Oxygen-releasing step of nickel ferrite based on Rietveld analysis for thermochemical two-step water-splitting

摘要

We investigated the thermal reduction (T-R) of NiFe_2O_4, either supported by m-ZrO_2 or unsupported, as the oxygen-releasing step of a solar thermochemical water splitting cycle based on a ferrite/wustite redox system, by performing the Rietveld analysis using powder X-ray diffraction. The solid materials obtained after the T-R step at 1300-1400℃ were subjected to Rietveld analysis. The amounts and chemical compositions of the wustite phase produced by the T-R step and the remaining ferrite phase were identified quantitatively. Chemical reaction formulas for the different T-R temperatures were determined from the results. Consistency for the chemical reactions of the thermal reduction was discussed and evaluated comparing the O_2 amounts predicted by the chemical reaction formulas and measured experimentally by mass spectrometry.