Enhancing the Regeneration Process of Consumed NaBH₄ for Hydrogen Storage

TLDR

Sodium borohydride is a promising hydrogen source, yet its irreversible hydrolysis and expensive regeneration limit large‑scale use. This work introduces the first convenient, economical NaBH4 regeneration method that does not rely on hydride starting materials. The method uses the hydrated hydrolysis products NaBO₂·2H₂O and NaBO₂·4H₂O with Mg at room temperature and atmospheric pressure, eliminating the high‑temperature drying step needed to produce NaBO₂. The approach achieves record regeneration yields of 68.55 % and 64.06 % from the two hydrates, cuts regeneration costs 34‑fold versus MgH₂‑based methods, and reveals the intermediate NaBH₃(OH) during the process.

Abstract

Abstract Sodium borohydride (NaBH 4 ) is regarded as an excellent hydrogen‐generated material, but its irreversibility of hydrolysis and high cost of regeneration restrict its large‐scale application. In this study a convenient and economical method for NaBH 4 regeneration is developed for the first time without hydrides used as starting materials for the reduction process. The real hydrolysis by‐products (NaBO 2 · 2H 2 O and NaBO 2 · 4H 2 O), instead of dehydrated sodium metaborate (NaBO 2 ), are applied for the regeneration of NaBH 4 with Mg at room temperature and atmospheric pressure. Therefore, the troublesome heat‐wasting process to obtain NaBO 2 using a drying procedure at over 350 °C from NaBO 2 · x H 2 O is omitted. Moreover, the highest regeneration yields of NaBH 4 are achieved to date with 68.55% and 64.06% from reaction with NaBO 2 · 2H 2 O and NaBO 2 · 4H 2 O, respectively. The cost of NaBH 4 regeneration shows a 34‐fold reduction compared to the previous study that uses MgH 2 as the reduction agent, where H 2 is obtained from a separate process. Furthermore, the regeneration mechanism of NaBH 4 is clarified and the intermediate compound, NaBH 3 (OH), is successfully observed for the first time during the regeneration process.