Thermal hydrolysis of solid-state sodium borohydride for noncatalytic hydrogen generation

Hydrogen from sodium borohydride (NaBH₄, SBH) can be generated by thermolysis or hydrolysis. Unfortunately, thermolysis of SBH requires high temperatures (>300 °C), while hydrolysis is conducted in the presence of catalyst and self-hydrolysis can cause safety concerns due to unexpected generation of hydrogen. In order for hydrolysis of SBH to be practical, efficient and safe methods to produce hydrogen are required. Here, we propose a new process, thermal hydrolysis of SBH, to generate hydrogen via hydrolysis in the solid phase. In this new process, SBH generates hydrogen by hydrolysis with water produced by thermal decomposition of boric acid (BA). Self-hydrolysis causing safety issues no longer occurs because the SBH-BA mixture in the solid-state is stable at below 80 °C. When heating the mixture, a rapid hydrogen evolution was observed at ~ 120 °C and a maximum H₂ equivalent of 3.9 was achieved at 150 °C for SBH:BA = 1:4. BA is dehydrated to form metaboric acid with a release of 1 mol H₂O at 150 °C and an additional 0.5 mol water at 200 °C. With recent progress in regeneration of SBH spent fuels, this newly proposed method is promising for hydrogen storage in proton exchange membrane fuel cell applications.