Hydrogen generation from hydrides in millimeter scale reactors for micro proton exchange membrane fuel cell applications

This paper introduces and discusses the feasibility of millimeter scale powder packed-bed reactors using high energy density chemical hydrides for micro-PEM fuel cell applications. Two different reactors were designed and tested using LiBH4, LiAlH4, NaAlH4 and CaH2 hydride fuels. The mechanisms that limit the total yield of H2 generated and impact the performance of the hydrogen generator are investigated in this paper, including density, solubility and porosity of the reaction byproducts. The volume expansion of the byproducts has significant effect on the total energy density of micro-hydrogen generators because the byproducts are left in the millimeter scale reactor after the reactions and the micro-hydrogen generators have limited fuel storage space. The SEM images of the reaction byproducts indicates that the byproducts of LiBH4 can form a single solid mass that clogged the reaction vessel and limit the full utilization of the hydride. However, the byproducts of LiAlH4 and CaH2 reactions are non-agglomerated and they do not form impermeable mass. The experimental results show that the highest yield of hydrogen generation was achieved with LiAlH4 and CaH2 fuels.