Fuel cell materials and components

Progress in material selection for solid oxide fuel cell technology: A review

Because of the generally lower activation energy associated with proton conduction in oxides compared to oxygen ion conduction, protonic ceramic fuel cells (PCFCs) should be able to operate at lower temperatures than solid oxide fuel cells (250° to 550°C versus ≥600°C) on hydrogen and hydrocarbon fuels if fabrication challenges and suitable cathodes can be developed. We fabricated the complete sandwich structure of PCFCs directly from raw precursor oxides with only one moderate-temperature processing step through the use of sintering agents such as copper oxide. We also developed a proton-, oxygen-ion–, and electron-hole–conducting PCFC-compatible cathode material, BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY0.1), that greatly improved oxygen reduction reaction kinetics at intermediate to low temperatures. We demonstrated high performance from five different types of PCFC button cells without degradation after 1400 hours. Power densities as high as 455 milliwatts per square centimeter at 500°C on H2 and 142 milliwatts per square centimeter on CH4 were achieved, and operation was possible even at 350°C.

https://science.sciencemag.org/content/sci/349/6254/1321.full.pdf

Readily processed protonic ceramic fuel cells with high performance at low temperatures

The increasing world population and the need to improve quality of life for a large percentage of human beings are the driving forces for the search for sustainable energy production systems, alternative to fossil fuel combustion. Among the various types of alternative energy production technologies, solid oxide fuel cells (SOFCs) operating at intermediate temperatures (400–700 °C) show the advantage of possible use both for stationary and mobile energy production. To reach the goal of reducing the SOFC operating temperature, proton-conducting oxides are gaining wide interest as electrolyte materials. This critical review provides a broad overview of the most recent progresses obtained tailoring the properties of proton-conducting oxides for fuel cell applications, analyzing and comparing the different strategies proposed to match high-proton conductivity with good chemical stability (170 references).

Materials challenges toward proton-conducting oxide fuel cells: a critical review

▪ Abstract After a brief survey of fuel cell types, attention is focused on material requirements for SOFC and PEMFC stacks, with an introductory section on materials technology for reformers. Materials cost and processing, together with durability issues, are emphasized as these now dominate materials selection processes for prototype stack units. In addition to optimizing the cell components, increasing attention is being given to the composition and processing of the bipolar plate component as the weight and volume of the relevant material has a major influence on the overall power density and cost of the fuel cell stack. It is concluded that the introduction of alternative materials/processes that would enable PEMFC stacks to operate at 150–200°C, and IT-SOFC stacks to operate at 500–700°C, would have a major impact on the successful commercialization of fuel cell technology.

Recent Advances in Materials for Fuel Cells

The performance of a solid oxide fuel cell (SOFC) with the configuration, H 2 . 3 wt % Pd-loaded FeO|25 mol % Y 3+ -doped BaCeO 3 (BCY25)|Ba 0.5 Pr 0.5 CoO 3 , air, was studied between 350 and 600°C. The BCY25 electrolyte showed higher ion conductivities than 8 mol % yttria-stabilized zirconia (YSZ) below 800°C and 20 mol % Sm 3+ -doped ceria (SDC) below 600°C, thus having the smallest ohmic resistance loss during cell discharge below 600°C among the three electrolytes. The overpotentials of the Pd-loaded FeO anode and the Ba 0.5 Pr 0.5 CoO 3 cathode at 600°C were 25 and 53 mV, respectively, at 200 mA cm -2 , which were less than one-fourth those of a Pt electrode. The resulting peak power density was higher than those obtained for two SOFCs using the YSZ and SDC electrolytes with a Ni-SDC anode and a Sm 0.5 Sr 0.5 CoO 3 cathode below 600°C.

A Solid Oxide Fuel Cell Using Y-Doped BaCeO3 with Pd-Loaded FeO Anode and Ba0.5Pr0.5CoO3 Cathode at Low Temperatures

Electrocatalytic oxidation of methane over anodes in single-chamber solid oxide fuel cells, 0-10 wt % Pd-30 wt % Ce 0.8 Sm 0.2 O 1.9 (samaria-doped ceria, SDC)-Ni|SDC|Sm 0.5 Sr 0.5 CoO 3 , was studied in a mixture of methane and air between 450 and 550°C. The addition of a small amount of Pd (0.145 mg cm 2 ) to the anode significantly promoted the partial oxidation of methane by oxygen to form hydrogen and carbon monoxide, which resulted in electromotive forces of ca. 900 mV from the cell and extremely small electrode-reaction resistances of the anode. The peak power densities, when using a 0.15 mm thick SDC electrolyte, reached 644, 467, and 269 mW cm -2 at 550, 500, and 450°C, respectively.

High Performance Anodes for SOFCs Operating in Methane-Air Mixture at Reduced Temperatures

Ru-catalyzed anode materials for direct hydrocarbon SOFCs

The promotion of direct electrochemical oxidation of hydrocarbons in a solid oxide fuel cell was investigated using a ceria-based electrolyte with different noble metals-containing anode at 600°C. The objective was to avoid interference from a large amount of steam and CO 2 being produced by discharging the cell, because these gases degrade the anode performance, especially at a high fuel utilization. Ru was an effective catalyst for removing these gases from the anode surface due to its high catalytic activity for the steam and CO 2 reforming of hydrocarbons. The resulting peak power densities reached 750 mW cm - 2 with dry methane, which was comparable to the peak power density of 769 mW cm - 2 with wet (2.9 vol %H 2 O) hydrogen. The cell performance was maintained at a high level regardless of the change in methane utilization from 12 to 46% but was significantly reduced by increasing hydrogen utilization from 13 to 42%. The anodic reaction of hydrogen was controlled by the slow surface diffusion of hydrogen, while the anodic reaction of methane was not subject to the onset of such a gas-diffusion process.

http://esl.ecsdl.org/content/5/11/A242.full.pdf

An Intermediate-Temperature Solid Oxide Fuel Cell Providing Higher Performance with Hydrocarbons than with Hydrogen

We propose a solid oxide fuel cell design based on a configuration of two electrodes on the same surface of the electrolyte in a flowing mixture of different hydrocarbons and air between 500 and 600°C. The ohmic resistance can be reduced without using a thin electrolyte film due to a significantly enhanced performance by the approach of the two electrodes to each other on the smooth electrolyte surface. The fuel cell performance, especially at reduced temperatures, is further improved by using a more reactive hydrocarbon fuel and a more catalytically active anode. The resulting power density reaches 122 mW cm -2 using 2 mm thicker electrolyte at 500°C.

Masanori Suzuki

Papers

A Solid Oxide Fuel Cell Using Y-Doped BaCeO3 with Pd-Loaded FeO Anode and Ba0.5Pr0.5CoO3 Cathode at Low Temperatures

High Performance Anodes for SOFCs Operating in Methane-Air Mixture at Reduced Temperatures

Ru-catalyzed anode materials for direct hydrocarbon SOFCs

An Intermediate-Temperature Solid Oxide Fuel Cell Providing Higher Performance with Hydrocarbons than with Hydrogen

A Solid Oxide Fuel Cell with a Novel Geometry That Eliminates the Need for Preparing a Thin Electrolyte Film