Effects of the hierarchical pyrolysis polyaniline on reversible hydrogen storage of LiBH4

In this work, LiBH4-20 wt% PP composite was prepared by ball-milling with as-synthesized hierarchical pyrolysis polyaniline (PP) and LiBH4, and the hydrogen sorption performance as well as catalytic mechanism of the composite was studied. It is found that the onset desorption temperature of the composite decreases to 75 degrees C, almost 235 degrees C lower than that of the milled LiBH4. Moreover, the composite could release 4.1 wt% H-2 and rehydrogenate a total of 4.4 wt% H-2 when the temperature raiseds up to 400 degrees C, showing an outstanding reversibility, which even 3.9 wt% H-2 can be kept after five cycles. Through scanning electron microscopy (SEM) observation and X-ray diffraction (XRD) analysis, we found that the PP surface forms some nanoholes after hydrogenation-dehydrogenation cycles, which leads to the confinement of some LiBH4 in the PP nanoporous structure, therefore, the hydrogen sorption kinetics and reversibility are significantly enhanced. In addition, we also found the oxygenic groups of the PP can react with LiBH4 forming LiBO2 and Li3BO3, where the containing Li-B-O bonds loaded in the porous structure of the PP catalyze the hydrogenation reaction of LiBH4.