A semi-global reaction rate model based on experimental data for the self-hydrolysis kinetics of aqueous sodium borohydride

This work studied the self-hydrolysis kinetics of aqueous sodium borohydride (NaBH4) for hydrogen generation and storage purposes. Two semi-global rate expressions of sodium borohydride and hydrogen ion consumption were derived from an extensive series of batch process experiments where the following parameters were systematically varied: solution temperature (298 K–348 K), NaBH4 concentration (0.5 wt% to 25.0 wt%), and sodium hydroxide (NaOH) concentration (0.0 wt% to 4.0 wt%). Transient hydrogen generation rates and transient solution pH were measured during the hydrolysis experiments. Given initial conditions (temperature, NaBH4 concentration, and H+ concentration), the two coupled semi-global rate equations can be integrated to obtain the transient time history of H2 generation (or NaBH4 consumption) and solution pH (or H+ concentration). Comparing analytical results of transient hydrogen generation rate and transient solution pH with experimental data, good agreement was reached for many conditions, especially for elevated solution pH values, levels at which NaBH4 solutions are used practically.

► Kinetic expressions for the self-hydrolysis of aqueous NaBH4 are proposed. ► Semi-global rate expressions of NaBH4 and H+ consumption were empirically derived. ► Expressions include solution temperature, NaBH4 and H+ concentrations as variables. ► Integrated equations provide the time history for H2 generation and solution pH. ► Good agreement between analytical and experimental transient rates were reached.