Proton-conducting Solid Oxide Fuel Cells Research Articles

A novel in situ diffusion strategy to fabricate high performance cathodes for low temperature proton-conducting solid oxide fuel cells

A novel in situ Pr diffusion strategy based on a Sm0.2Ce0.8O2−δ–Pr(Pr0.5Ba1.5)Cu3O7−δ (3 : 7 wt%) compound is developed to achieve a perovskite-related proton-blocking composite cathode Ce1−xPrxO2−δ–Ba2CeCu3O7.4–Sm2Ba1.33Ce0.67Cu3O9–CuO for BaZr0.1Ce0.7Y0.2O3−δ-based proton-conducting 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.

Proton Conducting Properties of Sr1+XLn1-XAlO4-δ (Ln=Pr,Sm) with Layered Perovskite Structure for Solid Oxide Fuel Cells

Perovskite material, such as SrCeO3,BaCeO3, SrZrO3 and BaZrO3 are expected for as electrolyte material of proton conductive SOFC due to their high proton conductivity at 500-700 ºC.[1] Proton conductive electrolyte is required not only high conductivity but also high ionic transport number, high proton transport number and high stability. BaCe1-xYxO3-δ(BCY) is reported as a high conductivity material but the chemical stability is not sufficient especially in CO2 atmosphere. Recently, we reported Pr doped Ba2In2O5(PBI)[2] for proton conducting SOFC. However, the SOFC with PBI demonstrated relatively low power density of 4.0mW/cm2 at 700○C. Therefore, the development of electrolyte material is still required for PC-SOFC. To develop the novel proton conductor, we focused on layered perovskite structures. We have reported the proton conductivity of Sr1+xPr1-xInO4-δ (SPI)[3], which has Ruddlesden-Popper structure (expressed in A’OAnBnO3n, when n=1 called as K2NiF4 structure). Due to introduction of rock salt layer (A’O layer), improving proton transport number was suggested due to the selective inhibition of oxide ion conduction and improvement of stability were also expected. With considering proton transport mechanism which is suggested as shown in Eq.1, the basicity (relating to electronegativity) of constituent element is also an index of proton transport number at high temperature by stabilizing OH-. As a result, the total conductivity of SPI was logσ≒-1.5 in 900 ºC in 8% humidified O2, and power generation was not stably operated at 500 ºC in H2 fuel. Their conductivity, stability and transport number in high temperature is a remaining issue to be improved. To improve conductivity and stability, we tentatively applied the tolerance factor of simple perovskite structure (Eq. 2) as an index of the structure symmetry of K2NiF4. When tolerance factor is near 1, the structure has good symmetry, so higher stability and better ionic conductivity is expected. For A and A’ site with large ionic radius and B site with small element are required to keep the tolerance factor near 1. Thus, in this work we chose Al for B site which has small ionic radius instead of In. Sr1+xPr1-xAlO4-δ (SPA) has good tolerance factor of 1.01. Moreover, we also focused on ionic valence which has the connection with oxygen deficiency to improve conductivity and proton transport number. Valence change will change amount of oxygen vacancy and which are estimated by Eq. 3-4. Pr ion is Pr3+ or Pr4+ and Sm ion is Sm3+ or Sm2+ .They have almost same ionic radius and electronegativity as shown in Table1. Therefore, we also investigated Sm instead of Pr for A site element to discuss the effect of ionic valence for the electrolyte properties. Sr1+xSm1-xAlO4-δ(SSA) also has good tolerance factor of 1.01. We synthesized SPA and SSA with different A/A’ ratio and observed their power generation characteristics to investigated the confirm the validity to use such index for the development of proton conductive materials. All samples were synthesized by solid phase reactions using the powders of Pr6O11, Sm2O3, Sr2CO3 and Al2O3 .After making the disk of SPA and SSA and sintering in 1400 ºC for 10 h, analysis of crystal structure was carried out by XRD measurement. The conductivities were measured by using AC impedance spectroscopy. Ionic transport numbers were evaluated by the configuration of H2 and O2 concentration cells. The power generation of SOFC with SPA and SSA electrolyte are carried out at 500 ~ 900℃. The total conductivities of SPA and SSA are lower than that of SPI in dry and humidify O2.On the other hand, SSA and SPA has proton conductivity and high proton transport number especially at 700 ~ 900 ºC. The power generation experiments using SOFC with the disks of SPA and SSA were carried out. [1] N. Kochetova et.al. RSC Adv., 2016, 6, 73222 [2]X.Li, M.Ihara, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 2015,162,8 [3]X.Li, H.Shimada, M.Ihara, ECS Transactions, 50(27), 3-14 (2013) Figure 1

