Thermochemical cycles produce hydrogen through a series of chemical reactions where the net result is the production of hydrogen and oxygen from water at much lower temperatures than from direct thermal decomposition. All chemicals within the cycle are 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 heat, hydrogen can be generated without producing greenhouse gasses, and can provide independence from our dwindling supplies of fossil fuels.

Among the high number of thermochemical water-splitting cycles proposed in the literature, the Sulfur-Iodine (S-I) cycle has generated considerable interest. The S-I cycle consists of three simultaneous reactions; the decomposition of hydroiodic acid (HI) to produce hydrogen and generate iodine for recycle, the decomposition of sulfuric acid to produce oxygen and generate SO₂ for recycle, and a main reaction where water and the recycle chemicals react to regenerate HI and sulfuric acid.

Previous literature has reported that activated carbon is a desirable catalyst for the decomposition of hydroiodic acid. The Idaho National Laboratory is currently exploring the activity and properties of activated carbon catalysts for the HI decomposition reaction. In this presentation, the activity and stability of activated carbon catalysts will be presented, focusing primarily on commercially available activated carbons. Catalyst characterization, including surface area, temperature programmed desorption (TPD), Boehm's titration results, and contact pH of the activated carbons will be discussed.