Acid Acceleration of Hydrogen Generation Using Seawater as a Reactant

The present study describes hydrogen generation from N_aBH₄ in the presence of acid accelerator, boric oxide or  B₂O₃, using seawater as a reactant. Reaction times and temperatures are adjusted using various delivery methods: bulk, addition funnel, and metering pump. It is found that the transition metal catalysts typically used to generate hydrogen gas are poisoned by seawater. B₂O₃ is not poisoned by seawater; in fact, reaction times are considerably faster in seawater using  B₂O₃. Reaction times and temperatures are compared for pure water and seawater for each delivery method. It is found that using B2O3 with pure water, bulk addition is 97% complete in 3 min; pump metering provides a convenient method to extend the time to 27 min, a factor of 9 increase above bulk addition. Using  B₂O₃ with seawater as a reactant, bulk addition is 97% complete in 1.35 min; pump metering extends the time to 23 min, a factor of 17 increase above bulk. A second acid accelerator, sodium bisulfate or NaHSO4, is investigated here for use with NaBH4 in seawater. Because it is non-reactive in seawater, i.e., no spontaneous H₂ generation, NaHSO₄ can be stored as a solution in seawater; because of its large solubility, it is ready to be metered into NaBH₄. With N_aHSO₄ in seawater, pump metering increases the time to 97% completion from 3.4 min to 21 min. Metering allows the instantaneous flow rate of H₂, and reaction times and temperatures, to be tailored to a particular application. In one application, the seawater hydrogen generator characterized here is ideal for supplying H₂ gas directly to Proton Exchange Membrane fuel cells in sea surface or subsea environments where a reliable source of power is needed.