Study of Bi_2O_3-based Rare Earth Solid Electrolyte Used in Fuel Cell

Solid ceramic electrolyte materials (Bi_2O_3)_(0.75)(Y_2O_3)_(0.25) and(Bi_2O_3)_(0.65)(Gd_2O_3 )_(0.35)were synthesized.Their crystal structure, XPS spectra and the change of ionic conductivity versus temperature were measured.A Bi_2O_3-based rare earth solid electrolyte fuel cell with ZrO_2-Y_2O_3 protection film was made.

Characteristic Analysis of the Solid Oxide Fuel Cell with Proton Conducting Ceramic Electrolyte

An electrolyte model for the solid oxide fuel cell (SOFC) with proton conducting perovskite electrolyte is developed in this study, in which four types of charge carriers including proton, oxygen vacancy (oxide ion), free electron and electron hole are taken into consideration. The electrochemical process within the SOFC with hydrogen as the fuel is theoretically analyzed. With the present model, the effects of some parameters, such as the thickness of electrolyte, operating temperature and gas composition, on the ionic transport (or gas permeation) through the electrolyte and the electrical performance, i.e., the electromotive force (EMF) and internal resistance of the cell, are investigated in detail. The theoretical results are tested partly by comparing with the experimental data obtained from SrCe0.95M0.05O3-α, (M=Yb, Y) cells.

Theoretical Aspects on Doped-Zirconia for Solid Oxide Fuel Cells:from Structure to Conductivity

Solid oxide fuel cells(SOFCs)are regarded to be a key clean energy system to convert chemical energy(e.g.H_(2) and O_(2))into electrical energy with high efficiency,low carbon footprint,and fuel flexibility.The electrolyte,typically doped zirconia,is the"state of the heart"of the fuel cell technologies,determining the performance and the operating temperature of the overall cells.Yttria stabilized zirconia(YSZ)have been widely used in SOFC due to its excellent oxide ion conductivity at high temperature.The composition and temperature dependence of the conductivity has been hotly studied in experiment and,more recently,by theoretical simulations.The characterization of the atomic structure for the mixed oxide system with different compositions is the key for elucidating the conductivity behavior,which,however,is of great challenge to both experiment and theory.This review presents recent theoretical progress on the structure and conductivity of YSZ electrolyte.We compare different theoretical methods and their results,outlining the merits and deficiencies of the methods.We highlight the recent results achieved by using stochastic surface walking global optimization with global neural network potential(SSW-NN)method,which appear to agree with available experimental data.The advent of machine-learning atomic simulation provides an affordable,efficient and accurate way to understand the complex material phenomena as encountered in solid electrolyte.The future research directions for design better electrolytes are also discussed.

Low temperature preparation and fuel cell properties of rare earth doped barium cerate solid electrolytes

The solid electrolytes, BaCe0.8Ln0.2O2.9(Ln: Gd, Sm, Eu), were prepared by the sol-gel method. XRD indicated that a pure orthorhombic phase was formed at 900°C. The synthesis temperature by the sol-gel method was about 600°C lower than the high temperature solid phase reaction method. The electrical conductivity and impedance spectra were measured and the conduction mechanism was studied. The grain-boundary resistance of the solid electrolyte could be reduced or eliminated by the sol-gel method. The conductivity of BaCe0.8Gd0.2O2.9 is 7.87 × 10-2 S· cm-1 at 800°C. The open-rireuit voltage of hydrogen-oxygen fuel cell using BaCe0.8Gd0.2O2.9 as electrolyte was near to 1 V and its maximum power density was 30 mW· cm-2.

Low Temperature Preparation of Ceria Solid Solutions Doubly Doped with Rare-Earth and Alkali-Earth and Their Properties as Solid Oxide Fuel Cells

A series of solid electrolytes, (Ce 0.8 Ln 0.2 ) 1- x M x O 2-δ (Ln= La, Nd, Sm, Gd, M:Alkali earth), were prepared by amorphous citrate gel method. XRD patterns indicate that a pure fluorite phase is formed at 800 ℃. The electrical conductivity and the AC impedance spectra were measured. XPS spectra show that the oxygen vacancies increase owing to the MO doping, which results in the increase of the oxygen ionic transport number and conductivity. The performance of ceria based solid electrolyte is improved. The effects of rare earth and alkali earth ions on the electricity were discussed. The open circuit voltages and maximum power density of planar solid oxide fuel cell using (Ce 0.8 Sm 0.2 ) 1-0.05 Ca 0.05 O 2- δ as electrolyte are 0.86 V and 33 mW·cm -2 , respectively.