Improved transport property of proton-conducting solid oxide fuel cell with multi-layered electrolyte structure

A multi-layered electrolyte structure is proposed for proton-conducting solid oxide fuel cells (SOFCs) to achieve higher power density and higher open-circuit voltage (OCV). Although recent proton-conducting SOFCs have demonstrated high power density, their OCVs have been lower than that of conventional SOFCs with stabilized zirconia because proton-conducting oxides intrinsically have electron-hole conduction. The proposed electrolyte structure has a porous BaZr0.1Ce0.7Y0.1Yb0.1O3–δ (BZCYYb) layer deposited on a dense BZCYYb layer. This structure effectively improves both cathode polarization and ionic transport property, resulting in higher power density with higher OCV. Also, discussion based on an equivalent circuit model of proton-conducting SOFCs clearly reveals a mechanism that determines OCV, namely, higher ohmic resistance and lower electrode polarization resistance lead to higher OCV. Our results suggest that higher electrode performance is essential for proton-conducting SOFCs to achieve higher OCV, particularly in the case of anode-supported configurations with thin electrolyte.

Preliminary Design for Manufacture and Assembly (DFMA) Cost Analysis of Low Temperature, Co-Generative Proton-Conducting Solid Oxide Fuel Cells (SOFC)

This work develops preliminary techno-economic models for a highly-innovative, next generation proton-conducting, anode-supported solid oxide fuel cell (SOFC) that integrates a methane coupling catalyst into the anode. This cell is under development by Argonne National Laboratory (ANL) and the Illinois Institute of Technology. The cell is currently at technology readiness level (TRL) 1, i.e. proof-of-concept at a laboratory bench scale. The cell is designed to co-produce electricity and fuels. This research develops a preliminary design for manufacture and assembly (DFMA) cost analysis for this cell design. This work summarizes (1) a specific physical embodiment of the ANL cell design modelled, (2) the bill of materials (BOM) for this modelled cell, and (3) preliminary cell, stack, and system cost estimates based on this cell. The techno-economic analysis (TEA) focuses on electrolyte-electrode assembly (EEA), or the ‘heart’ of the electrochemical cell, where the anode and cathode half-reactions occur. The project methodology is as follows: Develop a physical embodiment of the design for the EEA.Develop a Bill of Materials (BOM) that specifies masses and/or quantities of components and materials in the EEA.Obtain price quotes for materials in the EEA.Estimate materials costs for the EEA to develop a ‘price floor’ for minimum costs.Identify cost drivers within the EEA.Estimate fuel cell stack costs for a 100 kWe net electric stack mass-produced at a rate of 50,000 systems per year.Estimate fuel cell system costs for a 100 kWe net electric stack mass-produced at a rate of 50,000 systems per year. Preliminary results indicate that EEA is estimated to cost 5.56 cents/cm2 or $278/kW of gross electric power from the cell or stack. Within the EEA, the primary cost driver for the EEA appears to be the anode substrate, which is composed of yttrium-doped barium zirconate (BZY or BaZr(1-x)YxO3-d or sometimes BaZr0.8Y0.2Ox or BaZr0.9Y0.1O3-d), with barium zirconate represented as (BaZrO3), and nickel oxide (NiO). The BZY and NiO anode substrate material is estimated to cost either 2.88 cents/cm2 [based on price quotes for BZY from TransTech Inc.] or 16.40 cents/cm2 [based on price quotes from Praxair Specialty Ceramics]. The secondary cost driver for the EEA appears to be the anode’s methane coupling catalyst. The methane coupling catalyst is modelled as a dual metal catalyst composed of Platinum (Pt), gallium(III) oxide (Ga2O3), and silicon dioxide (SiO2). The catalyst material is estimated to cost 2.45 cents/cm2. About 94% of its cost is due to the material cost of platinum as a catalyst. Preliminary results also indicate that, for a 100 kW net electric stack mass-produced at a rate of 50,000 systems per year, the fuel cell stack subsystem cost is estimated to be ~$478/kW of net electric power from the system. This cost is approximately 74% higher than a ‘plain vanilla’ SOFC subsystem, analyzed by the author for DOE in a prior analysis. For a 100 kW net electric stack mass-produced at a rate of 50,000 systems per year, the overall fuel cell system cost including all BOP components is estimated to be ~$597/kW of net electric power from the system. This cost is approximately 48% higher than the entire ‘plain vanilla’ SOFC system, analyzed by the author for DOE in a prior analysis.

