Pushing the limits of sodium borohydride hydrolysis for on-board hydrogen generation systems

Sodium borohydride (SBH) is a promising hydrogen (H2) carrier; however, its successful deployment has been limited to unmanned aerial vehicle applications. We reevaluated SBH hydrolysis for on-board vehicular applications from an entirely new perspective using solid-phase SBH hydrolysis with a CO2-derived acid at elevated temperatures and pressures, enabling extremely efficient water utilization. This strategy afforded a high H2 storage density of 6.33 wt%, which could be extended to 10.4 wt% via water recovery from fuel cells. High-purity H2 with carbon monoxide levels below 10 ppm was obtained after methanation. Importantly, an energy-efficient SBH regeneration method using residual NaHCO2 was developed. A 1.2-kWe-level SBH hydrogen generation was evaluated with the fuel-cell operation, and a 20-kWe-level compact system was developed with a system-based volumetric H2 storage density of 25 g-H2/L. This technology will accelerate SBH-based vehicular applications at a level of 50 g-H2/L.