Catalysis for Thermochemical Hydrogen Production Cycles 

Daniel M. Ginosar
Idaho National Laboratory
Interfacial Chemistry

To achieve energy security and independence, the U.S. needs to utilize all of its resources in an integrated and efficient manner. This will increase the demand for hydrogen which can be produced using the primary energy delivered from high temperature nuclear reactors or solar thermal systems. Thermochemical cycles can be used to split water through a series of chemical reactions where the net result is the production of hydrogen and oxygen at much lower temperatures than direct thermal decomposition. All chemicals within the cycle are fully recycled and the heat to drive the reactions, which tend to be endothermic, must be provided by a primary energy source. When the primary energy driver is nuclear or solar energy, hydrogen can be generated with a minimal green-house gas footprint.

The sulfur-based family of thermochemical cycles, including the Sulfur-Iodine cycle (S-I), and the Hybrid Sulfur cycle appear promising for producing hydrogen using nuclear heat. These cycles employ a high-temperature sulfuric acid decomposition reaction step. The reaction produces oxygen and generates SO2, which is used in other reaction steps of the cycles. The reaction takes place from 750 to 900°C, or higher, and is facilitated by heterogeneous catalysts. The S-I cycle produces hydrogen by the catalytic decomposition of HI. The various cycles all present requirements of high-temperatures and harsh chemical reaction conditions which present significantly challenging environments for catalytic materials.

This presentation will focus on the catalyst needs of themochemical cycles that are candidates for being powered by nuclear reactors. Specific catalyst activity and stability testing results will be provided for the decomposition of sulfuric acid for the production of oxygen in the sulfur-based family of cycles and for the catalytic decomposition of hydroiodic acid for the production of hydrogen in the S-I process.

Presentation Slides