Influence of KH on Reversible Dehydriding Performance of Na-Al-H Complex Hydride

The Na-Al-H complex hydride was prepared by reactive ball milling (NaH/Al+CeCl3) and (NaH/Al+CeCl3/yKH) (y=0.02, 0.04) composites under a hydrogen pressure of 3 MPa at room temperature, using NaH and Al powder as raw materials, as well as 2% (molar fraction) CeCl3 and 2% CeCl3/y% KH (y=0.02, 0.04) as dopant, respectively. The de-/hydrogenation properties show that the addition of KH can effectively improve the dehydrogenation kinetics of second decomposition step for Na-Al-H system. The (NaH/Al+CeCl3/0.02KH) composite can complete dehydrogenation process within 20 min at 170, with good de-/hydrogenation cycling performance at relatively low temperature (100-140). Calculation by Kissenger method shows that the addition of KH could decrease the apparent activation energy of second decomposition step for Na-Al-H system, resulting in the decrease of desorption peak temperatures. Phase structure analysis shows that the enhanced second step dehydrogenation kinetics of Na-Al-H composite system is mainly ascribed to the lattice volume expansion of Na3AlH6 resulted from the addition of KH.