A passive lithium hydride based hydrogen generator for low power fuel cells for long-duration sensor networks

• Passive lithium hydride hydrogen generator demonstrated for low power applications.
• Lithium hydride fuel for PEM fuel cell has energy density of up to 4900 Wh/kg.
• A critical challenge is packing lithium hydride to enable reaction completion.
• Thick layers of LiH can't be fully reacted using water vapor due to choking by LiOH.
• An experimentally validated model is presented that describes this choking behavior.

This paper focuses on developing an efficient fuel storage and release method for hydrogen using lithium hydride hydrolysis for use in PEM fuel cells for low power sensor network modules over long durations. Lithium hydride has high hydrogen storage density and achieves up to 95–100% yield. It is shown to extract water vapor freely from the air to generate hydrogen and has a theoretical fuel specific energy of up to 4900 Wh/kg. A critical challenge is how to package lithium hydride to achieve reaction completion. Experiments here show that thick layers of lithium hydride nearly chokes the reaction due to buildup of lithium hydroxide impeding water transport and preventing reaction completion. A model has been developed that describes this lithium hydride hydrolysis behavior. The model accurately predicts the performance of an experimental system than ran for 1400 h and consists of a passive lithium hydride hydrogen generator and PEM fuel cells. These results offer important design guidelines to enable reaction completion and build long-duration lithium hydride hydrogen generators for low power applications.