Stability of alkaline aqueous solutions of sodium borohydride

Experimental results regarding long-term stability of the alkaline-water borohydride solutions for hydrogen generation are presented. The influence of the concentration of sodium borohydride and sodium hydroxide on the rate of borohydride hydrolysis is analyzed at various temperatures, such as 25 °C, 40 °C, and 80 °C, and various concentrations of NaOH. The rate of hydrolysis decreases with the increase of the water to sodium borohydride mole ratio. For diluted solutions at H2O/NaBH4 >30, the rate of hydrolysis and hydrogen generation at a given temperature remains constant. At room temperature in 1.0 N NaOH, the degree of hydrolysis is 0.01% NaBH4/h that meets the stability requirements for the borohydride solutions during the long-term storage.

► Alkaline aqueous sodium borohydride solutions were evaluated in terms of their stability and storage capacity between active cycles in hydrogen generators. ► The natural rate of hydrolysis in a broad concentration range of sodium borohydride and sodium hydroxide at various temperatures was estimated. ► At room temperature in 1.0 N NaOH, the degree of hydrolysis is 0.01% NaBH4/h and meets the stability requirements for the sodium borohydride solutions in hydrogen generators.