Hydrogen Production Using Nuclear Reactors Offers Energy, Environmental Benefits

	Researchers Jennifer Mawdsley (Chemical Engineering Division, right), and Bilge Yildiz (Nuclear Engineering Division, left) prepare to conduct electrochemical tests of a high-temperature steam electrolysis electrode material.

Argonne is investigating two approaches to make hydrogen from water for the "hydrogen economy" using a nuclear reactor as a source of heat and electricity. There are advantages to both approaches—high-temperature (steam) electrolysis, and hybrid thermochemical-electrochemical cycles—but there also are challenges related to chemistry and materials, which Argonne is working to meet.

Argonne's Research:  High-Temperature (Steam) Electrolysis 

High-temperature electrolysis (HTE), or steam electrolysis, uses electricity to produce hydrogen from steam, instead of liquid water. High-temperature electrolysis is more efficient than traditional room-temperature electrolysis because some of the energy is supplied as heat, which is cheaper than electricity, and because the electrolysis reaction is more efficient at higher temperatures.

Argonne is part of a team demonstrating the feasibility of this process. Argonne’s background in solid oxide fuel cell designs and materials is leading toward improvements in high-temperature electrolysis efficiency and reductions in costs. The major source of inefficiency in both solid oxide fuel cells and solid oxide electrolysis cells is poor electrode performance and durability, which results in large systems and high materials costs. Argonne is developing oxygen and hydrogen electrode materials for better hydrogen production efficiency and materials durability.

Hybrid Thermochemical-Electrochemical Cycles

Recent research indicates strong potential for using thermochemical water splitting processes to produce hydrogen. Thermochemical cycles are a series of chemical reactions that convert water to hydrogen and oxygen using catalysts at high temperatures. These processes offer the potential for high-efficiency hydrogen production at large-scale production rates, but the technology is relatively immature.

Argonne is investigating a number of hybrid thermochemical hydrogen production cycles that produce hydrogen from water using heat and electricity from a nuclear reactor. One cycle under investigation is an adaptation of sulfuric acid (H₂SO₄) synthesis and decomposition processes, termed the sulfur-iodine cycle. The standard sulfur-iodine cycle requires temperatures above 850°C for one step in the cycle, the decomposition of sulfur trioxide (SO₃). The other reactions in the cycle can be performed below 500°C.

Argonne is investigating means to lower the temperature of the SO₃ to SO₂ reaction to 500-600°C. The benefits of lowering the maximum operating temperature of the cycle are that it allows the use of a lower temperature heat source, eliminates the need for expensive high-temperature heat exchangers, and it mitigates the problems associated with corrosion at higher temperatures. In Argonne’s approach the maximum temperature is lowered by electrolyzing SO₃ using oxide-ion-conducting electrolysis cells. Argonne is working to develop improved materials and cell designs to maximize the efficiency of this step in the hydrogen production cycle for operation at ~500°C.

For more information, contact Jennifer Mawdsley, Chemical Engineering Division (630-252-4608, mawdsley@cmt.anl.gov, or Bilge Yildiz, Nuclear Engineering Division (630-252-1769, byildiz@anl.gov

Other Nuclear Hydrogen Initiative R&D at Argonne

• A Standard Methodology for Comparing Alternative Thermochemical Cycles
• Calcium-Bromine Cycle
• Assessing Current, Near-Term, and Long-Term U.S. Hydrogen Markets
• Operational dynamics and safety of linking a hydrogen plant to a nuclear heat source
• Nuclear hydrogen delivery options
• Computational fluid dynamics of solid-oxide electrolysis cells
• Economics of low-temperature and high-temperature electrolysis
• Atomic Layer Deposition for the Fabrication of Solid-Oxide Electrolysis Cell Components
• Using the Advanced Photon Source to Study In-Situ Electrochemical Behavior of Electrolysis Cells