Assessing Doping Effects on Surface Chemical Stability By in Situ AP-Xps in Barium Perovskites, BaCexZr0.9-XY0.1O2.95 (x = 0.9 ; 0.2 ; 0)

The two major proton-conducting solid oxide fuel cell (PCFC) performance limitations are the long-term stability as well as the concentration and mobility of proton defects in the electrolyte. The main electrolyte candidates are perovskite type, in particular, yttrium doped barium Ba(Zr/Ce/Y)O3-s materials. However the poor grain boundary conductivity of BaZr0.9Y0.1O2.95 (BZY) and the lack of chemical stability of BaCe0.9Y0.1O2.95 (BCY) impede their application. The first issue can be addressed by the development of grain boundary-free thin films which exhibit conductivity level up to three orders of magnitude higher than standard sintered pellets.[1] A solid solution of BZY and BCY, BaCe0.2Zr0.7Y0.1O2.95 (BCZY), demonstrates further optimized conductivity levels and chemical stability.[2, 3] However, due to the low concentration of protons and surface gas sensitivity of these materials, detailed knowledge on the chemical interaction between elements from oxide host lattice and fuel cell environment is still lacking, hindering PCFC development. In this work, we developed BaCexZr0.9-xY0.1O2.95 epitaxial thin films and characterized their performance with electrochemical impedance spectroscopy. We investigated the doping effect on surface chemistry by using Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS) in fuel cell environments (100 mtorr of H2O, H2, O2 or CO2) at operating temperature (>400°C). Upon applying water partial pressure, changes in the O 1s and Y 3d core level spectra were observed with a clear dopant dependency. These results indicate the formation of degradation products at the surface. The correlation between surface activity, composition, chemical stability, and conductivity level as well as associated new insights into the dopant effect on hydration and degradation mechanisms will be discussed.

Analysis of an intermediate-temperature proton-conducting SOFC hybrid system

ABSTRACTThe performance of an intermediate-temperature proton-conducting solid oxide fuel cell (pSOFC) hybrid system is investigated in this work. The hybrid system consists of a 20-kW pSOFC, a micro gas turbine (MGT), and heat exchangers. Heat exchangers are used to recover waste heat from pSOFC and MGT. The performance of the system is analyzed by using Matlab/Simulink/Thermolib. Flow rates of air and hydrogen are controlled by assigning different stoichiometric ratio (St). St considered in this study is between 2 and 3.5 for air, and between 1.25 and 1.45 for hydrogen. Results show that the combined heat and power (CHP) efficiency increases as the fuel St decreases or air St increases. This is because lowering fuel St means fewer fuel will be wasted from the fuel cell stack, so the CHP efficiency increases. On the other hand, as air St increases, the amount of recovered waste heat increases, so does the CHP efficiency.

In-Situ Exsolved Co-Fe Alloy Nanoparticles on Double Layered Perovskite for the Cogeneration of Elethylene and Electricity in Proton Conducting Fuel Cell