Development of Doped Lanthanum Gallate Solid Electrolytes

Development of the doped lanthanum gallate solid electrolytes in the recent years was reviewed. The structure and oxygen ion transference mechanism were discussed. Effects of alkali earths, transition metals, and impurities on electrical conductivity of the doped lanthanum gallates were also discussed. The applications of doped lanthanum gallate were described. The current problems and corresponding strategies were explored.

Past, present and future of fuel cells

Though the fuel cell was invented by Grove in 1839,there are no commercially viable products at present.The development of fuel cells can be conveniently divided into three phases exploratory phase(1839-1967).The main emphasis of the work is to increase the area of the three phase interface at the electrode.The problem was solved by Bacon who invented the dual porosity,biporous nickel electrode.He demonstrated the first H 2/O 2 fuel cell(180℃,20atm).This cell was later improved and scaled up to power the Apollo lunar mission.However,the cost is too high for civilian applications and we come to the development phase (1967-2001).The main emphasis has been on the use of Teflon bonded electrodes and novel catalysts(PtRu,Pt/WO 3 and Pt Ru/WO 3 anode catalyst for the anodic oxidation of impure H 2 and methanol.In addition,the recent discovery of gadolinium doped ceria has reduced the operating temperature of solid oxide electrolytes to ～500℃ instead of 1?000℃.From 2001 onwards,we may be entering the breakthrough phase where the most favourable candidates are direct methanol vapor fuel cells and solid oxide electrolyte fuel cells.In the former case,there is a need to reduce the cross over of methanol to the cathode compartment and the development of air cathode catalyst which are less affected by methanol and in the latter case,there is a need to improve the activity of the anode and cathode catalysts.

Cone-shaped cylindrical Ce_(0.9)Gd_(0.1)O_(1.95) electrolyte prepared by slip casting and its application to solid oxide fuel cells

A cone-shaped gadolinium doped ceria（Ce0.9Gd0.1O1.95,GDC） electrolyte cylinder with a thin wall was fabricated using slip cast-ing technique.The diameter of the larger open end of the cone-shaped cylinder was 0.85 cm,the length was 1.0 cm,and the thickness of the wall was 0.026 cm after sintering.Both the electrolyte and electrode powders were fabricated by using a glycine-nitrate process.A single solid oxide fuel cell（SOFC） was prepared with the cone-shaped electrolyte,NiO-GDC（70：30 wt.%） anode and Sm0.5Sr0.5CoO3（SSC） cathode.Its electrochemical performance（I-V curve） and electrochemical impedance spectroscopy（EIS） were studied with humidified hydrogen as the fuel and air as the oxidant.The maximum output power density was about 300 ？mW/cm2 at 700 oC.The EIS results showed that the dominant loss of the SOFC was from the ohmic resistance of the electrolyte.

A real proton-conductive,robust,and cobalt-free cathode for proton-conducting solid oxide fuel cells with exceptional performance

The development of proton,oxygen-ion,and electron mixed conducting materials,known as triple-conduction materials,as cathodes for proton-conducting solid oxide fuel cells(H-SOFCs)is highly desired because they can increase fuel cell performance by extending the reaction active area.Although oxygen-ion and electron conductions can be measured directly,proton conduction in these oxides is usually estimated indirectly.Because of the instability of cathode materials in a reducing environment,direct measurement of proton conduction in cathode oxide is difficult.The La0.8Sr0.2Sc0.5Fe0.5O3–δ(LSSF)cathode material is proposed for H-SOFCs in this study,which can survive in an H_(2)-containing atmosphere,allowing measurement of proton conduction in LSSF by hydrogen permeation technology.Furthermore,LSSF is discovered to be a unique proton and electron mixed-conductive material with limited oxygen diffusion capability that is specifically designed for H-SOFCs.The LSSF is an appealing cathode choice for H-SOFCs due to its outstanding CO_(2)tolerance and matched thermal expansion coefficient,producing a record-high performance of 2032 mW cm^(−2)at 700℃and good long-term stability under operational conditions.The current study reveals that a new type of proton–electron mixed conducting cathode can provide promising performance for H-SOFCs,opening the way for developing high-performance cathodes.

