Reversible hydrogen storage system of 3NaBH4-0.5ScF3-0.5YF3 : The synergistic effect of ScF3 and YF3

A new reversible hydrogen storage system, 3NaBH(4)-0.5ScF(3)-0.5YF(3), was synthesized by using the ball-milling method. It is shown that no reaction occurs during the ball-milling process. The hydrogen desorption process of the ball-milled composite can be divided into three consecutive steps: (i) An initial stage from room temperature to 320 degrees C with about 0.42 wt% of hydrogen released, that can be ascribed to the substitution of H- by F- in NaBH4; (ii) The second stage starts from 320 degrees C to 450 degrees C, releasing about 1.06 wt% of hydrogen; (iii) The final stage ranges from 450 degrees C to 480 degrees C, with 2.58 wt% of hydrogen released. The total yield of hydrogen reaches 4.06 wt% at 480 degrees C. The completely dehydrogenated products of the 3NaBH(4)-0.5ScF(3)-0.5YF(3) composite can absorb 2.15 wt% of hydrogen at 380 degrees C in 6.5 h, which shows greatly enhanced reversibility when compared with sole ScF3 addition. It should be noted that one of the destabilizers ScF3 was also regenerated besides NaBH4 in the rehydrogenated products. Based on the XRD and FTIR analyses, the synergistic effects of 3d transition metal fluoride ScF3 and rare earth metal fluoride YF(3 )on the hydrogen desorption and absorption performance of NaBH4 were discussed. (C) 2019 Elsevier B.V. All rights reserved.