Ethylene plays a crucial role in modern society. Currently, tube furnace steam cracking is the dominant technology in ethylene production, and about 99% of global ethylene production employs the tube furnace pyrolysis method [1]. However, the cracking reactions are highly endothermic, reversible, and severely limited by thermodynamic equilibrium. Moreover, CO and CO2 are largely formed because of the existence of oxygen sources [2]. According to the mechanism of ethane dehydrogenation, if one of the products, hydrogen, can be selectively removed from the reaction system, the conversion is no longer limited by thermodynamic equilibrium, allowing ethane conversion rate to increase at a lower temperature and thus, making the ethylene production more economical. In response to the critical need for a cleaner energy technology, proton conducting solid oxide fuel cell (PCFC) has been investigated as a potential candidate for the ethane dehydrogenation. Desired chemicals (ethylene) and electricity can be produced simultaneously. For a typical PCFC for ethane dehydrogenation, ethane is dehydrogenated to ethylene at anode, protons from hydrogen pass through the proton conducting electrolyte to react with the oxygen ions at cathode. However, anode catalysts reported in PCFC have not met the requirements of excellent electrochemical performance and high ethylene yield. Therefore, it is of great interest to develop new catalysts with excellent catalytic activity and good coking tolerance for the ethane dehydrogenation [3]. Recently, double layered perovskites have been investigated as the anode materials due to their good stability and high mixed ionic and electronic conductivity for the partial oxidation of hydrocarbons [4]. Also, it is known that Co-Fe bi-metallic alloy is an excellent electrochemical catalyst, and has been widely used as a catalyst in fuel cell anode materials. Moreover, both Co and Fe have been utilized as effective alloying elements to enhance the performance of anode materials and the combination of Co-Fe alloy catalyst favors the formation of C2-C4 alkenes [5]. In this work, in-situ exsolved Co-Fe alloy nanoparticles uniformly distributed on a double layered perovskite (Pr0.4Sr0.6)3(Fe0.85Mo0.15)2O7 (CoFe-PSFM) anode backbone by reducing the cubic perovskite Pr0.4Sr0.6Co0.2Fe0.7Mo0.1O3-δ (PSCFM) in a 10% H2/N2 atmosphere was synthesized at 900 °C. It was fabricated as the anode in a BaCe0.7Zr0.1Y0.2O3-δ (BCZY) electrolyte-supported PEFC. The maximum output power densities of 348.84 mW cm−2 in C2H6 and 496.2 mW cm−2 in H2 were achieved at 750 °C. More importantly, a high ethylene yield, increasing from 13.2% at 650 °C to 41.5% at 750 °C with a remarkable ethylene selectivity over 91% and no CO2 emission, was achieved due to the considerably efficient catalysis of the in-situ Co-Fe alloy nanoparticles which were homogeneously distributed on the PSFM backbone. Furthermore, galvanic static test up to 100 h under a constant current load of 0.65 A cm-2 showed no detectable degradation. The results clearly indicate that the CoFe-PSFM anode material possesses high ethane partial dehydrogenation activity, enhanced electro-catalytic activity, and good stability. Based on its remarkable performance in cogeneration of electricity and ethylene in PCFC, CoFe-PSFM ceramic material is an attractive anode for a directly hydrocarbon fueled solid oxide fuel cell (SOFC). Figure 1

A strategy of tailoring stable electrolyte material for high performance proton-conducting solid oxide fuel cells (SOFCs)

A facile strategy was proposed to synthesize Nb-containing BaCeO3-based material, which is a potential electrolyte for proton-conducting solid oxide fuel cells (SOFCs), via a wet chemical route while the conventional synthesis of Nb-containing oxides relied on the solid state reaction method due to the unavailability of suitable Nb-precursors such as Nb-nitrates resulting in a less desirable fuel cell performance when used as an electrolyte. The BaCe0.7Nb0.1Y0.2O3−δ (BCNY) electrolyte material in this study persisted a good chemical stability against CO2 and exhibited good performance in the fuel cell application. The fuel cell with BCNY electrolyte film showed a high performance of 533mWcm−2 at 700°C. This cell performance based on BCNY electrolyte was superior to that of many stable modified BaCeO3-based proton-conducting SOFCs where the electrolytes were tailored by other strategies. This result indicated that the strategy presented in this study could be an effective way to prepare a stable electrolyte for high performance proton-conducting SOFCs, which could advance the development of proton-conducting SOFCs.

Poisoning of Proton Conducting SOFC By Hydrogen Sulfide and Carbon Dioxide Fuel Contaminants