Preparation of microtubular solid oxide fuel cells based on highly asymmetric structured electrolyte hollow fibers

A simple and cost-effective method has been developed for the fabrication of microtubular solid oxide fuel cells (MT-SOFCs). Highly asymmetric electrolyte hollow fibers composed of a thin dense skin layer and a thick porous substrate are first prepared by a modified phase inversion/sintering technique. The porous substrate is then formed into the anode by deposition of a Ni catalyst via an electroless plating method inside the pores while the thin dense skin layer serves directly as the electrolyte film of the fuel cells. A porous cathode layer is produced on the outer surface of the Ni-deposited hollow fibers by slurry coating and subsequent sintering to form a complete micro tubular fuel cell. The process has been employed to fabricate yttrium stabilized zirconia (YSZ) supported Ni-YSZ-YSZ-La0.6Sr0.4Co0.2Fe0.8O3-(LSCF) microtubular fuel cells. The maximum output of the resulting cells is 159.6 mW cm-2 at 800 °C when using H2 as the fuel feed and air as the oxidant.

Preparation of electrolyte membranes for micro tubular solid oxide fuel cells

Yttria-stabilized zirconia (YSZ) micro tubular electrolyte membranes for solid oxide fuel cells (SOFCs) were prepared via the combined wet phase inversion and sintering technique. The as-derived YSZ mi- cro tubes consist of a thin dense skin layer and a thick porous layer that can serve as the electrode of fuel cells. The dense and the porous electrolyte layers have the thickness of 3-5 μm and 70-90 μm, respectively, while the inner surface porosity of the porous layer is higher than 28.1%. The two layers are perfectly integrated together to preclude the crack or flake of electrolyte film from the electrode. The presented method possesses distinct advantages such as technological simplicity, low cost and high reliability, and thus provides a new route for the preparation of micro tubular SOFCs.

SOFC composite electrolyte based on LSGM-8282 and zirconia or doped zirconia from zircon concentrate

The aim of this research is to study zirconia-based electrolyte materials to increase the commercial value of zircon concentrate as a side product of fin mining industries. Synthesis of CaO-Y2O3-ZrO2 （CYZ） and 8mol% Y2O3-ZrO2 （8YSZ） was carried out by solid state reaction. The result shows that ZrO2 presents in tetragonal phase. Doping of Y203 into ZrO2 allows a phase transformation from tetragonal into cubic structure with small percentage of monoclinic phase. Meanwhile, doping of CaO-Y2O3 allows a phase transformation into a single cubic phase. These phase transformations enhance the ionic conductivity of the material. Introduction of 10wt% of LSGM-8282 into CYZ （CYZ-L90：10） allows further improvement of inter-grain contact shown by SEM morphological analysis and leads to the enhancement of ionic conductivity.

Influence of characteristics of stabilized zirconia electrolyte on performance of cermet supported tubular SOFCs

Ni-Al_(2)O_(3)cermet supported tubular SOFC was fabricated by thermal spraying.Flame-sprayed Al_(2)O_(3)-Ni cermet coating plays dual roles of a support tube and an anode current collector.4.5mol.%yttria-stabilized zirconia(YSZ)and 10mol.%scandia-stabilized zirconia(ScSZ)coatings were deposited by atmospheric plasma spraying(APS)as the electrolyte in present study.The electrical conductivity of electrolyte was measured using DC method.The post treatment was employed using nitrate solution infiltration to densify APS electrolyte layer for improvement of gas permeability.The electrical conductivity of electrolyte and the performance of single cell were investigated to optimize SOFC performance.The electrical conductivity of the as-sprayed YSZ and ScSZ coating is about 0.03 and 0.07 S·cm^(-1)at 1000℃,respectively.The ohmic polarization significantly influences the performance of SOFC.The maximum output power density at 1000℃increases from 0.47 to 0.76 W·cm^(-2)as the YSZ electrolyte thickness reduces from 100μm to 40μm.Using APS ScSZ coating of about 40μm as the electrolyte,the test cell presents a maximum power output density of over 0.89 W·cm^(-2)at 1000℃.

Synthesis and characterization of Y and Dy co-doped ceria solid electrolytes for IT-SOFCs:a microwave sintering

In this communication,the electrical conductivities and thermal expansion studies of microwave sintered co-doped ceria Ce_(0.8)Y_(0.2-x)Dy_(x)O_(2-δ)(x=0,0.05,0.10,0.15 and 0.20) solid electrolyte materials for intermediate temperature solid oxide fuel cells(IT-SOFCs)synthesized by sol-gel auto-combustion method were discussed.Microwave sintering at 1300℃ for 30 min was used for making dense powder compacts.The relative densities of all the samples are noticed above 95%.Raman spectrum was characterized by the presence of a very strong band near 460 cm^(-1),which along with X-ray diffraction(XRD) analysis ascertain the sample formation with a single-phase cubic fluorite structure.The lattice parameter values were calculated from XRD patterns.SEM images show nearly uniform grains with distinct grain boundaries.The thermal expansion coefficients(TECs) are found to vary linearly with temperature and were measured in the range from 14.15 to 13.20×10^(-6)℃^(-1).The investigation on total ionic conductivity(TIC) was executed with variation in dopant concentration and relative oxygen vacancies.The impedance analysis reveals that the sample Ce_(0.80)Y_(0.10)Dy_(0.10)O_(2-δ) displays the highest TIC,i.e.,7.5×10^(-3) S·cm^(-1) at 500℃ and minimum activation energy 0.90 eV compared to others.With the highest TIC and minimum activation energy,the Ce_(0.80)Y_(0.10)Dy_(0.10)O_(2-δ)might be the possible material as the solid electrolyte in intermediate temperature SOFCs.

