Reaction experiments for thermochemical water-splitting. [Classes of cycles: metal-metal oxide; metal oxide-metal hydroxide; metal oxide-metal sulfate; metal-metal halide; metal oxide-metal halide]
Almost all known pure thermochemical hydrogen production cycles can be grouped into five generic classes, each involving either a metal oxide or a metal halide as an intermediate. In general, those cycles with the highest-temperature endothermic reactions and the least number of reactions are the most efficient. This is expected because thermochemical cycles are special types of heat engines. The ''maximum attainable'' efficiency of known published cycles is about 65 percent with 1225/sup 0/C input heat and assuming present technology for conversion of heat to work. The most difficult step in any thermochemical cycle is usually the one involving a change in metal oxidation state, usually the reduction. It is often necessary to operate such a step with some work input, such as electrolysis. Because of this, few of the truly efficient and workable hydrogen production cycles are purely thermochemical. Of these thermochemical hydrogen production cycles that are known to be workable with reagent-grade materials, more than two-thirds are of the group constructed from compounds of iron, chlorine, hydrogen, and oxygen. The ''maximum attainable'' efficiency for cycles of this group is about 47 percent with 925/sup 0/C input heat and present technology for conversion of heat to work. This efficiency drops to about 43 percent if the reaction steps are assumed to operate attemperatures based on thermodynamics.
- Research Organization:
- Inst. of Gas Tech., Chicago
- OSTI ID:
- 7262835
- Journal Information:
- Am. Chem. Soc., Div. Fuel Chem., Prepr.; (United States), Journal Name: Am. Chem. Soc., Div. Fuel Chem., Prepr.; (United States) Vol. 21:3; ISSN ACFPA
- Country of Publication:
- United States
- Language:
- English
Similar Records
Hydrogen production from water by means of chemical cycles
Engineering considerations for thermochemical hydrogen production. [Energy efficiency determinations]