Conversion of Concentrated Solar Thermal Energy into Chemical Energy
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When a concentrated solar beam is irradiated to the ceramics such as Ni-ferrite, the high-energy flux in the range of 1500–2500 kW/m2 is absorbed by an excess Frenkel defect formation. This non-equilibrium state defect is generated not by heating at a low heating-rate (30 K/min), but by irradiating high flux energy of concentrated solar beam rapidly at a high heating rate (200 K/min). The defect can be spontaneously converted to chemical energy of a cation-excess spinel structure (reduced-oxide form) at the temperature around 1773 K. Thus, the O2 releasing reaction (α-O2 releasing reaction) proceeds in two-steps; (1) high flux energy of concentrated solar beam absorption by formation of the non-equilibrium Frenkel defect and (2) the O2 gas formation from the O2− in the Frenkel defect even in air atmosphere. The 2nd step proceeds without the solar radiation. We may say that the 1st step is light reaction, and 2nd step, dark reaction, just like in photosynthesis process.
KeywordsNi-ferrite Solar hydrogen Frenkel defect α-O2 releasing reaction Concentrated solar heat
I would like to express my gratitude to my colleagues in our institute, prof. Hirhoshi Kaneko, Mr. Satoshi Shigeta, Mr. Yousuke Ishikawa, Mr. Chong-il Lee, who made enormous contribution to this paper, and like to appreciate Ministry of Education, Culture, Sports, Science & Technology for the Science Research Grant on this paper (Grant; (A)21246147)).
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