Storage and production of hydrogen by the redox of modified iron oxides

Pure hydrogen could be supplied directly to PEFC through the decomposition of water by reduced iron oxide at low temperatures < 573 K. Effects of various metal additives in the reduced iron oxide on the production of hydrogen from water have been examined at a temperature range 373-873 K. The decomposition of water was caused by the oxidation of iron with water (3Fe + 4H2O →Fe3O4 + 4H2). Among 26 metal elements examined, Al, Mo and Zr were favorable additives for preserving the Fe/Fe3O4 sample from decaying its reactivity by repeated cycles. The decomposition of water was most repetitive for the reduced iron oxide added with Al. The addition of Rh or Ir enhanced the rate of H20 decomposition remarkably at < 573 K. However, these noble metals could not suppress the sintering of the host iron or iron oxide. Co-addition of Rh and Al to the reduced iron oxide accelerated remarkably the decomposition of water at 573 K. It is suggested that Rh metal would catalyze the dissociation of H2O at low temperature while the compound oxides formed between iron and additives mitigate the coagulation of iron and iron oxide particles during repeated reaction cycles. The hydrogen supply system based on the decomposition of water by the reduced iron oxides with the additive elements described above was designed and manufactured. The system worked well at <573 K, recovering hydrogen repeatedly by ca. 4.5 wt% of Fe. (author)