Gaps, challenges, and opportunities of sodium borohydride alcoholysis for hydrogen
Enzo Catapano, Umit B. Demirci
Abstract
Sodium borohydride (NaBH 4 ) has a high potential for chemical hydrogen storage. While its hydrolysis in water has been widely studied, increasing attention is being directed toward alcoholysis reactions, particularly methanolysis, which offer distinct benefits. These include (i) the possibility of generating hydrogen at subzero temperatures, which are conditions under which hydrolysis is ineffective, and (ii) the formation of sodium tetramethoxyborate, a by-product that may facilitate borohydride regeneration. This review provides a comprehensive analysis of sodium borohydride alcoholysis, with a primary focus on methanolysis, and identifies the key knowledge gaps, challenges and opportunities. With respect to methanolysis, beyond the well-studied catalytic acceleration of hydrogen production, several critical aspects remain insufficiently explored: the impact of water as impurity in methanol on hydrogen production rates, the fate of acids used as accelerators, the nature of by-products formed under various conditions, and the hydrogen purity. Addressing these issues is essential for optimizing gravimetric hydrogen storage capacity and advancing practical regeneration strategies. Other alcohols such as ethanol, ethylene glycol, and propylene glycol are also considered, as they may offer additional advantages depending on the application context. Ultimately, the long-term viability of sodium borohydride alcoholysis will depend on a deeper understanding of the nature, stability, and recyclability of its by-products, an area that requires targeted and intensified research efforts.