| Hydrogen is stored chemically by Fe metal and produced by reacting with water(H2O) vapour in this way:during the first step(step 1:Fe3O4+4H2â†'3Fe+4H2O or Fe2O3+3H2â†'2Fe+3H2O),Fe3O4(initial Fe2O3) is reduced to active Fe metal with H2.In the second step(step 2:3Fe+4H2Oâ†'Fe3O4+4H2),pure H2 will be formed to PEFC and Fe3O4 will be regenerated by the addition of water.Compared with other hydrogen storage methods,this one is a novel,safe,low cost,environmentally compatible and promising alterative technology.The hydrogen storage capacity is 4.8 wt.%,which is near the criteria of IEA(5 wt%or 50 kg H2/m3).Based on our previous research,there are three kinds of nanomorphology of Fe2O3 prepared by hydrothermal synthesis,such as particulate,piece and tube.The modified samples with Mo were prepared by hydrothermal synthesis and the effect of Mo cations in the modified samples on hydrogen production was investigated.The effects of the rate of rising temperature,the modified method and the various metal cations on hydrogen production were investigated.The process of the redox and the kinetics of the oxidation of the iron oxide were investigated.In addition,the catalysis of Mo cations in the process of the redox was investigated.From the results of research,we can learn as follows:Considering the amount of hydrogen production and the cycles' stability of the samples, the effect of the rate of rising temperature with 4℃/min is better than others.Of all the samples,Fe2O3-8%Mo(modified with 8%(mol)Mo) of piece morphology modified by hydrothermal synthesis was the most effective for decreasing the temperature of H2 formation and increasing the rate of H2 formation,such as the average temperature of H2 forming 274℃and the average formation rates of H2 666.8μmol·min-1g-Fe-1 at 300℃.In addition,Fe2O3-8%Al was the most was the most effective for increasing the rate of H2 formation at low temperature,such as the average temperature of H2 forming 207℃and the average formation rates of H2 318μmol·min-1g-Fe-1 at 219℃.Compared with hydrothermal synthesis,the impregnation was not proper for the nanoconfiguration of iron oxide.According the conventional and Jander models,the apparent activation energies of the oxidation process are about 55.53～65.30 kJ·mol-1 for unmodified Fe2O3 and about 36.17～45.19 kJ·mol-1 for Fe2O3-8%Mo;the oxidation process for both the samples is a gas—solid non—catalytic reaction with the 1.5th order by the conventional model and a three—dimensional diffusion reaction of a gaseous phase by Jander model.In the first cycle,the Fe2O3 was reduced via Fe3O4 to Fe and subsequently the Fe was oxided via FeO to Fe3O4.Then in the second cycle,the Fe3O4 was reduced via FeO to Fe and subsequently the Fe was oxided via FeO to Fe3O4.The reason that Mo cations accelerated hydrogen production was investigated by SEM,XRD and TPR.The change of valence of Mo cations during repeated redox cycles resulted in the change of composition and structure of the samples,which suppressed sintering.The cooperative effect of Mo cations and active Fe changed the reaction path of decomposition of water,which lowered the activation energy. |
PDF Full Text Request