Applications and recent advances of rare earth in solid oxide fuel cells

Solid oxide fuel cells(SOFCs)are an all-solid energy conversion device from the chemical energy of fuels to electric energy at intermediate and high temperatures.Up to now,massive efforts have been made in developing different components of solid oxide fuel cells,including electrolyte,anode,cathode and interconnect materials.Rare earth elements play an indispensable role in different components of SOFCs which have been extensively studied in the recent decades.In this review,we concentrate upon the rare earth application and recent advances in SOFCs and related materials.Materials structure involves perovskites,Ruddlesden-Popper,fluorite,spinel,pyrochlore,apatite and so on.Moreover,the effects of rare earth based oxides as matrix or dopants in different components are also discussed.Structures and properties of the materials are related to the element type,valence,coordination and ion radius.This article will provide a comprehensive research direction towards SOFCs components for their composition,structural design and mechanisms research.

Research of processing techniques used in fabrication of solid oxide fuel cells and study of their selected properties

The processing techniques used in the fabrication of solid oxide fuel cells (SOFC) were studied. A fast, simple and convenient method of studying and fabricating SOFC was found. The properties of the single cell and the series stack of the SOFC were measured and studied. The maximum open voltage and short current density of the single cell are 1 18V and 360 mA/cm\+2,respectively. And the maximum open voltage and short current density of the series stack of 7 cells are 7.30 and 400 mA/cm\+2 respectively and the output power is about 2.0 W. Some simple applications were tried by using the SOFC series stack.

Study on Electrolytes (CeO_2 )_( 0.7-x) (MO) _x (La_2O_3)_(0.3)(M=Mg,Ca, Sr)

Solid electrolytes(CeO2)0.7-x(MO)x (La2O3) 0.3(M = Mg,Ca,Sr)were synthesized.Their crystal structure,conductivity, XPS spectrum,ionic transferance number and the V-1 curve of the obtained fuel cell were measured.(CeO2)0.7z (La2O3)0.3 doped with Ca2+,Mg2+,and Sr2+can perform the oxygen ionic electrolyte,and so enhance the open voltage and power output of the fuel cell.

Mircostructural and electrical properties of Ce_(0.8)Sm_(0.2)O_(2-δ)-BaZr_(0.9)Y_(0.1)O_(3-δ) composite electrolyte

The (1-x)BaZr0.9Y0.1O3-δ(BZY)-xCe0.8Sm0.2O2-δ(SDC, x =0.1,0.3,0.5 and 0.7) composite electrolytes were prepared by combining a gel polymerization method with a ball milling. X-ray diffraction (XRD) patterns show the mixture of BZY and SDC is only crystalline phase as the composite electrolyte. The relative density,grain size and total conductivity of composite electrolytes increase significantly with the increase of SDC content. The maximum conductivity of 0.1 BZY-0.9 SDC reaches 2×10^2 S·cm^-1 at 600 ℃ in wet air,which is close to the conductivity of SDC.

Study on Properties of LSGM Electrolyte Made by Tape Casting Method and Applications in SOFC

Solid oxide fuel cell is attracting more attention in recent years for its lower pollution emission and high energy convert efficiency. La0.9Sr0.1Ga0.8Mg0.2O3-δis a new kind of electrolyte for intermediate temperature SOFC. In this paper, La0.9Sr0.1Ga0.8Mg0.2O3-δ(LSGM) was prepared by solid state reaction method and formed by tape casting process to make a planar electrolyte. The appropriate amount of the dispersive was obtained by viscosity test. The densities of sintered samples increase with the increasing sintering temperature. It was found that the relative density of electrolyte can approach the value of 95 % by the isostatic pressing treatment of the green tape. The average thermal expansion coefficient of the LSGM is 11 .4×10-6 /℃at temperature range (200 ~ 1200℃). Measurements of the current-voltage and power-current characteristics of the Hi-Air cell show that the open-circuit voltage is 1.067 V at 800℃, peak current density is 0.56 A·cm -2 and the maximum power output is 0.147 W·cm -2.