configurations. Cycles with more than 3 steps and hybrid cycles Cycles based on sulfur chemistry Due to sulfur's high covalence, it can form up to 6 chemical bonds with other elements such as oxygen, resulting in a large number of oxidation states. Thus, there exist several redox reactions involving sulfur compounds. This freedom allows numerous chemical steps with different entropy changes, increasing the odds of meeting the criteria for a thermochemical cycle. Much of the initial research was conducted in the United States, with sulfate- and sulfide-based cycles studied at Kentucky University, the Los Alamos National Laboratory and General Atomics. Significant research based on sulfates (e.g., FeSO4 and CuSO4) was conducted in Germany and Japan. The sulfur-iodine cycle, discovered by General Atomics, has been proposed as a way of supplying a hydrogen economy without the need for hydrocarbons. Cycles based on the reversed Deacon process Above 973K, the Deacon reaction is reversed, yielding hydrogen chloride and oxygen from water and chlorine: H2O + Cl2 → 2 HCl + 1/2 O2 See also Iron oxide cycle Cerium(IV) oxide-cerium(III) oxide cycle Copper-chlorine cycle Hybrid sulfur cycle Hydrosol-2 Sulfur-iodine cycle Zinc zinc-oxide cycle UT-3 cycle References Thermochemistry