Methanolysis of sodium borohydride (NaBH4) is one of the methods efficient enough to release, on demand, the hydrogen stored in the hydride as well as in 4 equivalents of methanol (CH3OH). It is generally reported that, in methanolysis, sodium tetramethoxyborate (NaB(OCH3)4) forms as single component of the spent fuel. It is however necessary to clearly investigate some critical aspects related to it. We first focused on the methanolysis reaction where NaBH4 was reacted with 2, 4, 8, 16 or 32 equivalents of CH3OH. With 2 equivalents of CH3OH, the conversion of NaBH4 is not complete. With 4 to 32 equivalents of CH3OH, NaBH4 is totally methanolized (conversion of 100%). The best conditions are those involving 4 equivalents of CH3OH as they offer the highest effective gravimetric hydrogen storage capacity with 4.8 wt%, an attractive H2 generation rate with 331 mL(H2) min1 – a performance achieved without any catalyst –, and the formation of NaB(OCH3)4 as single product as identified by XRD, FTIR and NMR. We then focused on the transformation of this product NaB(OCH3)4 into sodium metaborate (NaBO2), via the formation of sodium tetrahydroxyborate (NaB(OH)4). NaB(OCH3)4 is easily transformed in water, by hydrolysis, at 80 °C and for 90 min, into NaB(OH)4 and 4 equivalents of CH3OH. In doing so, the cycle with CH3OH is closed. Subsequently, NaB(OH)4 is recovered and converted into NaBO2 under heating at 500 °C. This reaction liberates 4 equivalents of H2O, which allows to close the cycle with water. Based on these achievements, we have finally proposed a triangular recycling scheme aiming at closing the cycle with the protic reactants of the aforementioned reactions. This scheme may be used as base for implementing a closed cycle with the couple NaBH4-CH3OH.
