Hydrogen.gov | C. High-Temperature Fuel Cells

C. High-Temperature Fuel Cells

Description: High-temperature fuel cells include solid-oxide types and molten-carbonate types. Solid oxide fuel cells (SOFC) use a ceramic electolyte, which results in a solid-state unit, and operate at about 1000 deg. C. The conduction mechanism is the migration of oxygen ions from the cathode to the anode through a solid-state, crystal lattice. The reaction is completed by the reaction of oxygen ions at the anode with hydrogen (from the fuel gas) to form water, releasing electrons to the external circuit. In a molten-carbonate fuel cell (MCFC), molten carbonate salts are the electrolyte. At 440 deg.C, the salts melt and conduct carbonate ions (CO3) from the cathode to the anode. At the cathode, the electrons react with oxygen from air and CO₂ recycled from the anode to form CO₃ ions that replenish the electrolyte and transfer current through the fuel cell. At the anode, hydrogen reacts with the ions to produce water, CO₂, and electrons that flow through the external circuit. SOFCs and MCFCs can extract hydrogen from a variety of fuels using either an internal or external reformer. Challenges for SOFC technology include increasing the power density and reducing cost, which requires improved seals and metallic interconnects. Significant technical challenges with MCFCs are the complexity of working with a liquid electrolyte rather than a solid, the inherent, relatively low power density, and high cost. A significant advantage of high-temperature fuel cells is fuel flexibility – since they are not very susceptible to CO poisoning, they can use gasified coal, natural gas, or, with minor modification, heavy fuels. Also, SOFCs and MCFCs work well with catalysts made of nickel, which is much less expensive than platinum. They can achieve an efficiency of 60% stand-alone, or up to 80% (net) if the waste heat is used for cogeneration. Currently, demonstration units exist up to 2 MW.

1. Stack
Goals: Cost reduction for manufacturing and materials, higher power density, lower temperature, and thermal cyclability.

a) Electrolyte
Description: Develop and characterize lower-temperature oxide-ion conductors. Lower-temperature operation would reduce the thermal durability problems of SOFCs and reduce material cost.

i. Ceramics (e.g., high-strength YSZ)

ii. Novel, synthetic solid-state materials (e.g., LSGM, doped ceria)

iii. Multi-layer, integrated structures

b) Electrodes
Goals: Reduced thickness, Improved sulfur tolerance, CTE, Interface performance

i. Anode – sulfur tolerance and carbon resistance

ii. Cathode – LSM alternatives such as LSF, LSCF, SSC

c) Seals
Goals: High-temperature durability, Resistance to thermal cycling

i. Glass composites

ii. Ceramics

d) Interconnects
Goals: Lightweight, Oxidation resistant

i. Ceramics

ii. Metallics

e) Sensors

i. Chemical Sensors

ii. Physical System Sensors

f) Manufacturing processes

i. Cathode materials
Description: Develop a continuous manufacturing process using self-propagating, high-temperature synthesis.

ii. Thin-film fabrication

iii. Modular designs
Description: Develop a low-cost module that is scalable from 5 W – 5 kW.

g) Microminiaturized design
Description: For handheld electronic devices.

h) Type Casting and Calendering

i. Screen printing

ii. Sintering

iii. Extrusion

iv. Deposition

v. Plasma spray

2. Other Components

a) Ancillaries

i. Pumps

ii. Valves

iii. Separators

iv. Interconnects

v. Compressors

b) Thermal management
Goals: Efficiency, Size, Cost

i. Heat exchangers

ii. Condensers

iii. Heaters

iv. Radiators

v. Heat recovery system

vi. Heat rejection materials

vii. Humidifiers

viii. Other system humidification techniques

c) Power management and distribution
Goals: Low EMC, High efficiency

i. High-power DC switching converters

ii. High-power, cryogenic DC switching converters

d) Fuel processor
Description: Miniature units integrated with an on-board unit
Goals: Power density, Cost, Longevity, Tolerance of sulfur and carbon

3. System Analysis
Description: Reliability, durability, and performance characterizations using modeling and testing.

a) Components

b) Subsystems and large-scale systems
Description: Test steady-state, transient, and dynamic operation, in both series and parallel configurations.

c) Microstructure analysis
Description: Characterize void and phase microstructures (in the anode, cathode, and electrolyte layers, and interfaces between them) as a function of position in system materials, in order to understand control of performance properties and life-cycle changes.

i. X-ray synchroton analysis
Description: Measure void and pore size, size distribution and connectivity, and reactivity.

ii. Microstructure models for SOFC performance prediction

d) Fueling station Description: Incorporate advanced high-temperature fuel cells into an integrated H2 production, building power, and fueling system, at distributed locations (see V.D.2 for a complete description).
Goal: Evaluate efficiency, durability, and gain real-world experience.

Back to Top

Why Hydrogen? | The President's Hydrogen Fuel Initiative | Federal Activities
Regulations | Funding Opportunities | News/Events