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 °C with about 0.42 wt% of hydrogen released, that can be ascribed to the substitution of H − by F − in NaBH 4 ; (ii) The second stage starts from 320 °C to 450 °C, releasing about 1.06 wt% of hydrogen; (iii) The final stage ranges from 450 °C to 480 °C, with 2.58 wt% of hydrogen released. The total yield of hydrogen reaches 4.06 wt% at 480 °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 °C in 6.5 h, which shows greatly enhanced reversibility when compared with sole ScF 3 addition. It should be noted that one of the destabilizers ScF 3 was also regenerated besides NaBH 4 in the rehydrogenated products. Based on the XRD and FTIR analyses, the synergistic effects of 3d transition metal fluoride ScF 3 and rare earth metal fluoride YF 3 on the hydrogen desorption and absorption performance of NaBH 4 were discussed.