 and 30 μm. The importance of the catalytic role of Ni was also studied by using different concentrations of Ni (10% and 20%) in the chromite and by tuning the Ni particle sizes through the control of the reduction temperature. Additionally, a ceramic–ceramic (cer–cer) composite electrode comprising a physical mixture of the optimized chromite and LWO phase was also considered. Finally, a kinetics study and modeling based on Langmuir–Hinshelwood mechanism was carried out in order to quantitatively describe the rate of dissociative adsorption of H2 on the Ni particles spread on the chromite surface.

The Effect of Particle Size on the Performance of LSFC Perovskite Anode of Proton Conducting Solid Oxide Fuel Cell (PC-SOFC)

A promising and stable perovskite structure anode material La0.3Sr0.7Fe0.7Cr0.3O3-x (LSFC) prepared by a glycine nitrate process was applied as the anode catalyst of a proton conducting solid oxide fuel cell (PC-SOFC). The particle size of the anode material could be controlled by varying the calcination temperatures. The influence of particle sizes on electrochemical performances had been studied. It was shown that the higher calcination temperature resulted in larger LSFC particles, which decreased the PC-SOFC performance significantly.

Optimization of the Lanthanum Tungstate/Pr2NiO4 Half Cell for Application in Proton Conducting Solid Oxide Fuel Cells

AbstractLa6WO12, recently reformulated La28–xW4+xO54+3x/2 exhibits a good level of protonic conductivity and chemical stability toward acidic gases. It is therefore a potential material for use as electrolyte in proton conducting solid oxide fuel cells (PC‐SOFC). Pr2NiO4 is a cathode material tested for SOFC in which proton conductivity has been demonstrated recently. In this study, compatibility between lanthanum tungstate and praseodymium nickelate has been investigated by powder X‐ray diffraction (XRD). Microstructure of symmetrical cells based on the lanthanum tungstate and Pr2NiO4 has been analyzed by scanning electron microscopy (SEM) and performance of the cathode has been evaluated by electrochemical impedance spectroscopy (EIS) through the value of the area specific resistance (ASR). To optimize the ASR value, different parameters were modified such as the Pr2NiO4 calcination temperature, the firing temperature of the symmetrical cells, the thickness of the Pr2NiO4 layer, and the composition of the composite cathode. An ASR value of 0.46 Ω cm2 at 700 °C has been obtained showing that lanthanum tungstate electrolyte associated with Pr2NiO4 cathode is a promising half cell for application in PC‐SOFC.

Modeling and Bifurcation Analysis of a Coionic Conducting Solid Oxide Fuel Cell

A macroscopic first-principles mathematical model of a solid oxide fuel cell (SOFC) with a BaCe1–xSmxO3-α type electrolyte is developed. This class of electrolytes exhibits both proton and oxygen-a...

Materials for Proton Conducting Solid Oxide Fuel Cells (H-SOFCs)

In this paper, we report our steps forward in the search of proton conducting metal oxides possessing disordered perovskite-type and B-site ordered double perovskites for application in solid oxide fuel cells (SOFCs) and mixed proton-electron conductors as anodes for SOFCs. Role of A- and B- site cations in the perovskite structures on electrical properties and their corresponding chemical stability in CO2, H2S and H2O have been studied. Partial substitution of the parent phase is one of the most effective and popular approaches in which certain ions in the lattice are replaced by foreign species. However, "the right recipes" are not usually obvious; optimization on the functional physical and chemical properties is often based upon "the trial and error" strategy. Here, we review our progress since 2005 in the development of the proton conducting solid oxide fuel cells (H-SOFCs).

Ceramic Proton Conducting Solid Oxide Fuel Cells (H-SOFCs): Materials and Challenges

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On the Choice of Anode Electrocatalyst for Alcohol Fuelled Proton Conducting Solid Oxide Fuel Cells

Proton conducting solid oxide fuel cells (H+-SOFC) offer reduced temperature operation when compared to traditional oxygen anion conducting SOFCs. However, one potential drawback is a loss of fuel flexibility as H+-SOFCs require hydrogen as a fuel. In this study we examine the use of Ni, Ni-Cu, and Cu-based anodes for the internal steam reforming of methanol and ethanol on the H+-SOFC anode. When compared to hydrogen fuel, the cell performance is lower in all of the alcohol fuels due to lower hydrogen content in the reformate. Ni provides substantially higher performance than Cu due to increased steam reforming activity towards hydrogen production and may increase hydrogen incorporation kinetics. Significant carbon deposition was noted on the Ni anode when operating on ethanol fuel, even with a 4:1 steam:carbon ratio. Only limited carbon deposition was noted for the Cu anode. Alloying Ni with Cu was shown to help limit carbon formation at the anode.

Electrochemical Properties of PSFC–BCYb Composites as Cathodes for Proton Conducting Solid Oxide Fuel Cells

AbstractThe electrochemical properties of mixed conducing ceramic–ceramic composites for proton conducting fuel cells have been investigated. Different ratios of Pr0.58Sr0.4Fe0.8Co0.2O3–δ–BaCe0.9Yb0.1O3–δ composites have been tested as cathodes in symmetrical cells based on BaCe0.9Y0.1O3–δ dense electrolytes. Impedance measurements have been carried out in the temperature range of 600–800 °C under wet (2.5%) air. Different dilutions on both oxygen partial pressure and water content have been performed as a function of the temperature in order to characterise the processes (surface reaction and charge transport) occurring at the composite electrode under oxidising conditions. The variation of the impedance spectra after replacing protonated water by heavy water has been studied in order to understand the role of the proton transport in the overall composite cathode operation. Additional four‐point DC‐conductivity measurements have been done under different atmospheres comprising different oxygen partial pressures and H2O/D2O saturation for composites and single materials.

ChemInform Abstract: Ca3‐xLaxCo4O9+δ (x = 0, 0.3): New Cobaltite Materials as Cathodes for Proton Conducting Solid Oxide Fuel Cell.

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