Chemical storage of hydrogen by modified iron oxides

Abstract

Pure hydrogen may be supplied directly to polymer electrolyte fuel cell (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 is caused by the oxidation of iron with water (3Fe+4H2O→Fe3O4+4H2). Among 26 metal elements examined as additives, Al, Mo and Ce were favorable ones 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 Mo. The addition of Rh or Ir enhanced the rate of H2O 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 Mo, Zr, Al or Ga to the reduced iron oxide accelerated remarkably the decomposition of water at 473 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.