It is well known that conventional solid oxide fuel cells (SOFCs) with oxygen ion conducting electrolyte and nickel (Ni) anode are susceptible to poisoning by trace amount of hydrogen sulfide (H2S) while not significantly impacted by presence of carbon dioxide (CO2) in the fuel stream. In comparison, the impacts of H2S and CO2 as fuel contaminants on proton-conducting SOFCs remain unexplored. Here we report our study aimed at revealing the poisoning behavior caused by H2S and CO2 for proton-conducting SOFCs. Anode-supported proton-conducting SOFCs with BaZe0.1Ce0.7Y0.1Yb0.1O3 (BZCYYb) electrolyte and Ni-BZCYYb anode and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode were subject to ppm-level H2S or percentage-level CO2 as fuel contaminants in hydrogen fuel. The response in cell electrochemical behavior and the change in materials microstructure and composition are characterized. Preliminary results suggest that, contrary to conventional SOFCs that show “sulfur poisoning” and “CO2 tolerance”, such Ni-BZCYYb anode/BZCYYb electrolyte/LSCF cathode proton-conducting SOFC button cells show good tolerance to H2S up to ~5 ppmv while severe poisoning by CO2 at even low percentage level. Experimental results aimed at understanding such different electrochemical behaviors for proton-conducting SOFCs versus conventional oxygen ion conducting SOFCs will be presented and their implications on the fundamental mechanism for anode hydrogen electrochemical oxidation reaction in proton conducting SOFCs will be discussed.

Use of Patterned Metal Anodes for Studying Hydrogen Electrochemical Oxidation Reaction in Proton-Conducting SOFCs

Despite the great potential for proton-conducting solid oxide fuel cells (SOFCs) for clean power generation at intermediate temperature (e.g., 400-700 oC), there are significant knowledge gaps about fundamental aspects for such cells. In particular, very little is known about the kinetics and reaction mechanism for the hydrogen electrochemical oxidation reaction in proton-conducting SOFCs. Here, we will report the preliminary results of our study using patterned metal anode over acceptor-doped Ba(Ce,Zr)O3 proton-conducting electrolyte. The effects of various factors such as choice of anode metal (e.g., nickel versus copper), anodic bias voltage, gas atmosphere, temperature, and electrode geometry (e.g., triple phase boundary TPB length and electrode area) on the electrochemical behaviors of proton-conducting SOFC will be studied. The results will be correlated to previous studies for hydrogen electrode reaction in conventional oxide-ion conducting SOFCs, and the implications on the fundamental reaction mechanism for the hydrogen electrode reaction involving proton-conducting oxides will be discussed.

Ba0.5Sr0.5Co0.8Fe0.2O3 Cathode for Intermediate Temperature Proton-Conducting Solid Oxide Fuel Cells

Comparing with conventional solid oxide fuel cells (SOFCs) that typically operate at ~750 oC and above, intermediate temperature SOFCs (IT-SOFCs) that operate at temperature of ~400-700 oC offer advantages such as the possibility for the use of lower cost sealing and interconnect materials and the potential for improved reliability and robustness due to the expected slower degradation at reduced temperature. For IT-SOFCs, proton-conducting oxides such as acceptor-doped Ba(Ce, Zr)O3 are often preferred as the electrolyte materials for their high ionic conductivity and low electronic transport number while Ni is almost always used for the anode. In comparison, researchers have not settled on a proper cathode or oxygen electrode, and various materials such as LSCF and SSC have been explored and show different degree of success. Here, we report the use of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) as cathode material for proton conducting IT-SOFC with BaZr0.1Ce0.7Y0.1Yb0.1O3 (BZCYYb) electrolyte. In particular, the chemical stability of BSCF cathode subjecting to different atmospheres containing water (H2O) vapor and CO2 and the compatibility of BSCF with BZCYYb electrolyte will be examined. In addition, the impacts of cell operating conditions including cathodic bias voltage, moisture and CO2 on the electrochemical performance of cathode including bulk and interfacial resistance will be reported using cathode symmetrical cells and/or anode-supported button cells. Preliminary results seem to suggest that BSCF cathode displays reasonable stability and compatibility under typical proton conducting IT-SOFC operating conditions, and cathode performance increases in humidified air compared with dry air. Finally, the directions for future design of cathode for proton conducting IT-SOFC will be discussed.

Characterization of Ba0.5Sr0.5Co0.7In0.1Fe0.2O3−δ as the Cathode Material for Proton‐conducting SOFCs

AbstractBa0.5Sr0.5Co0.7In0.1Fe0.2O3−δ powders are successfully synthesized as the cathode materials for proton‐conducting solid oxide fuel cells (SOFCs). The prepared cells consisting of the structure of a BaZr0.1Ce0.7Y0.2O3−δ (BZCY7)‐NiO anode substrate, a BZCY7 electrolyte membrane and a cathode layer, are measured from 600 to 700 °C with humidified hydrogen (ca. 3% H2O) as the fuel. The electrochemical results show that the cell exhibits a high power density which could obtain an open‐circuit potential of 0.986 V and a maximum power density of 400.84 mW cm−2 at 700 °C. The polarization resistance measured at the open‐circuit condition is only 0.15 Ω cm2 at 700 °C.

