Air-Stable Nanoporous Aluminum/Lithium Borohydride Fuel Pellets for Onboard Hydrogen Generation by Hydrolysis with Pure Water

Hydrolysis of water-reactive nanoporous nonprecious metals to produce hydrogen fuel on-demand for nonstationary applications is a promising method to overcome infrastructural limitations associated with current hydrogen storage and delivery systems. However, the pyrophoricity of highly reactive nanoporous nonprecious metals presents safety and stability issues. Herein, we demonstrate a method to stabilize pyrophoric nanoporous nonprecious metals using a composite pellet structure consisting of a nanoporous nonprecious metal and a highly hygroscopic material that (i) can trap and absorb high quantities of water vapor to prevent heat buildup and subsequent pyrophoric ignition from exothermic oxidation from oxygen and (ii) can also undergo hydrolysis to produce hydrogen, thus making it possible to suppress pyrophoricity without sacrificing the overall hydrogen generation yield of the composite. Lithium hydroxide and lithium borohydride were investigated as two candidate hygroscopic materials for their ability to absorb water vapor. Lithium borohydride showed a higher affinity for water vapor, as confirmed by in situ weight change and X-ray diffraction measurements. Nanoporous aluminum/lithium borohydride pellets as well as nanoporous aluminum/lithium hydroxide pellets with various compositions were created and investigated. We found that pellets with a nanoporous aluminum-to-lithium borohydride ratio of 90:10 wt % are highly air-stable and show no pyrophoricity when exposed to ambient air. These safety improvements are expected to pave the way to use nanoporous nonprecious metals created by dealloying for on-demand hydrogen generation for nonstationary fuel cell applications.