LiBH₄ (LB in short) with a hydrogen capacity as high as 18.5 wt% and a low molecular weight (21.78 g mol⁻¹ ) is among the most promising candidates for the hydrogen-based economy. However, current major technologies in (re)generation of LB rely heavily on energy-intensive processes, which greatly prohibits practical scaling-up of applications. Here we report a sustainable and effective approach to (re)generate LB via converting renewable H⁺ in crystalline water into H^- , achieving a desirable yield of ~50%. This one-step synthesis method relies on the reaction between spent fuels, specifically LiBO₂⋅xH₂O, and Mg-based alloys to form LB under ambient atmosphere. Notably, our approach surpasses the efficiency of other conventional method, such as LiH-B-H2 and MgH₂-LiBO₂ systems, which not only bypasses the energy-intensive dehydration procedure of LiBO₂⋅xH₂O (~470 ℃) but also eliminates the use of costly hydrides or high-pressure H₂. Our findings indicate that Mg participated in the regeneration process prior to Al in Mg-Al alloys and [BH4] - is gradually evolved from other intermediate species [BH_x(OH)_4-x] ^- (x = 0, 1, 2, 3). By combining hydrogen release and efficient storage of hydrogen-rich substrate in a closed materials cycle, this study may shed light on a promising step toward application of renewable hydrogen in a fuel cell-based hydrogen economy.