LSC cathode prepared by polymeric complexation method for proton-conducting SOFC application

Single-phase, submicron La0.6Sr0.4CoO3−δ (LSC) powder was prepared via a polymeric complexation method at various heating/cooling rates. The optimum powder slurry was used to fabricate LSC/BCZY64/LSC half-cells using BaCe0.54Zr0.36Y0.1O2.95 (BCZY64) as the electrolyte material. The produced powder was characterized by thermal gravimetric analyzer (TGA), X-ray diffractometer (XRD) and scanning electron microscope (SEM) and the half-cell, by electrochemical impedance spectroscopy. TGA results showed that the thermal decomposition temperature (T td) increased as the heating rate increased. The minimum and maximum T td was observed at 600 °C (2 °C min−1) and 750 °C (15 °C min−1), respectively. The XRD results confirmed that a single perovskite phase of LSC formed at heating/cooling rates of 2, 5 and 10 °C min−1 at calcination temperatures of 800, 900 and 1000 °C, respectively. A single perovskite phase of LSC was not observed at a heating/cooling rate of 15 °C min−1. The smallest particle size (130–260 nm) was obtained at 800 °C with a heating/cooling rate of 5 °C min−1, as shown in the SEM micrographs. The area specific resistance of the half-cell was 2.96, 0.97, 0.48 and 0.19 Ω cm2 at 500, 600, 700 and 800 °C, respectively. This result indicates that the prepared LSC cathode has the potential to be used with the BCZY64 electrolyte for an intermediate temperature proton-conducting SOFC.

イットリアとすずをドープしたバリウム・ジルコニア電解質を用いた中温度プロトン伝導体固体酸化物燃料電池

In comparison with the conventional SOFC based on the conduction of oxide ion, the proton-conducting SOFC can be facilitated to high output power densities at significantly reduced operating temperatures between 600-800°C. Moreover, with the advantage of proton-conducting in this type of SOFC, a new alternative power generation system by integrating the proton-conducting SOFC with biomass gasification is very interesting in the near future. In this study a proton-conducting SOFC using BaZr0.7Sn0.1Y0.2O3-δ (BZSY) proton conductor was investigated. The solid oxide fuel cell with BZSY thin electrolyte was fabricated via simple and cost-effective dipping and sintering process. Although there was some cross-over of the single cell, the dense electrolyte was successfully developed with reduced sintering temperature at 1500°C by employing small amount of nickle oxide (NiO) as a sintering aid.

A-site deficient La0.2Sr0.7TiO3−δ anode material for proton conducting ethane fuel cell to cogenerate ethylene and electricity

A site deficient La0.2Sr0.7TiO3−δ (LSTA) and a highly proton conductive electrolyte BaCe0.7Zr0.1Y0.2O3−δ (BCZY) are synthesized by using solid state reaction method. The performance of the electrolyte-supported single cell, comprised of LSTA + Cr2O3 + Cu//BCZY//(La0.60Sr0.40)0.95Co0.20Fe0.80O3−δ (LSCF)+BCZY, is fabricated and investigated. LSTA shows remarkably high electrical performance, with a conductivity as high as 27.78 Scm−1 at 1150 °C in a 10% H2/N2 reducing atmosphere. As a main anode component, it shows good catalytic activity towards the oxidation of ethane, causing the power density to considerably increase from 158.4 mW cm−2 to 320.9 mW cm−2 and the ethane conversion to significantly rise from 12.6% to 30.9%, when the temperature increases from 650 °C to 750 °C. These changes agree well with the polarization resistance which dramatically decreases from 0.346 Ωcm2 to 0.112 Ωcm2. EDX measurement shows that no element diffusion exists (chemical compatibility) between anode (LSTA + Cr2O3+Cu) and electrolyte (BCZY). With these properties, the pure phase LSTA is evaluated as a high electro-catalytic activity anode material for ethane proton conducting solid oxide fuel cell (PC-SOFC).

