Closing the hydrogen cycle with the couple sodium borohydride‐methanol, via the formation of sodium tetramethoxyborate and sodium metaborate

Abstract

Methanolysis of sodium borohydride (NaBH 4) is one of the methods efficient enough to release, on demand, the hydrogen stored in the hydride as well as in 4 equiv of methanol (CH 3 OH). It is generally reported that, in methanolysis, sodium tetramethoxyborate (NaB(OCH 3) 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 NaBH 4 was reacted with 2, 4, 8, 16, or 32 equiv of CH 3 OH. With 2 equiv of CH 3 OH, the conversion of NaBH 4 is not complete. With 4 to 32 equiv of CH 3 OH, NaBH 4 is totally methanolized (conversion of 100%). The best conditions are those involving 4 equiv of CH 3 OH as they offer the highest effective gravimetric hydrogen storage capacity with 4.8 wt%, an attractive H 2 generation rate with 331 mL(H 2) min −1-a performance achieved without any catalyst-and the formation of NaB(OCH 3) 4 as single product as identified by X-ray diffraction, Fourier transform infrared spectroscopy, and nuclear magnetic resonance. We then focused on the transformation of this product NaB(OCH 3) 4 into sodium metaborate (NaBO 2), via the formation of sodium tetrahydroxyborate (NaB (OH) 4). NaB(OCH 3) 4 is easily transformed in water, by hydrolysis, at 80 C and for 90 minutes, into NaB(OH) 4 and 4 equiv of CH 3 OH. In doing so, the cycle with CH 3 OH is closed. Subsequently, NaB(OH) 4 is recovered and converted into NaBO 2 under heating at 500 C. This reaction liberates 4 equiv of H 2 O, 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 NaBH 4-CH 3 OH.

Electrospun Co Nanoparticles@PVDF-HFP Nanofibers as Efficient Catalyst for Dehydrogenation of Sodium Borohydride

“…NaB(OCH 3 ) 4 is formed during methanolysis; in contrast to NaB(OH) 4 , it does not have a high tendency to polymerize into polyborates. This aids in preventing their precipitation, which may lead to clogged pores and poisoned catalysts [ 55 , 56 ]. Hongming et al [ 3 ] used hydrothermal and reduction approaches to produce Co NPs@carbon nanostructures for SBH dehydrogenation.…”

Membrane Nanofiber-Supported Cobalt–Nickel Nanoparticles as an Effective and Durable Catalyst for H2 Evolution via Sodium Borohydride Hydrolysis

“…Sodium tetramethoxy borate is produced as a byproduct of methanolysis, and it does not readily form polyborate complexes. Furthermore, it is capable of preventing catalyst poisoning by avoiding the precipitation of NaB(OH) 4 [ 48 , 49 ]. Sodium tetramethoxy borate reacts with water to produce sodium borate and methanol, both of which are carried away by the washing process’s excess water.…”

CuNi Alloy NPs Anchored on Electrospun PVDF-HFP NFs Catalyst for H2 Production from Sodium Borohydride

“…For example, the by-product, NaB(OCH 3 ) 4 , does not rapidly polymerize into various types of polyborates. Preventing the precipitation of NaB(OH) 4 is necessary to stop the poisoning of the catalyst [ 58 , 59 ]. Hongming et al [ 60 ] used hydrothermal and reduction procedures to prepare ultrafine Co NPs@carbon nanospheres as an effective catalyst for the generation of H 2 from SBH hydrolysis.…”