_{A new process for producing sodium borohydride (NaBH4) as an H-storage material has been developed where the "spent fuel" as sodium metaborate (NaBO2•4H2O) and borax (Na2BO}•10H₂O) as abundant natural resource were used to prepare anhydrous metaborate (NaBO₂). NaBH₄ was produced at the contact surface between Al(powder-state with larger specific surface area) and NaBO₂ that forms binary liquid solution with Na₂O under H₂ atmospheres during the system temperature being increased over 570^oC from a solid phase of NaBO₂ :NaOH = 3 : 4 to a liquid phase. The dissociation of diatomic hydrogen (H₂) to protide (H^-: hydride ion) occurs at the extreme surface of Al when H^- is transferred to NaBO₂ in exchange with the formation of NaBH₄ and NaAlO₂ as shown in Eq. 1; 4/3Al + 2H₂ + NaBO₂ + 2/3Na₂O → NaBH₄ + 4/3NaAlO₂ (1) In the previous works on the dynamic hydriding-dehydriding behaviors of Mg and H₂, Mg was found to prepare the active surface as O-acceptor for releasing O^2- in NaBO₂ and H-donor for forming NaBH₄. However, it has not been proven experimentally the role of Al-surface in the exchange reaction between gaseous hydrogen and NaBO₂ during dynamic temperature changes. The yield of NaBH₄ was found to exceed > 75% by a single process.

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