Numerical analysis of mass and heat transport in proton-conducting SOFCs with direct internal reforming

A computational model to investigate proton-conducting Solid-Oxide Fuel Cells (SOFCs) with direct internal reforming is developed. The numerical framework employs a 42-step elementary heterogeneous mechanism for Ni catalysts, using mean-field approximation. Mass transport through the porous media is described by the dusty gas model (DGM). Electrochemical parameters are deduced by reproducing two sets of experimental data, via the non-linear Butler–Volmer equation. A simple 1-D energy balance model is used to predict temperature profiles. The performance of the cell is analyzed by assuming the co-flow planar cell to be adiabatic. Simulations are carried out to understand the influence of various operating conditions on temperature distribution, species transport, and electrochemistry in the cell. The effect of dividing the anode into four zones, with different specific catalytic areas, on macroscopic performance parameters is investigated.

Y and Ni Co-Doped BaZrO3 as a Proton-Conducting Solid Oxide Fuel Cell Electrolyte Exhibiting Superior Power Performance

The fabrication of anode supported single cells based on BaZr0.8Y0.2O3-δ (BZY20) electrolyte is challenging due to its poor sinteractive nature. The acceleration of shrinkage behavior, improved sinterability and larger grain size were achieved by the partial substitution of Zr with Ni in the BZY perovskite. Phase pure Ni-doped BZY powders of nominal compositions BaZr0.8-xY0.2NixO3-δ were synthesized up to x = 0.04 using a wet chemical combustion synthesis route. BaZr0.76Y0.2Ni0.04O3-δ (BZYNi04) exhibited adequate total conductivity and the open circuit voltage (OCV) values measured on the BZYNi04 pellet suggested lack of significant electronic contribution. The improved sinterability of BZYNi04 assisted the ease in film fabrication and this coupled with the application of an anode functional layer and a suitable cathode, PrBaCo2O5+δ (PBCO), resulted in a superior fuel cell power performance. With humidified hydrogen and static air as the fuel and oxidant, respectively, a peak power density value of 428 and 240 mW cm−2 was obtained at 700 and 600°C, respectively.

Ionic Conduction and Power Generation Characteristics of Pr-Doped Ba2In2O5 for Proton-Conducting SOFCs

Highly Pr-doped Ba2In2O5 (PBI) was successfully fabricated and its ionic conduction and power generation characteristics were studied in this work. Two PBI materials of different concentration ratio were evaluated: Pr:Ba:In = 0.9:1.1:1 (PBI910) and Pr:Ba:In = 1:1:1 (PBI000). PBI910 material was confirmed as single phase with cubic perovskite structure. However, PBI000 had both cubic phase and impurity phase. In a hydrogen concentration cell, the measured proton transfer number of PBI910 at 500°C was 0.81 and then decreased with increasing temperature, whereas the oxide ion transfer number was 0.07 and then increased with increasing temperature. Power generation experiments were evaluated at 500°C to 900°C using PBI as electrolyte and H2 as fuel. Results revealed that and showed different dependency on temperature and significantly affected the power density. Proton conduction dominated from 500°C∼600°C, and power density increased with increasing operating temperature due to improved proton conductivities. However, at 600∼800°C, proton conductivities decreased, which caused a decrease in power density. Further increase in temperature into the 800°C∼900°C range showed oxide ion conduction to then dominate, and the consequent improved oxide ion conductivity again increased the power density despite a decrease in open current voltage (OCV).

Chemically stable BaZr0.7Pr0.1Y0.2O3-δ-BaCe0.8Y0.2O3-δ bilayer electrolyte for intermediate temperature solid oxide fuel cells

A thin BaZr0.7Pr0.1Y0.2O3-δ (BZPY) layer (∼3.3μm) is fabricated on anode-supported BaCe0.8Y0.2O3-δ (BCY) electrolyte layer (∼28μm) with pulsed laser deposition (PLD) technique. The BZPY/BCY bilayer electrolyte shows better chemical stability against CO2 atmosphere compared with the BCY single electrolyte layer. The open circuit voltages (OCVs) of 0.966, 0.997 and 1.021V with maximum power densities of 250, 177, 122mWcm−2 are measured in the bilayer electrolyte cell at 700, 650 and 600°C, respectively. Besides, the BZPY/BCY bilayer electrolyte cell also exhibits a good long-term stability under the operating condition. BZPY thin film deposited with PLD technique can improve chemical stability with little effect on the electrochemical performance of proton-conducting SOFC.