Structural Manipulation Of Novel Non-noble Fe-and Ni-based Nanocatalysts And Their Catalytic Performance For Hydrogen Production

Hydrogen is an ideal alternative to fossil fuels because of its renewability,easy storage and wide availability.It has become a hot topic in current clean energy research to search for high density hydrogen storage materials and develop highly efficient non-noble metal catalysts for a clean hydrogen energy system.Both ammonia and ammonia borane have high hydrogen capacity(i.e.,17.6 and 19.6wt%)and can be easily stored and transported.Therefore,the two hydrogen storage materials have attracted increasing interests.The highly efficient catalysts for ammonia decomposition and hydrolytic dehydrogenation of ammonia borane mainly focus onnoble metal catalysts(e.g.,Ru and Pt).However,because of the high price and limited availability of noble metals,much attention has been paid to develop nonprecious,low cost and abundant metal catalysts(e.g.,Fe,Ni and Co)with high efficiency.In addition,being typical structure-sensitive reactions,ammonia decomposition and hydrolytic dehydrogenation of ammonia boranecanalso be usedas model reaction systemsto investigate the effects of the surface structure and electronic properties of catalystson their catalytic performance.In this work,we focused on the study of effects of the parameters for catalytic chemical vapor deposition(CCVD)methods on the manipulation of the morphology of Ni and Fe particles as well as their catalytic behavior in order to establish the structure-catalytic performance relationship over the catalysts.(1)Effects of partial pressure of carbon source and growth time of carbon nanofibers on the morphology of Fe nanoparticles were studied.It is found that higher partial pressure of the carbon source favors the formation of Fe particles with long polyhedral morphology,while lower partial pressure results in the formation of Fe particles with irregular morphology.Moreover,extending the growth time of carbon fiber can lead to the reconstruction of Fe nanoparticles.Comparatively,Fe nanoparticles with polyhedral morphology exhibited superior ammonia decomposition activity.(2)A comparative study has been carried out to understand the different catalytic performance between Fe and Ni based catalysts prepared by CCVD method and traditional impregnation method.Combined the experimental results with the theoretical calculation,the mechanism for the influence of surface C and sub-surface C on ammonia decomposition over Fe and Ni catalysts was revealed,which explained the opposite activity trend.(3)NiB amorphous alloy were prepared by chemical reduction method and further supported on different supports.The obtained catalysts were characterized usingN2-BET,XRD and TEM and the support effects onhydrolytic dehydrogenation of ammonia borane have been explored.Kinetics study and isotopic experiments show that the CNTs supported NiB amorphous alloy catalyst can promote the activation of water,and thus reduce activation energy and improve the catalytic performance.