Preparation And Hydrogen Storage Properties Of The Modified Iron Oxide Research

An ideal solid hydrogen storage material should meet the U.S.Department of Energy(DOE)or International Energy Agency(lEA)criteria for hydrogen storage volumetric and gravimetric capacities(6.5 wt%and 62kg/m³ or 5 wt%and 50 kg H₂/m³,respectively)and the reversibility criteria for hydrogen storing and supplying cycles.There is,as yet,no material known to meet all of the criteria stated previously. On the basis of that result,a series of modified iron oxide samples,Fe-Mo,Fe-Al, Fe-Mo-Al,Fe-Mo-Ni,Fe₂O₃-Mo,Fe₂O₃-Ag,Fe₂O₃-La,Fe₂O₃-Ce,Fe₂O₃-Pr, Fe₂O₃-Nd,Fe₂O₃-Zr,Fe₂O₃-Mo-Zr,Fe₂O₃-Mo-Ag,Fe₂O₃-Mo-La,Fe₂O₃-Mo-Ce, Fe-2O₃-Mo-Pr,Fe₂O₃-Mo-Nd,Fe₃O₄-Mo,Fe₃O₄-La,Fe₃O₄-Ce,Fe₃O₄-Pr and Fe₃O₄-Nd,which can store and supply pure hydrogen for polymer electrolyte fuel cells(PEFC)through repeated redox reactions(Fe₃O₄ + 4H₂←�'3Fe + 4H₂O),were prepared by impregnation and co-precipitation.Effects of various metal additives in the modified samples on the hydrogen production from water decomposition were investigated.The samples before and after cycles were characterized by X-ray powder diffraction,SEM and BET surface area analyzer.The results are as follows:Among all the single metal cation-modified Fe,Fe₂O₃ and Fe₃O₄ samples,Mo was the most favorable one for enhancing the reoxidation performance of the reduced modified samples at lower temperatures.The addition of Mo to Fe,Fe₂O₃ and Fe₃O₄ not only decreased the temperature of water decomposition significantly;(i.e. increased the production of hydrogen at lower temperatures)but improved the stability of the modified samples during repeated redox cycling.The temperature of H₂ production decreased from 500 to 290℃for Mo-modified Fe,from 527 to 285℃for Mo-modified Fe₂O₃ and from 305 to 299 for Mo-modified Fe₃O₄ in the repeated cycle.The average hydrogen storage capacities through 10 redox cycles reached 4.53 wt%(72.06 kg H₂/m³)for Mo-modified Fe,4.47 wt%(73.83 kg H₂/m³)for Mo-modified Fe₂O₃ and 4.49 wt%for Mo-modified Fe₃O₄.No obvious decrease in the reactivity was observed for both the Mo-modified Fe and Fe₂O₃ samples after 10 repeated redox cycles.Among all the double metal cation-modified Fe and Fe₂O₃ samples,Mo-Zr was the most favorable one for enhancing the reoxidation performance of the reduced modified samples at lower temperatures.The temperature of H₂ production decreased from 500 to 278℃and the average hydrogen storage capacities through 10 redox cycles reached 4.68 wt%for the Mo-Zr-modified Fe₂O₃ sample.It can be seen that the Fe₂O₃ Mo-Zr sample was the best one among all the samples tested in this work.In addition,the addition of the rare earth metal cations to Fe₂O₃ and Fe₃O₄ would not obviously improved the performance of hydrogen storage for the rare earth metal cation-modifed samples.