Due to the rapid depletion of fossil fuels and pollution from their use, fi nding an alternative fuel is becoming increasingly

important. Hydrogen is considered one of the best contenders, as its by-product is water. However, safe methods to store

hydrogen must be developed to use hydrogen as an eff ective energy carrier or source. Sodium borohydride (NaBH 4 , SBH) has

been attracting great attention as a hydrogen storage material because of its relatively high hydrogen content and low material

cost. Hydrogen can be produced through thermolysis or hydrolysis of SBH. Unfortunately, thermolysis requires extremely

high temperatures (> 300 °C), while hydrolysis needs an excessive amount of water because the solubilities of SBH and the

spent fuel in water are low. In addition, when SBH is present with water, it can cause problems in safety and storage due to

the spontaneous generation of hydrogen. In our prior work, it has been demonstrated that solid-state hydrolysis of SBH off ers

improved safety and high hydrogen yield. Despite these favorable outcomes, separating the products to regenerate spent

fuel to lower the overall cost remains challenging. Here, we proposed the hydrolysis of SBH and water formed by thermal

dehydration of sodium metaborate tetrahydrate (NaBO 2 4H 2 O, SMB4H). Since the mixture of SBH and SMB4H is stable

at ambient conditions, the safety risk due to self-hydrolysis of SBH is eliminated. Additionally, since the fi nal products are

homogeneous with sodium metaborate (NaBO 4 · x H 2 O, SMB), a product of the hydrolysis of SBH, it is expected that separation

cost can be saved when regenerating the spent fuel. Using this approach, maximum overall H 2 yields of 4.7 and 5.1wt% were

obtained at 200 and 250 °C, respectively. With high hydrogen yield and safety and potential reduction in separating process

costs during regeneration, this proposed method is promising for hydrogen storage for fuel cell applications.