Use of oxides in thermochemical water-splitting cycles for solar heat sources. Cobalt oxides
The concept of utilizing oxide decompositions in advanced thermochemical hydrogen cycles for solar heat sources is introduced. It has particular interest in allowing direct transmission of energy to the process through an air window. A cycle for the Co/sub 3/O/sub 4/-CoO pair would be, schematically: (1) Co/sub 3/O/sub 4/ = 3CoO + 1/2 O/sub 2/; (2) I/sub 2/(s,1) + Mg(OH)/sub 2/ + 3CoO = MgI/sub 2/(aq) + Co/sub 3/O/sub 4/ + H/sub 2/O(1); (3) H/sub 2/O + MgI/sub 2/(aq) = MgO + 2HI; (4) 2 HI = H/sub 2/ + I/sub 2/; and (5) MgO + H/sub 2/O = Mg(OH)/sub 2/. Reaction (2) should give a high concentration of MgI/sub 2/ that would be favorable for (3). The solutions would also contain iodine dissolved as polyiodide, partly offsetting this advantage. Preliminary results indicate that reaction (2) is slow at 150/sup 0/I/sub 2/ (4); and Mg. It is surmised that the mechanism of (2) consists of the iodine disproportional reaction (6), followed by reaction (7); (6) I/sub 2/(s,1) + Mg(OH)/sub 2/ = 5/6 MgI/sub 2/(aq) + 1/6 Mg(IO/sub 3/)/sub 2/(aq) + H/sub 2/O(1); and (7) 1/6 Mg(IO/sub 3/0/sub 2/(aq) + 3 CoO = 1/6 MgI/sub 2/(aq) + Co/sub 3/O/sub 4/. Other workers have found (6) to be relatively fast and with a good yield at 150/sup 0/C. We have found reaction (7) to be sufficiently slow at 150/sup 0/C to account for the slowness of (2). The yield of (7) was found to be proportional to the square root of the time, which suggests that iodate must diffuse through an adherent, accumulating Co/sub 3/O/sub 4/ layer. Since (7) is much faster when Mg(IO/sub 3/)/sub 2/ is replaced by KIO/sub 3/, the magnesium ion may catalyze formation of an adherent Co/sub 3/O/sub 4/ spinel layer or enter into the structure of the layer. The reactivity of CoO in the KIO/sub 3/ analog of (7) is greatly decreased by exposure to high temperature.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 5358669
- Report Number(s):
- LA-UR-82-584; CONF-820605-15; ON: DE82011977
- Resource Relation:
- Conference: World hydrogen energy conference, Pasadena, CA, USA, 13 Jun 1982
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
14 SOLAR ENERGY
COBALT OXIDES
CHEMICAL REACTION KINETICS
OXIDATION
HYDROGEN PRODUCTION
THERMOCHEMICAL PROCESSES
IODATES
MAGNESIUM COMPOUNDS
SOLAR FURNACES
WATER
ALKALINE EARTH METAL COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
COBALT COMPOUNDS
EQUIPMENT
FURNACES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
IODINE COMPOUNDS
KINETICS
OXIDES
OXYGEN COMPOUNDS
REACTION KINETICS
SOLAR EQUIPMENT
TRANSITION ELEMENT COMPOUNDS
080102* - Hydrogen- Production- Thermochemical Processes
141000 - Solar Collectors & Concentrators