Fuel cell materials and components

Transport properties of solid oxide electrolyte ceramics: a brief review

A complete polarization model of a solid oxide fuel cell and its sensitivity to the change of cell component thickness

This critical review presents an overview of the various classes of oxide materials exhibiting fast oxide-ion or proton conductivity for use as solid electrolytes in clean energy applications such as solid oxide fuel cells. Emphasis is placed on the relationship between structural and mechanistic features of the crystalline materials and their ion conduction properties. After describing well-established classes such as fluorite- and perovskite-based oxides, new materials and structure-types are presented. These include a variety of molybdate, gallate, apatite silicate/germanate and niobate systems, many of which contain flexible structural networks, and exhibit different defect properties and transport mechanisms to the conventional materials. It is concluded that the rich chemistry of these important systems provides diverse possibilities for developing superior ionic conductors for use as solid electrolytes in fuel cells and related applications. In most cases, a greater atomic-level understanding of the structures, defects and conduction mechanisms is achieved through a combination of experimental and computational techniques (217 references).

Oxide-ion and proton conducting electrolyte materials for clean energy applications: structural and mechanistic features

The performance of a single-chamber solid oxide fuel cell was studied using a ceria-based solid electrolyte at temperatures below 773 kelvin. Electromotive forces of ∼900 millivolts were generated from the cell in a flowing mixture of ethane or propane and air, where the solid electrolyte functioned as a purely ionic conductor. The electrode-reaction resistance was negligibly small in the total internal resistances of the cell. The resulting peak power density reached 403 and 101 milliwatts per square centimeter at 773 and 623 kelvin, respectively.

https://science.sciencemag.org/content/sci/288/5473/2031.full.pdf

A low-operating-temperature solid oxide fuel cell in hydrocarbon-Air mixtures

The performance of La0.8Sr0.2Ga0.83Mg0.17O2.815 (LSGM) as an optimized electrolyte of a solid oxide fuel cell was tested on single cells having a 500-µm-thick electrolyte membrane. The reactivity of NiO and LSGM suggested use of an interlayer to prevent formation of LaNiO3. The interlayer Sm-CeO2 was selected and sandwiched between the electrolyte and anode. Comparison of Sm-CeO2/Sm-CeO2+ Ni and Sm-CeO2+ Ni as anodes showed that Sm-CeO2/Sm-CeO2+ Ni gave an exchange current density 4 times higher than that of Sm-CeO2+ Ni. The peak power density of the interlayered cell is 100 mW higher than that of the standard cell without the interlayer. This improvement is due to a significant reduction of the anode overpotential; the overpotential of the cathode La0.6Sr0.4CoO3-delta (LSCo) remained unchanged. Comparison of the peak power density in this study and with that of a previous study, also with a 500-µm-thick electrolyte, indicates a factor of 2 improvement, i.e., from 270 mW/cm2 to 550 mW/cm2 at 800°C. The excellent cell performance showed that an LSGM-based thick membrane SOFC operating at temperatures 600° < Top < 800°C is a realistic goal.

Superior perovskite oxide-ion conductor; Strontium- and magnesium-doped LaGaO3 : III. Performance tests of single ceramic fuel cells

The electrode performance of a single oxide fuel cell was evaluated using a 500 {micro}m thick La{sub 0.9}Sr{sub 0.1}Ga{sub 0.8}Mg{sub 0.2}O{sub 2.85} (LSGM) as the electrolyte membrane. Comparison of La{sub 0.6}Sr{sub 0.4}CoO{sub 3{minus}{delta}} (LSCo) and La{sub 0.9}Sr{sub 0.1}MnO{sub 3} (LSM) as cathodes showed LSCo gave an exchange current density two orders of magnitude higher than that of LSM. Comparison of CeO{sub 2}/Ni and LSGM/Ni as anodes showed a degradation of the latter with time, and studies of the anode-electrolyte interface and the reactivity of NiO and LSGM suggest better anode performances can be obtained with a buffer layer that prevents formation of LaNiO{sub 3}. The cell performance showed that, with a proper choice of electrode materials and LSGM as the electrolyte, a SOFC operating at temperatures 600 C < T{sub op} < 800 C is a realistic goal.

/pdf/electrode-performance-test-on-single-ceramic-fuel-cells-320vdpuqxg.pdf

Electrode performance test on single ceramic fuel cells using as electrolyte Sr- and Mg-doped LaGaO3

Fuel Cells with Doped Lanthanum Gallate Electrolyte

Samaria-doped ceria solid oxide fuel cells (SOFC) single cells have demonstrated power densities >250 mW/cm{sup 2} at 700 C and stable performance for 15,000 h. Though encouraging, issues of stack performance and efficiency due to mixed conduction remain. Stacks operated on H{sub 2}/3% H{sub 2}O show approximately half the power density expected from single cells. A coupled thermal-electrochemical model which included conduction heat transfer in the solid and convection to the reactant gases was developed. The model was used to predict stack efficiencies using ceria-based SOFCs in power plant applications. Analyses indicate that ceria SOFCs may provide as high as 42% electrical efficiency when operated on humidified hydrogen fuel. These efficiencies are surprisingly high and challenge the notion that mixed conductors are unsuitable for such applications.

Evaluation of ceria electrolytes in solid oxide fuel cells electric power generation

Cation-doped CeO2 electrolyte has been evaluated in single-cell and short-stack tests in solid oxide fuel cell environments and applications. These results, along with conductivity measurements, indicate that an ionic transference number of ∼0.75 can be expected at 800°C. Single cells have shown a power density >350 mW/cm2. Multicell stacks have demonstrated a peak performance of >100 mW/cm2 at 700°C using metallic separators.

Christopher Milliken

Papers

Superior perovskite oxide-ion conductor; Strontium- and magnesium-doped LaGaO3 : III. Performance tests of single ceramic fuel cells

Electrode performance test on single ceramic fuel cells using as electrolyte Sr- and Mg-doped LaGaO3

Fuel Cells with Doped Lanthanum Gallate Electrolyte

Evaluation of ceria electrolytes in solid oxide fuel cells electric power generation

Properties and Performance of Cation‐Doped Ceria Electrolyte Materials in Solid Oxide Fuel Cell Applications