Acid acceleration of hydrogen generation using seawater as a reactant

摘要

The present study describes hydrogen generation from NaBH4 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 H-2 generation, NaHSO4 can be stored as a solution in seawater; because of its large solubility, it is ready to be metered into NaBH4. With NaHSO4 in seawater, pump metering increases the time to 97% completion from 3.4 min to 21 min. Metering allows the instantaneous flow rate of H-2, 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 H-2 gas directly to Proton Exchange Membrane fuel cells in sea surface or subsea environments where a reliable source of power is needed. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.