PROGRAM AREA OVERVIEW --

New materials ideas and concepts are required to significantly improve performance and reduce the costs of existing fossil systems or to enable the development of new systems and capabilities. The Fossil Energy Materials Program conducts research and development on high-performance materials for longer-term fossil energy applications, including gas separations and storage. The program is concerned with operation in the hostile conditions created when fossil fuels are converted to energy. These conditions include high temperatures, elevated pressures, corrosive environments (reducing conditions, gaseous alkali), and surface coating or fouling. Grant applications are sought only in the following subtopics:

a. High Temperature Electrolysis, Hydrogen Separation, and Storage Materials—Applications of high temperature electrolysis range from small natural gas systems to hydrogen units for automotive fueling stations to large electrolyzers for use in conjunction with nuclear power. The development of high temperature electrolysis systems could be efficiently accomplished using traditional solid oxide fuel cell (SOFC) architectures. Although some differences, such as electrode materials, do exist between SOFCs and high temperature electrolyzers, the development is expected to be synergistic. One area of concern in all of these systems is the sealing of the hydrogen collection area. Grant applications are sought to develop and demonstrate a high temperature electrolysis system based on solid-oxide fuel cell technology and architecture. The work should proceed from concept demonstration to small system demonstration. Technology development projects also will be considered.

Hydrogen separation membranes are critical supporting technologies for next generation power systems. Two types of membranes are being investigated for the recovery of hydrogen from coal gasification streams: membranes which are selective for hydrogen and membranes which are selective for carbon dioxide. Grant applications are sought to further the development of either or both types of these membranes for commercial hydrogen production.

For hydrogen membranes, approaches should have the potential to meet or exceed the targets outlined in the table below. Because the proposed membrane type may differ from that used to develop this target table, the hydrogen separation membrane system should aim for: (1) a high flux rate; (2) low cost; (3) improved durability; (4) low parasitic power requirements; and (5) low membrane fabrication costs.

Characteristics	Units	Status	Target
Flux Rate	scf/hr-ft²	60	200
Cost	$/ft²	150-200	<100
Durability	Hrs	<1,000	100,000
Operating Temp	^oC	300-600	300-600
Parasitic Power	kWh/ 1,000 scf	3.2	<2.8

CO₂-selective membranes are another way to concentrate the hydrogen on the high-pressure side of the separation device. A novel material that appears to have the potential to accomplish this type of separation consists of carbon nanotubes. CO₂ is adsorbed on nanotubes in special configurations, allowing separation from H₂. However, other separation systems may provide cost-effective means of leaving hydrogen on the high-pressure side of the system. Grant applications are sought to develop systems that will separate carbon dioxide from the exit stream of a water-gas shift reactor. Proposed approaches must demonstrate that the hydrogen left on the high-pressure side of the separation system can be produced in large quantities and at high purity. Also, proposed approaches should include simulations, experiments to measure isosteric heats of adsorption, and the characterization of binding sites and energies.

Another critical need is the development of materials for hydrogen storage as a necessary precursor to the eventual implementation of the hydrogen economy. There are several advantages to using hydrogen over carbon fuels for transportation applications. First, the chemical energy per unit mass of hydrogen is higher than that for liquid hydrocarbons. Secondly, the combustion of hydrogen with oxygen or the electrochemical reaction of hydrogen with oxygen in a fuel cell eliminates carbon emissions. Therefore, grant applications are sought to develop materials that provide high hydrogen storage density and stability at commercially relevant conditions of temperature and pressure. The materials currently being investigated for hydrogen storage include metal organic frameworks; alloys and intermetallics; sodium and lithium alanates; nanocubes; carbon nanotubes; and other emerging materials. These materials should have the potential for achieving DOE’s long-term hydrogen storage goal of 3 kWh/kg (9 wt %) at a cost of $2/kWh. The materials to be investigated must be amenable to realistic processing conditions and to the likelihood of large-scale manufacturing. For practical transportation applications, the hydrogen storage material must function in the temperature range of 0-100°C and pressure range of 1-10 bar.

b. Nanotechnology for Coatings in Coal-Fired Environments—In fossil energy power generation applications, where sulfur and water vapor can cause severe oxidation problems, typical examples of surface damage include: (1) accelerated high-temperature fire-side corrosion associated with the presence of molten alkali-containing salts; (2) accelerated medium-temperature fire-side corrosion associated with the presence of a low oxygen activity environment and sulfur; and (3) steam-side oxidation of tubing, piping, and valves in fossil fuel-fired boilers. In order to achieve higher operating temperatures, the corrosion resistance of Fe- and Ni-based alloys must be improved. Grant applications are sought to develop nanotechnology approaches to protective coatings and coating techniques for the Fe- and Ni-based alloys, and for nickel-based superalloys as well. At least one ferritic and one austenitic alloy should be selected as substrate materials for study. The coatings must provide superior corrosion resistance in oxidizing, sulfidizing, carburizing, and water-containing environments, and should show adhesion on the substrate (the tube outsides) as well as slide- and anti-stick-properties on the surface at the same time. The protective coatings and coating techniques should be optimally designed as part of the overall power generation system, should be maintainable, and should be capable of non-intrusive evaluation to determine remaining life. To this end, model coatings should be fabricated for corrosion testing and diffusion studies, in order to provide sufficient data to evaluate lifetime performance in applicable environments.

c. Novel Coating Processes and Materials Sets for Turbine Blades—Both current gas turbines and those being designed for coal-based synthesis gas operation will greatly benefit from improved manufacturing processes to coat turbine blades, coupled with new material sets that can withstand higher firing temperatures. Grant applications are sought to develop novel, low cost blade coating processes and new material sets that improve thermal barrier coating (TBC) structures and turbine blade robustness, thereby allowing higher temperatures in natural gas and synthesis gas environments. TBC systems aimed at enhancing the effective operating temperature of cooled super alloys by as much as 165°C are needed. Coating systems with diminished thermal conductivity have evident appeal and are of interest; however, such approaches must address how to avert uncertainties in their life expectancy, in order to avoid compromising the survivability of the underlying component. While recognizing the need for coatings with improved base capabilities, the overarching issue for advanced gas turbines is prime reliance; namely, the coating should be an integral part of the overall design, rather than an add-on feature. If the operating envelope is to be pushed significantly beyond its current limit, both alloys and ceramics will have to depend on the capabilities, durability, and reliability of the coatings to achieve the requisite performance.

Subtopic a: High Temperature Electrolysis, Hydrogen Separation, and Storage Materials

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2. Norby, T. and Larring, Y., “Mixed Hydrogen Ion-Electronic Conductors for Hydrogen Permeable Membranes,” Solid State Ionics, 136-137:139-148, 2000. (ISSN: 0167-2738)

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